Patent Description:
One of the most time-consuming parts of designing well-fitting and comfortable dental appliances such as splints, nightguards, mouthguards, bleaching trays, aligners and surgical guides, is to ensure a spacing between the tooth margin and the appliance. On gypsum or stone models on which dental appliances such as splints are created, fissures and interproximal spaces need to be waxed as well to have a splint that can be both positioned and removed. This is normally a time consuming, manual process which can typically take up to <NUM>-<NUM> minutes.

For example, <CIT> and <CIT> disclose computer implemented methods of designing orthodontic appliances, such as aligners.

Providing a digital / computer implemented method of designing such dental appliances without the need for large amounts of manual labor is of great interest. In the following, such a method will be disclosed and, in particular a process that allows for improved appliance design.

The invention pertains to a computer implemented method for generating a model for creating a dental appliance on as defined in the appended claims <NUM> to <NUM>.

In one aspect there is disclosed a computer implemented method for generating a dental appliance or for generating a model for creating the dental appliance on, comprising:.

Accordingly, it is thus possible to create a representation of a dental appliance, or a model for creating the dental appliance on, where unwanted features such as sharp edges, undercuts etc. can be eliminated or ameliorated. In some cases, it may be advantageous to have more points in certain areas, such as near the margin between the teeth and the gingiva or above the occlusal surfaces of the molars, since this will allow for differential resolution of the resulting 3D digital surface representation. The defined value of the dilation may be set automatically or by the user. For example, a default value may be indicated depending upon which dental appliance is being generated. There may also be a graphical user interface, in which the user can set the dilation value, for example by inputting a value in mm, or moving a slider.

In some embodiments, distances to points outside the first 3D digital surface representation are given a positive value and points inside the first 3D digital surface representation are given a negative value or vice versa.

By defining the distance values in this way, it is always known which points are inside and which points are outside the surface in 3D space. This makes it possible to determine which points are inside and which points are outside the 3D digital surface. Other ways of defining the distances, such as offsetting the distance values by some factor, or similar, are also possible.

In some embodiments, each of the 3D digital surface representations are a mesh model.

In 3D modelling, it is possible to work with various graphical representations, such as voxels and meshes. In the case of working with surface representations, it may be preferred to work with meshes. This has numerous advantages. For example, the amount of data storage needed is lower for a mesh than for a voxel model, and therefore the processing power and time needed to work with a mesh model is, as a general rule, lower than for working with a voxel model.

According to the claimed invention, generating the modified 3D digital surface representation further comprises interpolating over the distances to the points from the surface of the first 3D digital surface representation.

It is advantageous to interpolate between the points, since this gives a more accurate modified 3D digital surface representation.

The number of points in 3D space around the first 3D digital surface representation are placed in a regular grid.

Placing a regular grid, i.e. a grid with evenly space points in three dimensions around the 3D digital surface representation makes a data structure that is easier to work with than if the points are randomly placed.

The method is particularly useful for dental appliances such as splints or nightguards where patient specific issues such as fissures, gaps in interproximal spaces and/or undercuts, need to be filled out for patient comfort and to achieve a splint design that can both be positioned and removed.

In some embodiments, dilation and erosion of the 3D digital surface representation of the one or more teeth minimizes concave features of the patient's molars to create space for liquid such as saliva between the splint or nightguard and the teeth of the patient.

By employing the morphological closing algorithm on the molars, the concave features of fissures on the occlusal side of the teeth will be smoothed out. Often, saliva which is not compressible, will sit in those fissures. If the splint or nightguard is designed without taking this into account, the fit of the splint to the patient's teeth may be compromised.

In some embodiments, the dental appliance is an aligner.

Clear aligner treatments are becoming more and more common as alternatives to regular braces for orthodontic treatment. The instant methods are particularly useful for designing aligners, since aligners are designed to have a tight fit against the patient's teeth, but also need to be comfortable to wear for extended periods of time.

In some embodiments, a plane or distance from the gingiva on each of the one or more teeth is defined, above which no dilation and erosion of the first 3D digital surface representation of the one or more teeth is performed.

