Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a dentaL construction
comprising a metal core of a non-precious metal alloy
contoured in a desired form and a porcelain covering bonded
thereto.
Dental restorations such as bridges, crowns, dentures,
partial dentures, inlays, onlays and the like have employed
gold alloy for many years. Because of its high cost, many
attempts have been made to make and employ non-precious metal
alloys in place of the gold. Such non-precious metal alloy
O compositions are illustrated, for example, by the patents, U.S.
No. 1,736,053: 2,089,587, 2,156,757 2,134,423 2,162,252:
2,631,095, 3,121,629, 3,464,817 and 3,544,315. Gold alloys,
however, has many advantageous properties as a dental alloy
and many of the previously prepared non-precious metal alloys
,~
.~ have been found to be unsatisfactory in various respects when
compared to the conventional gold alloy.
One of the problems encountered in attempts to use
.:
, non-precious metal alloys for dental work in place of gold
is that many of these alloys have been hard to cast because
~' 20 of a too high melting range. In order to be accepted generally
by dental laboratory technicians, the melting temperature of
the alloy should not be much in excess of 2400F. It is
desirably within the range of about 2000 to 2350F, more
preferably, nearer the lower limits. A practical reason for
~- this is that many dental loboratories use torches of the gas
oxygen type which will not heat to much above 2500F so that
if higher melting alloys are used then special heating equipment
such as oxygen-acetylene torches must be obtained for working
the metal. Although attempts have been made to adapt these
alloys by modifying casting techniques such as by changing
, shape, dimensions, number and point of attachment of sprues, by
,, ~
,:
_
using special investment materials, or by using special
aftercastir,g treatments, the advantages of the heretofore
available non-precious metal alloys have not been sufficient
to serve toward general acceptance of these alloys as a
preferred substitute for gold alloy in dental constructions.
Another problem with many of the heretofore known
non-precious metal dental alloys is one of corrosion. The
non-precious metal alloys generally are not as resistant as
` gold with respect to corrosion by mouth acids. Not only
~ 10 does corrosion cause loss of structural metal but in the case
of those dental restorations such as porcelain ~ackets, crowns,
ii
- bridges, etc., which are faced with porcelain, corrosion may
cause, in the case of certain non-precious metal alloys
formation of colored ions which discolor the porcelain. Thus,
; for example, the presence of cobalt, copper or iron in the
metal alloy in an appreciable amount tends to discolor the
porcelain bonded thereto.
A still further serious problem encountered in
constructing a metal core or framework is the difficulty
~s 20 of soldering the non-precious metal alloy parts to themselves
or to gold by using the conventional readily available dental
solders. Moreover, when conventional solders such as gold
alloy solders are used with non-precious metal alloy there
'r,' iS a tendency for galvanic corrosion to accur at the interface.
;~ Also, since non-precious metal dental alloy materials
heretofore designed for use as structural metals are
frequently substantially harder than gold, there is the
added disadvantage of greater time and effort which must
be spent on grinding the metal core for precise fit after
30 casting.
In addition to the problems relative to the properties
S -2-
,
of the prior non-precious metal alloy as a general dental
alloy, certain additional requirements exist in connection
with the use of the dental alloy as a material which is to
be faced with tooth enamel simulating material such as
porcelain. Thus, the coefficient of expansion must be
compatible with that of porcelain. Where there is not the
desired compatibility in the coefficient of expansion between
the metal and porcelain, fractures may develop in the
porcelain during the firing and subsequent cooling. The
preferred relationship of porcelain to metal is such that
at room temperature there is compression in the porcelain
or glass layer and tension in the metal. Further, the fusion
temperature of the alloy, while it should not be so high as
to be difficult to cast, it must be sufficiently above the
firing temperature of the porcelain so that there is no
deformation of the metallic core during firing. Moreover,
metal alloys must bond adequately to porcelain so that when
subjected to mechanical stress, there does not occur a
separation at the interface in whole or in part.
Thus, it is the object of the present invention to
provide for a dental construction such as bridges, crowns,
etc., having a metal core of a non-precious metal alloy and
a tooth enamel simulating outer covering bonded thereto
wherein said non-precious metal alloy is free from the objec-
tions enumerated above and moreover the relationship of the
physical properties between the metal core and outer covering
are such that the foregoing problems are met. The preparation
of a non-precious metal dental alloy which is particularly
suitable in dental constructions but which may be employed
.:
in other dental applica~ions is another object of the present
invention. Another object is to provide for a dental cons-
:,
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.,
.
.
truction which employs a non-precious metal alloy which is
not only less co~tly than gold but has advantages over gold
as a dental structural material. A further object is the
provision of a dental alloy which may be employed without
appreciably changing present techniques or equipment.
' It has now been discovered that a dental construction
comprising an appropriately contoured metal core of a non-
precious metal alloy with a porcelain covering bonded thereto
may be prepared which accomplishes the objects hereinbefore
lO enumerated by employing for the metal core, a metal alloy
having a fusion temperature within the range of from about
13.5 x lO 6 in/in/C to about 13.8 x lO 6 in/in/C.
