. Descriptive anatomy of the human teeth . sely occluded points. With the aftermovements of the teeth, by which they are more perfectlyarranged, this difficulty disappears. 189. The line from before backward on which the oc-clusion occurs is not quite a plane; in the lower jaw it pre-sents a slight curve, or concavity, and in the upper jaw a con-vexity (Fig. 131, c to d). This concavity of the line of theocclusal surfaces of the lower teeth is a little greater than theconvexity of the upper, so that the cutting edges of the lowerincisors pass a little beyond, and to the lingual of the cuttinge
. Descriptive anatomy of the human teeth . sely occluded points. With the aftermovements of the teeth, by which they are more perfectlyarranged, this difficulty disappears. 189. The line from before backward on which the oc-clusion occurs is not quite a plane; in the lower jaw it pre-sents a slight curve, or concavity, and in the upper jaw a con-vexity (Fig. 131, c to d). This concavity of the line of theocclusal surfaces of the lower teeth is a little greater than theconvexity of the upper, so that the cutting edges of the lowerincisors pass a little beyond, and to the lingual of the cuttingedges of the upper incisors. 190. In the occlusion the relative mesio-distal positionof the particular teeth of the upper jaw to the lower is im-portant (Fig. 131). At their cutting edges, the upper centralincisors are about one-third wider mesio-distally than thelower centrals. The upper central, therefore, occludes withthe lower central, and also with from one-third to one-halfof the lower lateral incisor. The upper lateral occludes with. Fig. 126. Fig. 126 (Par. 187).—The Elliptical Form of the Arch. The crowns of theteeth of both upper and lower jaws, drawn from the casts of a very regularlyformed arch, and the line of a true ellipse (in dots) placed over them, showing thecomparative size of the upper and lower arch, and the deviations from perfectregularity. ARRANGEMENT OF THE TEETH. 135 the remaining portion of the lower lateral and the mesialportion of the lower cuspid. The upper cuspid is usuallyrather broader mesio-distally than the lower, and in occlu-sion covers its distal two-thirds and about half of the lowerfirst bicuspid, so that its lingual, or triangular ridge, is be-tween the cusp of the lower cuspid and the buccal cusp ofthe lower first bicuspid, the point of its cusp overlappingthe lower teeth. The buccal cusp of the lower first bicuspidoccludes in the space between the upper cuspid and upperfirst bicuspid. This order is now maintained between thebicuspids.
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