Patent Publication Number: US-2023157788-A1

Title: Method and a system usable in creating a subsequent dental appliance

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/200,445, filed Nov. 26, 2018, which is a continuation of U.S. application Ser. No. 13/605,949, filed Sep. 6, 2012, now abandoned, and which are incorporated herein by reference in their entirety and to which applications we claim priority under 35 USC § 120. 
    
    
     BACKGROUND 
     Frequently a patient will wear some type of dental appliance, such as a retainer, positioner, or splint, after their orthodontic braces have been removed in order to prevent the positions of the patient&#39;s teeth from deviating from the accomplished teeth arrangement. A set of braces is one example of what shall be referred to herein as a “current dental appliance.” A dental appliance that is worn after removal of the current dental appliance shall be referred to herein as a “subsequent dental appliance.” Retainers are an example of a subsequent dental appliance. Alternatively, patients in orthodontic braces may wish to discontinue wearing the bonded braces during treatment and finish the remainder of their treatment with additional dental appliances such as a clear removable plastic aligner. In the event that the treatment consists of a combination of braces followed by removable aligners, a transition between the braces and aligners without having to manufacture a temporary holding retainer (to minimize tooth movement after the braces are removed) between the two phases of treatment is desired. 
     To manufacture the subsequent dental appliance, physical impressions may be taken with the current dental appliance still affixed to the patient&#39;s teeth in order to minimize the amount of undesirable tooth movement which may occur between the time after the removal of the current dental appliance and the time that the subsequent dental appliance is delivered. By leaving the current dental appliance on for the impressions, it is hoped that the subsequent dental appliance can be manufactured while the teeth are held in place with the current dental appliance and delivered immediately after the current dental appliances are removed. However, the impressions that are taken with the current dental appliance affixed on the patient can be difficult—not only for the clinician, but also for the patient—because of the undercuts present in the current dental appliance which lock in the impression material as it sets. This is not only uncomfortable and messy for the patient, but can also lead to impression distortion if, for example, excessive force is required to free the locked impression from the teeth when the current dental appliances are still present. As a result of any distortion in the impression, the subsequent dental appliances may not fit well on the patient&#39;s teeth when they are delivered. Even after the impression is taken, a technician will have to spend considerable effort manually cleaning up any model made from the impression and manually removing all parts of the current appliance and any distortion and other defects arising from taking the impression. These are just a few examples of why physical impressions are undesirable. 
     More often, the treating professional waits until the current dental appliance is removed before taking an impression. This eliminates some of the difficulties in taking the impression with the current appliance but, results in a need for a temporary retainer or no retainer for the period in which it takes to make a subsequent dental appliance. The later risks teeth movement before the subsequent dental appliance can be applied to the teeth. In either case, it also necessitates another appointment with the treating professional to fit and apply the subsequent appliance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of this Description of Embodiments, illustrate various embodiments of the present invention and, together with the description, serve to explain the principles discussed below: 
         FIGS.  1   a   - 1   d,    1   f,    1   g  illustrate a patient&#39;s set of physical teeth with respective physical teeth and gingiva and examples of dental appliances attached to the patient&#39;s set of physical teeth, according to various embodiments. 
         FIG.  1   e    illustrates a patient&#39;s physical teeth after the removal of an orthodontic band, according to one embodiment. 
         FIGS.  2   a - 6   c    illustrate techniques for creating a new digital dental model, according to various embodiments. 
         FIG.  7    illustrates changes to a patient&#39;s gingiva, according to one embodiment. 
         FIGS.  8   a  and  8   b    depict examples of temporary anchorage devices (TADs)  800  attached inside the patient&#39;s oral cavity, according to various embodiments. 
         FIG.  9    is a block diagram of a system for creating a subsequent dental appliance prior to removal of a current dental appliance from a set of physical teeth for a patient, according to one embodiment. 
         FIG.  10    depicts a flow chart of a method of creating a subsequent dental appliance prior to removal of a current dental appliance from a set of physical teeth for a patient, according to one embodiment. 
         FIGS.  11 - 15    depict flowcharts of methods for creating a new digital dental model, according to various embodiments. 
         FIG.  16    depicts a digital tooth  1600  that represents one of the patient&#39;s set of physical teeth that may be moved from one position of treatment to another position of treatment, according to one embodiment. 
         FIGS.  17 - 19    illustrate a technique for identifying the gingival margin that defines the boundary between tooth and gum in the patient&#39;s dentition and simulating changes in the gingiva, according to one embodiment. 
     
    
    
     The drawings referred to in this Brief Description should not be understood as being drawn to scale unless specifically noted. 
     DESCRIPTION OF EMBODIMENTS 
     According to one embodiment, a current digital dental model, such as a digital image, is made of the patient&#39;s physical teeth with one or more current dental appliances attached to the physical teeth normally just before the current dental appliance is to be removed and replaced with a subsequent dental appliance. If the subsequent appliance is an end-of-treatment retainer, the teeth are usually at or near a desired arrangement of the teeth. If the subsequent appliance is a middle-of-treatment appliance, the teeth are at a treatment arrangement that is between the initial arrangement and the desired arrangement. 
     Various types of direct or indirect scanning or imaging (such as an intraoral scan, CBCT, or various types of scan of physical models or impressions including laser and computed tomography) can be used for creating the current digital dental model. According to a preferred embodiment, the current digital dental model is a direct digital scan of the set of physical teeth with the current dental appliance attached to one or more of the physical teeth. Various embodiments may also be used with a current dental appliance that is attached to the patient&#39;s oral cavity, such as to the patient&#39;s bone beneath the gingiva. 
     Examples of a current dental appliance include any dental appliance suitable for attachment to one or more of the patient&#39;s teeth and a dental appliance suitable for attachment to the patient&#39;s bone beneath the gingival, among others. More specifically, the current dental appliance may consist of one or more items and may be all or a portion of a set of braces (which may include bonded brackets, buttons, cemented bands, or a combination thereof), a temporary anchorage device (TAD) that is attached to the patient&#39;s oral cavity, or a dental attachment that is suitable for use with a removable plastic positioning dental appliance (also referred to herein as an “aligner”), a dental appliance suitable for attachment to bone under the gingiva of the patient, a sleep apnea appliance, a splint, a bridge, an implant, an orthodontic band, a fixed lingual retainer, a set of lingual braces or any item that has been fixedly attached to any portion of the oral cavity, as examples. Examples of types of TADs are a mini screw, a mini plate, a ball type, a bracket type and a hook type. The current dental appliance may be positioned on either the facial/buccal surface, the lingual surface of the patient&#39;s physical teeth, the gingiva, or a combination thereof. 
