Tin and Gold - Part 1
Tin is also employed in combination with gold-foil. The metals are combined in various proportions ; some operators enclose a sheet of No. 4 tin between two sheets of No. 4 gold-foil, and then either twist it into a rope or cut it into ribbons ; others fold a sheet of No. 3 tin in a sheet of No. 4 gold-foil, and then twist it into ropes of various sizes or cut it into ribbons of varying widths to suit the case in hand. The ropes may also be cut into pellets or the ribbons rolled into eylinders.
This mixture of the metals works with about the same degree of softness as tin alone, and can be as readily adapted to the walls of the cavity.
Non-cohesive gold-foil is generally used in combination with tin, but some operators use cohesive foil, and then cover the surface of the filling with gold, claiming by this combination they are able to weld the gold to the tin and gold base.
Fillings which are made of tin and gold combined have a yellowish-gray appearance when first finished, but they soon become more "or less discolored upon the surface by oxidation.
After a time some chemical change, which at present is not understood, takes place in the mass, rendering it exceedingly hard and giving it the appearance of an amalgam. It does not, however, stain the tooth-structure, as might be expected, and seems to exert a very decided preventive effect upon caries. Such fillings will resist the attrition of mastication as well as gold, but they have the disadvantage of being unsightly in color, and should not therefore be placed in any conspicuous part of the mouth.
Fillings made of this combination of metals do not conduct thermal changes so readily as gold alone, and consequently are better adapted to sensitive teeth. Such fillings are in every way superior to amalgam, and find their greatest field of usefulness in the bicuspids ,and molars during the periods of childhood and adolescence, and in persons subject to persistent caries.
It can be introduced as rapidly as tin alone, makes a very durable filling, and possesses a conserving action upon tooth-structure not possessed by gold alone or by amalgam.
Methods of introducing Tin and Tin and Gold.- The methods of introducing fillings composed of tin and tin and gold, are the same as those used in introducing non cohesive gold-foil. Some operators prefer to use cylinders and wedge-pointed pluggers and hand-pressure; others use pellets and foot-shaped pluggers with the hand or mechanical mallet, finishing the filling by driving a hard-rolled pellet into the central portion of the plug, and then thoroughly condensing the surface towards the enamel margins with broad-faced pluggers and afterwards thoroughly burnishing.
Fillings made from tin or tin and gold combined should be finished with the same degree of care and thoroughness as is expended upon those made from gold. The labor, however, is much less, as the material is not so resistant as gold.
Finishing Fillings.- The beauty and the utility of gold fillings are greatly enhanced by perfect finishing. Fillings which have been well and carefully introduced sometimes fail for the reason that the margins have not been entirely freed from overhanging portions of gold, or the gold has not been cut down and finished flush with the enamel margins and highly polished. These imperfections are most often found at the cervical border of approximal fillings, particularly in the bicuspids and molars, where there is a tendency to bifurcation of the root, and the cavity extends beneath the gum, making a clear view of the cervical border very difficult to obtain.
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