U.S. patent application number 12/104958 was filed with the patent office on 2008-09-04 for laser shaped green metal body and orthodontic bracket.
This patent application is currently assigned to Ultradent Products, Inc.. Invention is credited to Norbert Abels, Claus-H. Backes.
Application Number | 20080213718 12/104958 |
Document ID | / |
Family ID | 36697225 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080213718 |
Kind Code |
A1 |
Abels; Norbert ; et
al. |
September 4, 2008 |
LASER SHAPED GREEN METAL BODY AND ORTHODONTIC BRACKET
Abstract
A green metal body is comprised of metal particles and a binder
in the shape of an orthodontic bracket and/or base plate. The green
metal body is fabricated by being laser-cut with a laser to shape
the green metal body into the shape of an orthodontic bracket
and/or or to carve recesses and/or undercuts into the bonding
surface of the bracket. The green metal body is sintered to shrink
its volume into a denser and less porous sintered metal body
configured to be an orthodontic bracket. The resultant sintered
orthodontic bracket includes recesses and/or undercuts in the
bonding surface to provide a mechanical aspect when bonded to a
tooth.
Inventors: |
Abels; Norbert; (Homburg,
DE) ; Backes; Claus-H.; (Saarbrucken, DE) |
Correspondence
Address: |
WORKMAN NYDEGGER
60 EAST SOUTH TEMPLE, 1000 EAGLE GATE TOWER
SALT LAKE CITY
UT
84111
US
|
Assignee: |
Ultradent Products, Inc.
South Jordan
UT
|
Family ID: |
36697225 |
Appl. No.: |
12/104958 |
Filed: |
April 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11193239 |
Jul 29, 2005 |
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12104958 |
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11042025 |
Jan 25, 2005 |
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11193239 |
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Current U.S.
Class: |
433/8 ;
75/313 |
Current CPC
Class: |
A61C 7/14 20130101; B23K
26/361 20151001; B22F 5/00 20130101; Y10T 29/49995 20150115; Y10T
29/49568 20150115; B33Y 70/00 20141201; A61C 9/004 20130101; B33Y
80/00 20141201; A61C 13/0022 20130101; B22F 3/10 20130101 |
Class at
Publication: |
433/8 ;
75/313 |
International
Class: |
A61C 7/14 20060101
A61C007/14 |
Claims
1. A laser-shaped green metal body for use in making an orthodontic
bracket, comprising: a plurality of metal particles; a binder in an
amount so as to hold the metal particles together as a green metal
body during laser-shaping of at least a portion of the green metal
body; and at least one laser-shaped portion formed by removing
metal particles from the green metal body, wherein the green metal
body at least approximates the shape of an orthodontic bracket that
is comprised of a base for attachment to a person's teeth and at
least one archwire slot for receiving an archwire therein, wherein
that portion of metal particles located on a surface of the
laser-shaped portion are not fused together as a result of laser
shaping prior to sintering the green metal body.
2. A laser-shaped green metal body as in claim 1, wherein the metal
particles are comprised of a metal selected from the group
consisting of aluminum, nickel, titanium, copper, cobalt, and
stainless steel.
3. A laser-shaped green metal body as in claim 1, wherein the
binder is an organic binder.
4. A laser-shaped green metal body as in claim 3, the organic
binder including at least one member selected from the group
consisting of wax, polypropylene, polyethylene, acrylic polymers,
polystyrene, polyethylene-vinyl acetate, polyethylene vinyl
alcohol, polyethylene acetate, chlorinated polyethylene,
polyisoprene, polybutadiene, styrene-butadiene di- and tri-block
polymers, polychloroprenes, polyethylene-propylene copolymers,
chlorosulfonated polyethylenes, polyurethanes, styrene-isoprene
copolymers, styrene ethylbutylene copolymers, styrene-butadiene
rubber latex, polychloroprene latex, polymethylmethacrylate,
polyethylmethacrylate, and polydimethylsiloxanes.
5. A laser-shaped green metal body as in claim 1, at least a
portion of the laser-shaped portion comprising a bonding surface
having at least one of recesses, protrusions, or undercuts.
6. An orthodontic bracket comprising: a sintered metal body formed
by sintering a green metal body comprised of a plurality of metal
particles held together with a binder, the sintered metal body
including a base for attachment of the bracket to a person's teeth
and at least one archwire slot for receiving an archwire therein;
and at least one laser-shaped portion formed by removing metal
particles from the green metal body using a laser and prior to
sintering, the laser-shaped portion being substantially devoid of
charring as otherwise occurs when laser shaping a solid metal body,
wherein the laser-shaped portion has a smoother topology compared
to a corresponding laser-cut portion of the green metal body that
existed prior to sintering to form the sintered metal body.
7. An orthodontic bracket as in claim 6, at least a portion of the
laser-shaped portion comprising a bonding surface having at least
one of recesses, protrusions, or undercuts.
8. An orthodontic bracket as in claim 6, at least the laser-shaped
portion of the sintered metal body having an oxidized surface
resulting from sintering the green metal body.
9. A laser-shaped green metal body for use in making an orthodontic
bracket, comprising: a plurality of metal particles; a binder in an
amount so as to hold the metal particles together as a green metal
body during laser-shaping of at least a portion of the green metal
body; and at least one laser-shaped portion formed by removing
metal particles from the green metal body, wherein the green metal
body at least approximates the shape of an orthodontic bracket that
is comprised of a base for attachment to a person's teeth and at
least one archwire slot for receiving an archwire therein, wherein
that portion of metal particles located on a surface of the
laser-shaped portion are at least partially fused together as a
result of laser shaping prior to sintering the green metal
body.
10. A laser-shaped green metal body as in claim 9, wherein the
metal particles are comprised of a metal selected from the group
consisting of aluminum, nickel, titanium, copper, cobalt, and
stainless steel.
11. A laser-shaped green metal body as in claim 9, wherein the
binder is an organic binder.
12. A laser-shaped green metal body as in claim 11, the organic
binder including at least one member selected from the group
consisting of wax, polypropylene, polyethylene, acrylic polymers,
polystyrene, polyethylene-vinyl acetate, polyethylene vinyl
alcohol, polyethylene acetate, chlorinated polyethylene,
polyisoprene, polybutadiene, styrene-butadiene di-and tri-block
polymers, polychloroprenes, polyethylene-propylene copolymers,
chlorosulfonated polyethylenes, polyurethanes, styrene-isoprene
copolymers, styrene ethylbutylene copolymers, styrene-butadiene
rubber latex, polychloroprene latex, polymethylmethacrylate,
polyethylmethacrylate, and polydimethylsiloxanes.