     A new digital dental model of the aligned teeth (either fully or partially) can be created based on a model of the current teeth with the current dental appliance present or from a previous model of the unaligned teeth without the current dental appliance present. For example, the new digital dental model may be created by removing the current dental appliance from the current digital dental model or by moving digital teeth of an earlier time point (of the same patient) without the dental appliance present into the same positions as the teeth in the current digital dental model (with the dental appliance present), among other things as described herein. According to one embodiment, the creation of the new digital dental model is computer automated. The creation of the new digital dental model can be fully automated or substantially-automated. 
     A new digital dental model can be used to manufacture a subsequent dental appliance prior to removing the current dental appliance from the patient&#39;s physical teeth. Examples of a subsequent dental appliance are a retainer, an (active) aligner, an expander, a splint or bite guard, or a positioner. The retainer may be a Hawley, an Essix-type, a bonded wire, any vacuum-formed type stent, a spring-retainer, a clear splint, or a combination thereof. At least one example of a splint is an orthognathic surgery splint, among others. 
     According to one embodiment, the current digital dental model and the new digital dental model includes a portion of the patient&#39;s gingiva. For example, the current digital dental model and the new digital dental model may include at least the portion of the patient&#39;s gingiva that would be covered over by or adjacent to a subsequent dental appliance. 
     According to one embodiment, the current digital dental model and a new digital dental model may include digital teeth that represent all of a patient&#39;s physical teeth clinically present (i.e. unerupted and/or impacted teeth not included) whether natural or prosthetic (e.g., dental crown or bridge pontic). For the sake of simplicity however, many of the figures depict a subset of the patient&#39;s physical teeth. 
     Figure la illustrates a patient&#39;s set of physical teeth  100  with respective physical teeth  100   a - 100   d  and gingiva  102 .  FIG.  1   b   - 1   d,    1   f  and  1   g  illustrate examples of dental appliances  112 ,  122 ,  132 ,  152 ,  162  attached to the patient&#39;s set of physical teeth  100 , according to various embodiments. For the sake of simplicity,  FIGS.  1   a - g    depicts a subset of the patient&#39;s physical teeth. 
     Example  110  depicts the patient&#39;s set of physical teeth  100  with a set of orthodontic braces  112  attached. The set of braces  112  may include one or more brackets, archwires, etc. Example  120  depicts the patient&#39;s set of physical teeth  100  with dental attachments  122  that are suitable for use with a removable plastic positioning dental appliance, such as an aligner. Example  130  depicts an orthodontic band attached to the patient&#39;s set of physical teeth  100 . Example  140  depicts spaces  142 ,  146  on the side of the tooth and a space  144  at the back of the tooth after the removal of the orthodontic band  132  has been removed. Example  150  depicts a fixed lingual retainer  152 . Example  160  depicts lingual braces. 
     The dental brackets and dental attachments as depicted in  FIGS.  1     b,    1   c,    1   d,    1   f,    1   g  are considered some examples of and shall be referred to a “current dental appliance” since the dental appliances  112 ,  122 ,  132 ,  132 ,  152 ,  162  are currently attached to the patient&#39;s physical teeth  100 . The dental attachments  122  may be aligner attachments for use with an aligner. 
     The patient&#39;s set of physical teeth  100  are at or close to a desired teeth arrangement, according to one embodiment. A desired teeth arrangement, according to one embodiment, is the final teeth arrangement that is accomplished as a result of orthodontic treatment. According to one embodiment, the patient&#39;s physical teeth  100  may be at the desired teeth arrangement as a result of an orthodontic treatment. According to another embodiment, the patient&#39;s physical teeth  100  are close to, but not exactly at the desired teeth arrangement. For example, due to the current dental appliance  112 , a feature such as a cemented orthodontic band  132  ( FIG.  1   d   ) may take up a small space in between two physical teeth adjacent to each other. A space  142 ,  146  ( FIG.  1   e   ) between the adjacent physical teeth can also be referred to as an “interproximal space.” When the bands are removed, the interproximal space that existed because of the bands will close. Various embodiments are also well-suited for physical teeth that are close to the desired teeth arrangement, but not exactly at the desired teeth arrangement. Another example is that a treating professional may want to start creating a subsequent appliance before the teeth have moved all the way to the desired tooth arrangement. 
     Although many embodiments are described in the context of a set of braces  112 , the current dental appliance may be any type of dental appliance that can be attached to one or more of the patient&#39;s physical teeth  100  or to the patient&#39;s tissues within the oral cavity. The current dental appliance may be any type of dental appliance that is suitable for use with a removable plastic positioning dental appliance. 
       FIGS.  2   a - c    illustrate a technique for creating a new digital dental model, according to one embodiment.  FIG.  2   a    depicts segmented digital teeth  200  of the patient,  FIG.  2   b    depicts a current digital dental model  210 , and  FIG.  2   c    depicts a new digital dental model  220 . The current digital dental model  210  is a representation of the patient&#39;s set of physical teeth  100  ( FIG.  1   a   ) and the dental appliance  112  ( FIG.  1   b   ) that is currently attached to the patient&#39;s physical teeth  100 . 
     According to one embodiment, a digital scan of the patient&#39;s physical teeth  100  is taken without any dental appliance being on the patient&#39;s physical teeth  100 . The digital scan can be processed to create segmented digital teeth  200  of the patient. Each  200   a - 200   d  of the segmented digital teeth  200  represents a different one  100   a - 100   d  ( FIG.  1   a   ) of the patient&#39;s physical teeth  100  ( FIG.  1   a   ). Each of the segmented digital teeth  200 , according to one embodiment, has one or more axes of their own and three dimensional (3D) coordinates so that each of the segmented digital teeth can be freely positioned in 3D space. For example, 3D coordinates alone or 3D coordinates in combination with one or more axes can be used for positioning each of the segmented digital teeth  200  based on the positions of each individual digital tooth  210   a - 210   d,    220   a - 220   a  associated with either the current digital dental model  210  or a new digital dental model  220 , as will be described in more detail in the context of  FIG.  16   . 
     Each of the segmented digital teeth  200   a - 200   d  can be superimposed on the corresponding digital teeth  210   a - 210   d  associated with the current digital dental model  210 . The surfaces shared in common (i.e. not covered by the dental appliance) can be used as references and the basis for the superimposition. A new location for the segmented digital teeth  200   a - 200   d  can then be assigned to each individual tooth, based on the position of the equivalent tooth in the new digital dental model  220  (the new digital dental model  220  can be segmented or unsegmented or partially segmented). The non-superimposed portion includes any portion of the current digital dental model  210  that is not part of the original digital dental model as represented by the segmented digital teeth  200 . For example, the non-superimposed portion can include the current dental appliance  112  and any cement that is used for attaching the current dental appliance  112  to the patient&#39;s physical teeth  100  ( FIG.  1   b   ). The non-superimposed portion may also include changes to the gingival contours (due to inflammation for example). The new digital dental model  220  can be created either by removing the non superimposed portion of the current digital dental model  210  or by creating the new digital dental model  220  based on the superimposed portion without the non superimposed portion. 
