U.S. patent application number 11/109978 was filed with the patent office on 2005-11-03 for method and system for incrementally moving teeth.
This patent application is currently assigned to ALIGN TECHNOLOGY, INC.. Invention is credited to Chishti, Muhammad, Wirth, Kelsey.
Application Number | 20050244782 11/109978 |
Document ID | / |
Family ID | 40090178 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050244782 |
Kind Code |
A1 |
Chishti, Muhammad ; et
al. |
November 3, 2005 |
Method and system for incrementally moving teeth
Abstract
A system for repositioning teeth comprises a plurality of
individual appliances. The appliances are configured to be placed
successively on the patient's teeth and to incrementally reposition
the teeth from an initial tooth arrangement, through a plurality of
intermediate tooth arrangements, and to a final tooth arrangement.
The system of appliances is usually configured at the outset of
treatment so that the patient may progress through treatment
without the need to have the treating professional perform each
successive step in the procedure.
Inventors: |
Chishti, Muhammad;
(Washington, DC) ; Wirth, Kelsey; (Cambridge,
MA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP (018563)
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
ALIGN TECHNOLOGY, INC.
Santa Clara
CA
95050-2903
|
Family ID: |
40090178 |
Appl. No.: |
11/109978 |
Filed: |
April 19, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11109978 |
Apr 19, 2005 |
|
|
|
10660857 |
Sep 12, 2003 |
|
|
|
10660857 |
Sep 12, 2003 |
|
|
|
10040269 |
Oct 29, 2001 |
|
|
|
6705863 |
|
|
|
|
10040269 |
Oct 29, 2001 |
|
|
|
09454278 |
Dec 3, 1999 |
|
|
|
6309215 |
|
|
|
|
10040269 |
|
|
|
|
09466353 |
Dec 17, 1999 |
|
|
|
6398548 |
|
|
|
|
09466353 |
Dec 17, 1999 |
|
|
|
PCT/US98/12861 |
Jun 19, 1998 |
|
|
|
10040269 |
|
|
|
|
09250962 |
Feb 16, 1999 |
|
|
|
6183248 |
|
|
|
|
10040269 |
|
|
|
|
09169034 |
Oct 8, 1998 |
|
|
|
6471511 |
|
|
|
|
09169034 |
Oct 8, 1998 |
|
|
|
08947080 |
Oct 8, 1997 |
|
|
|
5975893 |
|
|
|
|
60110881 |
Dec 4, 1998 |
|
|
|
60110189 |
Nov 30, 1998 |
|
|
|
60050342 |
Jun 20, 1997 |
|
|
|
Current U.S.
Class: |
433/24 |
Current CPC
Class: |
A61C 7/00 20130101; A61C
2007/004 20130101; A61C 7/002 20130101; A61C 7/08 20130101; A61C
9/00 20130101; G06T 17/10 20130101; A61C 9/0046 20130101; G06T
2210/41 20130101; B33Y 50/00 20141201; B33Y 80/00 20141201 |
Class at
Publication: |
433/024 |
International
Class: |
A61C 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 19, 1998 |
WO |
PCT/US98/12861 |
Claims
What is claimed is:
1. A system for repositioning teeth, said system comprising: at
least four polymeric shell appliances having cavities selected to
receive and progressively reposition teeth from an initial
arrangement through four successive tooth arrangements.
2. A system as in claim 1, wherein the system comprises from 4 to
10 polymeric shell appliances.
3. A system as in claim 1, further comprising instructions which
set forth that the patient is to wear the appliances in a
predetermined order to achieve said progressive repositioning.
4. A system as in claim 1, wherein the appliances are marked to
indicate order of use.
5. A system as in claim 1, wherein the appliances are marked with
sequential numbering directly on the appliances.
6. A system as in claim 4, wherein the appliances are marked on
tags which are affixed to the appliances.
7. A system as in claim 4, wherein the appliances are marked by
placement in a pouch.
8. A method for repositioning teeth, said method comprising:
providing the patient with a system including at least four
polymeric shell appliances, wherein said appliances each have a
geometry which is selected to receive and progressively reposition
teeth from an initial position through at least four successive
tooth arrangements.
9. A method as in claim 8, wherein from four to ten appliances are
provided to the patient at one time to provide a treatment.
10. A method as in claim 8, wherein the appliances are marked to
allow the patient to determine order of use.
11. A method for fabricating a set of tooth repositioning
appliances, said method comprising: fabricating at least four
polymeric shell appliances, wherein said appliances each have a
geometry which is selected to receive and progressively reposition
teeth from an initial position through at least four successive
tooth arrangements.
12. A method as in claim 11, wherein from four to ten appliances
are fabricated.
13. A method as in claim 12, further comprising placing all of said
appliances in a single package which can be given to the
patient.
14. A method as in claim 13, further comprising marking the
appliances with an order of use.
15. A method as in claim 14, wherein marking comprises placing
sequential numbering directly on each appliance.
16. A method as in claim 14, wherein marking comprises affixing
marked tags on the appliances.
17. A method as in claim 14, wherein marking comprises placing the
appliances in marked pouches.
18. A system for repositioning teeth, comprising: a plurality of
appliances having geometries selected to progressively reposition
the teeth, wherein at least some of the appliances are marked to
indicate their order of use.
19. A system for repositioning teeth from an initial tooth
arrangement to a final tooth arrangement, said system comprising a
plurality of dental incremental position adjustment appliances
including: one or more appliances having geometries selected to
progressively reposition the teeth; and a final appliance having a
geometry selected to progressively reposition the teeth to the
final tooth arrangement, wherein at least some of the appliances
are marked to indicate their order of use.
20. A system for repositioning teeth from an initial tooth
arrangement to a final tooth arrangement, said system comprising a
plurality of dental incremental position adjustment appliances
including: a first appliance having a geometry selected to
reposition the teeth from the initial tooth arrangement to a first
intermediate arrangement; one or more intermediate appliances
having geometries selected to progressively reposition the teeth
from the first intermediate arrangement to successive intermediate
arrangements; and a final appliance having a geometry selected to
progressively reposition the teeth from the last intermediate
arrangement to the final tooth arrangement, wherein at least some
of the appliances are marked to indicate their order of use.
21. A system for repositioning teeth, comprising: one or more
appliances having geometries selected to progressively reposition
the teeth from to successive intermediate arrangements; and
instructions which set forth that the patient is to wear the
appliances in a predetermined order which will progressively move
the patient's teeth, a package, said package containing said one
more appliances, wherein the appliances are provided in a single
package to the patient.
22. A system for repositioning teeth from an initial tooth
arrangement to a final tooth arrangement, said system comprising a
plurality of dental incremental position adjustment appliances
including: a first appliance having a geometry selected to
reposition the teeth from the initial tooth arrangement to a first
intermediate arrangement; one or more intermediate appliances
having geometries selected to progressively reposition the teeth
from the first intermediate arrangement to successive intermediate
arrangements; a final appliance having a geometry selected to
progressively reposition the teeth from the last intermediate
arrangement to the final tooth arrangement; and instructions which
set forth that the patient is to wear the individual appliances in
a predetermined order which will progressively move the patient's
teeth toward the final arrangement, a package, said package
containing said first appliance, said one more intermediate
appliances and said final appliance, wherein the appliances are
provided in a single package to the patient.
23. A system for repositioning teeth from a first tooth arrangement
to a second tooth arrangement, comprising: a plurality of
appliances having geometries selected to progressively reposition
the teeth from the first intermediate arrangement to successive
arrangements; instructions which set forth that the patient is to
wear the individual appliances in a predetermined order which will
progressively move the patient's teeth toward the second
arrangement; and a package containing said appliances, wherein the
appliances are provided in a single package to the patient.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
10/660,857 (Attorney Docket No. 018563-001140/AT-00014.1), filed on
Sep. 12, 2003, which was a continuation of application Ser. No.
10/040,269 (Attorney Docket No. 018563-001120/AT-00014.1), filed on
Oct. 29, 2001, which was a continuation-in-part of application Ser.
No. 09/454,278 (Attorney Docket No. 018563-001110/AT-00014), filed
Dec. 3, 1999 (now U.S. Pat. No. 6,309,215, which claimed the
benefit of provisional application Ser. No. 60/110,881 (Attorney
Docket No. 018563-001100/AT-00013), filed Dec. 4, 1998. Application
Ser. No. 10/040,269 was also a continuation-in-part of application
Ser. No. 09/466,353 (Attorney Docket No. 018563-000120/AT-00003),
filed Dec. 17, 1999 (now U.S. Pat. No. 6,398,584), which was a
continuation of PCT/US98/12861 (Attorney Docket No.
018563-00120PC/AT-00003PC), filed Jun. 19, 1998, which was a
continuation-in-part of application Ser. No. 08/947,080 (Attorney
Docket No. 018563-000110/AT-00002), filed on Oct. 8, 1997, now U.S.
Pat. No. 5,975,893, which claimed the benefit of provisional
application No. 60/050,342 (Attorney Docket No.
018563-000100/AT-00001), filed on Jun. 20, 1997. Application Ser.
