WO2021219228A1

WO2021219228A1 - Preparation of a restorative object

Info

Publication number: WO2021219228A1
Application number: PCT/EP2020/062073
Authority: WO
Inventors: Teemu ROUVINEN; Reijo Lappalainen; Pekka Vallittu
Original assignee: Rayo 3D-Toothfill Oy
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2021-11-04

Abstract

A method comprising: obtaining a digital representation of a shape of a restorative object, determining a first surface area of the digital representation of the shape of the restorative object, determining a second surface area of the digital representation of the shape of the restorative object, modifying the second surface area such that its roughness is increased, determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, defining printing instructions for the mould, and defining filling instructions for the mould.

Description

PREPARATION OF A RESTORATIVE OBJECT FIELD

The present disclosure relates to preparing a restorative object that may be used in a sensitive environment. BACKGROUND

3D printing may be utilized in various fields and for various purposes. It may allow printing of various objects that may then be used as such as restorative parts. 3D printing may also be utilized to produce intermediate parts that help to produce the desired object, which may be a restorative object. This is beneficial for example if the object is targeted to a sensitive environment and preparing the object outside of the sensitive environment allows the preparation to be done in a more efficient manner.

BRIEF DESCRIPTION

According to an aspect there is provided a method comprising: obtaining a digital representation of a shape of a restorative object, determining a first surface area of the digital representation of the shape of the restorative object, determining a second surface area of the digital representation of the shape of the restorative object, modifying the surface area such that its roughness is increased, determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, defining printing instructions for the mould, and defining filling instructions for the mould.

According to another aspect there is provided an apparatus comprising at least one processor, and at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to obtain a digital representation of a shape of a restorative object, determine a first surface area of the digital representation of the shape of the restorative object, determine a second surface area of the digital representation of the shape of the restorative object, modify the second surface area such that its roughness is increased, determine a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, define printing instructions for the mould, and define filling instructions for the mould.

According to another aspect there is provided an apparatus comprising means for obtaining a digital representation of a shape of a restorative object, determining a first surface area of the digital representation of the shape of the restorative object, determining a second surface area of the digital representation of the shape of the restorative object, modifying the second surface area such that its roughness is increased, determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, defining printing instructions for the mould, and defining filling instructions for the mould. According to an aspect there is provided a computer program product which when executed by a computing apparatus causes the apparatus to perform obtaining a digital representation of a shape of a restorative object, determining a first surface area of the digital representation of the shape of the restorative object, determining a second surface area of the digital representation of the shape of the restorative object, modifying the second surface area such that its roughness is increased, determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, defining printing instructions for the mould, and defining filling instructions for the mould. According to another aspect there is provided a computer program product comprising computer program code stored in a non-transitory memory medium, the computer program code being configured to cause an apparatus, when executing the program code by a processor circuitry, to perform at least the following: obtain a digital representation of a shape of a restorative object, determine a first surface area of the digital representation of the shape of the restorative object, determine a second surface area of the digital representation of the shape of the restorative object, modify the second surface area such that its roughness is increased, determine a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area, define printing instructions for the mould, and define filling instructions for the mould.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an exemplary embodiment of a restorative object.

Figure 2 illustrates a flow chart according to an exemplary embodiment.

Figure 3 illustrates an exemplary embodiment of a prominence line and a digital representation of a mould.

Figures 4-8 illustrate flow charts according to exemplary embodiments.

Figure 9 illustrate exemplary embodiments of parts of a device.

DETAILED DESCRIPTION

The following embodiments are exemplifying. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

