Effect of freezing damage of the periosteum on the growth of the mandibular condylar process in the rat

The regulatory effect of the periosteum on the growth of the mandibular condylar process has previously been investigated by relieving the periosteal tension, e.g. by dividing the periosteum, but no unanimous conclusion has been reached. In the present investigation, a different experimental design was applied in that the growth of the condylar process was observed following a provoked periosteal damage. Using 15-day-old rats, the mandibular ramus on the right side was exposed, and the periosteum subjacent to the condylar cartilage was frozen by a cryotechnique. Controls were treated similarly, with the exception of the freezing. The height of the ramus and the length of the mandibular corpus were measured on separated dry mandibular halves 15 or 30 days postoperatively. The measurements showed that the mandibular halves on which the periosteum had been frozen were significantly smaller than the contralateral ones. A tendency in the same direction was also found in the sham-operated animals. It can be concluded that the presumably increased restriction following damage to the periosteum, and evidently also scarring resulting from the operation, has an inhibitory effect on the growth of the condylar process. However, it is still open to discussion whether the reduced growth is transmitted by mechanical means according to the periosteal-tension hypothesis and/or by hen unspecified mitogenic factors.