No. 10/040,269 was also a continuation-in-part of application Ser.
No. 09/250,962 (Attorney Docket No. 018563-000510/AT-00006), filed
on Feb. 16, 1999, now U.S. Pat. No. 6,183,248, which claimed the
benefit of provisional application No. 60/110,189 (Attorney Docket
No. 018563-000500/AT-00005), filed on Nov. 30, 1998. Application
Ser. No. 10/040,269 was also a continuation-in-part of application
Ser. No. 09/169,034 (Attorney Docket No. 018563-005000/AT-00107),
filed on Oct. 8, 1998 (now U.S. Pat. No. 6,471,511), which was a
continuation-in-part of application Ser. No. 08/947,080 (Attorney
Docket No. 018563-000110/AT-00002), filed on Oct. 8, 1997, now U.S.
Pat. No. 5,975,893, which claimed the benefit of provisional
application No. 60/050,342 (Attorney Docket No.
018563-000100/AT-00001), filed on Jun. 20, 1997. This application
has a specification identical to that of application Ser. No.
08/947,080, and is being called a continuation for that reason. The
full disclosures of each of these applications are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is related generally to the field of
orthodontics. More particularly, the present invention is related
to a method and system for incrementally moving teeth from an
initial tooth arrangement to a final tooth arrangement.
[0004] Repositioning teeth for aesthetic or other reasons is
accomplished conventionally by wearing what are commonly referred
to as "braces." Braces comprise a variety of appliances such as
brackets, archwires, ligatures, and 0-rings. Attaching the
appliances to a patient's teeth is a tedious and time consuming
enterprise requiring many meetings with the treating orthodontist.
Consequently, conventional orthodontic treatment limits an
orthodontist's patient capacity and makes orthodontic treatment
quite expensive.
[0005] Before fastening braces to a patient's teeth, at least one
appointment is typically scheduled with the orthodontist, dentist,
and/or X-ray laboratory so that X-rays and photographs of the
patient's teeth and jaw structure can be taken. Also during this
preliminary meeting, or possibly at a later meeting, an alginate
mold of the patient's teeth is typically made. This mold provides a
model of the patient's teeth that the orthodontist uses in
conjunction with the X-rays and photographs to formulate a
treatment strategy. The orthodontist then typically schedules one
or more appointments during which braces will be attached to the
patient's teeth.
[0006] At the meeting during which braces are first attached, the
teeth surfaces are initially treated with a weak acid. The acid
optimizes the adhesion properties of the teeth surfaces for
brackets and bands that are to be bonded to them. The brackets and
bands serve as anchors for other appliances to be added later.
After the acid step, the brackets and bands are cemented to the
patient's teeth using a suitable bonding material. No
force-inducing appliances are added until the cement is set. For
this reason, it is common for the orthodontist to schedule a later
appointment to ensure that the brackets and bands are well bonded
to the teeth.
[0007] The primary force-inducing appliance in a conventional set
of braces is the archwire. The archwire is resilient and is
attached to the brackets by way of slots in the brackets. The
archwire links the brackets together and exerts forces on them to
move the teeth over time. Twisted wires or elastomeric O-rings are
commonly used to reinforce attachment of the archwire to the
brackets. Attachment of the archwire to the brackets is known in
the art of orthodontia as "ligation" and wires used in this
procedure are called "ligatures." The elastomeric O-rings are
called "plastics." After the archwire is in place, periodic
meetings with the orthodontist are required, during which the
patient's braces will be adjusted by installing a different
archwire having different force-inducing properties or by replacing
or tightening existing ligatures. Typically, these meetings are
scheduled every three to six weeks.
[0008] As the above illustrates, the use of conventional braces is
a tedious and time consuming process and requires many visits to
the orthodontist's office. Moreover, from the patient's
perspective, the use of braces is unsightly, uncomfortable,
presents a risk of infection, and makes brushing, flossing, and
other dental hygiene procedures difficult.
[0009] For these reasons, it would be desirable to provide
alternative methods and systems for repositioning teeth. Such
methods and systems should be economical, and in particular should
reduce the amount of time required by the orthodontist in planning
and overseeing each individual patient. The methods and systems
should also be more acceptable to the patient, in particular being
less visible, less uncomfortable, less prone to infection, and more
compatible with daily dental hygiene. At least some of these
objectives will be met by the methods and systems of the present
invention described hereinafter.
[0010] 2. Description of the Background Art
[0011] Tooth positioners for finishing orthodontic treatment are
described by Kesling in the Am. J. Orthod. Oral. Surg. 31:297-304
(1945) and 32:285-293 (1946). The use of silicone positioners for
the comprehensive orthodontic realignment of a patient's teeth is
described in Warunek et al. (1989) J. Clin. Orthod. 23:694-700.
Clear plastic retainers for finishing and maintaining tooth
positions are commercially available from Raintree Essix, Inc., New
Orleans, La. 70125, and Tru-Tain Plastics, Rochester, Minn. 55902.
The manufacture of orthodontic positioners is described in U.S.
Pat. Nos. 5,186,623; 5,059,118; 5,055,039; 5,035,613; 4,856,991;
4,798,534; and 4,755,139.
[0012] Other publications describing the fabrication and use of
dental positioners include Kleemann and Janssen (1996) J. Clin.
Orthodon. 30:673-680; Cureton (1996) J. Clin. Orthodon. 30:390-395;
Chiappone (1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971)
Am. J. Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics
58:351-366; and Cottingham (1969) Am. J Orthodontics 55:23-31.
[0013] Kuroda et al. (1996) Am. J. Orthodontics 110:365-369
describes a method for laser scanning a plaster dental cast to
produce a digital image of the cast. See also U.S. Pat. No.
5,605,459.
[0014] U.S. Pat. Nos. 5,533,895; 5,474,448; 5,454,717; 5,447,432;
5,431,562; 5,395,238; 5,368,478; and 5,139,419, assigned to Ormco
Corporation, describe methods for manipulating digital images of
teeth for designing orthodontic appliances.
[0015] U.S. Pat. No. 5,011,405 describes a method for digitally
imaging a tooth and determining optimum bracket positioning for
orthodontic treatment. Laser scanning of a molded tooth to produce
a three-dimensional model is described in U.S. Pat. No. 5,338,198.
U.S. Pat. No. 5,452,219 describes a method for laser scanning a
tooth model and milling a tooth mold. Digital computer manipulation
of tooth contours is described in U.S. Pat. Nos. 5,607,305 and
5,587,912. Computerized digital imaging of the jaw is described in
U.S. Pat. Nos. 5,342,202 and 5,340,309. Other patents of interest
include U.S. Pat. Nos. 5,549,476; 5,382,164; 5,273,429; 4,936,862;
3,860,803; 3,660,900; 5,645,421; 5,055,039; 4,798,534; 4,856,991;
5,035,613; 5,059,118; 5,186,623; and 4,755,139.
BRIEF SUMMARY OF THE INVENTION
[0016] The present invention provides improved methods and systems
for repositioning teeth from an initial tooth arrangement to a
final tooth arrangement. Repositioning is accomplished with a
system comprising a series of appliances configured to receive the
teeth in a cavity and incrementally reposition individual teeth in
a series of at least three successive steps, usually including at
least four successive steps, often including at least ten steps,
sometimes including at least twenty-five steps, and occasionally
including forty or more steps. Most often, the methods and systems
will reposition teeth in from ten to twenty-five successive steps,
although complex cases involving many of the patient's teeth may
take forty or more steps. The successive use of a number of such
appliances permits each appliance to be configured to move
individual teeth in small increments, typically less than 2 mm,
preferably less than 1 mm, and more preferably less than 0.5 mm.
These limits refer to the maximum linear translation of any point
on a tooth as a result of using a single appliance. The movements
provided by successive appliances, of course, will usually not be
the same for any particular tooth. Thus, one point on a tooth may
be moved by a particular distance as a result of the use of one
appliance and thereafter moved by a different distance and/or in a
different direction by a later appliance.
[0017] The individual appliances will preferably comprise a
polymeric shell having the teeth-receiving cavity formed therein,
typically by molding as described below. Each individual appliance
will be configured so that its tooth-receiving cavity has a
geometry corresponding to an intermediate or end tooth arrangement
intended for that appliance. That is, when an appliance is first
worn by the patient, certain of the teeth will be misaligned
relative to an undeformed geometry of the appliance cavity. The
appliance, however, is sufficiently resilient to accommodate or
conform to the misaligned teeth, and will apply sufficient
resilient force against such misaligned teeth in order to
reposition the teeth to the intermediate or end arrangement desired
for that treatment step.
[0018] Systems according to the present invention will include at
least a first appliance having a geometry selected to reposition a
patient's teeth from the initial tooth arrangement to a first
intermediate arrangement where individual teeth will be
incrementally repositioned. The system will further comprise at
least one intermediate appliance having a geometry selective to
progressively reposition teeth from the first intermediate
arrangement to one or more successive intermediate arrangements.
The system will still further comprise a final appliance having a
geometry selected to progressively reposition teeth from the last
intermediate arrangement to the desired final tooth arrangement. In
some cases, it will be desirable to form the final appliance or
several appliances to "over correct" the final tooth position, as
discussed in more detail below.