13. A laser-shaped green metal body as in claim 9, at least a
portion of the laser-shaped portion comprising a bonding surface
having at least one of recesses, protrusions, or undercuts.
14. An orthodontic bracket comprising: a sintered metal body formed
by sintering a green metal body comprised of a plurality of metal
particles held together with a binder, the sintered metal body
including a base for attachment of the bracket to a person's teeth
and at least one archwire slot for receiving an archwire therein;
and at least one laser-shaped portion formed by removing metal
particles from the green metal body using a laser and prior to
sintering, the laser-shaped portion being substantially devoid of
charring as otherwise occurs when laser shaping a solid metal body,
at least the laser-shaped portion of the sintered body having an
oxidized surface resulting from sintering the green metal body.
15. An orthodontic bracket as in claim 14, at least a portion of
the laser-shaped portion comprising a bonding surface having at
least one of recesses, protrusions, or undercuts.
16. An orthodontic bracket as in claim 14, at least the
laser-shaped portion of the sintered metal body having an oxidized
surface resulting from sintering the green metal body.
17. An orthodontic bracket comprising: a sintered metal body formed
by sintering a green metal body comprised of a plurality of metal
particles held together with a binder; an exterior surface of the
sintered metal body defining a shape of an orthodontic bracket; and
at least one laser-cut portion on the exterior surface of the
sintered metal body formed by cutting the green metal body with a
laser, wherein the laser-cut portion is substantially devoid of
being charred by being cut with the laser before sintering, wherein
the at least one laser-cut portion on the exterior surface of the
sintered metal body has a topology characterized by a plurality of
irregular elevations formed by melting a portion of the metal
particles of the green metal body with a laser.
18. An orthodontic bracket as in claim 17, at least a portion of
the laser-shaped portion comprising a bonding surface having at
least one of recesses, protrusions, or undercuts.
19. An orthodontic bracket as in claim 17, at least the
laser-shaped portion of the sintered metal body having an oxidized
surface resulting from sintering the green metal body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of copending U.S. application
Ser. No. 11/193,239, filed Jul. 29, 2005, which is a
continuation-in-part of copending U.S. application Ser. No.
11/042,025, filed Feb. 25, 2005, with Norbert Abels and Claus H.
Backes as inventors. The disclosures of the foregoing applications
are incorporated herein in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. The Field of the Invention
[0003] The present invention relates to orthodontic brackets. More
particularly, the present invention relates to cutting and shaping
an orthodontic bracket shaped green metal body with a laser prior
to sintering.
[0004] 2. The Relevant Technology
[0005] Orthodontic brackets have been used extensively for
correcting dental malformations such as crooked teeth or large gaps
between teeth. The treatment can involve applying force to the
teeth in order to move the teeth into a correct alignment. The
brackets are configured to provide a force to the teeth in the arch
that are being aligned. As such, each bracket has a bonding surface
that is configured to be affixed to a tooth. Accordingly, a bond is
formed between the bonding surface and the tooth that can withstand
the forces required to properly align the teeth for the duration of
the treatment.
[0006] Various types of materials have been used to make
orthodontic brackets, including metals, polymers, and composites.
Metals are commonly used for the brackets because of their strength
and their ability to be fabricated into many different shapes.
Accordingly, brackets can be formed by molding and sintering metal
particles, or by milling a metal piece into the shape of a base
plate. A common method of producing an orthodontic bracket can
include forming a green metal body in a mold, and sintering the
green metal body into a finished part. Additionally, a new mold may
have to be created for each orthodontic bracket configured to fit
on each tooth because a universal bracket design may be
impracticable to provide sufficient bonding with different shaped
teeth. For example, a universal bonding surface curvature may not
provide adequate bonding for all teeth because the lingual and/or
buccal surfaces often vary in curvature between different types of
teeth as well as between people.
[0007] Typically, an adhesive is used to form a chemical bond
between the bonding surface of the bracket and the tooth. The
chemical bond between the bonding surface and the tooth can be weak
and subject to failure because of the physical properties of the
bonding surface. Additionally, a smooth bonding surface, which is
an unfavorable characteristic in terms of bonding, can increase the
chance of the bond failing. However, improvements in dental bonding
techniques have resulted in the bonding surface to be fabricated to
include recesses or undercuts. These recesses or undercuts in the
bonding surface can increase the bond strength between the dental
bracket and the tooth because the adhesive can fill into these
physical formations and harden in order to provide a mechanical
aspect to the bond.
[0008] In order to provide recesses into the bonding surface a mold
can be configured to include raised portions, recessed portions, or
irregularities in the base surface. Alternatively, a bracket that
is hardened by sintering can be cut or shaped to include recesses
or undercuts. This can be performed by cutting into the hardened
metal bonding surface with a laser or other milling apparatus. As
such, cutting and milling a sintered piece with a laser can result
in a decrease in the biocompatibility of the bracket because the
cut piece will be charred or blackened as is characteristic of
being cut with a laser. Also, any cutting or milling of a bracket
that has been sintered can decrease its biocompatibility because
the oxidized external surface that results from sintering will be
destroyed.
[0009] Although a bracket bonding surface having recesses or
undercuts can be produced, there are drawbacks to the current
processes. The size limitations of the base result in extremely
small recesses, undercuts, or overhangs, which can be exceedingly
difficult to form by merely using a mold. On the other hand,
milling or cutting a hardened sintered metal can require durable
cutting machinery or a laser that is strong enough to cut into the
hardened metal in order to form recesses or overhangs. However,
improper milling or cutting can create fissures or otherwise ruin
an orthodontic bracket that is nearly finished. Additionally,
milling or shaping a hardened metal can waste valuable materials
that have already been solidified into a finished and usable
state.
[0010] Therefore, what is needed is an improved process for
producing and shaping an orthodontic bracket that does not cut or
mill hardened metal. In addition, an improved process is needed
that produces a base surface with recesses and overhangs.
BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION
[0011] Generally, an embodiment of the present invention provides
for a green metal body having a shape of an orthodontic bracket,
which can be used during a process for making an orthodontic
bracket. Alternatively the green metal body can have the shape of
an orthodontic bracket base plate. As such, a green metal body
includes a plurality of metal particles and a binder in an amount
and disposition within the plurality of metal particles sufficient
to hold the metal particles together prior to sintering to form a
usable bracket. The metal particles are held together sufficiently
to define an exterior surface in substantially the shape of an
orthodontic bracket and/or orthodontic bracket base plate.
