Dental preparation guide

Abstract

A method for validating a preparation of at least one tooth in a prepared set of teeth for determining whether the prepared tooth is capable of accepting a dental restoration includes obtaining a virtual dental preparation guide configured for validating the preparation of the at least one tooth; obtaining a digital 3D representation of the prepared set of teeth; visualizing the virtual dental preparation guide together with the digital 3D representation of the prepared set of teeth; and validating from the visualization of the virtual dental preparation guide together with the digital 3D representation of the prepared set of teeth whether the prepared at least one tooth is shaped such that it can accept the dental restoration.

Claims

1. A non-transitory computer readable medium encoded with a program to cause a computer to execute a method for creating a virtual dental preparation guide for manufacturing a physical dental preparation guide configured for validating preparation of at least one prepared tooth for a dental restoration, said method comprising obtaining a digital 3D representation of a pre-prepared set of teeth; virtually removing said at least one tooth from the digital 3D representation of the pre-prepared set of teeth, such that a digital 3D representation of a remaining set of teeth is formed; obtaining a virtual target dental restoration expressing a target shape of the dental restoration; creating a virtual validation surface for the dental preparation guide based on the virtual target dental restoration; creating a virtual preparation guide surface by combining the virtual validation surface and at least part of the surface of the digital 3D representation of the remaining set of teeth; and creating a virtual preparation guide having the virtual preparation guide surface, wherein: the physical dental preparation guide to be manufactured based on the virtual dental preparation guide includes a validation surface based on the virtual preparation guide surface, and the validation surface is configured such that the physical dental preparation guide does not collide with the prepared tooth when the physical dental preparation guide is arranged at the prepared tooth.

2. The non-transitory computer readable medium according to claim 1, wherein the method comprises creating a virtual replacement surface configured for at least partly closing a virtual hole defined in the digital 3D representation of the remaining set of teeth when virtually removing said at least one tooth.

3. The non-transitory computer readable medium according to claim 2, wherein the virtual replacement surface comprises a virtual gingival surface configured for closing a gingival part of the virtual hole.

4. The non-transitory computer readable medium according to claim 2, wherein the virtual replacement surface comprises a virtual interproximal surface configured for closing an interproximal part of the virtual hole.

5. The non-transitory computer readable medium according to claim 2, wherein the method comprises making the virtual replacement surface part of the digital 3D representation of the remaining set of teeth.

6. The non-transitory computer readable medium according to claim 1, wherein the method comprises creating a virtual minimum preparation surface.

7. The non-transitory computer readable medium according to claim 6, wherein the virtual minimum preparation surface of the tooth is determined from the virtual target dental restoration.

8. The non-transitory computer readable medium according to claim 6, wherein the virtual validation surface is based on the virtual minimum preparation surface.

9. The non-transitory computer readable medium according to claim 8, wherein the virtual preparation guide surface is created by virtually connecting the virtual minimum preparation surface and the digital 3D representation of the remaining set of teeth.

10. The non-transitory computer readable medium according to claim 1, wherein the virtual preparation guide surface at least in part is created by a Boolean addition of the digital 3D representation of the remaining set of teeth and the virtual validation surface.

11. The non-transitory computer readable medium according to claim 1, wherein the method comprises generating a connecting surface configured for connecting the virtual validation surface and the digital 3D representation of the remaining set of teeth.

12. The non-transitory computer readable medium according to claim 1, wherein the method comprises generating a virtual dental preparation guide from the virtual preparation guide surface.

