Metallic alloys to be used in dentistry

The present invention relates to a method for obtaining metallic alloys, to be used particularly in the field of dentistry. This method allows to accomplish a basic face-centered cubic lattice adapted to form the alloys, in which a homogeneous distribution of the atoms of the different elements is obtained, by precisely determining the number of atoms of each element forming the alloy, in close numerical relationship with the number of atoms of the other elements; it also allows the achievement of a plurality of alloys consisting of at least three among the following elements: gold, platinum, palladium, silver and copper, these alloys respecting the physico-chemical specifications necessary in the particular field of dentistry.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to a method for obtaining metallic alloys 
composed of a combination of several metallic elements, to be used in 
dentistry. 
A great number of alloys for dental applications are in commun use; they 
are composed of different combinations of the most used elements for such 
applications, such as gold, platinum, palladium, silver and copper with 
the addition of a certain number of other elements introduced therein in 
order to comply with specific requirements or to fulfil peculiar 
functions. 
The alloys normally used, owing to the lack of data concerning their 
properties, are essentially of empirical origin, the studying and 
producing of the same being almost exclusively based on the fundamental 
principles and essential features of its composing elements and on the 
experimental results of tests. 
The formulating of a satisfactory general theory concerning the metallic 
alloys has not yet reached its achievement and still requires much work 
based on the experimental and theoretical data in order to define and 
understand the numerous factors influencing the structure of the 
alloy-forming phases and the complexity of the interactions which the 
different elements exert on each other. 
The main factors concerning the solid-state solubility between several 
elements can be summarized as follows: 
size of atoms; a favourable condition is that of a maximum difference in 
sizes of 15%; 
type of crystal lattice; only the elements having the same crystal lattice 
allow the formation of complete series of substitution solid solutions; 
the same valence; metals having the same valence are more suitable to form 
substitution solid solutions. 
Keeping in mind these factors and the fact that if a metal should have a 
perfectly regular crystal structure, that is to say devoid of simple or 
multiple vacancies or dislocations, it could exhibit quite superior 
qualities with respect to those found in reality, it appears necessary, 
when forming alloys, to achieve the best distribution and uniformity of 
the elements in the crystal lattice; on the contrary, it is usually 
possible to notice an almost causal distribution of the solute atoms in 
the solvent lattice and, as a result, the presence of vacancies and 
dislocations. 
The atoms of the elements in use respect the above mentioned 
characteristics required for the formation of substitution solid 
solutions, as well as the physico-chemical properties suitable for dental 
applications but the alloys actually in use, owing to their empirical 
formulas, do only casually possess all the necessary mechanical and 
electro-chemical features which can only be obtained by forming a 
perfectly uniform and balanced lattice. 
OBJECTS 
It is therefore an object of the present invention to achieve a homogeneous 
and uniform distribution of the atoms of the elements constituting the 
alloy at the inside of the crystal lattice, ensuring an improved 
electrochemical homogeneity in order to achieve the highest resistance to 
the action of oxidizing and sulfurating chemical agents and simultaneously 
a greater phisico-chemical resistance of the alloy crystal structure. 
Furthermore, such homogeneous and uniform distribution must be 
accomplished while respecting the physico-chemical specifications 
(ductility, malleability, corrosion strength, etc.) dictated by the 
particular dental applications and using the lowest indispensable quantity 
of copper, this element controlling the alloy melting range, but causing 
the formation of electrochemical cells with the other nobler elements and 
being easy to oxidize and sulphurize. Finally, from the above purposes it 
results a plurality of alloys consisting of different combinations of the 
above mentioned elements exhibiting a homogeneous crystal lattice and 
physico-chemical characteristics suitable for the specifications 
concerning these particular applications. 