       FIGS.  3   a - 3   c    illustrates a technique for creating a new digital dental model, according to one embodiment.  FIG.  3   a    depicts a representation  300  of the current dental appliance,  FIG.  3   b    the current digital dental model  210  ( FIG.  2   b   ), and  FIG.  3   c    depicts a new digital dental model  320 . The representation of the current dental appliance  300  may be an image that was taken of the same physical dental appliance. For example, a digital image of the dental appliance  112  ( FIG.  1   b   ) may have been taken when the dental appliance  112  was not applied to the patient&#39;s physical teeth  100  ( FIG.  1   a   ). The representation of the current dental appliance  300  or portion  300   a,    300   b  may be an image obtained, for example, from a library of dental appliances of different types. The obtained image may be an image of a different physical dental appliance that is the same type or a similar type of as the current dental appliance  112  ( FIG.  1   b   ). For example, the obtained image may be an image of a different physical dental appliance that is the same make or model, or a combination thereof, as the current dental appliance  112  ( FIG.  1   b   ). 
     A representation of all  300  or a portion  300   a,    300   b  of the current dental appliance  112  ( FIG.  1   b   ) may be superimposed. Examples of a portion  300   a,    300   b  of the current dental appliance  112  ( FIG.  1   b   ) are a bracket, a wire, a band, a tube, a cleat, a button, a ligature wire, a hook, an aligner attachment, and an O-ring. 
     The representation of the current dental appliance  300  can be superimposed on the current digital dental model  210  ( FIG.  2   b   ). The portion of the current digital dental model  210  that is superimposed by the representation of the current dental appliance  300  or by the portion  300   a,    300   b  can be determined. The new digital dental model  320  can be created, for example, by removing the superimposed portion from the current digital dental model  210  or by creating the new digital dental model  320  based on the non superimposed portion without the superimposed portion. 
     According to one embodiment, the new digital dental model  320  may include representations of excess cement or offsets to the surfaces of the physical teeth due to the cement, or a combination thereof. Therefore, a subsequent dental appliance that is created based on the new digital dental model  320  will fit the patient&#39;s physical teeth  100  ( FIG.  1   a   ) but may be slightly larger than a subsequent dental appliance created, for example, using a new digital dental model  220  ( FIG.  2   b   ). Various embodiments can be used to remove the representations of the excess cement. For example, at least various embodiments described in the context of  FIGS.  5   a - 5   c    may be used to remove the representations of the excess cement. 
       FIGS.  4   a - 4   c    illustrate a technique for creating a new digital dental model, according to one embodiment.  FIG.  4   a    depicts a bracket base  400 , a digital tooth  210   b  that is a part of a current digital dental model  210 , and a representation  420   b  that is a part of a new digital dental model  420 . The bracket base  400  is associated with a current dental appliance  112  ( FIG.  1   b   ) for the patient or is associated with a dental appliance that is a similar type or the same type as the current dental appliance  112  ( FIG.  1   b   ). The underneath surface  402  of the bracket base  400  has a contour  404  that approximates the contour  450  of the digital tooth  210   b &#39;s portion  440 . 
     As depicted in  FIG.  4   b   , a bracket base  400  is attached to a portion  440  of a digital tooth  210   b  with cement  430 . According to one embodiment, the contour  450  of the portion  440  of the digital tooth  210   b  associated with the current digital dental model  210  ( FIG.  2   b   ) is estimated based on the contour  404  of the underneath surface  402  of the bracket base  400 . 
     Various embodiments are well-suited for approximating the contour  450  of a portion  440  a digital tooth portion  440  based on other portions, as discussed herein, of a dental appliance besides a bracket base, as discussed herein. For example, if a portion of a digital tooth is beneath a bonded lingual wire, various embodiments are well-suited for using a contour underneath the bonded lingual wire to estimate the contour of a portion of digital tooth that would be beneath that wire. 
     Referring to  FIG.  4   c   , according to one embodiment, the new digital tooth  420   b  of the new digital dental model  420  may include representations of excess cement  430  or offsets to the surfaces of the physical teeth due to the cement  430 , or a combination thereof. For example, cement  430  may appear to be part of the digital tooth  210   b.  Therefore, a subsequent dental appliance that would be created based on the new digital dental model  420  ( FIG.  4   c   ) would fit the patient&#39;s physical teeth  100  ( FIG.  1   a   ) but may be slightly larger than a subsequent dental appliance created, for example, using a new digital dental model  220  ( FIG.  2   b   ). Therefore, it is desirable to remove such representations of excess cement and or offsets. Various embodiments can be used to remove the representations of the excess cement  430 . For example, at least various embodiments described in the context of  FIGS.  5   a - 5   c    may be used to remove the representations of the excess cement  430 . 
       FIGS.  5   a - 5   c    illustrate a technique for creating a new digital dental model, according to one embodiment.  FIG.  5   a    depicts digital teeth  500   a - 500   d  that are each similar to respective digital teeth  210   a - 210   d  ( FIG.  2   b   ) associated with a current digital dental model  210 . A similar digital tooth  500   a - 500   d  may be obtained by averaging a plurality of digital teeth from a library of digital teeth, for example. A similar digital tooth  500   a - 500   d  may be an image of another physical tooth associated with the patient. For example, because of midplane symmetry of most individuals, a patient&#39;s two front teeth  100   b,    100   c  ( FIG.  1   a   ) are approximate mirror images of each other. A digital image of one of a patient&#39;s front teeth  100   b  can be created based on a mirror image of a digital image of the patient&#39;s contralateral front tooth  100   c.  Physical teeth  100   a  and  100   d  ( FIG.  1   a   ) are also examples of teeth that may be similar to each other. For example, a mirror image of physical tooth  100   a  could be superimposed on digital tooth  210   d  or a mirror image of physical tooth  100   d  could be superimposed on digital tooth  210   a.  The similar digital teeth  500  may be images of physical teeth from another person besides the patient. For example, the other person may be selected based on similar demographics as the patient. Examples of demographics used in determining if digital teeth are similar to each other include sex, age, ethnicity, size of teeth, such as small, medium, or large, and shape of the teeth, such as bulbous or flat, square or tapered. 
     A similar digital tooth  500   a - 500   d  may be resized based on the size of a digital tooth  210   a - 210   d  ( FIG.  2   b   ) in the current digital dental model  210  ( FIG.  2   b   ). For example, the similar digital tooth  500   a - 500   d  may be resized to match or approximately match one of the digital teeth  210   a - 210   d  in the current digital dental model  210 . According to one embodiment, the similar digital tooth  500   a - 500   d  is resized to be slightly larger than the digital tooth  210   a - 210   d  that it will superimpose to ensure that the subsequent dental appliance fits the patient&#39;s physical teeth  100  ( FIG.  1   a   ). 