The expression "dental construction" as herein
employed is meant a metal core of a non-precious metal alloy
contoured in a desired form and at least one layer of porcelain
' bonded thereto. "Porcelain" as herein employed is meant dental
porcelain as is known in the art and which is subsequently
more fully described and illustrated. Normally in dental
restorations porcelain is applied in several coatings and
20 firings. In all coatings subsequent to the first coating,
porcelain is bonded to porcelain. In the first coating,
~- porcelain is bonded to metal and the problems to be solved
are concerned particularly with the porcelain to metal
relationship. Under present practice the porcelain which is
~ bonded to metal is that understood in the art as opaque
v porcelain, as subsequently illustrated, but the present
invention is not limited thereto. The expression "core"
as herein employed is the metal framework or base, at least
a portion of which is to be covered with porcelain. It may
30 have any shape, depending on the dental restoration intended;
it is necessary only that a portion thereof is to have
-4-
:,
porcelain bonded thereto. The "coefficient of expansion"
for the metal alloy as herein employed is the linear thermal
expansion coefficient determined in the usual manner from
values obtained on heating from room temperature up to 600C
at a rate of 15/minute.
The metal alloys in such core and which of themselves
constitute a part of the invention, are prepared from nickel,
chromium, and silicon together with other elements in the
proportions and manner hereinafter more fully described. The
preferred alloys for use as structural metals for the prepara-
tion of bridges, crowns, copings etc., or for use in inlays
and onlays contain in addition to the nickel, chromium and
silicon, small amounts of molybdenum together with boron.
The alloys of the present invention contain about 65 to 75%
nickel, about 15 to 23.5 percent, preferably 15 to 21 percent
chromium and about 3.5 to 6 percent silicon, together with
; 3 to 5 percent molybdenum and 0.2 to 2 percent boron. The
properties of the alloys, in addition to the fusion temperature
and coefficient of expansion above recited, are good corrosion
;~ 20 resistance, good oxidation resistance, a tensile strength of
at least 90,000 p.s.i., a percent elongation of about 0.5 to
5.0, a Rockwell C hardness within the range of about 25 to 33.
The alloys bond well to porcelain and shear strengths at the
- interface designated as porcelain bonding strength may be
obtained which are greater than 7300 p.s.i.
These properties are particularly advantageous for
the preparation of the dental constructions and further in
imparting desirable properties to the dental constructions
made therefrom as hereinafter more fully described.
The dental construction of the present invention
comprise an appropriately contoured core of a novel non-precious
-5-
metal alloy with a porcelain covering bonded thereto. The
novel metal alloys which are an aspect of the present
invention have a fusion temperature within the range of
2050 to 2250F and a coefficient of expansion in the range
` of from about 13.5 x 10 6 in/in/C to about 13.8 x 10 6
in/in/C and consists essentially of nickel, chromium and
silicon, and have added thereto minor amounts of molybdenum
and boron.
More specifically, in accordance with a broad aspect
of the invention a dental restorative construction comprises a
metal core of a non-precious metal alloy contoured in a desired
form and a porcelain covering bonded thereto. The metal core
'- is an alloy consisting essentially of, on a weight basis,
about 65 to 75 percent nickel, about 15 to 23.5 percent
chromium, about 3.5 to 6 percent silicon, about 3 to 5 percent
,~ .
' molybdenum, and about 0.2 to 2 percent boron. The alloy has a
' fusion temperature within the range of 2050F. to 2350F. and
a coefficient of expansion in the range of from about 13.0
x 10 6 in/in/C. to about 13.8 x 10 6 in/in.& .
~- 20 The composition of the novel alloys are from about
65 to 75 percent nickel, about 15 to 23.5 percent, preferably
15-21 percent chromium, about 3.5 to 6 percent silicon, about
.,
3 to 5 percent molybdenum and about 0.2 to 2 percent boron.
Manganese in amounts up to 1 percent may be substituted for
boron in some compositions but is less preferred. In the
; specification and claims, the percentages are on a weight
basis.
These alloys have properties suitable for use as a
~; structural metal in dental constructions, where they are to
be faced with a tooth enamel simulating material and a dental
construction of the instant alloy faced with a tooth enamel
simulating material, especially when such material is a
porcelain, constitutes a part of the present invention. They
; - 6 -
may also be faced with plastics guch as acrylics and
further are useful as a dental metal without a facing. Those
with boron content at the lower range are also useful for
inlays, onlays and partial dentures. In addition to the
above cited fusion temperatures and coefficient of expansion, .
other properties exhibited by the alloy include good corrosion
resistance, good oxidation resistance, an ultimate tensile
strength in the range of 90,000 to 150,000 p.s.i., a percent
elongation of about 0.5 to 5.0, a Rockwell C hardness within
... .
., .
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rc~
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,.,, : :
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~ ~ - 6a -
,
the range of about 25 to 33.
Within the scope of suitable alloys, a preferred
;' composition is that consisting essentially of in percent
~' by weight: about 69 to 72% of nickel, about 18 to 20%
chromium, about 4 to 5.5% silicon, about 4 to 4.5% molybdenum
and about 1 to 1.5% boron. The fusion temperature of the
alloys of the preferred composition is in the range of about
2050 to 216 5 F .
