US3413723A - Noble metal alloy adapted to receive porcelain cladding, artificial dental constructions and method of preparing the same - Google Patents

Description

Dec. 3, 1968 E. WAGNER ETAL 3,413,723

NOBLE METAL ALLOY ADAPTED TO RECEIVE PORCELAIN (IL-ADDING. ARTIFICIAL DENTAL CONSTRUCTIONS AND METHOD OF PREPARING THE SAME Filed Jan. 30, 1963 514 440 Was/V5115 INVENTQRS 14444725? 'rQKST 4001406 P/FWLOM ATTORNEYS The present invention relates to novel noble metal alloys which are especially adapted to have porcelain fired on the surfaces thereof for dental purposes and to artificial ceramic dental constructions of a novel composition especially of the ceramic layer and adaption of this ceramic layer to the metal substrate. Further the invention relates to a ceramic covering directly fired on a metal alloy substrate.

Attempts have been made for some time to combine noble metal alloys with dental ceramic masses in the production of crowns and bridges for use in the front tooth region by firing dental ceramic masses on caps or structures of platinum iridium alloys which were either cast or soldered together from Wires or strips. Although the dental work thus clad on the normally visible surfaces thereof were entirely satisfactory from an esthetic as well 30 as a functional viewpoint, they did not meet with commercial success as the processing techniques were very difficult and as, in view of the differences in the mechanical and physical properties of the ceramic masses and the 9 alloys, failures often occurred.

Most recently, attempts have been made to camouflage single crowns by firing ceramic masses onto the visible labial side thereof or by casting noble metal alloy structures on previously produced porcelain facets. The porcelain masses, however, were not satisfactory from 21 cosmetic viewpoint and the alloys which are known therefore either are of too low strength or were difficult to cast in view of their very high melting point range.

The usual noble metal dental alloys, which are based on gold, silver and copper or palladium, silver and copper and often also contain additions of platinum metals, do not meet the requirements which must be met by an alloy upon which ceramic masses are to be fired, namely, that the solidus point of such alloys must be over the temperature required for firing the ceramic masses thereon and furthermore no oxides can be formed, while the ceramic masses are fired thereon, which react with the ceramic masses and discolor them. On the other hand, the formation of bonding oxides to a moderate degree is desired for effecting a bond between the ceramic masses and the alloy. The alloy furthermore must possess a sufficiently high strength as even very slight elastic or plastic changes in shape can lead to spalling off of the ceramic masses because of the differences in the mechanical and physical properties of the alloys and the ceramics.

Finally, it is also desirable that the alloys have as yellow a color tone as possible so that they do not contrast too greatly with the dental work in the less visible portions of the month which is in its entirety produced from gold alloys.

In the last few years special alloys adapted to have dental ceramic masses fired thereon have become known, but they met the requirements to only a limited extent. Alloys which can consist of platinum metals have a very high melting range and as a consequence can only be nited States Patent 0 Patented Dec. 3, 1968 melted and cast with difficulty, if at all, with the usual equipment of a dental technical laboratory. Also, their color is not very pleasing. Also, at times, the content of base metals in such alloys is so high that discolorations occur when the ceramic masses are fired on.

Alloys composed of about 85% gold, 05% of palladium and up to 15% of platinum adapted to have ceramic masses fired thereon, it is true, are easy to melt and their color tone meets the requirements. However, they are relatively soft and as a consequence are not suited for bridges.

Alloys have also become known which in addition to the constituents indicated above also contain up to 5% of silver and small quantities of up to about 1% of indium and/or tin. These alloys despite some favorable properties still possess appreciable disadvantages. The coarse grained dental castings during firing on of the ceramic masses usually tend to a further coarsening of grain structure by recrystallization. As a consequence, the strength thereof is reduced and the inhomogeneity of the individual crystals usually linked with the coarse grained structure can lead to discolorations in the mouth.

It is known that the grain structure of gold alloys even those containing palladium and platinum both in as cast and in recrystallized state can be refined by the addition of small quantities of metals such as iridium, rhodium and ruthenium. The grain refining effect decreases sharply with increasing melting or casting temperature so that the effectiveness with alloys of the above composition remains doubtful.