[0019] As will be described in more detail below in connection with
the methods of the present invention, the systems may be planned
and all individual appliances fabricated at the outset of
treatment, and the appliances may thus be provided to the patient
as a single package or system. The order in which the appliances
are to be used will be clearly marked, (e.g. by sequential
numbering) so that the patient can place the appliances over his or
her teeth at a frequency prescribed by the orthodontist or other
treating professional. Unlike braces, the patient need not visit
the treating professional every time an adjustment in the treatment
is made. While the patients will usually want to visit their
treating professionals periodically to assure that treatment is
going according to the original plan, eliminating the need to visit
the treating professional each time an adjustment is to be made
allows the treatment to be carried out in many more, but smaller,
successive steps while still reducing the time spent by the
treating professional with the individual patient. Moreover, the
ability to use polymeric shell appliances which are more
comfortable, less visible, and removable by the patient, greatly
improves patient compliance, comfort, and satisfaction.
[0020] According to a method of the present invention, a patient's
teeth are repositioned from an initial tooth arrangement to a final
tooth arrangement by placing a series of incremental position
adjustment appliances in the patient's mouth. Conveniently, the
appliances are not affixed and the patient may place and replace
the appliances at any time during the procedure. The first
appliance of the series will have a geometry selected to reposition
the teeth from the initial tooth arrangement to a first
intermediate arrangement. After the first intermediate arrangement
is approached or achieved, one or more additional (intermediate)
appliances will be successively placed on the teeth, where such
additional appliances have geometries selected to progressively
reposition teeth from the first intermediate arrangement through
successive intermediate arrangement(s). The treatment will be
finished by placing a final appliance in the patient's mouth, where
the final appliance has a geometry selected to progressively
reposition teeth from the last intermediate arrangement to the
final tooth arrangement. The final appliance or several appliances
in the series may have a geometry or geometries selected to over
correct the tooth arrangement, i.e. have a geometry which would (if
fully achieved) move individual teeth beyond the tooth arrangement
which has been selected as the "final." Such over correction may be
desirable in order to offset potential relapse after the
repositioning method has been terminated, i.e. to permit some
movement of individual teeth back toward their pre-corrected
positions. Over correction may also be beneficial to speed the rate
of correction, i.e. by having an appliance with a geometry that is
positioned beyond a desired intermediate or final position, the
individual teeth will be shifted toward the position at a greater
rate. In such cases, treatment can be terminated before the teeth
reach the positions defined by the final appliance or appliances.
The method will usually comprise placing at least two additional
appliances, often comprising placing at least ten additional
appliances, sometimes placing at least twenty-five additional
appliances, and occasionally placing at least forty or more
additional appliances. Successive appliances will be replaced when
the teeth either approach (within a preselected tolerance) or have
reached the target end arrangement for that stage of treatment,
typically being replaced at an interval in the range from 2 days to
20 days, usually at an interval in the range from 5 days to 10
days.
[0021] Often, it may be desirable to replace the appliances at a
time before the "end" tooth arrangement of that treatment stage is
actually achieved. It will be appreciated that as the teeth are
gradually repositioned and approach the geometry defined by a
particular appliance, the repositioning force on the individual
teeth will diminish greatly. Thus, it may be possible to reduce the
overall treatment time by replacing an earlier appliance with the
successive appliance at a time when the teeth have been only
partially repositioned by the earlier appliance. Thus, the final
digital data set (referred to hereinafter as the FDDS) can actually
represent an over correction of the final tooth position. This both
speeds the treatment and can offset patient relapse.
[0022] In general, the transition to the next appliance can be
based on a number of factors. Most simply, the appliances can be
replaced on a predetermined schedule or at a fixed time interval
(i.e. number of days for each appliance) determined at the outset
based on an expected or typical patient response. Alternatively,
actual patient response can be taken into account, e.g. a patient
can advance to the next appliance when that patient no longer
perceives pressure on their teeth from a current appliance, i.e.
the appliance they have been wearing fits easily over the patient's
teeth and the patient experiences little or no pressure or
discomfort on his or her teeth. In some cases, for patients whose
teeth are responding very quickly, it may be possible for a
treating professional to decide to skip one or more intermediate
appliances, i.e. reduce the total number of appliances being used
below the number determined at the outset. In this way, the overall
treatment time for a particular patient can be reduced.
[0023] In another aspect, methods of the present invention comprise
repositioning teeth using appliances comprising polymeric shells
having cavities shaped to receive and resiliently reposition teeth
to produce a final tooth arrangement. The present invention
provides improvements to such methods which comprise determining at
the outset of treatment geometries for at least three of the
appliances which are to be worn successively by a patient to
reposition teeth from an initial tooth arrangement to the final
tooth arrangement. Preferably, at least four geometries will be
determined in the outset, often at least ten geometries, frequently
at least twenty-five geometries, and sometimes forty or more
geometries. Usually, the tooth positions defined by the cavities in
each successive geometry differ from those defined by the prior
geometry by no more than 2 mm, preferably no more than 1 mm, and
often no more than 0.5 mm, as defined above.
[0024] In yet another aspect, methods are provided for producing a
digital data set representing a final tooth arrangement. The
methods comprise providing an initial data set representing an
initial tooth arrangement, and presenting a visual image based on
the initial data set. The visual image is then manipulated to
reposition individual teeth in the visual image. A final digital
data set is then produced which represents the final tooth
arrangement with repositioned teeth as observed in the visual
image. Conveniently, the initial digital data set may be provided
by conventional techniques, including digitizing X-ray images,
images produced by computer-aided tomography (CAT scans), images
produced by magnetic resonance imaging (MRI), and the like.
Preferably, the images will be three-dimensional images and
digitization may be accomplished using conventional technology.
Usually, the initial digital data set is provided by producing a
plaster cast of the patient's teeth (prior to treatment) by
conventional techniques. The plaster cast so produced may then be
scanned using laser or other scanning equipment to produce a high
resolution digital representation of the plaster cast of the
patient's teeth. Use of the plaster cast is preferred since it does
not expose the patient to X-rays or subject the patient to the
inconvenience of an MRI scan.
[0025] In a preferred embodiment, a wax bite is also obtained from
the patient using standard methods. The wax bite allows plaster
casts of a patient's upper and lower dentition to be placed
relative to one another in the centric occlusal position. The pair
of casts are then scanned to provide information on the relative
position of the jaw in this position. This information is then
incorporated into the initial digital data set (referred to
hereinafter as the IDDS) for both arches.
[0026] Once the digital data set is acquired, an image can be
presented and manipulated on a suitable computer system equipped
with computer-aided design software, as described in greater detail
below. The image manipulation will usually comprise defining
boundaries about at least some of the individual teeth, and causing
the images of the teeth to be moved relative to the jaw and other
teeth by manipulation of the image via the computer. Methods are
also provided for detecting cusp information for the teeth. The
image manipulation can be done entirely subjectively, i.e. the user
may simply reposition teeth in an aesthetically and/or
therapeutically desired manner based on observation of the image
alone. Alternatively, the computer system could be provided with
rules and algorithms which assist the user in repositioning the
teeth. In some instances, it will be possible to provide rules and
algorithms which reposition the teeth in a fully automatic manner,
i.e. without user intervention. Once the individual teeth have been
repositioned, a final digital data set representing the desired
final tooth arrangement will be generated and stored.
[0027] A preferred method for determining the final tooth
arrangement is for the treating professional to define the final
tooth positions, e.g. by writing a prescription. The use of
prescriptions for defining the desired outcomes of orthodontic
procedures is well known in the art. When a prescription or other
final designation is provided, the image can then be manipulated to
match the prescription. In some cases, it would be possible to
provide software which could interpret the prescription in order to
generate the final image and thus the digital data set representing
the final tooth arrangement.
[0028] In yet another aspect, methods according to the present
invention are provided for producing a plurality of digital data
sets representing a series of discrete tooth arrangements
progressing from an initial tooth arrangement to a final tooth
arrangement. Such methods comprise providing a digital data set
representing an initial tooth arrangement (which may be
accomplished according to any of the techniques set forth above). A
digital data set representing a final tooth arrangement is also
provided. Such final digital data set may be determined by the
methods described previously. The plurality of successive digital
data sets are then produced based on the initial digital data set
and the final digital data set. Usually, the successive digital
data sets are produced by determining positional differences
between selected individual teeth in the initial data set and in
the final data set and interpolating said differences. Such
interpolation may be performed over as many discrete stages as may
be desired, usually at least three, often at least four, more often
at least ten, sometimes at least twenty-five, and occasionally
forty or more. Many times, the interpolation will be linear
interpolation for some or all of the positional differences.
Alternatively, the interpolation may be non-linear. In a preferred
embodiment, non-linear interpolation is computed automatically by
the computer using path scheduling and collision detection
techniques to avoid interferences between individual teeth. The
positional differences will correspond to tooth movements where the
maximum linear movement of any point on a tooth is 2 mm or less,
usually being 1 mm or less, and often being 0.5 mm or less.
