Undercut filling method for digital dental models and manufacturing method for dental instruments of digital dental models

Abstract

An undercut filling method for digital dental models and a manufacturing method for dental instruments. The undercut filling method can achieve fuller and more anatomically accurate undercut filling for digital dental models. The undercut filling method for digital dental models comprises: acquiring a digital dental model (S101); generating a control point generation model with radius R for each undercut region (S102); moving the control point generation model so that the control point generation model is simultaneously tangent to the buccal and lingual surfaces of two adjacent teeth, and obtaining a set of control points for each tooth on the basis of the tangency points between the control point generation model and each tooth (S103); connecting each set of control points in a predetermined sequence to obtain an undercut control boundary that is used to form an undercut model (S104); interconnecting two undercut control boundaries to generate a corresponding digital undercut model (S105); and performing filling processing on the digital dental model according to the digital undercut model (S106).

Description

Method for filling undercuts of digital jaw models and method for manufacturing dental instruments thereof CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on the Chinese patent application with application number "202410390740.4" and application date of April 1, 2024, and claims the priority of the above-mentioned Chinese patent application. The entire content of the above-mentioned Chinese patent application is hereby incorporated into this application by introduction. Technical Field

[0002] The present application relates to the technical field of dental orthodontics, and in particular to a method for filling undercuts in a digital jaw model and a method for manufacturing a dental appliance thereof. Background Art

[0003] At present, computer-aided technology for generating dental models and braces has been widely used. The digital generation of dental braces can speed up production and reduce manpower and material resources. Existing digital models basically first obtain the patient's dental data after scanning; then, based on the basic morphology of the patient's teeth, the doctor designs the corresponding correction plan, and automatically generates a digital tooth model corresponding to each step of the correction. These digital tooth models are then used to manufacture a series of physical tooth models using rapid prototyping methods or CNC machine tool processing methods, and each physical tooth model is then hot-pressed to produce the corresponding shell-shaped braces.

[0004] During the generation process of the above-mentioned digital tooth model, the tooth model is not filled with undercuts. If such a digital tooth model is directly manufactured into a physical tooth model, and an orthodontic appliance is manufactured based on the physical tooth model, it will lead to the difficulty of demolding the orthodontic appliance after the positive mold is completed. Secondly, since the orthodontic appliance is not designed with the undercut areas corresponding to the adjacent teeth, it may cause discomfort to the patient when wearing the invisible braces. Moreover, such an orthodontic appliance is easily stuck in the undercut when worn and cannot be smoothly removed, making it inconvenient for the patient to remove the orthodontic appliance.

[0005] To address this issue, the current practice is to fill the undercuts on the physical tooth model before hot pressing it to create invisible braces. This involves filling the undercuts between adjacent teeth with a solid filler. This method increases the number of processing steps, reduces production efficiency, and increases production costs. Furthermore, because the amount of undercuts filled by different people is difficult to control, the quality of the resulting braces is difficult to guarantee, which can affect the corrective effect of the braces.

[0006] In response to the shortcomings of manual filling of undercuts, there is currently a solution that first automatically generates undercuts on a digital tooth model to obtain a digital tooth model after the undercuts are filled. The quality of the shell-shaped appliance obtained by hot-pressing the physical tooth model based on the digital tooth model after the undercuts are filled has been improved. However, the existing methods for automatically generating undercuts are mostly based on designers selecting a number of control points on two adjacent teeth in the undercut area based on experience, and then generating a digital undercut model based on the control points. The digital undercut model is then filled into the undercut area of ​​the digital tooth model. The shape of this automatically generated undercut is mostly not full enough, which will cause the braces to break to a certain extent during the production process. In order to meet the requirements of the braces production process and taking into account the patient's experience of wearing braces, automatically generating fuller undercut blocks has become an important part of the automation of braces production. Summary of the Invention

[0007] The main purpose of this application is to propose a method for filling undercuts in a digital dental model and a method for manufacturing a dental instrument thereof, aiming to achieve a fuller and more realistic undercut filling in the digital dental model.

[0008] To achieve the above-mentioned purpose, an embodiment of the present application provides a method for filling undercuts in a digitized dental model, comprising the following steps: obtaining a digitized dental model, wherein there is an undercut area between two adjacent teeth of the digitized dental model; generating a control point generation model with a radius R for each undercut area; moving the control point generation model so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth, and obtaining a group of control points for each tooth based on the tangent points between the control point generation model and each tooth, wherein at least two tangent points corresponding to a first position and a second position are respectively obtained on the buccal surface and the lingual surface of each tooth, and the second position is located above the first position; connecting each group of control points according to a set order to obtain an undercut control boundary for forming an undercut model; connecting the two undercut control boundaries to each other to generate a corresponding digitized undercut model; and filling the digitized dental model according to the digitized undercut model.

[0009] In some embodiments, the spherical model is moved so as to keep the spherical model always tangent to the two adjacent teeth during the movement, and the spherical model is at least moved 360 degrees around the central axis of the two adjacent teeth, where the central axis is the line connecting the reference centers of the two adjacent teeth.

[0010] In some embodiments, a plurality of cutting planes are generated based on the central axis of the two adjacent teeth, wherein the central axis is a line connecting the reference centers of the two adjacent teeth; the circular model is generated on each cutting plane respectively, so as to move the circular model so that the circular model is tangent to the tooth cross-sectional contours of the two adjacent teeth at the same time.

[0011] In some embodiments, the normal direction of the initial cutting plane is a cross product of the buccal-lingual direction of any one of the two adjacent teeth and the central axis.

[0012] In some embodiments, the angles between adjacent cutting planes are the same.

[0013] In some embodiments, the angles between adjacent cutting planes are different.

[0014] In some embodiments, the cutting plane is rotated at least 180 degrees about the central axis.

[0015] In some embodiments, in generating a control point generation model with a radius R for each undercut area, the generated control point generation model has a different radius R for each undercut area.

[0016] In some embodiments, the radius R is 1.1 to 2 times the distance between the two adjacent teeth.

[0017] In some embodiments, when there is no gap between the two adjacent teeth, the radius R of the control point generation model is set to 3mm-6mm; when there is a gap between the two adjacent teeth, the radius R of the control point generation model is obtained based on the distance between the two adjacent teeth.

[0018] In some embodiments, at least one tangency point is offset toward the inside of the tooth along a normal direction of the tangency point on the surface of the tooth.

[0019] In some embodiments, the included angle between the offset direction of each tangent point toward the inside of the tooth where it is located and the central axis of the two adjacent teeth is [0, 30°].

[0020] In some embodiments, the offset does not exceed the maximum distance of the tangent point on the tooth along the central axis.

[0021] In some embodiments, the offset does not exceed 1 / 2 of the maximum distance.

[0022] In some embodiments, when the adjacent tangent point pairs continue to be moved in the corresponding offset direction, if there is a tangent point located outside the corresponding tooth in the adjacent tangent point pairs after continuing to move the first step length, the adjacent tangent point pairs are moved back to their original positions and then continued to be moved with a second step length, which is smaller than the first step length.

[0023] In some embodiments, when the adjacent tangent point pairs continue to be moved in the corresponding offset direction, if only one tangent point in the adjacent tangent point pairs after moving the preset distance is located outside the corresponding tooth, the tangent point is moved back to its original position and the tangent point is continued to be moved with a second step length.

[0024] In some embodiments, the surface forming the contour between the two groups of control points is subjected to patch refinement and smoothing processing, including: inserting multiple interpolation insertion points between each pair of control point lines; and connecting the control points at corresponding positions of the two concave control boundaries and the multiple interpolation insertion points to each other.

