DENTAL PROSTHESIS AND PROCESS FOR THE MAKING THEREOF

Abstract: The present invention relates to a dental prosthesis comprising at least two separately, arranged synthetic layers, wherein a first synthetic layer serves as an underlayer for the dental prosthesis and a second synthetic layer serves as an incisal, cutting mass for the dental prosthesis and wherein preferably a dental prosthesis to claim 1, wherein at least one of the separately arranged synthetic layers comprises one or more organic compounds, preferably in the form of dental composite.

Description: DENTAL PROSTHESIS AND PROCESS FOR THE MAKING THEREOF The present invention relates to a dental prosthesis and to a process for the making thereof. Dental prostheses are often formed from a simple block of for example dental porcelain, A problem with these type of prostheses is that in order to aesthetically correspond with the natural teeth to be replaced, the prosthetic material has to be made translucent, which however provides a prosthesis which is intrinsically very weak in dental strengths. In order to provide a prosthesis having the desired structural, dental strength, an opaque colouring of the prosthesis often results whereby the aesthetic qualities of the prosthesis leave a lot to be desired. An object of the present invention is to provide a dental prosthesis which improves on this situation. According to a first aspect of the present invention there is provided a dental prosthesis according to claims 1-23. The inventors have shown that by making a dental prostheses by separately, preferably automatically, arranging synthetic layers one on top of the other to provide a dental prosthesis, wherein a first synthetic layer serves as a bodylayer and a second synthetic layer serves as an incisal, cutting mass, and whereby the differing layers preferably comprise organic composite material, both a desired dental aesthetic effect and a desired dental functional strength, are provided. According to a second aspect of the present invention, there is provided a process for providing this dental prosthesis according to claims 24 and 25. The invention will now be described by way of the following description, with reference to the figures, wherein: - figures 1A-E schematically show the formation of a base die and the arranging of the dental prosthesis layers thereon; - figure 2 is a partially, cut away side view: of a mold wherein the underground die is frased during arranging of the differing dental prosthesis layers thereon; - figure 3 shows a perspective view of a base layer of a dental prosthesis according to the present invention on a molded, plaster underground; and - figure 4 a partially, cut away perspective view of a dental prostheses according to the present invention on an underground. A base die (1) figure 1A, which is preferably made of plaster, is molded to the form of a tooth stump, figure IB, for which the dental prosthesis according to the present invention is to be provided. To obtain this die (1) , an impression of the tooth stump is firstly cast in plaster. The plastermodel - thus obtained is scanned and the data entered into a computer with the aid of a digital camera . The lower part of the cast model is painted black in order to mark the lower edge of the prosthesis to be made. On scanning of the plaster model, a fast laser strip scan method can be used, whereby the 3-dimensional geometry of the plastermodel of the tooth stump and the surrounding teeth can be determined. The formation of a plaster model can be omitted when the 3-dimensional form for the dental prosthesis can be determined directly in the mouth. Information concerning the 3-dimensional form and geometry of the dental prosthesis is fed into a computer. If desired, further information can be provided concerning the precise lower edge of the prosthesis to be formed, the separation lines with neighboring dental elements and the like. From this information, the location of the occlusion line can be determined. Within the parameters which have been provided or determined with respect to the form and geometry of the prosthesis to be formed, a choice can be made from a number of standard forms or, if this information is available use can be made of information concerning the form or geometry of the original tooth. Use can also be made, for example of a mirror image form dental element, whereby this information can be scanned and entered into a computer and utilized as a starting point for provision of the prosthesis. These last aspects concern the outer form of the prosthesis to be formed, which has the form of the tooth stump or base for the prosthesis determined the internal service