The authors have studied how the size of the jaw relates to the tcoth sine with the -p ]aster models of upper and lower jaws which were made frcm 78 Korean males and ´70 females, ranging from 12 to 18 years old, with normal occlusion.
The results are as follows:
1) There is no significant difference in the tcoth size tetween left and right incisors,
2) The size of incisors, anterior arch length and width, and posterior arch width are slightly larger in, males than females.
3) The ratio of the sum of the size of four upper incisors to the lower´s is 1:0.74,
4) As the sum of the size of the upper incisors increases to 0.5mm, the anterior arch :length increases about 0.3mm also. -
5) The premolar and molar index of Koreans are revealed to be 81.5 and 63.1 respectively.
6) The formulas for prediction of dental arch width are as follows:
Premolar width=the the sum of the size of upper incisors+7(mm) Molar width=the sum of the size of upper incisors+ 7+ 11(mm)
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