[0029] Often, the user will specify certain target intermediate
tooth arrangements, referred to as "key frames," which are
incorporated directly into the intermediate digital data sets. The
methods of the present invention then determine successive digital
data sets between the key frames in the manner described above,
e.g. by linear or non-linear interpolation between the key frames.
The key frames may be determined by a user, e.g. the individual
manipulating a visual image at the computer used for generating the
digital data sets, or alternatively may be provided by the treating
professional as a prescription in the same manner as the
prescription for the final tooth arrangement.
[0030] In still another aspect, methods according to the present
invention provide for fabricating a plurality of dental incremental
position adjustment appliances. Said methods comprise providing an
initial digital data set, a final digital data set, and producing a
plurality of successive digital data sets representing the target
successive tooth arrangements, generally as just described. The
dental appliances are then fabricated based on at least some of the
digital data sets representing the successive tooth arrangements.
Preferably, the fabricating step comprises controlling a
fabrication machine based on the successive digital data sets to
produce successive positive models of the desired tooth
arrangements. The dental appliances are then produced as negatives
of the positive models using conventional positive pressure or
vacuum fabrication techniques. The fabrication machine may comprise
a stereolithography or other similar machine which relies on
selectively hardening a volume of non-hardened polymeric resin by
scanning a laser to selectively harden the resin in a shape based
on the digital data set. Other fabrication machines which could be
utilized in the methods of the present invention include tooling
machines and wax deposition machines.
[0031] In still another aspect, methods of the present invention
for fabricating a dental appliance comprise providing a digital
data set representing a modified tooth arrangement for a patient. A
fabrication machine is then used to produce a positive model of the
modified tooth arrangement based on the digital data set. The
dental appliance is then produced as a negative of the positive
model. The fabrication machine may be a stereolithography or other
machine as described above, and the positive model is produced by
conventional pressure or vacuum molding techniques.
[0032] In a still further aspect, methods for fabricating a dental
appliance according to the present invention comprise providing a
first digital data set representing a modified tooth arrangement
for a patient. A second digital data set is then produced from the
first digital data set, where the second data set represents a
negative model of the modified tooth arrangement. The fabrication
machine is then controlled based on the second digital data set to
produce the dental appliance. The fabrication machine will usually
rely on selectively hardening a non-hardened resin to produce the
appliance. The appliance typically comprises a polymeric shell
having a cavity shape to receive and resiliently reposition teeth
from an initial tooth arrangement to the modified tooth
arrangement.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A illustrates a patient's jaw and provides a general
indication of how teeth may be moved by the methods and apparatus
of the present invention.
[0034] FIG. 1B illustrates a single tooth from FIG. 1A and defines
how tooth movement distances are determined.
[0035] FIG. 1C illustrates the jaw of FIG. 1A together with an
incremental position adjustment appliance which has been configured
according to the methods of the present invention.
[0036] FIG. 2 is a block diagram illustrating the steps of the
present invention for producing a system of incremental position
adjustment appliances.
[0037] FIG. 3 is a block diagram setting forth the steps for
manipulating an initial digital data set representing an initial
tooth arrangement to produce a final digital data set corresponding
to a desired final tooth arrangement.
[0038] FIG. 4A is a flow chart illustrating an eraser tool for the
methods herein.
[0039] FIG. 4B illustrates the volume of space which is being
erased by the program of FIG. 4A.
[0040] FIG. 5 is a flow chart illustrating a program for matching
high-resolution and low-resolution components in the manipulation
of data sets of FIG. 3.
[0041] FIG. 6A is a flow chart illustrating a program for
performing the "detection" stage of the cusp detection
algorithm.
[0042] FIG. 6B is a flow chart illustrating a program for
performing the "rejection" stage of the cusp detection
algorithm.
[0043] FIG. 7 illustrates the method for generating multiple
intermediate digital data sets which are used for producing the
adjustment appliances of the present invention.
[0044] FIG. 8A is a flow chart illustrating the steps performed by
the path scheduling algorithm.
[0045] FIG. 8B is a flow chart illustrating the steps for
performing the "visibility" function according to one embodiment of
the present invention.
[0046] FIG. 8C is a flow chart illustrating the steps for
performing the "children" function according to one embodiment of
the present invention.
[0047] FIG. 8D is a flow chart illustrating the steps for
performing path scheduling step 128 of FIG. 8A.
[0048] FIG. 9A is a flow chart illustrating the steps for
performing recursive collision testing during collision
detection.
[0049] FIG. 9B is a flow chart illustrating node splitting
performed during collision detection according to an embodiment of
the present invention.
[0050] FIG. 9C is a flow chart illustrating steps for providing
additional motion information to the collision detection
process.
[0051] FIG. 10 illustrates alternative processes for producing a
plurality of appliances according to the methods of the present
invention utilizing digital data sets representing the intermediate
and final appliance designs.
[0052] FIG. 11 is a simplified block diagram of a data processing
system incorporating an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0053] According to the present invention, systems and methods are
provided for incrementally moving teeth using a plurality of
discrete appliances, where each appliance successively moves one or
more of the patient's teeth by relatively small amounts. The tooth
movements will be those normally associated with orthodontic
treatment, including translation in all three orthogonal directions
relative to a vertical centerline, rotation of the tooth centerline
in the two orthodontic directions ("root angulation" and "torque"),
as well as rotation about the centerline.
[0054] Referring now to FIG. 1A, a representative jaw 100 includes
sixteen teeth 102. The present invention is intended to move at
least some of these teeth from an initial tooth arrangement to a
final tooth arrangement. To understand how the teeth may be moved,
an arbitrary centerline (CL) is drawn through one of the teeth 102.
With reference to this centerline (CL), the teeth may be moved in
the orthogonal directions represented by axes 104, 106, and 108
(where 104 is the centerline). The centerline may be rotated about
the axis 108 (root angulation) and 104 (torque) as indicated by
arrows 110 and 112, respectively. Additionally, the tooth may be
rotated about the centerline, as represented by arrow 114. Thus,
all possible free-form motions of the tooth can be performed.
Referring now to FIG. 1B, the magnitude of any tooth movement
achieved by the methods and devices of the present invention will
be defined in terms of the maximum linear translation of any point
P on a tooth 102. Each point P.sub.i will undergo a cumulative
translation as that tooth is moved in any of the orthogonal or
rotational directions defined in FIG. 1A. That is, while the point
will usually follow a non-linear path, there will be a linear
distance between any point in the tooth when determined at any two
times during the treatment. Thus, an arbitrary point P.sub.1 may in
fact undergo a true side-to-side translation as indicated by arrow
d1, while a second arbitrary point P.sub.2 may travel along an
arcuate path, resulting in a final translation d2. Many aspects of
the present invention are defined in terms of the maximum
permissible movement of a point P.sub.i induced by the methods in
any particular tooth. Such maximum tooth movement, in turn, is
defined as the maximum linear translation of that point P.sub.i on
the tooth which undergoes the maximum movement for that tooth in
any treatment step.
[0055] Referring now to FIG. 1C, systems according to the present
invention will comprise a plurality of incremental position
adjustment appliances. The appliances are intended to effect
incremental repositioning of individual teeth in the jaw as
described generally above. In a broadest sense, the methods of the
present invention can employ any of the known positioners,
retainers, or other removable appliances which are known for
finishing and maintaining teeth positions in connection with
conventional orthodontic treatment. The systems of the present
invention, in contrast with prior apparatus and systems, will
provide a plurality of such appliances intended to be worn by a
patient successively in order to achieve the gradual tooth
repositioning as described herein. A preferred appliance 111 will
comprise a polymeric shell having a cavity shaped to receive and
resiliently reposition teeth from one tooth arrangement to a
successive tooth arrangement. The polymeric shell will preferably,
but not necessarily, fit over all teeth present in the upper or
lower jaw. Often, only certain one(s) of the teeth will be
repositioned while others of the teeth will provide a base or
anchor region for holding the repositioning appliance in place as
it applies the resilient repositioning force against the tooth or
teeth to be repositioned. In complex cases, however, many or most
of the teeth will be repositioned at some point during the
treatment. In such cases, the teeth which are moved can also serve
as a base or anchor region for holding the repositioning appliance.
Additionally, the gums and/or the palette can serve as an anchor
region, thus allowing all or nearly all of the teeth to be
repositioned simultaneously.
[0056] The polymeric appliance 111 of FIG. 1C is preferably formed
from a thin sheet of a suitable elastomeric polymeric, such as
Tru-Tain 0.03 in. thermal forming dental material, Tru-Tain
Plastics, Rochester, Minn. 55902. Usually, no wires or other means
will be provided for holding the appliance in place over the teeth.
In some cases, however, it will be desirable or necessary to
provide individual anchors on teeth with corresponding receptacles
or apertures in the appliance 111 so that the appliance can apply
an upward force on the tooth which would not be possible in the
absence of such an anchor. Specific methods for producing the
appliances 111 are described hereinafter.
[0057] Referring now to FIG. 2, the overall method of the present
invention for producing the incremental position adjustment
appliances for subsequent use by a patient to reposition the
patient's teeth will be described. As a first step, a digital data
set representing an initial tooth arrangement is obtained (IDDS).
