|Publication number||WO2009097054 A1|
|Publication date||6 Aug 2009|
|Filing date||12 Dec 2008|
|Priority date||29 Jan 2008|
|Also published as||EP2237738A1, US8899977, US20090191502, US20150004554|
|Publication number||PCT/2008/86647, PCT/US/2008/086647, PCT/US/2008/86647, PCT/US/8/086647, PCT/US/8/86647, PCT/US2008/086647, PCT/US2008/86647, PCT/US2008086647, PCT/US200886647, PCT/US8/086647, PCT/US8/86647, PCT/US8086647, PCT/US886647, WO 2009/097054 A1, WO 2009097054 A1, WO 2009097054A1, WO-A1-2009097054, WO2009/097054A1, WO2009097054 A1, WO2009097054A1|
|Inventors||Heng CAO, Vadim Matov, John Morton, John Moss, Ryan Kimura|
|Applicant||Align Technology, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Non-Patent Citations (1), Referenced by (2), Classifications (4), Legal Events (2)|
|External Links: Patentscope, Espacenet|
ORTHODONTIC REPOSITIONING APPLIANCES HAVING IMPROVED GEOMETRY, METHODS AND SYSTEMS
CROSS-REFERENCE TO RELATED APPLICATION
 The present invention claims the benefit of priority under 35 U.S. C. § 119(e) of U.S.
Provisional Application No. 61/024,536, filed January 29, 2008 (Attorney Docket No. 018563-014400US), the entire content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
 The present invention relates generally to the field of orthodontics, and more particularly to dental repositioning appliances having improved or optimized geometries incorporating one or more shaped features or protrusions.
 An objective of orthodontics is to move a patient's teeth to positions where function and/or aesthetics are optimized. Traditionally, appliances such as braces are applied to a patient's teeth by an orthodontist or dentist and the set of braces exerts continual force on the teeth and gradually urges them toward their intended positions. Over time and with a series of clinical visits and adjustments to the braces, the orthodontist adjusts the appliances to move the teeth toward their final destination.
 More recently, alternatives to conventional orthodontic treatment with traditional affixed appliances (e.g., braces) have become available. For example, systems including a series of preformed aligners have become commercially available from Align Technology, Inc., Santa Clara, CA, under the tradename Invisalign® System. The Invisalign® System is described in numerous patents and patent applications assigned to Align Technology, Inc. including, for example in U.S. Pat. Nos. 6,450,807, and 5,975,893, as well as on the company's website, which is accessible on the World Wide Web (see, e.g., the url "align.com"). The Invisalign® System includes designing and/or fabricating multiple, and sometimes all, of the aligners to be worn by the patient before the aligners are administered to the patient and used to reposition the teeth (e.g., at the outset of treatment). Often, designing and planning a customized treatment for a patient makes use of computer-based 3- dimensional planning/design tools, such as software technology available from Align Technology, Inc. The design of the aligners can rely on computer modeling of a series of planned successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and elastically reposition the teeth to each of the planned tooth arrangements.
 Orthodontic appliances, in general, apply force and torque on a tooth crown to move teeth, with the applied force typically normal with respect to the surface of a tooth or attachment positioned on the tooth. The tooth root and/or other anatomical structures may hinder the desired tooth movement and render the center of resistance down below the gingival line and in the tooth bone socket, which can make certain movements difficult to accomplish by application of force to the tooth crown. If a translational movement is desired, for example, the translational force is optimally applied through the center of resistance or with sufficient counterbalancing forces, otherwise force on the tooth crown by an appliance can cause unwanted torque with respect to the center of resistance. Clinically, the unwanted torque can result in unwanted tooth movement and root movement, thereby decreasing the effectiveness of the treatment. As appliances are designed to contact and apply forces to the crown of the tooth, and the tooth center of resistance lies below the gingival line, applying forces more directly about the center of resistance is difficult with existing appliances. Accordingly, improved appliances and techniques are needed for applying more effective tooth movement forces to the teeth during orthodontic treatment, and reducing unwanted tooth movements.
SUMMARY OF THE INVENTION
 The present invention provides improved orthodontic appliances and related methods for more effectively applying tooth moving forces and repositioning teeth into a desired arrangement. Appliances of the invention include repositioning appliances having improved or optimized geometries incorporating one or more shaped features or protrusions.
 In one aspect, the present invention provides methods and systems, including an appliance having teeth receiving cavities shaped such that, when worn by a patient, apply a repositioning force to move the patient's teeth from a first arrangement toward a subsequent or target arrangement. Appliances can include a cavity having one or more shaped features or protrusions. Such features or protrusions can be shaped and/or positioned to apply a desired force to a patient's tooth received in the cavity so as to more effectively move the tooth along a desired path or direction.  For a fuller understanding of the nature and advantages of the present invention, reference should be made to the ensuing detailed description and accompanying drawings. Other aspects, objects and advantages of the invention will be apparent from the drawings and detailed description that follows.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. IA illustrates a jaw together with an incremental positioning adjustment appliance according to an embodiment of the present invention.
 FIGS. IB- IE illustrate various protrusion configurations and orientations including horizontal continuous ridge (FIG. IB), vertical continuous ridge (FIG. 1C), and discontinuous ridge (FIGS. ID and IE), according to several embodiments of the present invention.
 FIGS. 2A-2F illustrate positioning of shaped features for buccal-Ungual translation, according to an embodiment of the present invention.
 FIGS. 3A-3D illustrate positioning of shaped features for distal-mesial translation, according to an embodiment of the present invention.
 FIGS. 4A-4C illustrate positioning of shaped features for extrusion-intrusion movements, according to an embodiment of the present invention.
 FIGS. 5A-5B illustrate positioning of shaped features for tooth rotations, according to an embodiment of the present invention.
 FIG. 6A is a flowchart of a process of specifying a course of treatment including a subprocess for calculating aligner shapes in accordance with the invention, according to an embodiment of the present invention.
 FIG. 6B is a flowchart of a process for calculating aligner shapes, according to an embodiment of the present invention.
 FIG. 7 is a flowchart of a subprocess for creating finite element models, according to an embodiment of the present invention.
 FIG. 8 is a flowchart of a subprocess for computing aligner changes, according to an embodiment of the present invention.  FIG. 9A is a flowchart of a subprocess for calculating changes in aligner shape, according to an embodiment of the present invention.
 FIG. 9B is a flowchart of a subprocess for calculating changes in aligner shape, according to an embodiment of the present invention.
 FIG. 9C is a flowchart of a subprocess for calculating changes in aligner shape, according to an embodiment of the present invention.
 FIG. 9D is a schematic illustrating the operation of the subprocess of FIG. 5B, according to an embodiment of the present invention.
 FIG. 10 is a flowchart of a process for computing shapes for sets of aligners, according to an embodiment of the present invention.
 FIGS. 1 IA-I IB illustrate an initial tooth position with a positioned dental appliance, and a resulting undesirable force vector, respectively, according to an embodiment of the present invention.
 FIGS. 1 IC-I ID illustrate a relief addition to the dental appliance to counteract the undesirable force vector around the tooth, and the resulting desired application of the predetermined force on the tooth by the dental appliance, respectively, according to an embodiment of the present invention.
 FIG. 12 illustrates a modified dental appliance geometry including an additional shape modification to remove a gap between the dental appliance and the tooth, according to an embodiment of the present invention.
 FIG. 13 is a flowchart illustrating the optimized shape geometry of the dental appliance, according to an embodiment of the present invention.
 FIG. 14 is a flowchart illustrating a process of shape feature design and positioning, according to an embodiment of the present invention.
 The invention described herein describes systems and methods including orthodontic appliances having geometries designed to provide more precise control of the forces and moments applied to a tooth, thereby providing better control of the type of tooth movement desired while avoiding unwanted movements, such as unwanted tipping. Appliances according to the present invention can be designed to include certain "shaped features", such as shaped protrusions (e.g., ridges, dimples, etc.) positioned in a tooth receiving cavity, incorporated into appliance design and structure.