[0025] To achieve the above-mentioned purpose, the present application also provides a method for manufacturing a dental instrument, comprising: designing a digital dental model that gradually adjusts the teeth from a first layout to a second layout; filling the undercuts of the digital dental model according to the above-mentioned undercut filling method; manufacturing a physical tooth model based on the digital dental model after the undercut filling; and manufacturing a shell-shaped dental instrument based on the digital dental model after the filling treatment.

[0026] Compared with the prior art, the present invention provides a method for filling undercuts in a digital jaw model and a method for manufacturing a dental appliance thereof, which has the following beneficial effects:

[0027] 1. This application generates a model by moving a control point with a radius of R. During the movement, the control point generation model is kept tangent to the buccal and lingual surfaces of two adjacent teeth. A set of control points for each tooth is obtained based on the tangent points between the control point generation model and each tooth. A digital undercut model is then obtained based on the two sets of control points on the two adjacent teeth for filling. Because the control point generation model follows the movement of the two adjacent teeth, this application can control the movement path of the control point generation model, thereby not only fully filling the undercut area and improving the filling effect, but also making the undercut more closely fit the actual teeth.

[0028] 2. This application uses a control point generation model to obtain simultaneous tangent points on the surfaces of two adjacent teeth and then moves them inside the teeth as control points. A digital undercut model is generated by the two sets of control points located inside the adjacent teeth, and then the digital tooth model is filled. This ensures that there is no gap between the filled undercut model and the digital dental model, and the undercut area is fully filled. In this way, when preparing shell-shaped dental appliances, the problem of difficulty in demolding in the prior art will not occur, and the wearing comfort of the shell-shaped dental appliances can be improved, avoiding the inconvenience of wearing and taking off. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplified descriptions do not constitute limitations on the embodiments.

[0030] FIG1 is a flow chart of a method for filling an undercut of a digital dental model in one embodiment of the present application;

[0031] FIG2 is a schematic diagram of a digital tooth model in an embodiment of the present application;

[0032] FIG3 is a schematic diagram showing selection of a first position and a second position in one embodiment of the present application;

[0033] FIG4 is a schematic diagram of a spherical model tangent to two adjacent teeth in one embodiment of the present application;

[0034] FIG5 is a schematic diagram of the spherical model in FIG4 and two adjacent teeth rolling and being tangent to each other at another position;

[0035] FIG6 is a schematic diagram of calculating the spacing in one embodiment of the present application;

[0036] FIG7 is a schematic diagram of generating a cutting plane between two adjacent teeth according to another embodiment of the present application;

[0037] FIG8 is a schematic diagram showing a circular model tangent to the cross-sectional profiles of two adjacent teeth in another embodiment of the present application;

[0038] FIG9 is a schematic diagram of the rotation of the cutting plane in another embodiment of the present application;

[0039] FIG10 is a schematic diagram of a digital undercut model generated in one embodiment of the present application;

[0040] FIG11 is a flow chart of a method for filling an undercut of a digital dental model in another embodiment of the present application;

[0041] FIG12 is a schematic diagram of an embodiment of the present application in which the tangent point is offset toward the inside of the tooth;

[0042] FIG13 is a schematic diagram showing determination of the offset of the tangent point to the inside of the tooth in one embodiment of the present application;

[0043] FIG14 is a schematic diagram of another embodiment of the present application in which the tangent point is offset toward the inside of the tooth;

[0044] FIG15 is a schematic diagram of another embodiment of the present application in which the tangent point is offset toward the inside of the tooth;

[0045] FIG16 is a schematic diagram of determining the offset direction in another embodiment of the present application;

[0046] FIG17 is a partial enlarged view of region G in the schematic diagram for determining the offset direction shown in FIG16 ;

[0047] FIG18 is a schematic diagram of a digital tooth model after the digitized undercut model is filled in accordance with an embodiment of the present application;

[0048] FIG. 19 is a flow chart of a method for manufacturing a shell-shaped dental appliance according to another embodiment of the present application. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, each embodiment of the present application will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in each embodiment of the present application, many technical details are proposed to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present application. The various embodiments can be combined and referenced with each other under the premise of no contradiction.

[0050] To simplify the drawings, only the parts relevant to this application are schematically shown in each figure. They do not represent the actual structure of the product. In addition, to simplify the drawings and facilitate understanding, in some figures, only one of the components with the same structure or function is schematically depicted or labeled. In this document, "one" not only means "only one" but also "more than one."

[0051] As can be seen from the background technology, the current methods of automatically generating undercuts are mostly through designers selecting several control points on two adjacent teeth in the undercut area based on experience, and then generating a digital undercut model based on the control points. The digital undercut model is then filled into the undercut area of ​​the digital tooth model. The shape of this automatically generated undercut is mostly not full enough, which may cause braces to break to a certain extent during the production process.

[0052] Based on this, the present application proposes a method for filling undercuts in a digital dental model, comprising: obtaining a digital dental model, wherein an undercut area is provided between two adjacent teeth of the digital dental model; generating a control point generation model with a radius R for each undercut area; moving the control point generation model so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth, and obtaining a group of control points for each tooth according to the tangent points between the control point generation model and each tooth, wherein at least two tangent points corresponding to a first position and a second position are obtained on the buccal surface and the lingual surface of each tooth, and the second position is located above the first position; connecting each group of control points according to a set order to obtain an undercut control boundary for forming an undercut model; connecting the two undercuts The concave control boundaries are interconnected to generate corresponding digital undercut models; the digital dental model is filled according to the digital undercut model. It can be seen that the present application generates a model by moving a control point with a radius of R, and during the movement, the control point generation model is kept tangent to the buccal surface and the lingual surface of the two adjacent teeth at the same time, so that a group of control points of each tooth is obtained according to the tangent point between the control point generation model and each tooth, and a digital undercut model is obtained based on the two groups of control points on the two adjacent teeth to be filled. Since the control point generation model fits the movement of the two adjacent teeth, the present application can control the moving path of the control point generation model, which not only can fully fill the undercut area and improve the effect of undercut filling, but also make the undercut result more in line with the actual teeth.

[0053] In order to make the purpose, technical solutions and advantages of the present application clearer, each embodiment of the present application will be described in detail below with reference to the accompanying drawings. However, it will be understood by those skilled in the art that in each embodiment of the present application, many technical details are provided to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can be implemented. The division of the following embodiments is for convenience of description and should not constitute any limitation on the specific implementation of the present application. The various embodiments can be combined and referenced with each other under the premise that there is no contradiction.

[0054] The implementation details of the undercut filling method of the digital dental model recorded in this application will be specifically described below in conjunction with specific embodiments. The following content is only the implementation details provided for ease of understanding and is not necessary for the implementation of this solution.

[0055] Example 1

[0056] This embodiment provides a method for filling undercuts in a digital dental model. A flowchart thereof is shown in FIG1 . The method for filling undercuts in a digital dental model can be applied to a terminal with communication, computing, and data storage capabilities, such as a computer, mobile phone, or other electronic device. The method includes the following steps:

[0057] In step S101 , a digital dental model is obtained, wherein the digital dental model has an undercut area between two adjacent teeth.

[0058] A digital dental model refers to a computer-processable digital model that represents a certain orthodontic state and is used to guide the manufacture of a physical tooth model (i.e., a positive mold). It can be observed, modified, or otherwise operated using a computer, workstation, or other data processing equipment with a graphical user interface. The above-mentioned orthodontic state includes a series of tooth states that are progressively corrected to the target state. Each digital dental model includes a data set representing the geometric shapes of several teeth and the positional relationships between the teeth.

