FR2511361A1 - Vitreous enamel for use on metal dental prostheses - contains borosilicate glass, and is used esp. on prostheses made of nickel-chromium alloy contg. no noble metals - Google Patents

Abstract

The enamel contains by wt. 40-60% SiO2, 15-30% B2O3, 3-9% Al2O3; and sufficient Na2O and/or K20 to provide the enamel with a baking temp. of max. 800 deg.C., and a coefft. of thermal expansion (CTE) of 9.5-11 ppm. in CGS units. The pref. enamel contains 44-54% SiO2, 16-30% B2O3, 13-20% Na2O, 3-9% Al2O3, and, all maxima, 4% K2O, 2.5% Li2O, 3% CaO, 5% CaF2, 6% ZrO2, 2% NiO, 1.5% CoO, 1.5% MnO2. The enamel is pref. baked onto an Ni-Cr alloy contg. min. 80% Ni + Cr, esp. with the compsn. 12-40% Cr, 50-80% Ni, 0.05-0.2% C, 0.05-0.5% Si, and, all maxima, 0.1% Mo, 15% Fe, 3% B, 5% Ti, 10% Co, 5% Zr, 5% Nb, 1% Mn, 3% Al. The enamel has a low baking temp., and excellent adhesion, esp. to Ni base alloys which are much less expensive than prostheses made of noble metals.

Description

 The present invention relates to a vitreous enamel composition for application to a metallic dental prosthesis.

 The invention also relates to dental prostheses thus coated and to a method for producing such prostheses.

 The metallic prostheses, coated with enamel, known until now, are made of gold or of a alloy of gold and other precious metals.

 The enameling of these prostheses is carried out by firing, generally around 90 ° -98 ° C. of a ceramic or an enamel obtained from a composition of borosilicate glass and other oxides.

 The gold and alloys of gold and precious metals used for these prostheses have two major drawbacks. On the one hand, their modulus of elasticity is 4 incompatible with the production of long-range prostheses or "bridges" and on the other hand, their price has become very high.

 Thus, for ten years, we have sought to replace gold and its alloys with stainless alloys, which are less expensive and have superior mechanical properties.

 In this regard, the alloys rich in nickel and chromium have the required qualities. However, the dental enamels used until now to coat prostheses in gold or in a gold alloy do not adhere to the aforementioned alloys based on nickel and chromium.

 It has been possible to obtain a certain adhesion of the enamel on such alloys by practicing roughness on the surface of the latter, such as streaks. However, the adhesion obtained using such devices is far from reaching that obtained when the support of the prosthesis is made of gold or a gold alloy.

 The object of the present invention is to create a vitreous enamel composition which makes it possible to obtain excellent adhesion to relatively inexpensive alloys and having good mechanical properties such as alloys rich in nickel and chromium.

According to the invention, this composition is characterized in that it contains the following compounds in the weight proportions indicated below:
SiO2: 40 to 60%
B203: 15 to 30%
Au203: 3 to 9%
Na2O and / or K2O: proportions determined so as to obtain an enamel with a firing temperature less than or equal to 8000C and a coefficient of thermal expansion between 95 and 110.10 7 (CGS units).

 Such an enamel composition exhibits excellent adhesion, not only on supports based on nickel and chromium alloys but also on supports made of ordinary steel.

 This remarkable adhesion can be explained on the one hand, by the relatively low firing temperature of the enamel which makes it possible to limit the surface oxidation of the alloy and to obtain a stable chemical bond with the latter, thanks to the lability of alkaline ions contained in enamel.

 The presence of alkaline oxides (Na2O and K20) makes it possible both to lower the firing temperature of the enamel and to obtain a coefficient of thermal expansion of between 95 and 110.10 7 (CGS units) for it, which is compatible with the Ni Cr alloy of the prosthesis, which makes it possible to limit the stresses likely to be generated between the enamel layer and the alloy, under the effect of temperature variations.

 Excellent results are thus obtained when the composition of the enamel contains between 13 and 20% by weight of Na 20.

According to a preferred version of the invention, the enamel composition contains the following compounds:
SiO2: 44 to 54%
B203: 16 to 30%
Na2O: 13 to 20%
K20: O at 4%
Li2O: at a 2.5%
CaO: O at 3% F2Ca: at å 5%
A1203: 3 to 9%
ZrO2: O at 6%
NiO: O at 2%
CoO: O at 1.5%
MnO:
The nickel-chromium-based alloy of the prosthesis coated with a vitreous enamel obtained by firing a composition in accordance with the invention is preferably such that the sum of the nickel and chromium concentrations is greater than 80% and that the ratio of the concentration of nickel to that of chromium is greater than 2.5.

 Such an alloy has very good mechanical properties and has excellent adhesion with the enamel obtained from the composition according to the invention.