The fusion temperature range of 2050 - 2250F
of the alloys are within the range in which the dental
laboratories are usually accustomed to work so that the alloy
may be cast for the preparation of metal cores and other
structural materials without change in equipment and technique.
However, the fusion temperature is sufficiently high so that
: ~
when the metal core is to be faced with porcelain it can
resist deformation during the firing steps in porcelainization.
- Thus, the fusion properties of the alloys are ideally suited
~ for dental construction to be faced with a tooth-simulating
,1 .
porcelain covering.
' 20 The coefficient of expansion in the range of 13.6 x
10 6 in/in/C to about 13.8 x 10 6 in/in/C is suited to be
employed with many dental porcelains. When suitable porcelains
as svbsequently more fully described are applied to the
surfaces of the novel alloys, they are resistant to checking
and other fractures which have tended to occur during the
process of heating to the firing temperature followed by
~; slow cooling to room temperature. Further, when employed
with porcelain with expansion and contraction characteristics
such that after cooling, the porcelain is under compression
at room tem~erature, especially good results are obtained.
Moreover, when bonded to porcelain, a good porcelain to metal
.: .
--7--
bond is formed. The shear strengths at the interface designated
as the porcelain bonding strength may be obtained which are
s greater than 7300 p.s.i.
In addition to the foregoing, another property
important in its function as a metal core which is to be
faced with porcelain is the absence of metals which form
colored metal ions. Many metal alloys which may be desirable
from strength and other properties frequently contain cobalt,
copper or iron and are therefore unsuitable for metal
10 structure which is to be faced with porcelain. The present
alloys possess desirable properties without inclusion of
such metals and a metal core of the present alloys may be
,. ~
faced with porcelain or plastic without staining.
In addition to the foregoing, other properties
of the alloys render them superior as dental structural
i materials whether or not they are to be faced with porcelain.
The alloys have good strength, hardness, corrosion resistance
and oxidation resistance while being lighter, stronger and
harder than gold. It is recognized that the term good is
. 20 relative, but as used herein it means good for the purposes
of use in dentistry for which the material is specified. Thus,
good strength and hardness as herein employed would be tensile
strength and hardness above that of the presently available
gold alloys. Good corrosion resistance would be resistance
$ to etching by hydrochloric acid and lactic acid superior to
that shown by presently commercially available non-precious
metal dental alloys and resistance to etching by aqueous
, sodium chloride solution comparable to that shown by
conventionally used dental alloys. Good oxidation resistance
would be such that the surface of the metal would not oxidize
during working to the degree that bonding to porcelain is made
~, -8-
?
,, .
.
:
difficult.
The ultimate tensile strength of about 90,000 to
150,000 p.s.i~ compare favorably with that of about 65,000
p.s.i. to 70,000 p.s.i. for gold. The hardness of below about
35 Rockwell C (below about 120 Rockwell B) compares favorably
with the about 86 Rockwell B hardness for gold. Thus, the
alloys have strength and hardness superior to gold while not
being so hard as to prevent grinding and polishing of dental
structures to the desired shape and smoothness. (The
~ lO Rockwell C hardness values of the present alloys may be
;~ converted to Rockwell B hardness for purposes of comparison
with gold using standard tables and calculations.)
The good corrosion resistance exhibited by the
alloys of the present invention may be seen by the minor
,,,
extent of etching as measured by weight loss after immersion
, at room temperature, for 20 days in 0.05% hydrochloric acid,
0.1% lactic acid or 1% sodium chloride solution. The extent
~, of etching on immersion in such hydrochloric acid solution is
;~ in the range of 0.1 to 0.2 milligram per square centimeter
per day (mg/cm2/day) and in such lactic acid solution is in
the range of 0.01 to 0.03 mg/cm /day, significantly less than
~i that of presently available non-precious metal alloys. The
extent of etching in a 1% sodium chloride solution is in the
range of about 0.0015 to 0.009 mg/cm /day, comparable to
and even superior to the 0.002 to 0.01 mg/cm /day of
conventional dental gold alloys.
The good oxidation resistance exhibited by the
alloys of the present invention may be seen by the minor
extent of oxide formation as measured by weight gain on
heating at 1800F for five minutes. The extent of oxidation
under such conditions is generally no greater than about
0.7 x 10 2 mg/cm - min, an amount: insufficient to interfere
with or make difficult the operation of bonding to porcelain.
In addition to the foregoing, the alloy can be
remelted and cast without loss of their excellent physical
properties, it may be used with the dental solders presently
employed when working with gold or with non-precious metal
alloy solders, and may be faced with dental plastic materials
such as the acrylics.
In the alloy compositions of the present invention,
not only is the actual amount of the metal component important
but also the relationship of certain components to each other.
One important relationship is that of chromium to nickel.
