Severe external apical root resorption--local cause or genetic predisposition?

Background: Current data suggest that a large extent of the variation in orthodontic root resorption may be explained by differences in individual genetic predisposition. This would imply, however, a similar root resorption reaction in all teeth.

Objective: To determine the incidence and extent of severe external apical root resorptions (SEARR) in maxillary incisors during multibracket (MB) appliance treatment.

Patients And Methods: Of the whole sample of patients having completed MB treatment at the University of Giessen between 1991 and 2010 (P(Total)=3198), all subjects exhibiting severe root resorptions on at least one maxillary incisor were selected. SEARR were defined according to Malmgren et al. [39] (grade-IV RR=resorption >1/3 root length). Evaluation was performed using orthopantomograms from before and after MB treatment. The crown and root length of the affected teeth were measured. The extent of SEARR was assessed taking pretreatment crown length into consideration.

Results: SEARR was detected in 16 patients. Thus, the incidence of SEARR on maxillary incisors during MB treatment totalled 0.5%. The median of SEARR of the affected incisors was 38.6% of the initial root length (minimum=33.4%, maximum=61.0%). Most subjects exhibited only single affected teeth. Only two subjects (0.06% absolute/12.5% relative) presented four maxillary incisors with SEARR.

Conclusions: The incidence of SEARR on maxillary incisors during MB treatment (0.5%) was very low compared to the literature. With only 12.5% of SEARR patients presenting four affected teeth, local rather than systemic/genetic factors seem to have predisposed the present subjects to SEARR.