13. A system for creating a virtual dental preparation guide for manufacturing a physical dental preparation guide configured for validating preparation of at least one prepared tooth for a dental restoration, the system comprising: a scanner configured for obtaining a digital 3D representation of a pre-prepared set of teeth; and a data processing device configured for generating the dental preparation guide from said digital 3D representation of the pre-prepared set of teeth and/or from a virtual target dental restoration, where the dental preparation guide is configured to provide that a preparation of the tooth according to the dental preparation guide will ensure that the dental restoration can be realized and can be inserted at the prepared tooth, and where said virtual target dental restoration expresses a target shape of the dental restoration; where the data processing device comprises a non-transitory computer readable medium encoded with a program to cause a computer to execute a method for creating the virtual dental preparation guide, said method comprising obtaining the digital 3D representation of the pre-prepared set of teeth; virtually removing said at least one tooth from the digital 3D representation of the pre-prepared set of teeth, such that a digital 3D representation of a remaining set of teeth is formed; obtaining a virtual target dental restoration expressing a target shape of the dental restoration; creating a virtual validation surface for the dental preparation guide based on the virtual target dental restoration; creating a virtual preparation guide surface by combining the virtual validation surface and at least part of the surface of the digital 3D representation of the remaining set of teeth; and creating a virtual preparation guide having the virtual preparation guide surface, wherein: the physical dental preparation guide to be manufactured based on the virtual dental preparation guide includes a validation surface based on the virtual preparation guide surface, and the validation surface is configured such that the physical dental preparation guide does not collide with the prepared tooth when the physical dental preparation guide is arranged at the prepared tooth.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and/or additional objects, features and advantages of the present invention, will be further elucidated by the following illustrative and non-limiting detailed description of embodiments of the present invention, with reference to the appended drawings, wherein:

(2) FIG. 1 shows a flowchart for an embodiment of the method for generating a dental preparation guide.

(3) FIG. 2 shows an example of a flowchart for generating a virtual dental preparation guide and for using it to validate a tooth preparation.

(4) FIGS. 3A and 3B show a schematic of teeth in one jaw of a patient and cross sectional presentations relating to some of the surfaces involved in generating the virtual preparation guide surface.

(5) FIG. 4 shows an example on how a digital 3D representation of the remaining set of teeth and a virtual validation surface can be connected.

(6) FIG. 5 shows an example of a virtual preparation guide surface

(7) FIG. 6 shows a path for manufacturing the dental preparation guide from the virtual preparation guide surface.

(8) FIG. 7 shows a path for manufacturing the dental preparation guide from the virtual preparation guide surface.

(9) FIG. 8 shows a situation where the insertion direction preferably should be taken into account.

(10) FIGS. 9A through 9C show how the insertion direction can be taken into account when designing the dental preparation guide.

(11) FIGS. 10A and 10B show screen shots in which the virtual removal of teeth introduces virtual holes in the digital 3D representation of the remaining teeth.

(12) FIGS. 11A through 11D show an example of an embodiment of the invention for forming a virtual preparation guide surface.

(13) FIG. 12 shows by way of a block diagram, a computerized device for generating a dental preparation guide.

(14) FIG. 13 shows a schematic of a user interface according to an embodiment of the invention.

(15) FIG. 14 shows a flowchart for an embodiment of the method for generating a dental preparation guide.

(16) FIGS. 15A through 15C show an example dental preparation guide formed as a two-piece device with a first part formed as a temporary crown.

(17) FIG. 16 shows an example of a dental preparation guide generated from a digital 3D representation of the prepared set of teeth and a required minimum thickness of the dental restoration.

(18) FIGS. 17A through 17C show an example of a preparation of a tooth and a dental preparation guide configured for validating the preparation of the tooth.

(19) In the following description, reference is made to the accompanying figures, which show by way of illustration how the invention may be practiced.

(20) In the flow-charts of FIGS. 1, 2 and 14, the vertical dotted line at the center divides the work-flows into a part relating to physical units (left-hand side) and a part relating to virtual units (right-hand side) in the work-flow.

(21) FIG. 14 shows a flowchart 1400 for an embodiment of the method for generating a dental preparation guide for validating the preparation of a tooth for a dental restoration.

(22) In step 1401a, a digital 3D representation of the pre-prepared set of teeth is obtained, e.g. by direct intra-oral scanning of the set of teeth or by scanning a physical model or an impression of the pre-prepared set of teeth.

(23) In step 1401b, the portion of this digital 3D representation corresponding to the tooth or teeth which the dental preparation guide is generated for is virtually removed such that a digital 3D representation of a remaining set of teeth is formed.

(24) In step 1403, a virtual target dental restoration is created. The virtual target dental restoration can be created based on a virtual diagnostic wax-up for the set of teeth where the virtual diagnostic wax-up expresses a target shape of the virtual target dental restoration.