[0059] In some examples, a plaster dental model is first made based on the patient's current dental condition, or the condition of the teeth and surrounding tissues (such as gums and facial soft tissues), and then the plaster dental model is scanned to generate a digital dental model representing the original state of the patient's teeth. Of course, it is also possible to directly obtain an image of the teeth or the teeth and surrounding tissues through optical scanning, three-dimensional photography, three-dimensional videography, or medical CT (Computed Tomography) scanning, and obtain a digital dental model representing the original state of the teeth after computer processing. Then, based on the digital dental model representing the original state of the teeth and the correction target for the patient's teeth, a computing and processing device forms a series of digital dental models that gradually achieve the correction target according to the digital dental model of the original state and the correction target, and each digital dental model represents one of the correction states.

[0060] Of course, after obtaining a digital jaw model representing the original state of the teeth, in some examples, a digital jaw model representing the target dentition layout can also be obtained based on the correction goal. Then, based on the digital jaw model representing the original state of the teeth and the digital jaw model representing the target dentition layout, a series of intermediate digital jaw models that gradually progress from the original state to the correction goal can be obtained. This application does not limit the method for obtaining the digital jaw model.

[0061] FIG2 shows a schematic diagram of a digital dental model, wherein the digital dental model includes a cusp part 31, a crown part 32 and a periodontal part 33. As can be seen from the figure, there is an undercut area 34 between every two adjacent teeth in the digital dental model. And the cross-section of the undercut area 34 along the mesiodistal direction is generally trapezoidal or triangular. Due to the existence of the undercut area 34, if a physical tooth model is directly generated using the digital dental model and an orthodontic appliance is produced based on the physical tooth model by lamination, the orthodontic appliance is difficult to demold and removed, and the orthodontic appliance is likely to cause discomfort to the patient and difficulty in wearing and removing. Therefore, it is necessary to fill the undercut area 34 of the digital dental model to avoid affecting the quality of the physical tooth model due to insufficient filling of the undercut area 34.

[0062] In step S102 , a control point generation model with a radius of R is generated for each undercut area.

[0063] In order to fully fill the undercut area, the present application considers that the undercut area after filling should be such that a sphere with a preset radius of R cannot enter the filled undercut area. Therefore, in some embodiments of the present application, the control point generation model is a spherical model or a circular model. When the control point generation model is a spherical model or a circular model, since the shapes of the sphere and the circle are arc-symmetrical objects, if they are determined not to be stuck, other shapes of similar size will not be stuck either. Therefore, the filling of the undercut area of ​​the digital dental model implemented by the control point generation model defined by the spherical model or the circular model can well ensure that the orthodontic appliance obtained by the model after the undercut is filled and subjected to the treatment of lamination and pressing will not be stuck in the undercut area. At the same time, the sphere or circle as a model can be more conveniently described, and the movement of the model can also be more conveniently described, thereby better performing the undercut filling.

[0064] In step S103, the control point generation model is moved so that the control point generation model is tangent to the buccal surface and the lingual surface of the two adjacent teeth at the same time, and a set of control points for each tooth is obtained based on the tangent points between the control point generation model and each tooth, wherein at least two tangent points corresponding to the first position and the second position are obtained on the buccal surface and the lingual surface of each tooth, respectively, and the second position is located above the first position.

[0065] In this embodiment, the first position is located between the gingival end and the midpoint of the first height, wherein the occlusal surface of each tooth has a first height with respect to the gingival end, and the second position is located between the occlusal surface and the midpoint of the first height. Taking the first position and the second position on the buccal surface as an example, the first height corresponds to the length of the buccal surface in the direction from the occlusal surface to the gingival end, and the first position is set close to the gingival end. The first position being located between the gingival end of the tooth and the midpoint of the first height means that the first position is located in the lower half of the buccal surface close to the gingival end, that is, the position of the first position will not exceed the midline of the buccal surface, which extends in the mesiodistal direction; the second position being located between the occlusal surface of the tooth and the midpoint of the first height means that the second position is located in the upper half of the buccal surface close to the occlusal surface, that is, the position of the second position will not be lower than the midline of the buccal surface. Taking the first position and the second position of the buccal surface of tooth No. 1 in the digital dental model as an example, as shown in Figure 3, the first height corresponds to the length of the buccal side surface A1 in the direction from the occlusal surface A0 to the gingival end A2. The first position is set close to the gingival end A2. The first position is located between the gingival end A2 of the tooth and the midpoint O of the first height, which means that the first position S0 is located in the lower half of the buccal side surface A1 close to the gingival end A2, that is, the position of the first position S0 will not exceed the midline L of the buccal side surface A1, and the midline L extends in the mesiodistal direction; the second position S1 is located between the occlusal surface of the tooth and the midpoint of the first height, which means that the second position S1 is located in the upper half of the buccal side surface A1 close to the occlusal surface A0, that is, the position of the second position S1 will not be lower than the midline L of the buccal side surface A1.

[0066] In some examples, the control point generation model is a spherical model with a radius R, and the control point generation model is moved so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of two adjacent teeth, including:

[0067] The spherical model is initially tangent to the buccal surface or lingual surface of two adjacent teeth at the same time; in some examples, the spherical model with a radius of R can be initially placed between two adjacent teeth and contact and be tangent to the two tooth models at the same time. The initial position of the spherical model can be the buccal side of the two adjacent teeth or the lingual side of the two adjacent teeth. This embodiment does not impose any restrictions, as long as it satisfies the requirement of contact and tangent to the two adjacent teeth at the same time. As shown in Figure 4, the spherical model 400 is initially contacted and tangent to the two adjacent teeth (401 and 402) at the same time.

[0068] The spherical model 400 is moved, and is kept tangent to two adjacent teeth at all times during the movement. As shown in FIG5 , during the movement, a trajectory line formed by the spherical model being tangent to each tooth is obtained.

[0069] In some examples, the spherical model is moved so that it is always tangent to two adjacent teeth during the movement, and at least several tangent points should be formed between the first position and the second position of the buccal surface and / or the lingual surface of each tooth. Generally speaking, if each tooth has only two tangent points on the buccal surface and the lingual surface as control points, that is, there are only four undercut control points on each tooth, the number of undercut control points will be too small, which will make the undercut boundary formed abrupt and not smooth, which is not conducive to filling the undercut area. Therefore, in this embodiment, by moving the spherical model so that it is always tangent to two adjacent teeth during the movement, at least one tangent point is formed between the first position and the second position of the buccal surface and / or the lingual surface of each tooth, thereby increasing the number of undercut control points and forming a smoother undercut boundary, which is conducive to filling the undercut area. Here, there are at least several tangent points between the first position and the second position of the buccal surface and / or the lingual surface of each tooth, which means that there are at least several tangent points between the first position and the second position of the buccal surface of each tooth, and / or there are at least several tangent points between the first position and the second position of the buccal surface of each tooth.

[0070] In some examples, in order to form at least one tangent point between the first position and the second position of the buccal surface and / or the lingual surface of each tooth, the spherical model can be rolled along the crown portion of the two adjacent teeth between the first position of the buccal surface and the first position of the lingual surface of the two adjacent teeth. During the rolling process, the spherical model always remains tangent to the two adjacent teeth at the same time, and the tangent point of the spherical model and each tooth forms a trajectory line on the corresponding tooth surface, wherein the spherical model can be rolled from the first position of the buccal surface of the two adjacent teeth to the first position of the lingual surface, or from the first position of the lingual surface of the two adjacent teeth to the first position of the buccal surface, or from a certain position in the middle to the first position of the buccal / or lingual surface, and then rolled from the first position of the buccal / or lingual surface to the first position of the lingual / or buccal surface.