     A similar digital tooth  500   a - 500   d,  according to one embodiment, has its own three-dimensional (3D) coordinates, as discussed herein, so that a similar digital tooth  500   a - 500   d  can be positioned, for example, based on the position of a corresponding digital tooth  210   a - 210   d  ( FIG.  2   b   ) associated with either the current digital dental model  210  or the new digital dental model  520 . 
     Each of the similar digital teeth  500   a - 500   d  can be superimposed on corresponding digital teeth  210   a - 210   d  ( FIG.  2   b   ) associated with the current digital dental model  210 . The 3D coordinates associated with each of the similar digital teeth  500   a - 500   d  can be reset as a part of the superimposing. The non superimposed portion can then be determined. For example, the non-superimposed portion includes the current dental appliance  112  ( FIG.  1   b   ). The new digital dental model  520  can be created by removing the non-superimposed portion of the current digital dental model  210  ( FIG.  2   b   ) or by creating the new digital dental model  520  based on the superimposed portion without the non superimposed portion. 
       FIGS.  6   a - c    illustrate a technique for creating a new digital dental model, according to one embodiment. An area or a subset  630  of a digital tooth  210   b  ( FIG.  2   b   ) in the current digital dental model  210  ( FIG.  2   b   ) may be beneath a portion of the current dental appliance  112  ( FIG.  1   b   ). Examples of a portion of the current dental appliance are a bracket, a wire, a tube, a cleat, a button, a ligature wire, a hook, a band, an aligner attachment, and an O-ring. According to one embodiment, a corresponding area or subset  610  of a similar digital tooth  600 , as described herein, can be used to estimate a contour of the hidden area or subset  630  of a digital tooth  210   b  in the current digital dental model  210 . The estimation can be used for creating a contour in a corresponding area of the subset  640  for a digital tooth  620   b  of the new digital dental model  620 . 
     According to one embodiment, the physical teeth  100  ( FIG.  1   a   ) may be close but not at the desired teeth arrangement when the current digital dental model  210  ( FIGS.  2   a - 6   c   ) is created. For example, the current dental appliance may have a feature, such as an orthodontic band  132  ( FIG.  1   d   ) that prevents complete closure of an interproximal space between adjacent physical teeth. In another example, the patient may be unavailable when their teeth  100  ( FIG.  1   a   ) are at the desired teeth arrangement, for example, due to travel plans. The current digital dental model  210  ( FIG.  2   b   ) may be created before the patient leaves on their trip so that a subsequent dental appliance, such as a retainer, will be available upon their return, at which time, the one or more of the current appliances would be removed. 
     Therefore, according to one embodiment, to create a current digital dental model  210  ( FIGS.  2   b - 6   b   ) when the patient&#39;s physical teeth  100  ( FIG.  1   a   ) are close but not at the desired teeth arrangement, positions of one or more digital teeth in the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) may be adjusted to the desired teeth arrangement. Information pertaining to one or more dimensions of the feature or descriptions of the feature can be used to determine how to adjust the positions of the one or more digital teeth in the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ). For example, in the case of an orthodontic band  132  ( FIG.  1   d   ), the width of the orthodontic band (either as a known dimension or a measurement derived from the scan) can be used to adjust the positions of the digital teeth to reflect that the interproximal space which had been maintained physically by the band will lessen when the band is removed. A subsequent dental appliance that is manufactured based on a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) adjusted to the desired teeth arrangement can be used to move the physical teeth to the desired teeth arrangement. An individual digital tooth&#39;s 3D coordinates can be adjusted as a part of adjusting positions, as discussed herein, meaning, for example, that the individually segmented digital teeth may be digitally repositioned within the arch. 
       FIG.  7    illustrates changes in a patient&#39;s gingiva, according to one embodiment.  FIG.  7    depicts one of the patient&#39;s teeth  700  and corresponding gingiva  710 . Frequently after a current dental appliance, such as a set of braces, the patient&#39;s gingiva  710  can be swollen or inflamed. With time and appropriate hygiene, the puffiness of the patient&#39;s gingiva  710  tends to reduce, causing the gingival contours to decrease. For example, as depicted in  FIG.  7   , the patient&#39;s gingiva  710  is at the baseline at t 0  (pre-treatment), becomes inflamed and is the most enlarged at time t 1 , and then less enlarged at time t 2  as the inflammation reduces, and is near or back to normal at time t 3 . 
     According to one embodiment, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) includes the portion of the patient&#39;s gingiva that is in proximity of the subsequent dental appliance or that would be covered by a subsequent dental appliance, or a combination thereof. According to one embodiment, a series of new digital dental models can be created, for example, that takes into account the changes in the patient&#39;s gingival contour  730 . For example, a new digital dental model may be created that accommodates the patient&#39;s gingiva  710  at time t 1 , a second new digital dental model may be created that accommodates the patient&#39;s gingiva  710  at time t 2 , and a third new digital dental model may be created that accommodates the patient&#39;s gingiva  710  at time t 3 . Further, as depicted in  FIG.  7   , the gingival contour  730  increases as indicated by  720 , for example, from time t 0  to t 1 . Various embodiments are also well-suited for swollen gingiva  710  due to a portion of a current dental appliance  112  ( FIG.  1   b   ) being placed near the patient&#39;s gingiva. 
     According to one embodiment, one or more changes in the patient&#39;s gingiva is simulated, as will be described in more detail in the context of  FIGS.  17 - 19   . According to another embodiment, the patient&#39;s gingival contour prior to treatment is used to estimate one or more changes in the patient&#39;s gingiva. For example, a digital dental model taken at time t 0  ( FIG.  7   ) of the patient&#39;s teeth and gingiva that was created prior to changes in the patient&#39;s gingiva or prior to application of a dental appliance may be used. Any type of imaging or scanning as discussed herein may be used for obtaining the digital dental model. Further, the current digital dental model may include a representation of the patient&#39;s gingiva contour when the patient&#39;s physical teeth are at a treatment position or at or close to the desired teeth arrangement. The prior digital dental model and the current digital dental model can be used to estimate the changes in the patient&#39;s gingival contour over time. For example, a linear or an exponential curve, among others, could be used to estimate the patient&#39;s expected gingival changes. According to one embodiment, the patient&#39;s gingival contour is modeled so that the subsequent dental appliance adapts well and does not leave any exposed edges that might irritate the tongue or surrounding soft tissue while at the same time providing an appliance that is not too tight, which might irritate the tissue underneath from the pressure exerted by the appliance. According to one embodiment, the patient&#39;s gingiva is selectively modeled. For example, assuming for the sake of illustration that a first portion of the patient&#39;s gingival at time t 3  is swollen and a second portion of the patient&#39;s gingiva at time t 3  has experienced recession or shrinkage. In this case, a first gingival modeling technique can be used on the first portion of the patient&#39;s gingiva and a second gingival modeling technique can be used on the second portion of the patient&#39;s gingiva. For example, the changes that will occur in the patient&#39;s gingiva after removal of the current dental appliance can be tracked using simulation or non-simulation embodiments on the first portion while the patient&#39;s pre-treatment gingival contour taken at time t 0  can be used for the second portion without or with minimal use of simulation or non-simulation embodiments. 
