Vanessa C. Jiménez Montenegro, Allan Jones, Peter Petocz, Carmen Gonzales, and M. Ali Darendeliler. Am J Orthod Dentofacial Orthop 2012;141:e1-e9

I ntroduction: Extrusive tooth movement has been overlooked in the literature on root resorption. The aims of this study were to quantify the effects of light and heavy controlled extrusive forces on root resorption and to localize the sites of prevalence in premolars. Methods: Ten patients (7 girls, 3 boys) who required bilateral maxillary first premolar extractions as part of their orthodontic treatment participated in this study. The total sample consisted of 20 maxillary first premolars. Light (25 g) or heavy (225 g) forces were applied to the right or left first premolar for 28 days. After the experimental period, the teeth were extracted without root damage and analyzed with microcomputed tomography. Each specimen was studied in 3 dimensions, and specially designed software was used to measure the volume of each crater. Wilcoxon signed rank tests were used for the statistical analysis. Results: There was a significant difference in the total root resorption caused by light and heavy forces ( P = 0.037). The discrepancy between the light and heavy groups was not significant for the cervical, middle, and apical regions separately. Only the distal surfaces were significantly different between the light and heavy forces ( P = 0.008). Conclusions: Greater root resorption was observed after heavy extrusive forces when compared with light forces. The distal surfaces of the tooth root were significantly more affected than other root surfaces and might be influenced by root morphology and initial angulation of the tooth. There was no significant difference in the cervical, middle, and apical thirds in relation to root resorption after light or heavy extrusive forces.