U.S. patent application number 13/047229 was filed with the patent office on 2011-06-30 for toothbrush employing acoustic waveguide.
This patent application is currently assigned to WASHINGTON, UNIVERSITY OF. Invention is credited to David A. Ballard, George A. Barrett, Frederick Jay Bennett, Gerald K. Brewer, James Christopher McInnes, Pierre D. Mourad.
Application Number | 20110159461 13/047229 |
Document ID | / |
Family ID | 34572960 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110159461 |
Kind Code |
A1 |
Mourad; Pierre D. ; et
al. |
June 30, 2011 |
TOOTHBRUSH EMPLOYING ACOUSTIC WAVEGUIDE
Abstract
A power toothbrush (10) is disclosed having a handle (15),
battery (12), ultrasonic drive circuit (14), motor (16), control
unit (18), and toothbrush head (20). The toothbrush head includes
bristles (26) and a waveguide (24) that is operatively connected to
an ultrasonic transducer (22). The waveguide facilitates the
transmission of acoustic energy into the dental fluid to achieve
improved cleaning and stain removal and improved cleaning in
interproximal and subgingival regions. In one embodiment an
ultrasound transducer module (30) includes a plurality of
piezoelectric elements (32, 34) that may be mechanically connected
in series, and electrically connected in parallel. One or more
contacts (36) connect the elements, and a waveguide structure (50).
An impedance matching layer (38) may be provided between the
waveguide and the ultrasonic transducer module. The waveguide may
be formed from a relatively soft material, for example, a polymer
having a hardness between 10 and 65 Shore A.
Inventors: |
Mourad; Pierre D.; (Seattle,
WA) ; McInnes; James Christopher; (Seattle, WA)
; Barrett; George A.; (Shoreline, WA) ; Ballard;
David A.; (Sammamish, WA) ; Brewer; Gerald K.;
(Redmond, WA) ; Bennett; Frederick Jay; (Kirkland,
WA) |
Assignee: |
WASHINGTON, UNIVERSITY OF
Seattle
WA
ULTREO, INC.
Redmond
WA
|
Family ID: |
34572960 |
Appl. No.: |
13/047229 |
Filed: |
March 14, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11416852 |
May 3, 2006 |
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13047229 |
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10981735 |
Nov 3, 2004 |
7296318 |
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11416852 |
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60677577 |
May 3, 2005 |
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60517638 |
Nov 4, 2003 |
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Current U.S.
Class: |
433/216 |
Current CPC
Class: |
A46B 2200/1066 20130101;
A61C 17/3481 20130101; A46B 15/0002 20130101; A61C 17/20 20130101;
A46B 15/0028 20130101 |
Class at
Publication: |
433/216 |
International
Class: |
A61C 17/16 20060101
A61C017/16 |
Goverment Interests
STATEMENT OF GOVERNMENT LICENSE RIGHTS
[0002] One or more of the inventions disclosed herein were made
with Government support under SBIR Contract No. 1-R43-DEO16761-01.
The Government may have certain rights in one or more of those
inventions.
Claims
1. A method for improving the loosening and removal of dental
plaque from dental surfaces in the presence of a dental fluid
containing microbubbles having a radius R.sub.0, comprising:
propagating ultrasonic waves having a frequency F.sub.0 into the
dental fluid under conditions that induce cavitation of the
microbubbles in the dental fluid.
2. The method of claim 1, comprising propagating ultrasonic waves
into the dental fluid to achieve a resonance formula of
F.sub.0R.sub.0=3.26, where F.sub.0 is given in MHz and the radius
R.sub.0 of the microbubbles is given in microns.
3. The method of claim 1, wherein the ultrasonic waves have a
frequency appropriate to resonate microbubbles in the dental fluid
having a diameter of between about 1 .mu.m and about 150 .mu.m.
4. The method of claim 1, wherein the ultrasonic waves have a
frequency between 20 kHz and 1 MHz.
5. The method of claim 1, wherein the ultrasonic waves propagate
from an acoustic waveguide extending from a toothbrush head.
6. The method of claim 5, wherein the acoustic waveguide is
acoustically coupled to an ultrasound wave generator disposed on
the toothbrush head.
7. The method of claim 5, wherein the acoustic waveguide is
acoustically coupled to an ultrasound wave generator disposed in a
toothbrush handle.
8. The method of claim 5, additionally comprising vibrating the
toothbrush head at a sonic frequency.
9. The method of claim 1, wherein the ultrasonic waves have a pulse
repetition frequency of from 0.5 Hz to 10,000 Hz.
10. The method of claim 1, wherein the ultrasonic waves produce a
mechanical index in the dental fluid of from 0.01 to 1.9.
11. The method of claim 1, wherein the ultrasonic waves produce a
mechanical index in the dental fluid of from 0.51 to 0.9.
12. The method of claim 1, additionally comprising introducing a
dentifrice into the dental fluid that facilitates the formation of
bubbles having a diameter of between about 1 .mu.m and about 150
.mu.m in the dental fluid.
13. The method of claim 1, wherein the ultrasonic waves
additionally induce acoustic streaming to achieve shear stresses of
at least about 1 Pa in the dental fluid.
14. A method for improving the loosening and removal of dental
plaque from dental surfaces in the presence of a dental fluid
containing microbubbles, comprising: propagating ultrasonic waves
into the dental fluid under conditions that induce acoustic
microstreaming as a result of the action of mechanical pressure
changes within the ultrasonic field on the microbubbles in the
dental fluid.
15. The method of claim 14, wherein the ultrasonic waves have a
frequency of from 20 kHz to 1 MHz in the dental fluid.
16. The method of claim 14, wherein the ultrasonic waves propagate
from an acoustic waveguide extending from a toothbrush head.
17. The method of claim 16, additionally comprising vibrating the
toothbrush head at a sonic frequency.
18. The method of claim 14, wherein the ultrasonic waves have a
pulse repetition frequency in the range from 10 Hz to 10,000
Hz.
19. The method of claim 14, additionally comprising introducing a
dentifrice that facilitates the formation of bubbles having a
diameter of between about 1 .mu.m and about 150 .mu.m in the dental
fluid.
20. The method of claim 14, wherein the ultrasonic waves
additionally induce acoustic streaming to achieve shear stresses of
at least about 1 Pa in the dental fluid.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/416,852, filed May 3, 2006, which claims the benefit of U.S.
Provisional Application No. 60/677,577, filed May 3, 2005, and also
is a continuation-in-part of U.S. application Ser. No. 10/981,735,
filed Nov. 3, 2004, now U.S. Pat. No. 7,296,318, which claims the
benefit of U.S. Provisional Application No. 60/517,638, filed Nov.
4, 2003. The disclosures of the priority patent applications are
expressly incorporated herein by reference in their entireties.
BACKGROUND
[0003] Existing power toothbrushes, even the most effective, leave
clinically significant plaque at tooth contact surfaces, at the
gingival-tooth contact points, below the gingiva, and beyond the
direct reach of the bristles or other toothbrush components.
Previous attempts at creating ultrasonic toothbrushes failed to
exploit microbubble formation in dental fluid for purposes of
facilitating plaque removal or failed to consider microbubbles and
macrobubbles as a potential impediment to ultrasound propagation
beyond the bristle tips. Some early toothbrushes that employed
ultrasound technology attempted propagation of ultrasound waves
from the base of the bristles either through the bristles
themselves or through the bubbly dental fluid that fills the spaces
between the bristles. See, e.g., U.S. Pat. No. 5,138,733, U.S. Pat.
No. 5,247,716, U.S. Pat. No. 5,369,831, and U.S. Pat. No.
5,546,624, to Bock. Because conventional toothbrush bristles and
bubbly dental fluid can reduce rather than facilitate the
propagation of ultrasound waves, those toothbrushes fell short of
achieving efficient ultrasound wave propagation. Also, the
ultrasound systems in prior art toothbrushes did not take advantage
of the specific bubbly structure within dental fluid.
Synopsis of the Art
[0004] U.S. Pat. No. 3,335,443, to Parisi, discloses a brush that
is coupled to an ultrasonic, vibratory, handheld dental instrument
that is capable of being vibrated at high sonic and ultrasonic
frequencies.
[0005] U.S. Pat. No. 3,809,977, to Balamuth et al., which reissued
as U.S. Pat. No. RE 28,752, discloses ultrasonic kits, ultrasonic
motor constructions, and ultrasonic converter designs for use alone
or in combination. The ultrasonic motor may be of piezoelectric
material having a removable tip and is contained in a housing
having an electrical contact means adapted to be plugged into an
adapter that is connected to a converter.
[0006] U.S. Pat. No. 3,828,770, to Kuris et al., discloses a method
for cleaning teeth employing bursts of ultrasonic mechanical
vibration at an applicator repeated at a sonic frequency to produce
both ultrasonic and sonic vibratory motion during use.
[0007] U.S. Pat. No. 3,840,932 and U.S. Pat. No. 3,941,424, to
Balamuth et al., disclose an ultrasonic toothbrush applicator in a
configuration to be ultrasonically vibrated to transmit mechanical
vibrations from one end to a bristle element positioned at the
other end.
[0008] U.S. Pat. No. 4,071,956, to Andress, discloses a device,
which is not a toothbrush, for removing dental plaque by ultrasonic
vibrations.
[0009] U.S. Pat. No. 4,192,035, to Kuris, discloses an apparatus
comprising an elongated member formed of a piezoelectric member
with a pair of contacting surfaces with a brush member adapted to
be received within the human mouth. A casing adapted into a handle
is configured to receive the piezoelectric member.
[0010] U.S. Pat. No. 4,333,197, to Kuris, discloses an ultrasonic
toothbrush that includes an elongated handle member in the form of
a hollow housing having disposed therein a low voltage coil and
cooperating ferrite core that is driven at ultrasonic frequencies.
A brush member is affixed to the core and is adhesively affixed to
an impedance transfer device that is adhesively affixed to the core
material. The impedance transfer device insures maximum transfer of
ultrasonic energy from the core material to the brush.
[0011] U.S. Pat. No. 4,991,249 and U.S. Pat. No. 5,150,492, to
Suroff, disclose an ultrasonic toothbrush having an exchangeable
toothbrush member that is removably attached to an ultrasonic power
member.
[0012] U.S. Pat. No. 5,138,733, to Bock, discloses an ultrasonic
toothbrush having a handle, a battery pack, an electronics driving
module, a piezoelectric member, and a removable brush head. The
piezoelectric crystal resonates, expands and contracts
volumetrically, in tune with the frequency supplied by the
electronic driving modules, thereby converting electronic energy
into sound-wave energy.
[0013] U.S. Pat. No. 5,247,716, to Bock, discloses a removable
brush head for an ultrasonic toothbrush having a plurality of
bristle clusters, a substantially tubular body constructed of a
flexible material, and tensioning means securing the brush head to
the ultrasonic device, providing for the efficient transmission of
ultrasonic frequency vibrations from the device via the brush
head.
[0014] U.S. Pat. No. 5,311,632, to Center, discloses a device for
removing plaque from teeth comprising a toothbrush having a thick,
cylindrical, hollow handle encompassing (1) an electric motor that
is actuable to cause rotation of an eccentrically mounted member
and vibration of the entire device, and (2) an ultrasonic
transducer actuable to produce high frequency sound waves along the
brush.
[0015] U.S. Pat. No. 5,369,831, to Bock, discloses a removable
brush head for an ultrasonic toothbrush.
[0016] U.S. Pat. No. 5,546,624, to Bock, discloses an ultrasonic
toothbrush including a handle constructed of a rigid material, a
battery pack, an electronics driving module, a piezoelectric
member, and a removable brush head. The piezoelectric crystal
resonates, expands and contracts volumetrically, in tune with the
frequency supplied by the electronic driving module and thereby
converts the electronic energy into sound-wave energy.
[0017] Japanese Application No. P1996-358359, Patent Laid Open
1998-165228, discloses a toothbrush utilizing ultrasonic waves in
which an ultrasonic wave generator is provided in the handle of a
manual or electrically powered toothbrush and an ultrasonic wave
vibrator is mounted in the brush and wired to the wave
generator.
[0018] Japanese Application No. P2002-353110, Patent Laid Open
2004-148079, discloses an ultrasonic toothbrush wherein ultrasonic
vibration is radiated from a piezoelectric vibrator arranged inside
a brush head and transmitted to the teeth via a rubber projection
group.
[0019] U.S. Pat. No. 6,203,320, to Williams et al., discloses an
electrically operated toothbrush and method for cleaning teeth. The
toothbrush includes a handle, a brush head connected to the handle
having a plurality of hollow filament bristles, passageways through
the handle and brush head for transporting fluid into and through
the hollow filament bristles, an electrical energy source in the
handle, and a vibratory element for imparting a pulsation to the
fluid being transported.
[0020] U.S. Patent Publication No. 2003/0079305, to Takahata et
al., discloses an electric toothbrush in which a brush body is
simultaneously oscillated and reciprocated. The electric toothbrush
comprises a casing main body, an arm extending above the casing
main body, a brush body arranged in a top end of the arm, and an
ultrasonic motor arranged in a top end inside of the arm for
driving the brush body.
[0021] U.S. Pat. No. RE 35,712, which is a reissue of U.S. Pat. No.
5,343,883, to Murayama, discloses an electric device (i.e., a
flosser) for removal of plaque from interproximal surfaces. The
device employs sonic energy and dental floss secured between two
tines of a flexible fork removably attached to a powered handle.
The electric motor revolves at sonic frequencies to generate sonic
energy that is transmitted to the flexible fork.
[0022] U.S. Pat. No. 6,619,957, to Mosch et al., discloses an
ultrasonic scaler comprising a scaler tip, actuator material, a
coil, a handpiece housing, and an air-driven electrical current
generator. The actuator material, coil, and air-driven electrical
current generator are all encompassed within the handpiece
housing.
