The early reparative process of orthodontically induced root resorption in adolescents--location and type of tissue.

The aim of this investigation was to determine the pattern of repair of root resorption regarding the location and type of tissue in adolescents after application of a well-controlled force magnitude. In 16 adolescents (mean age 13.8 years), the maxillary first premolars were buccally moved with a weekly reactivated force of 50 cN (approximately 50 g) for 6 weeks following which the appliance was made passive for 2, 3, 6, and 7 weeks. The subjects were divided into two groups of eight individuals for which the retention periods were 2 and 6 weeks (Group I), or 3 and 7 weeks (Group II), implying intra-individual differences of 4 weeks. Reparative cementum in the resorption cavities was seen in all test teeth, significantly more often after 6 and 7 weeks of retention (82 per cent) compared with 2 and 3 weeks (35 and 44 per cent, respectively). The reparative process appeared to commence in the bottom of the resorption cavity, frequently covered by a thin layer of acellular cementum. However, most of the reparative cementum was of the cellular type and always covered the initially formed acellular cementum. There were great individual variations regarding the occurrence of healing of orthodontically-induced root resorption.