 Appliances having teeth receiving cavities that receive and reposition teeth, e.g., via application of force due to appliance resiliency, are generally illustrated with regard to FIG. IA. As illustrated, FIG. IA shows one exemplary adjustment appliance 10 which is worn by the patient in order to achieve an incremental repositioning of individual teeth in the jaw 11. The appliance can include a shell (e.g., polymeric shell) having teeth-receiving cavities that receive and resiliently reposition the teeth. Similar appliances, including those utilized in the Invisalign® System, are described in numerous patents and patent applications assigned to Align Technology, Inc. including, for example in U.S. Pat. Nos. 6,450,807, and 5,975,893, as well as on the company's website, which is accessible on the World Wide Web (see, e.g., the url "align.com"). Appliances according to the present invention further include one or more shaped features disposed in a tooth receiving cavity of the appliance, as further described below. As further described herein, shapes features can be designed, located and distributed to precisely control the moments produced on a patient's tooth as the appliance is worn by the patient. Incorporation of such protrusions and shaped features as described herein can advantageously improve design and effectiveness of appliances and clinical results by more precisely applying force vectors of necessary magnitude and direction for desired movement. Appliances of the present invention having shaped features as described further provide efficient force distribution mechanism that can more effectively reduce unwanted force and moment. Furthermore, inclusion of a force driven method of treatment design that focuses on the causes of tooth movement provides advantages in effectiveness and movement control compared to existing displacement driven treatment designs.
 As set forth in the prior applications, an appliance can be designed and/or provided as part of a set or plurality of appliances. In such an embodiment, each appliance may be configured so that its tooth-receiving cavity has a geometry corresponding to an intermediate or final tooth arrangement intended for the appliance. The patient's teeth are progressively repositioned from their initial tooth arrangement to a final tooth arrangement by placing a series of incremental position adjustment appliances over the patient's teeth. The adjustment appliances can be generated all at the same stage or in sets or batches, e.g., at the beginning of a stage of the treatment, and the patient wears each appliance until the pressure of each appliance on the teeth can no longer be felt. A plurality of different appliances (e.g., set) can be designed and even fabricated prior to the patient wearing any appliance of the plurality. At that point, the patient replaces the current adjustment appliance with the next adjustment appliance in the series until no more appliances remain. The appliances are generally not affixed to the teeth and the patient may place and replace the appliances at any time during the procedure. The final appliance or several appliances in the series may have a geometry or geometries selected to overcorrect 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 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, the use of an appliance can be terminated before the teeth reach the positions defined by the appliance.
 Orthodontic appliances, such as illustrated in FIG. IA, impart forces to the crown of a tooth at each point of contact between a tooth receiving cavity of the appliance and received tooth. The magnitude of each of these forces and their distribution on the surface of the tooth determines the type of orthodontic tooth movement which results. Types of tooth movement are conventionally delineated as tipping, translation and root movement. Tooth movement of the crown greater than the movement of the root is referred to as tipping. Equivalent movement of the crown and root is referred as translation. Movement of the root greater than the crown is referred to as root movement.
 The supporting structures of the tooth offer resistance to movement of the tooth. The multitude of resistances offered by the tissues may be considered all as one, effectively offering resistance centered about a point located within the root of the tooth, termed the center of resistance. A force imparted directly to the center of resistance would result in translation of the tooth. Appliances are often not capable of providing force at the center of resistance. A force imparted to the crown of the tooth can produce a moment about the center of resistance that results in tipping of the tooth. A second force (and/or additional forces) applied to the crown of the tooth can be selected produce a moment to counteract the initial moment. If the moment produced by the second force is equivalent in magnitude an opposite in direction the moments are cancelled and translation of the tooth is accomplished. Increase of the moment produced by the second force beyond balancing the initial moment will result in root movement.
 For illustrative purposes, three types of tooth movement can be identified as divisions of a continuum of possible movements. Tooth movements may be in any direction in any plane of space. The present disclosure uses the orthodontic convention of delineating movements in three dimensional space into three classifications: first order, second order and third order.
 The magnitudes of the forces selected and applied to the teeth, and the proper selection of the locations and distributions on the tooth surface upon which they act, are important to controlling the type of tooth movement which is achieved. Previously existing appliance technology does not provide for the specific selecting of the location of force application as provided herein, or the calibrated magnitude of force or determination of the moments produced by the forces.
 In one aspect, the present invention describes appliances having a design and configuration selected to provide more precise control of relationships of the forces and moments applied to a tooth, hence, better controlling the type of tooth movement achieved and increasing the ability of the aligner to achieve all types of tooth movement (e.g., first order, second order, third order). In particular, the present invention describes incorporation of certain "shaped features" into appliance design and structure. As further described herein, shapes features can be designed, located and distributed to precisely control the moments produced on a patient's teeth as an appliance is worn by the patient. Any number of shaped features can be utilized for improved teeth repositioning as described herein. Embodiments described herein can include features including various shaped protrusions in an appliance cavity (e.g., ridge-like protrusions, dimples, etc.). In one example, a combination of shaped features, such as a combination of attachment- type and non-attachment type (e.g., protrusions) shaped features can be utilized to control the force system produced by an orthodontic appliance.
 Shaped features can be incorporated into an appliance design, more particularly, design of teeth receiving cavities of an appliance as illustrated above (see, e.g., FIG. IA). Shaped features can be designed both in terms of physical/structural features as well as positioning and/or location within a tooth receiving cavity, to distribute appropriate forces in terms of direction and magnitude onto the crown of the received tooth. Thus, the force direction and/or force magnitude can be selected and controlled by positioning the features for contact at different areas or locations on the crown, as well as by the parameters of the feature itself. Exemplary parameters of the shaped feature include but are not limited to cross section shape, prominence, length, width, and radius. Shaped features can be integrated with or added to the existing surfaces of an appliance that is shaped and designed based on (e.g., matching) the position of the patient's teeth at a subsequent arrangement (e.g., n + 1 arrangement).
 In another embodiment, however, an appliance surface or cavity feature can be further modified to compensate for an effect (e.g., appliance distortion) due to incorporating the shaped feature into the appliance design/use. In one embodiment, for example, appliance modification can include an altered or inflated appliance surface, where the appliance surface is modified so as to remove certain forces coming only from those features of the appliance in contact with the crown other than the shaped features. Modification in this manner provides optimization of use of the shaped features, as well as a precise delivery system for force and moment only necessary for desired tooth movement.
 Various designs, orientations, and/or configurations of shaped features are available for use according to the present invention. Shaped features to achieve force profiles favorable to specific types of tooth movement can include both attachment-type features as well as non-attachment type features. Non-attachment type features can include various shaped alterations or protrusions in a surface of an appliance, such as ridges (e.g., interior or exterior), dimples, and the like. The terms "non-attachment type feature" and "protrusion" (e.g., appliance protrusion) are typically used interchangeably herein. Dimples include protrusions having substantially the same dimensions along a width compared to the protrusion length. Ridges, by comparison, include protrusions having unequal length and width. Interior protrusions, such as interior ridges, include a groove or protrusion in an appliance that recesses toward an inner surface (e.g., tooth contacting surface) of the appliance, whereas exterior protrusions and ridges bulge toward an exterior surface of the appliance. Protrusion type features, such as dimples and ridges can be either filled with material (e.g., composite material) or left unfilled. If it is filled, the composite can be controlled to solidify after desired shape and/or volume of the filler is obtained. In the following discussion, the general term feature will be used. But the methods apply on any feature as appropriate.  In some instances, ridge-shaped protrusions may provide differences and/or advantages for force application compared to other protrusion shapes, such as dimples. For example, dimples having substantially equal length compared to with will typically provide more of a point application of a force to a surface of a tooth. By comparison, a ridge-shaped protrusion may allow application force application more evenly distributed along a surface of a tooth, and may provide more precisely controlled tooth movement in some instances. Further, ridge-shaped protrusions by providing more protrusion configuration and design options, provide a greater range of force values that can be selected and delivered to the target tooth compared to non-ridge shapes, such as dimples, and can therefore be more likely to impart the desired load. As such, use of ridges compared to other more simplified shapes (e.g., a single dimple) provide a greater range of available force values or selections for imparting the desired load vector, or force direction and/or magnitude along a tooth surface, thereby providing more treatment options.