According to the invention it was unexpectedly found that a small addition of rhenium to alloys essentially consisting of gold, platinum, indium and tin and, if desired, can also contain small quantities of palladium, silver, iridium, copper and/or zinc will cause a considerable improvement in the properties of such alloys which evidently essentially depends upon a very thorough grain refinement. It was also found that the bond of ceramic masses to such alloys is noticeably improved by the addition of the rhenium. The alloys concerned essentially consist of 80-90%0f gold, 515% of platinum, 0.1-2% of indium, 0.1-2% of tin and ODS-1% of rhenium. Rheniurn contents of 0.1 to 0.5% are especially advantageous. The alloys can also contain up to 5% of palladium, up to 5% of silver, up to 1% of copper, up to 0.5% of zinc and/or 0.05 to .5% of iridium. Especially good results are obtained with alloys containing 0.5 to 5% of palladium.

In order to show the influence of the addition of rhenium according to the invention, the following Table 1 gives the grain fineness measured in grain count per mm. and Vickers hardness values are given for alloys A and B of the following composition:

1 15 minutes 800 C. 15 minutes 800 C.+15 minutes 500 C. 3 15 minutes 950 C. 4 15 minutes 950 C.+15 minutes 500 C.

As can be seen from such table that a notable grain refinement which considerably improved the strength and homogeneity of the alloy was achieved practically without causing any change in the hardness values.

A further considerable advantage of the alloys according to the invention as already indicated above resides in the better bonds obtained to porcelain masses fired thereon. In order to determine the bond, platelets of the various alloys measuring about 10 x 6 x 4 mm. were provided on one side with a porcelain coating fused on at 950-1000 C. The samples were then embedded in a synthetic resin so that the porcelain clad side was directed upwardly and such porcelain clad side then subjected to the action of a 50 g. falling hammer which was allowed to drop upon the porcelain surface from varying heights. At first the height from which the falling hammer was dropped was increased by 10 cm. measurements until a height of 60 cm. was reached and then the hammer was repeatedly dropped from such height until the porcelain coating splintered off.

In these tests, alloys of compositions A and B concerned in Table l were again employed as Well as a further pair of alloys C and D of the following compositions were employed:

Au Pt Pd Ag In Sn I1 Re The porcelain coatings on the test pieces in one series were fired thereon under normal atmosphere (series a) and in the other series they were fired thereon under vacuum (series b).

The results obtained are given in the following table:

The increased resistance of the porcelain coated rhenium containing alloys according to the invention against the splintering off of the porcelain when subjected to impact clearly indicates the special suitability of the alloys to receive fired on porcelain coverings in view of the improved bond to the porcelain obtained.

The porcelain coverings which can be fused on the alloys according to the invention are of compositions usually employed for these purposes.

Preferred porcelain coverings fused on alloys result in artificial ceramic dental constructions, as specified hereunder. These constructions are particularly suited for the replacement of missing teeth or for capping existing teeth which may be damaged. The novel tooth structures are distinguished by the fact that, on the one hand, they can be prepared by novel working methods in a facilitated manner and are especially adapted for individual preparation by the dentist in the laboratory and, on the other hand, they exhibit novel and improved optical and physical characteristics due to a novel composition especially of the ceramic layer and adaptation of this ceramic layer to the metal substrate.

The requirements of dental poreclains, particularly with respect to their physical and optical characteristics, are numerous and exacting. Among the factors of importance are, for example, coverage of the color range of the natural teeth, suflicient translucency, compatibility with the tissues, insolubility, mechanical strength, bond strength of individual structural parts of the artificial tooth to one another, suitable fusion intervals, satisfactory performance of the porcelain, e.g. with respect to its mineralogical structure and its coeflicient of expansion during fusion to the metal, etc.