       FIGS.  8   a  and  8   b    depict examples of temporary anchorage devices (TAD)  800  attached to the patient&#39;s oral cavity, according to various embodiments.  FIG.  8   a    depicts TADs  800  located on the labial (or facial) side of the oral cavity  810   a  and  FIG.  8   b    depicts a TAD with buttons  820  bonded to teeth located on the lingual side of the oral cavity  810   b.  A temporary anchorage device  800  is an example of a current dental appliance that could be a part of a current digital dental model  210  ( FIGS.  2   b - 6   b   ) and that various embodiments are well-suited for creating a new digital dental model that excludes the temporary anchorage device  800 . Examples of portions of the oral cavity  810  that may be a part of a current digital dental model and a new digital dental model for the purposes of various embodiments is any portion of the oral cavity  810  that a subsequent dental appliance, such as a retainer, may overlap. The alveolar bone under the gingiva is an example of a portion of the patient&#39;s oral cavity  810 . Other examples of anchorage devices are a bonescrew and a plate. A TAD  800  may have a ball, a bracket or a hook, among other things, on the end that is exposed to the oral cavity for the purpose of attaching, for example, a wire, elastic, or a ligature, among other things. 
     Various embodiments are also well-suited for changes in the gingiva that result from a TAD or other types of devices that cause changes to the gingiva. For example, a portion of a TAD will typically be embedded in the gingiva into the bone beneath, which can cause a portion of the gingiva to swell. Various embodiments, such as a simulation, not requiring a simulation, and using the patient&#39;s original gingiva contour (depicted at time t 0  in  FIG.  7   ), as described herein, are well-suited for calculating, estimating, determining the changes in the patient&#39;s gingiva due to a dental appliance that is attached to the oral cavity. 
     As discussed herein, for the sake of simplicity, many embodiments were described in the context of a current digital dental model  210  that is a representation that included a set of braces. However, as discussed herein, embodiments are well suited for removing a current dental appliance  122  ( FIG.  1   b   ) that is suited-for use with a removable plastic positioning dental appliance, such as an aligner. For example, various embodiments are well suited for a current digital dental model that includes a representation of the set of physical teeth  100  ( FIG.  1   a   ) for the patient with the current dental appliance  122  attached to the physical teeth  100 . According to one embodiment, the geometry of the current dental appliance  122  in combination with the geometry of the physical teeth  100 , for example as represented by segmented digital teeth  200 , can be superimposed on a current digital dental model to determine portions to be kept or removed as a part of creating a new digital dental model using various embodiments discussed herein. Further, embodiments are well suited for using different embodiments for different teeth. For example, if a physical tooth, which does not have a current dental appliance  122  attached, has been altered due to esthetics or removal of heavy contacts for occlusion adjustment, among other things, a digital tooth from the current digital dental model that corresponds to that physical tooth can be superimposed back onto itself. In another example, if a physical tooth has a current dental appliance  122  attached to it, a digital image of that physical tooth taken prior to application of the current dental appliance  122  can be superimposed. 
     According to one embodiment, the creation of a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) is computer automated. For example, one or more computer processors may be used for creating the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ). According to one embodiment, the creation is entirely automatic without human intervention or without requiring human intervention. According to another embodiment, the creation is substantially automatic with some human intervention for clean up and double checking. According to one embodiment, the system is not merely a computer graphics system that a human uses to manually remove digital portions using a digital eraser or to copy digital portions of the current digital dental model  210  ( FIGS.  2   b - 6   b   ) as a part of creating the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ). The phrase “computer automated” shall be used to refer to entirely automatic or substantially automatic. One example of substantially automatic is where a user can select a point, such as any voxel or 3D triangle, of a depicted orthodontic bracket of a current digital dental model  210  ( FIGS.  2   b - 6   b   ) and the system can detect the remaining portions connected to the selected region which can include, for example, the bracket or the bracket and the cement. In this case, the user may only identify and select one point for up to 32 digital teeth on a current digital dental model  210  ( FIGS.  2   b - 6   b   ). 
     According to various embodiments, a current digital dental model  210  ( FIGS.  2   b - 6   b   ) and the new digital dental models  220 - 620  ( FIGS.  2   c - 6   c   ) are three dimensional models. According to various embodiments, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) can be used to manufacture a subsequent dental appliance prior to removing the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) from the patient&#39;s physical teeth  100  ( FIG.  1   a   ). For example, the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) may be used to manufacture a subsequent dental appliance, such as a retainer, a splint or a positioner, among others, as discussed herein. A new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) can be segmented or unsegmented or partially segmented, among other things. 
     According to one embodiment, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) does not include or does not require the inclusion of any digital roots corresponding to any of the patient&#39;s physical teeth  100   a - 100   d  ( FIG.  1   a   ). According to one embodiment, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) does not include or does not require the inclusion of any digital crowns. According to one embodiment, the current teeth arrangement of the digital teeth  210   a - 210   d  ( FIG.  2   b   ) of the current digital dental model  210  ( FIGS.  2   b - 6   b   ) is a current planned teeth arrangement that did not occur out of error or out of deviations but occurred due to the planned treatment. Therefore, according to various embodiments, neither a current digital dental model  210  ( FIGS.  2   b - 6   b   ) nor a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) is used or is required to be used as a part of causing the patient&#39;s physical teeth  100   a - 100   d  ( FIG.  1   a   ) to be positioned at a teeth arrangement that preceded the current planned teeth arrangement associated with the current digital dental model  210  ( FIGS.  2   b - 6   b   ). 
       FIG.  9    is a block diagram of a system for creating a subsequent dental appliance prior to removal of a current dental appliance from a set of physical teeth for a patient, according to one embodiment. The blocks that represent features in  FIG.  9    can be arranged differently than as illustrated and can implement additional or fewer features than what are described herein. Further, the features represented by the blocks in  FIG.  9    can be combined in various ways. The system  900  can be implemented using hardware, hardware and software, hardware and firmware, or a combination thereof. 