When the chromium content with respect to the nickel is
permitted to become too high, the thermal expansion of the
alloy is found to be too low to obtain good matching with
porcelain. Where the chromium content becomes too low, the
alloy is generally found to have substantially poorer
oxidation and corrosion resistance than desirable. A chromium
to nickel ratio of about 0.24 to 0.30 has been found to
impart desirable properties to the alloy. A preferred ratio
range is from 0.26 to 0.27 These ratios are to be considered
together with the total nickel in the alloys.
As previously indicated, the silicon is preferably
present in the range of about 4 to 5.5% by weight. Where
used in amounts much below 4%, the fusion temperature of the
alloy is found to be above 2400F, which is undesirably high.
When the silicon content is increased to much above 5.5% the
alloy tends to become brittle and lose some of its mechanical
strength. For the purposes intended it is critical and
essential that the silicon contenc of the alloy not exceed
about 6%.
,,
--10--
.'~
The addition of molybdenum to the nickel, chromium
and silicon stabilizes the thermal expansion property of the
alloy against change which tends to occur during the repeated
firing which are necessary procedures when porcelain is fused
' to the structural metal during the preparation of jackets,
crown~, bridges and the like. Further, molybdenum has the
property of improving corrosion resistance.
, Inclusion of the boron or manganese improves the
~, bonding strength between the alloy and porcelain. However,
' 10 addition of manganese tends to decrease corrosion resistance
and tends to discolor the porcelain. Hence, the preferred
alloy compositions contemplate the use of boron. However,
', it is critical and essential that boron not be employed in
,; excess of about 2% by weight since boron tends to increase
'~ brittleness.
~- In addition to the criticality of the maximum amount
of boron which should be added, there is a critical relation-
ship between the relative amounts of silicon and boron. Thus,
when the amount of boron is increased, the amount of silicon
20 is decreased. Within the limits of the amount of silicon
and a~ount of boron which may be present in the alloy composi-
tion, the boron to silicon ratio is preferably between about
0.4 to about 0.15.
The dental alloy composition intended for use as
structural metal may contain minor amounts of other materials
which may be present as impurities in the metals employed to
~, prepare the alloy. None of these are essential in the dental
alloy compositions of the present invention. Accordingly, the
alloy compositions of the present invention consist essentially
of nickel, chromium and silicon with molybdenum and boron or
~` less preferably with manganese replacing a portion of the boron.
~'
--11--
, : ' ' ' ' ' '
: :
The alloy may be prepared in a conventional manner
such as by placing the components in a fused alumina crucible
and fusing the ingredients with appropriate mixing. While in
the molten state, the alloy may be poured into molds for
ingot formation.
The dental alloys of the present invention intended
for use as structural metals may be employed in the replacement
of the heavier and more expensive gold which has been the
conventional structural metal used for dental purposes. The
alloys are ideally suited for use where bonding of the alloy
to a porcelain is required, as in the preparation of artificial
teeth, crowns, bridges and the like.
The alloy may also be used in the preparation of
veneers, both plastic as well as porcelain. Their physical
properties also make the alloys highly useful for the prepara-
tion of metal crowns where the metal acts to completely cover
the prepared tooth and for the preparation of inlays and onlays.
In such usage the dental alloys of the present invention are
found to be not only as good as the gold which has heretofore
been used but in many respects superior to such gold.
The dental constructions of the present invention
may be obtained by first preparing an appropriately contoured
metal core made of the novel metal alloy of the present
invention by casting according to conventional procedures
and thereafter painting the metal core with porcelain and
firing to secure the porcelain on the metal by bonding.
Thereafter, additional layers of porcelain are applied with
firing after each step to obtain an artificial tooth or other
dental restoration.
By "porcelain" is meant dental porcelain as is known
in the art and embraces dental glasses. They generally contain
silicon oxide, aluminum oxide, sodium oxide, potassium oxides
-12-
,, _
' :
,
and minor amounts of other oxides. Normally, the porcelain
covering which is first applied to the metal is an opaque por-
7 celain. An opaque porcelain reduces the tendency of the metal
I to be seen through the final coating. Opaque porcelains are
available commercially and include in the oxide composition
either zirconium oxide, tin oxide, zinc oxide, titanium
oxide or zirconium silicate as an opaquing agent. The opaque
porcelain is normally coated with additional layers of body
porcelain followed by a layer of incisal porcelain under
10 conventional procedures. The body porcelain is available
commercially as gingival porcelain and may have a small amount
; of opaquing agent and incisal porcelain has no opaquing agent.
The exact composition of the porcelains is not
critical although generally speaking, the porcelains are to
be selected from those employing orthoclase feldspar as raw
material. It is essential however that certain properties be
observed in the selection of an appropriate porcelain. Thus,
the porcelains should have a fusion temperature maximum of
about 1850F and coefficient of thermal expansion in the range
of about 10 x 10 6 in/in/C to about 21 x 10 6 in/in/C. It
is recognized that a meaningful single coefficient of expansion
' is not obtainable for porcelain as it is for metal over the
broad temperature range of from about room temperature up to
600C and that coefficients of expansion values are valid only
for a narrower range of temperatures. Porcelains which may be
employed with the metal alloy of the present invention will be
those whose several coefficients of expansion are within the
above ranges when determined at several temperature ranges up
to about 575 - 600C.