[0071] In some examples, in order to form at least one tangent point between the first position and the second position of the buccal surface and / or the lingual surface of each tooth, the spherical model can be rolled at least 360 degrees around the central axis of two adjacent teeth, wherein the central axis is the line connecting the reference centers of the two adjacent teeth. As mentioned above, the reference center of each tooth model can be one of the center of gravity, geometric center, and center of mass of the tooth model, or it can be the average of all vertices of each tooth model or the weighted average of the area of ​​the vertex and its neighborhood ring, etc. During the process of rolling 360 degrees around the central axis of two adjacent teeth, the spherical model always remains tangent to the two adjacent teeth at the same time. The tangent points of the spherical model and each tooth form a trajectory line when the spherical model moves. After the spherical model rolls 360 degrees around the central axis of two adjacent teeth, the trajectory line on each tooth model can form a closed curve.

[0072] When the spherical model is kept tangent to the two adjacent teeth and rolled around the central axis of the two adjacent teeth between the first position on the buccal surface and the first position on the lingual surface of the two adjacent teeth, or rolled 360 degrees around the central axis of the two adjacent teeth, all the tangent points can be selected as control points, or corresponding point pairs can be sampled on the trajectory line of the two adjacent teeth to obtain a set of control points on each tooth, wherein the sampling rule should make the sampling points as evenly distributed as possible on the trajectory line.

[0073] As shown in FIG2 , there is an undercut area between each two adjacent teeth in the digital dental model. For each undercut area, the control point generation model has a different radius R. In some examples, the radius R can be obtained based on the distance between the two adjacent teeth. In some examples, the distance between the two adjacent teeth is obtained by the following steps:

[0074] Obtain the intersection points of the reference center lines of two adjacent teeth and the two teeth;

[0075] Calculate the distances between the two intersection points and the reference centers of the teeth where they are located;

[0076] The spacing value between the two adjacent teeth is obtained based on the distance between the reference centers of the two adjacent teeth and the distances between the two intersection points and the reference centers of the teeth where they are located.

[0077] As shown in Figure 6, for adjacent teeth 100 and 200, the spacing between teeth 100 and 200 is calculated. The respective tooth reference centers O1 and O2 are selected. The reference center can be any one of the center of gravity, geometric center, and centroid of the tooth, or the mean of all vertices of each tooth model or the weighted mean of the area of ​​the vertex and its neighborhood. The reference centers of the two adjacent teeth are connected to obtain the central axis O1O2. The central axis O1O2 intersects with teeth 100 and 200 at two points q1 and q2, respectively. The spacing between teeth 100 and 200 is calculated as:

[0078] d=||O1O2||-||O1q1||-||O2q2||.

[0079] After the distance d between two adjacent teeth is obtained, the radius R of the spherical model corresponding to the undercut area between the two adjacent teeth can be obtained based on the distance d. The radius R of the spherical model is:

[0080] R = η × d.

[0081] Among them, η>1, its specific value depends on the wax filling requirements, and generally the value of η is 1.1-2, for example, η=1.5.

[0082] It should be noted that the size of the radius R of the spherical model can control the size of the undercut model. When the radius R increases, the undercuts filled increase, and when the radius R decreases, the undercuts filled decrease. The designer can control the undercuts filled by designing η.

[0083] It can be seen that the present application utilizes a spherical model to maintain tangency with two adjacent teeth at the same time and rolls 360 degrees around the central axis of the two adjacent teeth, thereby obtaining the tangency point on each tooth as a control point, so that the spherical model cannot enter the concave area between the two adjacent teeth from all angles, so that the concave area can be fully filled, thereby improving the effect of the undercut filling; in addition, the present application designs the radius R of the spherical model according to the distance between the two adjacent teeth, so that the undercut area to be filled can be automatically adjusted according to the different distances, and the filling of the undercut area is more reasonable.

[0084] Of course, the radius R of the spherical model can also be pre-set by the designer, that is, the designer can give the corresponding radius R of the spherical model by manually observing the distance between two adjacent teeth, wherein a different radius R can be preset for the undercut area between each two adjacent teeth, or a unified preset radius R can be given to all undercut areas based on an overall observation of all undercut areas of the digital tooth model. In some examples, the unified preset radius R can be between 3mm and 6mm. In some examples, when there is no missing tooth gap between two adjacent teeth, the radius R of the control point generation model is set to 3mm-6mm; when there is a missing tooth gap between two adjacent teeth, the radius R of the control point generation model can be obtained based on the distance between the two adjacent teeth.

[0085] In some examples, the control point generation model may also be a circular model with a radius of R. For each undercut area, a control point generation model with a radius of R is generated, including:

[0086] generating a plurality of cutting planes based on the central axis of two adjacent teeth, where the central axis is a line connecting the reference centers of the two adjacent teeth;

[0087] Generate circular models on each cutting plane.

[0088] Accordingly, the control point generation model is moved so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth, including:

[0089] generating a plurality of cutting planes based on the central axis of two adjacent teeth, where the central axis is a line connecting the reference centers of the two adjacent teeth;

[0090] Obtaining a tooth cross-sectional profile of each of two adjacent teeth using each cutting plane;

[0091] Generate a circular model on each cutting plane, and move the circular model so that the circular model is tangent to the tooth cross-sectional contours of the two teeth at the same time;

[0092] All the tangent points between the tooth cross-section contour of each tooth and the corresponding circular model are used as a set of control points.

[0093] As mentioned above, the central axis is the line connecting the reference centers of two adjacent teeth, wherein the reference center of each tooth model can be any one of the center of gravity, geometric center, and centroid of the tooth model, or it can be the mean of all vertices of each tooth model or the weighted mean of the area of ​​the vertex and its neighboring ring, etc. Taking the center line of two adjacent teeth connected to form the central axis O1O2 as an example, as shown in Figure 7, a cutting plane s is generated through the central axis. The normal of the cutting plane s is perpendicular to the central axis O1O2, and its direction can be any direction. In some examples, a coordinate system can be established based on the two adjacent teeth, and the coordinate origin is located on the central axis O1O2. The central axis O1O2 is used as the first axis, such as the X-axis. The third axis, namely the Z-axis, is obtained by passing through the coordinate origin along the buccal-lingual direction perpendicular to the central axis O1O2. The second axis, namely the Y-axis, is obtained by cross-producting the X-axis and the Z-axis. The normal direction of the cutting plane can be the direction of the cross product of the Y-axis and the central axis O1O2, namely the Z-axis direction, but the present application is not limited to this. After generating the cutting plane, the cutting plane can be used to intercept the models of two adjacent teeth to obtain the tooth cross-sectional contours of the two adjacent teeth.

[0094] A circular model with a radius of R is generated on the cutting plane, and then the circular model is moved so that the boundary of the circular model is in contact and tangent to the tooth cross-sectional contours of the two adjacent tooth models at the same time. As shown in FIG8 , the circular model and the tooth cross-sectional contours of the two adjacent teeth (tooth 100 and tooth 200) respectively obtain tangent points a1 and b1 as well as c1 and d1, wherein the tangent points a1 and b1 as well as the tangent points c1 and d1 are respectively located on both sides of the central axis O1O2.

[0095] As shown in Figure 9, the cutting plane s is rotated around the central axis O1O2, and the angle of each rotation is a. For example, the cutting plane is rotated around the central axis O1O2 by an angle a for the first time. The rotated cutting plane will re-intersect with the two adjacent teeth to obtain a new tooth cross-sectional contour. Then, a circular model with the same radius R is re-generated on the cutting plane. The circular model is moved so that the boundary of the circular model is in contact with and tangent to the tooth cross-sectional contours of the two adjacent tooth models at the same time, and the tangent points a2 and b2, as well as the tangent points c2 and d2 with the new tooth cross-sectional contour are obtained. ; Continue to rotate the cutting plane around the central axis by an angle a, ..., and so on. After rotating by an angle a in sequence, the tangent points a1, a2, a3... and b1, b2, b3... and c1, c2, c3... and d1, d2, d3... are obtained in sequence, among which the tangent points a1, a2, a3... and c1, c2, c3... are located on the same tooth and serve as a set of control points on the tooth. The tangent points b1, b2, b3... and d1, d2, d3... are located on another tooth and serve as a set of control points on the other tooth.

