Histological Study on Reversed Tooth Movement in Dogs

Abstract

The purpose of this study is to examine how newly formed bone and degenerated periodontal ligament will react to orthodontic force in reversed tooth movement. After moving the maxillary first premolars in ten adult dogs with a continuous force of 100 grams in a distal direction for three weeks, the teeth were subsequently moved in a mesial direction for five days. Light and fluorescence microscopes, and microradiography were used for histological investigation.
On the pressure side, new bone created during distal movement was cancellous and not well calcified. In five days, the new bone was undermined from the numerous marrow spaces and was more readily resorbed than old one when it was subjected to pressure. On the tension side, there were extensive bone resorption on the periodontal surface and marrow space of old bone by osteoclasts, whereas hyalinized area still remained. When subjected to tension, the hyalinized tissue was extended and osteoclasts migrated away from Howships lacunae. However, resorptive process persisted in the marrow space up to five days. Mineralization was found on the stretched periodontal ligament at one and three days, and it disappeared at five days.
From these findings, we concluded that newly formed bone during distal movement will not resist against orthodontic force, because the reversed tooth movement will bring about comprehensive bone remodeling within the periodontal tissue. We must take into consideration that reversed tooth movement is likely to result in calcification or mineralization of the periodontal ligament.