 As noted, various designs, orientations, and/or configurations of shaped features are available for use according to the present invention and can depend, at least partially, on the desired application of force and tooth movement. Exemplary designs/configurations of ridged protrusions are illustrated with reference to FIGS. IB- IE. FIG. IB illustrates a ridge 12 formed by a continuous protrusion in an appliance surface or a ridge. While the geometric features of ridge 12 may vary along the length, the ridge is continuous in the sense that it is configured to contact a tooth surface along an uninterrupted length. Ridge 12 is illustrated as having a more horizontal orientation relative to the tooth or, in other words, perpendicular to the tooth in the crown to root direction. Referring to FIG. 1C, a continuous ridge 14 is illustrated disposed in an appliance cavity in a vertical orientation. FIG. ID illustrates a non- continuous ridge 15 that is disposed in an appliance surface and vertically oriented. FIG. IE shows a cross-sectional view of ridge 15, illustrating the sort of corrugated surface forming the non-continuous ridge by a series of dimples or bump-like protrusions 16a, 16b, 16c. As illustrated, such bump-like protrusions can each include a portion of the protrusion that contacts a tooth surface, with each tooth contacting surface of a protrusion separated by non- tooth contacting regions of the ridge having a different height. Parameters of tooth contacting and non-contacting aspects of a non-continuous ridge, as illustrated, can be defined, as least in part, by fabrication methods (e.g., direct fabrication, vacuum molding, etc.) used. Both continuous and non-continuous type ridges function to apply a force vector along a length of the tooth, rather than at a single point as with a single dimple or bump-like protrusion. Shaped features, such as ridges can be designed in various shapes (e.g., curve, "L" shaped, "T" shaped, hook, etc.), as well as orientations (e.g., vertical, horizontal, slanted, etc.) and are not limited to any particular shape or orientation.
 Any number of one or more shaped features can be included in design and fabrication of an improved appliance of the present invention. In one embodiment, a cavity of an appliance can include a plurality of shaped features, such as protrusions. For example, a cavity can include at least two shaped features such as protrusions that are shaped and positioned within the cavity such that each of the protrusions are brought into contact with the received patient's tooth when the appliance is initially worn by the patient. Thus, a number of protrusions (e.g., two or more) can configured and incorporated in appliance such that each of those protrusions will each engage the received tooth when the appliance is initially worn by the patient and before the tooth has been moved by the appliance.
 Besides protrusions or non-attachment type shaped features, the shaped features of the present invention can optionally include attachment type features. Attachment, as used herein, may be any form of material that may be attached to the tooth whether preformed, formed using a template or in an amorphous form that is attached to the surface of the tooth. It can be disposed on the tooth surface using an adhesive material, or the adhesive material itself may be disposed on the surface of the tooth as an attachment.
 Generally, the attachments operate to provide "bumps" on a surface of the tooth which otherwise would be difficult for the dental appliance to grip. Attachments may also be engaged by the appliance in a manner that favors delivery of desired force directions and magnitudes. Attachments typically include a material bonded or attached to a surface of the tooth, with a corresponding receiving portion or couple built into the tooth receiving appliance. In one example, an attachment-type feature can include an orphan attachment, or any appropriate shaped material bonded to crown surface, but with no receptacle or receiving portion built into the appliance to receive the attachment shape. Instead, the generated force concentrates on contact area between appliance surface and attachment.
 Various tooth movements can be accomplished according to the present invention. Examples of specific movements that can be included and which are further described below include translation, such as buccal-labial lingual translation, mesio-distal translation, extrusion, intrusion, root movements, first order rotation, second order root movement, and third order root movement. However, the methods can be applied to achieve any type of tooth movement, in any direction, in any arbitrary plane of space.
 Non-attachment type shaped features or protrusions can be included in the present invention, and may optionally be utilized in conjunction with use of attachment type features as described above. In some instances, such protrusions can be described in an analogous manner to description in regard to attachments, for example, in terms positioning and application of selected forces to a tooth. In certain aspects, however, use of protrusion features (e.g., ridge-like protrusions) can provide numerous differences and/or advantages compared to use of attachments.
 In still another aspect, the aligner features may be designed and fabricated to limit movement of the tooth. For example, the aligner may be designed to be a physical boundary through which the tooth cannot move providing safety against unwanted movements that may be deleterious to the patient's health. Further, the aligner in another aspect may be configured to function as a guiding surface along which the tooth moves. More particularly, the aligner may be configured to impart a force system to the tooth and the tooth may be guided into a specific location and orientation assisted by the guidance of the aligner.
 As set forth above, incorporation of one or more protrusions in appliance design according to the present invention can be utilized for various tooth movements. Non-limiting examples of specific movements that can be accomplished and which are further described below include translation, such as buccal-labial lingual translation, mesio-distal translation, extrusion, intrusion, first order rotation, second order root movement, and third order root movement. Exemplary tooth movements and corresponding positioning of shaped features are described below with reference to corresponding figures (see, e.g., FIGS. 2A-2F, 3A-3D, 4A-4C, and 5A-5B).
 Shaped features, including protrusions or ridge shaped features can be used for tooth translation, such as buccal or lingual translation. FIGS. 2A-2F illustrate an appliance positioned on a tooth receiving cavity of the appliance including shaped feature(s) positioning for lingual translation. Illustrated shaped features include appliance protrusions, orphan attachments, or a combination thereof. As illustrated, to achieve lingual translation, features on the buccal side are closer the gingival line than the features on the lingual side. Stated another way, attachment to center of resistance (CR) length is greater on the lingual side compared to the buccal side. FIG. 2A shows interior ridge features are added to an appliance, including an interior ridge 18a on the buccal side and positioned closer to the gingival line (or to the center of resistance), and an interior ridge 18b on the lingual side and positioned more distally compared to the buccal side ridge 18a. The parameters of the features will be selected and designed such that the lingual force generated from buccal features will be greater than the buccal force from the lingual features. However, the directions of these two force components are opposite. The lingual force has longer arm to the center of resistance than the buccal force does. By adjusting the positions and parameters of the buccal and lingual features, the tipping moment from buccal features can be cancelled out by the counter balancing moment from lingual features and the resultant is the lingual translation. FIG. 2B and FIG. 2C illustrate a similar concept, but with use of shaped features in the forms of exterior ridges 20a, 20b (FIG. 2B) and orphan attachments 22a, 22b (FIG. 2C) used for lingual translation.
 In certain embodiments, a tooth receiving cavity may include only a single protrusion or ridge-shaped feature. FIGS. 2D through 2E illustrate use of a single protrusion for lingual translation. If there is no feature added to the buccal side of aligner, the buccal surface of aligner will generate a translation force toward lingual direction. In another embodiment, a feature can be added to lingual side alone to create a counter balance torque to the force generated from an appliance surface in contact with the tooth on the opposing buccal side. FIG. 2D illustrates a single protrusion feature 24 positioned on the buccal side to impart a lingual force and illicit a counter balance torque from the contact between the tooth and appliance. Fig. 2E shows a single protrusion feature 26 in the form of interior ridge on lingual side only of appliance cavity.
 In another embodiment, a single protrusion can be used in conjunction with an attachment-type feature for the desired tooth movement. FIG. 2F shows a buccal side orphan attachment 28 used with interior ridge 30 on lingual side of the appliance cavity. The various different shapes and types of features and protrusions can be utilized and/or combined to accomplish lingual translation as described above.
