Page:The American Cyclopædia (1879) Volume VI.djvu/31

 DENTISTRY 23 attention was formerly given to shaping the cavity, in order that by its contracted aper- ture the filling should be held in as by dovetail- ing; but by the use of gold foil and sponge gold specially prepared for this purpose, it is now found practicable to apply the metal in successive portions, and build up a solid block of any shape by incorporating each portion with' that which preceded it. This is done by carefully packing it with suitable instru- ments, and the gold may be thus rendered so compact, it is affirmed, that its specific gravity shall equal that of the cast metal. In wide- mouthed cavities the filling is secured by being built upon plugging carefully introduced into the cavities of the roots, and also by lateral pins of the gold filling made to enter from this into little holes or grooves drilled for the pur- pose into the walls of the tooth. It has been generally considered impracticable to preserve a tooth when the decay has reached into the internal or pulp cavity. In this condition in- flammation often takes place at the root, and matter collects, forming an ulcer between the periosteum of the tooth and the bone. If the discharge of this be stopped by filling the cavity, the matter will find its way through the gum, causing a gum boil near the root ; or it pro- duces inflammation of the face, often attended with great suffering, which is relieved only by the removal of the tooth. The modern treat- ment is to perforate the sac at the root by a fine drill passed through the cavity ; and if the pulp be sensitive, it is cut out and removed by a delicate steel wire furnished with a hook at the end, so small that it can pass freely into the nerve cavity. A solution of creosote or carbolic acid is then injected into the cavity, and as soon as a healthy action has taken place tooth may be safely filled, with the liability 1 further trouble from the same cause greatly luced. The only unobjectionable material >r filling teeth is gold foil or the sponge gold ecially prepared for this purpose. The latter iterial is produced by dissolving gold free 3m copper in nitro-hydrochloric acid, placing le solution in a flat-bottomed vessel, and heat- and precipitating by strong solution of ox- lie acid. In a few hours the gold is wholly >sited, and the supernatant liquid may be ited off, taking care not to disturb the )ld at the bottom. The vessel is then several les filled with boiling water and decanted, itil the last washings contain no more oxalic iid. The gold is now carefully slipped upon piece of filtering paper, and by means of a ~>atula gently pressed into the form of the de- red cake, but a little thicker. It is then re- loved to a porcelain crucible, and heated for short time, somewhat below a red heat, rhen it shrinks and becomes coherent. Tin )il may be used, and its malleability and cheap- 38 well adapt it for large and badly shaped ivities and for temporary fillings in sensi- ive teeth ; but it is liable to oxidize and pro- ice discoloration. Temporary fillings, for the purpose of protecting the cavity while it is be- ing prepared for gold filling, are often made of gutta percha. A preparation of it known as Hill's stopping, made by incorporating with it a powder made of quicklime, quartz, and feld- spar, is highly recommended. When this com- position is used a condensing instrument large enough to cover the filling should be held upon it until the nerve becomes cool. A mixture of chloride and oxide of zinc, called oxychlo- ride of zinc, or os artificiel, has lately been much used as a temporary filling, and also for pulp cavities. Exposed nerves have also been covered with it, and gold used to complete the filling. The operations for filling teeth are varied and complicated. Many ingenious ma- chines have been lately introduced for prepar- ing cavities and condensing the filling. Drills worked by treadles, and also by galvanism as a motor force, and automatic mallets have been successfully applied. The extraction of the teeth is an important branch of dental practice ; safe and easy with good instruments in skilful hands, but, as practised by the un- professional operator, not a little hazardous. The improved instruments of modern times, however, have greatly lessened this risk, and pain is avoided by the use of anaasthetic agents. The last department of dentistry to be no- ticed is the construction and application of artificial teeth. These were formerly carved from ivory of the tusk of the elephant or the tooth of the hippopotamus. They were obtained also by altering the shape of the teeth of some of the inferior animals ; and the crowns of hu- man teeth were often conveniently engrafted upon the roots of the original front teeth. All these materials are objectionable from their susceptibility to the action of the fluids of the mouth ; ivory soon becomes offensive from being saturated with these fluids; and all of them are liable to decay, inducing at the same time disease in the sound teeth re- maining. Porcelain teeth perfectly resist the corrosive action of the fluids of the mouth, and imitate so perfectly in color and ani- mated appearance the natural teeth, that they are often not easily distinguished from them. Various methods of securing artificial teeth in their places have been in use. So long ago as 400 years B. C. they were fastened by ligatures of flax or silk, and with wire of gold or silver, to the natural teeth that remained. In modern times metallic clasps, spiral springs, and fasten- ings of gutta percha and of caoutchouc have been used for this purpose ; but the most perfect method is to secure the teeth, either in whole or partial sets, to a plate of gold or other metal, which is so accurately fitted to the gums that it is firmly retained by atmospheric pres- sure. In making an artificial set of teeth, the first object is to obtain in some hard metal an exact model of the mouth in which the plate is to. be fitted. For this purpose, yellow or white wax, free from mixture of grease, and softened by warm water, is placed in a shal-