[0023] U.S. Pat. No. 6,190,167, to Sharp, discloses an ultrasonic
dental scaler for use with a dental scaler insert having a resonant
frequency. The dental scaler insert is removably attached to a
handpiece having an energizing coil coupled to a selectively
tunable oscillator circuit to generate a control signal having an
oscillation frequency for vibrating the dental scaler.
[0024] U.S. Pat. No. 4,731,019, to Martin, discloses a dental
instrument for scaling by ultrasonic operation. The instrument of
the dental instrument has a distal end with a hook-like
configuration with a conical pointed end and comprising abrasive
particles, typically diamond particles.
[0025] U.S. Pat. No. 5,150,492, to Suroff, discloses an ultrasonic
toothbrush having an exchangeable ultrasonic implement that may be
removably mounted to an ultrasonic power means that is encompassed
within the toothbrush handle.
[0026] U.S. Pat. No. 5,378,153, to Giuliani, discloses a dental
hygiene apparatus having a body portion and an extended resonator
arm. The apparatus employs an electromagnet in its body that acts
in combination with two permanent magnets to achieve an oscillating
action about a torsion pin. The arm is driven such that the
bristle-tips operate within ranges of amplitude and frequency to
produce a bristle tip velocity greater than 1.5 meters per second
to achieve cleansing beyond the tips of the bristles.
[0027] There remains a need in the art for toothbrush designs that
achieve improved dental cleaning properties between the teeth and
gums, at points of contact between the teeth, and beyond the direct
action of the bristles.
SUMMARY
[0028] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
[0029] The present invention fulfills these and other related needs
by providing toothbrushes, including power and manual toothbrushes,
that employ an acoustic waveguide, either alone or in combination
with an ultrasonic transducer and/or sonic component, to achieve
improved plaque and stain removal and user experience. Accordingly,
within certain embodiments, the present invention provides power
toothbrushes having one or more acoustic waveguide(s) that is
capable of propagating and may function to focus acoustic waves
transmitted by an ultrasonic transducer into the dental fluid,
thereby inducing cavitation of microbubbles and, in addition or
alternately, inducing acoustic streaming, with a consequent
improvement in the loosening and removal of dental plaque from
dental surfaces and interproximal regions. When used in combination
with a sonic component, the acoustic waveguide can, additionally or
alternatively, be made to vibrate such that the acoustic waveguide
contributes to enhanced fluid flow in the oral cavity and to the
formation of microbubbles in the dental fluid, beyond the reach of
the acoustic waveguide and/or toothbrush head bristle tips. When
used in combination with a sonic component, the enhanced bubbly
fluid flow generated by the acoustic waveguide can, additionally or
alternatively, work synergistically with the ultrasound transmitted
through the acoustic waveguide to further facilitate plaque and
stain removal beyond the reach of the acoustic waveguide and/or
toothbrush head bristle tips.
[0030] In an embodiment of the present invention, an ultrasonic
transducer is utilized at the toothbrush head, at the base of and
in operable proximity to an acoustic waveguide or, alternatively,
mechanically coupled to the toothbrush head from within the
toothbrush handle via an acoustically transmitting conduit (made,
for example, from metal, gel, or fluid). In either embodiment, the
ultrasonic transducer transmits ultrasonic waves to the acoustic
waveguide that, in turn, propagates those ultrasonic waves into the
dental fluid such that the waves are effective in causing
cavitation of microbubbles within the dental fluid and,
alternatively or additionally, acoustic streaming. Within certain
embodiments, toothbrushes of the present invention may also
comprise one or more toothbrush bristle tufts that contribute to
the generation of microbubbles within the dental fluid. The
ultrasonic waves cause cavitation of those microbubbles that, in
turn, results in the improved plaque and stain removal properties
of toothbrushes disclosed herein.
[0031] Additional embodiments of the present invention provide
power toothbrushes having an ultrasonic transducer and an acoustic
waveguide in further combination with a sonic component that
operates within the audible frequencies to mechanically move the
brush head, including the bristles and acoustic waveguide, to
increase flow of the dental fluid at a velocity and intensity
required to contribute to microbubble production. The acoustic
waveguide and ultrasonic waves that it transmits act in a
synergistic fashion to produce a scrubbing bubbly jet within the
dental fluid, both by increasing the instantaneous spatial
distribution of bubbles available for activation, and by increasing
the distribution of ultrasound owing to the sonic motion of the
acoustic waveguide. The acoustic waveguide and ultrasonic waves
also act synergistically to create a bubbly jet by each
contributing to the acceleration of the bubbly fluid, the acoustic
waveguide by pushing fluid directly and the ultrasonic waves by
inducing acoustic streaming.
DESCRIPTION OF THE DRAWINGS
[0032] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0033] FIG. 1A is a schematic, partially cross-sectional diagram
depicting an exemplary power toothbrush of the present
invention;
[0034] FIG. 1B is a perspective view of one embodiment of an
ultrasonic transducer module of the present invention;
[0035] FIG. 1C is a perspective, partially broken-away view of one
embodiment of an acoustic waveguide in combination with the
ultrasonic transducer module shown in FIG. 1B;
[0036] FIG. 2A is a diagram depicting a cross-sectional view of an
exemplary power toothbrush head similar to the embodiment
illustrated in FIG. 1A, showing a handle, bristles, an ultrasonic
transducer, and an acoustic waveguide shaped generally as a
rectangular solid with a convex tip;
[0037] FIG. 2B is a diagram depicting a finite element model
simulation geometry of the exemplary toothbrush head shown in FIG.
2A (shown here without bristles);
[0038] FIG. 2C is a diagram depicting the simulated ultrasound wave
field at 1.2 ms post-pulse wherein the ultrasonic waves remain
mainly in the acoustic waveguide;
[0039] FIG. 2D is a diagram depicting the simulated ultrasound wave
field at 2.0 ms post-pulse, wherein the ultrasonic waves have
substantially left the acoustic waveguide;
[0040] FIG. 3A is a diagram depicting a finite element model
simulation geometry of a toothbrush head wherein the exemplary
acoustic waveguide has a tapered profile;
[0041] FIG. 3B is a perspective view of the tapered profile
waveguide shown in FIG. 3A;
[0042] FIG. 3C is a side view of the simulated wave field plot soon
after ultrasonic transmission, showing propagation within the
acoustic waveguide;
[0043] FIG. 3D is a side view of the simulated wave field plot at a
later time subsequent to ultrasonic transmission showing acoustic
waveguide propagation of the ultrasonic wave front into the fluid
emulsion;
[0044] FIG. 3E is an end view of the simulated wave field plot at
the same simulation time as FIG. 3C;
[0045] FIG. 3F is an end view of the simulated wave field plot at
the same simulation time as FIG. 3D;
[0046] FIG. 4A is a finite element model simulation geometry of
another exemplary acoustic waveguide, wherein the waveguide tip is
curved;
[0047] FIG. 4B is a perspective view of the waveguide shown in FIG.
4A, wherein the portion beyond the curved dotted line is
removed;
[0048] FIG. 4C is the simulated wave field plot soon after
ultrasonic transmission, showing propagation within the acoustic
waveguide;
[0049] FIG. 4D is a wave field plot at a later time subsequent to
ultrasonic transmission showing the focusing of the ultrasonic wave
front beyond the tip of the acoustic waveguide and propagation of
that ultrasonic wave front into the fluid emulsion;
[0050] FIGS. 5A-5D are ultrasound images of fluid flow generated by
an ultrasonic toothbrush with and without a waveguide;
[0051] FIG. 5A is a combined Doppler (inside the box) and B-mode
(outside the box) image depicting fluid flow induced by an
ultrasonic toothbrush without an acoustic waveguide and without
bristle tip motion (bristle tips (BT) and bristle plate (BP) at the
bottom of bristles);
[0052] FIG. 5B is a combined Doppler and B-mode image depicting
fluid flow induced by an ultrasonic toothbrush without an acoustic
waveguide but with bristle tip motion (MB) and demonstrating
absence of any measurable fluid flow (FF) beyond the bristles;
[0053] FIG. 5C is a B-mode ultrasound image depicting fluid flow
induced by an ultrasonic toothbrush with an acoustic waveguide,
wherein the waveguide is made to vibrate by a sonic component and
showing that the vibrating acoustic waveguide generated a jet of
bubbly fluid moving away from the toothbrush head;
[0054] FIG. 5D is a Doppler and B-mode ultrasound image of the same
ultrasonic toothbrush as described for FIG. 5C, further showing
significant fluid flow (FF) and bubble (B) formation beyond the
bristle tips;
[0055] FIG. 6 is a plot comparing the measured acoustic pressure
levels at the tip of a flat versus a focused lens acoustic
waveguide;
[0056] FIG. 7 is a plot showing the absorption of ultrasound waves
transmitted through a dental fluid/bubble emulsion versus
frequency;
[0057] FIG. 8 is a plot showing the percent of suspended red blood
cells destroyed by shear stress induced by acoustic microstreaming
associated with a stably oscillating bubble. The inset depicts a
thin, hollow wire with air in its center, placed within a vial of
suspended red blood cells;
[0058] FIGS. 9A-H depict geometries of various exemplary acoustic
waveguides for use in the toothbrush heads of the present
invention; and
[0059] FIG. 10 is a bar graph of data demonstrating the safety of a
toothbrush according to the present invention, as measured using
the cell lysis assay described in Example 5.
DETAILED DESCRIPTION
[0060] The present invention is based upon the discovery that a
toothbrush employing an acoustic waveguide, either alone or in
combination with an ultrasonic transducer and/or sonic component,
yields improved cleaning properties as compared to existing power
toothbrush technologies. It is contemplated that toothbrushes
according to the present invention may or may not include a number
of conventional bristle tufts, as discussed below. In one
embodiment, for example, a toothbrush employs a waveguide structure
in combination with bristle tufts and a sonic component for
vibrating the waveguide structure and bristle tufts at sonic
frequencies. In another embodiment, a toothbrush employs an
acoustic waveguide structure in combination with an ultrasonic wave
generator. In yet another embodiment, a toothbrush employs an
acoustic waveguide structure in combination with an ultrasonic wave
generator and a sonic component.
[0061] As described in detail herein, toothbrushes according to the
present invention are effective in (1) increasing bubbly fluid flow
by motion, including sonic motion, of the acoustic waveguide and
bubble formation by the waveguide and/or one or more toothbrush
bristles; (2) transmitting focused ultrasonic waves generated by an
ultrasonic transducer and propagating those waves through an
acoustic waveguide into the dental fluid to achieve improved plaque
disruption and removal; and/or (3) facilitating bubbly fluid flow
and transmitting ultrasound to interact optimally and maximally at
and beyond-the-bristles (e.g., between about 0.5 mm and about 5 mm
from the bristle tips, more typically between about 1 mm and about
3 mm from the bristle-tips), within the dental fluid.
[0062] Thus, within certain embodiments, the present invention
provides toothbrushes, including manual toothbrushes and power
toothbrushes, comprising an acoustic waveguide. In certain
embodiments of the present invention, toothbrushes are provided
that comprise an acoustic waveguide in combination with an
ultrasonic transducer that, together, act upon the microscopic
bubbly flow within the dental fluid, either as a consequence of
brushing with a bristled toothbrush head and/or the motion of the
acoustic waveguide acted upon by the sonic component to induce
cavitation, acoustic streaming, and/or acoustic microstreaming
within the dental fluid. Therefore, yet additional embodiments of
the present invention provide toothbrushes comprising an acoustic
waveguide in combination with an ultrasonic component and in
further combination with a sonic component. The sonic component, in
combination with an acoustic waveguide, being fabricated of a
suitable material, and/or in combination with one or more
toothbrush bristles, is further responsible for generating a
favorable mouth feel, stimulating and massaging the gums and other
dental tissue, and promoting an improved dental cleaning
experience.
[0063] All references to ranges of parameters described in this
specification are understood to include reference to a range equal
to and greater than the lower value of each range, as well as
ranges equal to and less than the higher value of each range. Thus,
for example, the recitation of a carrier frequency of between about
250 and about 500 kHz in this specification is interpreted to
include carrier frequencies of 250 kHz and greater; carrier
frequencies of 500 kHz and less; as well as carrier frequencies
within the stated range. All U.S. and foreign patents and patent
applications and all other references cited herein are hereby
incorporated by reference in their entireties.
Definitions and Parameters Governing the Operation of Inventive
Toothbrush Technologies
[0064] As used herein, the terms "ultrasound" or "ultrasonic" refer
to acoustic energy, or sound, of a frequency higher than and
outside of the normal audible range of the human ear--generally of
a frequency higher than approximately 20 kHz. Typically, ultrasonic
transducers employed in the toothbrushes of the present invention
are capable of producing ultrasonic frequencies within the range of
about 20 kHz to about 5000 kHz, more typically, from about 100 kHz
to about 750 kHz, still more typically, from about 250 kHz to about
750 kHz and, in some embodiments, from about 250-350 kHz. The term
"sonic" refers to acoustic energy, or sound, of a frequency that is
within the audible range of the human ear--generally up to about 20
kHZ--for example, between 20 Hz and 20 kHz.
[0065] As used herein, the term "cavitation" refers to the
generation and/or stimulation of bubbles by sound. More
specifically, the term "cavitation" is used herein to refer to the
interaction between an ultrasonic field in a liquid and in gaseous
inclusions (e.g., microbubbles) within the insonated medium. By
"generation" is meant the creation of bubbles; by "stimulation" is
meant the action that causes the bubbles to become dynamically
active: that is, to move, to get bigger and smaller, to grow, to
dissipate, all with associated mechanical and/or chemical effects
in and around the fluid surrounding the bubbles and within the gas
inside the bubbles.
