to pack at the cervical wall a layer of non-cohesive gold; this is followed by a layer of semi-cohesive blocks or cylinders; then from this continue with cohesive gold as desired.

Another plan is to fill the margins and the body of the cavity with semi-cohesive gold, filling the centre and finishing the filling with cohesive.

PLASTIC FILLINGS.

Amalgam, Oxychloride of Zinc, Oxyphosphate of Zinc, and Gutta-Percha are the plastic fillings now used.

Amalgam is the only plastic metal filling. It is compatible with tooth substance, consequently tooth-saving; it has comparatively low conducting power, hence it is less likely than gold to produce inflammation of the pulp; it is easily introduced into the cavity, hence it is applicable in places difficult of access and in cavities with frail walls. It is thought by some, however, to exert a deleterious effect upon frail enamel walls. Its color is objectionable, and it is inclined to assume the spherical form and consequently to draw away from the walls of the cavity. Careful preparation and thorough packing will greatly modify, if not entirely overcome, the shrinkage and the tendency to assume the spherical form, and will add greatly to its preserving qualities, and nice polishing and burnishing will improve the color.

The best amalgam is fine-grained, plastic-working, sets quickly, has good edge-strength, sufficient hardness to resist wear and density to take a good polish.

Silver, tin and mercury are the essential constituents of amalgam. Gold, copper, zinc and other metals are frequently added in proportions varying from three to seven per cent.

Gold decreases the shrinkage and improves the color, and copper is thought to have a preservative effect on the dentine, and to render the filling less likely to induce irritation of the pulp in deep cavities. Zinc, not exceeding one and onehalf per cent. of the alloy, renders the amalgam more plastic,

thus improving its working qualities. It also improves the color, and for this object it may be used in larger quantity, even to ten per cent., but the plasticity of the amalgam will be lessened.

Cadmium must not be used, as it is highly destructive to the

teeth.

An amalgam is made of copper and mercury only, which is serviceable. It becomes very dark in color, but it saves the teeth well and does not stain. It neither shrinks nor expands.

Silver and mercury alone make an amalgam very hard, dense and serviceable, but it turns very dark in color, owing to the sulphide of silver.

Tin so modifies and improves the filling that it has come to be esteemed an essential element of all silver amalgams. It makes the alloy amalgamate much more easily, makes the filling finer grained, more plastic, and improves the color from the first and prevents its turning dark. It softens it, but not to its detriment. The proportions in which tin is used range from thirty-five to sixty per cent. of the alloy.

To prepare an amalgam filling, place a sufficient quantity of the filings in a small wedgewood or ground glass mortar, or in the palm of the hand, add mercury, and rub them thoroughly together with the pestle or with the finger; add, if necessary, a little more of the filings to harden, or mercury to soften. The paste should be soft enough to cohere when pressed, but hard enough so that mercury may not be expressed by pressure between the thumb and finger. A little practice will enable one to judge correctly. A balance may be used with good results by pouring the filings in one end and the mercury in the opposite cup, the balance showing the proper proportionate weight of each. The balance must be adjusted for each quality of alloy.

Have the cavity dry and protected from moisture, insert the filling in small pieces, placing it in perfect contact with all parts of the walls of the cavity by rubbing and gently tapping with the plugger, exercising the same care as with a gold filling,

especially at the cervical wall and in undercuts. The tapping process condenses amalgam with remarkable facility and thoroughness.

Amalgam may be very thoroughly and satisfactorily packed by inserting enough to half fill the cavity, covering with a layer or a pellet of cotton or bibulous paper and rotating the burnisher upon this with pressure, either with the engine or with a hand burnisher. Then add more amalgam and repeat the burnishing until the cavity is filled.

Remove surplus and burnish toward the edges until it has begun to set, then leave it, and at a subsequent sitting dress down and polish.

If the tooth to be filled is much broken down, there may be adjusted to the tooth a band matrix, cut to fit the occlusion and filled and allowed to remain until the amalgam is hard, when it may be removed and the filling finished as in other

cases.

