Histometric study of healing of periodontal tissues in rats after surgical injury. I. Design of a standardized surgical procedure.

A standardized surgical procedure in rats is described which allowed a histometric registration of the repair of cementum, periondontal ligaments and bone, and which eliminated the possibility of interference of pocket epithelium during the healing process. Using an extraoral incision, the lateral surface of the mandible was exposed, and a cavity was cut through the vestibular bone plate, the periodontal ligaments and into the root surface, using a specially designed handpiece and bur. This procedure was performed in 20 male Wistar rats, 9 weeks old. The observation period was 12 weeks. The systematic error, precision and interanimal variation were examined for histometric registrations of the repair of cementum, periodontal ligaments and bone. The precision of the histometric procedures was in this study found to be 5% or less for most of the different structures measured, and the estimated combined systematic errors probably less than 5% for cementum repair. The coefficient of variation in cementum repair among different rats was 24%. This variance has two components, the combined influence of systematic errors and precision of histologic and histometric procedures and the other the biological variance due to inter-animal differences. The precision and systematic errors probably do not account for more than one third of this variance, the remaining two thirds being inter-animal differences. These differences could not be completely controlled in this study in spite of the use of a controlled genetic strain of rats bred in litters of the same size under SPF conditions.