EP1519694A2

EP1519694A2 - Method for the production of a dental bridge frame and positive model therefor

Info

Publication number: EP1519694A2
Application number: EP03762573A
Authority: EP
Inventors: Hans-Ullrich Meier; Philip Von Schroeter; Peter Kreuder; Manfred Schuck; Frank Fuchs; Heiner HÖRHOLD; Bianca WÖLKI; Thomas Döring; Walter Kienzle
Original assignee: Degudent GmbH
Current assignee: Degudent GmbH
Priority date: 2002-07-02
Filing date: 2003-07-02
Publication date: 2005-04-06
Also published as: WO2004004595A3; WO2004004595A2; AU2003263166A1

Abstract

The invention relates to a dental bridge frame and a method for the production of a dental bridge frame made of a ceramic material more particularly containing or consisting of zirconium oxide. One aim of the invention is to produce a ceramic bridge frame whereby the length thereof is greater than that of the ceramic blanks usually available therefor. Another aim of the invention is to enable bridge frames to be placed on teeth stumps which do not necessarily run parallel or which do not run in a substantially parallel manner in relation to each other. The bridge frame thus consists of two sliding parts. Each sliding part is made of a ceramic blank which is machined in a CAM process. A CAD model or hand-modelled model is used as a basis for the machining of the at least one blank.

Description

Process for producing a dental bridge framework and positive model for such

The invention relates to a method for producing a dental bridge framework made of ceramic material, in particular containing zirconium oxide or consisting of this. Furthermore, the invention relates to a positive model for a bridge framework consisting of or containing ceramic material such as, in particular, zirconium oxide, which can be produced from a blank of preferably pre-sintered ceramic material such as zirconium oxide on the basis of the positive model in the CAM process. In particular, the invention also relates to a bridge framework using at least one blank made of ceramic material, which is processed by the CAM method.

A large number of devices and methods for producing artificial dental bridges are known. In general, after the dental preparation, in which the teeth serving for anchoring are prepared for the tooth bridge by grinding or e.g. B. a pin is implanted, an impression of the tooth stumps receiving the bridge, their surroundings and the jaw. This is usually done with silicone potting compounds, although other materials can also be used. From the impression, which shows the situation in the patient's mouth negatively, a so-called plaster cast is made. Master model made. This master model shows the situation in the patient's mouth positively. On this master model, the dental technician uses his manual skills to model a positive model of the basic framework of the dental prosthesis made of wax or plastic that melts and polymerizes at a low temperature. A positive model produced in this way then serves as the basis for the dentures.

Traditionally, the positive model created by the dental technician is embedded in refractory materials and melted out. The basic structure can be created in the usual metallic dental alloys by investment casting in the resulting casting mold. At least anterior tooth areas are provided with a ceramic or plastic veneer.

From WO 99/47065 it is known, after the formation of a wax model, to completely digitize its outer and inner surface. For this purpose, the wax model can be rotated up to 180 ° in order to digitize the surfaces that are accessible from the occlusal and cavity. The dental prosthesis is then produced on the basis of a model produced in this way.

Metallic bridge structures are known in various designs. There are also so-called Attachments that serve as detachable connections for removable partial dentures or superstructures or as firmly cemented or adhesively attached connections. Assembled auxiliary parts for wax models can be used to create attachment parts on cast metal bridge frameworks. Individually modeled wax constructions for the production of attachment parts on cast metal bridge frameworks are also known.

Furthermore, one-piece bridge structures made of high-performance ceramics are known, which, for. B. consist of zirconia or yttria-stabilized zirconia. From US 5,788,498 a method for producing tooth crowns and dental bridges using a prefabricated ceramic reinforcing element is known, which is designed as attachment. The prefabricated reinforcement element is machined in one or two dimensions to avoid the use of expensive CAD / CAM systems.

From DE 195 41 701 AI a primary part of an attachment for connecting implants is known, which is cast or soldered to a crown. The primary part is cast, using a cast core having the shape of the primary part, which is made of plastic and burns without residue during casting.