[0066] Cavitation of existing microbubbles may be subdivided, to a
first approximation, into two general categories--"stable
cavitation" and "inertial cavitation." "Stable cavitation" is the
induction of stable, low-amplitude, resonant oscillations of
preexisting microbubbles by low-intensity ultrasound energy that,
in turn, generates local shear forces within the fluid flow
(referred to herein as acoustic microstreaming) near and adjacent
to the microbubbles. As the ultrasound intensity is increased, the
amplitude of oscillation also rises until the bubble becomes
unstable and collapses due to the inertia of the inrushing fluid,
giving rise to "inertial cavitation."
[0067] The resulting extremes of pressure and temperature within a
violently collapsing bubble (one typically more active than those
required for the present invention) can be sufficient to initiate
free radical generation by hydrolysis of contained water vapor. If
bubble collapse occurs in proximity to a fluid/solid interface (for
example, a dental surface), shear forces within the medium and high
velocity fluid jets are directed toward the solid structures, i.e.,
the teeth and gums. In the context of the present invention,
cavitation effects include ultrasound-induced stimulation of
microbubbles already present in the dental fluid due to the action
of bristles into stable cavitation that, through the resulting
scrubbing action from the shear forces associated with
microstreaming, displaces or loosens plaque and other debris from
dental surfaces and interproximal surfaces. Another effect can be
the generation of coherent fluid flow away from the transducer,
called acoustic streaming, whose strength is enhanced by the
interaction of the ultrasound and microbubbles. Generally,
ultrasonic transducers incorporated in toothbrushes of the present
invention induce cavitation of microbubbles that are between about
1 .mu.m and about 150 .mu.m in diameter.
[0068] Toothbrushes of the present invention incorporating an
ultrasound transducer and acoustic waveguide typically promote at
least stable cavitation--that is, simple volumetric changes in
bubbles where factors in addition to and/or instead of the inertia
in the surrounding fluid govern the bubble behavior. Bubbles have a
primary resonant frequency that varies inversely with the bubbles'
radius and also strongly depends on other factors, such as gas
content and surface tension. Typically, for example, bubbles in
dental fluid having a diameter of between about 1 .mu.m and about
150 .mu.m resonate when ultrasound is applied to those bubbles with
an ultrasound transducer operating in the 20 kHz to 3 MHz range.
More typically, bubbles in dental fluid having a diameter of
between about 1 .mu.m and about 100 .mu.m resonate when ultrasound
is applied to those bubbles with an ultrasound transducer operating
in the 30 kHz to 3 MHz range. Still more typically, bubbles in
dental fluid having a diameter of between about 4.3 .mu.m and about
33 .mu.m resonate when ultrasound is applied to those bubbles with
an ultrasound transducer operating in the 100 kHz to 750 kHz range.
Still more typically, bubbles in dental fluid having a diameter of
between about 5 .mu.m and about 30 .mu.m resonate when ultrasound
is applied to those bubbles with an ultrasound transducer operating
in the 100 kHz to 600 kHz range. Still more typically, bubbles in
dental fluid having a diameter of between about 6.5 .mu.m and about
22 .mu.m resonate when ultrasound is applied to those bubbles with
an ultrasound transducer operating in the 150 kHz to 500 kHz range.
In an exemplary toothbrush presented herein, bubbles in dental
fluid having a diameter of between about 12 .mu.m and about 26
.mu.m resonate when ultrasound is applied to those bubbles with an
ultrasound transducer operating in the 250 kHz to 500 kHz range.
Whether or not the applied ultrasonic frequency differs from a
bubble's resonant frequency, low levels of ultrasound induce
temporal variations in bubble volume that are initially small and
sinusoidal, both within an acoustic cycle and over many acoustic
cycles. And, whether or not the applied ultrasonic frequency
differs from a bubble's resonant frequency, those induced temporal
variations in bubble volume generate movement within the fluid in
proximity to the bubble, whose mechanical effects assist in and
promote the removal of plaque.
[0069] Due to geometric properties and impedance mismatch,
cavitating bubbles scatter and emit sound. Compression and
rarefaction of a bubble undergoing stable cavitation cause an
emission of sound, primarily at the frequency of the applied signal
for low levels of ultrasound. As bubbles grow toward their resonant
frequency (which can happen in only a few cycles) or as the applied
sound field increases, the volumetric changes in the bubble evolve
to more complex functions of time within an acoustic cycle, as do
the acoustic emissions, whether or not those changes remain
radially symmetric. As a function of growing bubble amplitude,
those emissions first include the superharmonics (2F0, 3F0, etc.)
of the applied signal (F0) (as well as acoustic emissions of F0
itself). Eventually, a once stabley-oscillating bubble may collapse
violently and/or become asymmetric, with an associated increase in
amplitude of the superharmonic emissions as well as broadband
acoustic emissions (i.e., non-integral values of F0) over a greater
range of frequencies, including the eventual emission of multiples
of the subharmonic of the applied signal (e.g., (1/2)F0). By
detecting these emissions--for example, via a hydrophone--the level
of cavitation activity within insonified material can be remotely
assessed and correlated with a variety of mechanical and chemical
effects associated with cavitation, such as, for example, plaque
removal, as demonstrated herein. See Chang et al., IEEE
Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
48(1):161-170 (2001); Poliachik et al., Ultrasound in Medicine and
Biology 27(11): 1567-1576 (2001); Leighton, Ultrasonics
Sonochemistry 2 (2): S123-S136 (1995); and Roy et al., J. Acoust.
Soc. Am 87(6):2451-2458 (1990). For example, when divided by the
amplitude of the applied signal, one can expect the normalized
amplitude of the superharmonics to increase as bubble activity
increases, with associated increases in plaque removal. In
addition, one can expect the integral over the spectral emission
band (from (1/2)F0 through 10F0, say) of the bubbly medium to
increase as bubble activity increases, with an associated increase
in plaque removal.
[0070] As used herein, the terms "microstreaming" and "acoustic
microstreaming" refer to the movement of fluid near and adjacent to
microbubbles that occurs as a result of the action of mechanical
pressure changes within the ultrasonic field on the microbubbles.
In the context of the present invention, shear forces are
associated with the cavitating microbubbles within dental fluid
that are distributed along the surfaces of the gums and teeth, as
well as in interproximal and subgingival spaces. These shear
forces, in turn, remove the plaque and/or stains on these
surfaces.
[0071] Several ultrasound parameters contribute to producing
"acoustic microstreaming" in the context of toothbrushes of the
present invention. The carrier frequency (i.e., the frequency of
the individual ultrasound waves) is generally above about 20 kHz;
typically between about 30 kHz and about 3 MHz; more typically
between about 100 kHz and about 750 kHz; in some embodiments
between about 100 kHz and about 600 kHz; in some embodiments
between about 150 kHz and about 500 kHz; and, in some embodiments,
between about 250 kHz and about 500 kHz. It will be understood that
the actual, optimal range of the carrier frequency will depend upon
the available bubble population and the size of ultrasound
transducer employed.
[0072] The "pulse repetition frequency" ("PRF"), i.e., the
frequency of packets or bursts of individual ultrasound waves,
typically, though not exclusively, ranges from about 0.5 Hz and
about 10,000 Hz; more typically between about 0.5 Hz and about
2,500 Hz, and still more typically between about 1 Hz and about 500
Hz. The desired PRF may depend upon the ultrasound frequency, the
number of cycles per burst and the environment in which the
toothbrush is operating, including the medium in which the
ultrasonic energy is being used. In toothpaste, for example, a
preferred PRF at a 10% duty cycle is generally less than about 20
Hz and may be less than about 10 Hz. In an aqueous environment,
though, a higher PRF may be used--typically over 40 Hz and in the
range of between 40 to 200 Hz. In some embodiments of toothbrushes
of the present invention that use ultrasound frequencies in
combination with sonic frequencies, the PRF is a small multiple
(generally two or greater, more typically four or greater) of the
sonic frequency (i.e., the frequency of movement of the bristles
and/or acoustic waveguide driven by a sonic component of a
toothbrush of the present invention).
[0073] The number of individual ultrasound waves within a packet or
burst of ultrasound (cycles per burst) is typically between about
10 and about 10,000; for many embodiments between about 500 and
10,000. The desired number of cycles per burst depends upon the
ultrasound frequency, the PRF, and the environment in which the
toothbrush is operating. For promoting acoustic microstreaming in
the context of toothbrushes of the present invention, relatively
long bursts and relatively low PRF are suitable. The product of PRF
and burst duration yields the duty cycle (i.e., the percentage of
time that the ultrasound is activated). Typically, the duty cycle
is between about 1% and about 15%. The ultrasonic components of
toothbrushes of the present invention preferably operate within
these ranges.
[0074] Preferred ultrasonic operating parameters depend, as
described above, on several interrelated factors, including the
ultrasonic frequency, the PRF, the number of cycles per burst, the
duty cycle, and the environment in which the device is operated.
For devices operated in a toothpaste emulsion environment, the
combinations of operating parameters described in the table below
are suitable.
TABLE-US-00001 Ultrasound Frequency Range Cycles/Burst PRF (Hz)
Duty Cycle 100-750 kHz 500-10,000 0.5-75 5% 100-750 kHz 500-10,000
1.0-150 10% 100-750 kHz 500-10,000 1.5-225 15% 250-500 kHz
500-10,000 1.3-50 5% 250-500 kHz 500-10,000 2.5-100 10% 250-500 kHz
500-10,000 3.8-150 15% 300 kHz 500-10,000 1.5-30 5% 300 kHz
500-10,000 3.0-60 10% 300 kHz 500-10,000 4.5-90 15%
[0075] For devices operated in a water environment, the
combinations of operating parameters described in the table below
are suitable.
TABLE-US-00002 Ultrasound Frequency Range Cycles/Burst PRF (Hz)
Duty Cycle 100-750 kHz 50-1,000 5-750 5% 100-750 kHz 50-1,000
10-1500 10% 100-750 kHz 50-1,000 15-2250 15% 250-500 kHz 50-1,000
12.5-500 5% 250-500 kHz 50-1,000 25-1000 10% 250-500 kHz 50-1,000
37.5-1500 15% 300 kHz 50-1,000 15-300 5% 300 kHz 50-1,000 30-600
10% 300 kHz 50-1,000 45-900 15%
[0076] In yet another embodiment, a toothbrush of the present
invention having an ultrasound transducer operates at an ultrasound
frequency of from 250-350 kHz, at a duty cycle of about 10% with
about 5,000 cycles per burst at a pulse repetition frequency of
about 6 Hz. In yet another embodiment, a toothbrush of the present
invention having an ultrasound transducer operates at an ultrasound
frequency of from 250-350 kHz, at a duty cycle of about 10% with
about 500 cycles per burst at a pulse repetition frequency of about
60 Hz.
[0077] As used herein, the term "acoustic streaming" refers to the
bulk or coherent flow of fluid that occurs due to momentum transfer
from an acoustic wave to a fluid as a result of attenuation of an
ultrasound beam. Ultrasound propagating into fluid, with or without
bubbles, can generate "acoustic streaming," which can be quite
significant in size and extent, and even greater with than without
bubbles in the fluid. Acoustic streaming generally requires higher
frequencies than required for stimulating the bubbles--the higher
the frequency, the greater the acoustic streaming.
[0078] The acoustic streaming velocity, V, is proportional to the
amplitude absorption coefficient, .alpha., of the fluid, which is
itself proportional to the frequency of the ultrasound under linear
acoustic propagation conditions, and even more strongly dependent
upon frequency under nonlinear acoustic propagation conditions, and
inversely proportional to its kinematic viscosity, v, as
follows:
V=(.alpha.l.sup.2I/cV)(G)
where I is the intensity in the beam of ultrasound and l the
ultrasound beam diameter, c is the velocity of sound and G is a
geometric factor that depends upon the size of the acoustic beam.
Zauhar et al., British J. of Radiology 71:297-302 (1998).
[0079] Ultrasound operating parameters for promoting "acoustic
streaming" in the context of toothbrushes of the present invention
may vary from those employed for promoting acoustic microstreaming.
The ultrasound parameters that generally promote acoustic streaming
include a carrier frequency typically greater than about 20 kHz;
more typically, between about 500 kHz and about 5,000 kHz or more,
to enhance acoustic absorption. The pulse repetition frequency
("PRF") is typically, though not exclusively, between about 1 Hz
and about 10,000 Hz; more typically between about 10 Hz and about
10,000 Hz; still more typically between about 100 Hz and about
10,000 Hz; and yet more typically, between about 1,000 Hz and about
10,000 Hz. The number of individual ultrasound waves within a
packet or burst of ultrasound is typically between 1 and 5,000
cycles/burst; more typically between about 5 and about 100
cycles/burst. To enhance "acoustic streaming," longer duty cycles
are typical, such as, for example, at least about 10%; more
typically between about 25% and about 100%; still more typically
between about 50% or about 75% and about 100%. Longer bursts, e.g.,
greater than about 100 waves at a frequency of about 1 MHz, with a
PRF of at least 1,000 Hz, are exemplified herein.
[0080] As used herein, the term "mechanical index" refers to a
measure of the onset of cavitation of a preexisting bubble
subjected to one cycle of applied acoustic pressure. Holland et
al., IEEE Transactions on Ultrasonics, Ferroelectrics, and
Frequency Control 36(2):204-208 (1989); and Apfel et al.,
Ultrasound Med. Biol. 17(2):179-185 (1991). This measure is
proportional to the peak negative pressure (MPa) amplitude and
inversely proportional to the square root of the frequency (MHz) of
the applied sound. When the value of mechanical index exceeds 1.9,
it is possible for ultrasound to produce inertial cavitation, the
most mechanically active type of cavitation, which is in excess of
the amount required to remove plaque. The governing assumptions
require isothermal growth of an optimally sized bubble, the neglect
of gas diffusion into the bubble, and that the fluid surrounding
the bubble is incompressible. These three assumptions produce the
most active bubble collapse, making the mechanical index a
conservative measure of the onset of inertial cavitation.