The difiiculties indicated above only by way of allusion and encountered in the direct preparation of artificial ceramic teeth by fusing porcelain onto metal substrates had the result that the problem of practical preparation of such tooth structures is considered as being solved on principle only recently in the art. Up to the present, the dental profession has made shift either with completely metallic auxiliary constructions or with restorations Where a separately formed and fired ceramic covering was bonded to a performed auxiliary metallic part. The shortcomings of these techniques had the result that recently several suggestions have been made recommending direct firing of a tooth-like enamel onto a metal substrate. Although an improvement was obtained by this technique. it appeared that the quality of these dental constructions had become poorer with respect to the cosmeticesthetic effect. Therefore, attempts have recently been made of improving this optical-esthetical effect of artificial teeth of this kind. The invention relates to tooth constructions which give particularly good results just in this respect.

It is long known that the coefficient of expansion of the dental composition must be adapted to that of the metal. In particular, it is known that the enamel should have a somewhat lower coeflicient of expansion than the metal because the resistance to pressure of all silicates, as is known, must be substantially higher than the tensile strength and, therefore, the outer ceramic layer of the artificial tooth must always be under compressive stress.

However, the artificial tooth structures known up to the present and prepared by the techniques described above invariably exhibit unsatisfactory optical-cosmetic characteristics. The art was not successful so far in imitating the esthetic effect of the natural tooth in the tooth structures of the type described in a manner such that an actually unobstrusive use of these artificial tooth structures, particularly in the visible part of the set of teeth would have been possible. A substantial reason for this resides in the following fact: When using a metal substrate in the artificial tooth, it is necessary to remove the optical effect of this metal which shows through with a gray-golden shade by means of an inner opaque covering layer. In practice, it has been necessary up to the present although the contrary is claimed in literature, to apply opaque enamel layers of relatively great thickness as a first covering to the metal core in order to prevent the metal effectively from showing through. This resulted in a relative restriction of the naturally available space for the translucent ceramic dental composition which imitates the tooth core and the tooth enamel so that the natural esthetic and optical effect could not be attained with such remaining space.

It is an object of the present invention to provide novel artificial tooth structures where a ceramic covering is directly fired onto a substructure of metal alloys, the tooth structures of the invention being distinguished by the fact that they represent products of high cosmetic quality which also satisfy all other requirements of such ceramic masses used for this purpose. In particular, it appeared that multi-layer artificial tooth structures can be prepared advantageously when using specific components in the enamel layers forming the covering of the artificial tooth while observing specific relative proportions by weight of the individual components. More particularly, the invention relates to artificial tooth structures which comprise at least two ceramic enamel layers fired onto the metal substrate, viz. an opaque enamel layer in direct contact with the metal, this layer being impermeable to light and, due to its outstanding optical activity, needs be only very thin, and a superimposed covering layer of a translucent enamel composition which, in a manenr known to persons in the art, may be colored at least partially with pigments. In this manner, a layer representing the tooth core and a clear enamel layer especially arranged in the cutting edges of the teeth are obtained.

The accompanying drawing shows a cross-section of a dental crown embodying the subject matter of the present invention.

In such drawing the dental alloy substrate 1 supports the opaque and translucent porcelain enamel coatings 2 and 3 which have been fired thereon.

Accordingly, one embodiment of the invention relates to multi-layer artificial tooth structures of any kind as replacement of missing teeth or for capping existing teeth, said structures comprising a metal substrate onto which at least two enamel layers are fired and characterized in that the metal substrate is coated with an opaque enamel base layer which is preferably thin and has a composition within the following ranges (based on the weight of the opaque base layer):

Percent S 48 to 59 A1203 t0 F6203 t0 TiO 2.70 to 3.30 CaO 1.20 to 1.45 K 0 8.40 to 10.30 Na O 5.70 to 7.00 F 0.00 to 0.50 ZrO 1.20 to 1.50 SnO 4.30 to 5.25 B205 to and which is surrounded by a translucent covering enamel layer having a composition within the following ranges (based on the weight of the translucent covering enamel):

Percent SiO 54.70 to 67.00 A1203 to K 0 8.70 to 10.60 Na O 6.60 to 8.10 CaO 1.70 to 2.10 F 0.00 to 0.50 TiO 0.25 to 0.29 Fe O 0.045 to 0.055