According to one of the versions of the process according to the invention, a first layer of an enamel obtained from a composition according to the invention, added with opacifying and / or devitrifying agents such as SnO2 and
ZrO2, then apply a second layer of enamel, the base glass of which may be different depending on the teeth to be produced.

 Glass is used, the main constituent of the first layer of enamel but with less mineral fillers to keep it a certain translucency. Coloring agents such as NiO or TiO2 are added to it at a low dose to give it the desired coloration.

 A glass with a different composition from the previous one is used when it comes to making a tooth such as the incisor, the shape and translucency of which are clearly determined. As before, a small dose of opacifying agents and colorants is added thereto.

According to a preferred version of the invention, the composition of this glass contains the following compounds:
SiO2: 45 to 68%
B: O at 8%
Na2O: 10 to 17%
K20: O 5%
Li2O: O at 2.58
CaO: 0 to 3%
F2Ca: 0 to 5%
Al 203 0 to 7%
Zr02: 4 to 12%
TiO2: O at 5%
BaO: O at 6%
The enamel obtained from the composition in accordance with the invention also exhibits excellent adhesion to an ordinary steel support, in particular when the first layer of enamel applied to this support contains oxides such as NiO, MnO 2 or CoO which prevent surface oxidation of the steel at the firing temperature of the enamel.

 Other features and advantages of the invention will appear in the description below.

 Some nonlimiting examples of embodiment of the invention are given below.

Example 1
Enameled prosthesis based on nickel and chromium alloy.

The composition of this alloy is as follows:
Cr: 21%
Ni: 62%
C: 0.05%
Fe: 11%
B: 3%
Ti: 3%
Mn: 1%
This alloy has mechanical properties compatible with the production of long-range prostheses or "bridges".

To enamel this alloy, we start with a borosilicate glass of the following composition:
SiO2: 52%
Na2O: 18%
K20: 1.5%
Li2O: 2.5%
A1203: 4%
B203: 18%
CaO: 2%
F2Ca: 2%
A first layer of enamel, less than or equal to about 0.5 mm thick, is applied to the alloy, obtained by baking at around 7800C with the following mixture:
Aforementioned glass: 70%
SnO2: 12%
ZrO2: 12%
A1203: 8%
The tin oxide (SnO2) added to the composition acts as an opacifier. Zirconium oxide (ZrO2) acts both as an opacifier and as a devitrification agent.

A second and possibly a third layer of enamel is applied, obtained by baking at 7950C under a partial vacuum of 10 mbar of the following mixture:
Aforementioned glass: 89%
TiO2: 1%
SiO2: 10%
NiO: 0.004%
Nickel oxide (NiO) and titanium oxide (TiO2) added to the composition give the enamel the desired color.

 The enamel applied to the prosthesis has a coefficient of thermal expansion close to 100.10-7 (CGS units).

 This enamel has excellent adhesion.

The latter is demonstrated by bending at right angles an alloy blade based on nickel and chromium coated with enamel. The latter cracks in the fold area, forming disjointed enamel blocks which, for the most part, remain adherent to the support.

The tests also showed that the adhesion of the enamel to the support was always excellent when the proportions of the constituents of the composition varied between the limits indicated below:
SiO2: 44 to 54%
B2O3: 16 to 30%
Na2O: 13 to 20% K2 t 0 to 4%
Li2O: 0 to 2.5%
CaO: 0 to 3%
F2Ca: 0 to 5%
A120: 3 to 9%
3.

ZrO2: at 6%
NiO: 0 to 2%
CoO: 0 to 1.5%
MnO2: 0 to 1.5%
The enamel obtained from such a composition has a firing temperature below 800 C and a coefficient of thermal expansion between 95 and 110.10 7 (CGS units).

Furthermore, the adhesion of such an enamel remains just as excellent when the constituents of the alloy based on nickel and chromium vary between the following limits:
Cr: 12 to 40%
Ni: 50 to 80%
C: 0.05 to 0.2%
If: 0.05 to 0.5%
Mo: 0 to 0.1%
Fe: 0 to 15%
B: 0 to 3%
Ti: 0 to 5%
Co: 0 to 10%
Zr: 0 to 5%
Nb: 0 to 5%
Mn: 0 to 1%
Al: 0 to 3%
Example 2
Enamelled prosthesis based on ordinary steel.

 The ordinary steel used has a carbon content of less than 0.1% and has mechanical properties compatible with the production of a prosthesis, in particular of long range.

To enamel this steel, we start with a borosilicate glass of the following composition:
SiO2: 46%
Na2O: 18.5%
K20: 0.5%
Li2O: 2.5%
Al2O3: 5.5%
B203: 19.5%
ZrO2 5%
CaO: 2.5%
A first layer of enamel with a thickness less than or equal to 0.5 mm obtained by baking at approximately 7950 of the following mixture is applied to ordinary steel:
Aforementioned glass: 68%
NiO: 1.5%
Mn02: 1.5% Zr 2: 13%
SnO2: 8%
Al2O3: 5%
3.