SUMMARY OF THE INVENTION 
These and other objects are accomplished by a method for obtaining metallic 
alloys to be used in dentistry and by determining a group of alloys 
obtained by said method which is generally characterized in that it 
provides the use of at least three among the following elements: gold Au, 
platinum Pt, palladium Pd, silver Ag and copper Cu, in percent ratios 
determined by the single atomic weights thereof, for every element forming 
the alloy defining a number of atoms in close numerical relationship with 
the atoms of the other elements, in order to reach a total number of 
fourteen atoms or a multiple thereof for every alloy, corresponding to the 
number of atoms constituting a crystal face-centered cubic lattice which 
exhibits a proper distribution of the atoms of every element; said percent 
ratios defining an alloy melting point not higher than 
1030.degree.-1040.degree. C. for the alloys used just as they are or as a 
base for synthetic resin coatings, and not lower than 
1140.degree.-1150.degree. C. for the alloys used as a base for ceramic 
coatings, an alloy melting rate not greater than 90.degree. C. and a 
Vickers hardness in the range from 120 to 1270. 
The method of the present invention for obtaining alloys characterized by a 
homogeneous distribution of atoms in the crystal lattice is based on the 
fact that for determined concentrations of the elements the solute atoms 
are distributed uniformly in the lattice. All the elements used, gold Au, 
platinum Pt, palladium Pd, silver Ag and copper Cu individually exhibit a 
crystal face-centered cubic lattice and differ from each other, as to the 
atom sizes, for a maximum of 10,7% and therefore they are in harmony with 
the factors conditioning the substitution solid solutions. 
The crystal lattice of the alloy which is a face-centered cubic lattice 
too, is achieved by suitably arranging fourteen atoms; in order to obtain 
a uniform and homogeneous arrangement between the different elements, it 
is necessary to carry out the formula calculations, so that the 
percentages of the different elements, deduced by their individual atomic 
weight, are suitable to ensure a total number of atoms in the solid 
solution which reflects the ratio existing therebetween in the crystal 
face-centered cubic lattice as a structural base unit. Obviously, the 
number of atoms present in the weight unit of the alloy can decrease or 
increase of more than 30% depending upon the presence therein of elements 
having a lower specific gravity, such as palladium, silver or copper, or a 
higher specific gravity, such as gold or platinum, consequently varying 
the number of the structural base units, that is the number of the 
face-centered cubes consisting each one of fourteen atoms; it is therefore 
necessary to calculate the percentages of the single elements in order to 
maintain the numerical relationship between the different types of atoms 
as close as possible. 
For the purpose the calculation of said percentages by weight based on 
weight units in the scale of the kilogram, by means of an electronic 
balance adapted to give millesimal values, appears particularly suitable, 
being necessary to carry out a rounding off to the nearest upper value in 
the case of noble metals and to the nearest lower value in the case of 
copper, which is a critical element owing to its facility to oxidize and 
sulphurize but which is necessary for adjusting the alloy melting range. 
Among all possible formulas it is necessary to choose those having 
physico-chemical and mechanical features which exclusively concern the 
dental field and which can be circumscribed keeping in check the following 
factors: 
a melting point not higher than 1030.degree.-1040.degree. C. for the alloys 
used just as they are or as a base for synthetic resin coatings in order 
to prevent silver from attracting oxygen during the melting, which can 
give rise to the formation of microporosities during the solidification 
phase; 
a melting point not lower than 1140.degree.-1150.degree. C. for the alloys 
used as a base for ceramic coatings; 
a melting rate not greater than 90.degree. C. in order to avoid the 
zonation, that is the uneven new distribution of the atoms of the 
different elements in the crystal lattice during solidification; in fact 
if the atoms do not return to a rest state in a short lapse of temperature 
and therefore in a short lapse of time, the atoms of the same element are 
inclined to join together and aggregate; 
a Vickers hardness varying from a minimum of 120 for annealed alloys to a 
maximum of 270; 
the lowest indispensable amount of copper in order to keep the melting 
range within predetermined limits said amount corresponding to the maximum 
quantity allowed by the percentage of noble metals present therein in 
order to avoid any risk of oxidation and sulphurization. 