The present invention is based on the problem of producing a method and a positive model of the type mentioned at the outset for producing a bridge framework made of ceramic, the length of which is greater than the usually available ceramic blanks. It should also be possible to apply bridge frameworks to tooth stumps that do not necessarily run parallel or essentially parallel to one another.

The problem is essentially solved according to the invention in that the bridge framework consists of at least two attachment parts, that each attachment part consists of a blank made of ceramic material processed in the CAM method and that a CAD model is used as a template for processing at least one blank or a hand-modeled model.

In particular, for the production of a corresponding bridge framework made of ceramic material, it is proposed that

Making an impression of a jaw comprising tooth stumps and their surroundings, which receives the bridge framework to be produced,

- making a master model from the impression,

- Modeling a coping on one (first) of the tooth stumps of the master model, Connecting the cap with a ready-made modeling aid part to form a primary part,

- manual processing of the modeling aid taking into account minimum geometries of a male part to be produced from the primary part at least in the CAM process,

Manual modeling of a secondary part to be placed on the modeling aid or on a male part made from a ceramic blank on the basis of the modeling aid, covering the further tooth stump,

- Removal of the primary and secondary part or the secondary part from the master model and the production of either the matrix and the male part when hand-modeling the secondary part on its modeling aid or from the male part when hand-modeling the secondary part on the male part from a ceramic blank for producing the bridge framework with dividing attachments ,

The bridge framework or the matrix, i. H. the sintered secondary part, and the patrix, d. H. the sintered primary part, after its manufacture, are veneered at least in the front area of the teeth.

Through the teaching according to the invention, a primary part of a positive model for a attachment attachment of a dental bridge is made available using the assembled modeling auxiliary part, in order to achieve lengths which exceed the existing blank lengths. The design of the ready-made modeling aid is based on minimum geometries of the bridge framework to be manufactured, i.e. H. the patrix ensures that tensile stresses and stress-increasing notch effects are limited, influences that are basically irrelevant for metallic bridge frameworks.

In practice, the manufacture of bridge frameworks from high-strength structural ceramics is generally computer-aided with machining. Different construction rules apply compared to metallic casting technology. This means that the geometry of ceramic parts is restricted, especially if the positive model is optically digitized. In particular, a prefabricated modeling aid is used, which consists of plastic and is composed of a cone-shaped web and a truncated cone, the web being connected to the cap in such a way that the modeling aid is aligned with the second tooth stump to be accommodated by the secondary part so that the longitudinal axis of the truncated cone runs parallel or approximately parallel to the second tooth stump, ie the direction of insertion, along which the die of the dividing attachment is pushed onto the second tooth stump.

In particular, the assembled modeling aid specifies a minimum cross-section and / or minimum radii at surface edges of the male part to be produced from the primary part.

According to a further feature of the invention to be emphasized, the auxiliary modeling part is machined with a milling tool specifying a minimum radius in the edge running on the basal side.

These measures and the geometry specifications of the assembled modeling aid can minimize mechanical tensile stresses that occur.

Furthermore, it is provided that the web and the truncated cone are designed on the inside and outside so that the primary part can be completely or almost completely digitized over its entire inner and outer surface in two positions rotated by 180 ° or approximately 180 ° to one another.

According to a further proposal of the invention, a ready-made modeling aid is used which has markings which indicate when minimum geometries are reached during processing. Of course, the modeling aid can also be processed additively. In a further embodiment of the invention it is provided that a film is applied to the truncated cone before the secondary part is modeled by hand in order to form a cement gap for the male part in the matrix to be produced from the secondary part.

A positive model for a bridge framework consisting in particular of zirconium oxide or containing it, the bridge framework being able to be produced from a blank such as pre-sintered zirconium oxide or containing this using the positive model in the CAM process, is characterized in that the positive model consists of a primary part and a secondary part consists in that the primary part consists of a coping surrounding a first tooth stump and a prefabricated modeling aid connected to it, which in turn consists of a web connected to the coping and a truncated cone emanating from it, that the web and the truncated cone have a cone geometry on the outside such that that there is complete or almost complete digitization of the inner and outer surfaces when the modeling aid is scanned in two positions rotated by 180 ° or almost 180 °, and that the modeling aid has minimum geometries for one specifies the male part to be produced. The minimum geometries are in particular the cross section of the web and / or radii on the respective surface edges of the truncated cone.

