US3548916A

US3548916A - Method of casting a dental gold alloy directly to prefabricated porcelain teeth

Info

Publication number: US3548916A
Application number: US774100A
Authority: US
Inventors: Emil M Prosen
Original assignee: Nobilium Products Inc
Current assignee: CMP INDUSTRIES Inc A CORP OF NY; Nobilium Products Inc
Priority date: 1968-11-07
Filing date: 1968-11-07
Publication date: 1970-12-22
Anticipated expiration: 1987-12-22
Also published as: DE1954278A1

Description

United States Patent Inventor Emil Pwsen 3,192,620 7/1965 Huizing etal 75/165X Bala-CynwydJ 3,315,358 4/1967 Brecht 164/91X 1 1 pp No, .1 0 3,470,935 10/1969 Prosen 164/34 [22] Fued 1968 Primary Examiner-J; Spencer Overholser [4s] Patented Dean 1970 Assistant Examiner-R Spencer Annear [73] Ass'gm Attorneys-Howard J. Churchill, Abraham Engel, Robert s.

r lg z 3' min Dunham, P. E. Henninger, Lester W. Clark, Gerald W.

mm nsy Griffin and Thomas F. Moran [54] METHOD OF CASTING A DENTAL GOLD ALLOY T PREFABRICATED PORCELAIN gg g 0 ABSTRACT: A method of casting a low melting point dental 10 claims 12 Drawing Figs gold alloy having a melting point of about 1401? F. directly to prefabricated porcelam teeth, each tooth having an aperture [52] US. Cl. 164/91, in its lingual face and preferably a platinum ring embedded in 164/351 164/114 the porcelain at the base of the aperture. The method com- [51] Int. Cl. Bzzd 19/00; prises h ste s of preparing a wax-up of a dental retention B229 9/04 member or restoration, including one or more such [50] Field ofSearch 164/9, 10, prefabricated porcelain teeth spruing the Same with an 341 35,91 1 [41244, eliminatable filament of relatively small diameter at the ,wax (dental D1ge$075l165 retention member for each tooth adjacent the lingual face aperture which is of relatively large diameter, and connecting [56] References Cited such eliminatable filaments radially to an arcuate wax metal UNITED STATES PATENTS reservoir membersuitably investing the wax-up, eliminating 2,374,995 5/1945 Hensel 75/165 the wax retention member, filaments, etc., by the lost wax 2,936,490 5/1960 Mason..... l64/98X process, and centrifugally casting a finished dental retention 3,114,948 12/1963 Poe 164/35 member or restoration including such prefabricated teeth, in 3,192,583 7/1965 Fryrear 164/34 the mold formed thereby.

ORCELAIN WAX M: 0/11 0,? mun/445w (0/7") 'PATENTEU niczelsm 3.548316 sum 3 BF 3 d ATTORA/Ef MEI'HOD or cxsrmc A DENTAL cow ALLOY DIRECTLY TO rnsrxmucx'rsn PORCELAIN TEETH The present invention relates to a method of casting dental 1 gold alloys directly to prefabricated porcelain teeth for i producing dental restorations.

More particularly, it provides a method of casting dental gold alloys directly to prefabricated porcelain teeth by utiliztion may be prepared by utilizing prefabricated porcelain teeth each having at least one aperture on its lingual face, and casting an anatomically carved retention and supporting area for such prefabricated porcelain teeth to provide a dental restoration.

Heretofore it has not been possible to cast a dental gold alloy'directly to a prefabricated porcelain tooth for the reason, among others, that the melting temperatures of dental gold alloys and hence the casting temperatures of such alloys are so high that the porcelain will check or crack when subjected to the heat and other conditions of casting. Also, such dental gold alloys on cooling have a high rate of shrinkage as compared with the limited expansion and contraction of porcelain. Hence, the shrinkage problem presented another difficulty in trying to cast dental gold alloys directly to prefabricated porcelain-teeth.

The porcelain which is generally used by the dental profes sio n i s usually fused at a temperature of about 2400 F. Dental gold alloys which are currently available usually melt at around I700 F. to 1800 F. or higher. The refractory material used in casting dental gold alloys can only be heated to l350 F. Hence, it has not been possible heretofore to cast such dental golds melting around I900 F. directly to prefabricated porcelain teeth in refractory molds which are only heated to l350 F. The alloy does not cool off sufficientlyduring castingv and hence shocks the porcelain and causes fractures.

