Reinforced jacket crown and method of construction

The reinforced jacket crown of the present invention comprises an inner structure including a thin metal foil of platinum conforming in shape to the tooth preparation to be restored, at least one fired on coating of a composition of finely divided particles of from about 1 to 100% by weight of a noble metal halide in combination with from zero to 99% by weight of a noble based metal and a relatively thick fired on outer coating of dental porcelain.

This invention relates to the field of dental restorations and more 
particularly to the porcelain jacket crown restoration and to a method for 
forming a porcelain jacket crown. 
Dental porcelain, a conventional material composed of a mixture of 
feldspar, quartz and kaolin is commonly used in fabricating dental 
restorations, for example jacket crowns. The full porcelain or jacket 
crown is esthetically superior to all other crown restorations and is 
virtually impossible to visually distinguish from a natural tooth. 
Accordingly, it should be commonplace but is, in general, indicated for 
use only as a full coverage for an anterior tooth where esthetics is the 
prime consideration. The limited use of the porcelain jacket crown is 
attributable to its present method of construction with the strength of 
the jacket crown dependent upon the strength of the porcelain material 
composition. Porcelain is inherently structurally weak and fragile. In 
addition, the present method of construction requires a high degree of 
proficiency to establish accurate marginal fit and finish and to avoid 
poor seating of the crown occlusally relative to the preparation. An 
improper fit at the gigival margin results in a cement line which readily 
washes away inviting decay and loosening the crown attachment. 
The more conventionally fabricated crown construction is the porcelain 
veneer cast metal crown. A relatively thick metal understructure is formed 
from casting an investment of a wax or plastic pattern from the prepared 
tooth. Dental porcelain is then applied in layers over part or all of the 
understructure and fired at high temperature to form a veneer. The metal 
understructure is preferably formed from a noble based metal or alloy 
predominantly of gold. The thickness of the cast metal understructure 
ranges from about 0.2 to 0.5 mm. A cast metal understructure is expensive 
and particularly so for a noble based metal composition. Moreover, since 
the bulk of the restoration should be no greater than that of the tooth 
structure which originally occupied the space, a thick metal 
understructure minimizes the permissible thickness for the translucent 
porcelain veneer. Furthermore, any exposure of the metal understructure 
will detract from the esthetics of the restoration. 
The present invention concerns itself with overcoming the shortcomings of 
the conventional porcelain jacket crown construction. In the conventional 
process for preparing a porcelain jacket crown a platinum foil is swaged 
about the prepared die of the tooth to form a matrix upon which the 
porcelain may be fired. The foil is then removed before the crown is 
cemented to the tooth preparation. The primary object of the present 
invention is to provide a reinforced jacket crown having a high resistance 
to fracture comparable with or even greater than the conventional 
porcelain veneer cast metal crown. 
In accordance with the present invention the jacket crown is formed as a 
composite body having an inner structure composed of a thin foil layer of 
material conforming in shape to the prepared tooth, with at least one 
intermediate layer of a predetermined material composition surrounding the 
foil core and fused to one face thereof at a predetermined elevated 
temperature and a relatively thick outer coating of dental ceramic 
material surrounding said inner structure and being bonded to the foil 
layer through the intermediate layer. The intermediate layer between the 
porcelain coating and the foil layer is formed from a finely divided 
particle composition comprising of from about 1 to 100% of a noble metal 
halide and from zero to 99% of noble based metal particles. 
The porcelain jacket crown of the present invention eliminates the need for 
waxing, casting and machining the understructure for a cast metal crown, 
is at least as strong as a cast metal crown and may be prepared at a 
substantially lower fabricating cost relative to the cast metal crown. 
Moreover, any type of margin preparation is equally acceptable for use 
with the composite jacket crown of the present invention. In addition, the 
composite jacket crown of the present invention minimizes the need for 
substantial contouring of the tooth preparation and as such minimizes the 
potential for tissue disease.