Furthermore, the modeling aid is characterized by the fact that in the unprocessed state it runs at a distance from its outer surface and, when processed, has at least one visible or visible marking after reaching a minimum geometry.

In a development of the invention, it is proposed that a film is provided between the primary part and the secondary part of the positive model arranged on a master model to form a gap in the overlap area of the matrix and patrix to be produced from the primary and secondary part. The film thus represents a removable placeholder and can be replaced by other elements with the same effect. The gap formation also offers the advantage of compensating for manufacturing tolerances. According to the invention, a two-part positive model, intended for a bridge framework made of high-strength ceramic, is provided in the form of a dividing attachment. By using the assembled modeling aid, it can be ensured that the final dimension of the bridge framework is given minimum dimensions that minimize possible tensile stresses. At the same time, it is ensured that the die can be aligned securely both to the section of the die defined by the truncated cone and to the tooth stump to be covered.

There is also the possibility of designing the intermediate member in such a way that it runs exclusively or essentially exclusively convexly on the basal side without there being any disadvantages in the attachment.

In particular, however, the invention is characterized by a bridge framework using at least one blank made of ceramic material which is processed by the CAM method, the bridge framework consisting of at least two parts, each part consisting of a blank made of ceramic material processed in the CAM method and serves as a template for the processing of at least one blank, a CAD model or a hand-modeled model. When using a CAD model, the secondary conditions that also apply to the hand-modeled model described above are essentially fulfilled, in particular with regard to the minimum geometries.

Instead of a hand-modeled positive model or part of it as a template for producing a attachment part by processing a blank in the CAM method, the template can also be generated on the basis of this data by scanning the master model of digitized data obtained and generating a CAD model. For this purpose, the model of a small cap can be calculated on the basis of the data obtained by scanning the master model and linked with data to be taken from libraries, in which outer geometries of the attachment parts to be produced taking into account the actual geometry of the master model or its areas, which connect to the bridge framework to be used , are filed. Further details, advantages and features of the invention result not only from the claims, the features to be extracted from them - by themselves and / or in combination - but also from the following description of a preferred embodiment to be taken from the drawing.

Show it:

1 shows a longitudinal section through a three-part bridge structure which has a dividing attachment and divergent pillars,

2 primary part of a positive model or patrix of the dividing attachment according to FIG. 1,

3 is a side view of a modeling aid,

4 shows the modeling aid according to FIG. 3 with the film attached,

5 rear view of the modeling aid according to FIG. 3,

Fig. 6 is a schematic diagram for generating a CAD model and

7 shows a CAD model.

The teaching according to the invention enables the creation of a dividing attachment for ceramic frameworks with a special geometry to minimize mechanical tensile stresses. For this purpose, a positive model is first produced, which consists of a primary part and a secondary part. The geometry of the positive model corresponds to that of the bridge framework. On the basis of the primary and secondary part, a matrix and a male are produced taking into account specifically specified geometry offsets. Geometry offsets must be taken into account in particular if A ceramic blank is produced from pre-sintered, in particular yttrium oxide-stabilized zirconium oxide, which is then sintered, the matrix and the male.

1 shows a longitudinal section through a three-part bridge framework 10, which is composed of a die 12 - a sintered secondary part - and a male part 14 - a sintered primary part 28. Between the die 12 and the male 14 there is a defined gap 16 into which binding agents such as cement or adhesive are introduced in order to connect the female 12 to the male 14. The male part 14 is pushed onto a first tooth stump and the female part 12 onto a second tooth stump, which do not necessarily have to run parallel to one another due to the teaching according to the invention.

In order to produce the die 12 and the male 14 from a blank, a positive model is first modeled on a master model or corresponding model, at least one assembled modeling aid 18 being used according to the invention, which forms the area 20 in the male 14.