(25) In step 1404 the virtual validation surface is created based in the virtual target dental restoration and in step 1405 the virtual preparation guide surface is created by connecting the virtual validation surface and the surface of the digital 3D representation of the remaining set of teeth.

(26) FIG. 1 shows a flowchart 100 for an embodiment of the method for generating a physical dental preparation guide for validating the preparation of a tooth.

(27) In step 101a a digital 3D representation of the pre-prepared set of teeth is obtained, e.g. by direct intra-oral scanning of the set of teeth or by scanning a physical model or an impression of the pre-prepared set of teeth.

(28) In step 101b, the portion of this digital 3D representation corresponding to the tooth or teeth which the dental preparation guide is generated for is virtually removed such that a digital 3D representation of a remaining set of teeth is formed.

(29) In step 102 a virtual diagnostic wax-up for the set of teeth is designed such that it expresses a target shape of the dental restoration. The virtual diagnostic wax-up is based on one or more aesthetic parameters which can relate to the shape of the individual teeth, the color of the teeth, and/or the relative arrangement of the teeth. The material of the dental restoration can be decided based on e.g. patient's choice or practical dental concerns, such as size and form of tooth or teeth that are to be restored. There must further be enough space for the dentist to perform the necessary steps in the preparation of the tooth and for inserting the dental restoration at the prepared tooth. The minimum thickness of the restoration material also depends on the desired change of color. A large change may require a larger thickness.

(30) The virtual target dental restoration is created based on the designed virtual diagnostic wax-up in step 103, and in step 104 the virtual validation surface is created based in the virtual target dental restoration.

(31) In step 105 the virtual preparation guide surface is created by connecting the virtual validation surface and the surface of the digital 3D representation of the remaining set of teeth.

(32) In step 106, at least a selected part of the virtual preparation guide surface is shelled such that the virtual dental preparation guide comprises an inner shell surface and an outer shell surface in the selected part.

(33) In some cases the outer shell surface is shaped according to the created virtual preparation guide surface and the shelling can be used to define the inner shelling surface from the outer surface, i.e. from the virtual preparation guide surface. In such cases, an intermediate physical model can be manufactured from the shelled virtual preparation guide surface in step 107 using direct digital manufacturing. The physical dental preparation guide is then manufactured in step 108 by shaping the material of the dental preparation guide using said intermediate physical model. The material of the dental preparation guide can be shaped by vacuum forming it onto the intermediate physical model.

(34) In some cases the inner shell surface is shaped according to the virtual preparation guide surface and the shelling can be used to define the outer shell surface from the inner shell surface, i.e. from the virtual preparation guide surface. In such cases, the physical dental preparation guide is manufactured in step 109 from the shelled virtual preparation guide surface using e.g. 3D printing.

(35) FIG. 2 shows an example of a flowchart for generating a virtual dental preparation guide and for using it to validate a tooth preparation. The flowchart contains a part 210 concerning the generation of the virtual dental preparation guide and a part 211 for using the generated virtual dental preparation guide to validate the preparation of the tooth.

(36) In step 2011, a digital 3D representation of the pre-prepared set of teeth is obtained by direct intra-oral scanning of the teeth. A virtual dental preparation guide is then created in step 212 using e.g. steps 102 to 106 of the workflow described in relation to FIG. 1 or steps 1401a to 1404 described in relation to FIG. 14.

(37) The tooth or teeth are prepared for the restoration by grinding away tooth material. The patient's set of teeth is then referred to as a prepared set of teeth.

(38) In step 2012 the intra-oral scanner is used to scan at least the region of the prepared set of teeth in which the prepared tooth or teeth are located in order to obtain a digital 3D representation of the prepared set of teeth.

(39) In step 214 the digital 3D representation of the prepared set of teeth and the virtual dental preparation guide are aligned and visualized together on a visual display unit, such as on a computer screen.

(40) Based on the aligned digital 3D representation of the prepared set of teeth and virtual dental preparation guide a validation of the tooth preparation is performed in step 215 to determine whether further preparation is required.

(41) If further preparation is required, the dentist continues the preparation in step 213. A new intra-oral scanning 2012, alignment 214 and validation 215 is then performed and the loop continues until no further preparation of the tooth is required and the dentist chooses to proceed to a following part of the dental procedure.