Referring to the above mentioned characteristics and to the 
physico-chemical limits concerning the possibility of utilizing an alloy 
in the dental field, the formation of a plurality of alloys consisting of 
different combinations of at least three among the above mentioned 
elements is achieved. The different types of alloys are listed 
hereinafter; they are formulated in accordance with the present invention, 
grouped according to conventional names, the amounts of the single 
elements being pointed out according to percentages by weight, global 
titre of noble metals expressed in g/1000 and specific gravity of the 
alloy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
______________________________________ 
LADIUM SILVER ALLOYS 
______________________________________ 
Au -- -- 
Pt -- -- 
Pd 7.266 14.546 
Ag 88.395 81.110 
Cu 4.339 4.344 
TITRE .Salinity. 72.66 145.46 
(Pd) 
SPECIFIC 10.53 10.64 
GRAVITY 
______________________________________ 
These ternary alloys provide a crystal face-centered cubic lattice having 
no more than an atom of copper, in order to avoid the risks of oxidation 
and/or sulphurization of this element as much as possible, in percentages 
varying from a minimum of g 4.339% to a maximum of g 4.344%, according to 
the presence of one or two atoms of palladium respectively in 
corresponding percentages of g 7.266% and g 14.546%, with a melting range 
not higher than 60.degree. C. Silver is present with 11 or 12 atoms for 
every lattice in percentages of g 81.110% and g 88.395% respectively. 
______________________________________ 
WHITE GOLD ALLOYS 
______________________________________ 
Au 12.680 12.692 23.983 
24.005 
Pt -- -- -- -- 
Pd 6.489 13.711 6.478 12.967 
Ag 76.381 69.503 65.671 
59.157 
Cu 4.090 4.094 3.868 3.871 
TITRE .Salinity. 
(Au + Pd) 195.29 264.03 304.61 
369.72 
SPECIFIC 11.64 11.75 12.64 12.74 
GRAVITY 
______________________________________ 
For these quaternary alloys formulas have been chosen providing no more 
than an atom of copper in the crystal face-centered cubic lattice in 
percentages varying from a minimum of g 3.868% to a maximum of g 4.094% 
according to the content of the other elements present in said formulas. 
Palladium is present with a minimum of 1 atom and a maximum of 2 atoms 
for each crystal lattice in percentages varying from a minimum of g 6.478% 
to a maximum of g 13.711% in order to avoid too high melting points and 
above all to have melting ranges not greater than 90.degree. C. Among 
these formulas having a high silver content the preference has been given 
to those having a melting point which does not remarkably exceed the 
silver melting point in order to avoid silver from attracting oxygen which 
is then liberated during the alloy solidification process, which gives 
rise to a particular microporosity called "pinhole microporosity". Silver 
is present with a number of atoms varying from a minimum of 9 to a maximum 
of 11, in minimum and maximum percentages of g 59.157% and g 76.381% 
respectively. In these alloys gold is present with one to two atoms for 
each crystal lattice in percentages varying from a minimum of g 12.680% to 
a maximum of g 24.005%. 
______________________________________ 
YELLOW LADIUM GOLD ALLOYS 
______________________________________ 
Au 34.124 43.272 51.566 52.792 
59.121 
Pt -- -- -- -- -- 
Pd 6.145 5.844 5.571 5.703 5.323 
Ag 56.062 47.395 39.536 34.693 
32.378 
Cu 3.699 3.489 3.327 6.812 3.178 
TITRE .Salinity. 
402.69 491.16 571.37 584.95 
644.44 
(Au + Pd) 
SPECIFIC 
13.53 14.33 15.06 15.12 15.73 
GRAVITY 
Au 60.463 67.464 68.960 73.880 
75.449 
Pt -- -- -- -- -- 
Pd 5.443 5.206 5.322 4.989 5.095 
Ag 27.593 21.112 16.185 15.173 
10.329 
Cu 6.501 6.218 9.533 5.958 9.127 
TITRE .Salinity. 
