gutta-percha. Teeth which have been wedged apart soon return to their normal positions when left to themselves.

Separating by cutting away the tooth substance may be done with chisels or“ hard bits," and when this is resorted to the teeth should be cut away toward the inside of the mouth, so as not to disfigure the external surfaces. Separation in this manner is applicable to the six anterior teeth of the upper jaw, and is recommended for them only.

It is not necessary nor wise to cut away enough to expose or endanger the dentine. As the normal point of contact near the cutting edge is left undisturbed, the separation is made permanent, leaving a surface which is self cleansing and which causes the filling in proximal cavities to present within

FIG. 64.*

the mouth, subject to examination. (Fig. 64.) This separation is produced by dressing away the proximo-palatal angle of the tooth, but not sufficiently to interfere with the front.

OPENING CAVITIES.

This consists in enlarging the orifice of a cavity of decay so as to render accessible all parts of the cavity. It is done by cutting down the enamel walls, and by removing sound dentine when necessary.

The instruments most suitable for opening crown cavities are chisels, burs and excavators; for buccal cavities, excavators and burs, and for proximal cavities hard bits, chisels and burs.

*The artist has exaggerated this somewhat. It indicates too much cutting

away.

In opening proximal cavities in superior incisors and cuspids, cut away the palatal wall till every part of the cavity can be seen by direct sight or in the mirror. A few prefer to cut away the labial portion of the enamel and expose the cavity to direct sight, so that it may be filled from the front and without the aid of a mirror.

Open proximal cavities in inferior incisors and cuspids from the labial surface, but distal cavities in inferior cuspids may sometimes be opened from the lingual surface.

After the teeth are separated proximal cavities in bicuspids and molars should be opened toward the grinding surfaces, except when small and near the gum. In such cases it may be better to open from the buccal surface. If decay is far advanced, the grinding surface should be cut through. When full contour is desired, separate by wedging, open the cavities as in other cases, and restore the contour by filling.

REMOVAL OF DECAYED DENTINE.

This is accomplished by means of excavators, chisels and burs of various forms and sizes, cutting, whenever possible, in a direction from the pulp, as this causes less pain.

In deep cavities, allow a thin layer of decalcified dentine to remain, to protect the pulp, but remove all softened tissue from the borders of cavities, and all discolorations from the enamel or near it, whenever possible, and from any connecting grooves, especially in bicuspids and molars. The deep portions of such cavities should be thoroughly disinfected.

FORMATION OF CAVITIES FOR FILLING.

As a rule, remove all frail and overhanging walls. Sometimes when it is desirable to save them, as in presenting surfaces, they may be strengthened by lining with cement. Remove all unsupported enamel from the cervical wall. This wall should be at right angles to the surface of the tooth.

Make the lateral walls of cavities in incisors and cuspids of such form as they will most conveniently take, and make a well-defined undercut at the cervical wall, and also at the part next the cutting edge, to retain the filling.

The lateral walls of proximal cavities in bicuspids and molars should generally be undercut or grooved, and if the grinding surface is not cut through, this also should be slightly undercut. If this surface is cut through, the grooves of the lateral walls may extend through the opening, thus presenting a dovetailed outline (Fig. 65), or the opening may be left as in Fig. 66. For making these grooves use a small bur, hoe or

chisel.

If the cavity is of considerable size, the lateral walls should be cut away, as shown in Fig. 67, so that when filled, the filling

only will come in contact with the adjoining tooth, leaving the margins free.

Let all angles be rounded and smooth. For filling with cohesive gold, retaining pits are usually made in which to start the filling. Use a small, flat, square-pointed drill, and drill the holes in the dentine near the enamel, and generally parallel with the long axis of the tooth. Avoid drilling toward the pulp. A depth equal to the diameter of the drill is sufficient. Retaining pits are condemned by many as unnecessary and a source of danger to the pulp. In bicuspids one retaining pit is usually sufficient, and is better made at the middle portion of the cervical wall, as the dentine is thickest at this point. These are not needed for non-cohesive gold or for plastic fillings.

In grinding surfaces the walls of the cavity should be nearly parallel, with slight undercuts at opposite points. The same rules apply to the formation of cavities on buccal, palatal or lingual surfaces. For the formation of these cavities various forms and sizes of burs are best suited, but the work may be well done with excavators and chisels.

EXCLUSION OF MOISTURE.

To obtain the best results, the cavity must be kept dry during the operation of filling. For this purpose use napkins, bibulous paper, the saliva-pump or rubber dam. Napkins from three to six inches square, folded into a small compass and held over the openings of the ducts of the salivary glands, and each side of the tooth to be operated upon, will exclude all moisture long enough for an ordinary operation, and if a saliva-pump be also used the cavity may be kept dry for an indefinite time by an occasional change of the napkins. Snow's saliva-pump is effective, but where water pressure can be obtained, the saliva ejector is the most desirable and efficient.

The rubber dam properly adjusted is the most perfect means for the exclusion of moisture. Take a piece of strong rubber dam of medium thickness, about seven inches square, and for application to the upper teeth punch some holes about one and a half inches from the edge and one-eighth to one-fourth of an inch apart, generally on a line parallel with the edge of the rubber.

For lower teeth punch the holes toward the lower part of the rubber, and not less than two inches from either edge.

The rubber may be placed upon the face, and the points for the holes indicated by marking over the tooth or teeth when the rubber is carried to place.

The rubber should be supported upon the face with the holder before stretching it over the teeth, as thus the edges are prevented from folding over and interfering with the applica tion of the rubber and the ligature or clamp.

For cavities in the cutting edges or grinding surface frequently only one tooth will need to be exposed, but if proximal fillings are to be made, two teeth at least must be exposed. To support the rubber dam upon the face, use a rubber dam holder-one made from a pair of ordinary sleeve catches connected by elastic braid is convenient and effective. (Fig. 68.) A good form, also, is Cogswell's holder, shown in Fig. 69, also Perry's, Fig. 70.

Before applying the rubber, prove by passing silk between the teeth, that there are no sharp edges to interfere with its

passage. For this purpose and for ligatures, floss silk, not too coarse, well waxed, is best. Binding-wire makes an excellent ligature in many instances, especially when the cavity is at or below the margin of the gum.

Fasten the dam-holder to each upper corner of the rubber, carry the elastic around the head and tighten it, bringing the upper edge of the rubber across the upper lip (Fig. 71), then with the forefinger of each hand stretch the rubber over the teeth. If the teeth are too close together for the rubber to pass easily, apply a little soap, and it may then be readily carried up with the ligature. The ligature should be passed