[0012] Additionally, the exterior surface includes at least one
laser-cut portion that has a topology characterized by a plurality
of recesses and/or elevations comprising metal particles. Such
recesses and/or elevations remain after sintering to yield a final
bracket and assist in bonding the bracket to a person's teeth
through, e.g., mechanical interlocking of an adhesive in and around
the recesses and/or elevations as well as increased surface area.
Other portions of the green metal body (e.g., archwire slot, tie
wings, etc.) may be formed by laser shaping. In some embodiments,
at least a portion of the metal particles disposed at or near the
green body surface may be fused together prior to sintering.
[0013] In many cases, the metal particles removed by laser-shaping
are not re-deposited onto the surface of the green metal body but
are removed and discarded. Whether or not the metal particles are
re-deposited largely depends on the relationship between the
temperature at which the organic binder melts, burns or decomposes
and the temperature at which the metal particles melt or become
vaporized. The higher the temperature differential, the greater the
likelihood that the laser will melt, burn or decompose the binder
without actually melting or vaporizing the metal particles. In
addition, one of skill in the art can, in light of the teachings
contained herein, select a laser and/or cutting procedure that
ensures clean removal of metal particles in order to prevent their
being re-deposited on the green metal body surface.
[0014] One embodiment of the present invention provides a method of
making a green metal body. The method can include introducing
(e.g., injecting) metal particles into a mold, and introducing
(e.g., injecting) a binder into the mold in an amount sufficient to
hold the metal particles together. The metal particles and the
binder are formed into a green metal body, where the metal
particles and binder can be shaped into a green metal body in
substantially the shape of an orthodontic bracket and/or a base
plate. Alternatively, the green metal body can be pressed into a
form that can be further shaped into the shape of an orthodontic
bracket.
[0015] Additionally, the green metal body is shaped with a laser by
cutting the exterior surface to form any of the features of an
orthodontic bracket and/or base plate. Also, the green metal body,
or more particularly, a surface thereof in the shape of a bonding
surface can have a plurality of elevations, recesses and/or
undercuts formed thereon with the laser.
[0016] Another embodiment of the present invention provides for
making an orthodontic bracket and/or base plate from a
laser-modified green metal body. Accordingly, the green metal body
can be processed into an orthodontic bracket and/or base plate by
sintering the laser-modified green metal body into a sintered metal
body. The exterior surface of the sintered metal body defines the
shape of an orthodontic bracket, and can include at least one
laser-cut portion thereon. The laser-cut portion is formed by
cutting the green metal body with a laser before being sintered.
This can cause the laser-cut portion of the sintered metal body to
be substantially devoid of charring as commonly occurs when a
sintered metal body is cut with a laser. Also, the laser-cut
portion can be a recess (e.g., an undercut) formed into the
exterior surface, or more particularly, formed into a bonding
surface on the orthodontic bracket and/or base plate.
[0017] Regardless of the fact that the green metal body is
substantially in the shape of the finished sintered bracket, the
green metal body is typically about 15-30% larger than the finished
bracket and is therefore not itself an orthodontic bracket. In
addition to being oversized, the green metal body lacks sufficient
strength to handle the strong torquing forces to which an actual
bracket is subjected to during an orthodontic treatment (e.g., as a
result of an archwire bearing down on the bracket within the
archwire slot in order to reposition the patient's tooth during
treatment). When the green metal body is sintered it shrinks to the
size of an orthodontic bracket and obtains sufficient strength to
function as an orthodontic bracket.
[0018] These and other advantages and features of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] To further clarify the above and other advantages and
features of the present invention, a more particular description of
the invention will be rendered by reference to specific embodiments
thereof which are illustrated in the appended drawings. It is
appreciated that these drawings depict only typical embodiments of
the invention and are therefore not to be considered limiting of
its scope. The invention will be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0020] FIG. 1 is a perspective view illustrating an exemplary
orthodontic bracket formed according to the invention;
[0021] FIG. 2A is a side view illustrating an exemplary green metal
body in the shape of an orthodontic bracket;
[0022] FIG. 2B is a side view illustrating an exemplary green metal
body in the shape of an orthodontic bracket base plate;
[0023] FIGS. 3A-3C are side views illustrating exemplary
embodiments of green metal bodies forming a portion of a bonding
surface of an orthodontic bracket; and
[0024] FIGS. 4A-4C are side views illustrating exemplary
embodiments of green metal bodies forming a portion of a bonding
surface of an orthodontic bracket.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0025] Embodiments of the present include orthodontic brackets,
green metal bodies, and associated methods of making or using the
brackets or green metal bodies. More particularly, embodiments of
the present invention include green metal bodies that are
laser-modified into the shape of an orthodontic bracket that can be
sintered into a functional orthodontic bracket. It should be
understood that terminology employed herein is used for the purpose
of describing particular embodiments only and is not intended to be
limiting.
[0026] FIG. 1 depicts an embodiment of an orthodontic bracket 10 in
accordance with the present invention. The orthodontic bracket 10
includes a body 12 and a base plate 14 integrated in a continuous
piece. The orthodontic bracket 10 also includes an external surface
16 that defines the shape of the bracket 10. The body 12 includes
at least one tie wing 18 and an archwire slot 20 that is open to
the upper side of the body 12. The base plate 14 includes a bonding
surface 22 having a rough topology 44 including a plurality of
protrusions, recesses, and/or undercuts. Additionally, the bonding
surface 22 can be configured to be the negative shape of a lingual
or buccal side of a tooth so as to fit thereon.
[0027] The body 12 can be configured into a ligature-requiring
bracket for use with a ligature or fastener to secure an archwire
to the bracket 10. The ligature can be essential to ensure that the
tensioned archwire is properly positioned around the dental arch,
and to prevent the wire from being dislodged from the bracket 10
during eating, teeth brushing, and other daily activities as well
as the force required to move and align the teeth. For example, the
ligature can be a small elastomeric O-ring, which is stretched
around the archwire and secured to the body 12. Metal ligatures can
also be used and are well known in the art.
[0028] In order to retain a ligature, the body 12 of each bracket
can include tie wings 18, or a pair of tie wings 18a. The tie wings
18 can include at least one lobe 34 that protrudes from the body
12. As such, the tie wings 18 can be configured to be couplable
with ligatures by having each lobe 34 curve into a ligature groove
30. The ligature groove 30 can be continuous with the external
surface 16, where the external surface 16 curves around the lobe 34
and in towards the center of the body 12. When the body 12 includes
a pair of tie wings 18a, a lobe spacer 32 defined by the exterior
surface 16 can separate the tie wings 18 into tie wing pairs 18a.
