Some Histopathologic Changes in the Hamster as the Result of a Continuously Acting Orthodontic Appliance

¹ Department of Pathology, School of Dentistry, University of Kansas City, Kansas City, Missouri

An orthodontic appliance was designed to produce constant mesial movement of the mandibular first molar tooth in laboratory rodents. This appliance was found to be satisfactory for this purpose. It was found that the hamster was superior to the rat as an experimental animal in this respect.

Evidence was found that the normal distal drift of the second and third molars could be reversed by a mesial movement of the first molar. Definite evidence was seen that mesial movement of the first molar was accomplished with the orthodontic appliance.

The first pathologic process seen at the pressure site was the necrosis of the fibroblasts and other cell elements in the upper 20 per cent of the periodontal membrane. The collagenous fibers were not destroyed. The pressure necrosis was followed later by the appearance of osteoclasts adjacent to the necrosed area.

New bone formation as a result of the applied orthodontic force was seen to begin at approximately 5 days after the appliance was placed and was continued through 9 days.

The final pathologic processes involved were not determined because they extended beyond 9 days.