Mandibles of 54 rats consisting of males and females of the same number (weighing around 200 to 260 gr.) were measured in 16 dimensions (weight, area and linear dimensions). In area and linear dimensions we used projective measurements with a certain constant enlargement of soft X-ray photographs and pictures of both right and left mandibles which were taken under the same conditions. Therefore we compared the mandible on the right and left sides in each measurement, for the presence or absence of asymmetry and one-sided dominance. As a result, mainly the following two findings were obtained. 1) The mean values of the dominant and non-dominant sides in each dimension showed significant difference (p <0.01 or <0.001). 2) Significant difference between the mean values of the right and left sides was not necessarily found in all dimensions but found in only a few dimensions, i.e., the height of angular process was significantly greater on the left side in both male (p <0.05) and female (p <0.001), and the area of the ramus and the length of the condyloid process and the length of the masseter muscle (the masseteric ridge to the posterior end of the angular process) showed significant difference (p<0.05) in only male, they were all greater on the left side. From these observation it was suggested that the phenomenon of asymmetry and one-sided dominance found in the height of the angular process and in some other dimensions was caused by the difference of the roughening or hyperostosis of bony area where masticatory muscles were given attachement.
1) In the group of normal occlusal subjects, the canine showed a tendency of mesial inclination to FH plane and, moreover, there was observed a gradual or incremental distal inclination from the first premolar to second molar in the mandible. In the maxilla, on the other hand, the second premolar approximated to a right angle to X axis, the first premolar showing the largest distal inclination followed by the canine. Inversely, the first and second molars revealed a heavy mesial inclination. In the group of overbite patients, on the other hand, axial inclination of the canine was found to be more or less at a right angle as compared with normal occlusal subjects and, further, the tendency of a slight distal inclination was observed from the maxillary first premolar to first molar. In the mandible, both the canine and first premolar gave more pronounced inclinations distally, whereas noticeable mesial inclinations were observed from the second premolar to second molar. 2) As for the axial cross angles of upper and lower jaws, the second premolar cross angle was found to be the largest, those of the canine and second molar tending to be smaller. In the group of overbite patients, on the other hand, the first premolar cross angle was the largest and even the canine cross angle was larger than that of normal occlusal subjects. 3) Various crown heights (cuspid in the case of canine, buccal cusp tip in the case of premolar, buccal surface groove in the case of molar, distance to FH plane for the upper teeth and distance to X axis for the lower teeth) of the normal occlusal subjects were observed to be more or less the same concerning the canine and first premolar in the maxilla, accompanied by a trend that a distance to FH plane became smaller as it went from the second premolar to second molar. As compared with normal subjects, respective distances from the first premolar and first molar to FH plane were considerably shorter. With the mandible, in particular, distance from the left second premolar to X axis was observed to have been reduced. 4) Various crown depths (cuspid in the case of canine, buccal cusp tip in the case of premolar, buccal surface groove in the case of molar and respective distances of the upper and lower teeth to Y axis) were found to be deeper bilaterally in the overbite patients than in normal occlusal subjects. 5) In all the normal occlusal subjects under study, there was observed no statistical difference between the right and left sides in common to the both jaws on all the measurement items. There existed a statistical difference, however, for the axial inclination angle of the maxillary second molar in the group of overbite patients. 6) The mandibular angle in overbite patients was generally smaller than in normal occlusal subjects, being indicative of the fact that the inclination of their mandibular basal planes tended to be rendered flat.
Based on studies in two dental schools (N=42 and 22), the hypotheses suggest that the utilization of personality, vision and anthropometric measures as supplemental indices to the currently utilized measures will result in higher concurrent validity than was previously possible (377 versus 48%).
In studying the characteristics of dental amalgam condensation by 36 dental students, it is concluded that : (1) A minimum force of 800 1 b/inch2 is required per condensation stroke in order for the condensation stroke to have any effect on the slow compressive strength test values as a predictor of marginal fracture. (2) A 30, 000 1 b/inch2 slow compressive strength test value may be derived from force utilization of 2, 000 1 b/inch2 per condensation stroke.