Typical porcelain compositions are found in standard
references such as Skinner and Phillips. "The Science of
-13-
Dental Materials, ~' p. 518, W.s. Saunders Company,
Philadelphia and London 1967; the compositions of several
commercial porcelains are listed on page 60 of Jean-Marc
Meyer, "Contributions à l'Etude de la Liaison Céramo-
metallique des Porcelaines cuites sur Alliages en Prosthèse
Dentaire", Thesis, University of Geneva, 1971. Suitable
porcelains include those having compositions described in
U.S. Patent 3,052,982 of the following oxide content: 61-67.8%
SiO2; 11.7-17.1% ~12O3; 0.1-2.6% CaO, 0.1-1.8% MgO; 2.37-9.6%
s 10 Na2O and 6.7-19.3% K2O. The foregoing composition may be
modified to include lithium oxide in amounts up to 5% and the
other oxides reduced or modified. In addition, the porcelain
may be modified to add from about 0.05 to about 25% of an
opaquing agent and the other oxides reduced or modified as
desired limited by the need to keep the temperature and
expansion properties within the desired limits. Suitable
opaque porcelains may have the oxides in the following
approximate ranges: SiO2 47 to 63%; A12O3 10 to 14%, CaO
0.6 to 1.3%, K2O 8.5 to 11%, Na2O 1.5 to 5%, MgO 0.4 to 0.8%,
and SnO2 9 to 25%. The present invention is not directed to
the chemical composition of the porcelain, thus, any
commercially available dental porcelain or porcelain composi-
tions prepared by a skilled artisan may be employed in the
dental construction provided the foregoing properties are met.
,,
From the porcelains of the type described above,
particular porcelains may be selected for bonding to the alloys
of the present invention to obtain good bonding properties
by empirical tests. One such test employs rods of alloy and
porcelain of the same dimensions, preferably thin rods about
2 inches in length. The rods are heated from room temperature
up to about 600C and the lengths measured at 575~C. Those
-14-
,
'f porcelain rods whose lengths are within about 6% of the length
of the alloy rods are considered to be a good match for
purposes of providing a covering for the alloy with good
bonding properties.
In carrying out the preparation of the dental
construction of the present invention from the novel alloy
of the present invention, the metal core is formed by casting
into casting investments which have previously been prepared
by conventional procedures. Pellets or slugs of the metal
alloy of the present invention are placed in a crucible, heated
in a conventional manner until the alloy melts. The alloy
melt is cast employing conventional procedures and apparatus
such as a centrifugal casting machine to obtain a casting
contoured roughly to the shape desired for the core. The
casting is recovered employing conventional procedures and
then ground to the desired final shape, and dried.
After the grinding step, the areas of the metal
- core which is to receive porcelain is sandblasted with a
quartz abrasive and the shoulders which are not to receive the
porcelain are polished. The cores then are placed in hydro-
fluoric acid for a short time (preferably about 5 minutes),
then rinsed in distilled water and thereafter cleaned, prefer-
ably ultrasonically in distilled water, and dried. The core
units are then ready to receive the porcelain.
` Porcelain, preferably opaque porcelain such as of
the composition previously described, is applied to the sand-
blasted area of the metal core. The thus painted core or
core units are (a) air dried, (b) placed into a furnace
preheated to 1200F and (c) fired first under vacuum (26-29
inches of mercury) by raising the temperature up to about 1700F
at a rate of about 90-100F/minute and then in air by breaking
the vacuum and continuing the heating to about 1840 - 1850F
'
.
P6
to obtain a dental construction comprising an appropriately
contoured metal core having porcelain covering bonded thereto
which is then removed from the furnace and cooled at ambient
temperature.
Although good bonding is obtained between the metal
alloy of the instant invention and porcelain having a coefficient
of expansion hereinbefore specified, a superior chemical bond
which imparts to the dental construction an even greater
resistance to separation on stress may be provided by employing
10 a bonding agent. The exact nature of the bonding agent is not
critical. Any suitable bonding agent may be employed. One of
~:
the preferred bonding agents is ~ aluminum-boron bonding agent
in an organic carrier. One composition is a 30 percent
composition of aluminum and boron in a 2:1 ratio in petrolatum.
When a bonding agent is employed, the procedural
$~ steps after the grinding of the casting is modified and
may be carried out as described hereinafter and more fully
in the above-identified application. The ground core is cleaned
ultrasonically with distilled water and dried. The bonding
20 agent is then applied to that portion of the metal core which
is to be coated with porcelain. The bonding agent is allowed
to dry and fired on the core by placing the treated metal
core in a furnace preheated to 1200F and thereafter raising
s the temperature of the furnace to 1850F in air. The core
is then removed from the furnace and allowed to cool at ambient
temperature. After cooling, the excess bonding agent is
mechanically removed, and the core thereafter cleaned and dried
to obtain a dental construction comprising an appropriately
conto~red metal core and a porcelain covering bonded thereto.