[0081] Empirical evidence indicates that plaque removal may be
achieved with mechanical indices as low as 0.1. Theoretical
considerations, however, suggest that plaque reduction may be
achieved with mechanical indices as low as 0.01. Krasovitski et
al., IEEE Transactions on Ultrasonics, Ferroelectrics, and
Frequency Control 51(8):973-979 (2004). For example, the shear
stress on a wall created by acoustic microstreaming associated with
a bubble suspended in water and subjected to ultrasound at a
frequency of 430 kHz and pressure amplitude of 10,000 Pa (e.g., a
mechanical index of approximately 0.01) is predicted to be
approximately 5 Pa, which is sufficient to remove plaque via steady
flow over plaque. Stoodley et al., J. Industrial Microbiology &
Biotechnology 29:361-367 (2002). The mechanical indices delivered
by toothbrushes of the present invention are generally in the range
of about 0.001 to about 1,000. More typically, mechanical indices
are in the range of about 0.001 to about 100, still more typically
in the range of about 0.002 to about 20, and even more typically in
the range of about 0.01 to about 5, or between about 0.01 and about
1.9. Toothbrushes delivering mechanical indices of less than about
1.9, more typically less than about 1.5, and frequently less than
about 1.2 are contemplated by the present invention.
[0082] The acoustic output of an ultrasound device, measured as the
peak negative acoustic pressure, is related to the mechanical
index. Suitable operating peak negative acoustic pressure
parameters in toothbrushes of the present invention are generally
in the range of from about 0.01 to 100 MPa; more typically in the
range of from 0.1 to 10 MPa; for many embodiments in the range of
from 0.1 to 1 MPa; for many embodiments in the range of from 0.25
to 0.6 MPa; and in yet other embodiments in the range of from 0.3
to 0.5 MPa.
[0083] As used herein, the term "microbubble" refers to microscopic
bubbles present in the oral cavity, for example, in the dental
fluid or plaque. "Microbubbles" may be endogenous to the fluid,
such as through the introduction of an appropriate dentifrice; may
be generated by toothbrush bristles through manual brushing; and/or
may be generated by bristles in combination with the sonic
component of certain of the presently disclosed power toothbrushes.
"Microbubbles" are acted upon by an ultrasonic signal transmitted
by an ultrasonic transducer and propagated by an acoustic
waveguide. "Microbubbles" resonate at or near a specific frequency
depending upon the microbubbles' diameter.
An Exemplary Toothbrush
[0084] FIG. 1A shows an exemplary toothbrush 10 according to the
present invention. The toothbrush 10 comprises a handle 15
constructed of a rigid or semirigid material, and typically houses
a rechargeable battery 12 that is preferably adapted to be
induction charged; electrical circuitry, including an ultrasonic
module drive circuit 14; a sonic component 16 comprising a motor,
preferably a DC motor for driving a toothbrush head 20 at sonic
frequencies; and a timer and motor control unit 18. Suitable
motors, ultrasonic drive circuits, rechargeable batteries, and
timer and motor control units are well known in the art.
[0085] Attached to the handle 15 is a toothbrush head 20 including
a support structure including a stem portion 21 and further
comprising an ultrasonic transducer 22 and an acoustic waveguide 24
in operable proximity and acoustically coupled to the ultrasonic
transducer 22. In the toothbrush embodiment presented in FIG. 1A,
an ultrasound reflection element 28 is shown behind, and extending
around each side of, the ultrasonic transducer 22. It will be
appreciated that the ultrasound reflection element 28 at least
partially reflects the ultrasound through the acoustic waveguide 24
and into the dental fluid. The toothbrush head 20 may be either
removably or fixedly attached to the handle 15. In general, the
toothbrush head 20 includes a plurality of bristle tufts 26
retained by the support structure 21 and disposed generally
adjacent to, or near to, the acoustic waveguide 24. The toothbrush
head 20 may optionally include an impedance matching layer 29. The
impedance matching layer 29 improves the efficiency of the device,
as discussed below.
[0086] In the disclosed embodiment, alternating current supplied by
the ultrasonic module drive circuit 14 drives the ultrasonic
transducer 22 such that the transducer 22 expands and contracts
primarily along one axis at or near resonance with the frequency
supplied by the ultrasonic module drive circuit 14, thereby
converting electrical energy into ultrasonic energy. The resulting
ultrasonic sound waves are conducted into, propagated through,
focused by, and radiated out of the acoustic waveguide 24. The
focused ultrasonic energy acts on microbubbles within the dental
fluid (typically saliva and dentifrice, not shown) to induce
cavitation, thereby loosening plaque deposited on the teeth and in
interproximal regions.
The Ultrasonic Transducer and Module
[0087] As described above, certain embodiments of the present
invention provide a toothbrush 10 that employs an ultrasonic
transducer 22 to generate ultrasonic energy in combination with an
acoustic waveguide 24 to efficiently propagate that ultrasonic
energy into the dental fluid. Microbubbles, either present in the
dental fluid through conventional, manual brushing action with a
manual toothbrush and/or formed by action of a sonic component 16
driving the motion of the toothbrush bristle tufts 26 and/or
acoustic waveguide 24 at sonic velocities (see below), are
stimulated through ultrasonic energy-induced cavitation to achieve
"scrubbing bubbles" that are effective in loosening and removing
plaque from a tooth surface and interproximal regions at a finite
distance from the toothbrush head.
[0088] Absent action of the ultrasonic transducer 22 of the present
invention, microbubbles are simply passive voids within the dental
fluid. The ultrasonic transducer 22 disclosed herein causes these
microbubbles to pulsate, thereby generating local fluid motion
around the individual bubbles. This effect is referred to herein as
"microstreaming" and, in combination with the ultrasonic cavitation
effects, achieves shear stresses that are sufficient to disrupt
plaque. Typically, shear stresses achieved by microstreaming
induced by the ultrasonic transducer 22 of the present invention,
are between about 0.1 N/m and about 1,000 N/m. More commonly, shear
stresses achieved by microstreaming are between about 0.2 N/m and
about 500 N/m. Still more commonly, shear stresses are between
about 0.3 N/m and about 150 N/m. And most commonly, shear stresses
are between about 1 N/m and about 30 N/m.
[0089] Another effect of the ultrasonic transducer 22 is that it
promotes acoustic streaming and produces momentum within the dental
fluid in a direction toward the teeth and interproximal and
subgingival spaces, thereby increasing the velocity and coherency
of the dental fluid. This bulk fluid-flow process is referred to
herein as acoustic streaming. Either through the generation of
acoustic microstreaming and/or acoustic streaming, the associated
shear and pressure forces act to erode and dislodge the plaque in a
manner and to an extent that is in excess of that achieved by the
toothbrush bristle tufts 26 alone. In particular, these ultrasonic
effects are facilitated by propagating the ultrasonic waves from
the ultrasonic transducer 22 through an acoustic waveguide 24 and
into the dental fluid near and beyond the tips of bristle tufts
26.
[0090] Ultrasonic transducers 22 that may be suitably employed in
the ultrasonic toothbrush 10 of the present invention are readily
available in the art (see, for example, U.S. Pat. No. 5,938,612 and
U.S. Pat. No. 6,500,121, each of which is incorporated herein by
reference in its entirety) and, most commonly, operate either by
the piezoelectric or magnetostrictive effect. Magnetostrictive
transducers can, for example, produce high intensity ultrasonic
sound in the 20-40 kHz range. Alternatively, ultrasound may be
produced by applying the output of an electronic oscillator to a
thin wafer of piezoelectric material, such as lead zirconate
titanate (PdZrTi or PZT). There is a wide variety of piezoelectric
PZT ceramic blends that can be used to fabricate ultrasonic
transducers suitable for use in the toothbrushes of the present
invention. Other transducer materials, such as piezopolymers,
single or multilayer polyvinylidene fluoride (PVDF), or crystalline
piezoelectric materials, such as lithium niobate (LiNbO.sub.3),
quartz, and barium titanites, may also be used. Ultrasound
transducers may be flat or curved (as, e.g., in a conic section) to
focus the ultrasonic waves.
[0091] In addition to piezoelectric materials, capacitive
micromachined ultrasonic transducer (cMUT) materials or
electrostatic polymer foams are also suitable. Many of these
materials can be used in a variety of vibrational modes, such as
radial, longitudinal, shear, etc., to generate the acoustic waves.
In addition, single-crystal piezoelectric materials, such as
Pb(Mg.sub.1/3Nb.sub.1/3)O.sub.3--PbTi0.sub.3 (PMN-PT),
K.sub.1/2Na.sub.1/2NbO.sub.3--LiTaO.sub.3--LiSbO.sub.3 (KNN-LT-LS)
as described in Lead-free piezoelectric ceramic in the
K.sub.1/2Na.sub.1/2NbO.sub.3 solid solution system, N. Marandian
Hagh, E. Ashbahian, and A. Safari presented at the UTA symposium
March 2006, and others, may be used to reduce
voltage/transmit-level ratios by as much as an order of
magnitude.
[0092] In addition to the transducer materials, one or multiple
impedance matching layers 29 (typically designed as quarter-wave
matching layers) can help to improve the efficiency and bandwidths
when transmitting from the commonly high-impedance transducer
materials into the much lower impedance acoustic waveguide
materials. Generally, a matching material is chosen with a
thickness that will support a quarter wave of the desired frequency
and an acoustic impedance optimally selected within the two
impedances to be matched. Appropriate materials can include
materials such as epoxy and metal particulate composites, graphite,
or a host of other candidate materials known by and readily
available to the skilled artisan.
[0093] In one embodiment, as illustrated in FIG. 1B, an ultrasound
transducer suitable for use in toothbrushes of the present
invention comprises two or more piezoelectric elements. In a
currently preferred embodiment the ultrasonic transducer 30 has a
rectangular or trapezoidal profile and includes two piezoelectric
elements 32 and 34 with one or more electrical contact(s) 36
contacting the piezoelectric elements and in electrical contact
with an ultrasonic module drive circuit 14 (FIG. 1A) handle 15. The
ultrasonic module drive circuit 14 may be placed elsewhere in the
apparatus, for example in the brush head 20. The piezoelectric
elements 32, 34 are stacked in series mechanically, and connected
in parallel electrically. Mechanical stacking the elements in
series provides that the displacements associated with the
individual piezoelectric elements 32, 34 are added. Electrically
connecting the piezoelectric elements 32, 34 in parallel provides
that the capacitance associated with the individual piezoelectric
elements 32, 34 are also additive. This provides a greater range of
electronics driving possibilities.
[0094] The ultrasonic transducer 30 may also comprise an impedance
matching layer 38 and one or more mounting prongs 40 for
interaction with an acoustic waveguide and/or to facilitate
placement of the transducer 30 in the brush head 20. Although a
generally rectangular ultrasonic transducer 30 structure is
illustrated, it will be appreciated that piezoelectric elements and
transducer structures may be provided in a variety of two and three
dimensional configurations and that non-rectangular ultrasonic
transducer structures may be used in toothbrushes without departing
from the present invention.
[0095] It is contemplated that the ultrasonic transducer 30 may be
provided as a component of an ultrasound generator module designed
for installation in toothbrushes of the present invention, the
module including one or more piezoelectric crystal(s) with attached
electrodes, one or more optional matching layer(s), one or more
acoustic waveguide(s), and a supporting structure. The supporting
structure is designed to direct ultrasonic wave propagation through
the optional matching layer(s) and waveguide. This may, for
example, be accomplished by selecting the supporting structure
coupling features to coincide with areas of minimal motion (nodal
mounting) on the piezoelectric ceramic, matching layer, and
waveguide. In one embodiment, the acoustic waveguide has a base
portion that is mounted over the transducer assembly and extends
from the transducer assembly. One suitable mounting orientation,
for example, is to locate the ultrasound transducer in the body of
the brush head with the acoustic waveguide extending from the base
of the brush head in the same direction as the bristle tufts. The
transducer module generally resides within the toothbrush head and
is replaced with the bristles and brush head when the toothbrush
head exceeds its useful life.
[0096] Additional waveguide supporting structures may also be
provided as structural features of the transducer module or the
brush head structure. A waveguide support flange may be provided in
proximity to the perimeter of the waveguide structure extending
from the brush base, for example, to provide a rigid structure
supporting the base of the waveguide.
[0097] Regardless of the precise configuration of the individual
elements that comprise the ultrasound module, the piezoelectric
element, matching layer and/or the waveguide shape are generally
designed to focus the acoustic energy at a desired location
relative to the emanating surface or to disperse the acoustic
energy in a specific beneficial pattern. The ultrasonic energy may,
for example, radiate directly from a generating source such as a
piezoelectric ceramic element directly into the oral cavity fluid
without an intervening matching layer or waveguide. Alternatively,
an acoustic waveguide may be placed directly on the piezoelectric
ceramic. In still further embodiments, the entire ultrasonic
module, including the acoustic waveguide, are fabricated from a
piezoelectric polymer.
[0098] The following section describes the acoustic waveguide
structure in greater detail.
