The Effect of Continuous Torquing Forces on Maxillary Central Incisors in Macaque Rhesus Monkeys

Abstract

Continuous torquing moments on the maxillary central incisors were studied cephalometrically and histologically. The experimental sample consisted of five Macaque rhesus monkeys which were subjected to continuous torquing moments applied to the maxillary central incisor for a period varying from nine to twenty weeks. The following conclusions were drawn: On the basis of cephalometric evaluation, the greater the magnitude of the amount of the moment the greater the amount of tooth movement that occurred. The total movement of the apices of the incisors diminished with a decrease in the level of the moment. The incisors (M V) which were subjected to a heavy torquing moment showed considerable root resorption. In contrast, the incisors which were exposed to intermediate (M IV) and light (M I and M II) moments exhibited minimal root resorption. Clinically, the lighter forces produced less mobility of the maxillary central incisors. The application of a heavy continuous moment (M V) resulted in excessive mobility of the incisors. Microscopically, there was no evidence in any of the monkeys of inflammation in the pulp or periodontal membrane of those teeth which were moved orthodontically. Depressive forces delivered by the base arch produced truncation of the apices of the incisors in each animal.