Radiographic evaluations of molar intrusion and changes with or without retention in rats

To describe radiographic changes caused by molar intrusion with or without retention methods in rats.

Thirty 12-week-old male rats were assigned to six groups (n  =  5 each). Molar intrusion was achieved with an intrusion spring to two maxillary molars for 2 weeks. The control group underwent the same experimental conditions, but without the intrusion spring. The intrusion and control groups were then euthanized. In four groups, the intrusion spring was disengaged after intrusion and the new molar positions were either retained or not with an occlusal bite-block for 1 or 2 weeks. Radiographic changes were measured in the cusp tip, root apices, and alveolar crests.

After 2 weeks of intrusion, the cusp tip and root apices had moved apically compared with the control group. However, the alveolar crests were similar in the intrusion and control groups. With retention bite-block, the new position of the intruded cusp tip was maintained, but the root apices had moved occlusally, and the alveolar crest between the two intruded molars had moved apically. Without retention, the cusp tip and root apices had moved occlusally, and the alveolar crest between the intruded molar and unintruded molars had moved occlusally compared with the intrusion group.

Rat molars were successfully intruded and maintained at the altered position with retention bite-block. However, the apical root resorption was observed as an instant response. The alveolar crest adjacent to the intruded molars was repositioned apically, but that was a delayed response compared to root resorption.