Root resorption in bicuspid intrusion. A scanning electron microscope study.

Apical root surfaces covered by cellular cementum are rapidly subjected to resorption under orthodontic loads of varying magnitude and duration. Within the experimental parameters employed, the intrusive forces applied to the teeth produced a striking increase in root resorption compared with the control teeth. The amount of resorption increased markedly with the duration of the force, and to a lesser extent with the magnitude of the appliance activation. After 70 days, cellular cementum repair accompanied the continuing resorption. Little variation was detected in the susceptibility of different patients to root resorption in the experimental teeth. The same intrusive load applied for the same duration to similar teeth produced a corresponding degree of root resorption in various individuals. On the other hand, there were individual differences in the amount of resorption on untreated control teeth. There is a need to extent our understanding of the periodontal ligament and its associated tissues which provide the basis for our professional services. Clearly, root resorption and the capacity for repair are orthodontic facts of life. In the current climate of technological innovation great emphasis has been given to cephalometrics and appliance mechanics, which provide the orthodontist with the clinical stimulus of visual and tactile involvement. This paper is presented as a contribution to our knowledge of the unseen biological consequences which accompany that orthodontic treatment.