Long-term Effects of Orthodontic Forces on the Morphology of the Rat-incisor Socket and its Location in the Mandible

Abstract

The effect of orthodontic force application on the rat-incisor socket and mandible was studied on roentgenograms. A mean linguo-intrusive force of 19 ± 0.6 g was applied continuously to the shortened left lower incisor for a period of two (group A) and four weeks (group B). A third group of rats, subjected to shortening of the left mandibular incisor only, served as a hypofunctional control (group C). A fourth group of normal rats constituted the intact control (group D). After a recovery period of three months, the animals were killed, and standardized roentgenograms of the cleaned mandibles were taken. Socket and mandibular dimensions were measured on magnified tracings of the roentgenograms. Comparison of groups A and B with the control groups, on the one hand, and of group C with group D, on the other, facilitated isolation of the hypofunctional factor. In groups A and B, the orthodontic forces caused changes in the parameters affected (i.e., socket area, alveolar bone thickness, mandibular dimensions) and not affected by hypofunction (i.e., socket angulation and location, anterior-socket length). The former finding implies modification of the adaptive capability of dental structures to functional demands. It is concluded that mechanical loading of the incisor for two to four weeks causes long-lasting changes in the socket and its surrounding bone.