proximal cavities in bicuspids and molars, some form of metal
shield, or matrix, is of great advantage, as they prevent the tin from
crushing or sliding out. By driving the tin firmly against the metal, a
well-condensed surface is secured; and as the metal yields a little, we
can with a bevel or thin plugger force the tin slightly between the
metal and the margin of the cavity, thus making sure of a tight filling,
with plenty of material to finish well. After removing the metal,
condense with thin burnishers and complete the finish the same as for
gold. Where no shield or matrix is used, or where it is used and removed
before completing the filling, it is often desirable to trim the
cervical border, for in either case there is more light and room to work
when only a portion of the cavity has been filled. Tin cuts so much
easier than gold, it is more readily trimmed down level with all
cervical margins.

Be sure that all margins are made perfect as the work progresses, and if
the cavity is deep and a wide shield shuts out the light, then use a
narrow one, which can be moved toward the occlusal surface from time to
time.

In filling the anterior teeth when the labial wall is gone, and the
lingual wall intact or nearly so, use a piece of thin metal
three-quarters of an inch long and wide enough to cover the cavity in
the tooth to be filled, insert it between the teeth, and bend the
lingual end over the cavity; the labial end is bent out of the way over
the labial surface of the adjoining tooth, as shown in Fig. 4. When the
labial wall is intact or nearly so, access to the cavity should be
obtained from the lingual side, and in this case the bending of the
shield would be reversed, as shown in Fig. 5. The shield is not
absolutely essential, but it helps support the tin, and also keeps a
separation.

[Illustration: FIG. 4.]

[Illustration: FIG. 5.]

It is preferable to save the labial wall and line it with (say) five
layers of No. 4 semi-cohesive gold folded into a mat and extended to the
outer edge of the cavity; this gives the tooth a lighter shade, and
bicuspids or molars can be filled in the same manner. Cases are on
record where incisors with translucent labial walls, filled by this
method, have lasted from twenty-three to thirty-seven years.

CHAPTER VII.

For the last ten years the writer has been using tin at the cervical
margin of proximal cavities in bicuspids and molars, especially in deep
cavit