The plane may for example be defined parallel but offset to the occlusal surface of the patient's teeth. Alternatively, the distance from the gingiva may be defined individually for each tooth, or collectively for all or a subset of the teeth. By having this boundary above which no dilation or erosion is performed, the occlusal surfaces in the resulting 3D digital representation will not be altered, which may be an advantage in aligner treatment, where it is important to control the forces working on the teeth accurately.

In some embodiments, the method further comprising:.

By automatically determining landmarks, such as cusps on the molars, the depth of the fissures or grooves in the occlusal surfaces can be determined. In this way, it is possible to restrict the morphological closing in these areas.

In some embodiments, the method further comprises generating a combined 3D digital surface representation by combining the first 3D digital surface representation and the resulting 3D digital surface representation.

The combination of the first and resulting 3D digital surface representations may be accomplished for example by using a Boolean addition operator on all or parts of the representations. By combining the first 3D digital surface representation and the resulting 3D digital surface representation, it is possible to keep features in certain areas that would otherwise be smoothed out during the process. In some cases, a lower number of points used in the process means that the resulting mesh will have a lower resolution than the first 3D mesh representing the patient's teeth. Therefore, by combining first and resulting 3D digital surface representations, it is possible to keep a high resolution of the mesh in specific areas of interest, for example the occlusal surfaces of the teeth.

In some embodiments, the method further comprises manufacturing the dental appliance. The dental appliance may be one of, but is not limited to, splints, nightguards, mouthguards, aligners, retainers, bleaching trays.

In some embodiments, a gypsum or stone model of the generated 3D digital surface representation is milled, printed or otherwise manufactured. The dental appliance may then be manufactured on top of this gypsum or stone model, for example by thermoforming techniques.

In another aspect, disclosed herein is a computer implemented method for generating a dental appliance, or for generating a model for creating the dental appliance on, comprising:.

This also allows for the use of this disclosure in volumetric representations, such as bone scans or cone beam computed tomography (CBCT) scans.

In some embodiments, the dental appliance is a bone supported and/or tooth supported surgical guide and further comprises decreasing concave areas on the bone, thereby creating a better fit of the bone supported and/or tooth supported surgical guide.

By using the above disclosed method of dilating and eroding the 3D digital volumetric representation for designing bone supported and/or tooth supported surgical guides, the resulting surgical guides will be more comfortable for the patient during surgery. Also, the resulting surgical guide will fit the patient better and/or require less adjustment of the patient jaw to fit.

In some embodiments, the method further comprises generating a combined 3D digital volumetric representation by combining the first 3D digital volumetric representation and the resulting 3D digital volumetric representation.

The combination of the first and resulting 3D digital volumetric representations may be accomplished for example by using a Boolean addition operator on all or parts of the representations. By combining the first 3D digital volumetric representation and the resulting 3D digital volumetric representation, it is possible to keep features in certain areas that would otherwise be smoothed out during the process.

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

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

An embodiment of the method disclosed herein is shown in <FIG>. In step <NUM> a 2D cross sectional view of a 3D digital surface representation <NUM> is shown. The algorithm is run in 3D, but the figures are simplified to only show 2D. In this case, a well-defined point cloud <NUM> is added to the space. The point cloud could also have been a 3D grid where the nodes would function like the points <NUM>. The shortest distance <NUM> from the point <NUM> to the 3D digital surface representation <NUM> is defined for all points. In step <NUM> a dilation distance is defined, and a new surface <NUM> is created by interpolation based on the known distances from <NUM>. In step <NUM> the new surface <NUM> is eroded back onto the surface of the 3D digital surface representation <NUM>, in a similar manner to the dilation. The areas with a decrease of the concave features <NUM> are marked black and convex features are not manipulated.

<FIG> shows a flow chart of embodiments of this disclosure. The method is initiated by importing or acquiring a 3D digital surface representation 201a of a patient's teeth. In step 201b either a grid with a specific resolution or a group of points can be added to the space with the 3D digital surface representation. The resolution and amount of points added to the space will have a direct influence on the result. A high resolution or large amount of points will create a smoother new surface, but it will also increase the algorithm's processing time. For step 201c the shortest distance from the nodes of the grid or from each point to the 3D digital surface representation are calculated. In step 202a a distance for dilation is defined. The larger this distance is the larger the decrease of the concave features will be. In step 202b a new surface is created by interpolation based on the values from step 201c and 202a. The new surface is eroded back in step <NUM>. The erosion distance can either be the same as the earlier defined dilation distance or a different value depending on the desired outcome.