Furthennore, such prefabricated porcelain teeth are customarily provided with a preformed aperture in the lingual face which contains a platinum retention ring and a nickelgold clad pin silver soldered thereto having an enlarged head for engagement in a correspondingly located aperture in the backing and retention area of the separately cast metal part of the dental restoration.

I have found that such nickel-gold clad pin deteriorates under normal casting temperatures and offers no retention. Hence, it is not possible to cast the currently available dental gold alloys having melting points ranging from 1700 F. to 1800 F. directly to such prefabricated porcelain teeth with such retention pins. Thus, up until the piesent time the art of providing dental restorations, including prefabricated porcelain teeth, has proceeded solely on the basis of casting the metal backing and retention areas first and then applying with a plastic material the prefabricated porcelain teeth to such backing and retention areas after they have been fully cast.

It is an object of the present invention to provide a method I of casting a dental gold alloy directly to prefabricated porcelain teeth and thereby to provide the backing and retention areas for the dental restoration.

It is a further object of the invention to provide a method of casting dental gold alloys to prefabricated porcelain teeth having apertures in their lingual faces which will not only provide 1 the backing and retention areas for the dental restoration, but whichwill also have integrally formed therewith retaining pins The method of the present invention starts, as a first requisite, with individual prefabricated porcelain teeth each having an aperture in its lingual face and preferably having a platinum ring embedded within such porcelain tooth at the base of the aperture,the aperture being of irregular contour.

The second requisite is a dental gold alloy preferably having a melting point approximating 1400 F. Such a dentalgold alloy is disclosed in my copending application Ser. No. 772,794, filed Nov. 1, 1968, wherein it is referred to as a yellow gold alloy and consists of gallium, nickel and gold in the preferred proportions of:

Gold

The third requisite is that the desired dental restoration utilizing one or more prefabricated porcelain teeth shall be suitably waxed by anatomical carving to provide the backing and retention areas of adequate strength for such prefabricated porcelain teeth and for the finished dental restoration.

The next requisite is that a very fine spruing element shall be connected to the backing area for each porcelain tooth adjacent the aperture in the lingual face of such tooth and that each such spruing element shall be connected at its other end to a waxed reservoir portion on a radial or spoked basis,- the waxed reservoir portion being sufficiently large to provide an adequate resource of molten metal for the casting operation.

After the porcelain teeth have been arranged, waxed andsprued, the assembly is suitably invested in a refractory material and the waxed portions and sprue filaments are removed by the well-known lost wax process,-leaving a casting cavity to receive the molten dental gold alloy.

The refractory mold thus fonned placed in a furnace and produced. The only things left to be done are to cut off the sprues, and to finish and polish the restoration.

For a better understanding of the present invention, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a grossly enlarged view in cross section of a prefabricated commercially available porcelain tooth having a retention pin.

FIG. 2 is a cross sectional view of the prefabricated porcelain tooth of FIG. 1, modified for use in accordance with the method of the present invention and showing in phantom the cingulum which has been ground away.

FIG. 3 is a plan view of a dental restoration comprising a plurality of prefabricated porcelain teeth which have been sprued and waxed according to the present invention, ready for investment in a refractory mold. v

FIG. 4 is a schematic view of a suitable dental centrifugal casting apparatus with a refractory mold containing the prefabricated porcelain teeth and the mold cavities to be filled by the dental gold alloy, and a crucible connecting with such mold cavities for receiving the molten metal.

' FIG. 5 is a sectional view of a modified prefabricated porcelain tooth of FIG. 2, showing its waxed backing, retention and sprued areas prior to casting.

FIG. 6 is a duplicate of FIG. 5 showing one such porcelain tooth with its metal backing face, anchoring means and sprue after casting.

FIG. 7 is a plan view of a dental restoration comprising four prefabricated teeth with dental gold alloy backings afiixed thereto, and with the cast sprues and metal reservoir still attached.

FIG. 8 is a side elevation of the dental restoration shown in FIG. 7.

FIGS. 9, l and 11 are sectional views in plan of four anterior teeth (two being broken away) showing a modification of the invention whereby retention pins are first cast.

FIG. 12. is a'view similar to FIG. 11 showing the casting produced, with cast sprues, etc.

Referring now to the drawings, FIG. 1 shows a cross section of a very much enlarged prefabricated porcelain tooth hav-- ing a lingual face 11, an aperture 12 in such lingual face containing at its base a platinum ring 13 to which is soldered a retaining pin 14 having an enlarged head 15. The prefabricated porcelain tooth as thus illustrated and described constitutes a prior art tooth and for convenience of disclosure has been so labeled in the accompanying drawings.

In FIG. 2 of the drawings there has been illustrated a modified form of the prefabricated porcelain tooth of FIG. 1. Such modified prefabricated porcelain tooth 20 has a lingual face 21 and an aperture 22 in such lingual face, such aperture being of irregular contour and having at its base an embedded platinum collar 23 of slightly larger dimension than the dimension of the aperture 22. The cingulum 24 of this prefabricated tooth has been ground away to provide less bulk in the finished denture and is therefore shown in phantom. Such prefabricated porcelain tooth 20 is characterized by the fact that it has a fusing temperature of approximately 2400 F and for convenience'in understanding the invention the legend fusing temperature 2400 F." has been applied to the drawings.

It will also be noted that aside from the fact that the cingulum 24 has been ground away, the only difference between the prefabricated porcelain tooth 10 of FIG. 1 and the prefabricated porcelain tooth of FIG. 2 is that the retention pin 14 of FIG. 1 with the enlarged head has been omitted from the tooth in FIG. 2 so that there is in the tooth in FIG. 2 an aperture 22 of irregular contour having a platinum ring 23 at its base embedded in the tooth and exposed to such aperture 22.

In FIG. 3 of the drawings there is shown in plan view a dental restoration in course of preparation according to the present invention. It comprises four

prefabricated porcelain teeth

20a, 20b, 20c, and 20d, to which have been applied

wax backings

26a, 26b, 26c, 26d, which are anatomically carved to conform to the desired dental restoration. Each of

such teeth

20a, 20b, 20c, 20d, has on its lingual face an aperture 22 as more particularly shown in FIG. 2 of the drawings.

According to the present invention there are provided nylon or the equivalent ash-free

disposable filaments

27a, 27b, 27c, 27d, each of which is embedded in the wax backing for the corresponding tooth and located adjacent the aperture in the lingual face of such tooth. As shown in FIG. 3 such filaments are disposed radially oras spokes of a wheel for a reason which will presently be made apparent.

The other end of each of the

filaments

27a, 27b, 27c, 27d, is connected to an enlarged arcuate waxed member 30 which for convenience will be referred to as a metal reservoir member." Inwardly of such reservoir member is an enlarged sprue of wax 31 which is connected to a wax conical or beehive-shaped member 34 which in'the casting operation becomes what is known in the art as the button.

Referringback to the very thin nylon or like

filaments

27a, 27b, 27c, 27d, it has been found that such filaments should have a preferred diameter of .017 inches to attain the maximum advantages of the present invention, although it has been found possible to vary such diameter by plus or minus .002 inches to .003 inches. Hence, for clarity of disclosure the preferred diameter of .017 inches has been shown on the drawings. Also, it has been found that such sprues should have an effective length of at least 'rinch.

When the assembly as shown in FIG. 3. comprising the prefabricated porcelain teeth, the waxed backing and reten tion areas, the nylon or like filaments, the metal reservoir member, the enlarged sprue and the conical or beehiveshaped member, has'been completed, such assembly 'is then ready for thenext step in the method of the present invention.

This step is not shown in the drawings for the mass; that it merely consists of investing such assembly in a' refractory mold and then heatingsuch mold to, a temperature approximating 1350 F. to eliminate the wax nylon filaments by the well-known lost wax process which is commonly used in the dental art. After such elimination, cavities are provided in the refractory mold corresponding to the backing and retention members for the prefabricated porcelain teeth, the nylon sprues, the metal reservoir member, the enlarged sprue and the button. i

As next shown in FIG. 4, such refractory mold 40 with such casting cavities and prefabricated teeth is placed on a centrifugal casting apparatus, having disposed axially and inwardly of such refractory mold acrucible 43 for receiving dental gold alloy 44. The centrifugal casting apparatus which is only schematically shown in FIG. 4 comprises a base member 46, containing a suitable motor or other driving means, an upstanding driven shaft 48, which rotates at a predetermined speed, a platform 49 rigidly connected to such shaft 48, said platform at one end having mounted thereonthe refractory mold 40 and crucible 43 and having at its opposite end a counterbalance weight 5 0.

The low melting point dental gold alloy 44 is placed in the crucible 43 and heated'to a temperature of 1450 F. The refractory mold 40 is maintained at a temperature of 1350 F. As pointed out in my copending application Ser. No. 772,794, the preferred yellow dental gold alloy which I disclosed has a melting point of approximately,l400 F. It will thus be. understood that in the practice of the present method I prefer to overheat the alloy by 50 F. to make a temperature differential between the molten alloy and the refractory mold of about F.

For clarity of disclosure of the method of the present invention, reference will now be made to FIG. 5 of the drawings which shows in very much enlarged cross section the wax-up of a prefabricated porcelain tooth ready for casting thereto a low melting point dental gold alloy. In such figure the prefabricated porcelain tooth 20 has an aperture 22 in the lingual face 21. At the base of such aperture there is embedded in the fused porcelain tooth 20 a platinum ring 23. It will be noted that the cingulum 24 as shown in phantom in FIG. 2 has been ground away from the lingual face of such tooth 20. The lingual face of the porcelain tooth 20 has been suitably waxed by anatomical carving to provide in wax the backing a retention areas 60 for the finished dental restoration, such waxed backing area including a waxed retaining pin portion 61 integral with the backing area 60 and extending into and filling completely the aperture 22.

A nylon or equivalent filament 27a is embedded in the wax backing 60 adjacent the aperture 22. The nylon filament 27a is of relatively small diameter as compared with the diameter of the aperture 22. The reason for this will shortly be made apparent. In the drawing the diameter of the nylon filament has been indicated as .017 inches. This'has been found to be the preferred diameter, although as mentioned earlier the diameter may vary as much as plus or minus .002 inches to .003

inches. As before mentioned, the filament 27a has a minimum exposed length of V2 inch.

The opposite end of the nylon filament is embedded in the wax reservoir member 30 which is of substantial diameter and which is of arcuate form in plan view as best seen in FIG. 3. The sprue 31 connected to the reservoir 30 is shown in part, but the button portion 34 (as seen/in FIG. 3) has not been shown in FIG. 5 in order to present the other elements on as large a scale as possible.

It will be understood that when the waxed-up dental restoration is invested in refractory material and eliminated from the refractory mold by the lost wax process, the backing and retention areas 60, including the retaining pin portion 61, the nylon filament 270,. the reservoir area 30, the sprue 31, and button portion 34, provide casting areas to receive the molten gold metal alloy. 1

The dental restoration which results from the wax-up of FIG. 5 is shown in section in FIG. 6 and comprises the prefabricated porcelain tooth 20, the cast dental gold alloy backing and retention areas 70 on the lingual face of the tooth and the integrally formed retaining pin 71 which is united with the platinum ring 23. There is also connected to the metal backing 70 the sprue 72 which is formed in the casting conduit provided in therefractory mold by the elimination of the nylon filament 27a. the enlarged metal piece. 73 at the other end of the sprue 72 is the casting which resulted from the reservoir 30. The sprue 72 is cut from the backing member 70 at approximately the point indicated by 75 in FIG. 6.

FIG. 7 is a plan view of the dental restoration shown in section in FIG. 6 comprising four prefabricated porcelain teeth 20, having backing and retention areas 70, each backing area being connected to the cast sprue 72, all ofwhich in turn are connected to the cast metal reservoir 73. Sprue 74 is also shown which corresponds to the metal sprue formed by wax sprue 31 in FIG. 3. The cast metal button which corresponds to the wax conical section 34 in FIG. 3has been removed from the restoration shown in FIGS. 6 and 7.

FIG. 8 shows aside elevation of the dental restoration shown in FIG. 7. Two porcelain teeth are seen .in this figure, one sprue 72, the cast reservoir 73, and the sprue 74.

As earlier mentioned, an important requisite of the method of the present invention is that the

nylon filaments

27a, 27b, 27c, and 27d, which connect the waxed backing and retention areas for the prefabricated porcelain teeth 20, be of very small diameter and preferably .of .017 inches, but of considerably smaller diameter'than the diameter of the retaining pin aperture 22. A l to 4 ratig-is preferred. Onaccount of the fact that prefabricated porcelain teeth are nonporous, any air which is entrapped in the aperture 22 of the prefabricated porcelain tooth shown in FIG. 2, can only be dissipatedby passing out through such aperture. Hence, it has been found in experiments with the method of the present invention that the molten dental gold alloy which is directed toward such aperture must be of a small enough stream tov force the air rearwardly so that it can be dissipated through the porous refractory mold. It is for this reason that it has been foundpreferable to have the

sprues

27a, 27b, 27c, and 27d, as shown in FIG. 3, not only of such small diameter but also directed toward such apertures-22 so that-such apertures 22 will be entirely filled with a cast dental gold alloy as an integral part of the finished dental restoration.

It has also been found that on account of the small diameter of

such sprue areas

27a, 27b, 27c, and 27d, which form part of the refractory mold, which is preferably maintained during casting at a temperature of 1350 F., the dental gold alloy which is preheated to a temperature of approximately 1450" F. (even though it has a melting point temperature of l400 F.) will cool off sufficiently while passing through such small diameter sprue conduits27a, 27b, 27c,and 27d, so as to cast and solidify at 1350" F. into the backing and retention area 70 and the integrally formed retaining pin 71.

A further feature of the invention which is believed to be a requisite to the successful practice of the method herein disclosed is that there should be a substantial reservoir of molten dental gold alloy at the rear of each 'of

thesprue conduits

27a, 27b, 27c, and 27d, so that an adequate resource of such molten alloy'will be available during the centrifugal casting operation.

The present method provides a wax reservoir 30 which then provides the comparable reservoir area in the refractory mold and which later becomes the cast reservoir 73 shown in FIGS. 6, 7 and 8. It will be noted that this reservoir has an arcuate form and that each of the nylon filaments27a, 27b, 27c, and

27d, are arranged radially or spokelike from such arcuate reservoir. This is done for the purpose of according to the molten metal during centrifugal casting a path of flow most nearly approximating the optimum path of flow during centrifugal casting. In order to be sure that the reservoir 30, shown in FIG. 3, in turn has an adequate supply of metal, an enlarged sprue 31 is connected thereto and the conical or beehiveshaped portion 34 for receiving such metal is connected to the sprue 31. With this construction it has been found possible to cast dental gold alloys having a melting point of approximately 1400 F. directly to prefabricated porcelain teeth to form dental restorations.

It will be noted in FIG. 4 that the refractory mold 40 has four prefabricated porcelain teeth 20 which are embedded in the refractory material 76 of such mold. All of the other spaces outlined in this FIG. and located within the refractory mold 40 constitute voids or casting areas corresponding to the wax and retention backing areas, the nylon or equivalent sprues 27a to 27d inclusive, the wax reservoir 30, the wax sprue 31, and the wax button 34.

Referring to FIGS. 9 to 12 of the accompanying drawings which illustrate a modification of the present invention, it should first be mentioned that up to this point the invention has only been described with reference to partial dental restorations. If, instead, it should be desired to prepare a full dental restoration, such for instance as a full upper, according to the present invention, by casting the complete retention area with a dental gold alloy, it has been found that it is preferably to .cast retention pins separately in the anterior teeth in advance of casting the full restoration.

Thus, FIG. 9 shows in plan cross section two anterior teeth 81, 82 and two adjoining

anterior teeth

83, 84 which will form part of a complete dental restoration. In FIG. 9 each of the anterior teeth 81, 82 has been provided with two apertures in side-by-side or laterally spaced, parallel arrangement each of such apertures having at its base a platinum retaining ring 85.

Anterior teeth

83, 84 plus the next adjacent anterior teeth (not shown) may be provided with either one or two such apertures, depending upon the size of the teeth. It is preferred, however, that all six anterior teeth should have precast retention pins if they are to form part of a full dental restoration.

The first step in casting such retention pins in the anterior teeth according to the present invention is toinsert within the apertures and lingual faces 86 of such teeth, a nylon or equivalent rod 87 of the diameter of the aperture. In practice a .036 inch diameter rod has been found to be most suitable. Such rod is also of sufficient length to protrude substantially outwardly of the lingual face of each tooth.

The second step in the method of forming such retention pins is shown in FIG. 10 wherein each such nylon rod 87 has been provided with a head 89 merely by applying a heated tool to the end of such rod 87 to cause the projecting end of the rod 87 to flow and enlarge.

The third step is illustrated in FIG. 11 wherein the heads 89 of teeth 81 and 82 have been joined by nylon or the equivalent material and then sprued by the thin sprue 90 intermediate the same. All of the

anterior teeth

83, 81, 82 and 84 are then inconnected to such link and the arcuate reservoir 98 is connected to such sprues.

Each ,of the

anterior teeth

83, 81, 82 and 84 with such precast pins, after removal of the sprues, is then in a condition to be cast into a full dental restoration and the dental gold alloy of such full restoration will then become integral with and form part of the metal structure of the full dental restoration.

While the present'invention has been described in its preferred form it will be understood that various changes may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

Iclaim:

l. The method of casting retention members to prefabricated porcelain teeth each having an aperture in its lingual face, comprising the steps of:

a. preparing a wax-up of the desired retention member which fills up and extends from such aperture;

b. spruing said retention members with eliminatable filaments of relatively small diameter compared with the diameter of the apertures in the prefabricated teeth;

c. connecting the opposite end of each filament with a metal reservoir wax member and suitably spruing the same to receive molten casting metal;

d. investing said wax-up in a refractory mold and eliminating by the lost wax process the wax and filament portions to provide a casting cavity of dimension and shape corresponding to the dimension and shape of the waxed retention members, the filament sprues, the metal reservoir and its suitable sprue, and maintaining such refractory mold at a temperature approximating 1350 F.;

e. heating a dental gold alloy having a melting point of about 1400 F. to a temperature approximating 1450 F.; and injecting such molten dental gold alloy into said casting areas of said refractory mold by centrifugal force, whereby there are formed cast retention members on the lingual faces of each tooth.

2. The method of casting metal backing and retention areas to prefabricated porcelain teeth each having an aperture in its lingual face, to provide a dental restoration, comprising the steps of:

a. preparing a wax-up of the desired dental restoration by anatomically carving in wax the backing and retention areas for such prefabricated porcelain teeth;

b. spruing said backing and retention areas adjacent the apertures in the lingual faces of the prefabricated teeth with eliminatable filaments of relatively small diameter compared with the diameter of the apertures in the prefabricated teeth;

d. investing said wax-up in a refractory mold and eliminating by the lost wax process the wax and filament portions to provide a casting cavity of dimension and shape corresponding to the dimension and shape of the waxed backing and retention members, the filament sprues, the metal reservoir and its suitable sprue, and maintaining such refractory mold at a temperature approximating 1350 F.;

e. heating a dental gold alloy having a melting point of about 1400 F. to a temperature approximating 1450 F.; and

. injecting such molten dental gold alloy into said casting areas of said refractory mold by centrifugal force, whereby there is formed a dental restoration having cast backing and retention members on the lingual faces of such teeth and a retaining pin within the aperture of each tooth which is integral with the backing and retention areas.

3. The method according to claim 1. wherein such eliminatable filaments are of nylon or equivalent material.

4. The method according to claim 1 wherein such eliminata ble filaments have a diameter of .017 inches plus or minus .002 inches to .003 inches.

5. The method according to claim 1 wherein said filaments have a diameter of .017 inches.

6. The method according to claim 1 wherein said filaments have a diameter of about .017 inches and the diameter of the aperture in each prefabricated tooth is at least twice the diameter of the filament.

7. The method according to claim 1 wherein said metal reservoir wax member is of arcuate form and said filaments are connected to the same and to the backing member for each said tooth radially and in spokelike fashion.

8. The method-according to claim 1 wherein each of said prefabricated teeth has a platinum ring embedded in such tooth at the base of the aperture, and said 'cast retaining pinc. spruing the wax-up of each pin with eliminatable fila-' ments of relatively small diameter compared with the diameter of the apertures in the prefabricated teeth;

d. connecting the opposite end of each filament with a metal reservoir wax member and suitably spruing the same to receive molten casting metal;

. investing said wax-up in a refractory mold and eliminating by the lost wax process the wax and filament portions to provide a casting cavity of dimension and shape 'corresponding to the dimension and shape of the retention pins, the filament sprues, the metal reservoir and its suitable sprue, and maintaining such refractory mold at a temperature approximating 1350 F f. heating a dental gold alloy having a melting point of about 1 0O F. to a temperature approximating 1450 F and g. injecting such molten dental gold alloy into said casting areas of said refractory mold by centrifugal force. whereby each of said prefabricated teeth is provided with a retention pin cast in its aperture.

10. The method according to claim 8 wherein some of the prefabricated porcelain teeth have two apertures in the lingual face, the headed rod projections are linked in the wax-up, and the eliminatable filaments for such linked headed rod projections are disposed intermediate the same.