(42) The intra-oral scanner may be configured for utilizing focus scanning, where the digital 3D representation of the scanned teeth is reconstructed from in-focus images acquired at different focus depths. The focus scanning technique can be performed by generating a probe light and transmitting this probe light towards the set of teeth such that at least a part of the set of teeth is illuminated. Light returning from the set of teeth is transmitted towards a camera and imaged onto an image sensor in the camera by means of an optical system, where the image sensor comprises an array of sensor elements. The position of the focus plane relative to the set of teeth is varied by means of focusing optics while images are obtained from said array of sensor elements. Based on the images, the in-focus position(s) of each of a plurality of the sensor elements or each of a plurality of groups of the sensor elements may be determined for a sequence of focus plane positions.

(43) The in-focus position can e.g. be calculated by determining the light oscillation amplitude for each of a plurality of the sensor elements or each of a plurality of groups of the sensor elements for a range of focus planes. From the in-focus positions, the digital 3D representation of the set of teeth can be derived.

(44) Creating the dental preparation guide and the use of it may run in parallel with the preparation of the tooth or teeth, and may as such not be part of a treatment on the patient but rather be a method for generating and for using a guide for validating the preparation of the teeth.

(45) In the text above the method is described in relation to the evaluation of one tooth preparation. The method is evidently also suited for simultaneously evaluating the preparation of a number of teeth.

(46) FIG. 3a shows a schematic of teeth in one jaw of a patient and a cross sectional plane at a tooth which is to be prepared.

(47) The set of teeth 300 has a tooth 316a which e.g. is ill and in need of a dental restoration such as a crown. The tooth must hence be prepared such that it is capable of accepting the crown. The plane in which the cross sectional view is obtained is defined by the line A-B crossing the tooth and the normal to the occlusal plane of the set of teeth, i.e. the plane is perpendicular to the occlusal plane.

(48) FIGS. 3b to 9, 11, and 15 to 17 show cross sectional representations of the teeth and the dental preparation guide as seen in the plane defined in FIG. 3a.

(49) FIG. 3b shows cross sectional presentations relating to some of the surfaces involved in generating the virtual preparation guide surface.

(50) The tooth portion 316b of digital 3D representation of the pre-prepared set of teeth is virtually removed at a boundary determined by the 3D sectioning spline 317. When the tooth is virtually removed a virtual hole is introduced in the digital 3D representation of the remaining set of teeth 318.

(51) In this example, the virtual target dental restoration is based on a virtual diagnostic wax-up 319 designed according e.g. to the patient's aesthetic preferences.

(52) The virtual validation surface 320 is based on a virtual minimum preparation surface defined by inward offsetting the virtual diagnostic wax-up 319 and by pushing a portion of the offset surface which extends beyond the tooth portion 316b onto the tooth portion to provide that the virtual validation surface follows the tooth surface at this part of the tooth. A virtual preparation line 321 is also illustrated in the figure.

(53) With the virtual validation surface 320 described by the minimum preparation surface, the virtual preparation guide surface can be created by connecting the digital 3D representation of the remaining set of teeth 318 and the virtual minimum preparation surface.

(54) FIG. 4 shows an example on how a digital 3D representation of the remaining set of teeth and a virtual validation surface can be connected.

(55) A 3D remaining teeth spline 4171 has been determined based on the 3D sectioning spline seen in FIG. 3. Since the virtual validation surface 420 which is based on the virtual minimum preparation surface is smaller than the corresponding part of the digital 3D representation of the pre-prepared set of teeth, there is a hole between the virtual validation surface 420 and the digital 3D representation of the remaining set of teeth 418.

(56) The virtual preparation guide surface is created by connecting the virtual validation surface 420 and the digital 3D representation of the remaining set of teeth 418. These surfaces are connected by creating a connecting surface 422 extending from the 3D remaining teeth spline 4171 to a 3D validation surface spline 423. Here the 3D validation surface spline 423 is arranged above the virtual preparation line 421, but it can in principle be arranged at any location on the virtual validation surface, such as substantially along the virtual preparation line 421.