Restorative objects may be understood as objects that are to complement or replace an existing object or, alternatively, are to be placed as new objects into a target environment. Restorative objects may be utilized in various manners. For example, in dental care or in other medical or veterinarian care when an object is to be inserted to human or animal body. Yet, restorative objects may also be utilized in the context of repairing part of an apparatus for example. If the restorative object is to be custom made to the target, an off-the-shelf-solution may not be appropriate. On the other hand, if the restorative object is to fit appropriately, it may not be easy to create it if the target environment is difficult to reach, such as the mouth or other part of the body of a human or an animal. Further, if the restorative object is to be made within a body, such as in a mouth, the materials that may be safely used in creating the restorative object may be limited. Further, that may also limit the usage of heat or chemicals for example when making the restorative object. Therefore, it would be beneficial to be able to make the restorative object outside of the target environment such that a ready-made restorative object may then be placed onto the target place in the target environment. If the shape of the restorative object is known, a mould may be created such that when the cavity of the mould is filled with suitable material used as a restorative filling, a new object with same shape as the known shape of restorative object is created. The mould may then be considered as an intermediate object that is used to create the restorative object and the cavity of the mould has a shape that corresponds to the shape of the restorative object. If such a mould is then filled with one or more suitable materials, in other words with one or more suitable restorative fillings, a custom-made restorative object may be created outside of the target environment. It is to be noted that the mould may be comprised of one or more parts that together then enable formation of the restorative object by for example having, when combined, a cavity corresponding to the shape of the restorative object. 3D printing allows to print such a mould once the shape of the object is available as a digital representation allowing printing instructions to be defined based on the digital representation. The mould may then be filled with one or more suitable materials used as restorative fillings and, if needed, the materials may be cured with any suitable curing method. The filling may be done manually, or it may be automated. For example, a device such as a robot, may be utilized to automatically fill the printed mould. If the mould is to be filled automatically by a device, instructions may be defined and provided to the device based on which the device may perform the filling, and in some examples also the curing of the one or more restorative fillings. In an exemplary embodiment, a restorative object is to be produced for dental purposes. In order to be able to produce such a restorative object, in this exemplary embodiment, scanning is performed in an oral cavity such that a section of the oral cavity is scanned. This may be done using any suitable scanner. In this exemplary embodiment, a dentist has prepared the cavity of a tooth such that it is ready for the restorative object to be placed onto the correct place, such as the tooth. Thus, the prepared cavity of the tooth may be understood to be comprised in the target environment for the restorative object. The tooth is comprised in the section of the oral cavity that is scanned in this exemplary embodiment. In some other exemplary embodiments, the target environment for the restorative object may comprise a prepared pilar of a tooth. It is to be noted that although one restorative object is mentioned in this exemplary embodiment, there may be more than one restorative objects needed and the dentist may have prepared a plurality of cavities for a plurality of restorative objects to be inserted respectively. Also, in some exemplary embodiments, one restorative object may be place onto a plurality of teeth that have been prepared for the restorative object. The target environment of the one or more restorative objects may be comprised in the section of the oral cavity that is scanned. Once the section of the oral cavity has been scanned, the scanned model of the target environment, that in this exemplary embodiment is comprised in the section of the oral cavity, is obtained. The scanned model of the oral cavity is in this exemplary embodiment in a digital format. Based on the scanned model of the oral cavity, a tooth is detected onto which a restorative object is to be placed. It is to be noted that in some other exemplary embodiments, teeth may be detected onto which a restorative object is to be placed. For example, a bridge may be needed as a restorative object to connect two or more teeth. For example, three or four teeth may be restored using a bridge. Figure 1 illustrates an example of such a tooth 110 that may be recognized based on the obtained scanned model of the section of the oral cavity. The recognition may be automated, based on one or more recognition algorithms executed by a computing device, or additionally or alternatively, may be defined by receiving input from a user defining the tooth 110.

In order to obtain the shape of the restorative object 120 user input may be obtained defining the desired shape. Alternatively, or additionally, algorithms may be executed by the computing device to obtain the shape of the restorative object. Further, in some exemplary embodiments, the shape of the restorative object may be obtained from any suitable source. The shape of the restorative object is to be such that when placed onto the tooth 110, the shape of a restored tooth 130 is obtained. The shape of the restorative object 120 may also be used to define printing instructions for a mould that may then be filled such that the restorative object with the determined shape is obtained and may be attached onto the tooth such that the restored tooth 130 is achieved.

A digital representation of a shape of a restorative object may be obtained based on the scanned model of the section of the oral cavity as described above. The scanned model of the section of the oral cavity may be obtained in any suitable manner. For example, it may be downloaded from a server or a cloud storage or it may be obtained using wired or wireless transmission techniques. An inner part of the restorative object may then be defined at least partly based on the digital representation of the shape of the restorative object. The inner part may be understood as a part of the restorative object that is beneath the surface of the restorative object. The inner part may reach the surface of the restorative object or there may be a distance between the surface and the inner part in which case the inner part of the restorative object does not fill the whole shape of the restorative object. In some exemplary embodiments, the inner part may be filled with a different material used as a restorative filling than the surface area and therefore it is beneficial if there is a distance between the surface and the inner part of the restorative object. This may be the case for example if the restorative object is to be used as a dental restorative object and the surface part is to be an enamel part that is to comprise different material than the inner part. It is to be noted that the one or more materials used may be understood as restorative fillings. Yet, it is to be noted that in some exemplary embodiments, the same material may be used to fill both the surface area and the inner part of the restorative object. It is further to be noticed that in some exemplary embodiment, in addition to the inner part and the surface area, there may be one or more additional layer areas between the inner part and the surface area. An advantage that may be associated with a plurality of layer areas is that it corresponds to the structure of tissue.

