The etiology of osseous deformities of the head, face, jaws and teeth . esistance in front, butbeing resisted by the incisors slightly at the side, must neces-sarily pass forward. The lateral is too weak to afford resist-ance. Even if the centrals could be acted upon by thepressure from behind, they could be prevented from assuming 454 THE HEAD, FACE, JAWS AND TEETH 455 aV-shape by the overlapping incisors above; for the morethe upper arch is compressed laterally, and the mesial angleof the central is turned outward, the more will the distal anglebe turned inward, and thus confine the lower in
The etiology of osseous deformities of the head, face, jaws and teeth . esistance in front, butbeing resisted by the incisors slightly at the side, must neces-sarily pass forward. The lateral is too weak to afford resist-ance. Even if the centrals could be acted upon by thepressure from behind, they could be prevented from assuming 454 THE HEAD, FACE, JAWS AND TEETH 455 aV-shape by the overlapping incisors above; for the morethe upper arch is compressed laterally, and the mesial angleof the central is turned outward, the more will the distal anglebe turned inward, and thus confine the lower incisors. The lower incisors being narrower than the upper onlyfavors this tendency. These conditions are necessarily mod-ified by the local peculiarities of the upper arch, the relativestrength of the teeth and the nature of the occlusion beingall-important factors in determining final results. Fig. 206 is a diagram of a normal lower maxilla. The linea h passes through the cuspids, bicuspids and molars, andshows the direction of the force exerted by the posterior col-. umn upon the anterior. For its growth it depends far moreupon function than the upper. The growth of the lower jawis limited to the posterior column, as has been mentioned,this being accomplished by the absorption of the anteriorborder of the rami, while bone-cells are deposited along itsposterior border. Its freedom of motion is, however, retardedby the arch of the upper maxilla, for which reason irregular-ities are much rarer in the lower than the upper jaw, as theoverlapping of the upper teeth tends to correct any predispo-sition to malarrangement. Irregularities of this jaw result more from local causes thanthose of the upper maxilla, except those found in the under-hung jaw. Its development depends largely on to its movements there are fewer irregularities in thismaxilla and the jaw is more apt to be normal. Irregularities 456 ETIOLOGY OF OSSEOUS DEFORMITIES OF back of the cuspid are veiy ra
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Keywords: ., bo, bookcentury1800, bookdecade1890, booksubjecthead, bookyear1894