The preferred starting material is shown in FIG. 1 in the form of a 
preformed metal foil strip 10 of rectangular geometry. The preformed foil 
strip 10 includes a thin base metal layer 12 preferably of platinum or 
another high fusing temperature matal, a first coating 14 of a 
predetermined material composition bonded to the layer 12 at a first 
elevated temperature and a second coating 16 applied over the first 
coating 14. The coating 14 is composed of a finely divided metal particle 
composition comprising a halide of a noble metal in a range from about 1 
to 100% by weight in combination with a noble based metal in a range from 
zero to 99% by weight. The preferred noble metal is selected from the 
group consisting of silver, palladium, platinum and gold with other noble 
metals such as indium, rhodium, osmium and iridium being less desirable. 
The halide is preferably selected from the group consisting of a chloride 
or fluoride, although a bromide or iodide may be used. The noble metal 
halide is a critical ingredient. Noble metal halides are commercially 
available in a granulated powder or crystalline form. For example, gold 
chloride is commercially available also as chlorauric acid (HAuCl.sub.4) 
in a powdered crystal form. The shape or form of the finely divided 
particles are not essential to the present invention but should preferably 
be of a size below about 10 microns. 
The noble based metal component of the coating 14 is preferably a gold 
based noble metal comprising at least about 50% by weight finely divided 
particles of gold with a remainder of one or more of other finely divided 
noble metal particles such as silver, platinum, palladium, rhodium and 
indium and may contain traces of preferably no more than a total of about 
5% by weight of any one or more non-precious metals such as copper, zinc, 
iron, tin, cadmium, magnesium, germanium, manganese, cobalt and nickel. It 
should be understood that although a predominantly gold based noble metal 
is preferred because it provides a desirable background color the present 
invention is not to be construed as limited thereto. Noble based metal is 
defined for purposes of the present invention as a metal or metal alloy 
containing one or more noble metal constituents representing all or a 
relatively substantial proportion by weight of such metal or metal alloy. 
The average particles size for the noble based metal component is 
preferably below about 10 microns and may be in any desired form such as 
flakes, granules or powder. 
The material composition of coating 14 is discussed in greater detail in a 
corresponding U.S. patent application Ser. No. 171,255 entitled Bonding 
Material And Method For Bonding A Ceramic To A Noble Based Metal At 
Elevated Temperature which is herein incorporated by reference. 
It is essential to the present invention that the first coating 14 be 
sintered to the base metal layer 12 at an elevated temperature above at 
least about 1600.degree. F. with the optimum sintering temperature lying 
in a range of between about 1875.degree. F. to 1975.degree. F. Within the 
optimum temperature range the first coating 14 is wetted uniformly over 
the full surface of the platinum layer 12. The sintering operation forms a 
clinically unbreakable bond between the coating 14 and the platinum layer 
12. Although the sintering operation is preferably performed before the 
foil 10 is adapted to the die 18 it should be understood that the process 
of the present invention broadly encompasses applying and sintering the 
coating 14 to the platinum layer 12 after the latter is adapted to the 
die. In fact, the coating 14 may be sintered simultaneously with the 
firing of the porcelain outer layers. This, however, would limit the 
sintering temperature to that normally used for firing porcelain which 
lies in general between 1600.degree.-1820.degree. F. 
The coating material 14 may be applied to the surface of the platinum layer 
12 with or without a suitable binder. It is preferred, however, to suspend 
the coating material 14 in a carrying vehicle so that it may be readily 
applied by brushing, painting, dripping or spraying onto the platinum 
layer. Any suitable carrying vehicle, preferably one which will volatilize 
in the sintering process without a residue, may be used including known 
water detergents or an organic resinous or synthetic resinous medium 
thinned with a suitable solvent. When a binder is not used the coating 
material 14 may be simply sprinkled over the platinum foil layer 12. The 
coating material 14 may be built up into a layer of any desired thickness. 