Further, two or more surface areas of the restorative object may be determined based on the digital representation of the shape of the restorative object. The shape of those surfaces may in some exemplary embodiments differ from each other. For example, a first surface may be smoother than a second surface. In other words, the second surface may be rougher than the first surface. Further, the first surface may be such that it will be exposed to the environment, such as the oral environment, and the second surface area may be an area that will be attached to the target cavity, such as a cavity of a tooth. The attachment may be done for example by using a bonding substrate. Therefore, in addition to having a different roughness of the surface area, the first surface area and the second surface area may in some exemplary embodiments comprise different coatings and/or surface treatments as well. A benefit that may be achieved, in some exemplary embodiments, by having a smooth surface is that it reduces bacterial attachment. A benefit that may be achieved, in some exemplary embodiments, by having a rougher second surface area compared to the first surface area is that it may enable an improved attachment to the target environment such as to the cavity of the tooth.

Figure 2 illustrates a flow chart according to an exemplary embodiment for defining the inner part of the restorative object. A computer program product may be utilized to define the inner part of the restorative object. First, in S1 , the digital representation of the shape of the restorative object is obtained and converted to a voxel representation. One or more algorithms may be utilized for the conversion. A voxel representation allows a volumetric representation of an object to be achieved. Thus, a volumetric representation, in a digital format, of the restorative object is obtained. Next, in S2, a first surface area of the shape of the restorative model is determined. In this exemplary embodiment, the first surface area corresponds to the dental enamel area that will be exposed to the environment within the mouth. The determination may be automatic such that one or more algorithms comprised in the computer program product are executed to determine the first surface area. Alternatively, or additionally, user input may be received defining the first surface area. For example, as a first determination the first surface area is determined automatically and as a second determination, user input is received further defining the first surface area. The first determination is performed first in this exemplary embodiment, but it is to be noted that in some other exemplary embodiments the second determination may be performed first and after that the first determination may be performed.

Next, in S3, a table is created that lists for a plurality of voxels comprised in the volumetric representation their shortest distance to the first surface area. This may be obtained by executing one or more algorithms comprised in the computer program product. In this exemplary embodiment, the shortest distance to the first surface area is determined for each voxel and the results are stored into a look-up table, but it is to be noted that in some exemplary embodiments it may not be necessary to determine the shortest distance to the first surface area for each voxel comprised in the volumetric representation. Further, in some exemplary embodiments, when determining the first surface area, some parts of the first surface area, for example some points comprised in the digital representation, may have been emphasized automatically or based on received user input for example. Such emphasis may be taken into account when determining the shortest distance for a voxel. For example, the shortest distance may be the shortest distance to the emphasized part of the first surface area. The emphasized part may then be for example a part defined by a user and to which the user may wish to affect in a manner that is different compared to the non-emphasized areas. In an exemplary embodiment, the emphasizing may be utilized to achieve a desired dividing of restorative filling between the first surface area and the inner part. For example, the restorative filling comprised in the surface area may be thicker at some parts of the first surface area and thinner in some other parts of the first surface area. This may be beneficial for example if the restorative object is to be attached to a tooth and the part of the restorative object corresponding to enamel is to be thinner for example in vertical parts compared to the part that is used for chewing. Next, in S4, it is determined based on the created table which voxel has the greatest distance to the first surface area. Using this voxel as a starting point, a selection of a group of voxels comprised in the volumetric representation is determined such that all voxels that have a distance greater than a threshold amount are selected. This selection may be performed using any suitable algorithm. In this exemplary embodiment the algorithm is a flood- fill type of an algorithm as illustrated in S5. The threshold value may be pre determined, or it may be determined based on a user input for example. Based on the selected group of voxels, a mesh is defined using one or more suitable algorithms that may be comprised in the computer program product. The mesh obtained is a representation of the inner part of the restorative object and may therefore be considered as a first mesh that in this exemplary embodiment is a mesh of the inner part of the restorative object. Optionally, the obtained first mesh may further be defined by executing a smoothing algorithm such as a Laplacian smoothing algorithm. A prominence line may also be defined for the mould. A prominence line may be understood as a line or a curve that may be determined for the digital representation of the restorative object. The determination may be done using one or more algorithms or it may be determined based on user input or based on a combination of both. In some exemplary embodiments, the points comprised in the prominence line approximate the most prominent point from a fixed centre axis, that may be a normally vertical axis, of the digital representation of the shape of the restorative object. Further, in some exemplary embodiments, the prominence line may be used as marker to split the mould, once produced as a physical mould, into at least two parts. Thus, the prominence line may be utilized when producing the mould such that the mould may be separated into two or more parts without undercut thereby enabling removal of the mould in a manner that does not harm the produced restorative object. The two or more parts of the mould may be attached, for example, using fastening, clamping or any other suitable way that allows two or more parts to be releasably attached. The direction of the release between mould parts when the mould is opened may be for example vertical, although other directions may be used as well. In some exemplary embodiments, the mould may be filled such that an opening for the filling is located along the prominence line.