thereof . If required, the final form of the prosthesis can be imaged in a computer simulation together with the neighboring dental elements in order to be sure that the prosthesis correctly cooperates with the neighboring teeth. The final form of the prosthesis to be provided is then able to be adjusted on the basis of gnathological rules. In this manner the form of the prosthesis can be adjusted in order to provide an optimum tooth on tooth contact with both neighbouring and opposing dental elements or teeth. Consideration is taken of the movement, and not only the static relation, between the prostheses and the neighboring or opposing dental elements or teeth. Especially in 3-dimensional mandibular movements, it is required that the normal working be maintained without interference from foreign objects and projections, which do not belong, and which could disturb the chewing movement leading to trauma and uneven distribution of stress over the dental elements and teeth. In this way an internal surface of the prosthesis, which is to be arranged on the tooth stand, and the outer surface of the prostheses can be optimally determined. After the interior and exterior prosthesis services have been determined, the interface surfaces between the cement and the core incisal composite and between the dentine composite and the cutting composite can be determined. Software is used to calculate the interior surface, corrected with marginal gap, overall cement thickness and composite core material thickness and the different interfaces between the material layers as specified by an operator. The build up of the prostheses, for example taking the form of a crown, ensures that the cement thickness between the composite core and the die, which is made from plaster on the basis of the computer registered data, is defined more than the marginal cement gap. In this way a better support for the high strength core material is provided which core material takes most of the load exerted on the prosthesis during placement and mastication. Stress on the core composite is relieved since the high strength core substructure is closest to the die. This means that no restrictions are placed on the type on preparation chosen- and that composite shoulders of the substructure prosthesis can be used for enhanced esthetics. A dental prosthesis according to the present invention can than be produced as follows: A block of predetermined material, see figure 1A, is fixed in a high precision vice in a milling machine, not shown, and the negative of the inner surface of the prosthesis is accurately milled using a cilindrical disk mill and a round hard metal mill controlled by a computer. The resulting die for the prosthesis is shown in figure lb. Figure 3 shows a base 1, see also figures 1, 2, and 4 provided with a head 2, as stated above, being made of plaster and being milled in a milling machine. During milling of the block, figure 1A, the double-prismatic ) ω t NJ H h- 1 LΠ o LΠ O Π o Lπ 3 3 rt H- 0 ) S if 0 ø CQ CD rt 0 CQ I-! 0 CD CD ϋ o o rt - Mi 0 if CD CQ ft (D if O W- CD CD c i-i O l_l. Hi O CD CD tr H- hi P. Ω CQ LQ 0 rt CD 0 CO SD H- Λ h{ rt 3 0 ø CD if P 0 CD Q CD 1-5 CO 3 3 rt H CD H- 0 H- α CQ P ) t-> P, J H- CD ø CQ Si s ■ <! Pi SD J 0 ) rt K CQ 3 • CQ ø 4 &. CD O 0 ) tr 0 ) t 0 ) 0 0 ) H < tf Q hj CD O CD ) - P. ø ■ <: H LQ S fD if H- & CD ) CQ ii * H- CD CD K ø SD Ii CD Hi 1 rr rt 00 H- if CD 0 CD H H- rt CQ hi CQ SD 0 PJ 3 ft ) i 3 hj 0 CD H- H Ω 3 J CD Ω 0 i H- LQ CQ CD 03 Pi Figure 4 shows the completed dental prosthesis, P, in the form of a crown consisting of the core 6, dentine 8 and cutting mass 10. As described above, a high strength base core layer 6 in the form of composite is injection moulded onto the die head 2 in excess, whereby it will be realized that the composite can comprise a resin binder, The form of the core layer can also be molded ' by means of a thermosetting resin binder, injection molding, spraying, or any suitable method, whereafter the composite can be cured by means of heating, chemically curing light curing and the like, whereafter the cured layer can then be milled in the milling machine to pre calculated designed thickness. When a UV-setting composite is used, for a bridge for example, this composite can be impregnated with glass fibres in the longitudinal direction of the bridge in order to strengthen this, before it is cured. An example of a suitable thermoplastic binder is polyamide or polyacetal . Examples of a thermosetting binder include epoxy resins, formaldehide, polyisocyanates and polyesters. The inorganic filler can comprise oxides or glass like materials in the form of balls discs or fibers. The last