The Acoustic Waveguide Structure
[0099] As indicated above, one aspect of the present invention is
based upon the observation that an acoustic waveguide used in
operable combination with an ultrasonic transducer is effective in
propagating ultrasonic waves from the transducer into the dental
fluid, thereby generating and/or causing cavitation of microscopic
bubbles (microbubbles) present within the dental fluid. Typically,
as shown in FIG. 1A, the ultrasonic transducer 22 is positioned at
the base of the toothbrush head 20, in operable proximity and
acoustically coupled to the acoustic waveguide 24, such that
ultrasonic waves are efficiently propagated into and through the
acoustic waveguide 24 and into the dental fluid (not shown). As
noted above, within certain embodiments, the present invention also
provides power toothbrushes 10 comprising a toothbrush head 20
having an acoustic waveguide 24 wherein the toothbrush head 20 is
operably connected to a sonic component 16 and wherein the sonic
component 16 causes the acoustic waveguide 24 to vibrate so as to
increase the flow and generation of microbubbles in the dental
fluid into which the acoustic waveguide 24 is immersed during
use.
[0100] Within still further embodiments are provided power
toothbrushes 10 comprising a combination of an acoustic waveguide
24 in operable proximity to an ultrasonic transducer 22 and
operably connected to a sonic component 16 to achieve still further
improved dental cleaning properties owing to the combined increase
in fluid flow and microbubble formation, as well as cavitation and
acoustic microstreaming effects. Here, operable connection can be
facilitated by putting the ultrasonic transducer 22 in direct
contact with the acoustic waveguide 24 or, alternatively,
ultrasound conducting material such as an impedance matching layer
29 can be placed between the ultrasonic transducer 22 and the
acoustic waveguide 24 both to increase the efficiency of ultrasound
transmission from the transducer 22 into the acoustic waveguide 24
or, alternatively or additionally, to usefully increase the
distance between the transducer 22 and the acoustic waveguide 24 to
facilitate the manufacturing process of the device, for
example.
[0101] The acoustic waveguide provides a conduit for the
transmission of ultrasonic waves from the ultrasonic transducer,
where they are generated, through an (optional) impedance matching
layer, to the fluid in the oral cavity. The acoustic waveguide, in
general, has a size and profile that is substantially larger than
that of an individual bristle or bristle tuft and is substantially
more effective in delivering ultrasonic energy to the fluid in the
oral cavity. The length of the waveguide is, typically, a factor of
approximately 1.5-2.5 times the wavelength of the ultrasonic waves
in the waveguide medium multiplied, although the length may vary in
increments of approximately one-half wavelength to achieve
efficient ultrasound wave propagation. The actual height and width
of the acoustic waveguide is determined by design parameters such
as the ultrasound transducer face area, mounting considerations,
and aesthetic requirements.
[0102] FIG. 1C illustrates an exemplary acoustic waveguide
structure 50 in combination with the exemplary ultrasonic
transducer 30 shown in FIG. 1B. The waveguide structure 50
comprises a base structure 52 sized to (at least partially) cover
the ultrasound transducer 30 and having a configuration generally
matching that of the ultrasound transducer. Base structure 52 is
generally mounted and anchored in a toothbrush head 20 (FIG. 1A)
with distal waveguide portion 54 extending outwardly from the brush
head structure. The waveguide structure 50 is preferably a unitary
structure having a generally block-like three-dimensional
configuration having multiple faces. In the embodiment illustrated,
the cross-sectional area of base structure 52 is generally larger
than the cross-sectional area of distal waveguide portion 54 and
opposing side walls 56 and end walls 58 are tapered and terminate
distally in a distal waveguide face 60. Distal waveguide face 60
may be curved in a generally convex configuration, as illustrated
in FIG. 1C. In alternative embodiments, distal waveguide face 60
may be generally flat, curved in a generally concave configuration,
or curved in a more complex configuration. The intersections of one
or more of the waveguide faces may be rounded or chamfered, as
shown, or they may form angular corners. Additional waveguide
embodiments are described in greater detail below.
[0103] Rigid acoustic waveguides, such as solid waveguides made
from aluminum or titanium, and hollow waveguides filled with
degassed water, have been described for the delivery of high
intensity focused ultrasound (HIFU) into living tissue for
therapeutic purposes (such as drug delivery and hemostasis) via
heat induction and/or for the generation of inertial cavitation.
See, e.g., U.S. Patent Publication No. 2003/0060736 to Martin et
al. and Mesiwala et al., Ultrasound in Medicine and Biology
28(1):389-400 (2002). These applications for acoustic waveguides
demonstrate the use of a physical member to facilitate propagation
of ultrasound beyond the face of an ultrasound transducer to
achieve therapeutic benefit. The currently preferred waveguide
structure is, in contrast, based upon the observation that acoustic
waveguides comprising a flexible member, typically having a flat
profile, may be employed in combination with an ultrasound
transducer to facilitate propagation of ultrasound into the oral
cavity to stimulate existing bubbles to remove plaque in a way that
also optimally generates a bubbly fluid jet (due to the flat aspect
of the profile) and promotes a favorable mouth feel.
[0104] The dental fluid into which the acoustic waveguide is
immersed during use is typically a saliva and toothpaste emulsion
that is very acoustically absorptive due to the presence of large
air pockets within individual bristle tufts and between neighboring
bristle tufts and, without the use of an acoustic waveguide, would
attenuate significant amounts of the ultrasound before the wave
front reached the tooth and gum surfaces. The air medium has very
low acoustic impedance, which creates a large impedance mismatch
with the high acoustic impedance materials generally used in the
ultrasonic transducer. This impedance mismatch is a significant
barrier to sound transmission from the ultrasonic transducer to the
tooth and gum surfaces. The acoustic waveguide serves as a bridge
across this acoustic mismatch by accepting, containing, and
transmitting the acoustic energy into the saliva and toothpaste
emulsion near the tooth surface, thereby overcoming the attenuation
effect normally encountered by the saliva and toothpaste
emulsion.
[0105] A variety of acoustic waveguide designs are contemplated by
the present invention as exemplified by the acoustic waveguides
illustrated in FIGS. 2-5 and 9A-9H. Depending upon the precise
embodiment of the present invention, the acoustic waveguide may be
used alone, in combination with a sonic component, and/or in
combination with an ultrasonic transducer. Suitable acoustic
waveguides have in common the capacity to physically move the
dental fluid and/or to efficiently facilitate the propagation and
possibly the focusing of ultrasonic waves transmitted by the
ultrasonic transducer, thereby enhancing fluid motion and the
associated effects of the resulting cavitation and micro
streaming.
[0106] FIG. 2A shows an embodiment of an exemplary power toothbrush
head 120 comprising an ultrasonic transducer 122 in combination
with an acoustic waveguide 124. The side view shows the acoustic
waveguide 124, which carries the ultrasonic energy from the
ultrasonic transducer 122 to the teeth and gums (not shown).
Acoustic waveguide 124 is in operable proximity and acoustically
coupled to the ultrasonic transducer 122 and adjacent to and
flanking, on one or more sides, bristle tufts 126. The size and
configuration of the base of acoustic waveguide 124, in this
embodiment, generally matches the size and configuration of
ultrasonic transducer 122 and/or impedance matching layer 129. The
tip of acoustic waveguide 124 distal from the ultrasonic transducer
122 has a smaller cross-sectional area than that of the base of
acoustic waveguide 124 in proximity to ultrasonic transducer
122.
[0107] The acoustic waveguide 124, in the embodiment illustrated in
FIG. 2A, has one dimension oriented generally along the
longitudinal axis of the brush head 120 (the length), that is wider
than the diameter of a bristle tuft 126 and, more preferably, has a
length that is greater than the (side-to-side) combined diameters
of two bristle tufts 126. In another embodiment, the length of the
acoustic waveguide 124 is greater than the (side-to-side) combined
diameters of five bristle tufts 126. In another dimension, the
width of the acoustic waveguide 124 (oriented generally transverse
to the longitudinal axis of the brush head 120 as shown in FIG. 2A)
at its base is generally greater than the diameter of a bristle
tuft 126 and, in some embodiments, is generally greater than the
(side-to-side) combined diameters of at least two bristle tufts
126.
[0108] In one embodiment, the height of the acoustic waveguide 124
exposed when the waveguide is mounted in the brush head 120 is less
than the exposed height of at least one bristle tuft 126 and, in
another embodiment, the height of the acoustic waveguide 124
exposed when the waveguide is mounted in the brush head 120 is less
than the exposed height of each of the bristle tufts 126. In
another embodiment, the height of the exposed acoustic waveguide
124 portion is greater than at least one bristle tuft 126 provided
in the brush head 120. In general, the exposed height of the
acoustic waveguide is greater than about 50% and less than about
120% of the exposed height of the bristle tufts 126. In yet another
embodiment, the exposed height of the acoustic waveguide 124 is
greater than about 70% and less than about 110% of the exposed
height of the bristle tufts 126. In some embodiments, the
cross-sectional area of waveguide 124 at its distal face is at
least five times greater than that of a bristle tuft 126; in
another embodiment, the cross-sectional area of waveguide 124 at
its distal face is at least ten times greater than that of a
bristle tuft 126; and in another embodiment, the cross-sectional
area of waveguide 124 at its distal face is at least twenty times
greater than that of a bristle tuft 126. In this exemplary design,
the acoustic waveguide 124 is made from a soft, smooth material,
such as silicone rubber, known for both its pleasant surface
texture and ability to transmit ultrasound. Impedance matching
layer 129 is disposed between acoustic waveguide 124 and ultrasonic
transducer 122.
[0109] Two parameters that substantially affect the transmission of
ultrasonic waves through an acoustic waveguide are (1) the material
from which the waveguide is fabricated, and (2) the geometry of the
waveguide. Each of these parameters is described in further detail
herein. Regardless of the precise acoustic waveguide material and
geometry employed, the present invention contemplates the selection
of parameters to achieve a favorable mouth feel. Thus, the material
from which the acoustic waveguide is fabricated or molded is
preferably soft enough to be appealing when placed within the mouth
and/or direct contact with the mouth. As will be appreciated by one
skilled in the art, an acoustic waveguide with an appealing texture
is ideally designed to efficiently couple in, conduct, coherently
focus, incoherently compress, and couple out the acoustic
energy.
[0110] The selection of suitable materials for fabricating an
acoustic waveguide for use in a toothbrush of the present invention
can be readily achieved by the skilled artisan in consideration of
the following guidelines. Various dielectric materials, such as
silicon dioxide (SiO.sub.2), silicon nitride (Si.sub.3N.sub.4), and
many polymers can be used as the waveguide material. For example,
silicone rubber and other types of rubbers, silicone materials such
as castable/moldable RTV, liquid injection-molded (LEVI) silicone,
thermoplastic elastomers, thermal plastic elastomer (TPE)
injection-molded processes, and closed or open cell foams may all
be used. Polymers have an advantage over other waveguide materials,
owing to their relatively low shear wave velocity. However, because
of their viscoelasticity, cross-linking may be necessary to avoid
excessive acoustic loss and provide equilibrium elastic stress,
thus providing a more stable waveguide layer.
[0111] The hardness of materials suitable for use in acoustic
waveguides of the present invention may be determined by either the
Shore (Durometer) test or the Rockwell hardness test. Both of these
hardness test methodologies are well known and readily available in
the art. These tests measure the resistance of materials to
indentation and provide an empirical hardness value. Shore
hardness, using either the Shore A or Shore D scale, is the
preferred method for rubbers/elastomers and is also commonly used
for "softer" plastics, such as polyolefins, fluoropolymers, and
vinyls. The Shore A scale is generally used for "softer" rubbers,
while the Shore D scale is generally used for "harder" materials.
Shore hardness is measured with a Durometer and, consequently, is
also known as Durometer hardness. The hardness value is determined
by the penetration of the Durometer indenter foot into the sample.
The ASTM test method designation is ASTM D2240. Related methods
include ISO 7619, ISO 868, DIN 53505, and JIS K 6253. Each of these
Durometer test methodologies is hereby incorporated by reference in
their entireties.
[0112] The Durometer measurement of acoustic waveguides employed in
toothbrushes of the present invention generally range in hardness
from 5 Shore A to 60 Shore D, more typically from 10 to 100 Shore
A, and still more typically from 10 to 65 Shore A. An acoustic
waveguide hardness of approximately 40 Shore A or less is preferred
for many applications to provide oral comfort. It will be apparent
to the skilled artisan that harder materials may be employed in the
acoustic waveguides used in conjunction with the power toothbrushes
of the present invention; however, harder materials may provide a
progressively unpleasant mouth feel. The waveguide material may
have isotropic or anisotropic properties or, in an alternative
embodiment, may comprise one material having isotropic properties
and another material having anisotropic properties.
[0113] The present invention also contemplates that more than one
material may be used in combination to achieve acoustic waveguides
having preferred properties of hardness and mouth feel and
providing an acoustic impedance matching function. Different
materials may be provided as multiple layers forming a unitary
component, or different materials may be provided in selected
locations to impart desired material and acoustic properties, the
latter including, for example, focusing of the ultrasound emitted
from the transducer to a point at and near the average distance
from the distal tip of the waveguide to the tooth surfaces within
the interproximal space and/or the lingal or buccal surfaces of the
teeth. For example, additional acoustic matching elements may be
embedded or stratified within the acoustic waveguide structure and
be in operable contact with the ultrasonic transducer via one or
more matching layers. Within certain embodiments, acoustic
waveguides of the present invention further provide a matching
layer at the waveguide tip to help coupling into low impedance
toothpaste emulsions (e.g., dental fluid). Ideally, there will also
be a significant specific acoustic impedance change between the
sides of the acoustic waveguide and the surrounding medium such
that the waves are not coupled substantially into the surrounding
medium by the sides of the acoustic waveguide. In one embodiment, a
matching layer of graphite, mineral, or metal-filled epoxy is
provided between a ceramic transducer element and the waveguide.
Another embodiment may combine the functions of a matching layer
and waveguide by fabricating a stratified part with varying
acoustical impedance in the direction of wave propagation. The
variation in acoustical impedance of the acoustic waveguide may be
a linear or nonlinear function.