659.06 726.70 742.82 788.69 
805.44 
(Au + Pd) 
SPECIFIC 
15.80 16.41 16.49 16.98 17.07 
GRAVIIY 
______________________________________ 
In these alloys gold varies from a minimum of 3 to a maximum of 8 atoms for 
every crystal lattice and has corresponding minimum and maximum 
percentages of g 34.124% and g 75.449%. Palladium is present in the 
quantity of 1 atom for each crystal lattice in percentages varying 
according to the other composing elements from a minimum of g 4.989% to a 
maximum of g 6.145%. The quantities shown for palladium, while ensuring a 
sufficient hardness to allow the alloy to be used in dentistry, avoid a 
high melting point which never exceeds 1015.degree. C. and therefore the 
risk that silver may attract oxygen above all in case of alloys having the 
highest silver content, ensuring at the same time a melting range not 
greater than 85.degree. C. in order to prevent the zonation phenomenon too 
and consequently the uneven distribution of the atoms of the different 
elements at the inside of the crystal lattice. Copper is present in 
quantities varying from a minimum of 1 atom to a maximum of 3 atoms for 
each crystal lattice, in corresponding percentages varying from a minimum 
of g 3.178% to a maximum of g 9.533% in the alloys having a higher gold 
and palladium content, this element being necessary in order to reduce the 
melting range in the alloys having a higher content of noble metals, since 
the risks of oxidation and/or sulphurization of the same decrease when 
gold and palladium contents increase. Finally, silver is present in 
quantities varying from a minimum of 2 to a maximum of 9 atoms in 
corresponding percentages of g 10.329% to g 56.062%. 
______________________________________ 
YELL0W PLATINUM GOLD ALLOYS 
______________________________________ 
Au 57.120 55.160 58.414 56.412 
54.407 
Pt 1.951 3.903 1.995 3.990 5.987 
Pd tc -- -- -- -- -- 
Ag 37.753 37.760 33.093 33.099 
33.106 
Cu 3.176 3.177 6.498 6.499 6.500 
TITRE .Salinity. 
590.71 590.63 604.09 604.02 
603.94 
(Au + Pt) 
SPECIFIC 
15.68 15.72 15.75 15.79 15.83 
GRAVITY 
Au 65.023 62.629 66.464 64.017 
71.538 
Pt 2.386 4.772 2.438 4.877 2.285 
Pd -- -- -- -- -- 
Ag 26.377 26.383 21.570 21.575 
20.222 
Cu 6.214 6.212 9.528 9.531 5.955 
TITRE .Salinity. 
674.09 674.01 689.02 688.94 
738.23 
(Au + Pt) 
SPECIFIC 
16.38 16.43 16.47 16.51 16.95 
GRAVITY 
Au 70.774 73.056 72.276 70.715 
69.154 
Pt 3.048 2.334 3.113 4.670 6.227 
Pd -- -- -- -- -- 
Ag 20.222 15.487 15.488 15.490 
15.493 
Cu 5.955 9.123 9.123 9.125 9.126 
TITRE .Salinity. 
738.22 753.90 753.89 753.85 
753.81 
(Au + Pt) 
SPECIFIC 
16.96 17.04 17.05 17.09 17.12 
GRAVITY 
Au 77.532 76.798 79.109 78.362 
76.866 
Pt 2.194 2.927 2.239 2.985 4.478 
Pd -- -- -- -- -- 
Ag 14.558 14.558 9.903 9.903 9.905 
Cu 5.716 5.717 8.749 8.750 8.751 
TITRE .Salinity. 
797.26 797.25 813.48 813.47 
813.44 
(Au + Pt) 
SPECIFIC 
17.47 17.49 17.57 17.58 17.61 
GRAVITY 
Au 75.370 
Pt 5.972 
Pd -- 
Ag 9.906 
Cu 8.752 
TITRE .Salinity. 
813.42 
(Au + Pt) 
SPECIFIC 
17.65 
GRAVITY 
______________________________________ 
In these alloys the number of gold atoms varies from a minimum of 6 to a 
maximum of 9 for each crystal lattice, for corresponding minimum and 
maximum percentages of g 57.120% and g 79.109%. Platinum, at its lowest 
percentage of g 1.951%, replaces one atom of gold every five crystal 
lattices, while at its highest percentage of g 6.227% replaces one atom of 
gold every three crystal lattices. Beyond this percentage which is 
considered as the highest advisable one, based on the experimental data, 
the melting point is extremely high and, as a result, there is the risk 
that silver may attract oxygen; furthermore, the melting range is greater 
than 90.degree. C., the highest recommended degree, and there is the risk 
of zonation. The lowest platinum percentages are provided when for some 
dental uses high-hardness alloys are not required. Copper is present with 
a minimum of 1 and a maximum of 3 atoms for every crystal lattice in 
minimum and maximum percentages of g 3.176% and g 9.531% respectively in 
the alloys having a higher gold and platinum content, this amount being 
however sufficient to reduce the melting ranges within such limits that 
the risk of zonation can be avoided during the solidification process, 
while at the same time it is ensured a reasonable melting point even when 
the alloys have the highest gold and platinum content. In these alloys 
silver is present with a minimum of 2 and a maximum of 7 atoms for every 
crystal lattice for corresponding percentages varying from g 9.903% to g 
37.760%. 