Figure 3 illustrates an example of a prominence line 310 and a mould 320. It is to be noted that these are mere illustrations for the purpose of helping to understand an example relationship between a prominence line and a mould and that other types of moulds and prominence lines may also be used. The prominence line 310 may be utilized for removing the mould 320 once the restorative object 120 has been obtained as was also described above. The prominence line 310 may allow the mould 320 to be split into two parts thereby allowing removing the mould 320 without causing damage to the obtained restorative object 120. The prominence line 310 may be defined for example by determining a projection of the digital representation of the shape of the restorative object to xz-plane. From this projection a group of points forming the outer line of the projection is determined and the group of points forms the prominence line. Further, among the points forming the prominence line are points that have the lowest value in the x- and z-coordinates and the points that have the greatest value in the x- and z- coordinates. These four points are included in the group of points determining the prominence line. The points may then be connected using an algorithm such as an A star algorithm. It is to be noted that in some exemplary embodiments, additionally or alternatively, user input may be received to determine the prominence line. In this exemplary embodiment, the prominence line 310 is determined by executing one or more algorithms comprised in the computer program product. It is also to be noted that the prominence line 310 may also be called as a division line. In some examples, it may be helpful to replace the prominence line by using a spline fit to original data to make this division line smoother.

It is to be noted that the coordinate system used may be any suitable coordination. For example, the positive y-axis may point upward, the positive x-axis towards right and the positive z-axis may point forward. With such a coordination, an edge of a projection of the digital representation of the shape of the restorative object onto a xz-plane comprises a group of points comprised in the digital representation of the shape of the restorative object. It is to be noted that in some exemplary embodiments it may not be unambiguous which points are comprised in the edge. In such an exemplary embodiment, user input may be received for example, to determine the group of points comprised in the edge. The points comprised in the edge may be for example points that have the lowest and the highest values in terms of x- and z-coordinate. Determination of the edge points may comprise for example determining the points that form an order that circulates in clockwise direction when the digital representation of the shape of the restorative object is viewed along the negative y-axis.

In the exemplary embodiment illustrated by the flow chart of Figure 2 it was mentioned that the first surface area is determined. Figure 4 illustrates an exemplary embodiment in which the first surface area, which in this exemplary embodiment is the dental enamel area, is determined. It is to be noted that also other suitable ways for determining the first surface area could be used. In this exemplary embodiment, the first surface area is determined by executing one or more algorithms comprised in the computer program product. First, in S1, the prominence line is determined. In case the prominence line has been determined earlier, determining the prominence line may comprise obtaining the prominence line that has been determined. Next, in S2, from the digital representation of the shape of the restorative object, a point with the highest y-coordinate value is determined. Starting from the point determined in S2, points to be comprised in the first surface area are determined by executing an algorithm, such as a flood-fill type of an algorithm, such that the stopping points are determined by the prominence line. This is illustrated in S3. The group of points obtained using the algorithm are a group of points comprised in the first surface area. In some exemplary embodiments, the group of points may be supplemented with an additional execution of a flood-fill type of an algorithm in which the stopping point is determined based on a rate of change of a surface normal direction of the shape of restorative object. It is to be noted that in some exemplary embodiments, there may be distances between the points comprised in the first surface area that may be interpreted as holes in the area. In such an exemplary embodiment, the flood fill algorithm may determine also points comprised outside of the first surface area to be included in the selection. Therefore, in some exemplary embodiments, automatic detection may be performed by executing one or more algorithms, or by receiving user input or by a combination of both, to verify that such erroneous selection is not performed.

As was mentioned above, a second surface area may also be determined for the digital representation of the shape of the restorative object. This surface area may be the surface area that is attached to a tooth. In order to determine the area, Figure 5 illustrates a flow chart of an exemplary embodiment in which the second surface area is determined using one or more algorithms comprised in the computer program product. First, in S1, it is determined from the digital representation of the shape of the restorative object points that are not comprised in the first surface area. Then, in S2, for the points determined not to be comprised in the first surface area the shortest distance to the first surface area is determined, respectively. In this exemplary embodiment the shortest distance is determined for each point determined not to be comprised in the first surface area, but it is to be noted that in some other exemplary embodiments, the distances may be determined to a subset of the determined points, for example to allow selection of points with distances higher than a certain threshold value.