 Protrusion and shaped feature use can by selected for buccal translation and feature positioning can be selected in a manner analogous to the above description regarding lingual translation (e.g., FIGS 2A-2F). In contrast to lingual translation, use of features for buccal translation will include positioning of a lingual side feature or component closer to the gingival line relative to buccal side feature/component placement.
 In another aspect, shaped features are used to accomplish mesial or distal translation. As seen in FIG. 3A, where the desired movement includes mesial translation, features (e.g., ridges) such as Feature 32a on the distal interproximal area will be positioned closer to the gingival line compared to features on the mesial interproximal area such as Feature 32b, while features on the mesial interproximal area will be closer to the occlusal plane. By controlling the parameters and positions of features, the selected forces can include a mesial force exceeding the distal force and the second order moment can be zeroed out. Spacing or room around the interproximal area can be created in the patient's dentition to accommodate the features of the appliance. In some embodiments, a single feature only may be included or features positioned only on a distal area or mesial area. FIG. 3 C show the Features 36 positioned only on mesial surface for distal translation. FIG. 3D illustrates Features 38 positioned only on the distal surface for mesial translation.
 Distal translation can be accomplished in a manner analogous to the above description regarding mesial translation, but with features on the mesial interproximal area positioned closer to the gingival line compared to features on the distal interproximal area, with features on the distal interproximal area positioned closer to the occlusal plane. FIG. 3B illustrates Features 34a, 34b positioning selected for distal translation.
Extrusion and Intrusion
 In another aspect, feature design and positioning can be selected for extrusion and intrusion movements, as illustrated in FIGS. 4A-4C. For extrusion, for example, features on appliance cavity can be positioned toward the gingival line, as the buccal and lingual surfaces in the gingival half of the crown are usually undercut, as shown in FIGS 4A (Features 40a, 40b) and 4C (Features 44a, 44b, 44c, 44d). By selecting the parameters and positions of the features, the undercutting contact areas can provide total contact force extrusive, because the forces from each feature will be normal to the undercutting contact area.
 For intrusion, the features on aligner can be selected and positioned closer toward the occlusal plane as the buccal and lingual surfaces in the occlusal half of the crown are usually convex, as shown in FIGS. 4B (Features 42a, 42b) and 4C (Features 44a, 44b, 44c, 44d). By tuning the parameters and positions of the features, the convex contact areas can provide total contact force intrusive, as the forces from each feature will be normal to the contact area.
Third Order Root Movement
 In another aspect, as will be recognized, use of features as described herein can be directed to various root movements. When a third order root movement (e.g., lingual root torque) is desired on tooth crown, the crown will rotate buccally much less than the root will rotate lingually. The features on the buccal side can be positioned closer to gingival line and the ones on lingual side are closer to occlusal plane (e.g., as shown in FIG. 2A). In such an instance, the features on the buccal side will generate lingual force and the lingual features will generate buccal force. By configuring the parameters and positions of features, feature positioning can be selected such that the lingual force exceeds buccal force. However, the directions of these two forces are opposite, with the lingual force having a longer arm to the center of resistance than the buccal force. By adjusting the positions and parameters of the buccal and lingual features, feature design/positioning can be selected such that the lingual features generate torquing moment greater than the buccal features, which combined with lingual total force results in lingual root torque. As illustrated in FIG. 2D, buccal surface only features may be selected, without features on lingual surface of appliance cavity. A similar mechanism as described above applies, now that the lingual surface of plain (e.g., no feature) appliance cavity surface works in place of lingual features. Buccal root torque can be figured out in an analogous manner.
Second Order Root Movement
 In another aspect, second order root movements can be accomplished. In one embodiment, for a second order mesial root movement, cavity design can be selected such that features on the distal interproximal area will be closer to the gingival line, while features on the mesial interproximal area will be closer to the occlusal plane (e.g., FIG. 3A). By controlling the parameters and positions of features, the mesial force prevails. However, the directions of these two forces from the two illustrated features are opposite, with the distal force having a longer arm to the center of resistance than the mesial force. By adjusting the positions and parameters of the mesial and distal features, the mesial features generate second order moment greater than the force generated by the distal features, which combined with mesial total force results in a second order root movement.  As above, features may be present only on one side of the appliance cavity. For example, FIG. 3D shows features only on a distal surface for second order mesial root movement. The same mechanism still applies as described above, now that the mesial surface of plain aligner works in place of mesial features.
 Second order distal root movement can be figured out in an analogous manner as described with regard to second order mesial root movement, but with features on the distal interproximal area positioned closer to the occlusal plan (see, e.g., FIG. 4B).
First Order Rotation
 In another aspect, first order rotations can be selected. In one embodiment of a first order rotation, the parameters and positions of features will be configured to provide a couple about the occlusal gingival direction, as shown in FIGS. 5A (e.g., Features 46a, 46b) and 5B (e.g., Features 48a, 48b). A couple is a moment generated by a pair of forces oriented parallel to one another, equal in magnitude and opposite in sense. The resultant force is zero.
 As described above, a patient's teeth are generally progressively repositioned according to a treatment plan. Exemplary methods treatment plan design, as well as appliance design and fabrication are described further below. Typically, appliance and/or treatment plan can optionally, though not necessarily, be accomplished using various computer based applications. It will be recognized that appliance design and fabrication is not limited to any particular method and can include various computer and non-computer based methodologies.
 Treatment planning, according to one embodiment of the present invention, is described. Patient data can be collected and analyzed, and specific treatment steps specified and/or prescribed. In one embodiment, a treatment plan can be generated and proposed for a dental practitioner to review. The dental practitioner can accept or request modifications to the treatment plan. Once the treatment plan is approved, manufacturing of appliance(s) can begin. Digital treatment plans are now possible with 3-dimensional orthodontic treatment planning tools such as software from Align Technology, Inc. or other software available from eModels and OrthoCAD, among others. These technologies allow the clinician to use the actual patient's dentition as a starting point for customizing the treatment plan. The software technology available from Align Technology, Inc., uses a patient-specific digital model to plot a treatment plan, and then use a scan of the achieved or actual treatment outcome to assess the degree of success of the outcome as compared to the original digital treatment plan as discussed in U.S. Patent Application Serial No. 10/640,439, filed August 21, 2003 and U.S. Patent Application Serial No. 10/225,889 filed August 22, 2002. The problem with the digital treatment plan and outcome assessment is the abundance of data and the lack of standards and efficient methodology by which to assess "treatment success" at an individual patient level. To analyze the information, a dental data mining system is used.
 FIG. 6 A illustrates the general flow of an exemplary process 100 for generating a treatment plan or defining and generating repositioning appliances for orthodontic treatment of a patient. The process 100 includes the methods, and is suitable for the apparatus, of the present invention, as will be described. The computational steps of the process are advantageously implemented as computer program modules for execution on one or more conventional digital computers.
 As an initial step, a mold or a scan of patient's teeth or mouth tissue is acquired (110). This step generally involves taking casts of the patient's teeth and gums, and may in addition or alternately involve taking wax bites, direct contact scanning, x-ray imaging, tomographic imaging, sonographic imaging, and other techniques for obtaining information about the position and structure of the teeth, jaws, gums and other orthodontically relevant tissue. From the data so obtained, a digital data set is derived that represents the initial (that is, pretreatment) arrangement of the patient's teeth and other tissues.
 The initial digital data set, which may include both raw data from scanning operations and data representing surface models derived from the raw data, is processed to segment the tissue constituents from each other (step 120). In particular, in this step, data structures that digitally represent individual tooth crowns are produced. Advantageously, digital models of entire teeth are produced, including measured or extrapolated hidden surfaces and root structures as well as surrounding bone and soft tissue.