Particularly favorable results in the construction of the novel tooth structures are obtained if the two layers give about the following analytical values:

Opaque base enamel Percent SiO 53.64 A1 0 18.18 F6203 TiO 2.18 CaO 1.32 K 0 9.35 Na O 6.35 F 0.25 ZrO 1.36 SnO 4.76 B 0 1.34

Translucent covering enamel Percent SiO 60.80 A1 0 19.36 K 0 9.66 N320 CaO 1.91 F 0.26 TiO 0.26 PC2013 Deviations from these specific values within the ranges given above may be desirable in order to obtain better adaptation of the physical characteristics of the enamel layers to the particular metal alloy used, it being especially possible, for example, to influence the coefficient of expansion of the enamel by varying its components in a manner known per se. It is possible in this manner to mask out successfully any suitable metal alloy combination discussed hereafter in greater detail by means of a suitable covering enamel in accordance with the invention.

Due to the fact that, in accordance with the invention, only extremely thin opaque covering enamel layers are necessary for efficiently masking out the metallic structure, it is possible to apply the translucent dentine enamel layer which, if desired, may be pigmented in conventional manner and also the translucent enamel layer imitating natural tooth enamel with a comparatively greater thickness than that of the opaque base enamel layer. This efficiently aids the improved esthetic-optical effect due to the novel and specific enamel compositions.

Alloys which are particularly suitable as substrate for the purposes of the invention chiefly include gold, platinum and palladium base alloys. However, base metal alloys known for use in dentistry may also be employed. All of these alloys are readily available and can be easily hardened under control. They are free from corrosion phenomena and mild to the tissue of the oral cavity. Their melting points range substantially lower than those of the previously used platinum-iridium alloys. This results in considerable improvement of the precision of the casting.

Particularly preferred as metal substrate for the purposes of the invention are specific alloys containing rhenium as described before. The enamel layers of the invention, particularly the composition, referred to as particularly preferred, of the opaque mass and of the associated transparent covering mass, have been found to have an outstanding bond strength to these metal alloys so that artificial tooth structures of excellent resistance to mechanical stress are obtained.

As mentioned above, the specific composition of the enamel masses is critical for the novel effect in physical and especially also in optical-esthetic respect. A very essential feature of these masses are the relative proportions of the alkali metal oxides present. It has been found surprisingly that, in contrast to statements in literature dealing with the prior art, just a relatively high content of sodium is critical for the novel elfects described. Accordingly, the enamels of the invention are characterized by relatively high contents of Na O. As was found surprisin-gly, corresponding glasses which contain very much less sodium and instead much more potassium as compared with sodium do not result in products having a comparable natural appearance. This fact could not be predicted.

The invention does not only comprise the finished tooth structures but also the preparation of both the opaque mass and the transparent mass. Improved technical results are in fact not only obtained with the combination as described above. Advantages are also obtained if, for example, the opaque mass is used as such in dentistry even if other combination elements are simultaneously used in preparing artificial tooth structures.

Preparation and processing of the raw enamel masses to the finished artificial tooth may be effected by techniques conventional in ceramic dentistry. Thus, if desired, conventional opacifiers and coloring pigments known to persons in the art may be added. Processing of the starting masses, e.g. for quantity preparation of artificial teeth, may be effected by methods usual in dental industry.

However, the invention also comprises a novel working method which is particularly suitable for dentists operating on a small scale on an individual basis. It has been found that it is possible with the components of the invention described above to prepare individually shaped dental constructions without the necessity of special technical equipment. Thus, the enamel can be applied manually to individually shaped metal substrates adapted to the requirements and firing onto the metal can be effected with or without the use of reduced pressure. This possibility of preparing on a small scale individually shaped ceramic dental constructions which are outstanding in physical and optical respect opens a new and important field in dentistry.

What is claimed is:

1. Dental alloy adapted to have porcelain coverings fired thereon consisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin and 0.05 to 1% of rhenium.

2. Dental alloy adapted to have porcelain coverings fired thereon consisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin and 0.1 to 0.5% of rheniurn.