step in the production of the dental prosthesis according to the present invention is the individual colouring and polishing of the prosthesis. Example 1 A bridge was made according to the present invention consisting of differing layers of a composite material, being a methacrylate synthetic resin provided with an Si0 2 filler. The methacrylate resin consisted of a mixture of : l-methylethyliden)bis 4-1-phenyloxy (2-hydroxy- 3.1 propaandiyl) bismethacrylate, 7.7.9-Trimethyl-4, 13-dioxo-3 , 14-dioxa-5, 12- diaza-hexadecaan-1, 16-diol-dimethacrylaat, and 1, 12-Dodecanol-dimethacrylaat in the weight ratio 11.5:30.5:13.5 wherein the Si0 2 filler consisted of Siliamin 1,1,1 Trymethyl-N- (trimethyl) "glasfrit" (a molten glass quenched in water and subsequently ground to fine size) to titaandioxide and zirkoondioxide in the weight ratio 3.0:45.0:8.0:8.0 wherein the filler of B and C respectively the body and incensal mass, consisted of siliciumdioxide and "glasfit" in the ratio of 6.0-75.0. Trace amount of a colouring pigment were also added. See table below. The composite base material 1 was injected via into a mold, see figure 2. The mold was closed off on the upper side by a plate and on the sides by a transparent plate, which connect onto the base of the mold. After the injection of the differing layers, each layer was radiation for 2 minutes with the aid of a Degulux (Degussa, BRD) whereby the layers were cured. Following curing each layer was then automatically milled to the desired computer registered form in the milling vice. The dentine layer B and cutting layer C were subsequently injection molded, cured and milled. Finally, the foundation 4 and base 1 were removed after which the prosthesis was polished. Example 2 In this example, a fiber strengthened composite provided with a thermosetting binder, polyamide, was injection moulded The methacrylate resin consisted of a mixture of: l-methylethyliden)bis [4-1-phenyloxy (2-hydroxy- 3-l-propaandiyl)bismethacrylaat, 7,7, 9-Trimethyl-4, 13-dioxo-3, 14-dioxa-5, 12- diaza-hexadecaan-1, 16-diol-dimethacrylaat and 1, 12-Dodecanol-dimethacrylaat in the weight ratio 11.5:30.5:13.5. The filler for the dentine and cutting layers consisted of silicium dioxide and "glasfrit" in the ratio 6.0:75.0. Furthermore trace amounts of a pigment were added. The composite material for the base was injected into the mold 300 °C, whereafter the prosthesis was processed as in example 1. The invention is not limited to the specific description, but is rather determined by the following claims .

Claims: CLAIMS 1. A dental prosthesis comprising at least two separately, arranged synthetic layers, wherein a first synthetic layer serves as an underlayer for the dental prosthesis and a second synthetic layer serves as an incisal, cutting mass for the dental prosthesis. 2. Dental prosthesis according to claim 1, wherein at least one of the separately arranged synthetic layers comprises one or more organic compounds, preferably in the form of dental composite. 3. A dental prosthesis according to claims 1 or 2, wherein at least one or more of the synthetic layers comprises one or more inorganic compounds, preferably ceramic material. 4. Dental prosthesis according to any of the claims 1-3, wherein the separate layers are automatically arrangeable one on top of the other, preferably by a computer controlled system utilizing geometric information preferably obtainable via a CAD/CAM system. 5. Dental prosthesis according to any of the preceding claims, wherein the organic compounds comprise a synthetic, curable resin. 6. Dental prosthesis according to claim 5, wherein the resin comprises one or more polymers. 7. A dental prosthesis according to claim 6, wherein the polymers comprise acrylic resin. 8. Dental prosthesis according to claim 7, wherein the acrylic resin comprises the thermoplastic polymers or co-polymers of acrylic acid, methacrylic acid, esters of these acids or acrylonitrile 9. Dental prosthesis according to claim 8, wherein the acrylic resin comprise one or more of the following esters of methacrylic acid - l-methylethylidene)bis [4, 1-phenyloxy (2- hydroxy-3.1-propandiyl) bismethacrylate; - 7,7, 9-Trimethyl-4,13-dioxo-3,14-dioxa-5,12- diaza-hexadecane-1, 16-diol-dimethacrylate; and - 1, 12-Dodecanol-dimethacrylate. 10. Dental prosthesis according to claim 9 wherein the esters are present therein in a 10% lying in the range of between 5 and 50%, preferably 10-40%, more preferably 15-30%, and even more preferably about 19%. 11. Dental prosthesis according to any of the preceding claims, wherein the organic compounds comprise a composite material. 