More particularly, the lobe spacer 32 can be a slot or gap that
separates the lobes 18 on the mesial side 36 of the body 12 from
the distal side 38 of the body 12.
[0029] The archwire slot 20 is configured to retain an archwire
therein. As such, the archwire slot 20 traverses the length of the
body 12 from the mesial end 40 to the distal end 42. The archwire
slot 20 can be squared (as depicted in FIG. 1) or rounded to
accommodate archwires having squared or rounded cross-sectional
areas. Alternatively, other archwire slot 20 shapes can be formed
into the bracket 10. Also the depth and/or width of the archwire
slot 20 can be varied.
[0030] In an alternative embodiment, the orthodontic bracket can be
configured into a self-ligating bracket (not shown). Self-ligating
brackets can be a single piece that includes a ligation cover
integrated with the body so that the ligation cover can be closed
over the archwire and secure the archwire to the bracket. The
ligation cover typically serves to replace the ligatures, and
includes an attachment member that releasably couples with the body
so as to contain the archwire therebetween.
[0031] Additionally, the bonding surface 22 on the base plate 14 is
configured to have a topology 44 that includes a plurality of
protrusions, recesses and/or undercuts (as shown in FIG. 2). The
topology 44 is designed to enhance the bonding with a tooth.
Accordingly, the protrusions, recesses, and/or undercuts of the
topology 44 can either independently or together serve to increase
the surface area of the bonding surface 22 for a bonding agent to
be applied thereto. In various embodiments, the topology 44 can
have rounded features to reduce friction points, and/or the
protrusions, recesses and/or undercuts can be spaced close together
or spread out across the bonding surface 22. Also, features in the
topology can be uniformly arranged or randomly distributed. The
bonding agent can encompass the protrusions and penetrate into the
recesses and/or the undercuts to impart a mechanical aspect to the
bonding between the bonding surface 22 and a tooth. This occurs
when the bonding agent solidifies and interlocks the bracket 10 to
the tooth.
[0032] In one embodiment, each orthodontic bracket 10 can be shaped
to fit on a particular type of tooth, or a particular tooth in a
person's mouth. Accordingly, the bonding surface 22 can be shaped
to have a curvature that mates with the tooth it is adhered to. In
order to identify which tooth the bonding surface 22 mates with,
the bonding surface 22 can include identification indicia 45 carved
therein. The identification indicia 45 can notify a dental
professional to which tooth the particular bracket applies, where
the identification indicia 45 can include the Universal Numbering
System, Palmer Notation, and FDI-Two Digit Notation. For example, a
bonding surface 22 that includes the number "22" uses the FDI-Two
Digit Notation and identifies the upper left lateral incisor. As
depicted, the identification indicia can either be carved into the
base as a recess, protrusion, or formed by undercuts, recesses and
protrusions.
[0033] In another embodiment, a three-dimensional model of the
patient's teeth can be used to form the shape of the bonding
surface 22. The three-dimensional model of a tooth can be
ascertained and input into a computer. The computer can then
determine the correct shape of the bonding surface 22 of each
bracket for a specific tooth. Also, the computer can generate other
features and positioning to be included on the bracket 10.
Accordingly, the base can be shaped according to the computer
specifications, as well as signing angulations and slot
positions.
[0034] FIGS. 2A and 2B depict alternative embodiments of green
metal bodies 50 in accordance with the present invention. FIG. 2A
depicts a green metal body 50 in the shape of an orthodontic
bracket 10, and FIG. 2B depicts a green metal body 50 in the shape
of a base plate that can be further processed into the shape of an
orthodontic bracket 10 as shown. The green metal body 50 can
include a body 12 and a base plate 14 cooperatively in the shape of
an orthodontic bracket 10 defined by an external surface 16. The
body 12 includes tie wings 18 and an archwire slot 20 that is open
to the upper side of the body 12. The tie wings 18 each include a
lobe 34 that is adjacent to a lobe recess 30. The base 14 includes
a bonding surface 22 comprised of a plurality of protrusions 24,
recesses, 26 and/or undercuts 28. The structure referred to as
"bonding surface 22" of green metal body 50 is not an actual
"bonding surface" because the green metal body 50 is not suitable
for use as a bracket prior to sintering to form a final sintered
bracket but is merely a precursor thereto.
[0035] The green metal body 50 has the shape of an orthodontic
bracket, and can be used to make an orthodontic bracket by
sintering the green metal body 50. As used herein, the terms
"shape," "form" or other similar terms are used to identify the
appearance of an object, and it is not intended to strictly
construe the dimensions or proportions of the object. For example,
while the green metal body 50 is in the shape of an orthodontic
bracket, this should be construed to include the precise dimensions
required to properly fit on a tooth as well as the larger
dimensions of a green metal body that will shrink during sintering.
As such, a green metal body 50 in the shape of an orthodontic
bracket can be larger than a finished sintered bracket that is
ready to be affixed to a tooth.
[0036] The green metal body 50 includes a plurality of metal
particles. The metal particles can be selected from aluminum,
nickel, titanium, copper, cobalt, stainless steel, and the like as
well as various alloys thereof. The metal particles can be
comprised of, for example, a nickel-titanium alloy powder.
Alternatively, the particles can be comprised of a mixture of
ceramic and metal. More particularly, it is preferable that the
metal particles be comprised of a metal that can be pulverized and
sintered. For example, if stainless steel brackets are desired, a
pre-alloyed fine-grained stainless steel powder can be used. The
characteristics of the powder can depend on the structure of the
planned green metal body as well as the finished orthodontic
bracket. In part, the size of the bracket can determine the size of
the metal particles, where smaller brackets may need smaller
particles. For example, the average diameter of the metal particles
can range from about 0.001 to about 1 mm.