The IDDS may be obtained in a variety of ways. For example, the
patient's teeth may be scanned or imaged using well known
technology, such as X-rays, three-dimensional X-rays,
computer-aided tomographic images or data sets, magnetic resonance
images, etc. Methods for digitizing such conventional images to
produce data sets useful in the present invention are well known
and described in the patent and medical literature. Usually,
however, the present invention will rely on first obtaining a
plaster cast of the patient's teeth by well known techniques, such
as those described in Graber, Orthodontics: Principle and Practice,
Second Edition, Saunders, Pa., 1969, pp. 401-415. After the tooth
casting is obtained, it can be digitally scanned using a
conventional laser scanner or other range acquisition system to
produce the IDDS. The data set produced by the range acquisition
system may, of course, be converted to other formats to be
compatible with the software which is used for manipulating images
within the data set, as described in more detail below. General
techniques for producing plaster casts of teeth and generating
digital models using laser scanning techniques are described, for
example, in U.S. Pat. No. 5,605,459, the full disclosure of which
is incorporated herein by reference.
[0058] There are a variety of range acquisition systems, generally
categorized by whether the process of acquisition requires contact
with the three dimensional object. A contact-type range acquisition
system utilizes a probe, having multiple degrees of translational
and/or rotational freedom. By recording the physical displacement
of the probe as it is drawn across the sample surface, a
computer-readable representation of the sample object is made. A
non-contact-type range acquisition device can be either a
reflective-type or transmissive-type system. There are a variety of
reflective systems in use. Some of these reflective systems utilize
non-optical incident energy sources such as microwave radar or
sonar. Others utilize optical energy. Those non-contact-type
systems working by reflected optical energy further contain special
instrumentation configured to permit certain measuring techniques
to be performed (e.g., imaging radar, triangulation and
interferometry).
[0059] A preferred range acquisition system is an optical,
reflective, non-contact-type scanner. Non-contact-type scanners are
preferred because they are inherently nondestructive (i.e., do not
damage the sample object), are generally characterized by a higher
capture resolution and scan a sample in a relatively short period
of time. One such scanner is the Cyberware Model 15 manufactured by
Cyberware, Inc., Monterey, Calif.
[0060] Either non-contact-type or contact-type scanners may also
include a color camera, that when synchronized with the scanning
capabilities, provides a means for capturing, in digital format, a
color representation of the sample object. The importance of this
further ability to capture not just the shape of the sample object
but also its color is discussed below.
[0061] In a preferred embodiment, a wax bite is also obtained from
a patient. The wax bite enables scanning of the relative positions
of the upper and lower dentition in centric occlusion. This is
usually accomplished by first placing the lower cast in front of
the scanner, with the teeth facing upwards, then placing the wax
bite on top of the lower cast, and finally by placing the upper
cast on top of the lower cast, with the teeth downwards, resting on
the wax bite. A cylindrical scan is then acquired for the lower and
upper casts in their relative positions. The scanned data provides
a digital model of medium resolution representing an object which
is the combination of the patient's arches positioned in the same
relative configuration as in the mouth.
[0062] The digital model acts as a template guiding the placement
of the two individual digital models (one per arch). More
precisely, using software, for example the CyberWare alignment
software, each digital arch is in turn aligned to the pair scan.
The individual models are then positioned relative to each other
corresponding to the arches in the patient's mouth.
[0063] The methods of the present invention will rely on
manipulating the IDDS at a computer or workstation having a
suitable graphical user interface (GUI) and software appropriate
for viewing and modifying the images. Specific aspects of the
software will be described in detail hereinafter. While the methods
will rely on computer manipulation of digital data, the systems of
the present invention comprising multiple dental appliances having
incrementally differing geometries may be produced by
non-computer-aided techniques. For example, plaster casts obtained
as described above may be cut using knives, saws, or other cutting
tools in order to permit repositioning of individual teeth within
the casting. The disconnected teeth may then be held in place by
soft wax or other malleable material, and a plurality of
intermediate tooth arrangements can then be prepared using such a
modified plaster casting of the patient's teeth. The different
arrangements can be used to prepare sets of multiple appliances,
generally as described below, using pressure and vacuum molding
techniques. While such manual creation of the appliance systems of
the present invention will generally be much less preferred,
systems so produced will come within the scope of the present
invention.
[0064] Referring again to FIG. 2, after the IDDS has been obtained,
the digital information will be introduced to the computer or other
workstation for manipulation. In the preferred approach, individual
teeth and other components will be "cut" to permit their individual
repositioning or removal from the digital data. After thus
"freeing" the components, the user will often follow a prescription
or other written specification provided by the treating
professional. Alternatively, the user may reposition them based on
the visual appearance or using rules and algorithms programmed into
the computer. Once the user is satisfied with the final
arrangement, the final tooth arrangement is incorporated into a
final digital data set (FDDS).
[0065] Based on both the IDDS and the FDDS, a plurality of
intermediate digital data sets (INTDDS's) are generated to
correspond to successive intermediate tooth arrangements. The
system of incremental position adjustment appliances can then be
fabricated based on the INTDDS's, as described in more detail
below.
[0066] FIG. 3 illustrates a representative technique for
manipulating the IDDS to produce the FDDS on the computer. Usually,
the data from the digital scanner will be in a high resolution
form. In order to reduce the computer time necessary to generate
images, a parallel set of digital data set representing the IDDS at
a lower resolution will be created. The user will manipulate the
lower resolution images while the computer will update the high
resolution data set as necessary. The user can also view/manipulate
the high resolution model if the extra detail provided in that
model is useful. The IDDS will also be converted into a quad edge
data structure if not already present in that form. A quad edge
data structure is a standard topological data structure defined in
Primitives for the Manipulation of General Subdivisions and the
Computation of Voronoi Diagrams, ACM Transactions of Graphics, Vol.
4, No. 2, April 1985, pp. 74-123. Other topological data
structures, such as the winged-edge data structure, could also be
used.
[0067] As an initial step, while viewing the three-dimensional
image of the patient's jaw, including the teeth, gingivae, and
other oral tissue, the user will usually delete structure which is
unnecessary for image manipulation and/or final production of an
appliance. These unwanted sections of the model may be removed
using an eraser tool to perform a solid modeling subtraction. The
tool is represented by a graphic box. The volume to be erased (the
dimensions, position, and orientation of the box) are set by the
user employing the GUI. Typically, unwanted sections would include
extraneous gum area and the base of the originally scanned cast.
Another application for this tool is to stimulate the extraction of
teeth and the "shaving down" of tooth surfaces. This is necessary
when additional space is needed in the jaw for the final
positioning of a tooth to be moved. The treating professional may
choose to determine which teeth will be shaved and/or which teeth
will be extracted. Shaving allows the patient to maintain their
teeth when only a small amount of space is needed. Typically,
extraction and shaving, of course, will be utilized in the
treatment planning only when the actual patient teeth are to be
extracted and/or shaved prior to initiating repositioning according
to the methods of the present invention.
[0068] Removing unwanted and/or unnecessary sections of the model
increases data processing speed and enhances the visual display.
Unnecessary sections include those not needed for creation of the
tooth repositioning appliance. The removal of these unwanted
sections reduces the complexity and size of the digital data set,
thus accelerating manipulations of the data set and other
operations.
[0069] After the user positions and sizes the eraser tool and
instructs the software to erase the unwanted section, all triangles
within the box set by the user will be removed and the border
triangles are modified to leave a smooth, linear border. The
software deletes all of the triangles within the box and clips all
triangles which cross the border of the box. This requires
generating new vertices on the border of the box. The holes created
in the model at the faces of the box are re-triangulated and closed
using the newly created vertices.
[0070] The saw tool is used to define the individual teeth (or
possibly groups of teeth) to be moved. The tool separates the
scanned image into individual graphic components enabling the
software to move the tooth or other component images independent of
remaining portions of the model. In one embodiment, the saw tool
defines a path for cutting the graphic image by using two cubic
B-spline curves lying in space, possibly constrained to parallel
planes, either open or closed. A set of lines connects the two
curves and shows the user the general cutting path. The user may
edit the control points on the cubic B-splines, the thickness of
the saw cut, and the number of erasers used, as described
below.
[0071] In an alternate preferred embodiment, the teeth are
separated by using the saw as a "coring" device, cutting the tooth
from above with vertical saw cuts. The crown of the tooth, as well
as the gingivae tissue immediately below the crown are separated
from the rest of the geometry, and treated as an individual unit,
referred to as a tooth. When this model is moved, the gingivae
tissue moves relative to the crown, creating a first order
approximation of the way that the gingivae will reform within a
patient's mouth.
[0072] Each tooth may also be separated from the original trimmed
model. Additionally, a base may be created from the original
trimmed model by cutting off the crowns of the teeth. The resulting
model is used as a base for moving the teeth. This facilitates the
eventual manufacture of a physical mold from the geometric model,
as described below.
