Long-term effect of intrusive loads of varying magnitude upon the eruptive potential of rat incisors

The present investigation deals with the functional recovery of the periodontium following application of intrusive loads of varying magnitudes to continuously growing rat incisors. The daily rate of eruption of these teeth served as an indicator of the functional capacity of their periodontal ligament. The left mandibular incisor was shortened to prevent occlusion in thirty experimental and ten control rats. The experimental animals were divided into three groups and constant, calibrated axial loads of 8 Gm./cm. 2 (light), 15 Gm./cm. 2 (medium), and 26 Gm./cm. 2 (heavy) were applied to their incisors by means of closed-coil springs for a period of 2 weeks. The daily eruption rate of all teeth was measured for 80 days following removal of the springs. In all experimental animals, severe and long-lasting impairment of the eruptive potential occurred. The least impairment was seen in the group with the light loads, their eruption rate being fully restored 64 days after removal of the loads, by which time 165 percent of all dental and periodontal tissues was renewed. In the medium-load group, renewal of the tissues reached 140 percent, while a gross impediment in normal eruption rate persisted throughout the entire experimental period. The teeth subjected to heavy loads received a diminished impact of the axially directed loads due to the strong horizontal component of force; consequently, they behaved like the incisors of the light-load group. The light loads proved to cause the least impairment and were the most beneficial to functional recovery.