[0114] Exemplified herein are prototype transducer assemblies
having a graphite impedance matching layer in operable contact with
a piezoelectric ultrasonic transducer. As shown in FIG. 9A, a
waveguide assembly 150A may include a graphite core portion 152A or
similar material that may be inserted into an injection mold, and
an elastomer outer portion 154A molded or otherwise provided around
it using, for example, the process of insert molding.
Alternatively, a multishot technique may be used to create a
gradient of materials with different acoustic and elastomeric
properties. As used herein, the term "multishot" refers to the
placement of several shots of thermoplastic material into one mold.
This process may be employed, for example, in acoustic waveguide
embodiments in which a first relatively hard material layer (e.g.,
about Shore 80 hardness or greater) is in operable proximity to the
ultrasonic transducer element; a second, relatively soft material
layer (e.g., between about Shore 20 and Shore 80) is immediately
adjacent to and in contact with the first material layer; and a
third, still softer (e.g., about Shore 20 hardness or less)
material layer is immediately adjacent to and in contact with the
second layer, for a very gentle feel against teeth. These exemplary
acoustic waveguide designs may either be formed as individual
pieces or, alternatively, they may be molded in combination with
the material forming the toothbrush head and/or the support for the
bristles.
[0115] In preferred embodiments, acoustic waveguides of the present
invention are substantially free from unfilled or gas-filled voids.
To the extent that multiple materials are used to form a waveguide,
those materials generally contact each other closely without
allowing the formation of air gaps between surfaces. For some
embodiments, however, it may be desirable to form one or more voids
in the acoustic waveguide and substantially fill the voids with a
material that has good acoustic transmission properties at the
ultrasound operating parameters described herein.
[0116] Thus, within certain embodiments, acoustic waveguides of the
present invention may comprise two or more plastic/elastomer
layers. For example, acoustic waveguides comprising three, four,
and/or five plastic/elastomer layers are contemplated for certain
applications. Such acoustic waveguides may further comprise one or
more inserted pieces for shaping the acoustic properties and
optimizing sonic properties. One function of an acoustic waveguide
used in combination with an ultrasound transducer is to focus the
ultrasound, as described above. In one embodiment, rigid or
semi-rigid layer may be positioned in front of (distal to) the
matching layer to provide improved acoustic properties. Using this
type of intermediate layer allows a lower durometer elastomer
waveguide to provide a softer feel to the teeth under sonic
conditions, which is preferred for some embodiments.
[0117] Referring now to FIGS. 9A-9H, it will be appreciated by the
artisan that acoustic waveguides may be formed in any of a variety
of three-dimensional shapes or geometries. For example, FIG. 9A
shows a waveguide 150A having a generally curved and tapered
geometry. The two opposing sidewalls of waveguide 150A taper from a
wider base portion to a narrower tip portion and are generally
planar, having a symmetrical curved profile. The taper angle,
defined as the angle between a line extending perpendicularly from
the base and the sidewall, is generally from about 0.5.degree. to
about 20.degree., more generally from about 1.degree. to about
10.degree., and the taper angle of each side wall is generally
substantially similar and in an opposite direction. The distal face
of waveguide 150A is generally symmetrically curved and generally
semi-circular. In alternative embodiments, the waveguide edge may
be asymmetrically curved or may form multiple curved apexes having
the same or different dimensions and configurations.
[0118] FIG. 9B illustrates an alternative waveguide 150B having a
generally rectangular portion and a converging or wedge-shaped
portion 152B. The generally rectangular portion forms a base that
is mounted in proximity to the acoustic waveguide. The taper angle
of the side walls forming the wedge-shaped portion 152B is
generally from about 5.degree. to about 65.degree., more generally
from about 10.degree. to about 45.degree., and the taper angle of
each side wall is generally substantially similar and in an
opposite direction. The faces of the side walls are generally
rectangular rather than presenting a curved profile. The edges of
the sidewalls may be chamfered or curved to provide a softer mouth
feel. In the embodiment illustrated, the base portion and the
tapered portion are generally equivalent in height. It will be
appreciated that the relative dimensions of each portion may vary,
depending on the properties of the materials used, the physical and
geometrical properties of the underlying ultrasound transducer, and
the acoustic transmission properties desired.
[0119] FIG. 9C shows an alternative waveguide 150C, wherein a
converging portion comprises a plurality of sections 152C that may
be separated by gaps 154C. The waveguide sections and gaps may be
spaced symmetrically or asymmetrically and may have uniform or
different sizes. In other words, one or more of the waveguide
sections may have a different profile or different dimensions than
other waveguide sections and, likewise, the waveguide gaps may be
non-uniform. Similarly, although waveguide sections and gaps are
shown having generally rectilinear faces and profiles, alternative
profiles may have curved or rounded components.
[0120] FIG. 9D shows an alternative waveguide 150D having a
generally round base suitable for use in combination with a
generally round ultrasound transducer and a bullet-shaped body 152D
with minor protuberances 154D to promote fluid flow. Protuberances
154D are arranged in a generally radially symmetrical arrangement
around the circumference of bullet-shaped body 152D and are
arranged along a curved path. The protuberances taper from a
narrower width at the smaller diameter portion of the bullet-shaped
body to a larger width at the larger diameter portion of the
bullet-shaped body. Although three protuberances are illustrated,
it will be appreciated that a greater number of protuberances may
be provides in a generally radially symmetrical arrangement.
[0121] FIG. 9E shows an alternative waveguide 150E having tapered
side walls and a converging portion 152E having a curved, generally
centrally located apex 154E formed on the distal face. It will be
appreciated that, although a simple, centrally placed curved apex
154E is shown, it may be desirable in some circumstances to provide
a more complex curved apex or curved distal faces having other
symmetrical or asymmetrical configurations.
[0122] FIG. 9F shows an alternative waveguide 150F that is
conically shaped. FIG. 9G shows an alternative waveguide 150G that
is biconical. FIG. 9H shows an alternative waveguide 150H having a
plurality of pyramid-shaped portions 152H. Certain design
considerations regarding selection of an appropriate waveguide
geometry will now be discussed. The shape of the waveguides may be
selected, for example, to achieve a particular compression and/or
focusing of the acoustic waves.
[0123] Within certain embodiments of the present invention,
acoustic waveguides are capable of acoustic coherent focusing of
the ultrasonic waves transmitted from the ultrasonic transducer.
Acoustic coherent focusing may be achieved, for example, by curving
the waveguide tip wherein the tip comprises a conductive medium
having a known sound speed. Alternatively, a section of
ultrasound-conducting polymer having a known wave speed may be
added to the end of a curved waveguide to nearly complete focusing
before entering a medium of variable sound speed (e.g., dispersive
bubbly medium). Within such embodiments, a single curve may be
employed to achieve a single focus, whereas a scalloped curve is
useful for producing multiple foci.
[0124] Within alternative embodiments, acoustic waveguides are
capable of acoustic incoherent focusing of the ultrasonic waves
transmitted from the ultrasonic transducer. Acoustic incoherent
focusing may be achieved, for example, by conical or wedge shapes
that conduct sound into a progressively smaller area in a
semicoherent manner such that intensity increases. Alternatively,
multiple conical tips may be employed to provide multiple areas of
higher acoustic intensity.
[0125] Suitable acoustic waveguides may also adopt a propeller-like
geometry such as a standard propeller design or a spiral design.
Alternatively, an acoustic waveguide may have a hinged
hydrofoil-like shape wherein its motion creates fluid lift and
consequent fluid flow. The acoustic waveguide may have a generally
smooth exterior surface, or the exterior surface may be rough or
irregular. In some embodiments, the acoustic waveguide may be
designed and fabricated to promote removal of plaque by direct
contact of portions of the acoustic waveguide with teeth. Contact
of the waveguide with tooth surfaces may be provided by altering
the three-dimensional surface of the waveguide, such as by
providing protrusions on waveguide surfaces, or by mounting or
embedding protrusions, such as fibers and the like, on waveguide
surfaces. Acoustic waveguides of the present invention may include,
for example, embedded bristle filaments, squeegee-shaped
protrusions, molded or shaped protrusions similar to bristles,
fibers, or the like. The protrusions or attached fibers may be
arranged in an ordered pattern, or they may be randomly arranged.
In alternative embodiments, the waveguide surface may be provided
with regularly or irregularly spaced depressions. These features
may additionally or alternatively ensure that a specified
separation distance is maintained between the tooth surface and the
bulk surface of the acoustic waveguide. This feature may find
application in those applications wherein it is desired to minimize
direct transmission of ultrasound into the tooth structure and/or
if bubble activation occurs at a distance from the end of the
acoustic waveguide and a spacing device is needed to maintain this
distance.
[0126] Regardless of the precise material and/or geometry, acoustic
waveguides of the present invention are fabricated to generate
fluid flow when moved on a toothbrush head. The desired fluid
motion and transmission of ultrasound into the dental fluid may be
achieved, for example, by employing a flexible mechanical
protrusion that extends into the dental fluid. In such cases,
motion of the acoustic waveguide may be side-to-side or oscillatory
or rotational.
[0127] When acoustic waveguide motion is rotational, the motion may
be generally about or parallel to a longitudinal axis of the
waveguide and may be achieved with a wedge or cone, multiple wedges
or cones in cross or star patterns, a pinwheel, and/or multiple
wedges in a star pattern without a center. Alternatively,
rotational motion may be about the axis along the toothbrush head,
as may be achieved with a wedge- or rectangular-shaped acoustic
waveguide.
[0128] Acoustic waveguides can also be designed to increase the
intensity of acoustic energy delivered to the surface of the teeth
and gums. For example, an acoustic waveguide can be designed to
contain and compress the propagating acoustic energy into a smaller
physical area. If the waveguide is designed with materials of low
acoustic attenuation and with appropriate sound speed, the quantity
of energy delivered from the end of the waveguide will be
comparable to that transmitted into the waveguide, but can be
compressed into a smaller area and will therefore have a higher
energy density and/or acoustic intensity. Waveguide tip motion
creates an "acoustic painting" effect to broadly distribute
acoustic energy.
[0129] In addition to low attenuation, waveguides are generally
designed to channel the acoustic energy along the waveguide, and
transmit or "leak" a minimum of acoustic energy into the
surrounding medium before it has propagated to the end of the
waveguide. One method for achieving this is to use a material
having a sound speed substantially lower than the surrounding fluid
and having shallow slopes on the sides of the waveguide (e.g.,
wedge shaped). The shallow slope of the waveguide walls causes the
propagating waves to contact the waveguide and fluid interface at
low grazing angles. Because the wavelength in the waveguide is
shorter than that of the surrounding medium, the waves will only
couple into less efficient subharmonic modes where the launch angle
is defined by the ratio of multiples of waveguide wavelengths to
surrounding media wavelengths. These poorly coupled modes of
transmission into the fluid do not extract large amounts of energy
from the waveguide.
[0130] The combination of containing, transmitting, and compressing
acoustic energy enables the generation of high intensity acoustic
fields at the waveguide tip and improves the efficiency of acoustic
energy delivery. Therefore, lower electrical power levels are
required to generate appropriate acoustic intensities for bubble
activation. FIGS. 2A-2D (for a rectangular waveguide 124), FIGS.
3A-3F (for a wedge-shaped waveguide 124X), and FIGS. 4A-4D (for a
wedge-shaped waveguide having a curved end 124Y) show finite
element model and simulation results illustrating waveguides
designed to compress the acoustic field. FIG. 2A shows a general,
simplified model of a toothbrush head 120 according to the present
invention, as discussed in detail above. FIG. 2B shows the
corresponding portions of the finite element model used to model
the toothbrush head 120, including a stem 121', an ultrasonic
transducer 122', an impedance matching layer 129', and a waveguide
124'. Plots showing the wave field soon after transmission showing
propagation in the waveguide are shown in FIGS. 2C, 3C, 3E, and 4C
for selected waveguides. These figures evidence a low level of
leakage into the surrounding fluid. FIGS. 2D, 3D, 3F, and 4D show a
wave field plot later, after transmission, at which time the
ultrasonic wave front is compressed into the tip of the waveguide
and the transmission into fluid emulsion is primarily from the
waveguide tip.
[0131] In addition to increasing the acoustic intensity delivered
by compressing the acoustic field, the waveguide can be designed to
coherently focus energy into surrounding media beyond the tip of
the waveguide. This is accomplished by shaping the end of the
acoustic waveguide to create an acoustic lens effect that will
focus the waves from the waveguide into a higher intensity field
beyond the waveguide. This focusing effect can be achieved with one
or multiple waveguide materials combined together and shaped to
create a focused field. For instance, a low attenuation, higher
sound speed material may be used at the end of the waveguide to
continue propagating and focusing the wave front before the wave
front emerges into the higher attenuation toothpaste emulsion. As
with the acoustic field compression described above, the increased
acoustic intensity achieved with the focusing effect improves the
device efficiency. Therefore, size, weight, power, and costs are
reduced and battery life is extended for a final device.
[0132] Still further embodiments provide that the acoustic
waveguide may be configured to exhibit improved fluid propulsion
properties when used in a power toothbrush head in combination with
a sonic component either with or without an ultrasonic
component.
[0133] The waveguide may be positioned having its longest dimension
generally aligned with the longitudinal axis of the toothbrush
head, as shown in FIG. 2A, and the waveguide may be configured to
approximate the contour of tooth surfaces throughout the mouth, the
location of which is not easily perceived by the user and
conversely the location of which is not required to be known by the
user for effective cleaning. Such an orientation is generally less
dependent on user brushing technique/style and allows the user to
brush as he/she would without concern about the waveguide
location.
