Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Z
AI:)MIX DENTAL ALLOY AND AMAI.GAM
BACKGROUND OF TEIE INVENrION
This invention relates in general to a dental compositi3n and
dental amalgam suitable for use in repairing carious tooth
structure. More specifically the invention relates ~o a
substantially uniEorm admixtuxe of two powdered alloys in the form
of spheriods and irregularly-shaped or cut particles which when
amalgamated with mexcury exhibit improved handling characteristics~
U.S. Patent 3,985,558 teaches an improved dental alloy having
a relatively low concentration of silver and a critical atomic
ra~io of silver plus copper to tin which exhibits enhanced
m~chanical properties and handling characteristics ~s compared to
conventional high silver alloysO The alloy is also more economical
to use than conventional alloys w~ich require higher silver
concentrations~
When the aboYe dental alloy is used in the spherical form and
not blended with an appreciable concentration of cut or irregularly
shaped al~oy particles, certain desirable working characteristics
such as resistance to condensation or packing within the ~oDth
cavity cannot be attained.
Prior art admix compositions generally combine two di~erent
alloy compositions for the respective spherical and irregularly
shaped components. This runs the risk that seqregation of
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individual components may result and lead to inconsistent
properties in the final amalgamated alloy. r
~BJECTS OF THE INVENTION
~j
It is therefore an object of this invention to provide an
improved dental alloy suitable for amalgamation with mercury which
exhibits outstanding physical and mechanical properti s and
handling characteristics.
It is another object of this invention to provide a dental
amalgam which exhibits outstanding physical and mechanical
properties and handling characteristicsO
SUMMARY OF THE INVENTION
It has now been discovered that when an alloy of the type
taught by ~.S. Patent 3,985,558 in the form of a substantially
uniform blend of two powdered alloys comprised of sphexoids and
irregularly shaped particles 9 iS amalgamated with mercury, the
final dental alloy exhibits enhanced handling characteristics.
A critical ratio of spherical to irregularly shaped particles for
this alloy ranges ~rom about 65 to ~5% spherical to 15 to ~5~ !
irregular. The alloy described above is amalgamated by trituration
with mercury in a concentration of about 45 to 55 weight percent
mercury with the balance of the amalgam comprising the alloy.
Prior to amal~amation, the alloys are annealed by techniques
well known in th~ art to control the work time o~ the final alloy.
The alloys are also cleaned ~y chemically treating with a dilute
acid ~
DRTArl.ED DESC~IPTION OF T~E INVENTION
The alloy of the present invention is composed of
an admixture of spherical and irregularly shaped or "cut"
particles. The alloy powder has a fine particle size ~all
about -325 mesh), of both the spherical and irregular
particles which allows the alloy to have the smooth carve
associated with all spherical alloys, but with a firmer
packing and carving consistency characteristic of
conventional alloys. The particle size range for both
components is from submicron to about 50 microns. Both
of the particle configurations are made to the same
composition: About 24 to 45 weight percent silver~ 28 to
42 weight percent copper and 29 to 34 weight percent tin,
and where the atomic percentage of the total amount of
silver plus copper is about 3 times greater than the atomic
; percentage of tinO The composition may also contain up to
2 weight percent zinc. A par~icularly preferred
composition comprises about 41% silver, 28% copper and 31
percent tin. The powder admixture must be maintained in a
weight ratio of about 65 to 85 percent spherical to 15 to
35 percent irregular in order to obtain the enhanced
properties described herein. The benefits of this
relationship are quite clear; both of the particle
configurations participate heavily in the reaction with
mercury during amalgamation, therefore enhancing the
consistency of the mix and the homogeneity of the amalgam.
Unlike the alloy of the present in~ention, many other prior
lcm/MAB
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art admixtures because o~ the different composition oE the
two components, risk segregation of the individual
components which may lead to inconsistencies. The fact
that each particle in the alloy of the present invention
contains copper, assures that it is distributed fully
throughout the amalgam to alloy with tin to prevent
formation of the unwanted gamma-2 (tin mercury) phase.
This admix alloy produces an amalgam with a smooth carve,
but with the body that can be comfortably worked. The
amalgam begins to "body-up" upon condensation, which allows
for carving to commence almost immediately, with the
lcm/MAB
resistance to carve increasing up until the end of working time
which can be controlled typically to vary from about 6 l/2 to ll
minutes.
In the following Table the physical properties for the average
of four lots of an amalgamated dental alloy of the present
invention are tabulated. The alloy composition used was the
preferred composition of 41% silver, 28~ copper and 31% tin in a
weight ratio of 70~ spherical to 30 percent irregular particles.
The concentration of mercury was 48% by weight and the admix alloy
constituted 52 weiqht percent. Both alloy components were of fine
particle size of less than 325 mesh. The tests were carried out
according to ADA specification No. l for Dental Amalgams.
TABLE
Four Lots
DC (Microns/cm.) -1.80
Tension ~psi)
lS min 857
l hr 2~20
24 hr 7870
7 day 8740
Compression (psi)
15 min 8320
1 hr 260~0 -
24 hr 75000
7 day 81300
Creep ~ .067
- 5 ~
In additlon to providing the advantages described
herein, the physical properties of the Alloy of the present
invention co~pare favorably to those of other commercial
dental alloys.
The term "spheroidal" as used to describe the
shape, configuration or Eorm of the first component in the
admixture of the present invention means that the
individual particles are spheres or shaped like a spheroid.
The spherical component may be formed by any technique
well known to the dental art. For example it may be
prepared by first forming a molten alloy in the above
concentration ranges and atomizing said alloy at
approximately 2,000F. Atomization is achieved in a
conventional manner as described in ~.S. Pat. No. 3,305,356
at column 2, lines 9 50. The alloy is then collected and
classified using a 325 mesh sieve. The fraction passing
through the sieve is retained as the dental alloy product.
The term "irregularly shaped" or "cut" as used to
describe the configuration or form of the second component
means that the individual particles are substantially non-
equiaxial and are multi-sided and generally angularly
shaped or irregular, and usually with rough or otherwise
relatively non-smooth surfaces. Typically they are in the
` form of what is variously referred to in the art as
microcut material, lathe-cut material, platelets or
filings. Conventional microcutting, lathe cutting or
lcm/MAB
2~01
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filing techniques, usually frorn a cast billet of the alloy,
can be employed satifactorily to o~tain the irregularly
shaped particles and are well known to those skilled in the
art. The irregular particles used in this inventiOn should
all be less than 325 mesh in size.
While it is essential that the dental composition
of this invention be in the form of a particulate mixture
of the two alloys when used, and may be supplied in such
form when supplied, it should be understood that for
distribution purposes the two alloys
lcm/MAB
6 ~ 4~
can be in the form of separate powders which can be mixed together
by the ultimate user in the required proport;ons. Alternatively,
the two admixed alloys in the xequired proportions can also be
pressed into a tablet, used in a capsule form for convenience, or
used in bulk powder dispensers. When used in table~ form, the
spherical to irregular weight ratio is preferably about 4 to 1; for
use in capsule form the preferred ratio is about 7 to 3.
Other modif ications and ramifications of the present invention
would appear to those skilled in the art upon reading this
disclosure. These are also intended to be within the scope of this
inventionO
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