[0096] In some examples, the angle of rotation of the cutting plane around the central axis should be such that there is at least one tangent point between the first position and the second position of the buccal surface and / or the lingual surface of each tooth, that is, there is at least one tangent point between the first position and the second position of the buccal surface of each tooth, and / or, there is at least one tangent point between the first position and the second position of the lingual surface of each tooth. In other words, when each tooth has only two tangent points on the buccal surface and the lingual surface as control points, that is, there are only four control points on each tooth, if the number of undercut control points is too small, the undercut boundary formed will be abrupt and not smooth enough, which is not conducive to filling the undercut area. Therefore, the present application increases the number of undercut control points by forming at least one tangent point between the first position and the second position of the buccal surface and the lingual surface of each tooth, so that the undercut boundary formed is smoother, which is conducive to filling the undercut area.

[0097] In some examples, the preset angles of rotation of each cutting plane may be different. For example, the cutting plane is rotated 45 degrees for the first time, and the 45-degree-rotated cutting plane intersects with two adjacent teeth to obtain the tooth cross-sectional contour and the tangent point. Then, the cutting plane can be rotated 30 degrees for the second time. Of course, it is also possible that only one or several of the rotation angles are different, for example, only the second rotation is 30 degrees, while the other rotations are 45 degrees. This application does not impose any restrictions on this. However, in order to fully fill the concave area, the number of selected control points should not be too small and the distance between the control points should not be too large. The angle of each rotation should not be too large. Selecting too many control points will also result in a large amount of calculation. Therefore, in some examples, the angle of each rotation of the cutting plane is preferably between 20 and 60 degrees, for example, 45 degrees. In some examples, the angle of rotation of the cutting plane each time can be the same, that is, the angles between adjacent cutting planes are the same. By rotating the cutting plane by the same angle each time, the obtained tangent points can be distributed more evenly on the tooth surface, thereby making the control points obtained based on each tangent point more uniform. The resulting undercut boundary is smoother and the undercut effect is better.

[0098] In order to further fully fill the undercut area, the cutting plane is rotated at least 180 degrees around the central axis. At this time, the effect of the undercut is roughly equivalent to using a spherical model to roll 360 degrees around the central axis of two adjacent teeth. This can prevent the circle with a radius of R from entering the undercut area between the two adjacent teeth from any angle, so that the undercut area can be fully filled, thereby improving the effect of the undercut filling.

[0099] In addition, for the design of the radius R in the circular model, reference may be made to the design of the radius R in the aforementioned spherical model, which will not be described in detail here.

[0100] In step S104, each group of control points is connected according to a set order to obtain an undercut control boundary for forming an undercut model.

[0101] For two adjacent teeth, by connecting each group of control points according to a set order, the undercut boundaries of the undercut areas between the two adjacent teeth are obtained respectively, wherein the set order can select one of the control points, and then connect the adjacent control points in a counterclockwise order to obtain the corresponding undercut control boundary. Of course, the set order is not limited to the counterclockwise order, and can also be a clockwise order, or according to the order in which the corresponding control points are obtained. For example, for the case where a spherical model is rolled on the buccal and lingual sides of two adjacent teeth for one circle to obtain the simultaneously tangent points as control points, the control points after the inward movement can be sorted according to the order of the trajectory lines obtained by the rolling of the spherical model, and the control points are sequentially adjacent according to the sorting results to obtain the undercut control boundary. For example, the spherical model rolls one circle between the adjacent teeth No. 1 and No. 2, and the control point set a1, a2, a3... located on tooth No. 1 is obtained in sequence, and then the control points a1, a2, a3... in the point set are connected in sequence to obtain the undercut control boundary on tooth No. 1.

[0102] After the undercut control boundary is obtained, a boundary control surface of the undercut model corresponding to the undercut area between the two adjacent teeth can be formed.

[0103] In the case where there are many control points obtained by rolling a spherical model to form a trajectory line, the concave control boundary formed by many control points will be smoother, and the obtained concave model effect will be better. However, if there are too few control points forming the concave control boundary, the obtained concave control boundary will not be smooth enough, and the resulting boundary control surface will not be smooth enough. In some examples, smoothing processing can use Laplace smoothing processing, that is, by inserting multiple interpolation points near the line connecting the control points forming the concave control boundary, the concave control boundary changes more smoothly, which is convenient for filling the concave area.

[0104] In step S105, the two undercut control boundaries are connected to each other to generate a corresponding digital undercut model.

[0105] After obtaining the two undercut control boundaries, the two undercut control boundaries are connected to form a digital undercut mesh. For example, by connecting the control points at corresponding positions on the undercut control boundaries, a digital undercut model corresponding to the undercut region can be generated.

[0106] Of course, in order to increase the smoothness of the undercut model, in some examples, the contour surface formed between the two sets of control points can also be subjected to patch refinement and smoothing. For example, a number of point sets can be inserted between the corresponding points of the undercut control boundaries of two adjacent teeth, and then a triangular patch is constructed on this basis to generate a digital undercut model, and the undercut model is smoothed, as shown in Figure 10. For example, for the control points a1 and a2 on tooth No. 1 and the control points b1 and b2 on tooth No. 2, in order to perform patch refinement and smoothing on the contour surface, a preset number of interpolation points can be inserted between a1 and b1, and a preset number of interpolation points can be inserted between a2 and b2. The interpolation points can be inserted at equal distances. These interpolation points make the contour line formed between the two sets of control points change more smoothly, so that the resulting digital undercut model is smoother, which is conducive to filling the undercut area.

[0107] In step S106, the digital dental model is filled according to the digital undercut model.

[0108] After the digital undercut model is generated, it can be used to fill the corresponding undercut area in the digital tooth model. The digital undercut model may overlap with the tooth model in the digital tooth model. A Boolean operation can be performed on the two models to obtain the digital tooth model with the undercut filled in.

[0109] Example 2

[0110] The flowchart of the method for filling undercuts in a digital dental model of this embodiment is shown in FIG11 . In this embodiment, a method for filling undercuts in a digital dental model comprises the following steps:

[0111] Step S201: obtaining a digital dental model, wherein the digital dental model has an undercut area between two adjacent teeth.

[0112] Step S202: For each undercut area, generate a control point generation model with a radius of R.

[0113] Step S203, move the control point generation model so that the control point generation model is tangent to the buccal surface and the lingual surface of the two adjacent teeth at the same time, wherein at least two tangent points corresponding to the first position and the second position are respectively obtained on the buccal surface and the lingual surface of each tooth, and the second position is located above the first position, and the tangent points between the control point generation model and each tooth are obtained, and the tangent points between the control point generation model and each tooth are offset toward the inside of the tooth to obtain a group of control points.

[0114] Step S204 : Connect each group of control points according to a set order to obtain an undercut control boundary for forming an undercut model.

[0115] Step S205: Connect the two undercut control boundaries to generate a corresponding digital undercut model.

[0116] Step S206: Filling the digital dental model according to the digital undercut model.

[0117] Since steps S201 , S202 , S204 - S206 are the same as steps S101 , S102 , S104 - S106 in the aforementioned embodiment, they are not described again here. This embodiment focuses on step S203 .