[0134] Alternatively, the waveguide may be positioned with its
longest dimension generally transverse to longitudinal axis of the
toothbrush head, which allows the waveguide to drop into the
interproximal space and provide tactile feedback to the user such
that the user may index movement from one interproximal space to
the next, thus providing cleaning induced by the ultrasound
interproximally--where it is needed most beyond the bristles. In
this orientation, the waveguide may rely on the natural tendency of
fluid to fill the interproximal space in the oral cavity due to
wetting of adjacent surfaces and wicking of fluid. Such an
orientation may be less reliant on the brush head to carry the
fluid and position it at the tip of the waveguide. Rather, it takes
advantage of the waveguide's penetration of the interproximal space
and activation of bubbles in the fluid naturally found in that
location. In another embodiment, the acoustic waveguide may be
oriented obliquely with respect to the longitudinal axis of the
brush head. The waveguide may be positioned at the end of the brush
head such that it can be effectively used either on the facial or
lingual surface, as well as on the posterior surfaces of the molar
teeth.
[0135] In addition to the functions performed by the acoustic
waveguide as described above, the waveguide, regardless of
orientation, may additionally function to: (a) act as a standoff to
prevent the user from using too much force when applying the
bristles against the teeth, thereby reducing the incidence of
gingival damage from excessive force during brushing; (b) act as a
scrubbing agent, thus cleansing the tooth surface, and as such may
contain a surface texture to enhance; (c) act as a gum massaging
agent, thus stimulating the gums (as often recommended by the
dental professional) to reduce swelling and to help contour the
tissue; (d) act as an agent to stimulate saliva flow, particularly
of interest to individuals with xerostomia.
The Sonic Component
[0136] Within certain embodiments, toothbrushes of the present
invention comprise a sonic component 16 (see, FIG. 1A) in
combination with the acoustic waveguide 24 and/or ultrasonic
transducer 22, described above. Typically, a sonic component 16
comprises a motor assembly that generates sonic vibrations that are
transmitted to the toothbrush head, thereby causing vibration of
the acoustic waveguide 24 and/or bristle tufts 26. Such sonic
vibrations generate bubbly flow within the dental fluid. For
example, by employing a sonic component 16, the acoustic waveguide
24 can be made to lift and push dental fluid towards the teeth as
well as interproximal and subgingival spaces, with an associated
fluid flow of sufficient pressure and shear force to cause the
erosion of plaque. A vibrating acoustic waveguide 24 of the present
invention is capable of moving fluid, including bubbly fluid, with
sufficient velocity and focus to achieve plaque removal from teeth
several millimeters beyond the bristles 26 of the toothbrush head
20. Motor assemblies that may be suitably employed in the
toothbrushes of the present invention are well known and readily
available to those of skill in the art, and are exemplified by the
toothbrush head drive mechanisms presented within U.S. Pat. No.
5,987,681, U.S. Pat. No. 6,421,865, U.S. Pat. No. 6,421,866, Pat.
No. RE 36,669, and U.S. Patent Publication Nos. 2002/0095734, No.
2002/0116775, No. 2002/0124333, and No. 2003/0079304. Each of these
U.S. patents and patent applications is hereby incorporated by
reference in their entireties.
[0137] Toothbrushes of the present invention are capable of
generating fluid flows at a range of about 1 cm/sec to about 50
cm/sec at a distance of between about 1 mm and 10 mm beyond the
toothbrush bristle tips and/or acoustic waveguide. More typically,
toothbrushes of the present invention are capable of generating
fluid flows at a range of about 2 cm/sec to about 30 cm/sec at a
distance of between about 1 mm and 10 mm beyond the toothbrush
bristle tips and/or acoustic waveguide. Exemplified herein are
toothbrushes that are capable of generating fluid flows of about 10
cm/sec at a distance of between about 1 mm and 10 mm beyond the
toothbrush bristle tips and/or acoustic waveguide.
[0138] It will be recognized by those skilled in the art that the
generation of bubbly flow by the sonic actions on the acoustic
waveguide 24 does not require the ultrasonic component 16 described
above. It is, however, the combination of the ultrasonic transducer
22, acoustic waveguide 24, and sonic component 16 that together
comprise a toothbrush head 20 in either removable or fixed
combination, with a handle 15 to achieve a preferred power
toothbrush embodiment of the present invention. It is this
combination of sonic and ultrasonic components that yields the most
surprising benefits of improved microscopic bubbly flow properties
in combination with enhanced cavitation and acoustic
microstreaming. These physical properties provide superior cleaning
properties of this embodiment of the present invention. That is,
the ultrasonic and sonic components, when used in combination to
achieve toothbrush designs disclosed herein, yield synergistic
cleaning effects that are substantially superior to the additive
effects of the sonic and ultrasonic components in isolation. For
example, the acoustic waveguide 24 can be optimized to move bubbly
fluid whose bubbles could facilitate acoustic streaming (thereby
further enhancing the fluid flow generated by the waveguide alone)
as well as acoustic microstreaming and cavitation.
[0139] The primary function of the sonic motion is to activate the
bristle tips such that they cleanse the tooth surface via direct
bristle contact. This motion also relates to the user's primary
perception of cleaning during a typical brushing event. In the
implementation of the combined effect of sonic and ultrasonic
cleaning, sonic bristle motion is also used to generate bubbles
within the dental fluid surrounding the waveguide. Furthermore, the
sonic motion propels dental slurry (including the fluid and the
bubbles) towards the surface of the teeth. This fluid motion
towards the teeth both acts to clean the teeth by dislodging plaque
bacteria and debris as well as propel the bubbles to the tooth
surface where they can be acted upon by the ultrasound. This bulk
fluid motion--itself enhanced by an optimally configured waveguide,
with or without ultrasound transmission--can also carry maximally
oxygenated dental fluid into the gingival and sub-gingival region,
with a therapeutic effect resulting from the reduction of anaerobic
plaque and other bacteria that reside in those regions.
[0140] The gaseous substance within bubbles in a dental fluid is
typically air found within the oral cavity during brushing.
Movement of the bristles, waveguide, and/or other brush head
components through the air/fluid interface (fluid may be saliva,
water, dentifrice, mouthwash and/or other present during typical
brushing) acts to fracture this interface entrapping bubbles within
the fluid. With respect to cleaning the tooth surface with shear
induced by cavitation and/or acoustic streaming, the positive
benefits of ultrasound are achieved when bubbles within the fluid
are stimulated to create cavitation and/or streaming. It is
desirable to use the sonic component of the toothbrush to generate
these bubbles within the dental slurry.
[0141] The dental slurry acts as both the source of the bubbles to
be activated by the ultrasound and as an ultrasound coupling media
(transfer of ultrasound from waveguide tip to the tooth surface,
which may be a gap from 0 to 10 mm, more typically 1 to 5 mm). If
there is insufficient bristle and/or waveguide motion, too few
bubbles are created within the dental slurry and the cleaning
effect of the ultrasound on the tooth surface is reduced. If there
are too many bubbles created in the dental fluid, the fraction of
air within the coupling media is too large, preventing the passage
of ultrasound from the waveguide tip to the tooth surface and
reducing the cleaning effect on the tooth surface.
Dentifrice Design and Compositions
[0142] Within certain related embodiments, it is contemplated to
provide a dentifrice that is particularly suitable for use with the
inventive power toothbrush described herein. For example, it is
herein contemplated that such a dentifrice will facilitate the
creation of a desirable bubble population that may be acted upon by
the ultrasonic transducer 22 and acoustic waveguide 24 disclosed
herein.
[0143] The natural bubble population within a dental fluid can be
assayed by the tendency of that fluid to absorb ultrasonic energy
that is transmitted through it. The higher the absorption, the more
bubbles that are present at the relevant size (given heuristically
by the resonance formula, developed originally for bubbles in pure
water at 37 degrees Celsius, although applicable as an
approximation for more general conditions F.sub.0R.sub.0=3.26,
where the frequency F.sub.0 is given in MHz and the radius R.sub.0
of the bubble is given in microns), although many bubbles
off-resonance would also create desired plaque and stain removal
effects.
[0144] A typical composition of dental slurry is 17% dentifrice in
fluid. The fluid may be, in part, water added to the toothbrush
prior to brushing, but, more typically, the fluid is largely saliva
generated by the user during brushing. Components within the
dentifrice (e.g., detergents, humectants, thickeners, etc.)
influence the formation of bubbles within the dental slurry.
Dentifrices according to the present invention facilitate the
formation of bubbles having a diameter of between about 1 .mu.m and
about 150 .mu.m within the dental fluid that resonate when
ultrasound is applied in the 20 kHz to 3 MHz frequency range. More
typically, dentifrices according to the present invention
facilitate the formation of bubbles having a diameter of between
about 1 .mu.m and about 100 .mu.m within the dental fluid that
resonate when ultrasound is applied in the 30 kHz to 3 MHz
frequency range. Still more typically, dentifrices according to the
present invention facilitate the formation of bubbles having a
diameter of between about 5 .mu.m and about 30 .mu.m within the
dental fluid that resonate when ultrasound is applied in the 100
kHz to 600 kHz frequency range. In an exemplary dentifrice
presented herein, bubbles that have a diameter of between about 12
.mu.m and about 26 .mu.m are formed in the dental fluid and
resonate when ultrasound is applied to those bubbles with an
ultrasound transducer operating in the 250 kHz to 500 kHz
range.
[0145] Dentifrices suitable for use with the toothbrushes disclosed
herein comprise a surfactant that produces surface tension values
that facilitate production and stabilization of bubbles in a
suitable size range for stimulation by the ultrasonic transducer in
combination with an acoustic waveguide. Typically, surfactants
employed in the dentifrices disclosed herein produce surface
tensions in the range of about 0.1 N/m to about 500 N/m, more
typically in the range of about 0.2 N/m to 250 N/m, and still more
typically in the range of about 0.5 N/m to about 50 N/m.
[0146] Alternatively, or in addition to providing a dentifrice as
described above that promotes bubble formation, bubbles having a
desired size range may be incorporated in a dentifrice or another
composition and introduced directly into the oral cavity by
application of the composition on a toothbrush or by introduction
of the composition into the oral cavity. Bubbles having a diameter
of between about 1 .mu.m and about 150 .mu.m, more typically
between about 1 .mu.m and about 100 .mu.m, in some embodiments
between about 5 .mu.m and about 30 .mu.m, and in yet other
embodiments between about 12 .mu.m and about 26 .mu.m may be
incorporated directly in a dentifrice composition or in another
composition, such as a mouthwash or another generally liquid,
gel-like or semi-solid carrier for delivery to the oral cavity.
[0147] Bubbles in the carrier material may be present as voids in
the composition itself, or as microspheres or other microstructures
forming gas-filled voids in the carrier material. The OPTISON.TM.
ultrasound contrast enhancing composition, for example, comprises a
suspension of microspheres having a mean diameter of 2.0-4.5 .mu.m,
the microspheres being formed from human serum albumin and being
filled with an octafluoropropane gas. A population of microspheres
of the desired size range (as described above), formed using a
material that's safe for human consumption and generally inert, and
filled with a gas that's safe for human consumption and generally
inert may be incorporated in a suitable carrier material and used,
in conjunction with toothbrushes of the present invention, to
promote effective cleaning.
[0148] The following examples are provided to exemplify, but not to
limit, the presently disclosed invention.
EXAMPLES
Example 1
Design and Construction of a Combined Sonic and Ultrasonic
Toothbrush
[0149] Prototype power toothbrushes were generated by replacing
internal bristle tufts of commercially available power toothbrushes
with an ultrasonic transducer and acoustic waveguide. Ultrasonic
transducers employed in these prototype toothbrushes had
significant power output within the frequency range of about 150 to
about 510 (generally 500) kHz that was sufficient to stimulate the
formation of an acoustically significant bubble population
susceptible to resonant stimulation by energy emitted by the
ultrasonic transducer. A polymer waveguide was molded onto the
toothbrush head in operable proximity to the ultrasonic transducer
and positioned such that ultrasonic waves generated by the
ultrasonic transducer were propagated and focused.
[0150] Several acoustic waveguides were used experimentally and
were located generally in the center of and along the longitudinal
axis of the brushhead. The most common dimensions were: length=11.4
mm; width=3.1 mm; maximum height at the center of a curved end
face=7.4 mm; height at the edges of a curved end face=4.3 mm. The
ultrasound operating parameters generally used experimentally were:
250 kHz frequency; 1-10% duty cycle; 10-1,000 cycles/second and
PRF=1-500.
Example 2
Ultrasonic Imaging and Plaque Removal by an Exemplary Ultrasonic
Power Toothbrush
[0151] This example discloses ultrasound imaging and plaque removal
data collected for one of the prototype power toothbrushes
described in Example 1.
[0152] In order to demonstrate the improved performance of a power
toothbrush employing an ultrasonic transducer in combination with
an acoustic waveguide, Doppler, and B-mode data were collected for
a prototype ultrasonic toothbrush with and without incorporating an
acoustic waveguide. FIG. 5A presents an ultrasound image of an
ultrasonic toothbrush without an acoustic waveguide. Doppler data
show fluid flow (within box) and B-mode data highlight acoustic
backscatter (outside of box) at the bristle tips (BT) and bristle
plate (BP) at bottom of bristles. FIG. 5B presents the same
ultrasonic toothbrush with moving bristles powered by a sonic
component. These data reveal that fluid flow (FF) beyond the
bristle tips is not detectable even though the bristles are moving
(MB). FIG. 5C presents an ultrasound B-mode image of a prototype
ultrasonic toothbrush in combination with an acoustic waveguide.
The sonic component drives the vibration of the acoustic waveguide
and generates a jet of bubbly fluid moving away from the brush.
FIG. 5D presents Doppler and B-mode ultrasound image data of the
same toothbrush showing significant fluid flow (FF) and bubbles (B)
beyond the bristles.
