Study on the Individual Biting Forces of the Human Deciduous Teeth

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In the present study, measurements were undertaken on a total of 5, 728 healthy deciduous teeth and those which had the first class amalgam restorations in a mixed group of boys and girls ranging in age from 36 to 72 postnatal months. For measurement purposes, use was made of the biting force measuring apparatus with the strain gauges attached in association with a multiple monitoring recorder. The measurement data were then analyzed in terms of postnatal months, sex distinctions, stability and resorption of the dental root, etc. As a result of these efforts, the following conclusions were obtained.1. Concerning individual biting forces of the deciduous teeth under study, there were not observed any significant differences between the sexes, upper and lower jaws and right and left sides of the body.2. The maximum biting force and the postnatal months in which each deciduous tobth registered the maximum value were as follows. As regards deciduous central incisors, the maximum biting forces that took place in the 48th postnatal month were respectively 6.34kg for the upper and 6.52kg for the lower jaws, and deciduous lateral incisors in the 60th postnatal month registered 7.04kg for the upper and 7.16kg for the lower jaws. Deciduous cuspids gave the maximum biting forces in the 72nd postnatal month respectively 13.70kg and 14.03kg for the upper and lowet jaws. The maximum biting forces of deciduous first molars in the 72nd postnatal month were 21.66kg for the upper and 22.02kg for the lower jaws and those of deciduous second molars in the 72nd postnatal month were 22.68kg for the upper and 23.27kg for the lower jaws.3. When the maximum biting forces of these deciduous teeth were compared with those of corresponding permanent successors (an age group of 20's males used by TAKAMIZAWA), the deciduous central incisors, lateral incisors, cuspids, first molars and second molars were respectively 0.4, 0.5, 0.5, 0.5 and 0.5 times in the case of upper jaw. On the other hand, in the case of lower jaw they were 0.3 for deciduous central incisors, 0.4 for lateral incisors, 0.5 for deciduous cuspids and first molars alike and 0.4 times for deciduous second molars.4. When chronological changes were investigated in the individual biting forces, a slight increase was observed between the 36th postnatal month to the 48th postnatal month with reference to the deciduous central incisors, and a decrease in the 60th postnatal month. As regards the deciduous lateral incisors, . on the other hand, there was observed a slighti ncrease between the 48th postnatal month and the 60th postnatal month and a decrease in the 72nd postnatal month. With reference to individual biting forces of deciduous cuspids and molars their individual biting forces increased in a period from the 48th postnatal month to the 72nd postnatal month.5. The root of deciduous central incisors had been already formed by the 36th postnatal month and the root resportation was observed occasionally. The root resorption progressed to a fair degree in the 48th postnatal month, in which the cases of good root stability and root resorption were observed more or less to the same extent. The majority had their roots resorbed by 1/2 and the cases where the root resorption was more than 1/2 were only few. However, the root resorption became much advanced in the 60th postnatal month. Here the root resorption was either by 1/2 or more than 1/2.6. As regards the deciduous lateral incisors, on the other hand, the root resorption had not yet begun in the 48th postnatal month with a few exceptions but after the 60th postnatal month it became quite apparent, in which the cases of root stability, apical resorption and 1/2 root resorption were mixedly found. In the 72nd postnatal month, the root resorption was further advanced and here all the cases were the root resorption by 1/2 or more than 1/2.