[0037] The green metal body 50 also includes a binder in an amount
and disposition within the plurality of metal particles sufficient
to hold the metal particles together. The binder can be a
thermoplastic made of at least one organic material. Examples of
organic binders that can be used to bind metal particles together
in accordance with the present invention include various polymers,
polyolefins, silicones, acrylics, latexes, waxes, oils, greases,
plasticizers, lignosulfonates, polysaccharides, celluloses and
derivatives thereof, starches and derivatives thereof, other
natural polymers (e.g., proteins), natural and synthetic rubbers,
and the like. More specific examples of polymeric binders can
include polypropylenes, polyethylenes, acrylic polymers,
polystyrenes, polyethylene-vinyl acetate, polyethylene vinyl
alcohol, polyethylene acetate, chlorinated polyethylenes,
polyisoprenes, polybutadienes, styrene-butadiene di- and tri-block
polymers, polychloroprenes, polyethylene-propylenes,
chlorosulfonated polyethylenes, polyurethanes, styrene isoprene
polymers, styrene ethylbutylene polymers, styrene butadiene rubber
latex, polychloroprene latex, polymethylmethacrylate,
polyethylmethacrylate, polydimethylsiloxanes, and the like. It
should be recognized that many other types of organic binders can
be used in order to bind the metal particles into green body
compositions for processing in accordance with the present
invention.
[0038] The ratio of metal particles and binder can vary depending
on the particle sizes and the type of binder as well as on other
factors. For example, the metal to binder weight ratio can range
from about 70:30 to about 98:2. Additionally, the weight ratio can
range from about 75:25 to about 95:5. It is to be understood that
such a range format is used merely for convenience and brevity and
should be interpreted flexibly to include not only the numerical
values explicitly recited as the limits of the ranges, but also to
include all the individual numerical values or sub-ranges
encompassed within that range as if each numerical value and
sub-range is explicitly recited. For example, the metal-binder
weight ratio of about 70:30 to about 98:2 should be interpreted to
include not only the explicitly recited limits of about 70:30 and
about 98:2, but also to include such individual ratios such as
75:25, 80:20, 85:15, as well as sub-ranges between these individual
ratios. Also, it should be recognized that any metal binder ratio
within the described increments can be used as long as green metal
body is sufficiently held together to be handled and shaped with a
laser in accordance with the present invention.
[0039] With continuing reference to FIGS. 2A and 2B, the green
metal body 50 can include at least one laser-cut portion 52 on the
exterior surface 16. The exterior surface 16 is intended to be any
surface on the exterior of the green metal body 50. As such, the
exterior surface 16 can include at least one laser-cut portion 52
having a topology 44 characterized by a plurality of irregular
elevations formed by the metal particles. Alternatively, the
irregular elevations can be in the size range to be either
macroscopically visible or microscopically visible. As used herein,
the term "macroscopic" can include features that are visual with
the naked eye. For example, the macroscopic irregular elevations
can be easily seen with the naked eye without any magnification.
Alternatively, the term "microscopic" as used herein refers to the
need for magnification to be used in order to visualize the
irregular elevations.
[0040] In one embodiment, the green metal body 50 can have a
laser-cut portion 52 on the external surface 16. The laser-cut
portion 52 is cut into the green metal body 50 so that a
significant amount of green material is removed in order to form
the orthodontic bracket shaped piece. Accordingly, the green metal
body 50 can initially have a rectangular cross-sectional area as
shown with the dashed-lines 56. As such, the laser-cut portion 52
can include the external surface 16 that is formed by cutting the
green metal body 50 into the shape of the orthodontic bracket as
shown. Alternatively, the green metal body 50 can be cut in to the
shape of a self-ligating orthodontic bracket (not shown). Thus, a
minor portion or a significant portion of the external surface 16
can be included within the laser-cut portion.
[0041] In another embodiment, the laser-cut portion 52 can include
a plurality of protrusions 24, recesses, 26 and/or undercuts 28. As
such, the exterior surface 16 can include a plurality of
protrusions 24, recesses 26, and/or undercuts 28, each having a
topology 44 formed by the metal particles. In some cases, at least
a portion of the metal particles disposed on the protrusions 24,
recesses 26, and/or undercuts 28 or topology 44 may be at least
partially fused or melted together. Whether this occurs depends on
whether the metal particles are heated to a high enough temperature
before being removed or ejected from the green metal body as a
result of locally melting, burning or decomposing the organic
binder that holds the metal particles together.
[0042] FIG. 2B depicts an orthodontic bracket base plate 14 that
can be integrated with a body 12 to form an orthodontic bracket 10
(shown by the dashed-lines 58). Accordingly, the base plate 14 can
also include at least one laser-cut portion 52 and/or a plurality
of protrusions 24, recesses 26, and/or undercuts 28. Additionally,
the bonding surface 22 or other laser-cut portion 52 can have a
topology 44 formed by metal particles, in some cases, where a
portion of the particles may be melted or fused together.
[0043] The metal green body 50 in the shape of the base plate 14
can later be integrated with the body 12 before or after being
sintered. The body 12 can be comprised of metal, ceramics, or
plastics. For example, a green metal body 50 in the shape of the
base plate 14 can be formed and sintered prior to being molded with
a ceramic or plastic to form the shape of an orthodontic bracket is
depicted by the dashed-line 58.
[0044] FIG. 3A depicts an embodiment of a green metal body 50
having a laser-cut portion 52 in accordance with the present
invention. The laser-cut portion 52 includes a topology 44 that
defines the exterior surface of the laser-cut portion 52. In one
embodiment, the laser-cut portion 52 can be on the bonding surface
22. The topology 44 includes a plurality of macroscopic or larger
irregular elevations 62 which can be protrusions 24, recesses 26,
and/or undercuts 28. The larger irregular elevations 62 can also
include microscopic or smaller irregular elevations 64, which can
also be micro-protrusions 66, micro-recesses 66, and
micro-undercuts 70.
[0045] The larger irregular elevations 62 as well as smaller
irregular elevations 64 can be comprised of a plurality of metal
particles and a binder holding the metal particles together to form
the green metal body 50. In one embodiment, a portion of the metal
particles on the topology 44 are melted together to form a melted
surface layer. In another embodiment, the metal particles on the
topology 44 are adhered together with the binder. In yet another
embodiment, a portion of the topology 44 of the green metal body 50
includes a charred layer or blackened layer. The charred layer or
blackened layer can be characterized by surface features that
result from the vaporizing, melting, and/or burning that accompany
the process of cutting the green metal body 50 with a laser.
[0046] When the laser-cut portion forms protrusions 24, recesses
26, and/or undercuts 28 into the bonding surface 22, the strength
of the bond formed between the orthodontic bracket and the tooth
can increase. This is because the bonding material or adhesive can
encapsulate around the protrusions 24 and penetrate into the
recesses 26 and undercuts 28. This interaction between the bonding
surface 22 and the adhesive can provide a mechanical aspect to the
bond when the adhesive hardens and interlocks with the topology 44.
