Page 154 - My FlipBook

142 MECHANICAL DENTISTRY AND METALLURGY.
at the desired points to the expansion arch, which thus
prevent the hgatures from shpping down the sides of the
arch. The nuts in front of the anchor tubes are occasion-
ally tightened as more room for the moving teeth is re-
quired, thus carr3nng all four teeth forward with the posi-
tive force of the screw. The action is practically that of
two jack-screws united.
As the expansion arch is very elastic, it exerts a powerful
lateral force upon the sides of the dental arch, through the
anchor bands and the ligatures upon the bicuspids. By

studying this fig'ure it will be seen how perfectly force is
being distributed to accomplish these various tooth move-
ments, and how^ as in all fine mechanisms, each part assists
and harmonizes with each other part.
In describing this appliance Dr. Angle says that occasion-
ally the tooth which it is desired to use as anchorage may
be found to incline forw'ard at such an angle that the sheath
on the " D band " will not properly line with the expansion
arch, in wdiich case the band should be removed and the
sheath be detached and resoldered at the proper angle.
This may be readily effected by placing a small piece of