[0153] A prototype ultrasonic power toothbrush was tested for
plaque removal in a plaque coated (Streptococcus mutans) artificial
tooth model system. Plaque was detected by staining a set of
artificial teeth before application of fluid flow generated by an
acoustic waveguide, without ultrasound, positioned several
millimeters beyond the toothbrush head bristle tips. Discrete
plaque colonies were reduced or removed after application of fluid
flow generated by the ultrasonic transducer in combination with the
acoustic waveguide.
[0154] An artificial tooth model for tooth areas outside the reach
of a toothbrush head bristle tip was also tested. Plaque was dyed
pink before application of ultrasonic energy from several
millimeters beyond the bristle tips. Discrete plaque colonies were
reduced or removed after application of ultrasound. Background
films of plaque were also reduced, leaving residual pink due
primarily to dye that has leached into the teeth. Plaque removal in
the same model system was also tested after application of fluid
flow generated by an acoustic waveguide and after application of
ultrasonic energy from several millimeters beyond the bristles.
Discrete plaque colonies were reduced or removed after treatment.
Background films of plaque were also reduced, leaving residual pink
due primarily to dye that has leached into the teeth. Superior
results were achieved while simultaneously using microscopic fluid
flow from the acoustic waveguide and ultrasound.
Example 3
Measurement of Physical Parameters of an Exemplary Ultrasonic Power
Toothbrush Employing an Acoustic Waveguide
[0155] This example discloses measurements of physical parameters
of an exemplary ultrasonic power toothbrush of the present
invention.
[0156] In order to compare the effectiveness of various acoustic
waveguide geometries, the transmitting pressures for a flat,
unfocused elastomeric/silicone polymer wedge waveguide (FIG. 3) was
compared to the transmitting pressures for a focused
elastomeric/silicone polymer wedge waveguide (FIG. 4). The plot of
acoustic pressure levels at the tip of each acoustic waveguide
presented in FIG. 6 demonstrates an approximately three-fold
increase in transmitting pressure for a focused waveguide
(.about.1.5 MPa tip pressure) versus an unfocused waveguide
(.about.0.5 MPa tip pressure).
[0157] The absorption of ultrasound transmitted through a model
dental fluid/bubble emulsion was measured as a function of
ultrasonic frequency in the 30 to 700 kHz frequency range.
Ultrasonic transducers were positioned, approximately 0.3 to 1 cm
apart, on opposite sides of a Petri dish containing simulated
dental fluid (i.e., an emulsification of dentifrice and water) and
the intensity of sound transmitted through the fluid was measured
and normalized by the intensity of sound transmitted into the
fluid. Results of an exemplary test are presented in FIG. 7, which
reveals a peak in attenuation due to absorption of sound at
approximately 200 kHz and a spurious dip in the curve at
approximately 350 kHz, owing to resonance between the length of the
ultrasound wave and the depth of the fluid. These data demonstrated
the presence of a significant bubble population available for
acoustic stimulation at frequencies between 100-500 kHz.
Example 4
Plaque Removal by an Exemplary Ultrasonic Power Toothbrush
[0158] This example discloses plaque removal with the bubbly jet
generated by the sonic vibration of an acoustic waveguide in
combination with ultrasound stimulation of the bubbles within the
jet.
[0159] A Streptococcus mutans model for dental plaque was employed
to assess plaque removal by an exemplary ultrasonic toothbrush of
the present invention. S. mutans (human-derived plaque) was allowed
to grow on frosted glass slides, then exposed to a prototype
toothbrush operated at the surface of a water bath and held a few
millimeters away from, in a perpendicular fashion, the surface of
the slide. A variety of ultrasound protocols were used, including
waveguide only (WG) and waveguide plus ultrasound (WG/US). The
slides were stained with a plaque-specific dye to indicate intact
plaque (pink) and plaque-free regions (white).
[0160] In an exemplary assay, the surface of an S. mutans-coated
slide was placed 4 mm from the longest bristles of a prototype
toothbrush. The ultrasound carrier frequency was 250 kHz, with a
PRF of 1000 Hz and with 24 cycles per burst; the Mechanical Index
was 0.75. With only the bubbly fluid jet produced by the acoustic
waveguide, there was a subtle reduction in the thickness of the
plaque, while in concert with ultrasound, significant plaque was
removed. For comparison, a commercially available power toothbrush
was held at the same distance from plaque grown on the frosted
glass slide. That control toothbrush did not remove meaningful
plaque.
[0161] A second assay system used hydroxyapatite (HA) disks
incubated for 48 hours prior to the experiment with S. Mutans. The
ultrasound protocol consisted of a 250 kHz run at 625 Hz PRF, 40
cycles/sec, 3 second exposure, and a Mechanical Index of 0.9
measured at 6 mm from the tip of the acoustic waveguide.
[0162] The action of the acoustic waveguide alone removed some
plaque; however, in combination with ultrasound, there was
significantly improved plaque removal. By comparison, a
commercially available power toothbrush did not remove any plaque,
while ultrasound alone removed only a few spots of plaque, in a
small region of the disk.
[0163] In a third experimental system, an ultrasound protocol was
followed that consisted of a 510 kHz run at 1,252 Hz PRF, with 2
cycles/sec, exposed for 3 seconds, with a Mechanical Index of 0.51
measured at 6 mm from the tip of the waveguide. Consistent with the
assays described above, the action of the acoustic waveguide alone
removed some plaque; but, in combination with ultrasound, there was
significantly improved plaque removal. By comparison, a
commercially available power toothbrush, held 1-2 mm away from the
front of the teeth, removed only some plaque, while ultrasound
alone only removed a few spots of plaque in a small region of the
disk. Thus, the bubbly fluid jet generated by the sonically
vibrating acoustic waveguide was sufficient to achieve more rapid
plaque removal beyond the reach of the bristles by a factor of at
least two-fold greater than the commercial power toothbrush.
[0164] Plaque removal was observed across a wide range of acoustic
protocols. Optimal plaque removal was achieved when the PRF was a
multiple, greater than one, of the sonic frequency. Without wishing
to be bound to any specific theory of operation, it is believed
that this protocol resulted in optimal plaque removal because it
allowed multiple pulses of ultrasound to interact with the bubbly
jet and the plaque as the flexible tip of the acoustic waveguide
was being oscillated back and forth across the face of the HA disk,
relevant portion of the glass slides, and/or the teeth. It is
further believed that this accounts, at least in part, to the
synergistic effect observed with the combined action of a bubbly
fluid jet and ultrasound.
[0165] In order to demonstrate this synergistic effect, the action
of ultrasound alone on a tooth/model of plaque removal was assessed
both with and without motion of the acoustic waveguide. An
ultrasound protocol was chosen that, by itself, did not yield
meaningful plaque removal (with or without the production of a
bubbly jet), but did so after introduction of dental fluid
containing artificial bubbles (Optison.TM.). The results of this
study also demonstrated that ultrasound alone was not responsible
for plaque removal; but, rather, it was the ultrasound stimulation
of the artificial bubbles that, in combination, yielded substantial
plaque removal.
[0166] Additional studies performed in an artificial tooth dental
plaque model for tooth areas beyond the reach of the toothbrush's
bristles demonstrated that a sonically vibrating acoustic waveguide
simultaneously emitting ultrasound at 450 kHz in the presence of
artificial bubbles removed plaque from a distance of 2-3 mm after
only 5 seconds of application, although that plaque removal pattern
actually appeared within a fraction of a second of ultrasound
onset. This plaque removal occurred over a larger area than with
ultrasound alone and occurred in an appreciably shorter length of
time than that created by the bubbly fluid jet alone. Therefore,
the ultrasound and sonically generated bubbly fluid flow acted
together in a synergistic fashion to rapidly and effectively remove
plaque over a large area, beyond the reach of the bristles.
[0167] Because a bubble's volume oscillates and associated stresses
act on a time scale governed by the ultrasound frequency, the
frequencies (on the order of 100 s of kHz), plaque removal can, in
principle, occur on time scales on the order of 0.00001 seconds
(i.e., approximately 10 microseconds). Therefore, ultrasound
toothbrushes of the present invention are capable of substantial
plaque removal at times that are approximately 100-to 1000-fold
shorter than the time required for plaque removal by existing power
toothbrushes.
Example 5
Absence of Cell Lysis by an Exemplary Ultrasonic Power
Toothbrush
[0168] This example discloses that ultrasonic power toothbrushes of
the present invention induces ultrasonic cavitation whose
mechanical effects were insufficient to induce cell lysis, yet were
able to remove plaque. These findings support the safety of
ultrasonic power toothbrushes provided herein.
[0169] A red blood cell model system was utilized (FIG. 8) to test
cell lysis caused by shear stresses induced by acoustic
microstreaming associated with stable oscillating bubbles by
Rooney, Science 169:869-871 (1970), who demonstrated that a single
bubble, placed within a vial of dilute red blood cells, could be
stimulated by ultrasound to produce "microstreaming" such that with
sufficient acoustic power, those blood cells could be disrupted. In
particular, a thin, hollow wire with air in its center was placed
in a vial of suspended red blood cells. Sufficient air was extruded
from the wire to form a hemisphere of gas (the microbubble) within
the suspension. Ultrasonic waves at a frequency of about 25 kHz
were applied to the container to stimulate oscillation of the
bubbles and sufficient to generate acoustic microstreaming. Under
these conditions, about 70% of the red blood cells were destroyed
at shear stresses comparable to those determined via independent
means. One hundred percent hemolysis was achieved by introduction
of a highly osmotic solution. Of particular interest here is the
difference in shear stress (greater than 450 Pa) necessary to break
up the cells, versus stress necessary to remove fresh plaque in
vitro (1-30 Pa). The shear required for detachment of P. aeruginosa
biofilms grown at shear stresses of 0.075 and 5.09 Pa were 5.09 Pa
and 25.3 Pa, respectively. Stoodley et al., Journal of Industrial
Microbiology & Biotechnology 29:361-367 (2002).
[0170] Acoustic microstreaming, just one of a variety of physical
processes associated with acoustic cavitation (the formation and/or
stimulation of bubbles by acoustic energy), can cause disruption of
biological systems such as red blood cells, as discussed herein. Of
particular interest is that the presence of bubbles can facilitate
stresses sufficient to remove plaque, for example, at acoustic
intensities far below that necessary to cause desired biological
effects, when no bubbles are present. In the present example,
Optison.TM., a microbubble ultrasound (US) contrast agent with a
diameter of about one micron, was used to demonstrate this point.
This example also shows that it is the ultrasound stimulation of
bubbles, not ultrasound cavitation alone, that removes plaque.
[0171] As evidence for the safety of ultrasonic toothbrushes of the
present invention, the following plaque removal assay system was
employed. Cell disruption by an exemplary toothbrush was determined
by assaying cell debris in the liquid above plated gingival cells
that were exposed to (1) an activated commercial power toothbrush
whose bristle tips were placed above the cells, (2) a bubbly fluid
jet caused by the sonic component of the prototype toothbrush held
above the cells, and (3) the combination of bubbly fluid jet and
ultrasound (sonic plus ultrasound) from the prototype toothbrush,
held above the cells. These results were compared to the results
achieved with a commercial power toothbrush whose bristle tips were
placed directly on the cells.
[0172] Following treatment, supernatants were evaluated for lysed
cells by a nonradioactive lactate dehydrogenase (LDH) assay
(Cytotox 96; Promega, Madison, Wis.) according to the
manufacturer's instructions. This assay system is a calorimetric
alternative to .sup.51Cr release cytotoxicity assays and has been
used to measure cell lysis by chemical and physical means. Singer
et al., J. Neurosci. 19:2455-2463 (1999). The assay quantitatively
measures LDH, a stable cytosolic enzyme that is released upon cell
lysis in much the same way as .sup.51Cr is released in radioactive
assays. Released LDH in culture supernatants is measured with a
30-minute coupled enzymatic assay, which results in the conversion
of a tetrazolium salt (INT) into a red formazan product. The amount
of color formed is proportional to the number of lysed cells.
[0173] Visible wavelength absorbance data were collected using a
standard 96 well plate reader. Methods for determination of LDH
utilizing tetrazolium salts in conjunction with diaphorase or
alternate electron acceptors are well known in the art. Variations
on this technology have been reported for measuring natural
cytotoxicity and have been demonstrated to be identical (within
experimental error) to values determined in parallel .sup.51Cr
release assays.
[0174] Cells remaining in plates following treatment were
photographed, lysed, and quantified using the LDH assay as
described above. Cell lysis induced by the beyond the bristle
effects of a sonic toothbrush was compared to cell lysis induced by
a prototype combined sonic/ultrasonic toothbrush of the present
invention.
[0175] Results of an exemplary assay are presented in FIG. 10,
which demonstrate that the cleaning action of a bubbly fluid jet
generated by an acoustic waveguide mounted on a toothbrush, in
combination with ultrasound propagated through the acoustic
waveguide, safely removed plaque. The "control" result was a
measure of cell lysis caused by the fluid action generated beyond
the reach of the bristles of a commercial power toothbrush; the
"sonic" result was a measure of such cell lysis by an exemplary
toothbrush without ultrasound; the "sonic+ultrasonic" result was a
measure of such cell lysis by an exemplary toothbrush with both a
sonic component and ultrasound; and the "control+contact" result
was a measure of cell lysis by a commercial power toothbrush whose
bristles were placed in direct contact with the cell surface. There
were no differences detected between the commercial toothbrush and
the prototypical toothbrush when their bristles did not touch the
cells. In contrast, there was substantial cell lysis generated by
the direct contact of the toothbrush bristles of a commercial power
toothbrush upon the cells.
[0176] While illustrative embodiments have been illustrated and
described, it will be appreciated that various changes can be made
therein without departing from the spirit and scope of the
invention.
* * * * *