 The desired final position of the teeth—that is, the desired and intended end result of orthodontic treatment— can be received from a clinician in the form of a prescription, can be calculated from basic orthodontic principles, or can be extrapolated computationally from a clinical prescription (step 130). With a specification of the desired final positions of the teeth and a digital representation of the teeth themselves, the final position and surface geometry of each tooth can be specified (step 140) to form a complete model of the teeth at the desired end of treatment. Generally, in this step, the position of every tooth is specified. The result of this step is a set of digital data structures that represents an orthodontically correct repositioning of the modeled teeth relative to presumed-stable tissue. The teeth and tissue are both represented as digital data.
 Having both a beginning position and a final position for each tooth, the process next defines a tooth path for the motion of each tooth. In one embodiment, the tooth paths are optimized in the aggregate so that the teeth are moved in the quickest fashion with the least amount of round-tripping to bring the teeth from their initial positions to their desired final positions. (Round-tripping is any motion of a tooth in any direction other than directly toward the desired final position. Round-tripping is sometimes necessary to allow teeth to move past each other.) The tooth paths are segmented. The segments are calculated so that each tooth's motion within a segment stays within threshold limits of linear and rotational translation. In this way, the end points of each path segment can constitute a clinically viable repositioning, and the aggregate of segment end points constitute a clinically viable sequence of tooth positions, so that moving from one point to the next in the sequence does not result in a collision of teeth.
 The threshold limits of linear and rotational translation are initialized, in one implementation, with default values based on the nature of the appliance to be used. More individually tailored limit values can be calculated using patient-specific data. The limit values can also be updated based on the result of an appliance-calculation (step 170, described later), which may determine that at one or more points along one or more tooth paths, the forces that can be generated by the appliance on the then-existing configuration of teeth and tissue is incapable of effecting the repositioning that is represented by one or more tooth path segments. With this information, the subprocess defining segmented paths (step 150) can recalculate the paths or the affected subpaths.
 At various stages of the process, and in particular after the segmented paths have been defined, the process can, and generally will, interact with a clinician responsible for the treatment of the patient (step 160). Clinician interaction can be implemented using a client process programmed to receive tooth positions and models, as well as path information from a server computer or process in which other steps of process 100 are implemented. The client process is advantageously programmed to allow the clinician to display an animation of the positions and paths and to allow the clinician to reset the final positions of one or more of the teeth and to specify constraints to be applied to the segmented paths. If the clinician makes any such changes, the subprocess of defining segmented paths (step 150) is performed again.  The segmented tooth paths and associated tooth position data are used to calculate clinically acceptable appliance configurations (or successive changes in appliance configuration) that will move the teeth on the defined treatment path in the steps specified by the path segments (step 170). Each appliance configuration represents a step along the treatment path for the patient. The steps are defined and calculated so that each discrete position can follow by straight-line tooth movement or simple rotation from the tooth positions achieved by the preceding discrete step and so that the amount of repositioning required at each step involves an orthodontically optimal amount of force on the patient's dentition. As with the path definition step, this appliance calculation step can include interactions and even iterative interactions with the clinician (step 160). The operation of a process step 200 implementing this step will be described more fully below.
 Having calculated appliance definitions, the process 100 can proceed to the manufacturing step (step 180) in which appliances defined by the process are manufactured, or electronic or printed information is produced that can be used by a manual or automated process to define appliance configurations or changes to appliance configurations.
 FIG. 6B illustrates a process 200 implementing the appliance-calculation step (FIG. 6 A, step 170) for polymeric shell aligners of the kind described in above-mentioned U.S. Patent No. 5,975,893. Inputs to the process include an initial aligner shape 202, various control parameters 204, and a desired end configuration for the teeth at the end of the current treatment path segment 206. Other inputs include digital models of the teeth in position in the jaw, models of the jaw tissue, and specifications of an initial aligner shape and of the aligner material. Using the input data, the process creates a finite element model of the aligner, teeth and tissue, with the aligner in place on the teeth (step 210). Next, the process applies a finite element analysis to the composite finite element model of aligner, teeth and tissue (step 220). The analysis runs until an exit condition is reached, at which time the process evaluates whether the teeth have reached the desired end position for the current path segment, or a position sufficiently close to the desired end position (step 230). If an acceptable end position is not reached by the teeth, the process calculates a new candidate aligner shape (step 240). If an acceptable end position is reached, the motions of the teeth calculated by the finite elements analysis are evaluated to determine whether they are orthodontically acceptable (step 232). If they are not, the process also proceeds to calculate a new candidate aligner shape (step 240). If the motions are orthodontically acceptable and the teeth have reached an acceptable position, the current aligner shape is compared to the previously calculated aligner shapes. If the current shape is the best solution so far (decision step 250), it is saved as the best candidate so far (step 260). If not, it is saved in an optional step as a possible intermediate result (step 252). If the current aligner shape is the best candidate so far, the process determines whether it is good enough to be accepted (decision step 270). If it is, the process exits. Otherwise, the process continues and calculates another candidate shape (step 240) for analysis.
 The finite element models can be created using computer program application software available from a variety of vendors. For creating solid geometry models, computer aided engineering (CAE) or computer aided design (CAD) programs can be used, such as the AutoCAD®, software products available from Autodesk, Inc., of San Rafael, Calif. For creating finite element models and analyzing them, program products from a number of vendors can be used, including the PoIyFEM product available from CADSI of Coralville, Iowa, the Pro/Mechanica simulation software available from Parametric Technology Corporation of Waltham, Mass., the I-DEAS design software products available from Structural Dynamics Research Corporation (SDRC) of Cincinnati, Ohio, and the
MSC/NASTRAN product available from MacNeal-Schwendler Corporation of Los Angeles, Calif.
 FIG. 7 shows a process 300 of creating a finite element model that can be used to perform step 210 of the process 200 (FIG. 6B). Input to the model creation process 300 includes input data 302 describing the teeth and tissues and input data 304 describing the aligner. The input data describing the teeth 302 include the digital models of the teeth; digital models of rigid tissue structures, if available; shape and viscosity specifications for a highly viscous fluid modeling the substrate tissue in which the teeth are embedded and to which the teeth are connected, in the absence of specific models of those tissues; and boundary conditions specifying the immovable boundaries of the model elements. In one implementation, the model elements include only models of the teeth, a model of a highly viscous embedding substrate fluid, and boundary conditions that define, in effect, a rigid container in which the modeled fluid is held. Note that fluid characteristics may differ by patient clusters, for example as a function of age.
 A finite element model of the initial configuration of the teeth and tissue is created (step 310) and optionally cached for reuse in later iterations of the process (step 320). As was done with the teeth and tissue, a finite element model is created of the polymeric shell aligner (step 330). The input data for this model includes data specifying the material of which the aligner is made and the shape of the aligner (data input 304).
 The model aligner is then computationally manipulated to place it over the modeled teeth in the model jaw to create a composite model of an in-place aligner (step 340). Optionally, the forces required to deform the aligner to fit over the teeth, including any hardware attached to the teeth, are computed and used as a figure of merit in measuring the acceptability of the particular aligner configuration. Optionally, the tooth positions used are as estimated from a probabilistic model based on prior treatment steps and other patient information. In a simpler alternative, however, the aligner deformation is modeled by applying enough force to its insides to make it large enough to fit over the teeth, placing the model aligner over the model teeth in the composite model, setting the conditions of the model teeth and tissue to be infinitely rigid, and allowing the model aligner to relax into position over the fixed teeth. The surfaces of the aligner and the teeth are modeled to interact without friction at this stage, so that the aligner model achieves the correct initial configuration over the model teeth before finite element analysis is begun to find a solution to the composite model and compute the movement of the teeth under the influence of the distorted aligner.
 FIG. 8 shows a process 400 for calculating the shape of a next aligner that can be used in the aligner calculations, step 240 of process 200 (FIG. 6B). A variety of inputs are used to calculate the next candidate aligner shape. These include inputs 402 of data generated by the finite element analysis solution of the composite model and data 404 defined by the current tooth path. The data 402 derived from the finite element analysis includes the amount of real elapsed time over which the simulated repositioning of the teeth took place; the actual end tooth positions calculated by the analysis; the maximum linear and torsional force applied to each tooth; the maximum linear and angular velocity of each tooth. From the input path information, the input data 404 includes the initial tooth positions for the current path segment, the desired tooth positions at the end of the current path segment, the maximum allowable displacement velocity for each tooth, and the maximum allowable force of each kind for each tooth.
