CA1251305A

CA1251305A - Transparent ceramic surface layer for a ceramo- metallic dental reconstruction

Info

Publication number: CA1251305A
Application number: CA000474153A
Authority: CA
Inventors: Michel Heurtaux
Original assignee: Suissor SA
Current assignee: Suissor SA
Priority date: 1984-02-15
Filing date: 1985-02-13
Publication date: 1989-03-21
Also published as: EP0152338A2; EP0152338A3; DE3571390D1; DK69385A; ES540354A0; JPS60195033A; DK69385D0; FR2559386A1; FR2559386B1; ES8601678A1; EP0152338B1; ATE44455T1

Abstract

PATENT

TRANSPARENT CERAMIC SURFACE LAYER FOR A CERAMO-METALLIC
DENTAL RECONSTRUCTION

SUISSOR S.A.

Inventor: Michel HEURTAUX

ABSTRACT
The present invention relates to a transparent ceramic surface layer of a ceramo-metallic dental recon-struction.
The transparent ceramic surface layer of a ceramo-metallic dental reconstruction is produced from a mixture containing at least two separate glass frits.
Preferably, the first glass frit is fusible and does not devitrify, and the second glass frit is more refractory and devitrifies partially to leucite. In addition, particle size can be less than 65 µm to improve the properties with respect to shrinkage.

Description

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The present invention relates to the technlcal field oF ceramo-metallic dental recons-tructions. More par-ticularly, it relates to the composition of the ceramic glass employed to form the transparent surface layer of a dental reconstruction such as crowns, inlays, bridges, and the like.
This type of dental reconstruc-tion is usually produced from a series of ceramic layers coa-ted on a metal coping, deposited, for example, on the stump of a tooth reduced after shaping with a drill.
This series of ceramic layers consists of a basal opacifying layer, two intermediate layers known under the terms of "dentine" and "incisal" and a transparent surface layer intended to resemble the gleam of the enamel of the natural tooth.
The subject of the present invention is aimed precisely at producing this last transparent surface layer.
In the present state of the art no ceramic layer is available which is endowed with a perfect translucency comparable to that of a glass pane. A really translucent ceramic surface layer would enable the user -to give -the prosthesis the esthetic appearance of a natural -tooth.
The present invention improves the quality of transparent ceramic layers of this type.
In accordance with the present invention, the ceramic layer is produced From a mixture containing at least two separate glass frits, namely:
approximately 90 % by weight of a first glass frit which is fusible and does not devitrify, and ~$

approximately 10 % by weight of a second glass frit which is more refractory and devitrifies partially to leucite.
Other features and advantages of the present invention will become apparent from the reading of the detailed description which follows, particularly relying on an illustrative example of practical implementation.
The transparent ceramic layer in a preferred form has expansion co-efficients which are stable and match all the precious or base alloys.
The glass frit employed is produced by mixing two separate glasses, one fusible and non-devitrifying, the other slightly more refractory and devitrifying partially to leucite, a mineral with high thermal expansion.
The first glass frit, which is fusible and does not devitrify 9 is employed as such. In contrast, the second glass frit is devitrified, for example, for approxima-tely 12 hours at a temperature of the order of 900C. During this thermal devitrifying treatment, an in situ crys-tallization phenomenon makes its appearance in a conventional manner.
It will also be noted that, during successive bakings, the fusible glass, at the limit of saturation with leucite, does not dissolve the leuci-te in the second glass and consequently its proportion remains cons-tant. In this way, a stable expansion is produced.
The hardness of the transparent ceramic layer can also be reduced by an increase in the percentage of fluxes, favoring Na20. The ceramic layer is formed from a ,~ , 36)~

mixture of two glass frits containing, in to-tal, from approximately 20 to approxima-tely 30 % by weight of fluxes, among which soda Na20 is present in a proportion of approximately 7 to approximately 8 % by weight.
The following overall composition of transparent ceramic layers produces satisfactory results in practice and is given below by way of an illustrative example.
SiO2 59 to 59.5 % by weight A1203 15 to 16 % by weight CaO 0.5 to 1.5 % by weight MgO O to 0.2 % by weight K20 11 to 13 % by weight Na20 7 to 8 % by weight B203 2.5 to 3.5 % by weight BaO O to 3 % by weight CaF2 0.5 to 3 % by weight TiO2 0.2 to 0.5 % by weight The ceramic layers according to the invention have also been adapted so as to be capable of avoiding any background coloring phenomenon due to the metal substrates. These metal substrates are usually made from an alloy of various metals, among which silver is, in particular, responsible for such a background coloring. In fact, the Ag~-~ ion migrates fairly readily in the ceramic and causes a greenish yellow coloring when reduced to the metal s-tate. It is precisely to avoid a phenomenon o-F this type that approximately 0.2 % by weight of cerium oxide CeO2 7 which is an active oxidizing agent which keeps the silver in the non-coloring oxide state 9 is added to the ~, ~ 2513~

mixtures of glass frits according to the invention. This cerium oxide is added after the grinding operation which produces the glass frit. The glass frits are obtained in a conventional manner by melting and homogenizing a powdered mixture of the basic components required for producing the abovementioned compositions.
To reduce shrinkage during the baking, the particle size distribution of the mixture of -the two glass frits has been adjusted as a result of the following observation. The voidage of a population of large particles (40 to 65 microns) is of the order of 40 %. By introducing particles of medium size (12 to 40 microns) in a proportion of approximately 5û % by weight relative to the large particles, the voidage drops to approximately 20 %. Lastly, when particles of much smaller sizes (below 5 microns) are added, the voidage becomes still smaller.
Consequently, this results in a lower shrinkage on baking.
A particle size distribution of this type also makes it possible to obtain better plasticity of the paste at the time of its use.
In order to produce a glass frit according to the invention, intended for producing a transparent surface layer, it is thus desirable to make use of a particle size distribution of the following type:
40 to 65~ ...... 40 to 50 % of the particles 12 to 40 ~ ..... 30 to 35 % of the particles ~ 12~u ......... 15 to 30 % of the particles.
Glass frits required for the production of transparent ceramic surFace layers are presented in the . ' ~ :, 3~S