[0073] Thickness: When a cut is used to separate a tooth, the user
will usually want the cut to be as thin as possible. However, the
user may want to make a thicker cut, for example, when shaving down
surrounding teeth, as described above. Graphically, the cut appears
as a curve bounded by the thickness of the cut on one side of the
curve.
[0074] Number of Erasers: A cut is comprised of multiple eraser
boxes arranged next to each other as a piecewise linear
approximation of the Saw Tool's curve path. The user chooses the
number of erasers, which determines the sophistication of the curve
created--the greater the number of segments, the more accurately
the cutting will follow the curve. The number of erasers is shown
graphically by the number of parallel lines connecting the two
cubic B-spline curves. Once a saw cut has been completely specified
the user applies the cut to the model. The cut is performed as a
sequence of erasings. A preferred algorithm is set forth in FIG.
4A. FIG. 4B shows a single erasing iteration of the cut as
described in the algorithm for a open ended B-spline curve. For a
vertical cut, the curves are closed with P.sub.A[O] and P.sub.A[S]
the same point and P.sub.B[O] and P.sub.B[S] being the same
point.
[0075] In one embodiment, the software may automatically partition
the saw tool into a set of erasers based upon a smoothness measure
input by the user. The saw is adaptively subdivided until an error
metric measures the deviation from the ideal representation to the
approximate representation to be less than a threshold specified by
the smoothness setting. The preferred error metric used compares
the linear length of the subdivided curve to the arclength of the
ideal spline curve. When the difference is greater than a threshold
computed from the smoothness setting, a subdivision point is added
along the spline curve.
[0076] A preview feature may also be provided in the software. The
preview feature visually displays a saw cut as the two surfaces
that represent opposed sides of the cut. This allows the user to
consider the final cut before applying it to the model data
set.
[0077] After the user has completed all desired cutting operations
with the saw tool, multiple graphic solids exist. However, at this
point, the software has not determined which triangles of the quad
edge data structure belong to which components. The software
chooses a random starting point in the data structure and traverses
the data structure using adjacency information to find all of the
triangles that are attached to each other, identifying an
individual component. This process is repeated starting with the
triangle whose component is not yet determined. Once the entire
data structure is traversed, all components have been
identified.
[0078] To the user, all changes made to the high resolution model
appear to occur simultaneously in the low resolution model, and
vice versa. However, there is not a one-to-one correlation between
the different resolution models. Therefore, the computer "matches"
the high resolution and low resolution components as best as it can
subject to defined limits. The algorithm is described in FIG.
5.
[0079] Cusp detection: In a preferred embodiment, the software
provides the ability to detect cusps for a tooth. Cusps are pointed
projections on the chewing surface of a tooth. Cusp detection can
be performed either before or after the cutting phase has been
performed. The algorithm used for cusp detection is composed of two
stages: (1) "detection" stage, during which a set of points on the
tooth are determined as candidates for cusp locations; and (2)
"rejection" stage, during which candidates from the set of points
are rejected if they do not satisfy a set of criteria associated
with cusps.
[0080] A preferred algorithm for the "detection" stage is set forth
in FIG. 6A. In the detection stage, a possible cusp is viewed as an
"island" on the surface of the tooth, with the candidate cusp at
the highest point on the island. "Highest" is measured with respect
to the coordinate system of the model, but could just as easily be
measured with respect to the local coordinate system of each tooth
if detection is performed after the cutting phase of treatment.
[0081] The set of all possible cusps is determined by looking for
all local maxima on the tooth model that are within a specified
distance of the top of the bounding box of the model. First, the
highest point on the model is designated as the first candidate
cusp. A plane is passed through this point, perpendicular to the
direction along which the height of a point is measured. The plane
is then lowered by a small predetermined distance along the Z axis.
Next, all vertices connected to the tooth and which are above the
plane and on some connected component are associated with the
candidate cusp as cusps. This step is also referred to as the
"flood fill" step. From each candidate cusp point, outward
"flooding" is performed, marking each vertex on the model visited
in this matter as "part of" the corresponding candidate cusp. After
the flood fill step is complete, every vertex on the model is
examined. Any vertex that is above the plane and has not been
visited by one of the flood fills is added to the list of candidate
cusps. These steps are repeated until the plane is traveled a
specified distance.
[0082] While this iterative approach can be more time consuming
than a local maximum search, the approach described above leads to
a shorter list of candidate cusps. Since the plane is lowered a
finite distance at each step, very small local maxima that can
occur due to noisy data are skipped over.
[0083] After the "detection" stage, the cusp detection algorithm
proceeds with the "rejection" stage. A preferred algorithm for the
"rejection" stage is set forth in FIG. 6B. In this stage, the local
geometries around each of cusp candidates are analyzed to determine
if they possess "non-cusp-like features." Cusp candidates that
exhibit "non-cusp-like features" are removed from the list of cusp
candidates.
[0084] Various criteria may be used to identify "non-cusp-like
features." According to one test, the local curvature of the
surface around the cusp candidate is used to determine whether the
candidate possesses non-cusp-like features. As depicted in FIG. 6B,
the local curvature of the surface around the cusp candidate is
approximated, and then analyzed to determine if it is too large
(very pointy surface) or too small (very flat surface), in which
case the candidate is removed from the list of cusp candidates.
Conservative values are used for the minimum and maximum curvatures
values to ensure that genuine cusps are not rejected by
mistake.
[0085] According to an alternate test, a measure of smoothness is
computed based on the average normal in an area around the
candidate cusp. If the average normal deviates from the normal at
the cusp by more than a specified amount, the candidate cusp is
rejected. In a preferred embodiment, the deviation of a normal
vector N from the cusp normal CN is approximated by the
formula:
1-Abs(N*CN),
[0086] which is zero at no deviation, and 1 when N and CN are
perpendicular.
[0087] Once the teeth have been separated, the FDDS can be created
from the IDDS. The FDDS is created by following the orthodontists
prescription, moving the teeth into their final prescription. In
one embodiment, the prescription is entered into a computer, which
algorithmically computes the final position of the teeth. In
alternate embodiments, a user may move the teeth into their final
positions by independently manipulating one or more teeth while
satisfying the constraints of the prescription. It should be
appreciated that various combinations of the above described
techniques may also be used to arrive at the final teeth
position.
[0088] The preferred method for creating the FDDS involves moving
the teeth in a specified sequence. First, the centers of each of
the teeth are aligned to a standard arch. Then, the teeth are
rotated until their roots are in the proper vertical position.
Next, the teeth are rotated around their vertical axis into the
proper orientation. The teeth are then observed from the side, and
translated vertically into their proper vertical position. Finally,
the two arches are placed together, and the teeth moved slightly to
ensure that the upper and lower arches properly mesh together. The
meshing of the upper and lower arches together is visualized using
the collision detection algorithm to highlight the contacting
points of the teeth in red.
[0089] After the teeth and other components have been placed or
removed so that the final tooth arrangement has been produced, it
is necessary to generate a treatment plan, as illustrated in FIG.
7. The treatment plan will ultimately produce the series of
INTDDS's and FDDS as described previously. To produce these data
sets, it is necessary to define or map the movement of selected
individual teeth from the initial position to the final position
over a series of successive steps. In addition, it may be necessary
to add other features to the data sets in order to produce desired
features in the treatment appliances. For example, it may be
desirable to add wax patches to the image in order to define
cavities or recesses for particular purposes. For example, it may
be desirable to maintain a space between the appliance and
particular regions of the teeth or jaw in order to reduce soreness
of the gums, avoid periodontal problems, allow for a cap, and the
like. Additionally, it will often be necessary to provide a
receptacle or aperture intended to accommodate an anchor which is
to be placed on a tooth in order to permit the tooth to be
manipulated in a manner that requires the anchor, e.g. lifted
relative to the jaw.
[0090] Some methods for manufacturing the tooth repositioning
appliances require that the separate, repositioned teeth and other
components be unified into a single continuous structure in order
to permit manufacturing. In these instances, "wax patches" are used
to attach otherwise disconnected components of the INTDDS's. These
patches are added to the data set underneath the teeth and above
the gum so that they do not effect the geometry of the tooth
repositioning appliances. The application software provides for a
variety of wax patches to be added to the model, including boxes
and spheres with adjustable dimensions. The wax patches that are
added are treated by the software as additional pieces of geometry,
identical to all other geometries. Thus, the wax patches can be
repositioned during the treatment path as well as the teeth and
other components. The preferred method of separating the teeth
using vertical coring, as described above, removes the need for
most of these "wax patches".
[0091] In the manufacturing process, which relies on generation of
positive models to produce the repositioning appliance, adding a
wax patch to the graphic model will generate a positive mold that
has the same added wax patch geometry. Because the mold is a
positive of the teeth and the appliance is a negative of the teeth,
when the appliance is formed over the mold, the appliance will also
form around the wax patch that has been added to the mold. When
placed in the patient's mouth, the appliance will thus allow for a
space between the inner cavity surface of the appliance and the
patient's teeth or gums. Additionally, the wax patch may be used to
form a recess or aperture within the appliance which engages an
anchor placed on the teeth in order to move the tooth in directions
which could not otherwise be accomplished.