 If a previously evaluated aligner was found to violate one or more constraints, additional input data 406 can optionally be used by the process 400. This data 406 can include information identifying the constraints violated by, and any identified suboptimal performance of, the previously evaluated aligner. Additionally, input data 408 relating to constraints violated by, and suboptimal performance of previous dental devices can be used by the process 400.
 Having received the initial input data (step 420), the process iterates over the movable teeth in the model. (Some of the teeth may be identified as, and constrained to be, immobile.) If the end position and dynamics of motion of the currently selected tooth by the previously selected aligner is acceptable ("yes" branch of decision step 440), the process continues by selecting for consideration a next tooth (step 430) until all teeth have been considered ("done" branch from step 430 to step 470). Otherwise ("no" branch from step 440), a change in the aligner is calculated in the region of the currently selected tooth (step 450). The process then moves back to select the next current tooth (step 430) as has been described.
 When all of the teeth have been considered, the aggregate changes made to the aligner are evaluated against previously defined constraints (step 470), examples of which have already been mentioned. Constraints can be defined with reference to a variety of further considerations, such as manufacturability. For example, constraints can be defined to set a maximum or minimum thickness of the aligner material, or to set a maximum or minimum coverage of the aligner over the crowns of the teeth. If the aligner constraints are satisfied, the changes are applied to define a new aligner shape (step 490). Otherwise, the changes to the aligner are revised to satisfy the constraints (step 480), and the revised changes are applied to define the new aligner shape (step 490).
 FIG. 9 A illustrates one implementation of the step of computing an aligner change in a region of a current tooth (step 450). In this implementation, a rule-based inference engine 456 is used to process the input data previously described (input 454) and a set of rules 452a-452n in a rule base of rules 452. The inference engine 456 and the rules 452 define a production system which, when applied to the factual input data, produces a set of output conclusions that specify the changes to be made to the aligner in the region of the current tooth (output 458).
 Rules 452a...452n have the conventional two-part form: an if-part defining a condition and a then-part defining a conclusion or action that is asserted if the condition is satisfied. Conditions can be simple or they can be complex conjunctions or disjunctions of multiple assertions. An exemplary set of rules, which defines changes to be made to the aligner, includes the following: if the motion of the tooth is too fast, add driving material to the aligner opposite the desired direction of motion; if the motion of the tooth is too slow, add driving material to overcorrect the position of the tooth; if the tooth is too far short of the desired end position, add material to overcorrect; if the tooth has been moved too far past the desired end position, add material to stiffen the aligner where the tooth moves to meet it; if a maximum amount of driving material has been added, add material to overcorrect the repositioning of the tooth and do not add driving material; if the motion of the tooth is in a direction other than the desired direction, remove and add material so as to redirect the tooth.
 In an alternative embodiment, illustrated in FIGS. 9B and 9C, an absolute configuration of the aligner is computed, rather than an incremental difference. As shown in FIG. 9B, a process 460 computes an absolute configuration for an aligner in a region of a current tooth. Using input data that has already been described, the process computes the difference between the desired end position and the achieved end position of the current tooth (462). Using the intersection of the tooth center line with the level of the gum tissue as the point of reference, the process computes the complement of the difference in all six degrees of freedom of motion, namely three degrees of translation and three degrees of rotation (step 464). Next, the model tooth is displaced from its desired end position by the amounts of the complement differences (step 466), which is illustrated in FIG. 9B.
 FIG. 9D shows a planar view of an illustrative model aligner 60 over an illustrative model tooth 62. The tooth is in its desired end position and the aligner shape is defined by the tooth in this end position. The actual motion of the tooth calculated by the finite element analysis is illustrated as placing the tooth in position 64 rather than in the desired position 62. A complement of the computed end position is illustrated as position 66. The next step of process 460 (FIG. 9B) defines the aligner in the region of the current tooth in this iteration of the process by the position of the displaced model tooth (step 468) calculated in the preceding step (466). This computed aligner configuration in the region of the current tooth is illustrated in FIG. 9D as shape 68 which is defined by the repositioned model tooth in position 66.
 A further step in process 460, which can also be implemented as a rule 452 (FIG. 9A), is shown in FIG. 9C. To move the current tooth in the direction of its central axis, the size of the model tooth defining that region of the aligner, or the amount of room allowed in the aligner for the tooth, is made smaller in the area away from which the process has decided to move the tooth (step 465).
 As shown in FIG. 10, the process 200 (FIG. 6B) of computing the shape for an aligner for a step in a treatment path is one step in a process 600 of computing the shapes of a series of aligners. This process 600 begins with an initialization step 602 in which initial data, control and constraint values are obtained.
 When an aligner configuration has been found for each step or segment of the treatment path (step 604), the process 600 determines whether all of the aligners are acceptable (step 606). If they are, the process is complete. Otherwise, the process optionally undertakes a set of steps 610 in an attempt to calculate a set of acceptable aligners. First, one or more of the constraints on the aligners is relaxed (step 612). Then, for each path segment with an unacceptable aligner, the process 200 (FIG. 6B) of shaping an aligner is performed with the new constraints (step 614). If all the aligners are now acceptable, the process 600 exits (step 616).
 Aligners may be unacceptable for a variety of reasons, some of which are handled by the process. For example, if any impossible movements were required (decision step 620), that is, if the shape calculation process 200 (FIG. 6B) was required to effect a motion for which no rule or adjustment was available, the process 600 proceeds to execute a module that calculates the configuration of a hardware attachment to the subject tooth to which forces can be applied to effect the required motion (step 640). Because adding hardware can have an effect that is more than local, when hardware is added to the model, the outer loop of the process 600 is executed again (step 642).
 If no impossible movements were required ("no" branch from step 620), the process transfers control to a path definition process (such as step 150, FIG. 6A) to redefine those parts of the treatment path having unacceptable aligners (step 630). This step can include both changing the increments of tooth motion, i.e., changing the segmentation, on the treatment path, changing the path followed by one or more teeth in the treatment path, or both. After the treatment path has been redefined, the outer loop of the process is executed again (step 632). The recalculation is advantageously limited to recalculating only those aligners on the redefined portions of the treatment path. If all the aligners are now acceptable, the process exits (step 634). If unacceptable aligners still remain, the process can be repeated until an acceptable set of aligners is found or an iteration limit is exceeded (step 650). At this point, as well as at other points in the processes that are described in this specification, such as at the computation of additional hardware (step 640), the process can interact with a human operator, such as a clinician or technician, to request assistance (step 652). Assistance that an operator provides can include defining or selecting suitable attachments to be attached to a tooth or a bone, defining an added elastic element to provide a needed force for one or more segments of the treatment path, suggesting an alteration to the treatment path, either in the motion path of a tooth or in the segmentation of the treatment path, and approving a deviation from or relaxation of an operative constraint.
 As was mentioned above, the process 600 is defined and parameterized by various items of input data (step 602). In one implementation, this initializing and defining data includes the following items: an iteration limit for the outer loop of the overall process; specification of figures of merit that are calculated to determine whether an aligner is good enough (see FIG. 6B, step 270); a specification of the aligner material; a specification of the constraints that the shape or configuration of an aligner must satisfy to be acceptable; a specification of the forces and positioning motions and velocities that are orthodontically acceptable; an initial treatment path, which includes the motion path for each tooth and a segmentation of the treatment path into segments, each segment to be accomplished by one aligner; a specification of the shapes and positions of any anchors installed on the teeth or otherwise; and a specification of a model for the jaw bone and other tissues in or on which the teeth are situated (in the implementation being described, this model consists of a model of a viscous substrate fluid in which the teeth are embedded and which has boundary conditions that essentially define a container for the fluid).
