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084 ORTironoXTfA AS AN OPERATIVE PROCEDURE.
The u|)|)(M' (Icntnl arcli is sliown in Fio;. 599. The six anterior teeth
are arranged in tlie segment of a circle. The l)iciis|)i(ls and molars
Fig. 599.
jiipitiiiiiiiiiiiiiiii*'!; .
Normal upper dental arch.
form almost straight diverging lines from the canines, though the posi-
tion of the third molar is somewhat outside of that line.
The normal occlusion of the teeth is shown in Fig. 600. The
six upper anterior teeth close over the six lower ihmi a third to a half
Fig. 600.
\T^'
Normal occlusion.
of the length of the latter. The lower second bicuspid occludes between
the cusps of the two upper bicuspids and is the hey to the occlusion;
this is a point easily remembered. Each bicuspid and molar of each
jaw, excepting the upper third molar, is antagonized by two of the