     The system  900  includes a current-digital-dental-model-receiving-component  910  and a new-digital-dental-model-creation-component  920 . The new-digital-dental-model can either be segmented, partially segmented or unsegmented. The current-digital-dental-model-receiving-component  910  is suitable for receiving a current digital dental model  210  ( FIGS.  2   b - 6   b   ) that includes a representation of the set of physical teeth  100  ( FIG.  1   a   ) for the patient with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) attached to the physical teeth  100  or oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ) where the physical teeth  100  ( FIG.  1   a   ) are at a position in treatment when all or a part of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  is desired to be removed from one or more of the set of physical teeth  100  and it is desired to use a subsequent appliance. Alternatively, the received current digital dental model  210  includes the representation of the set of physical teeth  100  for the patient with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  attached to the physical teeth  100  that are at or close to a desired teeth arrangement. According to one embodiment, the received current digital dental model  210  ( FIG.  2   b - 6   b   ) is a direct digital scan of the set of physical teeth  100  and the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820 . 
     The new-digital-dental-model-creation-component  920  is suitable for computer automated creation of a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) that includes the representation of the set of physical teeth  100  without including the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) where the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) includes electronic data suitable for manufacturing of the subsequent dental appliance prior to removal of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800  from the set of physical teeth  100  ( FIG.  1   a   ) or the oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ). 
     The new-digital-dental-model-creation-component  920  may be further suitable for superimposing a segmented digital tooth  200   a - 200   d  ( FIG.  2   a   ) of the patient on corresponding individual digital tooth  210   a - 210   d  ( FIG.  2   b   ) associated with the current digital dental model  210  ( FIG.  2   b   ) where the segmented digital tooth  200   a - 200   d  was obtained from a digital dental model taken of the set of physical teeth  100  of the patient without the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) attached. The new-digital-dental-model-creation-component  920  may be further suitable for superimposing a second representation of all  300  ( FIG.  3   a   ) or a portion  300   a,    300   b  ( FIG.  3   a   ) of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) on the current dental appliance  122  ( FIG.  1   b   ) associated with the first representation  210 , wherein the second representation  300 ,  300   a,    300   b  ( FIG.  3   a   ) of the current dental appliance is obtained from a source selected from a group consisting of a library of dental appliances and an image of the current dental appliance when not applied to the set of physical teeth. The new-digital-dental-model-creation-component  920  may be further suitable for estimating a contour  450  of a subset  440  of a digital tooth  210   b  included in the current digital dental model  210  ( FIGS.  2   b - 6   b   ) where the estimating is based on a contour  404  of the underneath surface  402  of a bracket base  400 . The new-digital-dental-model-creation-component  920  may be further suitable for creating a similar digital tooth  600  based on an average of a plurality of physical teeth and determining a contour of a portion  630  of the digital tooth  210   b  of the current digital dental model  210  ( FIGS.  2   b - 6   b   ) based on a corresponding portion  610  the similar digital tooth  600 . 
     According to one embodiment, the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) is an intermediate digital dental model and the new-digital-dental-model-creation-component  920  is further suitable for creating one of a series of intermediate digital dental models (also referred to herein as “a series of new digital dental models”). The series of intermediate digital dental models may approximate a series of changes in gingival contour  730  ( FIG.  7   ) of the patient, as discussed herein. The changes in the gingival contour  730  of the patient can be determined or estimated based on a simulation, as discussed herein. The changes in the gingival contour  730  of the patient can be determined or estimated based on an original gingival contour of the patient without requiring simulation, as discussed herein. The changes in the gingival contour  730  of the patient may be due to the gingival contour changing at various points in time t 0  to t 3  ( FIG.  7   ). 
     According to one embodiment, the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) is an intermediate digital dental model and the new-digital-dental-model-creation-component  920  is further suitable for creating one of a series of intermediate digital dental models (also referred to herein as “a series of new digital dental models”), as discussed herein. 
       FIG.  10    depicts a flow chart  1000  of a method of creating a subsequent dental appliance prior to removal of a current dental appliance from a set of physical teeth for a patient, according to one embodiment. A current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) is attached to a patient&#39;s set of physical teeth  100  ( FIG.  1   a   ) or oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ). A current digital dental model  210  ( FIG.  2   b   ) can be created using various types of scanning or imaging. For example, an intraoral scan of the patient&#39;s physical teeth  100  ( FIG.  1   a   ) or of the patient&#39;s physical teeth  100  and oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ) with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162  ( FIG.  1     b,    1   c,    1   d,    1   f,    1   g ) attached can be used to create a current digital dental model  210  ( FIGS.  2   b - 6   b   ). According to one embodiment, the current digital dental model is a direct digital scan of the set of physical teeth and the current dental appliance 
     At  1010 , the method begins. At  1020 , a current digital dental model  210  ( FIGS.  1   b - 6   b   ) is received that includes a representation of the set of physical teeth  100  ( FIG.  1   a   ) for the patient with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) attached to the physical teeth  100  ( FIG.  1   a   ) or oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ), where the physical teeth  100  are at a position in treatment when all or a part of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  is desired to be removed from one or more of the set of physical teeth  100  and it is desired to use a subsequent appliance. According to another embodiment, the received current digital dental model  210  includes the representation of the set of physical teeth  100  for the patient with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  attached to the physical teeth  100  that are at or close to a desired teeth arrangement. 
     The current dental appliance may be any dental appliance that can be attached to one or more of the patient&#39;s physical teeth  100  ( FIG.  1   a   ) or to the patient&#39;s oral cavity  810 ,  810   b  ( FIGS.  8   a ,  8   b   ). 
     At  1030 , a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) that includes the representation of the set of physical teeth  100  ( FIG.  1   a   ) without including the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) is created based on the current digital dental model  210  ( FIG.  2   b   ). Various embodiments can be used for creating a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ), which shall be described in the context of  FIGS.  11 - 15   , among others. 
     Referring to  FIGS.  2   a - 2   c    and  11 , at  1120  each  200   a - 200   d  of segmented digital teeth  200  of the patient is superimposed on corresponding digital teeth  210   a - 210   d  associated with the current digital dental model  210 . The segmented digital teeth  200   a - 200   d  are derived from the set of physical teeth  100  without any dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) applied to the set of physical teeth  100 . At  1130 , a non-superimposed portion of the current digital dental model  210  is determined based on the superimposing  1120 . At  1140 , the new digital dental model  220  is created by removing the non-superimposed portion of the current digital dental model  210  that was determined at  1130 . 
     Referring to  FIGS.  3   a - 3   c    and  12 , at  1220  a second representation  300 ,  300   a,    300   b  of all or a portion of the current dental appliance is superimposed on the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) associated with the first representation  210 , where the first representation  210  is the current digital dental model  210 . At  1230 , a superimposed portion of the first representation  210  ( FIG.  3   b   ) is determined based on the superimposing at  1220 . The new digital dental model  320  ( FIG.  3   c   ) is created at  1240  by removing the superimposed portion, associated with  300 ,  300   a,    300   b  ( FIG.  3   a   ), of the first representation  210  that was determined at  1230 . 