 Various tooth root imaging and/or modeling (e.g., statistical root modeling) may be utilized. The teeth movement can be guided in part using a root-based sequencing system. In one embodiment, the movement is constrained by a surface area constraint, while in another embodiment, the movement is constrained by a volume constraint.
 Optionally, other features are added to the tooth model data sets to produce desired features in the aligners. For example, it may be desirable to add digital wax patches to define cavities or recesses to maintain a space between the aligner and particular regions of the teeth or jaw. It may also be desirable to add digital wax patches to define corrugated or other structural forms to create regions having particular stiffness or other structural properties. In manufacturing processes that rely on generation of positive models to produce the repositioning appliance, adding a wax patch to the digital model will generate a positive mold that has the same added wax patch geometry. This can be done globally in defining the base shape of the aligners or in the calculation of particular aligner shapes. One feature that can be added is a rim around the gumline, which can be produced by adding a digital model wire at the gumline of the digital model teeth from which the aligner is manufactured. When an aligner is manufactured by pressure fitting polymeric material over a positive physical model of the digital teeth, the wire along the gumlines causes the aligner to have a rim around it providing additional stiffness along the gumline.
 In another optional manufacturing technique, two or more sheets of material are pressure fit over the positive tooth model, where one of the sheets is cut along the apex arch of the aligner and the other(s) is overlaid on top. This provides at least a double thickness of aligner material along the vertical walls of the teeth.
 The changes that can be made to the design of an aligner are constrained by the manufacturing technique that will be used to produce it. For example, if the aligner will be made by pressure fitting a polymeric sheet over a positive model, the thickness of the aligner is determined by the thickness of the sheet. As a consequence, the system will generally adjust the performance of the aligner by changing the orientation of the model teeth, the sizes of parts of the model teeth, the position and selection of attachments, and the addition or removal of material (e.g., adding virtual wires or creating protrusions (e.g., ridges, dimples, etc.), creating modification (e.g., modifications to compensate for protrusion mediated distortions)) to change the structure of the aligner. The system can optionally adjust the aligner by specifying that one or more of the aligners are to be made of a sheet of a thickness other than the standard one, to provide more or less force to the teeth. On the other hand, if the aligner will be made by a stereo lithography process, the thickness of the aligner can be varied locally, and structural features such as rims, dimples, and corrugations can be added without modifying the digital model of the teeth.
 The system can also be used to model the effects of more traditional appliances such as retainers and braces and therefore be used to generate optimal designs and treatment programs for particular patients.
 Thus, one or more shaped features or protrusions can be selectively added and included in appliance design and fabrication, with appliance design and fabrication, and incorporation of appliances in a treatment plan as described above. In some instances, however, incorporation of a shaped feature or protrusion into an appliance may result in a subsequent change in the geometry of the appliance at other surfaces of the appliance, e.g., when worn by the patient. Such changes or alterations can result in changes in property or location of contact surfaces between the tooth and the appliance, sometimes in an undesirable manner. As such, changes or distortions can be modeled or accounted for in appliance design. For example, changes, distortions and the like can be analyzed or determined computationally in terms of probability of occurrence, as well as whether such changes/distortions would be beneficial or detrimental to the desired loading and tooth movement. Methods can be included to determine the effect of these geometric changes and compensate for them by identifying new surfaces or shapes, and loadings to accomplish the desired movement. Appliance geometry can therefore be improved in this iterative design process, as the process in turn considers each feature and its effect on the appliance geometry, on surfaces of contact, and on the force system produced in the designing of an appliance.
 Modification of an appliance surface to compensate for an effect (e.g., distortion effect) due to incorporation of a protrusion, according to an embodiment of the present invention, is illustrated with reference to FIGS. 1 IA-11C, and FIG. 12. FIGS. 1 IA-I IB illustrate an initial tooth position with a positioned dental appliance, and a resulting undesirable force vector, respectively. Referring to the Figures, in an example where the tooth as shown is being moved in a facial direction along the x-direction, upon positioning of the dental appliance such as the polymeric shell aligner, over the tooth, the aligner shape geometry is configured to apply a predetermined force upon the tooth to reposition the tooth in accordance with a treatment plan for the particular treatment stage. For example, as shown in FIG. 1 IB, the dental appliance is configured to fit over the tooth to reposition the tooth in the x-direction as shown, but, rather, results in the application of a predetermined force in the +χ/-z direction as shown and illustrated by the arrow. Appliances can include one or more shaped features disposed in a cavity.
 Accordingly, in one aspect, the aligner shape geometry may be optimized to compensate for the undesirable but resulting force vector so as to counteract its force and further, to apply the intended force in the direction based on the treatment plan for the treatment stage under consideration. One exemplary modification can include addition of a relief component. FIGS. 1 IC-I ID illustrate a relief addition to the dental appliance to counteract the undesirable force vector around the tooth, and the resulting desired application of the predetermined force on the tooth by the dental appliance, respectively. In one aspect, to compensate for the undesirable force (for example, as shown in FIG. 1 IB by the arrow), a predetermined relief (for example, but not limited to, 0.1 to 0.3 mm) may be provided such that the contact between the aligner and the tooth that resulted in the undesirable force vector is avoided, but still retaining the desired force, for example, along the x-axis as discussed above.
 Referring to FIGS. 11C, the predetermined relief on the aligner is illustrated by the shown arrow, whereby the engagement between the aligner and the tooth at the location resulting in the undesirable force is removed by modifying the shape of the aligner geometry. In this manner, in one aspect, and as shown in FIG. 1 ID, the intended and desirable force applied upon the tooth for example, in the x-direction, is achieved by, for example, modifying the aligner shape geometry.
 FIG. 12 illustrates a modified dental appliance geometry including an additional shape modification to remove a gap between the dental appliance and the tooth. Referring to FIG. 12, it is to be noted that while the modification of the aligner shape geometry (for example, discussed above in conjunction with FIGS. 1 IC-I ID), results in the desired predetermined force applied upon the tooth as planned for the dental treatment, there may be a gap or pocket that forms between the tooth and the aligner, for example, as shown in FIG. 12, near the gingival area. In one aspect, to account for this gap or pocket generated, the aligner shape geometry may be further modified or optimized, for example, to better adapt in the direction towards the tooth when the aligner is in the active (or stretched) state.
 Referring to FIG. 12, the optimization of the aligner shape geometry to address the formed gap or pocket is illustrated by the arrow in one embodiment, in the direction of which, the aligner shape may be modified. Moreover, it should be noted that the optimization of the aligner shape to account for the gap may potentially effect the direction of the applied force on the tooth by the aligner, and thus, may further require additional modification or optimization.
 In one aspect, the modification of the dental aligner shape geometry with one or more areas of modification (e.g., relief, etc.), as well as recontouring for looser or tighter adaptation, respectively, to achieve the desired force vector, while avoiding friction and other undesirable force vectors provides improved and customized aligner shape for the treatment of the dental conditions.  In manufacturing of the dental appliances, in one aspect, the stereolithography mold may be adjusted during the build process to take shape of the desired geometry based on, for example, digitally adding and/or subtracting the relief and/or protrusion in predefined or relevant locations of the mold.
 In one aspect, based on the force behavior determined from the material properties and the amount of surface area perpendicular to the composite vector resulting from the movement vector for the particular treatment stage, additional surface area may be added to the tooth by employing a shaped feature specifically suited for the desired movement. In this manner, in one aspect, the cross section and/or orientation of the surface area may be determined for a particular tooth, and the shaped feature(s) can be incorporated on one or more teeth to enhance or improve upon the necessary surface area to cooperate or engage with the dental appliance to effect the desired movement vector or the predetermined level of force upon the tooth in the accurate direction for the treatment stage.