(57) The connecting surface 422 can be created in a lofting process.

(58) The 3D remaining teeth spline 4171 can be determined by modifying the 3D sectioning spline which was defined in relation to the digital 3D representation of the pre-prepared set of teeth. In some embodiments, the modification is aided by visualizing the 3D sectioning spline in relation to the surface of a virtually removed tooth or a tooth of the virtual target dental restoration. When visualized in relation to a virtually removed tooth, any interproximal holes on the virtually removed tooth may have been closed previously using e.g. curvature-based algorithms.

(59) In order to provide a watertight virtual preparation guide surface, further hole-closing may be needed. This may be performed using curvature based hole-closing algorithms.

(60) FIG. 5 shows an example of a virtual preparation guide surface.

(61) The virtual preparation guide surface 524 illustrated in this figure is created from the virtual validation surface, the connecting surface, and the digital 3D representation of the remaining set of teeth as seen in FIG. 4. The virtual preparation guide surface 524 is here aligned with a digital 3D representation of the prepared set of teeth 525.

(62) Due to the location of the 3D validation surface spline above the virtual preparation line in FIG. 4, a safety zone 526 is provided at the preparation line allowing the dentist some room for maneuvering, such as to adjust the actual position of the preparation line during the dental procedure.

(63) FIG. 6 shows one path for manufacturing the dental preparation guide from the virtual preparation guide surface. In this embodiment, the physical dental preparation guide is manufactured directly from the virtual dental preparation guide.

(64) The virtual preparation guide surface 624 representing an inner shell surface is offset outward to provide an outer shell surface 627. Based on the shelled virtual preparation guide surface, a physical dental preparation guide 628 can be manufactured using direct digital manufacturing such as 3D printing. The surface of the dental preparation guide facing the set of teeth is shaped according to the virtual preparation guide surface.

(65) In the context of the present invention, the phrase “surface is offset outward” corresponds to offsetting the surface away from the position where the teeth are located when the dental preparation guide is arranged in relation to the patient's teeth.

(66) FIG. 7 shows one path for manufacturing the dental preparation guide from the virtual preparation guide surface. In this embodiment, the physical dental preparation guide is manufactured via an intermediate physical model formed based on the virtual dental preparation guide.

(67) The virtual preparation guide surface 724 representing an outer shell surface is offset inward to provide an inner shell surface 729. Based on the shelled virtual preparation guide surface, an intermediate physical model 730 can be manufactured using direct digital manufacturing, such as 3D printing. In the context of the present invention, the phrase “surface is offset inward” corresponds to offsetting the surface towards the position where the teeth are located when the dental preparation guide is arranged in relation to the patient's teeth.

(68) Dental preparation guide material 731 is then shaped according to the intermediate physical model 730 by e.g. vacuum forming the material 731 onto the intermediate physical model 730. The dental preparation guide material 731 is then separated from the intermediate model 730 to provide the physical dental preparation guide 728, where the surface facing the set of teeth is shaped according to the virtual preparation guide surface.

(69) FIG. 8 shows a situation where the insertion direction preferably should be taken into account in order to generate a dental preparation guide which also takes into account that the dental restoration moves along a path when being arranged in relation to the patient's set of teeth.

(70) A dental restoration 832 is moved along a path determined by the insertion direction 833 towards its target position relative to the prepared set of teeth 834. The inner surface 835 of the dental restoration 832 matches the corresponding portion of the prepared set of teeth.

(71) The lines 836 indicate the trace of a margin line 837 of the dental restoration when the dental restoration is moved along the path determined by the insertion direction 833. One of these lines cut through the prepared set of teeth 834 showing that a collision between the prepared set of teeth 834 and the cervical part of the dental restoration will prevent the dental restoration 832 from being arranged in the target position unless the region 838 is removed. That is the virtual preparation guide surface may be shaped to ensure that if the tooth is prepared according to the virtual preparation guide surface, the dental restoration 832 can be moved into the target position without any collisions.

(72) FIG. 9 shows how the insertion direction can be taken into account when designing the dental preparation guide. Instead of using an approach where the dental restoration is trimmed to compensate for the insertion direction, the dental preparation guide is trimmed.