[0118] If the tangent points between the control point generation model and the two adjacent teeth are directly used as control points, since the tooth surface is often uneven and may be bumpy, the undercut boundary formed by these control points may be located outside the corresponding tooth model. After the undercut model formed in this way is filled into the three-dimensional tooth model, there may be a gap between the undercut model and the three-dimensional tooth model, which will still cause problems such as difficulty in demolding, discomfort for patients when wearing, and inconvenience in removing. Therefore, to solve this problem, in this embodiment, the tangent points are not directly used as control points, but each tangent point is offset to the inside of the tooth where it is located and used as the control point of the undercut boundary. In order to prevent there from being a gap between the undercut model and the three-dimensional tooth model, the offset control points should make the line between each adjacent control point located inside the tooth where it is located, that is, there is no intersection with the tooth where it is located.

[0119] When offsetting each tangent point toward the inside of the tooth, it is necessary to consider the offset direction and offset amount of each tangent point. The offset direction and offset amount of each tangent point need to consider both the ability to quickly move to the inside of the tooth and the minimization of the filled undercut area. In some embodiments, the offset direction of each tangent point can be based on the central axis of the two adjacent teeth. As shown in FIG12 , there is an undercut area between the two adjacent teeth 100 and 200. Taking the tangent point a1 on the tooth 100 (the tangent point b1 on the tooth 200 shown in the figure corresponds to the tangent point a1, and the subsequent figures are similar to this, and the tangent point b1 will not be described in detail) as an example, the tangent point a1 is offset toward the inside of the tooth. The angle between the internal offset direction s1 of the tooth and the central axis of the two adjacent teeth is β (s0 in the figure (i.e., the side where the angle β is not marked in the figure) is parallel to the central axis O1O2, i.e., it represents the direction of the central axis), wherein 0≤β≤90°, the tangent point a1 is offset to a1' along the offset direction s1 toward the inside of the tooth 100, and the corresponding control point a1' is obtained, wherein the central axis O1O2 is the line connecting the reference centers of the two adjacent teeth. This application limits the angle between the offset direction of each tangent point toward the inside of the tooth and the central axis of the two adjacent teeth to 0 to 90°, so that the tangent point can be quickly moved to the inside of the tooth model of the tooth.

[0120] Considering that the more the offset direction of the tangent point deviates from the central axis, the greater the change in the distance between the offset control point and the central axis and the distance between the original tangent point and the central axis will be, this will affect the gingival-mandibular height of the formed digital undercut model, thereby affecting the filling amount of the undercut area. Therefore, in some examples, the angle between the offset direction of each tangent point toward the inside of the tooth where it is located and the central axis of the two adjacent teeth is 0≤β≤30°. This application limits the angle between the offset direction of each tangent point and the central axis to 0° to 90°, so as to try to ensure the gingival-mandibular height of the final digital undercut model and the final filling amount of the undercut area.

[0121] In some examples, in order to ensure the final filling amount of the undercut area as much as possible, it is necessary to design the offset of each tangent point along the offset direction s1. For example, the offset of each tangent point to the inside of the tooth should make the difference between the distance between the offset control point and the central axis of the two adjacent teeth and the distance between the tangent point and the central axis of the two adjacent teeth within the set threshold. As shown in Figure 13, the tangent point a1 is offset toward the inside of the tooth along the offset direction s1. Assuming that the angle between it and the central axis O1O2 is β, the corresponding control point a1' is obtained after the tangent point a1 is offset by a distance S. In order to ensure that the gingival and maxillary height of the digital undercut model obtained based on the control point a1' does not change too much compared with the gingival and maxillary height of the digital undercut model obtained directly based on the tangent point a1, the difference between the distance d1 between the offset control point a1' and the central axis O1O2 and the distance d2 between the tangent point a1 and the central axis O1O2 is limited to within the set threshold T, that is:

[0122] |d1-d2|≤T,

[0123] Wherein, |d1-d2|=S×sinβ, and the set threshold T can be set by designers based on experience. For example, in this embodiment, the set threshold T is 0.5 mm to 2 mm.

[0124] If the tangent point is directly offset inward along the central axis of the two adjacent teeth, the distance between the control point and the central axis after the inward shift remains unchanged from the distance between the tangent point and the central axis before the inward shift. The resulting gingival and maxillary height of the digital undercut model is closer to the gingival and maxillary height of the digital undercut model directly based on the tangent point, thus ensuring that the undercut area is fully filled. Therefore, in some examples, at least one tangent point is offset inward along the central axis of the two adjacent teeth. As shown in Figure 14, in some examples, each tangent point can be offset inward along the central axis of the two adjacent teeth (s1 in Figure 14 generally refers to the offset direction of the tangent point on the tooth, rather than a single, specific direction). On this basis, it is sufficient to ensure that the tangent point is located inward of the tooth after the offset. In this case, the offset of the tangent point should generally not exceed the maximum distance D of the tangent point along the central axis on the tooth. The maximum distance D is the distance between the tangent point and another intersection point of a line passing through the tangent point and parallel to the central axis and the tooth. Of course, too large an offset may cause the control point after the offset to be located at or adjacent to the side of the tooth away from the undercut area, which may cause the undercut boundary formed by the control point after the offset to still fall outside the tooth. Therefore, in order to make the undercut boundary formed by the inward-moved control point located inside the tooth, the offset of the tangent point is preferably not more than 1 / 2 of the maximum distance D of the tangent point on the tooth along the central axis. In some examples, the offset of the tangent point can be selected to be 0.5mm to 3mm, for example 1mm, so that the tangent point can enter the tooth more quickly without passing through the tooth and being located outside the tooth.

[0125] In some examples, the offset direction of each tangent point can also be based on the normal direction of the tangent point on the tooth surface. As shown in Figure 15, the offset direction s1 of each tangent point toward the inside of the tooth is the same as the normal direction of the tangent point on the tooth surface. The angle is γ, where 0°≤γ<90°. In some examples, if γ=0°, at this time, at least one tangent point is offset toward the inside of the tooth along the normal direction of the tangent point on the tooth surface, which means that each tangent point is offset toward the inside of the tooth along the normal direction of the tooth surface. The present application can also enable the tangent point to be quickly moved to the inside of the tooth model of the tooth by limiting the offset direction of each tangent point toward the inside of the tooth and the normal direction of the tangent point on the tooth surface to 0° to 90° (not 90°).

[0126] As mentioned above, generally speaking, the more the offset direction of the tangent point deviates from the central axis, the greater the change in the distance between the offset control point and the central axis and the distance between the original tangent point and the central axis, thereby affecting the filling amount of the formed undercut model. Therefore, in order to reduce the change in the distance relative to the central axis after the tangent point moves inward, the angle between the offset direction of each tangent point to the inside of the tooth and the normal direction of the tangent point on the tooth surface is less than or equal to the normal direction of the tangent point on the tooth surface. The angle between the center axis of the two adjacent teeth is shown in Figures 16 and 17. a1 is the tangent point on the tooth 100, and its normal The included angle between the center axis direction O1O2 and the offset direction s1 is θ. The angle should be smaller than γ.

[0127] Similarly, to ensure adequate filling of the undercut area, the offset in this offset direction also needs to be designed. Similar to the previous example, the offset of each tangent point toward the interior of the tooth where it is located should ensure that the difference between the distance between the offset control point and the central axis of the two adjacent teeth and the distance between the tangent point and the central axis of the two adjacent teeth is within a set threshold. Since the design of the offset has been detailed in the previous embodiment, it will not be repeated here.

[0128] In the present application, to ensure that the undercut area is fully filled, the control points after offset should be such that the line between adjacent control points is located inside the tooth, that is, the line between adjacent control points does not intersect with the tooth.