SiO2: 3%
The nickel and manganese oxides added to the composition make it possible to avoid the surface oxidation of the steel at the firing temperature. A second layer of enamel with the same composition as that of Example 1 is then applied.

Example 3
Gold-enameled prosthesis:
To enamel the gold support of the prosthesis, we start with a borosilicate glass of the following composition:
If 2: 50%
B203: 20%
Na2O: 18%
Li2O: 2%
CaO: 2%
F2Ca: 3%
At 203: 5%
As in the previous examples, a first layer of enamel obtained by baking the following mixture is applied to the gold of the prosthesis
Glass: 72%
ZrO2 8%
Sn 2: 8%
A1203: 4%
A second layer of enamel obtained from the following composition is then applied to this first layer:
Glass: 92%
TiO2: 0.8%
NiO: 0.0058
Si02: 7.2%
The aforementioned glass having the following composition:
Si02: 64%
Na2O: 14%
K2O: 4%
CaO: 1.8%
CaF2: 1.2%
BaO: 5.2%
ZrO2: 9.8%
Of course, the invention is not limited to the examples which have just been described and many modifications can be made to them, without departing from the scope of the invention.

 Thus, there are many metals or alloys other than those described whose mechanical properties are compatible with the production of dental prostheses and which are capable of allowing excellent adhesion of an enamel layer obtained by baking a composition in accordance with the invention.

Claims (8)

 1. Composition of vitreous enamel intended to be applied to a metallic prosthesis, characterized in that it contains the following compounds in the weight properties indicated below:  SiO2: 40 to 60%  B2O3: 15 to 30%  Al2O3: 3 to 9%  Na2O  and / or K2O: proportions determined so as to obtain an enamel having a firing temperature less than or equal to 8000C and a coefficient of thermal expansion between 95 and 110.10-7 (CGS units).  2. Composition according to claim 1, characterized in that it contains between 13 and 20% by weight of Na 20.  3. Composition according to any one of claims 1 or 2, characterized in that it contains the following compounds:  SiO2: 44 to 54%  B203: 16 to 30%  Na2O: 13 to 20%  K20: 0 to 4%  Li2O: 0 to 2.5%  CaO = at 3%  F2Ca: 0 to 5%  Al2O3: 3 to 9% ZrO2 t to 6%  NiO: 0 to 2%  CoO: 0 to 1.5%  Mn02: 0 to 1.5%  4. Metal prosthesis coated with a vitreous enamel obtained by firing a composition according to any one of claims 1 to 3, characterized in that it is made of an alloy based on nickel and chromium, such as sum of the nickel and chromium concentrations is greater than or equal to 80% and the ratio of the nickel concentration to that of chromium is greater than or equal to 2.5.  5. Prosthesis according to claim 4, characterized in that the alloy has the following composition:  Cr: 12 to 40%  Ni: 50 to 80%  C: 0.05 to 0.2%  If: 0.05 to 0.5%  Mo: 0 to 0.1%  Fe: O at 15%  B: 0 to 3%  Ti: 0 to 58  Co: 0 to 10% Zr: 0 to 5%  Nb: 0 to 5%  Mn: 0 to 1%  Al: 0 to 3%  6. Method for producing an enameled prosthesis, according to any one of claims 4 or 5, characterized in that a first layer of enamel obtained from a composition according to any one of claims 1 to 3, supplemented with opacifying and / or devitrifying agents such as SnO2 and ZrO2 and then applying a second layer of an enamel obtained from the above composition added with agents such as NiO or TiO2 providing the enamel with the desired coloration.  7. Method for producing an enameled prosthesis, according to any one of claims 4 or 5, characterized in that a first layer of an enamel obtained from a composition according to any one of claims 1 to 3, supplemented with opacifying and / or devitrifying agents such as SnO2 and ZrO2 and then applying a second layer of an enamel obtained from a glass substantially corresponding to the composition next:  If 2: 64%  Na2O: 14%  K20: 4%  CaO: 1.8%  CaF2: 1.2%  BaO: 5.2%  ZrO2: 9.8%  this glass being optionally charged with opacifying and / or coloring agents.  8. A method for producing an ordinary steel prosthesis, coated with a vitreous enamel obtained from a composition in accordance with one of claims 1 to 3, characterized in that a first layer of d is applied to ordinary steel. enamel with added NiO, MnO2, and / or CoO and opacifying agents such as SnO2 and ZrO2 and a second layer is then applied from a above-mentioned composition added with agents such as NiO and TiO2 providing the enamel with the desired coloration.