[0092] In addition to such wax patches, an individual component,
usually a tooth, can be scaled to a smaller or larger size which
will result in a manufactured appliance having a tighter or looser
fit, respectively.
[0093] Treatment planning is extremely flexible in defining the
movement of teeth and other components. The user may change the
number of treatment stages, as well as individually control the
path and speed of components.
[0094] Number of Treatment Stages: The user can change the number
of desired treatment stages from the initial to the target stages
of the teeth. Any component that is not moved is assumed to remain
stationary, and thus its final position is assumed to be the same
as the initial position (likewise for all intermediate positions,
unless one or more key frames are defined for that component).
[0095] Key frames: The user may also specify "key frames" by
selecting an intermediate state and making changes to component
position(s). Unless instructed otherwise, the software
automatically linearly interpolates between all user-specified
positions (including the initial position, all key frame positions,
and the target position). For example, if only a final position is
defined for a particular component, each subsequent stage after the
initial stage will simply show the component at equal linear
distance and rotation (specified by a quaternion) closer to the
final position. If the user specifies two key frames for that
component, it will "move" linearly from the initial position
through different stages to the position defined by the first key
frame. It will then move, possibly in a different direction,
linearly to the position defined by the second key frame. Finally,
it will move, possibly in yet a different direction, linearly to
the target position.
[0096] The user can also specify non-linear interpolation between
the key frames. A spline curve is used to specify the interpolating
function in a conventional manner.
[0097] These operations may be done independently to each
component, so that a key frame for one component will not affect
another component, unless the other component is also moved by the
user in that key frame. One component may accelerate along a curve
between stages 3 and 8, while another moves linearly from stage 1
to 5, and then changes direction suddenly and slows down along a
linear path to stage 10. This flexibility allows a great deal of
freedom in planning a patient's treatment.
[0098] In one embodiment, the software automatically determines the
treatment path, based upon the IDDS and the FDDS. This is usually
accomplished using a path scheduling algorithm which determines the
rate at which each component, i.e. a tooth, moves along a straight
path from the initial position to the final position. The path
scheduling algorithm used by the present invention determines the
treatment path while avoiding "round-tripping" which is the term
used by orthodontists referring to moving a tooth along a distance
greater than absolutely necessary to straighten the teeth. Such
motion is highly undesirable, and has potential negative side
effects on the patient. In order to avoid "round-tripping", the
path scheduling algorithm schedules or stages the movements of all
the teeth by constraining them to the shortest straight-line path
between the initial and final position, while avoiding all
interferences between separate teeth.
[0099] The path scheduling algorithm utilizes a randomized search
technique to find an unobstructed path through a configuration
space which describes possible treatment plans. A preferred
embodiment of the algorithm for scheduling motion between two user
defined global keyframes is described below. Scheduling over a time
interval which includes intermediate keyframes is accomplished by
dividing the time interval into subintervals which do not include
intermediate keyframes, scheduling each of these intervals
independently, and then concatenating the resulting schedules.
[0100] Flow chart 120 in FIG. 8A depicts a simplified path
scheduling algorithm according to one embodiment of the present
invention. As shown in FIG. 8A, first step 122 involves
construction of the "configuration space" description. A
"configuration," in this context, refers to a given set of
positions of all the teeth being considered for movement. Each of
these positions may be described in multiple ways. In a preferred
embodiment of the present invention, the positions are described by
one affine transformation to specify change in location and one
rotational transformation to specify the change in orientation of a
tooth from its initial position to its final position. The
intermediate positions of each tooth are described by a pair of
numbers which specify how far to interpolate the location and
orientation between the two endpoints. A "configuration" thus
consists of two numbers for each tooth being moved, and the
"configuration space" refers to the space of all such number pairs.
Thus, the configuration space is a Cartesian space, any location in
which can be interpreted as specifying the positions of all
teeth.
[0101] The affine transformation describing the movement of each
tooth from its starting position to its ending position is
decomposed into translational and rotational components; these
transformations are independently interpolated with scalar
parameters which are considered two dimensions of the configuration
space. The entire configuration space thus consists of two
dimensions per moved tooth, all of which are treated equivalently
during the subsequent search.
[0102] The configuration space is made of "free space" and
"obstructed space." "Free" configurations are those which represent
valid, physically realizable positions of teeth, while "obstructed"
configurations are those which do not. To determine whether a
configuration is free or obstructed, a model is created for the
positions of the teeth which the configuration describes. A
collision detection algorithm is then applied to determine if any
of the geometries describing the tooth surfaces intersect. If there
are no obstructions, the space is considered free; otherwise it is
obstructed. The collision detect algorithm is discussed below in
more detail. At step 124, a "visibility" function V(s.sub.i,
s.sub.2) is defined which takes two vectors in the configuration
space, "s.sub.1" and "s.sub.2", as input and returns a true or
false boolean value. The visibility function returns a true value
if and only if a straight line path connecting s.sub.1 and s.sub.2
passes entirely through a free and unobstructed region of the
configuration space. A preferred algorithm for the visibility
function is set forth in FIG. 8B. The visibility function is
approximately computed by testing the teeth model for interferences
at discretely sampled points along the line s.sub.1-s.sub.2.
Techniques, such as early termination on failure or choosing the
order of sample points by recursively subdividing the interval to
be tested, may be used to increase the efficiency of the visibility
function.
[0103] At step 126 of FIG. 8A, a "children" function C(s) is
defined whose input parameter, "s", is a vector in the
configuration space and which returns a set of vectors, "s.sub.c"
in the configuration space. FIG. 8C depicts a simplified flow chart
illustrating the steps followed for computing children function
C(s). Each vector within set sc satisfies the property that V(s,
s.sub.c) is true and that each of its components are greater than
or equal to the corresponding component of "s." This implies that
any state represented by such a vector is reachable from "s"
without encountering any interferences and without performing any
motion which is not in the direction prescribed by treatment. Each
vector of set "s.sub.c" is created by perturbing each component of
"s" by some random, positive amount. The visibility function V(s,
s.sub.c) is then computed and "s" added to the set "s.sub.c" if the
visibility function returns a true boolean value. Additionally, for
each such vector generated, a pointer to its parent "s" is recorded
for later use.
[0104] After the configuration space has been defined, at step 128,
path scheduling is performed between an initial state "s.sub.init"
and a final state "s.sub.final". FIG. 8D depicts a preferred flow
chart for performing step 128 depicted in FIG. 8A. As illustrated
in FIG. 8D, at step 128a, a set of states "W" is defined to
initially contain only the initial state s.sub.init. Next, at step
128b, the visibility function is invoked to determine if V(s.sub.i,
s.sub.final) is true for at least one state s.sub.i in W. If the
visibility function returns a false boolean value, at step 128c,
the set of states "W" is replaced with the union of C(s.sub.i) for
all s.sub.i in W. Steps 128b and 128c are repeated until V(s.sub.i,
s.sub.final) returns a true boolean value for any s.sub.i belonging
to W.
[0105] At step 128d, for each s.sub.i for which V(s.sub.i,
s.sub.final) is true, an unobstructed path P.sub.i is constructed
from s.sub.i to s.sub.init by following the parent pointers back to
s.sub.init. At step 128e, the path from s.sub.init to s.sub.final
is then constructed by concatenating the paths P.sub.i with the
final step from s.sub.i to s.sub.final. If there are multiple paths
from s.sub.init to s.sub.final, the total length of each path is
computed at step 128f. Finally, at step 128g, the path with the
shortest length is then chosen as the final path. The length of the
chosen path corresponds to the total time and stages required for a
treatment plan.
[0106] The resulting final path consists of a series of vectors,
each of which represents a group of values of the interpolation
parameters of the translational and rotational components of the
transformations of the moving teeth. Taken together, these
constitute a schedule of tooth movement which avoids tooth-to-tooth
interferences.
[0107] Collision detect algorithm: The collision or interference
detection algorithm employed by the present invention is based on
the algorithm described in SIGGRAPH article, Stefan Gottschalk et
al. (1996): "OBBTree: A Hierarchical Structure for Rapid
Interference Detection. " The contents of the SIGGRAPH article are
herein incorporated by reference.
[0108] The algorithm is centered around a recursive subdivision of
the space occupied by an object, which is organized in a
binary-tree like fashion. Triangles are used to represent the teeth
in the DDS. Each node of the tree is referred to as an oriented
bounding box (OBB) and contains a subset of triangles appearing in
the node's parent. The children of a parent node contain between
them all of the triangle data stored in the parent node.
[0109] The bounding box of a node is oriented so it tightly fits
around all of the triangles in that node. Leaf nodes in the tree
ideally contain a single triangle, but can possibly contain more
than one triangle. Detecting collisions between two objects
involves determining if the OBB trees of the objects intersect.
FIG. 9A sets forth a flow chart depicting a simplified version of a
recursive collision test to check if a node "N1" from a first
object intersects with node "N2" of a second object. If the OBBs of
the root nodes of the trees overlap, the root's children are
checked for overlap. The algorithm proceeds in a recursive fashion
until the leaf nodes are reached. At this point, a robust triangle
intersection routine is used to determine if the triangles at the
leaves are involved in a collision.
