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796 ORTHODONTIA AS AN OPERATIVE PROCEDURE.

till thev wort' practically parallel (Fig. 818). To prevent the crowns
sli(lini>: past each other and overlapping, a guide was constructed as
sliown in Fig. 819. The same ap[)liance will serve for retention.
If after extracting a crowded lower incisor the teeth on each side
of the space are found to lean toward each other, as in Fig. 820,
Fig. 820.

Appliance for moving roots of lower incisor and cuspid.
the roots may be moved toward each other so that the crowns will
be parallel to each other. Dr. C. S. Case has devised an appliance
for this purpose, shown in Figs. 821 and 822. Bands are fitted
to the teeth on each side of the space, and sometimes to the second
tooth also. From these bands stiff bars extend downward parallel
with the surface of the gum from an eighth to a third of an inch below

Fig. 821. Fig. 822.

Appliance for moving roots.
the margin. On the lingual surface similar bars extend about the
same distance. On the free ends of the bars are soldered hooks or
headed pins, so that a rubber band or a ligature can be extended
from one labial bar to the other, and from one lingual bar to the
other. The direction of force is thus brought low enough to move
the roots as well as the crown of the teeth. Suture wire may be
substituted for the rubber band or ligature for retention.
In some cases of upper protrusion the alveolar process is so promi-
nent that when the crowns of the teeth are moved back to the desired