Left maxillary molar teeth were extracted from twenty-four six-week old rats, and two weeks later they and twenty-four control animals were given 1μCi/gm of body weight of tritiated proline by intraperitoneal injection; four animals from each group were killed after a further 12 hours, 1, 2, 4, 7 or 12 days. Following autoradiography, grain densities were determined in crestal, mid-root and apical areas of the periodontal ligament, and regression lines of log grain density on time after H3-proline administration calculated.

Half-lives derived from the linear regression lines were attributable to collagen turn-over and varied from 2.45 days in all apical areas to 6.42 days in the crestal areas of opposed teeth. This high turnover rate seemed to occur throughout the whole width of the ligament allowing the tissue remodelling associated with tooth movement. Over-eruption of the unopposed teeth resulted in a half-life of 5.25 days in the crestal area, suggesting that turnover rate depends partly on the amount of tooth movement required.