In some implementations, the erosion step <NUM> may include substeps similar to dilation steps 201b, 201c, 202a and 202b. Since the new surface is created in the same 3D space as the 3D digital surface representation 201a, it is possible to use the same points/grid for the erosion as was used for the dilation. Alternatively, a new set of points/grid can be added to the space containing the new surface created in step 202b. The shortest distance between the nodes of the grid or from each point to the new 3D digital surface representation are calculated. The distance for erosion is then defined. This may be either the same as the previously used dilation distance, or have a different value depending on the desired outcome. A resulting 3D digital surface representation is then generated by applying the erosion distance to the new 3D digital surface representation.

Both steps 201b and 202a can be done for specific areas of the 3D digital surface representation, meaning that there can be different degrees of morphological closing for different local areas of the surface representation.

<FIG> and <FIG> gives examples of different results that can be created based on the methods described in <FIG> and <FIG>. In <FIG> step 301a a 3D digital surface representation <NUM> is shown. Steps 303a-b and 403c-e shows the results after different surfaces are eroded back and a decrease of concave features are obtained.

In steps 303a and 303b the resolution of the grid utilized is the same, but the dilation distance is different. For 303a a smaller offset distance is used while 303b has decreased the concave features more by using a larger offset value. In step 403c the morphological closing algorithm has had different dilation values for different parts of the 3D digital surface representation. The offset value has been higher locally around a missing tooth <NUM> while the rest of the 3D digital surface representation <NUM> is affected with a lower and uniform offset value. If the patient had had several missing teeth or a pontic that needed higher degree of closing, several local areas with a higher offset value could be created. In 403d the algorithm has been restricted and has only had an effect on the undercuts <NUM> of the 3D digital surface representation <NUM>. The restriction can be done in many ways. For example, it can be done manually by the user defining areas where no effect is desired, or automatically by defining landmarks on the 3D digital surface representation to determine the areas with grooves and block them out from the algorithm. One technique that can be used to define areas to block out from the algorithm, is to segment the 3D digital surface representation, i.e. determine what part of the surface belongs to teeth, what belongs to gingiva, etc. Segmentation can be done both manually and/or automatically, with various segmentation techniques known in the field.

Another restricted method is shown in 403e. The algorithm detects the areas of the surface model where there is a contact point between teeth <NUM> and between teeth and gingiva <NUM>. These areas of the surface are manipulated by morphological closing, resulting in fissures not being affected.

Another way of compensating for missing tooth, pontics or deep grooves is to run through the flow chart described in <FIG> with a global offset value. After eroding the surface back, a new manipulated 3D digital file is created. Superimposing the manipulated file and the original 3D digital representation the concave areas that have been decreased can be identified by determining the areas between the two surfaces that are not in contact. Areas where no effect is desired can be chosen and compensated for.

In 403f the different methods are combined. Locally around a missing tooth, a high offset value <NUM> is used. The undercuts and proximal areas <NUM> are filled out with a lower offset value, while the grooves on the occlusal surface of the tooth are not affected <NUM>.

<FIG> depicts a CBCT model of a patient's mandible. In this example, the mandible bone has three holes: two from the mental foramens <NUM> and one larger socket from a tooth extraction <NUM>. Depending on the offset value, the concave features will either be decreased or fully covered. The new algorithm will also decrease inward bumps that may be caused by lower resolution CT images and/or caused by voxel filling. Since a voxel in a CBCT model has the average hardness of the volume, if for example the actual bone surface is <NUM>/<NUM> of the way into a certain voxel, it may be below the threshold, while <NUM>/<NUM> may put it above the threshold. In this scenario, two neighboring voxels will result in one voxel "overestimating" the surface while the second voxel "underestimates" the surface. 503a has been modified by a lower offset value than 503b.