Then in S3, a point that has the shortest distance to the first surface area is determined. The shortest distance may, in some exemplary embodiments, be the shortest distance that is determined to be the shortest distance after a threshold distance. The threshold distance may be used to verify that the point indeed is not part of the first surface area or too close to that. After this, in S4, an algorithm such as a flood-fill type of an algorithm is executed starting from the determined point and using the distances of each point to the first surface area as criteria for a point to be comprised in the group of points selected by the executed algorithm. Thus, a group of points comprised in the second surface area is determined. In S5 a subset of the points comprised in the second surface area are selected. The selection may be based on pre-determ ined criteria or the selection may be a random selection. Next, in S6, the selected subset of points are relocated such that the surface of the second surface area becomes rougher compared to the first surface area. In some exemplary embodiments, the relocation may be based on pre-determ ined criteria that may be based on experimental results obtained and/or based on the material to be used to fill the mould. The relocation may be performed in any suitable manner. In this exemplary embodiment, the relocation is performed by moving the points a pre-determined distance to a direction opposite to the normal vector. In general, roughness of the second surface area may be increased for example by modifying vertex positions of points comprised in the second surface area. It is to be noted that this procedure does not increase the size of the restorative object discussed above but may be used to increase the surface roughness in a controlled manner. Once the points comprised in the second surface area have been relocated, a modified digital representation of the shape of the restorative object is obtained.

A benefit that may be obtained by the second surface area, of the restorative object once it is in a physical format, having topography rougher than that of the first surface area is that the strength of the attachment to the tooth may be increased. It is to be noted that topography, as used herein, may be understood as referring to the surface shapes and features of the physical restorative object. This is desirable in dental care as the better the strength, the less likely it is that the restorative object placed onto the tooth will fall out of place or fracture. The better the attachment, the less likely it is also that bacteria will be able to reside between the tooth and the restorative object. A further benefit is that by roughening the surface of the second surface area, the desired topography of the restorative object may be achieved without measures such as abrasive grit-blast which may leave residual particles to the restorative object that should not be left. It is to be noted that the increased strength of the attachments may be beneficial in other use cases than dental care as well.

As mentioned above, the second surface is the surface that is attached to the tooth. For the attachment, any suitable bonding agent or bonding resin may be utilized. For example, resin luting cements may be used. In an example, various roughness levels of the topography of the second surface were tested using in all tests the same material but varying the roughness of the topography of the second surface area. The test results may be seen in the table below. With 0 roughness addition, the topography of the second surface area was not roughened by relocating points comprised in the second surface area of the digital representation of the shape of the restorative object. Roughness addition 100 on the other hand describes the topography of the second surface area with the roughest topography. In each case, 6 identical samples were used for testing M1-M6 and they were taken into account when estimating the shear strength endurance.

Table 1

As can be seen from the table above, the interface shear bond strength of the filling may be improved by adding roughness to the topography of the second surface of the restorative object. Dental filling materials may need curing for a solid hard form to be utilized in restorations. The mould material that is to be in contact with the second surface area of the restorative object may be itself or by help of a coating such that it inhibits free radical curing of the resin composite used for creating the restorative object. This may be beneficial for example for the layer comprised in the second surface area. Inhibited curing layer of the second surface of the restorative object may allow luting cement to be polymerized to the restorative object and form a bonding that is a durable bonding between the luting cement and the restorative object.

Once the shape of the restorative object, the roughness of the first and the second surface areas, the volumetric representation of the restorative object and the prominence line are determined in a digital format, a digital representation of the mould may be created. Figure 6 illustrates a flow chart according to an exemplary embodiment in which the mould is, at least partly, defined as a digital representation. In S 1 , the point with the highest y- coordinate value is determined from the digital representation of the restorative object. Next, in S2, a prominence line is determined. In case the prominence line has already been determined, the prominence line may be obtained. In S3, an algorithm such as a flood-fill type of an algorithm is executed starting from the determined point with the highest y-coordinate value and ending at the prominence line. In this exemplary embodiment, the points comprised in the prominence line are comprised from the selection of points obtained by executing the algorithm. Next, in S4, a mesh is formed based on the points comprised in the selection. This mesh may be understood as an upper part mesh. In S5 the points that were not comprised in the selection obtained by executing the algorithm, are selected as another group to which points comprised in the prominence line are also added. Next, in S6, another mesh is created based on the points comprised in the selection made in S5. This mesh may be understood as a lower part mesh.