The modeling aid 18 consists of a truncated cone-shaped outer section (truncated cone 22) which is connected via a web 24 to a cap 26 which is first placed on a first tooth stump.

The modeling aid 18 forms together with the cap 26 a primary part 28, which is the template for the male 14. In order to design this on the basis of the primary part 28, the outer surfaces of the web 24 and the truncated cone 22 and the inner and outer surfaces of the cap 26 run along Koni, so that there is the possibility. To completely digitize the top and bottom of the modeling aid part 18 and the cap 26 by digitizing the primary part 28 in two positions rotated by 180 °.

The modeling aid 18 is also designed such that minimum geometries for the male part 14 to be produced are observed. Obtain these minimum geometries refer among other things to the cross section of the web 24 and inner radii 30, 32 on all surface edges.

Furthermore, it is provided that a desired minimum radius 27 is maintained by means of a milling tool when processing the lower edge of the web 24, that is to say the basal regions. When the basal contour is worked out additively, a modeling aid (round element) can also be used to achieve a desired minimum radius 27.

The predetermined minimum geometries and the fact that the modeling aid 18 is assembled results in the advantage that machining notches are minimized and both a defined minimum cross section in the web area and desired inner radii in the transition area between the web and the adjacent surfaces are maintained, so that mechanical minimization Tension is achievable.

Since the modeling aid 18 is joined to the coping 26 on the processing side after the coping 26 is placed on the corresponding tooth stump, there is the further advantage that the axial direction of the truncated cone 22 to be referred to as the conical main part of the modeling aid 18 can be aligned parallel to the stump, onto which the die 12 can be pushed (parallel to the direction of insertion).

Furthermore, one or more markings 36 are provided below the unprocessed outer surface of the modeling aid part 18, which markings indicate when predetermined minimum geometries are reached during processing. This signals that further material removal is not to be expected.

From Fig. 1 it can also be seen that the attachment is intra-coronal, ie that the attachment runs in an intermediate link. As the rear view of the modeling aid 18 according to FIG. 5 illustrates, the outer surfaces of both the web 24 and the conical section 22 are conical, so that the desired digitization of the entire outer surface is possible.

In order to specifically form the gap 16 between the die 12 and the male 14, a further development of the invention provides that a cap-shaped element is applied to the frustoconical section 22 of the modeling aid part 18 and in some areas along the web 24, on which a template is applied for the matrix 12 forming secondary part of the positive model is modeled. Before the corresponding secondary part is scanned, the assembled cap element 38 is then removed, so that, as a result, a desired gap is formed in the finished die 12 with respect to the section 20 of the male part 14.

Instead of the cap-shaped element 38, a film (placeholder) can be provided.

In order to manufacture the attachment according to the invention in the form of the matrix 12 and the male 14 of the ceramic bridge framework from the positive model thus produced, i.e. the primary part 28 and the secondary part (not shown), the primary part 28 or the secondary part is clamped in a holding frame, which in turn is mounted on a frame Shaft is mounted to allow rotation by 180 °. Furthermore, the shaft is on one in three axes x, y. z precisely movable table mounted. The axis of rotation of the shaft lies, for example, in the y direction. The table drive can be mounted in a device housing. The opening required in the device housing for the movement of the table can be covered in any manner known per se, e.g. B. by a bellows or a cuff.

Furthermore, an optical scanning unit for distance measurement is accommodated in the device housing. The scanning unit comprises a laser beam source, not shown, e.g. B. a laser diode, and appropriately a device for reflecting the light of the laser diode into the beam path of the scanning unit and other optical elements, as well as a CCD camera matched to the sensitivity of the laser. In front of the CCD camera, a birefringent crystal is arranged, which separates the laser light reflected from the primary or secondary part into a neat and an extraordinary part, whereby holograms with border areas that can be measured precisely and on the basis of which the exact distance to the measured point can be determined.

