Page 22 - My FlipBook

20 MACROSCOPIC ASATOMY OF THE Ili'MAX TEKTII.
curve from front to rear, oi' tj^rcatcr or less (leo;ro(> in dilfercnt forms of
the arch. Tims it is liioli at the incisors, cnrvinu' downward at the bicns-
pids, roachino- its lowest [)oint at the first molar; it curves upward rap-
idly at the second molar, and is highest, again, at the third. In the
rounded arch the plane is more flattened, and it exhibits the extreme

Fig. 4.

The horizon of the line of occlusion and plane of occlusion.

dowuAvard curve in the square arch. Between these extremes there
is of course every variety of modification. Tlie form of the plane of
occlusion is shown in Fig. 4, C.
Fjg. 5.

The apposition of the upper and lower teeth.

The tendency of the bolus of food is toward the low^est part of the
curve at the region of the lower first molar, so that the extraction of
this tooth alw^ays affects the performance of mastication.
In the apposition of the teeth of the opposite jaw's the mechanical