Histometric study of healing of periodontal tissues in rats after surgical injury. II. Healing events of alveolar bone, periodontal ligaments and cementum.

A standardized surgical periodontal injury was performed in 67 male Wistar rats 9 weeks of age. An osteotomy was made with a burr through the vestibular bone plate and the periodontal ligaments and into the superficial part of the root surface of the mandibular first molar. The rats were sacrificed with observation periods ranging from 1 day to 2 years postoperatively. A histometric registration was made of the repair of alveolar bone, periodontal ligaments and cementum. Bone repair was found after 7 days and included a bony alkalosis. On the period from 7 to 14 days after surgery this ankylosis was removed by resorption process. Argyrophilic reticulin fibers were present 3 to 5 days after surgery. Precollagen fibers were found after 4 days, whereas mature collagen fibers inserting in new formed cementum, was seen after 14 days. The number of collagen fibers increased substantially until 28 days after surgery. Initial cementum repair was found after 14 days and increased substantially with increasing observation periods tending to reach the thickness of the contralateral control tooth. Based on these findings a new concept of healing of the surgically injured periodontium in rats is presented. According to this the healing occurs in three successive phases. 1. Bone repair with formation of an ankylosis. 2. Repair of the periodontal ligament including removal of the established ankylosis. 3. Repair of Cementum.