The scanning unit is fastened in the device housing in such a way that a emitted laser beam runs along the z-axis. After a one-off calibration during assembly, the scanning unit supplies absolute information about the distance to the object reflecting the laser beam, that is to say to the primary or secondary part clamped in the holding frame according to the so-called conoscopic holography. Details of this measuring method are described for example in WO 99/64916, US 5,953,137, WO 99/42908, US 5,892,602, US 5,291,314, EP 0 394 137, EP 0 394 138 and US 4,976,504.

The high intensity of the laser light allows the use of an imaging lens with a relatively small aperture, so that there is a depth of field that is greater than, for example, the typical height of the dental bridge.

Since the previously described scanning unit outputs measured values over the absolute distance of the point illuminated by the laser beam due to the reflection as a measured value, not only is the scanning unit adjusted when the device is installed such that the laser beam runs parallel to the z-axis of the table, but also The scanning unit is also calibrated via a reference plate that is clamped in the holding frame. The range of tolerable blurring (depth of field) can be determined by moving the table in the z direction.

During a later measurement of the positive model or its parts, the holding frame is moved accordingly over the table along the z-axis of the table into the focus area of the scanning unit. The plaster or positive model is now digital. siert by the holding frame and the table experience along the x and y axis, z. B. rows or columns, and this information with the distance information determined stony is linked. The position of the table and thus of the model to be measured in the z direction is subtracted from the distance value which the scanning unit outputs in order to form the measurement data record. While the model is being scanned, the table is not moved along the z-axis, but only in the x and y directions.

By linking the x and y position values with the distance information of the scanning unit, a data pattern is generated which reflects the three-dimensional design of the side of the positive model or its parts facing the scanning unit.

For complete three-dimensional acquisition of the entire model, each part of the positive model together with the holding frame after scanning one side by 180 ° z. B. rotated about the y-axis and the back is measured in the same way.

However, a pre-scan (pre-run of the method) can also be carried out before the start of the measurement of the first side of the positive model in order to determine an extreme value of the positive model in the z direction, e.g. B. the model point with the smallest distance to the scanning unit, and the associated z-value of the coordinates as a reference value and thus the distance information is standardized to the model point as a reference point. This reference value can be used to form a reference plane perpendicular to the z-axis. In this way, the maximum dimensions of the measured model can be taken directly from the data set generated.

Insofar as redundant measurement data are generated by the measurement from two sides, these can be removed later by appropriate post-processing by software when the volume model is formed, in order to avoid malfunctions in the later activation of a processing machine or a processing tool such as a milling cutter. Such a milling cutter is expediently integrated into a housing, for example in relation to the table opposite the optical scanning unit. The milling cutter expediently has a fixed spindle. A ceramic blank, for example made of a pre-sintered yttrium oxide-stabilized zirconium oxide, is clamped in a further holding frame which is connected to the rear end of the shaft. The feed movements in the x, y and z directions required for machining the side of the blank facing the milling cutter are carried out by correspondingly moving the table with the shaft and the holding frame. Once the side of the blank facing the milling cutter has been finished, the blank can be moved away from the milling cutter by advancing in the z direction and the holding frame can be rotated by 180 ° around the other side of the blank as when scanning the positive model or its parts to edit.

It should be noted that, after hand-modeling the modeling aid, a male part can be produced from a ceramic blank such as zirconium oxide, which is then sintered. This male part then forms the basis for the secondary part to be produced.

An arrangement is shown in principle in FIG. 6 with which a positive model or primary or secondary part of such an arrangement is not generated by hand modeling, but rather by scanning a master model 40 as CAD model 42. For this purpose, the master model 40 is scanned in the usual way with a scanner 44. The model of a cap is derived from the digitized data obtained in this way in a computer 46.

, __ £ 2 chens (calculated and linked to data from a library in which outer geometries of positive models to be produced or parts thereof are stored in the form of attachment parts. The corresponding data are linked to the digitized data of the master model 40 in order to produce the CAD model 42 7 on the basis of which a denture or attachment part is produced from a blank in the CAM process.