     Referring to  FIGS.  4   a - 4   c    and  13 , at  1320 , a contour  450  of a portion  440  of a digital tooth  210   b  associated with the current digital dental model  210  is estimated based on a contour  404  of the underneath surface  402  of a bracket base  400  associated with the current dental appliance  112 . At  1330 , the current dental appliance  112  is removed from the representation  210 , for example, as described in the context of  FIGS.  3   a - c    and  12 . 
     Referring to  FIGS.  5   a - 5   c    and  14 , at  1420  a second digital tooth  500   b  is superimposed onto a first digital tooth  210   b  of the current digital dental model  210 , wherein the first digital tooth  210   b  and the second digital tooth  500   b  are similar. In a first example, the second digital tooth  500   b  that is superimposed on the first digital tooth  210   b  can be an average of a plurality of digital teeth that are not derived from the physical teeth  100  of the patient. In a second example, the first and second digital teeth  210   b,    500   b  may represent different physical teeth of the patient. In a third example, the second digital tooth  500   b  may represent a physical tooth of a person that is not the patient. The size of the second digital tooth  500   b  may be scaled based on the size of the first digital tooth  210   b  that it is suited to superimpose. For example, the second digital tooth  500   b  may be sized to match or slightly exceed the first digital tooth  210   b &#39;s size. At  1430 , the new digital dental model  520  is created by removing a non superimposed portion of the representation. 
     Referring to  FIGS.  6   a - 6   c    and  15 , at  1520 , the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) is digitally removed from the representation  210 . At  1530 , an area  630  of a first digital tooth  210   b  beneath a virtual portion of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) is determined, where the first digital tooth  210   b  is associated with the current digital dental model  210  and the virtual portion is associated with the current dental appliance  1112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ). Examples of the virtual portion are a bracket, a wire, button, a cleat, a tube, a hook, a band, a ligature wire, an aligner attachment and an O-ring. 
     The following is an example of combining various embodiments to create a new digital dental model. The current dental appliance  300  can be removed from the representation  210 , as illustrated  FIGS.  3   a   - 3   c,  for example. An area  440  of a first digital tooth  210   b  beneath a virtual portion  400  of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) can be determined, where the first digital tooth  210   b  is associated with the current digital dental model  210  and the virtual portion  400  is associated with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ), as described illustrated in  FIGS.  4   a   - 4   c,  for example. An area  610  of a second digital tooth  600  that is similar to the first digital tooth  210   b  is received and a contour of the first digital tooth&#39;s area  630  is reconstructed based on the second digital tooth  600 &#39;s area  610 , as illustrated in  FIGS.  6   a   - 6   c,  for example. 
     The following is another example of combining various embodiments to create a new digital dental model. A segmented digital tooth  200   a - 200   d  of the patient can be superimposed on a first digital tooth  210   a  associated with the current digital dental model  210  as illustrated in  FIGS.  2   a   - 2   c.  A second representation  300 ,  300   a,    300   b  of all or a portion of the current dental appliance can be superimposed on the current dental appliance associated with the current digital dental model  210  as discussed in the context of  FIGS.  3   a   - 3   c.  A contour of a portion of a second digital tooth  210   b  of the current digital dental model  210  can be estimated based on a contour  404  of the underneath surface  402  of a portion  400  of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) as illustrated in  FIG.  4   b   . All or a portion  610  of a similar digital tooth  500   c,    600  can be superimposed on a third digital tooth  210   c  of the current digital dental model  210  as discussed in the context of  FIGS.  5   a ,  5   b  and  6   a   . According to one embodiment, the first digital tooth  210   a,  the second digital tooth  210   b  and the third digital tooth  210   c  correspond to different ones of the patient&#39;s physical teeth  100   a - 100   c.    
     Various embodiments for creating a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) are also well-suited for including the gingiva  710  ( FIG.  7   ) in a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) or changes to the gingiva  710 , as indicated by  720  ( FIG.  7   ), in a series of new digital dental models  220 - 620  ( FIGS.  2   c - 6   c   ) as discussed herein. Various embodiments are well-suited for changes in the gingiva due to a TAD  800  ( FIGS.  8   a ,  8   b   ), or any other type of dental appliance that may cause the gingival to change, as discussed herein. 
     According to one embodiment, the physical teeth  100  ( FIG.  1   a   ) are close but not at the desired teeth arrangement when the current digital dental model  210  ( FIGS.  2   b - 6   b   ) is created. Therefore, according to one embodiment, when the current digital dental model  210  ( FIGS.  2   b - 6   b   ) is created when the patient&#39;s physical teeth  100  are close but not at the desired teeth arrangement, positions of one or more digital teeth in the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) are adjusted to the desired teeth arrangement. According to one embodiment, there may be an interproximal space between two physical teeth  100  due to a feature of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ), such as an orthodontic band  132  ( FIG.  1   d   ). Information pertaining to one or more dimensions of the feature or descriptions of the feature can be used to determine how to adjust the positions of the one or more digital teeth in the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ). A subsequent dental appliance that is manufactured based on a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) adjusted to the desired teeth arrangement can be used to move the physical teeth  100  ( FIG.  1   a   ) to the desired teeth arrangement. A digital tooth&#39;s 3D coordinates can be used as a part of adjusting positions, as discussed herein. According to one embodiment, the current digital dental model  210  ( FIGS.  2   b - 6   b   ) and the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) include digital teeth that each correspond to one of the patient&#39;s physical teeth  100   a - 100   b  ( FIG.  1   a   ). 
     At  1040 , digital data suitable for use in manufacturing the subsequent dental appliance is provided based on electronic data included in the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) prior to removal of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) from the set of physical teeth  100  or the oral cavity  810   a,    810   b  ( FIGS.  1     a,    8   a,    8   b ). Examples of a subsequent dental appliance are a retainer, an (active) aligner, a splint, an expander, or a positioner. The retainer may be a Hawley, an Essix-type retainer, a bonded wire, a vacuum-formed stent, spring-retainer type, a clear splint type, or a combination thereof. In the event that treatment is a combination between braces and removable aligners, the subsequent device may be a clear removable aligner or series of aligners similar to a retainer, but designed to continue with orthodontic movement of the teeth. At least one example of a splint is an orthognathic surgery splint, among others. According to one embodiment,  1040  is optional. 
     At  1050 , the method ends. The receiving at  1020  and the creating at  1030  are performed by one or more computer processors, according to one embodiment. Although specific operations are disclosed in flowchart  1000 , such operations are exemplary. That is, embodiments of the present invention are well-suited to performing various other operations or variations of the operations recited in flowchart  1000 . It is appreciated that the operations in flowchart  1000  may be performed in an order different than presented, and that not all of the operations in flowchart  1000  may be performed. 
     According to one embodiment, a subsequent dental appliance can be manufactured based on the provided digital data, such as electronic data included in the new digital dental model, prior to removal of all or part of the current dental appliance from the set of physical teeth. For example, the electronic data included in the new digital dental model can be used to fabricate a mold using a rapid-prototyping machine or milling machine and forming the subsequent dental appliance over the mold. 