While this can occur with the larger or macroscopic irregular
elevations 62, the mechanical bond can be enhanced when the
laser-cut portion 52 also includes the smaller or microscopic
irregular elevations 64 comprised of micro-protrusions 66,
micro-recesses 68, and/or micro-undercuts 70. In another aspect,
the microscopic irregular elevations 64 can increase the
interfacial surface that is capable of coming into contact with the
adhesive.
[0047] FIG. 3B depicts another embodiment of a green metal body 50
having a laser-cut portion 52 in accordance with the present
invention. The laser-cut portion 52 includes a topology 44 that
defines the exterior surface of the laser-cut portion 52, which can
be on the bonding surface 22. The topology 44 includes a plurality
of macroscopic or larger elevations 62 which can be protrusions 24,
recesses 26, and/or undercuts 28. The larger elevations 62 can be
cut into the green metal body 50 to be characterized by having a
topology 44 that is substantially smooth so that the larger
irregular elevations 62 have surfaces 63 that are substantially
devoid of microscopic irregular elevations. Accordingly, the
topology 44 of the laser-cut portion 52 on the green metal body 50
can be configured to range from being rough to smooth.
[0048] Without being bound to any particular methodology, it is
thought that the smoother topology 44 depicted in FIG. 3B compared
to the topology 44 of FIG. 3A can be obtained by using variations
in the method of cutting the green metal body 50 with a laser. As
such, the power of the laser, the atmosphere, and/or the
orientation of the surface being laser-cut can be varied. Also, the
composition of the green metal body can be varied to achieve
topologies having varying degrees of smoothness or roughness.
[0049] FIG. 3C depicts another embodiment of a green metal body 50
having a laser-cut portion 52 in accordance with the present
invention. The laser-cut portion 52 includes a plurality of
trapezoidal protrusions 24 formed by cutting trapezoidal recesses
26 therein to form undercuts 28 in the green metal body 50. The
protrusions 24, recesses 26, and undercuts 28 yield a bonding
surface 22 that increases the bond of the final sintered
orthodontic bracket to a person's tooth.
[0050] In some embodiments, a smoother topology on a laser-cut
portion can lend to laser-shaping a substantially rectangular green
metal body into the shape of an orthodontic bracket. This is
because the smoother topology on a green metal body can be even
smoother to the touch after being sintered. As such, the sintered
body can be smooth enough that the bracket may not have to undergo
any post-sintering grinding or sanding to render a surface that has
the proper characteristics for being placed into a mouth. As such,
the tie wings, lobes, archwire slot, ligature grooves,
self-ligating features, and other features can be carved into a
green metal body with a laser.
[0051] FIGS. 4A, 4B, and 4C depict various alternative examples,
without limitation, of laser-cut portions 52 on the bonding surface
22 of a green metal body 50 having the shape of an orthodontic
bracket (not shown) and/or a base 14. In FIG. 4A, the laser-cut
portions 52 are comprised of long columnar protrusions 80 separated
by deep recesses 82 defined by the surface of the laser cut
portions 52. Additionally, the long columnar protrusions 80 can
include smaller recesses 84 cut therein. Also, the long columnar
protrusions 80 can be formed to include undercuts 86 to aid in
mechanically bonding the orthodontic bracket to the tooth.
[0052] In alternative embodiments, FIGS. 4B and 4C depict a green
metal body 50 base 14 having laser cut portions 52 cut into the
bonding surface 22. The laser-cut portions 52 can remove portions
of the green metal body 50 to provide for recesses 88, undercuts
89, and overhangs 90. The recesses 88, undercuts 89, and overhangs
90 can be wedge shaped slices cut into the bonding surface 22 to
provide voids for receiving the bonding agent or adhesive when the
bracket is affixed to the tooth. As depicted, the undercuts 89 can
be formed by hitting the bonding surface with a laser at an angle,
which also forms the overhangs 90.
[0053] Additionally, the green metal body can be cut with a laser
to form the identification indicia that determines which tooth the
bracket will be adhered to. Accordingly, the identification indicia
can be formed by being a recess, a protrusion, or a plurality of
irregular elevations. The identification indicia carved into the
green metal body can include the Universal Numbering System, Palmer
Notation, and FDI-Two Digit Notation.
[0054] In another embodiment, a three-dimensional model of the
patient's teeth can be used to form the shape of the bonding
surface 22 in the green metal body. The three-dimensional model can
be ascertained and input into a computer. The computer can then
determine the correct shape of the bonding surface 22 of the green
metal body. Also, the computer can generate other features and
positioning indicators to be carved into the green metal body.
Accordingly, the green metal body can be shaped according to the
computer specifications to include signing angulations and slot
positions.
[0055] While certain features and configurations of the recesses,
protrusions, and undercuts have been depicted and discussed, the
present invention should not be construed to be limited thereto.
Accordingly, the general features of the present invention could be
applied to other configurations to provide increased surface areas
for mechanically bonding the bracket to the tooth.
[0056] The present invention also provides for methods of making a
green metal body having a shape of an orthodontic bracket and/or a
base plate. As used herein, the methods described in making an
orthodontic bracket can also be used for making a base plate.
Accordingly, in the following discussion a method of making a base
plate is intended to be included in the method for making the
orthodontic bracket. An embodiment of such a method can include
introducing (e.g., injecting) metal particles into a mold. The
metal particles can be in the form of a dry powder or a mixture
that has been admixed with a binder in a mixing or kneading
machine, or heated blender. When the metal particles are admixed
with a binder prior to being injected into the mold, the mixing
conditions can be selected based on various conditions such as
particle diameters and shapes. In some cases, the binder at least
partially coats or encapsulates the metal particles. Also, the
binder may be disposed into the interstitial spaces between the
metal particles by heating and mixing the binder with the
particles. Alternatively, the metal particles and binder can be
pelletized prior to being injected into the mold.
[0057] Since various types of metal powders that can be sintered
are usable in the present invention, the metal particles can be
selected from aluminum, nickel, titanium, copper, cobalt, stainless
steel, and the like as well as various alloys thereof. However,
since the green metal body will be sintered into an orthodontic
bracket and/or base plate, it is preferable to use a
dental-compatible material such as titanium, titanium alloy, and
stainless steel. This is because the bracket needs to withstand the
forces applied to the bracket by the archwire and/or ligatures that
impart a high level of strain thereto. As such, the brackets should
have a high level of strength and toughness so as not to be damaged
during use. The metal is preferably safe for use in a person's
mouth (i.e., having little or no toxicity). It is, of course,
within the scope of the invention to coat the finished brackets
with a protective coating in order to provide additional safety in
the case where the metal used to make the brackets may not be safe
if left uncoated.