It is, however, preferred that it be applied as a thin film in about the 
same thickness range as that of the thin platinum layer 12 which varies 
from about 0.0015 mm to 0.05 mm thick. There is, in fact, no limitation to 
the thickness of the layer of coating material 14 except as it relates to 
the physical and handling properties of the foil 10 after sintering. If 
the layer 14 is too thick it will make the foil 10 too rigid to adapt to 
the die. 
Although the preformed foil 10 preferably includes a second coating 16; the 
second coating 16 is not essential to the invention. Moreover, the coating 
16 may be applied over the first coating 14 after the foil is adapted to 
the die and thereafter sintered before or concurrent with the firing of 
the porcelain coating. The second coating 16 consists of a composition 
equivalent to the composition of coating 14 although not necessarily with 
the noble metal halide component and the noble based metal component in 
the same chosen proportion as coating 14. The coating material 16 may 
similarly be suspended in a carrying vehicle for controllably applying the 
material over the surface of the first coating 14. Application of the 
second coating 16 should be relatively uniform with a thickness equal to 
or less than the thickness of the first coating 14. The sintering 
operation for the second coating 16 should be conducted at a sintering 
temperature sufficient to convert the finely divided particle composition 
of coating 16 into globules or beads of substantially spherical geometry 
which are preferably irregular in size. The beaded particles have been 
shown to operate as stress breakers for increasing fracture resistance of 
the jacket crown to external forces. Optimum beading appears to occur at a 
temperature range between about 1775.degree. F. to 1875.degree. F. 
Sintering of the second coating 16 forms an unbreakable bond between the 
first and second coatings 14 and 16 respectively. 
FIGS. 2 and 3 illustrate the sequence used to adapt the rectangular foil 10 
to the die 18. The die 18 is conventionally prepared from an impression of 
the prepared tooth and is a replica thereof. The foil is wrapped tightly 
about the die 18 to form overlapping ends 20 which are trimmed down and 
folded over to form flaps 22 and 24. The foil 10 should also extend over 
the gingival margin 16 to form a skirt 28. The die 18 and foil 10 is then 
placed in a swaging device or pressure applied to the foil by hand to 
adapt it to the die 18. The foil 10 is then removed from the die 18 
leaving a free standing structure, as shown in FIG. 4, over which any 
number of porcelain layers may be applied and fired for forming the jacket 
crown of the invention. Generally, three or more layers of varying dental 
porcelain composition starting with an opaque layer are built up and fired 
at temperatures in a range from about 1600.degree. to 1820.degree. F. 
Before firing the final glaze the extended skirt 28 is cut and the 
porcelain shaped and finished to the correct gingival margin of the 
prepared tooth. 
After the final glaze the crown is ready to be inserted into the mouth and 
cemented to the tooth. The uncoated side of the platinum layer 12 is 
preferably roughened to firmly engage and contact the tooth preparation in 
the mouth. This roughness may be formed before or after adapting the foil 
10 to the die by sandblasting or grinding one face of the platinum strip. 
Any conventional cement material may be used to cement the crown to the 
tooth preparation. 
The jacket crown of the present invention is suited to all conventional 
gingival margin teeth preparations as illustrated in FIGS. 5 to 8. Any one 
of these types may be suitable for the whole circumferance of the crown or 
may be used with any other type. A comparative test was conducted to 
demonstrate the strength of the porcelain jacket crown of the present 
invention relative to a conventional porcelain to cast metal crown. An 
upper central incisor foil crown was formed in accordance with the 
teachings of the present invention and secured to a metal base. A metal 
pin was positioned in contact with the incisal edge of the crown. A 100 
gram iron cylinder was dropped from 20 cm over the pin without causing any 
apparent damage. The weight was then dropped from 40 cm over the pin. This 
causes a limited area of porcelain breakage. A similar test was conducted 
with a conventionally prepared porcelain to cast metal crown. The 100 gram 
weight was dropped from 20 cm over a pin contacting the same incisal edge 
position. The drop of the weight caused a large part of the buccal 
porcelain to break off. In each case the porcelain was an identical 
ceramic porcelain composition from Ceramco.