30 Other suitabie methods appropriate for the bonding agent`
chosen may also be employed.
; -16-
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Generally, additional layers of porcelains are fired
onto the foregoing dental construction to obtain dental
construction which is an aesthetically pleasing artificial
tooth or other dental restoration. The additional layers of
porcelains are provided by a gingival porcelain which forms
the principal bulk of the body of the artificial tooth and
an incisal porcelain which provides translucency to the outer
tipso In carrying out the preparation of a dental construction
which is an aesthetically pleasing dental restoration, several
10 layers of gingival porcelain and thereafter layers of incisal
porcelain are applied on the dental construction having a
covering of opaque porcelain bonded thereto and fired by
heating from 1200F to 1700F under vacuum (26"-29" HG) and
further to 1800F in air, and then cooling at room temperature,
in separate sequential operations. More than one firing may be
necessary. The dental construction thus obtained is useful in
dental prosthesis.
The following examples illustrate the invention
but are not to be construed as limiting:
EXAMPLE
r :
G' Into a fused alumina crucible, is added 1.4 grams
of boron powder, 4.1 grams of particulated silicon in the form
of small blocks, 4,2 grams of molybdenum and 19.0 grams of
chromium in plate form. There is then added 71.3 grams of
nickel shot. The crucible is then heated by induction heat in
an argon atmosphere to prevent oxidation. The contents are ~;~
; brought to a temperature of about 1600C. The melt is then
; permitted to cool to about 500C at which time the solid alloy
lS removed.
Test bars of this alloy are cast and are found to
30 have an Ultimate Tensile Strength of 132,000 pounds per square
-17-
inch, a Yielding Strength of 110,000 pounds per square inch, a
Modulus of Elasticity of 25xlO per square inch, a Percent
Elongation of 1.45% and a Rockwell ]3 hardness of 106 RB. The
alloy also has a thermal Expansion Coefficient of 79xlO
; in/in/C, a melting temperature within the range of 2250 to
2300F, and a casting temperature of 2400 F.
Portions of the alloy prepared in the above manner
are tested for its casting characteristics using standard Lost
Wax Technique casting procedures. The alloy is found to cast
10 well.
Using standard techniques, portions of the alloy are
used in the preparation of metal crowns and bridges; and
porcelain bonded crowns and bridges where the porcelain is
.t
' fused to the metal. No discoloration of porcelain is observed
, and good bonding is obtained.
The alloy may also be used for plastic bonded crowns
. . .
and bridges using the conventional techniques employed in making
;~ the same.
When working the alloy, it is preferred to use an
20 oxygen-gas flame for melting rather than an oxygen-acetylene
t' flame although the latter can be employed if care is taken.
i EXAMPLE 2
Employing the same technique as described in Example
1, a dental alloy is prepared having the composition in,
percent by weight, of:
Nickel67.8%
Chromium 22.0%
Molybdenum 4.2%
Silicon 5 0%
Manganese 1.0%
.
-18-
, _
,, .
This alloy has an Ultimate Tensile Strength of
118,500 pounds per square inch, a Yielding Strength of 85,000
~ pounds per square inch, a Modulus of Elasticity of 24X106
; pounds per square inch, a percentage of Elongation of 3.5%
and a Rockwell B hardness of 98 RB.
The alloy is also found to cast well using the Lost
Wax Technique and found to handle well in the preparation
of metal crowns and bridges, porcelain bonded crowns and
bridges, the preparation of inlays and onlays, and in the
preparation of plastic bonded crowns and bridges. No staining
is noted of the porcelain where porcelain and metal bonds are
made. Also, excellent bond strengths are obtained.
EXAMPLE 3
The following Tables I and II set forth data
~- comparing the corrosion resistance and oxidation resistance
of alloys of Examples 1 and 2 with the corrosion resistance
and oxidation resistance of representative presently
commercially available materials. In order that uniform
~-~ comparative results be obtained, all samples used in the -
oxidation and corrosion tests are prepared in the same manner.
The samples are heated to their casting temperatures and then
cast in air in accordance with standard Lost Wax Technique.
~- The castings after cooling to room temperature are ground with
grinding papers to 600 grits, then polished with cotton using
0.3 ~m alumina polishing powders.
For testing for corrosion resistance, Table I, the
polished samples are washed in water, followed by washing in
acetone. The samples are then heated in air to 1,000 F and
then placed in a desiccator to cool. The samples are then
30 weighed, and the weight recorded.
.
19--
, The samples are then placed in aqueous solutions
of the concentration indicated and remain immersed in such
~ solution at ambient temperature for 20 days. The samples
-/ are then dried, weighed, and the loss in weight calculated.
he Table I, Corrosion Resistance, values are given
also for human tooth enamel, dental amalgam, and a copper
zinc dental alloy. These values are those published by
Kazuo Nagai in the Journal of Hihon University School of
Dentistry, Tokyo, Japan, Volume 11, No. 4 Issue, 1969. Mr.
10 Nagai in describing his method of sample preparation stated
that the samples were cast and then polished-in accordance
with the manufacturer's instructions.