Figure 7 illustrates a flow chart according to an exemplary embodiment in which the creation of the digital representation of the mould is continued. First, in S1 , a projection of the digital representation of the shape of the restorative object onto the xz-plane is created. Next, in S2, a rectangular shape is defined along a division plane, that may be determined based on the projection line, such that the rectangular shape defines the outer boundaries of the mould. Then, in S3, a group of points evenly distributed along the division plane are defined. From this defined group of points, such points that are comprised in the projection, are removed as illustrated in S4. Then, as illustrated in S5, value of y-coordinate is determined for each point comprised in the group of points and based on those points, a mesh is created. This mesh may be understood as a mesh of the division plane. When determining the value of the y-coordinate for each of the points comprised in the group, a weighed average value may be utilized. This weighed average may be determined based on for example the distance from the point to the outer boundary and to the points comprised in the prominence line. This procedure may help to make division surface of the mould smoother and easier for mould preparation and use.

Next, in S6, the exemplary embodiment continues by defining a digital representation of the lower part of the mould. The mesh of the division plane is placed to a cuboid as an upper side of the cuboid. Then, as illustrated in S7, the inner part of the cuboid is formed as an impression of the second surface area of the shape of the restorative object. An impression may be understood as a space determined by one or more objects which, when filled with filling material, causes to filling material to have a shape of the digital representation of the restorative object.

The upper part of the digital representation of the mould is defined as illustrated in S8 and S9. First, in S8, the mesh of the division plane is placed as a lower side of a cuboid, which is a different cuboid than in S6 and S7.

Next, the inner part of this cuboid is defined as an impression of the first surface area of the shape of the restorative object. Thus, the upper side of the mould that comprises the format of the first surface area is obtained.

The mould may be defined further by defining a digital representation of the part of the mould that is for producing the inner part of the restorative object as illustrated in the flow chart according to an exemplary embodiment in Figure 8. In S1, a mesh is defined based on the difference between the shape of the restorative object and the shape of the inner part of the restorative object. Then, in S2, parts of the defined mesh that are left below the prominence line are removed. Next, the mesh is inserted into a cuboid such that the mesh forms the lower part of the cuboid. It is to be noted that the cuboid is in this exemplary embodiment a virtual representation of a cuboid.

The exemplary embodiments described above illustrate how a digital representation of a mould can be created when a custom-made restorative object is to be created by filling the mould. As mentioned above, the filling may be done in some exemplary embodiments using a device that may be an automation device such as a filling robot. When the mould is filled, the material, in other words the restorative filling, used to fill the mould may shrink during the curing of the material for example. When filling the mould, this shrinkage is to be taken into account for the restorative object to fit correctly to the target environment. The shrinkage may be compensated for example by using enough restorative filling material to allow the shrinkage to happen such that after the shrinkage has happened, the restorative part fits correctly to the target environment. This shrinkage compensation may be done with any one or more suitable algorithm, for example isotropically or along a certain axis or plane. In some exemplary embodiments, the correct shrinkage compensation may be determined for different shapes of restorations experimentally and then used for calculating optimal compensation for a certain specific filling. To allow material used as restorative filling to be inserted into the mould, a filling hole is to be inserted to the mould and, optionally, also one or more smaller holes that allow air to flow out of the mould when it is filled. The mould may further be designed such that the shrinkage is taken into account when determining the volumetric profile of the mould. The shrinkage may be dependent of the material used as restorative filling and the shrinkage percentage of the material used as restorative filling may be pre-determined. As mentioned, the shrinkage of one or more materials used as a restorative filling may be compensated when the digital representation of the mould is determined. In some examples, the optimal shrinkage compensation may be determined by testing using for example 1% stepwise compensations. The test results may then indicate for a certain material the optimal shrinkage percentage compensation to be used when determining the digital representation of the mould that is to be filled with the tested material.

A hole for filling the mould may be defined in the digital representation using a mesh. The shape of the mesh may be a cylinder, or it may be a cone or their combination. A hole for the air to flow out may also be defined in the digital representation using a mesh that has the shape of a cylinder. Once the meshes for the holes have been defined, the points in the digital representation of the mould that coincide with the defined meshes for the holes, are removed.

In the exemplary embodiments described above, a digital representation of the mould is obtained. This may be achieved by executing one or more algorithms comprised in the computer program product. Once the digital representation of the mould is ready, the mould may be printed using any suitable 3D printing device. For the 3D printing device to be able to print the mould, printing instructions are defined. These printing instructions are then provided to the 3D printer. Correspondingly, instructions regarding how to fill the mould are defined. These filling instructions are then provided to the device that is used to fill the mould.

The mould may be printed using any suitable material. The material may be considered as suitable if it allows for example polymerization of resin composite if that is the material used as a restorative filling to fill to mould. For example, if the mould is first filled and then cured using curing light for example, the mould material inevitably absorbs the light. Yet, the amount of light absorbed may be such that the curing may still be obtained. In some exemplary embodiments, the mould may be flexible, which may be beneficial for removal of the mould.

