External apical root resorption in Class II malocclusion: a retrospective review of 1- versus 2-phase treatment

External apical root resorption (EARR) is an imperfectly understood problem of orthodontic treatment. The records of 138 children with Class II malocclusion (overjet > 7 mm) participating in a randomized clinical trial of early orthodontic treatment were reviewed. The patients were treated in either 1 phase with fixed appliances only (n = 49) or 2 phases with headgear (n = 49) or bionator (n = 40) followed by fixed appliances. The 3 groups were similar in age, sex, and malocclusion severity at enrollment. The records examined included anamnestic data, clinical examination records, panoramic radiographs before and after fixed appliance therapy, and posttreatment periapical radiographs. All radiographs were reviewed and scored independently by 2 examiners for maxillary incisor root development, morphology, and EARR. Of the 532 incisors scored, 11% of central and 14% of lateral incisors demonstrated moderate to severe (>2 mm) EARR. The proportion of incisors with moderate to severe EARR was slightly greater in the 1-phase treatment group. There was no difference in the incidence of EARR between teeth that had had trauma and those that had not, and there was only a slight increase in frequency of root resorption in teeth with unusual root morphology. Significant associations exist among EARR, the magnitude of overjet reduction, and the time spent wearing fixed appliances. However, not all incisors in a child respond in the same way, so other variables must play a role in determining the root response to orthodontic forces.