, For testing oxidation resistance, Table II, the
polished samples are then washed in water followed by washing
in acetone. The same are then heated in air to 1,000F., and
then placed in a desiccator. On cooling the samples are
weighed and weight recorded. The samples are then placed
'~ in a small furnace, 3x3xll/2 inches and heated at a temperature
j of 1800F., for five minutes. The furnace is equated to the
20 1800F temperature before insertion of samples. After the
five minute heating, the samples are removed and again placed
in a desiccator and cooled. The samples are then weighed and
the weight recorded with the difference in weight indicating
the degree of oxidation.
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EXAMPLE 4
Employing similar procedures alloys are prepared
having the compositions and properties set forth in Table III.
~ TABLE III
,i-: '~
~COMPOSITION (in weiqht percent)
.
Alloy Alloy Alloy Alloy
A B C D
; Ni 71.3 71.3 71.3 71.3
Cr 19.1 19.1 19.1 19.1
Si 4 0 4.1 4.6 5.1
Mo 4.1 4.1 3.7 3.5
B 1.5 1.4 1.3 1.0
.,~,. .
Ultimate Tensile
Strength (p.s.i.) 112,800 128,000135,670 146,120
; Percent Elonga-
l tion 1.0 1.25 1.45 1.8
~s Hardness (Rc)33 31 28 26
Samples of the alloy are tested for cutting, grinding
and polishing properties as follows: (a) cutting, on a high
speed lathe with a Dedco cutting wheel (carborundum wheel
.~
manufactured by Dental Development & Manufacturing Corp.,
Brooklyn, New York), (b) grinding with SHOFUTM Dura Green stone
(silicate, product of Shofu Dental Corp., Menlo Park,
` California) followed by SHOFU Dura White Stone (aluminum
oxide, product of Shofu Dental Corp., Menlo Park, California);
(c) Polishing sequentially with (i) SHOFU Dura White Stone,
(ii) Dedco light glaze wheel with-25 ~m aluminum oxide powder,
(iii) 1.5 inch felt wheels with 9.5 ~m aluminum oxide and
(iv) felt wheels with diamond paste.
.~ r - ..
-23-
' .
.~ .
The foregoing properties which when applied to gold
alloys would be described as Easy, may be characterized as
Moderate for Alloys C and D and Hard for Alloys A and B,
the latter requiring diamond paste for achieving a polish.
Alloy B when tested for corrosion resistance as
$ described in Example 3, is found to have a weight loss of
0.111 mg/cm2 per day in 0.05% hydrochloric acid, of 0.0239
mg/cm per day in 1.0% lactic acid and of 0.0080 mg/cm per
-day in 1.0% aqueous sodium chloride. Alloy B when tested
for oxidation resistance as described in Example 3, is found
to have a weight gain of 0.4765 x 10 mg/cm - min.
~All alloys are found to have thermal expansion
s-comparable to gold alloys.
EXAMPLE 5
Into a crucible is added in order: tl) 47.5 pounds
of nickel shot: (2) 2.8 pounds of boron blocks, 8.2 pounds
of silicon blocks and 8.2 pounds of molybdenum plates, (3)
25 4 pounds of chromium plates, and (4) 47.5 pounds of nickel
shot, and the crucible heated to a temperature of between
20 about 1400C and 1600C to melt the conltents, the heating
carried out in an argon atmosphere to prevent oxidation. After
the initial melt is obtained, 12.8 pounds of chromium and
-~47.6 pounds of nickel are placed in the crucible and the
heating continued to 2700F to obtain a completely molten
alloy. The melt is poured into resin shell molds for rods
5/16" in diameter.
The composition of the alloy is given below in
weight percent. The original composition is the weight of
raw material added the final composition is the weight of
~30 elements on analysis of the alloy. The differences between
;the original and final composition is partly due to the fact
-24-
.
',', ,
that the final composition represents analytical data and
partly to changes occuring at elevated temperatures.
ALLOY COMPOSITIO~
Initial Final
~ickel 71.3 69.63
Chromium19.1 19.40
Silicon 4.1 3.87
Molybdenum 4.1 4.24
Boron 1.4 1.36
10 Carbon -- 0.04
Ingots (about 1 cm) are prepared from the rods
and the ingots recast into tensile bars to determine mechanical
properties which are found to be:
Ultimate Tensile Strength 115,000 p.s.i.
Yield Strength 90,000 p.s.i.
Percent Elongatlon 1.0 - 1.1%
Some of the ingots are employed to prepare coping
,.~
and the latter tested for hardness; the Rockwell C hardness
~ is found to be 31 Rc.
j ~ 20 Separate melting point determinations give the
following ranges: 2150-2265F; 2100-2200F; and 2066-2170F.
In testing for porcelain to metal bonding strength,
TM
commercial CERAMCO opaque porcelain (product of CERAMCO, Inc.,
Long Island City, New York) is coated around 14 gauge cast
alloy rod and fired at about 1850F forming porcelain disks
0.055 to 0.082 inch thick. The disks are supported by dental
stone and a tensile load applied at a crosshead rate of 0.05
cm/min. Stress values computed by dividing the tensile load
by the measured bonding surface area show bond strengths
significantly greater than 7300 p.s.i.