(73) FIG. 9a shows the virtual validation surface 920 which is intersected by one of the paths 9361 which are arranged to pass through the virtual preparation line 921. Here the paths 9361 are arranged at an angle of 5 degrees relative to the insertion direction 933 to provide that the prepared tooth is tapered. In the illustrated situation, the taper is only strictly necessary on the path cutting through the virtual validation surface 920.

(74) In order to take into account the insertion direction 933 (and in this example also the taper angle) the virtual validation surface 920 is trimmed such that the surface of the intersected part is aligned with the path intersecting it, thereby removing the region blocking the path of the cervical part of the dental restoration. The trimmed virtual validation surface 920 is seen in FIG. 9b.

(75) The trimmed virtual validation surface 920 can then be connected to the digital 3D representation of the remaining set of teeth 918 at the 3D remaining teeth spline 9171 to provide the virtual preparation guide surface using e.g. lofting as described above.

(76) FIG. 9c then shows the situation after the insertion direction has been taken into account when designing the virtual validation surface and hence the virtual preparation guide surface.

(77) Now the dental restoration 932 can moved along the path 936 determined by the insertion direction 933 towards its target position relative to the prepared set of teeth 934 without being blocked by tooth material.

(78) A slight angle is seen between the path 936 and the portion of the prepared set of teeth 934 corresponding to the trimmed portion of the virtual validation surface. This is caused by the taper angle.

(79) FIG. 10 shows screen shots in which the virtual removal of teeth introduces virtual holes in the digital 3D representation of the remaining teeth 3D sectioning splines 1017 are defined in relation to the digital 3D representation of the pre-prepared set of teeth 1037 such that 4 teeth can be virtually removed. The 3D sectioning splines 1017 may be defined automatically by e.g. extracting boundaries of the teeth portion of the digital 3D representation of the pre-prepared set of teeth.

(80) When the teeth are virtually removed, virtual holes appear in the digital 3D representation of the remaining set of teeth 1018. The virtual holes include four virtual gingival holes 1038, and interproximal holes 1039 at the portions of the digital 3D representation of the remaining set of teeth corresponding to the neighboring teeth. Here no boundary exist between each interproximal hole is and the neighboring gingival hole.

(81) A virtual hole can be closed by a virtual replacement surface or be closed by virtual gingival and virtual interproximal surfaces.

(82) When a virtual hole is closed using a virtual replacement surface, the interproximal sections of the 3D remaining teeth spline can be defined in relation to this virtual replacement surface. The 3D remaining teeth spline may be arranged to divide a portion of the virtual replacement surface into a virtual gingival surface and a virtual interproximal surface.

(83) FIG. 11 shows how a virtual preparation guide surface with a virtual validation surface according to a diagnostic wax-up can be created.

(84) In FIG. 11a, a virtual hole in the digital 3D representation of the remaining set of teeth 1118 is bounded by a 3D remaining teeth spline 11171. The 3D remaining teeth spline can be determined from a 3D sectioning spline such as the 3D sectioning spline 1017 illustrated in FIG. 10.

(85) In FIG. 11b, a virtual replacement surface 1140 is connected to the digital 3D representation of the remaining set of teeth 1118 at the 3D remaining teeth spline 11171 such that the virtual hole in the digital 3D representation of the remaining set of teeth 1118 is closed.

(86) In FIG. 11c, a virtual target dental restoration 1141 defined from a virtual diagnostic wax-up is aligned with the digital 3D representation of the remaining set of teeth 1118 such that it is intersected by the portion corresponding to the virtual replacement surface. The virtual validation surface can here be considered to be the portion of the virtual target dental restoration 1141 arranged above the digital 3D representation of the remaining set of teeth 1118.

(87) The virtual preparation guide surface 1124 can then be created by a Boolean addition of the virtual target dental restoration 1141 and the digital 3D representation of the remaining set of teeth 1118. The resulting virtual preparation guide surface 1124 is seen in FIG. 11d.