12. Dental prosthesis according to claim 11, wherein the composite material further comprises one or more of the following inorganic materials: - a dental prosthetic filler and/or a dental prosthetic pigment. 13. Dental prosthesis according to claim 12, wherein the dental prosthetic filler material comprises ceramic. 14. Dental prosthesis according to claim 13, wherein one or more of the layers further comprises a glass component, preferably comprising: 55-75 wt.-% Sio 2 , 0,5-30 wt.-% A1 2 0 3 , 0,5-30 wt.-% K , 0,5-15 wt.-% Na 2 0 en 0,5-30 wt . % Li0 2 , and optionally, in 5 wt . % or less one or more of the following: BaO, CaO, SrO, La 2 0 3 , Sb 2 0 3 , Ti0 2 , F 2 , B 2 0 3 , ZnO, MgO en Ce0 2 . 15. Dental prosthesis according to any of the preceding claims, substantial consisting of three separately, preferably automatically, arranged, separately cured and separately milled to a predetermined form layers, which layers correspond to a base layer, a dentine layer and a cutting layer, of a tooth. 16. Dental prosthesis according to claim 14, wherein the base layer comprises at least 20, for example 30, 40, 50 or 60, preferably at least 70 and more preferably at least 80 % filler, the balance being made of the organic compounds and pigment wherein the pigment is present in a maximum weight percentage of 5, preferably a maximum of at least 2 , most preferably a maximum of at least 1 weight % . 17. Dental prosthesis according to claims 15 or 16 wherein the dentine layer comprises at least 50, for examples 60 or 70 weight %, preferably at least 80, most preferably at least around 90 weight % filler, the balance being made of the organic compounds and pigment, wherein the pigment is present at a maximum weight percentage of 5, preferably 2, more preferably 1 weight % . 18. Dental prosthesis according to any of the claims 15-17, wherein the weight percentage of filler in the dentine and/or the cutting layer is at least twice as much as present in the base layer. 19. Dental prosthesis according to any of the claims 15-18, wherein the weight percentage of organic compounds in the base is at least one and a half, preferably at least twice the amount of organic compounds present in the dentine and/or the cutting layer. 20. Dental prosthesis according to any of the preceding claims, comprising an Si0 2 filler material and a methacrylate synthetic resin wherein the methacrylate synthetic resin consists of a mixture of: - l-methylethylidene)bis [4, 1-phenyloxy (2- hydroxy-3. l-propandiyl)bismethacrylate; - 7,7, 9-Trimethyl-4,13-dioxo-3,14-dioxa-5,12- diaza-hexadane-1, 16-diol-dimetacrylate; and - 1, 12-Dodecanol-dimethacrylate, preferably in the weight ratio of about 11,5:30,5:13,5. 21. Dental prosthesis according to claim 20 further comprising fibre-glass reinforcing material, wherein the fibre-glass is preferably exclusively present in the base layer. 22. Dental prosthesis according to any of the preceding claims, wherein the base layer has a 3-point bending strength of at least 200, for example 300, preferably at least 380 Mpa. 23. Dental prosthesis according to claim 22, wherein the body and the incisal mass have a 3-point bending strength of at least 40, for example at least 60, most preferably at least 80 Mpa. 24. Dental prosthesis according to any of the preceding claims, wherein the base layer has a transparency lying in the range of 0-10, preferably lying in a range of 0-5%, the dentine layer has a transparency lying in the range of 10-50, for example 10-40, preferably 20-25% and the cutting layer has a transparency lying in the range of 20-80, for example 25- 50 and preferably 30-40%. 25. Process for providing a dental prosthesis according to any of the preceding claims, comprising the steps of: - providing a template for the dental prosthesis, - automatically arranging a first synthetic layer on this template, - curing this synthetic layer, and - subsequently milling the cured synthetic layer to a computer determined form, followed by - repeating these steps for one or more further layers, to form the dental prosthesis. 26. Process according to claim 25, wherein the template is made utilizing of data obtained by a computersystem, preferably a CAD/CAM-system, and wherein the template is preferably made of plaster. 27. Dental prosthesis obtainable according to any of the claims 25-26. 28. Use of the dental prosthesis, according to claim 27, or any of the claims 1-25 for replacing partially or completely one or more teeth.

Inventors: VAN DER ZEL JOSEPH MARIA, VAN DER ZEL, JOSEPH, MARIA
Applicants: CICERO DENTAL SYSTEMS B V, ZEL JOSEPH MARIA V D, CICERO DENTAL SYSTEMS B.V., VAN DER ZEL, JOSEPH, MARIA
Application year: 2001
Main classification: A61C13
IPC codes: A61C13, A61K6