For example, a dental curing light that uses a custom, multiwavelength light emitting diode, LED, for producing high-intensity light at 385-515 nm capable of polymerizing light-cure dental materials may be used for curing. The curing light of this example may also penetrate porcelain and is capable of curing underlying resin cements. One or more mould materials may then be tested with this curing light and one or more restorative filling material to determine the amount of light absorbed and its effect on the curing of the restorative filling material. The results may then be utilized when determining the filling instructions for example. In some examples, the mould material may absorb the light and reduce intensity but the desired curing may still be achieved by further curing.

In this exemplary embodiment, the mould obtained is filled using a device that has one or more syringes for filling the mould and is able to obtain instructions based on which the obtained mould is filled using a selected filling material. For the device to be able to control the filling, the device comprises at least one processor, at least one memory and computer program code stored in the at least one memory and which when executed, directs the device to fill the obtained mould. Further, the device may comprise a user interface that may be used to receive user input and to output information for a user. Figure 9 illustrates an example of such a user interface 910. The device is capable of receiving the mould 920. This may be for example due to a dedicated placement comprised in the device. The one or more syringes may be controlled by the device according to instructions received from the user interface or by executing a computer program that causes the device to fill the mould 920 according to the obtained filling instructions. The device may also comprise various sensors that monitor the movements of the one or more syringes. For example, it may be determined that a door of the device is to be closed before the syringes are moved. There may be sensors detecting the location of the syringes piston and sensors for detecting movements of the syringes piston. This may enable for example verifying that the syringes do not collide in an unintended manner as in some exemplary embodiments, the syrings may collide with the mould which may be intentional. Also, it may be monitored using one or more sensors that a tip of a syringe 930 is not inserted too far into the mould. It may also be monitored using one or more sensors that the tip of the syringe is not clogged, the syringe is primed and it works normally.

If there are for example two syringes, each syringe may comprise different filling material enabling a mould to be filled with more than one material. In some exemplary embodiments, each layer may need a different mould top part. For example, a mould may be first filled with one filling material. After this the filling material may be cured using curing means comprised in the device. The curing means may comprise for example chemical curing, light curing and/or heat curing. After the curing, the mould may be filled again with different filling that may be inserted using a different syringe. After the second filling, the curing may be performed again. This enables multi-layered filling using the mould. It is to be noted that also filling with just one filling material is possible.

The device is capable of receiving filling instructions that may be defined when the mould is defined using the computer program product. The material to be used for 3D printing of the mould may be known as well as the material or materials used as restorative filling. Also, the volumetric profile of the mould is determined when defining the digital representation of the mould. As it is known that the restorative filling material may be subject to shrinking and the shrinking may be known for each restorative filling material, the volumetric profile of the mould may be designed such that it is larger than the intended size of the restorative object. Thus, the restorative object is of the correct size after the shrinkage has taken place. Additionally, the filling instructions may instruct the device to fill the mould with more filling than the volumetric profile of the mould thereby overfilling the mould and causing excess pressure to occur in the mould. This way possible air bubbles that may occur within the filling or in the mould may also be, at least partly, removed. The filling instruction may for example define for how long the mould is to be filled by the one or more syringes. For the mould to endure the excess pressure, a cone shape of the filling hole may be beneficial as it may allow the syringe tip 930 to be inserted tightly enough to endure the excess pressure. It is to be noted that in some exemplary embodiments, properties comprised in a 3D printer that allow for compensation that takes into account the properties of the mould material that is used such that of the mould design to be printed such that the actual size is as desired, may be utilized. The properties of the mould material that is to be used may be obtained from the manufacturer or may be obtained based on tests performed or in any other suitable way.

Various materials may be used as restorative fillings. For example, polymeric, ceramic materials or composite. Additionally, in some exemplary embodiments, the first surface area, which may be the area exposed to the oral cavity for example, of the restorative object may further be coated with for example gel that enhances the properties of the restorative object. Examples of polymer composites are particulate filler and fiber filler resin composites with resin matrix of made of dimethacrylate monomers and light-curing, dual-curing or chemical curing initiator systems. Viscosity of the composite should be of flow-type in order to inject the composite into the mould. Ceramic material is used in a form of ceramic particle - resin slurry of leusite, lithium disilicate, zirconia or alumina ceramic. Injected slurry is prepolymerized in the mould and after removal from the mould sintered at elevated temperature to homogenous ceramic restorative filling, crown or dental bridge. In the similar manner, modern metallic materials may be used in the form of powder metallurgy slurry, which is applied in the mould, preinserted in the mould and further sintered outside mould at high temperature to a metallic restorative object.