 In this manner, in one aspect, a dental aligner may be manufactured or simulated using a computer aided design tool or system, where, a representation of the tooth to be moved is first modeled. Thereafter, the aligner that defines the target position of the tooth is modeled with shape geometry properties defined. Thereafter, the force necessary to reposition the tooth from the initial location to the target location is determined or modeled, for example, using FEA modeling, or other suitable computation and/or modeling techniques. In one aspect, it is possible to define the force using a physical model of the teeth connected to force measurement sensors, such that the optimal forces may be determined using the readouts obtained from the physical model, and thus altering the shapes of features (e.g., ridge protrusions, dimpled protrusions, etc.) and aligner configurations based at least in part on the feedback from the physical force gauge.
 As a result, a movement vector is defined which establishes the direction of the applied force, as well as the level of force and its properties which are necessary to reposition the tooth from the initial position to the target position. Based on the movement vector, and the modeled aligner shape, the aligner is further modified or reconfigured to factor in the determined movement vector. That is, after having defined the movement vector which identifies the force properties necessary for the tooth repositioning, the dental appliance shape is altered or optimized based on the determined movement vector. Additionally, the appliance shape may be further optimized to counteract the undesirable forces or force components, or appliance distortion (e.g., due to a protrusion) that may result based on the defined movement vector.
 Thereafter, the modified or optimized dental appliance may be manufactured through stereolithography or other suitable techniques to attain the desired tooth movement. Further, this process may be repeated for the optimization of dental appliance for each treatment stage of the treatment plan such that the aligner performance and therefore, the treatment plan result is improved.
 Furthermore, in yet still another aspect, shaped feature placement may be determined based on the location of the maximum amount of surface area available perpendicular to the desired direction of the tooth movement. Further, if the force on any given tooth in the treatment plan is at or below a predefined level, the feature (e.g., protrusion) may be added to the tooth or appliance to supplement the desired surface area or increase the friction coefficient of the tooth, thereby improving the force profile of the aligner on the tooth.
 In one aspect, the data set associated with the teeth, gingiva and/or other oral tissue or structures may be intentionally altered through, for example, addition, partial or total subtraction, uniform or non-uniform scaling, Boolean or non-Boolean algorithm, or geometric operations, or one or more combinations thereof, for the configuration, modeling and/or manufacturing of the dental appliance that may be optimized for the desired or intended treatment goal.
 Accordingly, in one aspect, the n+1 or subsequent/target tooth position is first determined. Thereafter, the direction of movement to reach the target tooth position from the initial tooth position is determined. After determining the direction of movement, the amount or magnitude and direction of force and torque to reposition the tooth from the initial position to the target position is determined. Thereafter, profile of the appliance cavity and features/protrusions disposed therein, such as the geometry that would provide the most suitable load vector in the direction of the planned tooth movement is determined, as well as the optimal position of the shaped feature relative to the tooth surface. In this manner, the force/torque generated by the dental appliance is accurately directed in the desired direction, and also is configured with sufficient magnitude to move the tooth into the next planned position.  In one aspect, the direction and the magnitude of the force/torque may be modified or optimized to generate counter-balancing force/torque to eliminate or minimize unwanted tipping torque, to attain root movement, and the like, by adjusting the profile and/or positioning of the shaped features relative to the crown surface, for example. The amount of the feature movement with respect to the tooth crown may also be correlated with the tooth movement to generate a treatment plan based on the movement of the features.
 FIG. 13 is a flowchart illustrating the optimized shape geometry of the dental appliance. Referring to FIG. 13, at step 2110, the initial position of the tooth is determined. Thereafter, at step 2120, the target position of the tooth based on the treatment plan is determined. In one aspect, the target position may include the next or n+1 treatment stage tooth position. Referring back to FIG. 13, after determining the target position of the tooth based on the treatment plan, a movement vector associated with the tooth movement from the initial position to the target position is calculated or determined at step 2130. That is, a force profile or attributes is determined which includes, for example, the magnitude of the force and the direction of the force, for example, that is associated with the tooth movement from the initial position to the target position.
 Referring again to FIG. 13, after determining the movement vector associated with the tooth movement from the initial position to the target position, at step 2140, the components associated with the movement vector are determined. For example, as discussed above, the force magnitude associated with the movement vector to reposition the tooth from the initial position to the target position is determined. Additionally, the force direction for the tooth movement, as well as counter forces for addressing unwanted or unintended forces are determined. Thereafter, based on the determined components associated with the movement vector which is associated with the tooth movement from the initial position to the target position, the cavity geometry of the dental appliance such as the aligner is modified.
 FIG. 22 is a flowchart illustrating the shaped feature(s) (e.g., ridges, dimples, etc.) profile determination and positioning. Referring to FIG. 22, at step 2210 the tooth position at a first treatment stage is determined. At step 2220 the tooth position at the second or n+1 treatment stage is determined. Thereafter, the movement vector associated with the tooth movement from the first treatment stage to the second treatment stage is determined at step 2230. After determining the movement vector associated with the tooth movement, one or more shaped feature(s) profile associated with the movement vector is determined at step 2240. Thereafter, at step 2250, the one or more shaped features are positioned, e.g., in the appliance (tooth receiving cavity), for contact with the corresponding tooth during the first treatment stage. The shaped feature profile and positioning are selected to achieve the desired tooth movement.
 In this manner, in one embodiment, the force/torque from the dental appliance is accurately applied to the tooth to reposition the tooth from the initial position to the target or second treatment stage position.
 The present invention can make use of various computer implemented embodiments of the methods described herein. For example, a computer implemented method in one embodiment includes establishing an initial position of a tooth, determining a target position of the tooth in a treatment plan, calculating a movement vector associated with the tooth movement from the initial position to the target position, determining a plurality of components corresponding to the movement vector, and determining a corresponding one or more positions/profiles of a respective one or more shaped features. The shaped features may be configured to apply a predetermined force on the dental appliance substantially at the surface plane of the tooth.
 An apparatus for modeling a dental appliance in another embodiment includes a data storage unit, and a processing unit coupled to the data storage unit and configured to determine an initial position of a tooth, determine a target position of the tooth in a treatment plan, calculate a movement vector associated with the tooth movement from the initial position to the target position, determine a plurality of components corresponding to the movement vector, and determine a profile and/or positioning of corresponding one or more shaped features.
 The data processing aspects of the invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. Data processing apparatus of the invention can be implemented in a computer program product tangibly embodied in a machine-readable storage device for execution by a programmable processor; and data processing method steps of the invention can be performed by a programmable processor executing a program of instructions to perform functions of the invention by operating on input data and generating output. The data processing aspects of the invention can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from and to transmit data and instructions to a data storage system, at least one input device, and at least one output device. Each computer program can be implemented in a high-level procedural or object oriented programming language, or in assembly or machine language, if desired; and, in any case, the language can be a compiled or interpreted language. Suitable processors include, by way of example, both general and special purpose microprocessors. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of nonvolatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. Any of the foregoing can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).
 To provide for interaction with a user, the invention can be implemented using a computer system having a display device such as a monitor or LCD (liquid crystal display) screen for displaying information to the user and input devices by which the user can provide input to the computer system such as a keyboard, a two-dimensional pointing device such as a mouse or a trackball, or a three-dimensional pointing device such as a data glove or a gyroscopic mouse. The computer system can be programmed to provide a graphical user interface through which computer programs interact with users. The computer system can be programmed to provide a virtual reality, three-dimensional display interface.
 Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US5975893 *||8 Oct 1997||2 Nov 1999||Align Technology, Inc.||Method and system for incrementally moving teeth|
|US20050048433 *||25 Aug 2004||3 Mar 2005||Hilliard Jack Keith||Automated method for producing improved orthodontic aligners|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|CN104224333A *||6 Jun 2014||24 Dec 2014||曾振文||orthodontic system and manufacturing method thereof|
|CN104224333B *||6 Jun 2014||30 Jun 2017||曾振文||牙齿矫正系统及其制造方法|
|Cooperative Classification||A61C7/002, A61C7/08|
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