Amalgam was formerly washed in alcohol or solution of bicarbonate of soda, but at present this is not in favor, and it is thought it injures it. This is questionable.

Copper amalgam is especially adapted to the filling of buccal cavities in teeth of inferior quality. It seems to exert a preservative influence. Its extreme hardness is an objection to its use in proximal cavities, as it is almost impossible to cut it, if its removal should from any cause become necessary.

GUTTA PERCHA.

Gutta percha for filling is used combined with oxide of zinc, and was first known as Hill's stopping, and since by many other names. It is useful for temporary fillings, for root filling, and for cavities with frail walls or if near the gum. In some instances it lasts a long time, ten years or more, but when exposed to wear it is soon destroyed, and some preparations of it are softened by the secretions.

It is best used by cutting in small pieces, laying them on a

warm slab of porcelain or tile until soft, and inserting one piece at a time until the cavity is full. Each piece should be warm enough to stick to the walls or to the portion already inserted, and thus make a homogeneous filling.

A coating of resin dissolved in ether applied to the walls of the cavity will cause the gutta percha to adhere firmly. Chloroform or oil of cajeput on the burnishers will soften the surface and aid in finishing.

CEMENTS.

Oxychloride of zinc is useful for root fillings and for partially filling cavities in crowns of teeth to whiten them. It is the lightest colored cement made. It is not serviceable for exposed fillings, though in a few exceptional cases it has lasted seventeen to twenty years.

Mix the liquid and powder on a palette to the consistency of thick paste, and insert in the cavity. Wait for it to harden and finish at same sitting. For use in root canals, see page 101.

Oxyphosphate of zinc is phosphoric acid and calcined oxide of zinc. This has almost entirely superseded the oxychloride of zinc for exposed fillings, as it is much more durable.

Mix with a flexible spatula, on a slab (a glazed tile four inches square), the acid and powder to the consistency of soft putty, working in the powder thoroughly, a little at a time, rubbing well with the spatula until it works smooth, and continuing the working until used, as it begins to set immediately on being allowed to rest. Insert quickly in convenient portions and insure perfect contact with the walls of the cavity, which should be perfectly dry. Dress off the surplus with a thin cutting instrument, well oiled, then burnish slightly toward the edge with oiled burnisher. Do not burnish hard enough to move the body of the filling after it has begun to set, as it breaks up the crystallization. The filling should be kept dry from fifteen to thirty minutes. It is well to cover it with gutta percha dissolved in chloroform and allow it to

remain to protect from moisture until it is fully hardened. When making permanent fillings it is better to use the rubber dam.

A good oxyphosphate of zinc filling may be expected to last from one year to five years.

The cervical wall may be protected with gutta-percha amalgam or tin filling and the cavity then filled with the cement, and thus be made more durable.

For use as temporary fillings the cement may be mixed much thinner and used quickly, and not kept dry. Such fillings may be cut out quite quickly.

A temperature of about 70° F. is the most favorable for mixing cements.

COMBINATION FILLINGS.

Gold and platinum are sometimes used in combination, being beaten together in the manufacture, the platinum between two layers of gold. This is manipulated in the same manner as cohesive gold. When finished and burnished the platinum comes to the surface and modifies the color of the filling according to the amount of platinum in the foil, rendering it less bright. The combination is also much harder than pure gold, a desirable quality for grinding surfaces or exposed edges.

A combination of gold and tin is made by laying together a sheet of gold and of tin, each No. 3, and then rolling this into ropes and preparing as directed for gold foil. This must be used as non-cohesive foil. It is claimed that this preserves the teeth better than gold; it is more easily packed than gold, and is harder than tin.

Fibrous foil is used in combination with gold as a foundation in large crown cavities or at the cervical wall in proximal fillings.

As much of the fibrous foil is used as seems desirable, and to this the gold foil is added and the filling finished.

Amalgam, also, may be used as a foundation, allowing it to thoroughly harden before adding the gold.