The filling instructions may further comprise information regarding curing. It may not be desirable for example for the polymerization of resin composite to be fully completed in the device. Thus, the filling instructions may comprise information regarding how and for how long to cure each restorative filling. The curing instructions may be determined based on the material to be used as restorative filling for example. The curing instruction may further be determined based on the material of the mould. The mould may comprise translucent material that may allow curing using curing light. The translucent material may then absorb some of the curing light and the absorbing may affect the curing time for example. As these properties may be known, those may be taken into account when determining the filling instructions.

The computer program product described in the above exemplary embodiments may be executed using a computing apparatus that comprises one or more processors and one or more memories configured to execute the computer program product. The computing apparatus may further comprise or be connected to a user interface and a connectivity unit that allows the computing apparatus to establish wired and/or wireless connections. In some exemplary embodiments the computing apparatus may be comprised in the device used for filling. Alternatively, the computing apparatus that executes the computer program product may be connected to the device used for filling. Additionally, the computing apparatus may be comprised in or connected to the 3D printer. Also, additionally or alternatively, the computing apparatus may be comprised in or connected to a device used for scanning the target environment such as the section of the oral cavity. The computer program product, the computing apparatus and the device used for filling the mould may be comprised in a system that is caused to define a mould for the restorative object and to fill the mould such that the restorative object is obtained.

Even though the invention has been described above with reference to exemplary embodiments according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly, and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described exemplary embodiments may, but are not required to, be combined with other exemplary embodiments in various ways.

Claims

1. A computer program product readable by a computer and, when executed by the computer, configured to cause the computer to execute a computer process comprising: obtaining a digital representation of a shape of a restorative object; determining a first surface area of the digital representation of the shape of the restorative object; determining a second surface area of the digital representation of the shape of the restorative object; modifying the second surface area such that its roughness is increased; determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area; defining printing instructions for the mould; and defining filling instructions for the mould.

2. A computer program product according to claim 1 further comprising determining a prominence line.

3. A computer program product according to claim 2 wherein determining the first surface area and the second surface area comprises executing a flood-fill type of an algorithm that stops on the prominence line.

4. A computer program product according to any previous claim further comprising determining for the mould a lower part based, at least partly, on the determined second surface area.

5. A computer program product according to any previous claim further comprising determining for the mould an upper part based, at least partly, on the determined first surface area.

6. A computer program product according to any previous claim further comprising determining for the mould one or more holes.

7. A computer program product according to claim 6, wherein at least one hole comprises the shape of a cone and/or cylinder.

8. A computer program product according to any previous claim further comprising transmitting the printing instructions to a printing device.

9. A system comprising the computer program product according to any of claim

1 to 8 and a device comprising at least one syringe for filling the mould and wherein the device is configured to obtain the filling instructions and, by executing the filling instructions, fill the mould using the at least one syringe.

10. A system according to claim 9, wherein the device comprises two syringes and the filling instructions cause the device to: fill the mould with a first filling material using a first syringe; cure the first filling according to the instructions obtained from the filling instructions; fill the mould with a second filling material using a second syringe; and cure the second filling according to the instructions obtained from the filling instructions.

11. An apparatus comprising means for: obtaining a digital representation of a shape of a restorative object; determining a first surface area of the digital representation of the shape of the restorative object; determining a second surface area of the digital representation of the shape of the restorative object; modifying the second surface area such that its roughness is increased; determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area; defining printing instructions for the mould; and defining filling instructions for the mould.

12. An apparatus according to claim 11 further comprising means for determining a prominence line.

13. An apparatus according to claim 12 wherein determining the first surface area and the second surface area comprises executing a flood-fill type of an algorithm that stops on the prominence line.

14. An apparatus according to any of claims 11-13 further comprising determining for the mould a lower part based, at least partly, on the determined second surface area.

15. An apparatus according to any of claims 11-14 further comprising determining for the mould an upper part based, at least partly, on the determined first surface area.

16. An apparatus according to any of claims 11-15 further comprising determining for the mould one or more holes.

17. An apparatus according to claim 16, wherein at least one hole comprises the shape of a cone and/or cylinder.

18. An apparatus according to any of claims 11-17 further comprising transmitting the printing instructions to a printing device.

19. A method comprising: obtaining a digital representation of a shape of a restorative object; determining a first surface area of the digital representation of the shape of the restorative object; determining a second surface area of the digital representation of the shape of the restorative object; modifying the second surface area such that its roughness is increased; determining a mould based on the digital representation of the shape of the restorative object, the first surface area and the second surface area; defining printing instructions for the mould; and defining filling instructions for the mould.