(88) Alternatively to connecting a virtual replacement surface to the digital 3D representation of the remaining set of teeth, the interproximal hole may at least partly be closed by a virtual interproximal surface while the gingival hole may be closed by a virtual tooth preparation or by a virtual gingival depending on whether a crown or a pontic is to be arranged at the location of the gingival hole. The virtual preparation guide surface may then be created by a Boolean addition of the digital 3D representation of the remaining set of teeth and the virtual tooth preparation or the virtual gingival. The boundary between the virtual interproximal surface and the virtual gingival or the virtual tooth preparation can be used for defining the 3D remaining teeth spline.

(89) FIG. 12 shows by way of a block diagram a system for generating a dental preparation guide according to an embodiment of the present invention. The system 1250 comprises a computer device 1251 comprising a computer readable medium 1252 and a processor 1253. The system further comprises a visual display unit 1256, a computer keyboard 1254 and a computer mouse 1255 for entering data and activating virtual buttons visualized on the visual display unit 1256. The visual display unit 1256 can e.g. be a computer screen. The computer device 1251 is capable of receiving a digital 3D representation of the patient's set of teeth from a scanning device 1257, such as the TRIOS intra-oral scanner manufactured by 3 shape A/S, or capable of receiving scan data from such a scanning device and forming a digital 3D representation of the patient's set of teeth based on such scan data. The digital 3D representation may be of a pre-prepared or a prepared set of teeth.

(90) The received or formed digital 3D representation can be stored in the computer readable medium 1252 and provided to the processor 1253. The processor 1253 is configured for virtually removing said at least one tooth from the digital 3D representation of the pre-prepared set of teeth, such that a digital 3D representation of a remaining set of teeth is formed. This can be done based on a 3D sectioning spline defined in relation to the digital 3D representation of the pre-prepared teeth e.g. by the operator using the computer mouse to mark relevant positions on the digital 3D representation of the pre-prepared teeth. A virtual target dental restoration expressing a target shape of the dental restoration can be provided to the processor 1253 from an external source or from the computer readable medium 1252. The processor 1253 is further configured for creating a virtual validation surface for the dental preparation guide based on the virtual target dental restoration, where the validation surface is such that the preparation of the tooth can be validated by the dental preparation guide; and for creating a virtual preparation guide surface by combining the virtual validation surface and at least part of the surface of the digital 3D representation of the remaining set of teeth. While creating the virtual validation surface and/or the virtual preparation guide surface one or more options can be presented to the operator, such as whether to connect the virtual validation surface to the digital 3D representation of the remaining set of teeth using a Boolean addition or by be creating a connecting surface by loofting. The options can be presented in a user interface visualized on the visual display unit 1256.

(91) In some cases, the processor 1253 is further configured for shelling at least a selected part of the virtual preparation guide surface such that the virtual dental preparation guide comprises an inner shell surface and an outer shell surface in the selected part. The system has a unit 1258 for transmitting the shelled virtual preparation guide surface to e.g. a computer aided manufacturing (CAM) device 1259 for manufacturing the dental preparation guide or for manufacturing an intermediate physical model from which the dental preparation guide can be formed by vacuum forming, or to another computer system e.g. located at a milling center where the dental preparation guide or the intermediate physical model is manufactured. The unit for transmitting the virtual 3D model can be a wired or a wireless connection.

(92) The scanning of the patient's set of teeth using the scanning device 1257 is most often performed at dentist's office. The designing and the manufacture of the dental preparation guide can be performed at the dentist's office or at a dental laboratory. In the latter case, the digital 3D representation of the patient's pre-prepared set of teeth can be provided via an internet connection between the dentist and the dental laboratory.

(93) FIG. 13 shows a schematic of a user interface according to an embodiment of the invention.

(94) The figure shows a first part 1371 of the user interface 1370 in which cross sectional views of different surfaces used in the designing of the dental preparation guide are visualized. In the illustrated example, the virtual validation surface, the digital 3D representation of the remaining set of teeth, the virtual preparation line, the 3D remaining teeth spline, and the 3D validation surface spline of FIG. 4 are seen on the first part.

(95) The second part 1372 of the user interface comprises a data entering section 1374 for entering data relating to e.g. whether the virtual validation surface is to be connected by a Boolean addition or by a surface created by a loofting process. A virtual push button 1373 is configured for providing the virtual preparation guide surface is created by combining the virtual validation surface and at least part of the surface of the digital 3D representation of the remaining set of teeth based on the data entered in the data entering section 1374.