[0129] Therefore, in some examples, each set of tangent points is offset toward the inside of the tooth to obtain a corresponding set of control points, including:

[0130] Move each tangent point along the corresponding offset direction toward the inside of the tooth by the first step length;

[0131] Check in sequence whether there are intersections between the lines connecting the adjacent tangent point pairs and the surface of the tooth digital model;

[0132] If there is no intersection, continue to detect the next adjacent tangent point pair. If there is an intersection, continue to move the adjacent tangent point pair along the corresponding offset direction by the first step length until the line between the adjacent tangent point pairs and the surface of the digitized dental model do not produce an intersection, and then continue to detect the next adjacent tangent point pair.

[0133] For example, for two sets of tangent points obtained on two adjacent teeth, such as a set of tangent points a1, a2, a3, ..., a on tooth 1 n And a group of tangent points b1, b2, b3, ..., bn on tooth 2 are moved inward respectively. For example, a group of tangent points a1, a2, a3, ..., an on tooth 1 are moved inward respectively. n, detect adjacent tangent point pairs in sequence, for example, first detect the point pair (a1, a2), and move a1 and a2 along the corresponding offset direction (for example, the offset direction is the central axis direction) toward the inside of the tooth by the first step length x to obtain a′1 and a′2. The first step length x can be preset by the designer based on experience, for example, 0.5mm≤x≤2mm. Assume that the first step length is set to 1mm in this embodiment, and then detect whether the line connecting a′1a′2 has an intersection with the tooth model No. 1. If there is no intersection, it means that the adjacent tangent point pair can be used as a control point, and continue to detect the next adjacent tangent point pair (a2, a3) until a is completed. n Detection of the line connecting a1; if there is an intersection, the adjacent tangent point pair (a′1, a′2) is moved along the central axis based on the first step, and the line connecting the inward-moved tangent points is detected again to see if there is an intersection with the tooth model 1, until the line connecting the inward-moved tangent points does not intersect with the tooth model 1, and then the next adjacent tangent point pair (a2, a3) is detected until a is completed. n After the above-mentioned tangent point inward shift detection, the lines between all adjacent tangent points fall inside the teeth. There will be no gap between the undercut model obtained by using it as a control point and the tooth model, thereby making the undercut area more fully filled.

[0134] Since teeth have irregular shapes with uneven surfaces, when the tangent point on the surface of the tooth model is moved inward toward the tooth by the first step length, the tangent point may move outside the tooth. For example, in the case of a molar, the occlusal surface is concave and dentate. When the tangent point is located at the mesio-buccal cusp, it may move outside the tooth when it is offset inward along the central axis by the first step length. This situation requires special handling. In some examples, when the adjacent tangent point pair is continued to be moved by the first step length in the corresponding offset direction, if the adjacent tangent point pair after the first step length has a tangent point located outside the corresponding tooth, the adjacent tangent point pair is moved back to its original position, the first step length is reduced as the second step length, and the adjacent tangent point pair is continued to be moved by the second step length. That is to say, when the tangent point moves outside the tooth, both tangent points are restored and the pair of tangent points is moved again with a reduced second step length until the line between the two tangent points no longer intersects with the tooth. This situation applies to both the situation where both tangent points move outside the tooth after being moved inward with the first step length, and the situation where only one tangent point moves outside the tooth after being moved inward with the first step length. In some examples, if only one tangent point in the adjacent tangent point pair is located outside the corresponding tooth after moving the first step length, it is also possible to move only the tangent point that has moved outside the tooth back to its original position, reduce the first step length as the second step length, and move the tangent point inward again with the second step length until the line between the two tangent point pairs no longer intersects with the tooth.

[0135] In this embodiment, after the digital undercut model is generated, the generated digital undercut model can be filled into the corresponding undercut area in the digital dental model. The digital undercut model may partially overlap with the tooth model in the digital dental model. A Boolean operation can be performed on the two models to obtain a digital tooth model with the undercut filled, as shown in FIG18 .

[0136] Example 3:

[0137] As shown in FIG19 , another embodiment of the present application further provides a method for manufacturing a dental instrument, comprising:

[0138] Step S301 : designing a digital dental model for gradually adjusting teeth from a first layout to a second layout.

[0139] As previously mentioned, a plaster dental model is first made based on the patient's current dental condition, or the condition of the teeth and surrounding tissues (such as gums and facial soft tissues). This plaster dental model is then scanned to generate a digital dental model representing the original state of the patient's teeth. Of course, an image of the teeth or the teeth and surrounding tissues can also be directly obtained through optical scanning, 3D photography, 3D videography, or medical CT scanning, and then processed by a computer to obtain a digital dental model representing the original state of the teeth. Then, based on the digital dental model representing the patient's original state and the treatment goal for the patient's teeth, a computing device generates a series of digital dental models that gradually achieve the treatment goal according to the digital dental model of the original state and the treatment goal. Each digital dental model represents one of the treatment states.

[0140] Step S302: filling the undercut of the digital dental model according to the undercut filling method of each of the aforementioned embodiments.

[0141] Since the filling of undercuts in the digital dental model has been described in detail in the aforementioned embodiments, it will not be repeated here.

[0142] Step S303: manufacturing a physical tooth model based on the digital jaw model after the undercut is filled.

[0143] In some cases, physical tooth models can be created using rapid prototyping. Rapid prototyping technologies can be categorized into the following typical prototyping processes: Stereo lithography apparatus (SLA), laminated object manufacturing (LOM), selective laser sintering (SLS), fused deposition modeling (FDM), and three-dimensional printing (3DP). Currently, the predominant prototyping materials used are organic polymers, such as photocurable resins, nylon, and wax. Among them, laser rapid prototyping (SLA) is a method of forming by using laser to irradiate light-curing resin point by point, inducing chemical changes in the material to solidify, while layered entity manufacturing (LOM) is a method of cutting foil (paper, ceramic foil, metal foil, etc.) by laser. The foils are bonded together by hot melt adhesive under the pressure and heat transfer of hot rollers, and are stacked layer by layer to form; selective laser sintering (SLS) is a method of using laser to irradiate powder material point by point to melt the material powder, or to melt the solid adhesive coated on the outside of the powder material to achieve material connection and formation, while fused deposition manufacturing (FDM) is a method of continuously feeding thermoplastic forming material into a nozzle, heating it, melting it, and ejecting it, gradually accumulating and forming. Three-dimensional printing manufacturing (3DP) is a method of spraying molten material into accumulation and forming similar to inkjet printing, or spraying adhesive to bond powder material point by point.

[0144] In some cases, to create a physical tooth model, a computer-controlled laser scans the liquid resin point by point along the contours of each layered cross-section of the tooth model, based on the polymerization reaction of photosensitive resin. This causes the scanned thin layer of resin to polymerize, gradually forming a line from the points, ultimately forming a solidified cross-section of a thin layer of the physical tooth model. The unscanned resin remains in its original liquid state. Once a layer is solidified, the lifting table moves a distance equal to the thickness of the layer, and a new layer of liquid resin is applied to the surface of the previously solidified resin layer for another scan and solidification. The newly solidified layer firmly bonds to the previous layer, and this cycle repeats until the entire physical tooth model is completed.

[0145] Although the rapid prototyping process steps of the present application are described using the laser rapid prototyping SLA method as an example, the present application is not limited to the laser rapid prototyping SLA method, but other rapid prototyping methods can be applied to manufacture physical tooth models.

[0146] Step S304: manufacturing a shell-shaped dental appliance according to the physical tooth model.