Portions of the alloy evaluated by a dental technician
-~5-
,,
$
are found to be satisfactory for use as a dental alloy. The
, alloy is found to melt and cast well using a gas/oxygen torch
with the oxygen pressure up to about 9 pounds per square inch.
The alloy is found to undergo the repeated application and
firing of porcelain without causing discoloration of the
porcelain. Crowns cast from alloy, after removal of investment
and metal buttons fit on original dies without difficulty.
~! The alloy also shows good properties for soldering, cutting,
grinding and polishing.
EXAMPLE 6
i Using the process of Example 1, alloys are prepared
having the compositions set forth in the following Table IV.
These alloys are used for the applications indicated in the
column identified "Applications". In each use of the alloy
~ is observed to perform well when used by standard accepted
3 dental laboratories techniques.
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The alloys of Table IV have the physical properties
set forth in Table V.
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EXAMPLE 7
... .
- A non-precious metal alloy pellet of the composition
described in Example 5, and weighing about 8 grams, is placed
in a crucible of an invested casting ring previously prepared
in a conventional manner and heated to melt, it is heated with
a gas/oxygen torch with about 9 pounds pressure of oxygen
s~ until the alloy melts. The ring then is placed in the cradle
of a centrifugal casting machine and the molten metal cast
in a conventional manner to obtain the desired casting of the
,,;
; 10 non-precious metal alloy. Thereafter, employing conventional
procedures, the casting is cooled, removed from the investment,
trimmed and then-ground first with SHOFU Dura Green Stone
(a silicate) and then with SHOFUTM Dura White Stone (an aluminum
oxide powder) to obtain an appropriately shaped non-precious
metal alloy core.
The metal core lS then sandblasted with quartz
abrasives in the areas to be covered with porcelain and
~; polished to a finish in the shoulders and areas not to be
.~ .
-~ covered with porcelain. The metal core is then placed in
hydrofluoric acid for about five minutes, rinsed with distilled
water, ultrasonically cleaned with distilled water for about
~; 15 minutes, then removed and dried.
Employing conventional procedures, an opaque
` porcelain having a chemical composition in-weight percent
of 55% SiO2, 11.65% A12O3, 9.6% K2O, 4.75% Na2O, 0.16% ZrO2,
15% SnO2, 0.04% Rb2O, 0.26% ZnO and 3.54% B2O3, CO2 and H2O,
is painted on the sandblasted area, then dried at elevated
temperatures by placing at the door of the furnace. The dried
,` metal core having a coating of opaque porcelain material is
placed in a furnace preheated to 1200F and thereafter heated
to 1700F under vacuum (26" - 29" Hg~. At 1700F, the vacuum
, .
~ -30-
Z~ ~
is broken and the heating continued in air until a temperature
of 1850F is reached to obtain the desired dental construction
comprising an appropriately contoured metal core having
porcelain covering bonded to it.
The dental construction thus obtained is allowed
to cool and thereafter successively painted with several layers
of body or gingival porcelain having a chemical composition
of 62.2% Sio2, 13.4% A12O3, 0.98% CaO, 11.3% K2O, 5.37% Na2O,
0.34% ZrO2, 0.5% SnO2, 0.06% Rb2O and 5.85% of B2O3, CO2 and
H2O, and then with incisal porcelain of similar composition
containing no tin oxide with firing after each application by
heating in the temperature range of 1200F to 1700F under
26"-29" Hg, followed by heating to 1800F in air, and th0n
allowing to cool to obtain a dental construction comprising
an artificial tooth. Corrections are made on the contour
of the tooth as necessary, a final glaze is obtained by heating
in air from 1200 to 1800F, and then cooled. The tooth is
` finished and polished to obtain an aesthetically pleasing
; artificial tooth having a metal core with porcelain bonded
20 thereto.
EXAMPLE 8
In a manner similar to that described in Example 7,
an appropriately contoured non-precious metal alloy core is
first prepared.
Thereafter, an aluminum-boron bonding agent of the
co-pending application and of the composition previously
described is applied by painting to the areas on the surface
of the metal which is to be covered with porcelain. The
bonding agent is placed in the furnace at 1200F and the
temperature raised to 1850F in air whereafter the core is
removed from the furnace and allowed to cool. After cooling,
-31-
the metal core is scrubbed with a tooth brush and water,
thereafter placed in distilled water in an ultrasonic cleaner
for five minutes, then removed and dried.
The metal core thus obtained is painted with opaque
porcelain and fired in the manner described in Example 7 to
obtain a dental construction having an appropriately contoured
metal core having a porcelain covering bonded thereto. The
dental construction thus obtained is painted and fired
successively with body porcelain and incisal porcelain and
then finished in the manner described in Example 7 to obtain
an artificial tooth having a metal core with porcelain bonded
thereto and having good aesthetic qualities.
This application is a division of Canadian application
no. 244,988, filed January 30, 1976.
-32-