[0058] A method of making a green metal body can also include
injecting a binder into the mold in an amount sufficient to hold
the metal particles together. As discussed, the binder can be
pre-mixed with the metal particles prior to injection.
Alternatively, the binder and metal particles can be injected into
a mold as different feed streams separately or simultaneously. When
the metal particles and binder are not premixed, it may be
advantageous for the binder to easily coat the particles by having
a high work of adhesion with respect to the metal particles, or to
be heated and mixed with the metal particles. Additionally, the
dispersement of the binder within the metal particles can be
enhanced by shaking or mixing the particles and binder after being
injected into the mold.
[0059] The weight ratio of the metal particles and binder can vary
depending on the molding conditions. For example, the metal to
binder weight ratio can range from about 70:30 to about 98:2.
Additionally, the weight ratio can range from about 75:25 to about
95:5. By setting the feed stock ratios within these ranges, a
combined metal powder and binder feed can have moderate
flowability, excellent molding properties, and can be formed into a
green metal body that can be further processed in accordance with
the present invention. However, it should be recognized that the
characteristics of the optimal composition will depend on the type
of metal particles and the type of binder as well as other
variables in the process of making a green metal body.
[0060] A method of making a green metal body can also include
forming a green metal body in the mold with the metal particles and
binder. After the feed stock(s) are injected into the mold, the
green metal body can be formed, for example, in an injection
molding machine. The green body is formed by increasing the
temperature and/or pressure so that the metal particles and binder
are pressed together into the shape of the mold. Accordingly, the
metal particles and binder can be set at temperature ranging from
about 20.degree. C. to about 380.degree. C., and more preferable
from about 8.degree. C. to about 340.degree. C. Also, the metal
particles and binder can be pressed together at a pressure range of
from about 2.9 MPa to about 200 MPa, or from about 19.6 MPa to
about 100 MPa, depending on the binder-metal system.
[0061] The shape of the mold can be varied to accommodate a
universal green metal body design or specific molds for each type
of tooth. As such, a series of molds can be fabricated that
correspond to different types of teeth to be used in forming a
green metal body that corresponds to different types of teeth.
Also, a series of molds can be generated for configuring the
bonding surface of the brackets to fit teeth having a certain
curvature. Alternatively, a substantially universal mold can be
used to provide a rough shape that can be further processed into a
green metal body shaped as an orthodontic bracket.
[0062] Accordingly, a method of making a green metal body also
includes shaping the green metal body with a laser. Accordingly, a
laser beam can be guided over the green metal body, where the path
of the laser can be manually or computer controlled. Also, the path
can be preset, or random depending on what portion of the green
metal body is being cut. The laser can cut, melt and/or vaporize
the metal particles and/or the binder to shape the green metal
body.
[0063] In one embodiment, shaping the green metal body with a laser
can result in a green metal body having the shape of an orthodontic
bracket. Accordingly, a substantially rectangular green metal body
can be cut with a laser to carve out the features described with
respect to FIGS. 1 and 2. Such features that can be laser-cut into
the green metal body can include tie wings, lobes, archwire slots,
ligation grooves, self-ligating features, and the like. Thus,
laser-shaping the green metal body can remove a substantial amount
of metal particles from the green metal material and form the shape
of an orthodontic bracket, including a self-ligating bracket.
[0064] Another embodiment of the present invention provides a
method of forming a bonding surface (e.g., so as to have undercuts)
in a green metal body having a shape of an orthodontic bracket. As
such, a green metal body can be fabricated in accordance with the
present invention. Alternatively, a green metal body in
substantially a shape of an orthodontic bracket can be
provided.
[0065] Additionally, a method of forming undercuts can include
cutting undercuts into the base surface with a laser. The undercuts
can be cut into the green metal body as described with respect to
any shaping of the green metal body with a laser. In one
embodiment, the undercuts, or any laser-cut portion, can have a
relatively smooth topology, where the smoothness can result from
fewer, smaller, or microscopic irregular elevations. Alternatively,
the laser-cutting can be conducted to form the undercuts or any
laser-shaped portion of the green metal body, specifically the
bonding surface, to include a relatively rough topology.
[0066] Without being bound to any particular theory of
laser-cutting phenomena, it is thought that the undercuts as well
as the recesses can be formed in the surface of a green metal body
by vaporizing, melting, and/or decomposing the organic binder with
a laser. In this process, the laser is guided over the green metal
body in a manner that melts, vaporizes, and/or decomposes the
organic binder and ejects the metal particles from the green body
from the point being hit by the laser. Additionally, the side wall
of a recess or a protrusion can be hit with the laser to eject the
green material therefrom, which can form additional recesses and
undercuts therein. As such, the laser can be applied to the surface
of the green metal body at various locations and at various angles
in order to achieve the desired or programmed topology. Also, the
size or depth of the features (e.g., protrusions, recesses, and
undercuts) carved into base surface can be varied.
[0067] Depending on the temperature and/or duration of the laser
over a particular location of the green metal body, it is possible
to cleanly remove the metal particles from the green metal body.
This occurs whenever the binder is melted, burned, or decomposed
but the metal particles remain below their vaporization
temperature. In such cases, the metal particles are ejected, fall
off by gravity, or are otherwise removed from the green metal body
entirely. It may also be possible to design a system in which at
least a portion of the metal particles removed from the green metal
body are re-deposited on the green body surface. This may occur, at
least in theory, in the case where the metal particles are melted
and/or vaporized but not ejected so far from the green metal body
as to prevent the metal from re-solidifying and attaching itself to
the green body surface. In the typical case, most or all of the
metal particles will be removed cleanly from the green metal body
and not become re-deposited.
[0068] The laser-cutting can be guided over the green metal body in
a grid-like pattern to produce rows and columns of individual
protrusions and individual recesses in a uniform pattern. As
desired, the laser-cutting can be configured to carve precise cuts
and features into the green metal body. Alternatively, other
geometrical conformations can be created by accurately carving the
green metal body with a laser such as identification indicia.
[0069] In one embodiment, a method of laser-cutting a green metal
body can be conducted in a vacuum. This can allow for the ejected
metal particles and/or binder to escape the surface without being
re-deposited adjacent to the recess or undercut formed by the
ejected material. In another embodiment, the laser-cut portion can
be oriented facing down (inverted) so that any material ejected
from the surface can fall away from and clear of the surface. When
laser-cutting is performed with an inverted surface, the green
metal body can be rotated so that each side of the orthodontic
bracket that is being formed can have the extra green body
materials fall free and clear of the external surface. Accordingly,
the process of laser-shaping a green metal body can be preformed so
that smooth surfaces and rounded features are formed in the
external surface.