[0110] The present invention provides several enhancements to the
collision detection algorithm described in the SIGGRAPH article. In
one embodiment, the present invention provides a unique method of
building OBB trees in a lazy fashion to save memory and time.
[0111] This approach stems from the observation that there are
parts of the model which will never be involved in a collision, and
consequently the OBB tree for such parts of the model need not be
computed. The OBB trees are expanded by splitting the internal
nodes of the tree as necessary during the recursive collision
determination algorithm, as depicted in FIG. 9B.
[0112] In another embodiment of the present invention, the
triangles in the model which are not required for collision data
may also be specifically excluded from consideration when building
an OBB tree. As depicted in FIG. 9C, additional information is
provided to the collision algorithm to specify objects in motion.
Motion may be viewed at two levels.
[0113] Objects may be conceptualized as "moving" in a global sense,
or they may be conceptualized as "moving" relative to other
objects. The additional information improves the time taken for the
collision detection by avoiding recomputation of collision
information between objects which are at rest relative to each
other since the state of the collision between such objects does
not change.
[0114] The software of the present invention may also incorporate
and the user may at any point use a "movie" feature to
automatically animate the movement from initial to target states.
This is helpful for visualizing overall component movement
throughout the treatment process.
[0115] Above it was described that the preferred user interface for
component identification is a three dimensional interactive GUI. A
three-dimensional GUI is also preferred for component manipulation.
Such an interface provides the treating professional or user with
instant and visual interaction with the digital model components.
It is preferred over interfaces that permit only simple low-level
commands for directing the computer to manipulate a particular
segment. In other words, a GUI adapted for manipulation is
preferred over an interface that accepts directives, for example,
only of the sort: "translate this component by 0.1 mm to the
right." Such low-level commands are useful for fine-tuning, but, if
they were the sole interface, the processes of component
manipulation would become a tiresome and time-consuming
interaction.
[0116] Before or during the manipulation process, one or more tooth
components may be augmented with template models of tooth roots.
Manipulation of a tooth model augmented with a root template is
useful, for example, in situations where impacting of teeth below
the gumline is a concern. These template models could, for example,
comprise a digitized representation of the patient's teeth
x-rays.
[0117] The software also allows for adding annotations to the
datasets which can comprise text and/or the sequence number of the
apparatus. The annotation is added as recessed text (i.e. it is 3-D
geometry), so that it will appear on the printed positive model. If
the annotation can be placed on a part of the mouth that will be
covered by a repositioning appliance, but is unimportant for the
tooth motion, the annotation may appear on the delivered
repositioning appliance(s).
[0118] The above-described component identification and component
manipulation software is designed to operate at a sophistication
commensurate with the operator's training level. For example, the
component manipulation software can assist a computer operator,
lacking orthodontic training, by providing feedback regarding
permissible and forbidden manipulations of the teeth. On the other
hand, an orthodontist, having greater skill in intraoral physiology
and teeth-moving dynamics, can simply use the component
identification and manipulation software as a tool and disable or
otherwise ignore the advice.
[0119] Once the intermediate and final data sets have been created,
the appliances may be fabricated as illustrated in FIG. 10.
Preferably, fabrication methods will employ a rapid prototyping
device 200 such as a stereolithography machine. A particularly
suitable rapid prototyping machine is Model SLA-250/50 available
from 3D System, Valencia, Calif. The rapid prototyping machine 200
will selectively harden a liquid or other non-hardened resin into a
three-dimensional structure which can be separated from the
remaining non-hardened resin, washed, and used either directly as
the appliance or indirectly as a mold for producing the appliance.
The prototyping machine 200 will receive the individual digital
data sets and produce one structure corresponding to each of the
desired appliances. Generally, because the rapid prototyping
machine 200 may utilize a resin having non-optimum mechanical
properties and which may not be generally acceptable for patient
use, it will be preferred to use the prototyping machine to produce
molds which are, in effect, positive tooth models of each
successive stage of the treatment. After the positive models are
prepared, a conventional pressure or vacuum molding machine may be
used to produce the appliances from a more suitable material, such
as 0.03 inch thermal forming dental material, available from
Tru-Tain Plastics, Rochester, Minn. 55902. Suitable pressure
molding equipment is available under the tradename BIOSTAR from
Great Lakes Orthodontics, Ltd., Tonawanda, N.Y. 14150. The molding
machine 250 produces each of the appliances directly from the
positive tooth model and the desired material. Suitable vacuum
molding machines are available from Raintree Essix, Inc.
[0120] After production, the plurality of appliances which comprise
the system of the present invention are preferably supplied to the
treating professional all at one time. The appliances will be
marked in some manner, typically by sequential numbering directly
on the appliances or on tags, pouches, or other items which are
affixed to or which enclose each appliance, to indicate their order
of use. Optionally, written instructions may accompany the system
which set forth that the patient is to wear the individual
appliances in the order marked on the appliances or elsewhere in
the packaging. Use of the appliances in such a manner will
reposition the patient's teeth progressively toward the final tooth
arrangement.
[0121] FIG. 11 is a simplified block diagram of a data processing
system 300 embodying the present invention. Data processing system
300 typically includes at least one processor 302 which
communicates with a number of peripheral devices via bus subsystem
304. These peripheral devices typically include a storage subsystem
306 (memory subsystem 308 and file storage subsystem 314), a set of
user interface input and output devices 318, and an interface to
outside networks 316, including the public switched telephone
network. This interface is shown schematically as "Modems and
Network Interface" block 316, and is coupled to corresponding
interface devices in other data processing systems via
communication network interface 324. Data processing system 300
could be a terminal or a low-end personal computer or a high-end
personal computer, workstation or mainframe.
[0122] The user interface input devices typically include a
keyboard and may further include a pointing device and a scanner.
The pointing device may be an indirect pointing device such as a
mouse, trackball, touchpad, or graphics tablet, or a direct
pointing device such as a touchscreen incorporated into the
display. Other types of user interface input devices, such as voice
recognition systems, are also possible.
[0123] User interface output devices typically include a printer
and a display subsystem, which includes a display controller and a
display device coupled to the controller. The display device may be
a cathode ray tube (CRT), a flat-panel device such as a liquid
crystal display (LCD), or a projection device. The display subsys
tern may also provide non-visual display such as audio output.
[0124] Storage subsystem 306 maintains the basic programming and
data constructs that provide the functionality of the present
invention. The software modules discussed above are typically
stored in storage subsystem 306. Storage subsystem 306 typically
comprises memory subsystem 308 and file storage subsystem 314.
[0125] Memory subsystem 308 typically includes a number of memories
including a main random access memory (RAM) 310 for storage of
instructions and data during program execution and a read only
memory (ROM) 312 in which fixed instructions are stored. In the
case of Macintosh-compatible personal computers the ROM would
include portions of the operating system; in the case of
IBM-compatible personal computers, this would include the BIOS
(basic input/output system).
[0126] File storage subsystem 314 provides persistent
(non-volatile) storage for program and data files, and typically
includes at least one hard disk drive and at least one floppy disk
drive (with associated removable media). There may also be other
devices such as a CD-ROM drive and optical drives (all with their
associated removable media). Additionally, the system may include
drives of the type with removable media cartridges. The removable
media cartridges may, for example be hard disk cartridges, such as
those marketed by Syquest and others, and flexible disk cartridges,
such as those marketed by Iomega. One or more of the drives may be
located at a remote location, such as in a server on a local area
network or at a site on the Internet's World Wide Web.
[0127] In this context, the term "bus subsystem" is used
generically so as to include any mechanism for letting the various
components and subsystems communicate with each other as intended.
With the exception of the input devices and the display, the other
components need not be at the same physical location. Thus, for
example, portions of the file storage system could be connected via
various local-area or wide-area network media, including telephone
lines. Similarly, the input devices and display need not be at the
same location as the processor, although it is anticipated that the
present invention will most often be implemented in the context of
PCs and workstations.
[0128] Bus subsystem 304 is shown schematically as a single bus,
but a typical system has a number of buses such as a local bus and
one or more expansion buses (e.g., ADB, SCSI, ISA, EISA, MCA,
NuBus, or PCI), as well as serial and parallel ports. Network
connections are usually established through a device such as a
network adapter on one of these expansion buses or a modem on a
serial port. The client computer may be a desktop system or a
portable system.
[0129] Scanner 320 is responsible for scanning casts of the
patient's teeth obtained either from the patient or from an
orthodontist and providing the scanned digital data set information
to data processing system 300 for further processing. In a
distributed environment, scanner 320 may be located at a remote
location and communicate scanned digital data set information to
data processing system 300 via network interface 324.
[0130] Fabrication machine 322 fabricates dental appliances based
on intermediate and final data set information received from data
processing system 300. In a distributed environment, fabrication
machine 322 may be located at a remote location and receive data
set information from data processing system 300 via network
interface 324.
[0131] While the above is a complete description of the preferred
embodiments of the invention, various alternatives, modifications,
and equivalents may be used. Therefore, the above description
should not be taken as limiting the scope of the invention which is
defined by the appended claims.
* * * * *