Claims

Patent claims Method for producing a dental bridge framework and positive model for one

1. Dental bridge framework using at least one blank made of ceramic material that is processed using the CAM process, so that the bridge framework consists of at least two attachment parts, that each attachment part consists of a blank made of ceramic material processed using the CAM process and that A CAD model or a hand-modeled model serves as a template for processing at least one blank.

2. Process for producing the dental bridge framework according to claim 1 from ceramic material such as zirconium oxide or containing it, characterized by the process steps

- Making an impression of a jaw comprising tooth stumps and their surroundings, which accommodates the bridge framework to be produced,

- Making a master model of the impression,

- modeling a cap on one (first) of the tooth stumps of the master model,

- Connecting the cap with a ready-made modeling aid to form a primary part of a positive model,

- manual processing of the modeling aid part, taking into account minimum geometries for a patrix of the bridge framework to be produced after the primary part, at least using the CAM process,

Hand modeling a secondary part that can be placed on the modeling auxiliary part or producing the male part from a ceramic blank based on the modeling auxiliary part, either removing the primary and secondary part from the master model and producing the male part and a female part or removing the secondary part from the master model and producing a matrix based on the secondary part, each from a ceramic blank using the CAM process.

3. The method according to claim 2, characterized in that the matrix and/or patrix is blinded to the desired extent.

4. The method according to claim 2 or 3, characterized in that a millable element made of plastic is used as the modeling aid, which consists of a web with a conical cross-section and a truncated cone, the web being connected to the cap in such a way that the modeling aid part is aligned with the (second) tooth stub receiving the secondary part in such a way that the longitudinal axis of the truncated cone runs parallel or substantially parallel to the second tooth stub.

5. The method according to at least one of the preceding claims, characterized in that the modeling aid part specifies a minimum geometry for the male part to be produced from the primary part in order to avoid impermissible tensile stresses in the bridge framework.

6. Method according to at least one of the preceding claims, characterized in that the modeling aid part specifies a minimum cross section in the web.

7. The method according to at least one of the preceding claims, characterized in that the modeling aid part is processed with a milling tool that specifies a minimum radius in the basal edge area.

8. The method according to at least one of the preceding claims, characterized in that a modeling aid such as a round element is used during additive processing of the basal contour to achieve a desired radius.

9. The method according to at least one of the preceding claims, which means that the modeling aid part has at least one marking that becomes visible when a minimum geometry to be maintained is reached.

10. The method according to at least one of the preceding claims, characterized in that the web and the truncated cone of the modeling aid part are designed in such a way that the primary part is completely or almost completely over in two positions rotated by 180 ° or approximately 180 ° to one another its entire top and bottom can be digitized.

11. The method according to at least one of the preceding claims, characterized by the fact that a film is applied to the truncated cone before hand modeling of the secondary part.

12. Positive model for a bridge framework made of a ceramic material such as zirconium oxide or containing zirconium oxide using the CAM process, characterized by the fact that the positive model consists of a primary part (28) and a secondary part, that the primary part consists of a surrounding a first tooth stump Cap (26) and an assembled modeling aid part (18) connected to it, which consists of a web (24) connected to the cap and a truncated cone (22) extending from it, and that the modeling aid part has minimum geometries for a CAM process the base of the primary part of the bridge framework (10) designed as a dividing attachment.

13. Positive model according to claim 12, characterized by the fact that the minimum geometry is the cross section of the web (24) of the modeling aid part (18) and/or radii (30) on surface edges between the web (24) and the truncated cone (22). are.

14. Positive model according to one of claims 12 and 13, characterized in that the assembled modeling aid part (18) has at least one marking (36) to identify the minimum geometries achieved.

15. Positive model according to one of claims 12 to 14, characterized in that a removable film (38) is arranged as a placeholder between the primary part (18) and the secondary part.

6. Positive model according to one of claims 12 to 15, characterized in that the positive model has a convex surface on all sides or essentially on all sides on the basal side.

17. Division attachment, which is produced in the CAM process on the basis of the positive model according to one of claims 12 to 16, wherein the matrix and male part of the division attachment are each made from a blank which consists of zirconium oxide or ceramic material containing zirconium oxide.