______________________________________ 
YELLOW PLATINUM AND LADIUM GOLD ALLOYS 
______________________________________ 
Au 42.854 43.913 42.750 
43.805 
42.580 
Pt 2.123 2.175 2.647 2.712 3.515 
Pd 4.630 4.745 4.330 4.436 3.833 
Ag 46.937 42.085 46.825 
41.982 
46.638 
Cu 3.456 7.082 3.448 7.065 3.434 
TITRE .Salinity. 
496.07 508.33 497.27 
509.53 
499.28 
(Au + Pt + Pd) 
SPECIFIC 14.51 14.54 14.55 14.60 14.63 
GRAVITY 
Au 43.627 52.295 51.968 
59.918 
61.296 
Pt 3.600 2.072 3.431 1.978 2.023 
Pd 3.927 4.520 3.743 4.316 4.415 
Ag 41.810 34.366 34.152 
27.345 
22.380 
Cu 7.036 6.747 6.706 6.443 9.886 
TITRE .Salinity. 
511.54 588.87 591.42 
662.12 
677.34 
(Au + Pt + Pd) 
SPECIFIC 14.68 15.28 15.38 15.95 16.02 
GRAVITY 
Au 59.562 62.738 60.923 
62.348 
66.740 
Pt 3.277 2.072 3.352 3.430 2.361 
Pd 3.575 4.519 3.657 3.742 3.863 
Ag 27.182 17.179 22.242 
17.072 
20.885 
Cu 6.404 13.492 9.826 13.408 
6.151 
TITRE .Salinity. 
664.14 693.29 679.32 
695.20 
729.64 
(Au + Pt + Pd) 
SPECIFIC 16.05 16.10 16.13 16.20 16.59 
GRAVITY 
Au 66.503 68.203 67.955 
69.733 
69.473 
Pt 3.136 2.412 3.205 2.466 3.277 
Pd 3.421 3.948 3.496 4.036 3.574 
Ag 20.811 16.008 15.949 
10.911 
10.870 
Cu 6.129 9.429 9.395 12.854 
12.806 
TITRE .Salinity. 
730.70 745.63 746.56 
762.35 
763.24 
(Au + Pt + Pd) 
SPECIFIC 16.65 16.67 16.73 16.76 16.82 
GRAVITY 
Au 74.656 74.395 76.258 
75.986 
Pt 2.310 3.070 2.360 3.136 
Pd 3.782 3.350 3.862 3.420 
Ag 10.221 10.185 5.220 5.202 
Cu 9.031 9.000 12.300 
12.256 
TITRE .Salinity. 
807.48 808.15 824.80 
825.42 
(Au + Pt + Pd) 
SPECIFIC 17.24 17.29 17.33 17.39 
______________________________________ 
The choice of these alloys results from the requirement of formulas giving 
a certain hardness without reaching very high melting points and too wide 
melting ranges. Therefore palladium partially replaces platinum for the 
above purposes and platinum and palladium together vary from a minimum of 
g 6.092% to a maximum of g 7.527%; so, in this range, adding suitable 
percentages of copper it is possible to achieve melting ranges not wider 
than 95.degree. C. and melting points not higher than 1040.degree. C. Gold 
varies from a minimum of 5 to a maximum of 8 atoms in corresponding 
percentages of g 42.580% and g 76.258%. Platinum varies from a minimum of 
g 2.023% to a maximum of g 3.600%, while palladium varies from a minimum 
of g 3.350% to a maximum of g 4.745% and together in their corresponding 
percentages suggested by the different formulas replace an atom of gold 
for every lattice. Copper varies from a minimum of 1 atom to a maximum of 
4 atoms for every crystal lattice in corresponding percentages varying 
from a minimum of g 3.434% to a maximum of g 13.408% in the alloys having 
a higher content of noble metals. Finally, silver is present in quantities 
in the range from 1 to 8 atoms in percentages varying respectively from g 
5.202% to g 46.937%. 
