Eskimo Dentition 65c 



of functional origin the result of extraordinary pressure along the line of teeth 

 most concerned in chewing. "(*) This growth may be clearly seen in Plates IV 

 and V. Hrdlicka advances no facts in support of his statement and consequently 

 one may consider it as merely a plausible guess. While it may seem like temerity 

 to take issue with so great an authority, nevertheless for several reasons, chiefly 

 dynamical, I believe he is wrong. In the first place pressure on the teeth is 

 met and counteracted, not by the sockets of the teeth, but by the resiliency of 

 the tangential and other fibres of the peridental membrane. (^) Only indirectly 

 are the alveoli concerned. In the second place the pressure is greatest at and 

 near its point of application, viz., on the molar series, and it is here that the 

 reinforcement is either slight or wanting. In this region, too, in the maxilla, 

 the roots of the teeth are in close relation to the floor of the antrum and there 

 is no trace of thickening of that structure to withstand the pressure. 



Lastly, in the premolar region where the bone development is greatest, if 

 it be argued that the growth is due to inward lateral pressure on the teeth, then 

 since, the pressure is equal and outward on the corresponding teeth of the 

 maxilla, one would naturally expect a corresponding reinforcement on the 

 buccal surface of the alveolus above these teeth; but such is not the case. 



A critical study of the mandibles — all of adult age — where the alveolar 

 reinforcement occurs, shows that not only the angles but the horizontal rami 

 are strongly everted, the lower margin of each jaw forming a very symmetrical 

 parabolic curve. The alveolar ridge of the horizontal rami consequently lies 

 markedly to the lingual of the lower margins so that the teeth are suspended 

 by means of the alveolar process within the jaw, whereas ordinarily they would 

 be placed directly upon it. In other words, owing to the strained form of the 

 mandible, from necessity the alveolar process has altered its position. It is no 

 longer possible to arrange it and the teeth over the jaw proper without increasing 

 the size of the arch to such an extent as to throw it out of proportion with the 

 rest of the face (Plate IV, Cat. No. XIV, H 4). ' 



With the beginning of eversion as a result of enormoils development in the 

 muscles of mastication concerned, the dynamics of the mandible have changed 

 from normal. After studying the forces involved and their mode of action I 

 have come to the conclusion that when the jaws are forcibly closed the horizontal 

 rami are under a tortional stress which tends to evert the lower and invert the 

 upper margin of the bone. This effect is greatest in the premolar region and 

 since the alveolar ridge is weakened by the sockets of the teeth a compensatory 

 growth of bone is provided on the lingual alveolar wall in an effort to counteract 

 the action of the powerful muscles involved. Plate IV shows very beautifully 

 the changed relations from the ordinary that exist between the molar teeth, 

 the coronoid process and the angle of the jaw. The thickness of the bone 

 in the bicuspid region should be noted — on the right side it is 18-3 mm. while 

 the lingual space between the rami at the same point is only 18-5 mm. 



There are other points of interest in the Eskimo dentition. The lower second 

 molar frequently carries five cusps and the third molar is occasionally so in- 

 verted that the upper half of the buccal surface occludes with the upper teeth. 

 Variation, too, is not entirely absent in the Eskimo. Frequently the third 

 molars vary appreciably in size on the two sides of the mouth, and in one case 

 (F-1) the upper lateral incisors are congenitally absent. In this skull, too, the 

 teeth are plentifully coated with tartar, probably due to disuse owing to an 

 osteitis of the temporo-mandibular joints (see drawing of the glenoid fossae). 



F-19 is the mandible of a child, probably between five and six years of age. 

 A close examination seems to indicate that the permanent teeth erupt rather 

 earlier than is the case in the civilized races, where more extended observations 

 have been possible. 



50844—5 



