The purpose of this study is to investigate the mechanism in the regeneration of the periodontal tissues after applying external injury to the tooth and gingiva.

The animals used in this experiment were 8 week-old male rats (Wistar-strain), and the periodontal tissues of the maxillary first molar were externally injured with a diamond point. Tooth reduction of the same area was also undertaken exposing the dentin surface, and the healing process was observed under a light and an electron microscope.

Complete epithelialization over the wound surface was observed 3-5 days following the initial wound. Afterwards, the regenerated epithelium differentiated into the sulcular and junctional epithelium. At 10-14 days, formation of junctional epithelium over the dentin surface was observed following epithelial attachment between it and the regenerated epithelium. Later, this junctional epithelium was found to move towards the coronal side, while connective tissue attachment formed over the exposed dentin surface. In this portion, cementum-like substance containing collagen fibers was found.

In conclusion, even after applying external injury which included tooth reduction around the healthy periodontal tissues of rats, they were capable of almost fully regenerating.

Epithelial attachment and connective tissue attachment containing cementum-like substance was thought to have formed on the exposed dentin surface.