______________________________________ 
BASIC WHITE AND YELLOW GOLD ALLOYS FOR 
CERAMIC (WITHOUT COPPER) 
______________________________________ 
Au 31.714 31.739 40.356 40.386 
48.243 
Pt 10.472 10.479 9.993 10.000 
9.557 
Pd 5.710 11.430 5.450 10.908 
5.212 
Ag 52.104 46.352 44.201 38.706 
36.988 
TITRE .Salinity. 
478.96 536.48 557.99 612.94 
630.12 
(Au + Pt + Pd) 
SPECIFIC 14.51 14.61 15.23 15.31 15.86 
GRAVITY 
Au 55.470 62.118 68.252 73.930 
79.202 
Pt 9.157 8.789 8.450 8.136 7.845 
Pd 4.995 4.794 4.608 4.438 4.278 
Ag 30.378 24.299 18.690 13.496 
8.675 
TITRE .Salinity. 
696.22 757.01 813.10 865.04 
913.25 
(Au + Pt + Pd) 
SPECIFIC 16.45 16.99 17.50 17.96 18.39 
GRAVITY 
Au 71.335 76.518 
Pt 15.701 15.158 
Pd 4.282 4.134 
Ag 8.682 4.190 
TITRE .Salinity. 
913.18 958.10 (Au + Pt + Pd) 
SPECIFIC 18.55 18.95 
GRAVITY 
______________________________________ 
Gold, in these alloys, is present in quantities varying from a minimum of 3 
to a maximum of 10 atoms with corresponding percentages in the range from 
minimum of g 31.714% in white alloys to a maximum of g 79.202% in yellow 
alloys. Platinum is present in quantities varying from 1 to 2 atoms for 
each crystal lattice in corresponding percentages of g 7.848% and g 
15.701%. Palladium is present with 1 or 2 atoms in percentages of g 4.134% 
in yellow alloys up to a maximum of g 11.430% in white alloys. Silver is 
present in quantities varying from 1 to 9 atoms for every crystal lattice 
in percentages varying from a minimum of g 4.190% in yellow alloys to a 
maximum of g 52.104% in white alloys. In every alloy of this kind there is 
also an iron and platinum compound according to the formula FePt3 in 
quantities of g 1.116% of iron and g 11.704% of platinum, these quantities 
being intended for every 1000 grams of basic alloy considered as gold, 
platinum, palladium and silver; this addition gives the alloy a particular 
hardness, as the iron, taking up platinum, allows the adding of further 
platinum in order to ensure a sufficient presence of atoms for an even 
distribution in the crystal lattice. 
In the above mentioned alloys it is also provided the addition of very 
small quantities of other elements such as indium, ruthenium, iridium or 
rhodium in maximum amounts in the range of g 0.03% which act as catalysts 
for crystal aggregation in order to have a fine-grained crystallization of 
the alloys. 
Obviously, any of the specific gravities referred to in the above mentioned 
formulas can be reproduced by means of other empirical combinations and 
the global titre of noble metals as well can be achieved by means of a 
series of different empirical combinations; however when a determined 
specific gravity of a formula has been given, as well as the corresponding 
global titre of noble metals, the remaining metal percentages can but be 
that of the formula itself; in other words, when a determined specific 
gravity of a formula has been given as well as the millesimal composition 
of any one of the components thereof, the other components can but be 
present in the millesimal percentages designed by the formula itself. 
The selected formulas, based on the reference principles and parameters 
mentioned above, according to the method of the present invention, allow 
the achievement of a homogeneous, uniform and constant composition of the 
crystal lattice of the different types of alloys, give a more homogeneous 
electro-chemical point-to-point bond and therefore offer a greater 
resistance to the action of the oxidizing and sulfurating chemical agents 
which are present in the oral cavity, as well as a greater 
physico-mechanical resistance.