<FIG> shows a schematic of a system according to an embodiment of the invention. The system <NUM> comprises a computer device <NUM> comprising a computer readable medium <NUM> and a microprocessor <NUM>. The system further comprises a visual display unit <NUM>, a computer keyboard <NUM> and a computer mouse <NUM> for entering data and activating virtual buttons visualized on the visual display unit <NUM>. The visual display unit <NUM> can be a computer screen. The computer device <NUM> is capable of obtaining 3D digital surface and/or volumetric representations of one or more teeth of a patient. The obtained 3D digital representations can be stored in the computer readable medium <NUM> and provided to the processor <NUM>. The computer device <NUM> is configured for executing the steps of the claimed methods.

The system comprises a unit <NUM>, which may be separate from or part of the computer device <NUM>, for transmitting the resulting 3D digital surface and/or volumetric representations to e.g. a computer aided manufacturing (CAM) device <NUM> for manufacturing the dental appliance, or to another computer system e.g. located at a separate manufacturing center where the dental appliances are manufactured. The unit for transmitting can be a wired or a wireless connection.

The 3D scanning of the patient's set of teeth using the 3D scanning device <NUM> can be performed at a dentist while the designing of the dental appliance may be performed either at the dentist or at a separate facility such as a dental laboratory. In such cases the 3D digital surface and/or volumetric representation of the patient's set of teeth can be provided via an internet connection between the dentist and the dental laboratory.

Rather than scanning the patient's teeth using an intraoral scanner to obtain the first 3D digital surface representation, it is also possible to take a traditional impression of the patient's teeth using manual methods. These impressions can then be sent to a dental laboratory, where they can either be scanned directly, or be used to pour a gypsum or stone model of the patient's dentition. In this scenario, the 3D scanning device <NUM> can by a desktop lab scanner situated at the dental laboratory, and the first 3D digital surface representation can then be obtained by scanning either the impressions directly, or by scanning the gypsum or stone models.

When the system <NUM> receives a 3D digital surface and/or volumetric representation the steps of the claimed methods are executed on the computer device <NUM> and the digital output is presented on the visual display unit <NUM>. If the user is not satisfied, the output can be edited by using the computer keyboard <NUM> and mouse <NUM>. When a satisfying result is achieved, it will be transmitted through <NUM> to a CAM device <NUM> where a physical appliance is produced. The desired output will depend on the type of physical appliance that is needed.

If a splint is the final product the output from <NUM> can be a negative model of the teeth, that is created based on the resulting 3D digital surface representation. The negative model of the teeth is thereafter transmitted to <NUM> for manufacturing. The output for a splint, after executing the claimed methods, can also be the first and resulting 3D digital surface representations combined. The combined model of the dental arch can then be used in ex. 3shape Splint Studio, on the computer device <NUM> to create a splint that is manufactured on <NUM>.

For an aligner the output which is transmitted by <NUM> to a CAM device <NUM> can be the first and resulting 3D surface representations combined. The combined surface representation of a dental arch can be printed or milled on <NUM> and used for thermoforming an aligner.

The output from a 3D digital volume representation can be used by the user with <NUM> to create a bone supported surgical guide in ex. 3shape Implant Studio, which is then transmitted through <NUM> to a CAM device <NUM>.

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 which is defined by the appended claims.

A claim may refer to any of the preceding claims, and "any" is understood to mean "any one or more" of the preceding claims.

The term "obtaining" as used in this specification may refer to physically acquiring for example medical images using a medical imaging device, but it may also refer for example to loading into a computer an image or a digital representation previously acquired.

Claim 1:
A computer implemented method for generating a model for creating a dental appliance on, comprising:
- obtaining a first 3D digital surface representation (<NUM>) of one or more teeth of a patient;
- creating a number of points (<NUM>) in 3D space around the 3D digital surface representation, wherein the number of points comprises a regular grid placed with evenly spaced points in three dimensions around the first 3D digital surface representation in the 3D space;
- calculating the shortest distance (<NUM>) from each of the points in the regular grid to the first 3D digital surface representation;
- receiving an automatically set or user defined dilation value;
- generating a modified 3D digital surface representation by dilating the surface of the first 3D digital surface representation, wherein the dilated surface is created by interpolation based on the calculated shortest distance and the dilation value; and
- generating a resulting 3D digital surface representation model for creating the dental appliance on, by erosion of the modified 3D digital surface representation inwards.