[0147] In some examples, a dental appliance can be manufactured by pressing a transparent polymer material (e.g., an elastic polymer, such as polycarbonate) onto a physical tooth model using a thermoforming device and positive pressure lamination technology to form a shell. However, the method for manufacturing a shell-shaped dental appliance based on a physical tooth model in this application is not limited to thermoforming, and this application is not limited thereto.

[0148] Those skilled in the art will appreciate that the above embodiments are specific embodiments for implementing the present application, and that in actual applications, various changes may be made thereto in form and detail without departing from the spirit and scope of the present application.

Claims

1. A method for filling undercuts in a digital dental model, comprising the following steps: Acquiring a digital dental model, wherein the digital dental model has an undercut area between two adjacent teeth; For each undercut area, generate a control point model with a radius of R; The control point generation model is moved so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth, and a set of control points for each tooth is obtained according to the tangent points between the control point generation model and each tooth, wherein: Obtaining at least two tangent points corresponding to a first position and a second position on the buccal surface and the lingual surface of each tooth, respectively, wherein the second position is located above the first position; Connecting each group of control points according to a set order to obtain an undercut control boundary for forming an undercut model; connecting the two undercut control boundaries to generate a corresponding digitized undercut model; The digital dental model is filled according to the digital undercut model.

2. The method for filling undercuts in a digital dental model according to claim 1, wherein: The occlusal surface and the gingival end of each tooth have a first height, and the first position is located between the gingival end and the midpoint of the first height.

3. The method for filling undercuts in a digital dental model according to claim 2, wherein: The second position is located between the occlusal surface and a midpoint of the first height.

4. The method for filling undercuts of a digital dental model according to claim 1, wherein: The control point generation model is a spherical model, and the control point generation model is moved so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth. A set of control points for each tooth is obtained based on the tangent points between the control point generation model and each tooth, including: Initially and simultaneously bringing the spherical model into contact with the buccal or lingual surfaces of the two adjacent teeth; Moving the spherical model, keeping the spherical model always tangent to two adjacent teeth during the movement, and obtaining a trajectory line formed by the spherical model being tangent to each tooth; The corresponding point pairs are sampled on the trajectory lines of two adjacent teeth to obtain a set of control points on each tooth.

5. The method for filling undercuts in a digital dental model according to claim 4, wherein: The spherical model is moved so as to be kept tangent to two adjacent teeth at all times during the movement, so that at least one tangent point exists between the first position and the second position of the buccal surface and / or the lingual surface of each tooth.

6. The method for filling undercuts in a digital dental model according to claim 1, wherein: The control point generation model is a circular model generated from a plurality of cutting planes generated based on the central axis of the two adjacent teeth. The control point generation model is moved so that the control point generation model is simultaneously tangent to the buccal surface and the lingual surface of the two adjacent teeth. A set of control points for each tooth is obtained based on the tangent points between the control point generation model and each tooth, including: For each cutting plane generated based on the central axis of the two adjacent teeth, obtaining a tooth cross-sectional profile of each tooth in the two adjacent teeth using each cutting plane; Moving the circular model generated on the cutting plane so that the circular model is tangent to the tooth cross-sectional contours of the two teeth at the same time; The tangent points of all tooth cross-sectional contours of each tooth and the corresponding circular model are taken as a set of control points.

7. The method for filling undercuts in a digital dental model according to claim 6, wherein: The plurality of cutting planes generated based on the central axes of the two adjacent teeth include: generating a cutting plane based on the central axes of the two adjacent teeth, wherein the normal of the cutting plane is perpendicular to the central axes; The cutting plane is rotated around the central axis to obtain a plurality of cutting planes.

8. The method for filling undercuts in a digital dental model according to claim 7, wherein: The angle of rotation of the cutting plane around the central axis should be such that there is at least one tangent point between the first position and the second position on the buccal surface and the lingual surface of each tooth.

9. The method for filling undercuts in a digital dental model according to claim 1, wherein: The R is obtained based on the distance between the two adjacent teeth, and the distance between the two adjacent teeth is obtained by the following steps: Obtain the intersection points of the reference center lines of two adjacent teeth and the two teeth; Calculate the distances between the two intersection points and the reference centers of the teeth where they are located; The spacing value between the two adjacent teeth is obtained based on the distance between the reference centers of the two adjacent teeth and the distances between the two intersection points and the reference centers of the teeth where they are located.

10. The method for filling undercuts in a digital dental model according to any one of claims 1 to 9, wherein: The step of obtaining a set of control points for each tooth based on the tangent points between the control point generation model and each tooth comprises: Each group of control points is obtained by offsetting the tangent point between the control point generation model and each tooth toward the inside of the tooth.

11. The method for filling undercuts of a digital dental model according to claim 10, wherein: The offset of each tangent point toward the inside of the tooth should make the line between the tangent points located inside the tooth.

12. The method for filling undercuts in a digital dental model according to claim 11, wherein: The included angle between the offset direction of each tangent point toward the inside of the tooth and the normal direction of the tangent point on the tooth surface is [0°, 90°).

13. The method for filling undercuts of a digital dental model according to claim 12, wherein: The angle between the offset direction of each tangent point toward the inside of the tooth and the normal direction of the tangent point on the tooth surface is less than or equal to the angle between the normal direction of the tangent point on the tooth surface and the central axis direction of the two adjacent teeth.

14. The method for filling undercuts of a digital dental model according to claim 11, wherein: The included angle between the offset direction of each tangent point toward the inside of the tooth where it is located and the central axis of the two adjacent teeth is [0, 90°].

15. The method for filling undercuts in a digital dental model according to claim 14, wherein: At least one tangent point is offset toward the inside of the teeth along the central axis direction of the two adjacent teeth.

16. The method for filling undercuts in a digital dental model according to claim 11, wherein: The offset direction and amount of each tangent point toward the inside of the tooth should ensure that the difference between the distance between the offset control point and the central axis of the two adjacent teeth and the distance between the tangent point and the central axis of the two adjacent teeth is within a set threshold.

17. The method for filling undercuts in a digital dental model according to claim 11, wherein: The step of offsetting each set of tangent points toward the inside of the teeth to obtain a corresponding set of control points includes: Move each tangent point along the corresponding offset direction toward the inside of the tooth by the first step length; sequentially detecting whether there are intersections between the lines connecting the adjacent pairs of tangent points and the surface of the digital dental model; If there is no intersection, continue to detect the next adjacent tangent point pair. If there is an intersection, continue to move the adjacent tangent point pair along the corresponding offset direction toward the inside of the tooth until the line between the adjacent tangent point pairs does not intersect with the surface of the digitized dental model, and then continue to detect the next adjacent tangent point pair.

18. The method for filling undercuts in a digital dental model according to any one of claims 1 to 9, wherein: The step of connecting each group of control points according to a set order to obtain an undercut control boundary for forming an undercut model includes: Connecting each group of control points according to a set order to obtain the undercut control boundary, thereby forming a boundary surface of the undercut model; When the number of control points in each group is less than a preset value, the boundary surface is subjected to patch refinement and smoothing.

19. The method for filling undercuts in a digital dental model according to claim 18, wherein: The step of connecting the two undercut control boundaries to generate a corresponding digital undercut model includes: connecting the control points at corresponding positions of the two undercut control boundaries to form a virtual grid of the undercut model; The contour-forming surface between the two groups of control points is subjected to patch refinement and smoothing processing.

20. A method for manufacturing a dental instrument, comprising: Designing a digital dental model for gradually adjusting teeth from a first layout to a second layout; Filling the undercut of the digital dental model according to the undercut filling method according to any one of claims 1 to 19; Make a physical tooth model based on the digital dental model after undercut filling; The shell-shaped dental appliance is manufactured based on the digital dental model after filling.

Images