[0070] Another embodiment of the present invention provides a
method of making an orthodontic bracket. Such a method can includes
a method for making a green body, which can be comprised of
injecting metal particles into a mold; injecting a binder into the
mold in an amount sufficient to hold the metal particles together;
forming, in the mold with the metal particles and binder, a green
metal body; and shaping the green metal body with a laser. However,
a green metal body in the shape of an orthodontic bracket,
optionally, with undercuts formed in the base surface thereof can
be provided. In either case, the method can include sintering the
green metal body to obtain an orthodontic bracket.
[0071] Optionally, prior to sintering the green metal body a
de-binding process can be carried out to remove the binder. As
such, the de-binding can be performed by heat treatment in a
non-oxidizing atmosphere, for instance, under a vacuum or in a low
pressure condition. For example, the de-binding can be performed at
about 1.times.10.sup.-1 Torr (13.3 Pa) to about 1.times.10.sup.-6
Torr (1.3.times.10.sup.4 Pa). Alternatively, the de-binding can be
performed in nitrogen, argon, or other inert gas by melting,
evaporating, or decomposing the binder. Additional de-binding
conditions such as temperature increase rate or de-binding
temperature can be modulated so as to avoid reactions with the
metal particles. In one embodiment, the de-binding temperature can
be within the range of about 150.degree. C. to about 750.degree.
C.
[0072] The sintering can be performed at a low pressure from about
1.times.10.sup.-1 Torr to about 1.times.10.sup.-6 Torr, or in a
vacuum or inert gas. As such, the green metal body can have the
binder removed during the sintering process. Alternatively, the
sintering process can remove a substantial amount, but not all of
binder, where some of the binder can remain depending on the
binding system. The sintering temperature can range from about
1000.degree. C. to about 1500.degree. C., or about 2400.degree. C.,
and sintering times can range from about 0.5 hours to about 10
hours. However, sometimes sintering can last up to about 24 hours.
Additionally, the sintering process should be modulated in order to
grow metal powder grains into a dense sintered body. Accordingly,
the sintered body should have a high density with a low porosity
compared to the green metal body. Also, the sintered body can have
a lower density and higher porosity compared to a cast metal.
[0073] When the green metal body is sintered, the volume shrinks as
the porosity decreases and the density increases. As such, the
green metal body can be fabricated and shaped to be larger than the
resultant orthodontic bracket to accommodate for the volume lost
during sintering. The volume decrease between the size of a green
metal body and the size of a sintered orthodontic bracket can range
from about 10% to about 30%. Typically, the volume decrease can be
about 20%.
[0074] Since the volume of the green metal body decreases during
sintering, various features of the green metal body can be
fabricated to take shrinkage into account. This can allow for the
laser-cut recesses and protrusions to be cut with a larger margin
of error, or to cut larger recesses than will be present after the
sintering process. Thus, when the green metal body is laser-cut the
intricate shaping can result in even more precise and intricate
features after sintering. Also, the manipulation of a larger green
metal body can aid in handling and shaping the green metal
body.
[0075] Another result of the shrinkage that occurs during sintering
can include the topology of the sintered metal body being smoother
compared to the green metal body prior to sintering. More
particularly, when small or microscopic irregular elevations are
formed during laser-cutting, these irregular elevations can be
smoothed out during sintering. Additionally, the sintering can be
carried out to round the larger or macroscopic irregular
elevations. However, this smoothing effect does not necessarily
have to remove the irregular elevations, but can create a better
surface with less obtuse or sharp edges. As such, the smoothing
effect can still retain the microscopic and/or macroscopic
irregular elevations. On the other hand, the sintering process can
be modulated to substantially remove the microscopic irregular
elevations during the shrinkage, but it can retain the macroscopic
irregular elevations. Alternatively, the macroscopic irregular
elevations can be more rounded after sintering in comparison to the
topology prior to sintering. Thus, at least one laser-cut portion
on the exterior surface of the sintered metal body can have a
smoother topology compared to at least one laser-cut portion on an
exterior surface of the green metal body.
[0076] Accordingly, an orthodontic bracket can include a sintered
metal body formed by sintering a green metal body comprised of a
plurality of metal particles held together with a binder. The
sintered metal body can include an exterior surface defining a
shape of an orthodontic bracket. Also, at least one laser-cut
portion on the exterior surface of the sintered metal body can be
formed by cutting the green metal body with a laser.
[0077] When the green metal body is cut with a laser prior to
sintering, the laser-cut portion on the sintered metal body can be
substantially devoid of being charred by being cut with the laser
before sintering. On the other hand, when a sintered piece is
laser-cut, these portions on the sintered piece can be charred and
rendered to be less biocompatible compared to an orthodontic
bracket that was laser-cut before being sintered. This is because
when a sintered metal body is cut with a laser, the cut portion can
be charred, burned, and/or blackened by the process. Additionally,
when a green metal body is cut with a laser, the laser-cut potions
can similarly have charred portions. However, the laser-cut portion
after sintering can be less charred than the same laser-cut portion
on the green metal body prior to being sintered.
[0078] The sintering process and/or the de-binding process can
function to partially de-char the metal particles, and hence the
sintered metal body. Without being bound to theory, it is thought
that when the binder melts or evaporates from the green metal body,
the binder draws the charred material away from the green metal
body. This can be because during sintering or de-binding, a portion
of the binder will melt and flow over the laser-cut portion and
leech the charred material away from the metal particles. Thus,
laser-cut charring can be diminished by laser-cuffing a green metal
body prior to sintering.
[0079] Also, without being bound to any particular theory, it is
thought that an oxidized layer forms over the exterior surface of
the green metal body as it is being sintered into an orthodontic
bracket. Accordingly, laser shaping the green metal body prior to
sintering can allow for the oxidized layer to form on the laser-cut
portion of the exterior surface during sintering. The oxidized
layer is thought to impart biocompatibility to the bracket.
However, cutting (e.g., with a laser) a solid metal body can
destroy the oxidized surface layer, and decrease biocompatibility.
Thus, at least one laser-cut portion on the exterior surface of the
sintered metal body can have a topology characterized by an
oxidized surface formed by sintering, where the sintering is
conducted after the green metal body has been laser-cut.
[0080] The present invention may be embodied in other specific
forms without departing from its spirit or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative and not restrictive. The scope of
the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes which come
within the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *