GB2199751A

GB2199751A - Composite layered crowns

Info

Publication number: GB2199751A
Application number: GB08728323A
Authority: GB
Inventors: Atsushi Yamashita; Ikuo Kyotani
Original assignee: GC Dental Industiral Corp
Current assignee: GC Corp
Priority date: 1986-12-12
Filing date: 1987-12-03
Publication date: 1988-07-20
Anticipated expiration: 2007-12-03
Also published as: BE1002150A5; AU8263787A; FR2608038A1; JPH0744937B2; DE3742134A1; GB8728323D0; CH675200A5; DE3742134C2; AU605220B2; JPS63147453A; GB2199751B

Description

i 01 219975 t - 1 COMPOSITE LAYERED CROWNS FOR RESTORING CROWNS _The

present invention relates to a composite layered crown for the restoration of a crown, which comprises an inner crown and an outer crown and, more particularly, to a composite layered crown for the restoration of a crown, an inner.crown of which is prepared by the deposition of a metal body composed primarily of a noble metal on a working model of a tooth by the electroplating process directly.

Composite layered crowns for the restoration of a crown are generally prepared by using either a metal casting or a metal foil. According to the method making use of a metal casting, an inner crown is formed of a metal casting. That is, the metal casting is prepared by the precise lost- wax casting process and adjusted, and is then fused thereto with porcelain or built up thereon with plastics to make a composite layered. crown for the restoration of a crown.

According to the method making use of a metal foil, on the other hand, a metal foil to form an inner crown is covered over a working model of a tooth without recourse to the lost-wax process, and is pressed against it by means of a spatula for pressing a foil. The metal foil is then swaged over the working model of a tooth by a swager to form a pressed metal foil or a metal coping, which is in turn fused thereto with porcelain or built up thereon with plastics to make a composite layered crown for the restoration of a crown.

When a composite layered crown for the restoration of a crown is made using the metal casting for its inner crown, a wax pattern is created on a working model of a tooth on uhich the state of a tooth to be restored is reproduced, provided with a sprue wire, and is invested in an investment. After the investment has been set, it is fired to burn out the wax pattern in it, and a molten metal is cast into the resulting void to prepare a metal casting, which is then washed, adjusted and polished. The thus treated casting is thereafter built up thereon with porcelain for fusing, or built up thereon with plastics for setting. Thus, this method involves, in addition to the building-up and fusing of porcelain or the building-up and setting of plastics, the preparation, investment and burning-out of the wax pattern, casting, and the polishing of the casting. In other words, the working, time required per tooth is about 30 minutes for the preparation of the wax pattern, about 1 hour for the investment thereof, about 1 hour for the burning-out thereof, about 10 minutes for casting, and about 30 minutes for the polishing of the casting. The time required for the successive works from the preparation of the wax pattern to the polishing of the casting thus totals up to about 3 hours.

Noble and base metal are generally used for metal castings. For fusing porcelain, on the one hand, Au-Pt-Pd and Au-Pd-Ag alloys and Ni-Cr, NiCrMo and Ni-Cr-Co-Mo alloys are used as the noble and base metal alloys, respectively, and for building up plastics, on the other hand, Au-Ag-Cu, Au-Ag-Pd and Ag-Pd alloys and Ni-Cr and Co-Cr alloys are employed as the noble and base metal alloys, respectively.

Turning to the preparation of a composite layered crown for the restoration of a crown using the metal foil for its inner crown, a noble metal foil, which is in the form of, e.g., an umbrella with a bull's-eye design, has a thickness of 50 micrometers and is of a fourlayer structure comprising 100 % Au; 85 % Au + 5 % Pt + 10 % Pd; 100 % Pt; and 80 % Au + 10 % Pd + 10 % the balance, is covered over a working model of tooth on which the state of a tooth to be restored is 1 Q r.

1 reproduced, and is formed thereon with 8 to 10 folds with the use of a pincette. The foil is repeatedly pressed against the working model of the tooth along its surface by means of a spatula for pressing a foil.

The noble metal foil is then swaged over the working model of the tooth by a swager which comprises an outer pipe and a cylindrical member finally fitted thereinto, has on its bottom, the working model of the tooth with the noble metal foil being pressed thereagainst, and produces a blowing and swaging action via rubber. Thereaf ter, the noble metal foil is taken out of the working model of the tooth, and is heated with a gas burner to melt the gold in the foil, thereby completing a pressed metal foil or a metal coping. Applied on this pressed metal foil or this metal coping is a layer of a pasty bonding agent, followed by fusing. The resulting product is built pp thereon with porcelain for fusing, or with plastics for setting.

With regard to the preparation of a composite layered crown for the restoration of a crown using the metal casting for its inner crown, the following problems arise.

1) In some cases, since the dimensional accuracy of the metal casting is not so good, it may not be well-fitted over a working model of a tooth on which the state of a tooth to be restored is reproduced.

This is because although the dimensional accuracy of the metal casting has to be corrected by the expansion of an investment for the reason that it is affected by dimensional changes occurring in a wax pattern, an investment and an alloy, in particular the casting shrinkage of an alloy, it is difficult to completely correct the dimensional accuracy of the metal casting due to the f act that such casting shrinkage is largely affected depending upon not only the type of alloy but also the shape of the inetal casting, the strength of the investment and the casting conditions.

2) Since the thickness of the metal casting is on the order of 4 to 300 micrometers, it is required to increase the amount of porcelain or plastics to be built up so as to obtain the configuration of a crown similar to that of a natural tooth and, at the same time, obtain the color tone corresponding to that of a natural tooth. For that reason, it is required to increase the amount of patient's tooth to be removed in the tooth preparation for fixed prosthodontics. This gives rise to an increase in the time required for the tooth preparation for fixed prosthodontics to be carried out by a dentist, and causes pain to a patient. For this, it is ideal to minimize the thickness of the metal casting. Actually, however, difficulty is encountered in reducing the thickness of the metal casting to 200 micrometers or less due to the occurrence of casting defects such as "rounded", cold shut, rough surface and micro shrink.

3) As already mentioned, the work from the preparation, investment and burning-out of the wax pattern to the polishing of the casting takes a period of time of at least 3 hours, and the preparation of the metal casting is timeconsuming to a person who carries it out.

With regard to the preparation of a composite layered crown for the restoration of a crown using the metal foil for its inner crown, on the other hand, the following problems arise.

1) The compatib;lity of the pressed metal foil or the metal coping with respect to the working model of the tooth is incomplete, even when a noble metal foil is covered over the working model of the tooth, is provided with 8 to 10 folds by an exclusive pincette, and is thereafter repeatedly pressed against the working model of the tooth along its surface with the use of an exclusive spatula for pressing a foil. Further, there is a certain limit in the compatibility of the pressed metal foil or the metal coping with respect to the working model of the tooth, even though the pressed metal foil or the metal 4 11 J coping pressed agains.t the working modei of the tooth is swaged by a swager.

2) When the pressed metal foil or the metal coping pressed against the working model of the tooth is swaged by a swager, the working model of the tooth may break down in dependence on the type, shape and size of the working model of the tooth or how to use the swager. Hence, fair experience and expertness are needed for precise swaging.

3) When the pressed metal foil or the metal coping is removed from the working model of the tooth after the pressed metal foil or the metal coping pressed against the working model of the tooth has been swaged by a swager, it tends to deform due to its limited strength. To facilitate such removal, there is a need for simplifying the preparation of the working model of the tooth, to which a dentist should pay attention - in the tooth preparation for fixed prosthodontics.

4) After the pressed metal foil or the metal coping has been removed from the working model of the tooth, it is finished up by heating with a gas burner. Although attention must then be paid to the position and time at and during which the pressed metal foil or the metal coping is exposed to flames of the gas burner, fair experience and expertness are needed to this end. This is because the gas burner heating is a difficultwork that a gold layer in the noble metal foil layer is molten and cast in between the 8-10 folds formed on the pressed metal foil or the metal coping to make it complete.

The present invention has been accomplished so as to considerably eliminate the limits imposed upon, or the problems arising in connection with, the compatibility accuracy and thickness of the inner crown, when preparing a composite layered crown for the restoration of a crown using a metal casting or foil for the inner crown thereof, and is characterized in that, instead of using a metal casting or foil for the inner crown, electroplating is applied ( e.g. to a working model of a tooth)to obtain a(uniform noble)metal deposit (e.g.40 to 300 micrometers in thicknessl thereby preparing the inner crown.

When preparing a full-baked type composite layered crown for the restoration of a crown, on the one hand, an outer crown formed of porcelain, plastics or a metal is mechanically or chemically bonded onto the inner crown. When preparing a veneer type composite layered crown for the restoration of a crown, on the other hand, an outer crown formed on the lingual side of a metal or plastics and on the labial side of porcelain, plastics or a metal is mechanically or chemically bonded onto the inner crown.

The metal to be used for the inner crown should preferably be a noble metal which can be electroplated, and can securely and hygienically be applied under the conditions in an oral cavity. Among others, platinum, palladium, rhodium, ruthenium, gold and silver are suitably used, and may be used in the form of alloys with other metals. When porcelain is built up and fused on the inner crown for bonding thereonto, or a metal is bonded onto the inner crown by the lost-wax casting process, it is required that use is made of a metal unlikely to be softened and deformed at a fusing temperature of porcelain and a casting temperature of the metal.

On the other hand, the outer crown is formed as a whole of porcelain, plastics or a metal in the case of the full-baked type composite layered crown for the restoration of a crown. In the case of the veneer type composite layered crown for the restoration of a crown, however, a labial crown portion formed of a metal or plastics is combined with a lingual crown portion formed of porcelain, plastics w4 1 ..I or a metal. The porcelain suitable for, use with the full-baked type or the labial crown portion of the veneer type is based on (K, Na).GAQ.0,- SiO.. In order to bond such porcelain onto the inner crown, it may be built up and fused on the inner crown which has been coated with a bonding agent. Alternatively, the porcelain built up and fired on another working model of a tooth may be bonded onto the inner crown with the use of a binder. Still alternatively, a ceramic material to be cut, e.g., a material based on 5i02-MgO-A2203-K,.0-B,O,-F may be lathed and, thereafter, bonded onto the inner crown by a binder. Usable as the plastics for the full-baked type and the lingual and labial sides of the veneer type are those such as acrylic, polycarbonate, -polystyrene, polyamide, polYimide, polyurethane and polyester base plastics. For the purpose of improving the physical and engineering properties of such plastics, inorganic fillers such as molten quartz, alumina, aluminosilicate glass, sodium glass, barium glass, borosilicate glass, beta-eucryptite or organic fillers obtained by the pulverization of compacts comprising plastics and colloidal silica may be added thereto. Further, such plastics may be polymerized and cured by heat or the irradiation of light. Still further, such plastics may be in the pasty form enough to give form thereto by the brush-on technique, and should more preferably assume various color tones such as Opaque, Cervical, Bo dy and Dentin so as to make it possible to prepare composite layered crowns for the restoration of crowns, which are nicer to look at. These plastics may be built up and cured on the inner crown for bonding. thereonto. Alternatively, they may be built. up and cured on another working model of a tooth, and then bonded onto the inner crown.

When plastics is used on the lingual side of the veneer type with a need of increased strength in particular, foils having a thickness of 20 to 80 micrometers such as stainless steel, amorphous alloys and titanium alloys may be embedded in plastics in a layered state.

Preferable for the metals used for the full-baked type and on the lingual and labial sides of the veneer type are noble metals such as platinum, palladium, rhodium, ruthenium, gold and silver as well as alloys thereof with other metals. Commercially available to this end are dental gold alloys, gold-silver-palladium alloys, palladium-silver alloys, silver alloys, Ni-Cr alloys, Ni-Cr-Mo alloys, Ni-Cr-Co-Mo alloys and titanium alloys. Such metals may be bonded directly to the inner crown by the lostwax casting process. Alternatively, they may be waxed up on another working model of a tooth, and then be bonded onto the inner crown by the lost-wax casting process with the use of a binder. Still alternatively, they may be lathed and then bonded onto the inner crown with the use of a binder. In the case of the fullbaked or veneer type, however, the metal to be bonded directly to the inner crown by the lost-wax casting process should have a melting point lower than that of the metal used for forming the inner crown so as to prevent the inner crown from being softened and deformed during casting process.

It is understood that bonding agents or binders may be used to join the inner crown to the outer crown, both of the full-baked type, or to join the inner crown to the outer crown, both of the veneer type. As such bonding agents, use may be made of a known pasty bonding agent comprising finely divided particles of gold and platinum or a gold alloy and platinum. As the binders, use may be made of known binders such as zinc phosphate Cement, silicate cement, silicophosphate cement, glass ionomer cement and resin cement. Among others, however, preference is given to the chemical or light cured resin cement having a low consistency, when taking mechanical strength and aesthetics in consideration.

Examples of the-composite layered crownsfor the restoration of crowns according to the present invention will now be explained in further detail with reference to the accompanying drawings, which are given for the purpose of illustration alone, and in which:

Figure 1 is a sectional view of the composite layered crowns (of the fullbaked type) for the restoration of anterior tooth crowns according to Examples 1,3 and 6; Figure 2 is a sectional view of the composite layered crowns (of the veneer type) for the restoration of anterior tooth crowns according to Examples 2, 5, 7 and 8; Figure 3 is a sectional view of the composite layered crown for the restoration of a molar tooth crown according to Example 4; and Figure 4 is a sectional view of the composite layered crown (of the veneer type) for the restoration of anterior tooth crowns according to Example 9.

Examples

Examp 1 e 1 A composite layered crown for the restoration of a anterior tooth crown, which was of the full-baked type comprising an inner crown 1 formed of platinum and an outer crown 2 formed of porcelain, as illustrated in the sectional view of Figure 1, was prepared in the following manner.

A layer of a pasty conductive coating material was applied on the surface of a working model of a tooth. Plating was then carried out in a bath of platinum deposits, using the working model of the tooth as the anode and platinum as the cathode, at a current density of 4.0 A/dn' for 9 hours to obtain a layer of deposits of 60 micrometers in thickness.

The product was treated with an ultrasonic cleaner, while immersed in a gypsum-dissolving liquid, to dissolve the working model of the tooth, and was then washed with acetone, dilute nitric acid and water and dried to prepare the inner crown 1 formed of platinum. Subsequently, a pasty bonding agent comprising finely divided particles of gold and platinum was applied on the inner crown 1, which was thereafter heated at 1070'C for 1 minute in an electric furnace to form a layer firmly bonded to the inner crown 1 by the fusion of gold particles and containing finely divided particles of platinum serving as a mechanical retainer with respect to porcelain. Thereafter, an amount of pasty porcelain based on (K, Na),O-AQ,0,-SiO, was built up on and fused to the bonding agent layer, thereby preparing the composite layered crown for the restoration of a crown in which the outer crown 2 formed of porcelain was joined onto the inner crown 1 formed of platinum.

Example 2

A composite layered crown for the restoration of an anterior tooth crown comprising an inner crown 1 formed of a palladium-nickel alloy, an outer lingual crown portion 2b formed of a Au-Ag-Pd alloy and an outer labial crown portion 2a formed of porcelain, as shown in the sectional view of Figure 2, was prepared in the following manner.

A layer of a pasty conductive coating material was applied on the surface of a working model of a tooth. Plating was then carried out in a bath of palladium-nickel alloy deposits, using the working modeloFthetooth as the anode and platinum as the cathode, at a current density of 4.3 A/W for 10 hours to obtain a layer of deposits of 70 micrometers in thickness.

The product was treated with an ultrasonic cleaner, while immersed in a gypsum-dissolving liquid, to dissolve the working model of the tooth, and was washed with acetone, dilute nitric acid and water and dried to prepare the inner crown 1 formed of an palladium- -1 nickel alloy. In this case, a wax pattern was made on the lingual side of the obtained inner crown 1, and was then provided with a sprue wire for investment.. After the investment was set, it was baked or fired to burn out the wax pattern inside. Au-Ag-Pd alloy was cast into the resulting space to make the outer lingual crown portion 2b formed of a metal casting, which was made integral with the inner crown 1 to obtain a cast crown having a maximum thickness of 800 micrometers. Then, a layer of a pasty bonding agent comprising finely divided particles of gold and platinum was applied on the cast crown comprising the inner crown 1 and the outer lingual crown portion 2b formed of a casting, which was thereafter heated at 1070C f or 1 minute in an electric furnace. Af terwards, an amount of pasty porcelain based on (K, Na),O-Ae,03-SiO, was built up on and fused to the bonding agent, thereby preparing the composite layered crown for the restoration of a crown in which the outer lingual crown portion 2b formed of Au-Ag-Pd alloy and the outer labial crown portion 2a formed of porcelain were bonded onto the inner crown 1 formed of a palladium-nickel alloy.

Example 3

A full-baked type composite layered crown for the restoration of ananterior tooth crown comprising an inner crown 1 of a gold-nickel alloy and an outer crown 2 of plastics, as illustrated in the sectional view of Figure 1, was prepared in the following manner.

The inner crown having a thickness of 80 microrneters and formed of a gold-nickel alloy was prepared in a manner similar to that of Ex. 1, provided that plating was carried out at a current density of 4.3 A/W for 9 hours, using a bath of gold-nickel alloy deposits.

Subsequently, a layer of a pasty bonding agent comprising finely divided particles of a gold-silver alloy and platinum was applied onto the inner crown 1, which was then heated at 9009C for 1 minute in an electric furnace. Afterwards, a paste of Bis GMA plastics belonging to acrylic plastics was built up on the bonding agent layer, and was cured by the irradiation of light, thereby preparing the composite layered crown for the restoration of a crown in which the outer crown 2 was bonded onto the inner crown I formed of a gold-nickel alloy.

Example 4

A composite layered crown for the restoration of a molar tooth crown comprising an inner crown I formed of palladium and an outer crown 2 formed of Au-Ag-Cu alloy, as shown in the sectional view of Figure 3, was prepared in the following manner.

The inner crown having a thickness of 70 microrneters and formed of palladium was made in a manner similar to that of Ex. 1, provided that a working model of a molar tooth was employed, and plating was carried out at a cur-rent density of 4.6 A/dM2 for 10 hours, using a bath of palladium deposits. Subsequently, a wax pattern in the form of a crown was made on the inner crown I formed of palladium, and was then provided with a sprue wire for investing in an investment. After the investment was set, the investment was fired to burn out the wax pattern inside. Au- Ag-Cu alloy was cast into the resulting space, and was made integral with the inner crown prepared by electroplating, thereby preparing the composite layered crown for the restoration of a molar tooth crown in which the outer crown 2 formed of Au-Ag-Cu alloy was bonded onto the inner crown I formed of palladium.

Example 5

A veneer type composite layered crown for the restoration of an anterior tooth crown comprising an inner crown of gold, an outer lingual crown portion 2b of plastics and an outer labial crown portion 2a of porcelain, as illusi7ated in the sectional view of Figure 2, was prepared in the following manner.

v S The inner crown 1 having a thickness of 75 micrometers and formed of gold was prepared in a manner similar to that of Ex. 2, provided that plating was carried out at a current density of 4.1 A/dm' for 8 hours, using a bath of gold deposits. Subsequently, after a bonding agent layer was formed on the inner crown in a manner similar to that of Ex. 3, a paste of UDMA plastics belonging to polyurethane plastics was built up on the lingual side by means of a brash-on technique, and was cured by heating, thereby bonding the outer lingual crown portion 2b onto the inner crown 1. Then, a paste of porcelain based on (K, Na),-AQ,O,-SiO, was built up and fired on another refractory cast of a tooth to form a porcelain shell, which was etched on the inner face with fluoric acid, washed and dried, and was coated with a binder for bonding to a metal-plastic combination crown comprising the inner crown 1 and the outer lingual crown portion 2b, thereby preparing the composite layered crown for the restoration of a crown in which the outer lingual crown portion 2b formed of plastics and the outer labial crown portion 2a were bonded onto the inner crown 1 formed of gold.

Example 6

A full-baked type composite layered crown for the restoration of an anterior crown comprising an inner crown 1 of a gold-copper alloy and an outer crown 2 of porcelain, as illustrated in the sectional view of Figure 1, was prepared in the following manner.

The inner crown 1 having a thickness of 53 micrometers and formed of a gold-copper alloy was made in a manner similar to that of Ex. 1, provided that plating was carried out at a current density of 4.3 AldM2 for 8 hours, using a bath of gold-copper alloy deposits. Then,. a paste of porcelain based on (K, Na) -AQ.03-SIO2 was built up and fired on another refractory cast of a tooth, and was etched on the inner face with fluoric acid. After washing and drying, the porcelain was coated with a binder for bonding onto the inner crown, thereby preparing the composite layered crown for the restoration of a crown in which the inner crown 1 formed of a gold-copper alloy was bonded to the outer crown 2 formed of porcelain.

Example 7

A veneer type composite layered crown for the restoration ofan anterior tooth crown comprising an inner crown I of a palladium-nickel alloy, an outer lingual crown portion'2b of Au-Ag-Cu alloy and an outer labial crown portion 2a of porcelain, as illustrated in the sectional view of Figure 2, was prepared in the following manner.

The inner crown 1 having a thickness of 56 micronmeters and formed of a palladium-nickel alloy was made in a manner similar to that of Ex. 2, provided that plating was carried out at a current density of 4.3 A/dmI for 8 hours, using a bath of palladium-nickel alloy deposits. Subsequently, the outer lingual crown portion 2b was prepared in a similar manner to that of Ex. 2, except for the use of an Au-Ag--Cu alloy, and was made integral with the inner crown I to make a cast crown having a maximum thickness of 750 micrometers. A bonding agent layer was then formed on the obtained cast crown in a manner similar to that of Ex. 2. Subsequently, a paste of porcelain based on (K, Na) 2-Ae.03-S'O, was built up and fired on another refractory cast of a tooth, and was etched on the inner face with fluoric acid. After washing and drying, the porcelain was coated with a binder for bonding to the cast crown, thereby preparing the composite layered crown for the restoration of a crown, in which the inner crown I of a palladiumnickel alloy, the outer lingual crown portion 2b of Au-Ag-Cu alloy and the outer labial crown portion 2a of porcelain were bonded together. Example 8 A veneer type composite layered crown for the restoration of an i S anterior tooth crown comprising an inner crown I of palladium, an outer lingual crown portion 2b of a silver-palladium alloy and an outer labial crown portion 2a -of porcelain, as illustrated in Figure 2, was prepared. in the following manner.

The inner crown I having a thickness of 63 micrometers was prepared in a manner similar to that of. Ex. 2, provided that plating was carried out at a current density of 4.5 A/dM2 for 9 hours, using a bath of palladium deposits. Subsequently, the outer lingual crown portion 2b was prepared in a manner similar to that of Ex. 2, except for the use of a silverpalladium alloy, and was then made integral with the inner crown I to make a cast crown having a maximum thickness of 780 micrometers. Afterwards, 'a bonding agent layer was formed on the cast crown in a manner similar to that of Ex. 2. Then, a paste of Bis GMA plastics belonging to acrylic plastics was built up on another cast crown model, and was cured by heating. The thus set plastics was coated on the inner face with a binder for-bonding to the cast crown, thereby making the composite layered crown for the restoration of a crown, in which the inner crown I of palladium, the outer lingual crown portion 2b of a silver-palladium alloy and the outer labial crown portion 2a of platics were bonded together.

Example

A veneer type composite layered crown for the restoration-of a crown comprising an inner crown I of gold, an outer lingual crown portion 2b of plastics and an outer labial crown portion 2a of AuAg-Cu alloy,I as illustrated in the sectional view of Figure 4, was prepared in the following manner.

The- inner crown I of gold having a thickness of 72 micrometers was prepared in a manner similar to that of Ex. 5, provided that plating was carried out at a current density of 4.5 A/dM2 for 7 hours. Subsequently, a bonding agent layer was built up on the inner crown I in a manner similar to that of Ex. 3. Thereafter, a paste of Bis GMA plastics belonging to acrylic plastics was built up on the outer lingual crown portion 2b by means of a brush-on technique, and was cured by the irradiation of light to make a metal-plastics combination crown. Then, a wax pattern of a portion corresponding to the outer lingual crown portion 2a was made onanother metal-plastics combination crown model, and was provided with a sprue wire. The wax pattern was removed from the working model, and was invested in an investment. After the investment had been set, it was fired to burn out the wax pattern inside, and Au-Ag--Cu alloy was cast into the resulting space to make a metal casting. The casting was washed with an acid, washed with water and dried, and was coated on the inner face with a binder for bonding to the metal-plastics combination crown, thereby making the composite layered crown for the restoration of a crown, in which the inner crown I of gold, the outer lingual crown portion 2b of plastics and the outer labial crown portion 2a of AuAg-Cu alloy were bonded together.

The composite layered crowns for the restoration of crowns according to the ahove examples introduce considerable improvements into dimensional accuracy, the amount of patient's tooth to be removed and the time required for a succession of operations from the preparation of wax patterns to the polishing of castings which have been the problems of the method for making inner crowns by the lost wax casting process, and into incomplete compatibility, expertness demanded on how to use a swager, deficiency in the strength of pressed metal foils or metal copings and expertness needed for casting which have been the problems of the method for making inner crowns of metal foils. ag ahove examples 0 p ng pp directly to a working model of a tooth to prepare an inner crown composed primarily of a noble metal and having an even thickness, and A r-r-n ?-A f- nt-lyú2 ' Int- C n 1;nA 4 1 l- porcelain, plastics or a metal is bonded onto the inner crown, thereby making a full-baked type composite layered crown for the restoration of a crown. When the aforesaid full-baked type composite layered crown may be cracked during use for the reason that, for instance, the lingual side of the outer crown is so thin that its strength is reduced,_ it is required to make a veneer type composite layered crown by lining the lingual side of the inner crown with other metal or plastics or a metal for reinforcement. Referring to metal lining for reinforcement, it is very difficult to achieve it by electroplating in view of time and configuration, since the portion to be lined, including the inner crown, has a maximum thickness of 0.7 to 1.0 mm. For that reason, after preparing an inner crown composed mainly of a noble metal and having an even thickness, a wax pattern is formed on the lingual side of the inner crown to be lined. The wax pattern is then invested, burned out, and cast out to obtain a cast crown integral with the inner crown. Bonded onto this cast crown is porcelain, plastics or a metal to thereby prepare a veneer type composite layered crown for the restoration of a crown. Turning to plastics lining for reinforcement, a plurality of pasty plastic layers by means of a brush-on technique are individually built up on the lingual side of the inner crown, while shaping, and are cured thereon for bonding onto the inner crown. Thereafter, porcelain, plastics or a metal is bonded onto the inner crown to thereby prepare a veneer type composite layered crown for the restoration of a crown.

The composite layered crown for the restoration of a crown -as-described above iirm has the following, advantages over the prior art composite layered crown in which a metal casting is used for the inner crown.

]) Since the inner crown is prepared by forming noble metal deposits directly on a working model of a tooth by electroplating, it is well compatible with the working model of the tooth without being affected by dimensional changes in the wax pattern, investment and alloy.

2) The thickness of the inner crown can be reduced to 200 micrometers or less without suffering from any casting defects such as rounded, cold shut, rough surface and micro shrink. Accordingly, since the amount of porcelain or plastics to be built up on the inner crown can be increased to make the outer crown thick, it is possible to impart to the composite layered crown the same configuration and color tone as those of a natural tooth. Further, since the amount of patient's tooth to be removed can be limited to a minimum in the tooth preparation for fixed prosthodontics, the time required for the tooth prepartion for fixed prosthodontics can be curtailed from the dentist's standpoint, while the pain can be relieved for the patient.

3) The inner crown can be made without recourse to a succession of works involving the preparation, investment and burning-out of wax patterns, casting and the polishing of castings. Thus, only by placing on a plating device a working model of a tooth on which one layer of a pasty conductive coating material has been applied, the inner crown can be prepared without relying upon any successive works.

The composite layered crown of the present invention has the following advantages over the prior art composite layered crowns obtained by using a metal foil for the inner crown.

1) Since the inner crown can be prepared by forming noble metal deposits directly on a working model of a tooth by electroplating, it is much more compatible with the working model of the tooth than a pressed metal foil or a metal coping obtained by covering a noble metal foil over a working model of a tooth and repeatedly pressing it against the working model of the tooth along the surface thereof.

2) Since there is no need of swaging a pressed metal foil or a f 1 C metal coping pressed against a working model of a tooth by means of a swager, the working model of the tooth may not break down in dependence on the type, configuration and size thereof or how to use a swager.

3) No attention is paid to the tooth preparation for fixed prosthodontics so as to facilitate the removal of the. pressed metal foil or the metal coping from the working model of the tooth. Hence, the tooth preparation can freely be prepared.

4) Further, there is no need of melting the metal in a noble metal foil layer and casting it in between folds on a pressed metal foil or a metal coping.

Claims

Claims:

1. A composite layered crown for the restoration of a crown, comprising an outer crown mechanically or chemically bonded onto an inner crown, the inner crown being a metal body formed by electroplating, and the outer crown being formed of porcelain, plastics or a metal.

2. A composite layered crown for the restoration of a crown, comprising an outer crown mechanically or chemically bonded onto an inner crown, the inner crown being a metal body formed by electroplating, and the outer crown being formed of porcelain, plastics, or a metal and being bonded to a cast crown formed on the inner crown by the lostwax casting process.

3. A composite layered crown for the restoration of a crown, comprising an outer crown mechanically or chemically bonded onto an inner crown, the inner crown being a metal body formed by electroplating, and the outer crown being formed of porcelain, plastics, or a metal and being bonded to a metal-plastics combination crown obtained by building up plastics on the inner crown by the brush-on technique and curing it.

4. A composite layered crown as claimed in any preceding claim', in which the inner crown has a thickness of 40 to 300 micrometers.

5. A composite layered crown substantially as described in any of Examples 1 to 9.

P,ibilste-1 1986 a -.-,e =ce 5,LaL., H cuse 66771 Righ H cbcrr., Londor WC 1 E 4-F Furilier copies may be bb.a-,--ie,' tro.- The Paten 0--ce Sales S. Ma-7 Cray. 0-pingion, Kent BR5 3RD Printed by Multiplex techiuques Itcl St Maxy Cray. Kent Cor. 1187