       FIG.  16    depicts a digital tooth  1600  that represents one of the patient&#39;s set of physical teeth that may be moved from one position of treatment to another position of treatment, according to one embodiment. According to one embodiment, the digital tooth  1600  represents a segmented or partially segmented digital tooth, that has one or more axes and three dimensional (3D) coordinates so that the digital tooth  1600  can be freely positioned in 3D space. For example, the 3D coordinates x, y, and z alone or 3D coordinates x, y, and z in combination with one or more axes  1604 ,  1606 ,  1608  can be used for positioning the digital tooth  1600 . 
     As a frame of reference describing how a digital tooth  1600  may be moved, an arbitrary centerline (CL) may be drawn through the digital tooth  1600 . With reference to this centerline (CL), a tooth  1600  may be moved in orthogonal directions represented by axes  1604 ,  1606 , and  1608  (where  1604  is the centerline). The centerline may be rotated about the axis  1608  (root angulation) and the axis  1604  (torque) as indicated by arrows  1610  and  1612 , respectively. Additionally, the tooth  1600  may be rotated about the centerline, as represented by an arrow  1612 . Thus, all possible free-form motions of the tooth  1600  can be performed. 
       FIGS.  17 - 19    illustrate a technique for identifying the gingival margin that defines the boundary between tooth and gum in the patient&#39;s dentition and simulating changes in the gingiva, according to one embodiment. This technique involves the creation of a series of horizontal 2D-planes  1780 , or slices, that intersect the dentition model roughly perpendicular to the occlusal plane. The cross-sectional surface  1782  of the dentition model in each of these planes  1780  includes cusps  1784 ,  1786  that represent the gingival margin. The computer identifies the gingival margin by applying one or more of the cusp detection techniques described above. 
     One technique is very similar to the neighborhood filtered cusp detection technique described above, in that voxel neighbrhoods  1788 ,  1790  are defined on one of the 2D-planes to focus the computer&#39;s search for cusps on adjacent 2D plane. Upon detecting a pair of cusps  1784 ,  1786  on one 2D plane, the computer defines one or more neighborhoods  1788 ,  1790  to include predetermined number of voxels surrounding the pair. The computer projects the neighborhoods onto an adjacent 2D plane by identifying the voxels on the adjacent plane that correspond to the voxel in the neighborhoods  1788 ,  1790  on the original plane. The computer then identifies the pair of black voxels that lie closest together in the two neighborhoods on the adjacent plane, labeling these voxels as lying in the cusp. The computer repeats this process for all remaining planes. 
     Many of these automated segmentation techniques are even more useful and efficient when used in conjunction with human-assisted techniques. For example, techniques that rely on the identification of the interproximal or gingival margins function more quickly and effectively when a human user first highlights the interproximal or gingival cusps in a graphical representation of the dentition model. One technique for receiving this type of information from the user is by displaying a 2D or 3D representation and allowing the user to highlight individual voxels in the display. Another technique allows the user to scroll through a series of 2D cross-sectional slices, identifying those voxels that represent key features such as interproximal or gingival cusps. Some of these techniques rely on user interface tools such as cursors and bounding-box markers. 
     In many instances, the computer creates proposals for segmenting the dentition model and then allows the user to select the best alternative. For example, one version of the arch curve fitting technique requires the computer to create a candidate catenary or spline curve, which the user allowed to modify by manipulating the mathematical control parameters. One technique involves displaying several surfaces that are candidates cutting surfaces and allowing the user to select the appropriate surfaces. 
     According to one embodiment, a tangible computer readable storage medium having computer-executable instructions stored thereon for causing a computer system to perform a method of creating a subsequent dental appliance prior to removal of a current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   b ) from a set of physical teeth  100  ( FIG.  1   a   ) for a patient is provided. According to one embodiment, the tangible computer readable storage medium provides for receiving  1020  a current digital dental model  210  ( FIG.  2   b - 6   b   ) that includes a representation of the set of physical teeth  100  ( FIG.  1   a   ) for the patient with the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) attached to the physical teeth  100  or oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ), where the current digital dental model  210  is a direct digital scan of the set of physical teeth  100  and the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  and wherein the physical teeth  100  are at a position in treatment when all or a part of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  is desired to be removed from one or more of the set of physical teeth  100  and it is desired to use a subsequent appliance. 
     According to one embodiment, the creating  1030  ( FIG.  10   ) is computer automated. According to one embodiment, the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) includes electronic data suitable for manufacturing of the subsequent dental appliance prior to removal of the current dental appliance  112 ,  122 ,  132 ,  152 ,  162 ,  800 ,  820  ( FIGS.  1     b,    1   c,    1   d,    1   f,    1   g,    8   a,    8   b ) from the set of physical teeth  100  ( FIG.  1   a   ) or oral cavity  810   a,    810   b  ( FIGS.  8   a ,  8   b   ). 
     A new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ), according to various embodiments, provides for more quickly, more cheaply making subsequent dental appliances that fit the patient&#39;s physical teeth and gingiva better. A new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ), according to various embodiments, provides for increased patient compliance (due to improved appliance comfort when worn, for example) and reduced chance of relapse as a result. A new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ), according to various embodiments, significantly reduces the chance of relapse because the subsequent digital appliance is made from the new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) while the current dental appliance is still attached to the patient&#39;s physical teeth. Further, the subsequent digital appliance can be applied immediately upon removal of the current dental appliance. Further, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) can be created without using physical impressions or without requiring the use of physical impressions and associated processes such as blocking out the teeth with wax, for example, prior to taking the impression. A new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ), according to various embodiments, reduces the number of patient appointments and/or additional appliances needed, or a combination thereof in comparison to methods involving physical impressions, since the appliance removal and subsequent appliance delivery can be combined into one appointment. Furthermore, a new digital dental model  220 - 620  ( FIGS.  2   c - 6   c   ) is not subject to the distortions that can occur while making a manual impression, so the risk of remaking the appliance and the additional time and effort associated due to poor subsequent appliance fit is reduced. The teeth are less likely to undergo a period of time without orthodontic restraint, as would be the case if the braces were removed and a period of time allowed to lapse before the retainer is delivered. A transitional dental appliance to prevent movement during this interim period becomes no longer needed, since the doctor can smoothly transition between braces and the subsequent dental appliance. 
     Example embodiments of the subject matter are thus described. Although the subject matter has been described in a language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. 
     Various embodiments have been described in various combinations and illustrations. However, any two or more embodiments or features may be combined. Further, any embodiment or feature may be used separately from any other embodiment or feature. Phrases, such as “an embodiment,” “one embodiment,” among others, used herein, are not necessarily referring to the same embodiment. Features, structures, or characteristics of any embodiment may be combined in any suitable manner with one or more other features, structures, or characteristics.