Some Asymmetries in the Weight, Area and Linear Dimensions of the Mandible of Rats

抄録

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.