form of a paste ready for use and intended to facilitate the work of the user whlle making it possible to achieve a saving in active product. Such frits are presented in -the form of a paste containing a suitable quantity of a plas-ticizer~ so as to enable them -to be packaged in a tube or a dispenser for paste of the aerosol type.
A typical example of formulation of glass frits according to the invention, packaged in an aerosol dispenser, is given below:
100 parts by weight of active products, 30 to ~0 parts by weight of plasticizer, 100 parts by weigh-t of a propellant agent 7 such as a Freon .
Qccording to a particular embodiment of glass frits of this type, the plasticizer is preferably chosen from diethylene glycol diethyl ether and propylene glycol methyl ether.
Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or -the scope of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Transparent ceramic surface layer of a ceramo-metallic dental reconstruction, which is produced from a mixture containing at least two separate glass frits, namely:
about 90% of a first glass frit which is fusible and does not devitrify, and about 10% of a second glass frit which is more refractory and devitrifies partially to leucite;
said glass frits having a particle size of less than about 65 µm, said mixture of glass frits containing from approximately 20 to approximately 30 % by weight of fluxes in which approximately 7 to approximately 8 % of Na2O by weight is present.

2. Ceramic layer as claimed in claim 17 in which the second glass frit is devitrified for approximately 12 hours at a temperature of the order of 900°C, before being mixed.

3. Ceramic layer as claimed in claim 1 or 2, which corresponds to the following overall composition:
SiO2 59 to 59.5 % by weight Al2O3 15 to 16 % by weight CaO 0.5 to 1.5 % by weight MgO 0 to 0.2 % by weight K2O 11 to 13 % by weight Na2O 7 to 8 % by weight B2O3 2.5 to 3.5 % by weight BaO 0 to 3 % by weight CaF2 0.5 to 3 % by weight TiO2 0.2 to 0.5 % by weight.

4. Ceramic layer as claimed in claim 1, which corresponds to the following overall composition:
SiO2 59 to 59.5 % by weight Al2O3 15 to 16 % by weight CaO 0.5 to 1.5 % by weight MgO 0 to 0.2 % by weight K2O 11 to 13 % by weight Na2O 7 to 8 % by weight B2O3 2.5 to 3.5 % by weight BaO 0 to 3 % by weight CaF2 0.5 to 3 % by weight TiO2 0.2 to 0.5 % by weight.

5. Ceramic layer as claimed in claim 1 or 2, in which the mixture of the two glass frits has a particle size distribution of the following type:
40 to 65 µ 40 to 50 % of the particles 12 to 40 µ 30 to 35 % of the particles < 12 µ 15 to 30 % of the particles.

6. Ceramic layer as claimed in claim 4, in which the mixture of the two glass frits has a particle size distribution of the following type:
40 to 65 µ 40 to 50 % of the particles 12 to 40 µ 30 to 35 % of the particles < 12 µ 15 to 30 % of the particles.

7. Ceramic layer as claimed in claim 1 or 2, in which the mixture of glass frits has a particle size distribution of the following type:
40 to 65 µ 40 to 50 % of the particles 12 to 40 µ 30 to 35 % of the particles < 12 µ 15 to 30 % of the particles which corresponds to the following overall composition:
SiO2 59 to 59.5 % by weight Al2O3 15 to 16 % by weight CaO 0.5 to 1.5 % by weight MgO 0 to 0.2 % by weight K2O 11 to 13 % by weight Na2O 7 to 8 % by weight B2O3 2.5 to 3.5 % by weight BaO 0 to 3 % by weight CaF2 0.5 to 3 % by weight TiO2 0.2 to 0.5 % by weight.

8. Glass frits required for the production of a ceramic layer as claimed in claim 1, 2 or 4, which are presented in the form of a paste ready for use containing a suitable quantity of a plasticizer, and suitable for being packaged in a tube or a dispenser for paste of the aerosol type.

9. Glass frits required for the production of a ceramic layer as claimed in claim 1 or 2, which are presented in the form of a paste ready for use containing a suitable quantity of a plasticizer, and suitable for being packaged in a tube or a dispenser for paste of the aerosol type, in which the plasticizer is chosen from diethylene glycol diethyl ether and propylene glycol methyl ether.

10. A transparent ceramic surface layer of a ceramo-metallic dental reconstruction, which is produced from a mixture containing at least two separate glass frits, namely, said mixture having the following overall composition:
SiO2 59 to 59.5 % by weight Al2O3 15 to 16 % by weight CaO 0.5 to 1.5 % by weight MgO 0 to 0.2 % by weight K2O 11 to 13 % by weight Na2O 7 to 8 % by weight B2O3 2.5 to 3.5 % by weight BaO 0 to 3 % by weight CaF2 0.5 to 3 % by weight and particles of said mixture having a size less than 65 µm.

11. A ceramic layer according to claim 10, in which the mixture of the two glass frits has a particle size distribution of the following type:
40 to 65 µ 40 to 50 % of the particles

12 to 40 µ 30 to 35 % of the particles < 12 µ 15 to 30 % of the particles.