The effects of horizontal tooth loading on the circulation and width of the periodontal ligament--an experimental study on beagle dogs.

The third premolars of Beagle dogs were subjected to tipping force of 20N, applied for between 20 minutes and 7 hours. Ten minutes before the end of the experiment the animals were injected intravenously with disulphine blue in order to show the capillary circulation and the tissue perfusion in the PDL under loading. The animals were then killed, and vertical histological sections were made of the loaded and the control teeth. The width of the PDL of the loaded and control teeth was measured at seven levels along the root surface and an analysis of variance was carried out. There was no circulatory disturbance and only slight irreversible changes in the shape of the PDL with loading for up to 3 hours. Only the teeth which had been loaded for at least 3 hours showed clear zones of irreversible compression and expansion. As the amount of irreversible compression increased so the blood supply and the circulation were impaired. Further increased compression of the periodontal ligament caused by long-term force application resulted in localized blood clotting.