(96) The user interface can be visualized on a visual display unit, such as a computer screen being part of a system configured for implementing the method according to the present invention. The user interface is also configured for performing at least some of the other steps in the method, such as the virtually removing of at least one tooth from the digital 3D representation of the pre-prepared set of teeth when forming the digital 3D representation of a remaining set of teeth. For these steps the virtual push buttons and the data entry sections provided in the second part 1372 may differ from those provided when connecting the virtual surface.

(97) FIG. 15 shows an example dental preparation guide formed as a two-piece device with a first part formed as a temporary crown.

(98) The two-piece dental preparation guide 1580 illustrated in FIG. 15a has a first part 1581 and a second part 1582, where the second part 1582 is designed to have an inner surface configured for engaging the outer surface of the first part 1581 and the second part 1582 can be arranged in relation the first part 1581 such that the first and the second part together form the dental preparation guide 1580. When the two-piece dental preparation guide 1580 is arranged in relation to the patient's set of teeth, the inner surface of the first part 1581 faces the prepared tooth 1583 and the second part contacts the gingiva 1584 at the prepared tooth.

(99) FIG. 15b shows the first part 1581 formed as a temporary crown and which is designed to have an outer surface 15812 shaped to resemble a normal tooth surface and an inner surface 15812 with a shape based on the virtual validation surface such that the first part can validate the preparation of the tooth.

(100) FIG. 15c shows the second part 1582 with its inner surface 15822a, 15822b and outer surface 15821. The inner surface has a portion 15822a configured for engaging the outer surface of the first part of the dental preparation guide and a second part 15822b configured for contacting the gingiva at the prepared tooth. The first portion 15822a provides that the first and second parts of the dental preparation guide can mate and be handled as a coherent unit while the second portion 15822b ensures that the dental preparation guide 1580 can be arranged correctly relative to the prepared tooth.

(101) When used for validating the tooth preparation, the two-piece dental preparation guide is operated as one coherent unit the inner surface 15812 of the first part 1581 of the dental restoration is used for the validation. When the dentist as satisfied with the preparation of the tooth the first part 1581 and second part 1582 are disengaged and the first part 1581 can be temporarily secured at the prepared tooth and function as a temporary crown while the final restoration is manufactured based on e.g. a scan of the prepared set of teeth.

(102) FIG. 16 shows an example of a dental preparation guide generated from a digital 3D representation of the prepared set of teeth and a required minimum thickness of the dental restoration.

(103) The obtained a digital 3D representation of a prepared set of teeth 1691 comprises a portion 1683 corresponding to the prepared tooth. Based on the prepared tooth portion 1683 and a required minimum thickness of the dental restoration a virtual minimum restoration surface 1690 is generated. This surface marks the surface of the smallest dental preparation which can be made to fulfill requirements relating to e.g. the mechanically stable or the color of the dental restoration when arranged at the prepared tooth in its present shape. Any overlaps 1692 between the generated virtual minimum restoration surface 1690 and the obtained digital 3D representation of the prepared set of teeth 1691 can then be determined and the dentist can evaluate whether the overlap is too large or whether a small portion of the neighboring teeth can be grinded away to provide the required space for a dental restoration manufactured according to the virtual minimum restoration surface.

(104) The overlaps 1692 can e.g. be visualized in a user interface by a color coding where e.g. the color red is used to identify the overlapping regions in the digital 3D representation of the prepared set of teeth.

(105) If the dentist decides that further processing is required he removes more tooth material and repeats the process until the overlap is removed or reduced to an insignificant size.

(106) Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims. In particular, it is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.

(107) In device claims enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

(108) A claim may refer to any of the preceding claims, and “any” is understood to mean “any one or more” of the preceding claims.

(109) It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

(110) The features of the method described above and in the following may be implemented in software and carried out on a data processing system or other processing means caused by the execution of computer-executable instructions. The instructions may be program code means loaded in a memory, such as a RAM, from a storage medium or from another computer via a computer network. Alternatively, the described features may be implemented by hardwired circuitry instead of software or in combination with software.