3. Dental alloy adapted to have porcelain coverings fired thereon consisting essentially of 80 to 90% of gold, 5 to 15% of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin, to of palladium, 0 to 5% of silver, 0 to 1% of copper, 0 to 0.5% of iridium, 0 to 0.5% of zinc and 0.05 to 1% of rhenium.

4. Dental alloy adapted to have porcelain coverings fired thereon consisting essentially of 80 to 90% of gold, 5 to of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin, 0.5 to 5% of palladium and 0.05 to 1% of rhenium.

5. A multi-layer artificial dental construction comprising a metal substrate and an enamel facing fired on and directly bonded to said metal substrate comprising a first opaque enamel base layer essentially consisting of the following composition:

Percent by weight 6. A multi-layer artificial dental construction according to claim 5 in which said enamel layers consist essentially of the following compositions in percent by Weight:

Opaque base enamel Percent SiO 53.64 A1 0 18.18 F6 0 TiO 2.98 CaO 1.32 K 0 9.35 W 3'32 2 ZI'OZ S1102 4.76 B 0 1.34

Transparent covering enamel SiO 60.90 A1 0 19.36 K 0 9.66 Nazo CaO 1.91

8 Transparent covering enamel-Continued Percent TiO 0.26 Fe O 0.05

7. Multi-layer artificial dental construction according to claim 5 in which said transparent covering enamel layer is subdivided into a conventionally pigmented dentine layer and a non-pigmented enamel layer, said non-pigmented enamel layer being especially present in the cutting edges of the tooth.

8. Multi-layer artificial dental construction according to claim 5 in which said transparent covering enamel layer is applied with a comparatively greater thickness than that of the opaque enamel base layer, the thickness of said transparent covering enamel layer being such as to obtain improved optical-cosmetic effects in the artificial tooth.

9. Multi-layer artificial dental construction according to claim 5 in which said metal substrate is composed of alloys mainly based on gold, platinum and palladium.

10. Multi-layer artificial dental construction according to claim 5 in which said metal substrate is an alloy consisting of to of gold, 5 to 15 of platinum, 0.1 to 2% of indium, 0.1 to 2% of tin and 0.05 to 1% of rhenium.

11. An opaque enamel for use in multi-layer artificial dental constructions having a metal substrate and an enamel facing fired onto said metal substrate consisting essentially of the following composition:

Percent by weight 12. An opaque enamel for use in multi-layer artificial dental constructions having a metal substrate and an enamel facing fired onto said metal substrate consisting essentially of the following composition:

Percent by weight S10 53.64 A1 0 18.18 F203 TiO 2.18 OaO 1.32 K 0 9.35 $3.20

2 0. s ZIO 1.36 SnO 4.76 B 0 1.34

13. A transparent enamel for use in multi-layer artificial dental constructions having a metal substrate and an enamel facing fired onto said metal substrate consisting essentially of the following composition:

Percent by weight SiO 60.80 A1 0 19.36 K 0 9.66 N320 CaO 1.91 F 0.26 TiO 0.26 Fe O 0.05

(References on following page) 9 10 References Cited 2,000,285 5/1935 Hoffmann 10635 UNITED STATES PATENTS 2,937,099 5/1960 KIltSChfil 106-35 9/1962 Weinstein et a1. 32-3 FOREIGN PATENTS 5/1922 Fahrenwald 75-465 5 1,106,966 5/1961 Germany.

12/1942 Leuser 75-165 4/1961 Coleman et aL 32 12 LOUIS G. MANCENE, Przmary Examiner.

9/1962 Weinstein et a1 32-12 CHARLES R. WENTZEL, Assistant Examiner.

Claims (1)

1. DENTAL ALLOY ADAPTED TO HAVE PORCELAIN COVERINGS FIRED THEREON CONSISTING ESSENTIALLY OF 80 TO 90% OF GOLD, 5 TO 15% OF PLATINUM, 0.1 TO 2% OF INDIUM, 0.1 TO 2% OF TIN AND 0.05 TO 1% OF RHENIUM.

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