Effect of incisor retraction magnitude and movement pattern on root resorption after premolar extraction in adults

The amount and type of maxillary incisor movement during extraction therapy may influence the severity of external apical root resorption (EARR); however, the threshold at which retraction increases the risk remains unclear. This study evaluated the association between incisor retraction magnitude, movement pattern, and EARR in adult patients treated with premolar extraction.

A retrospective sample of 180 adults (mean age, 24.73 ± 4.83 years) treated with at least 2 maxillary premolar extractions was divided into 3 groups according to maxillary incisor retraction distance: <4 mm (group 1), 4-8 mm (group 2), and ≥8 mm (group 3). EARR was quantified on panoramic radiographs using the relative root-to-crown ratio and the Malmgren index. Cephalometric variables were used to characterize tooth movement (translation vs tipping) and skeletal change. Multivariable linear regression was performed to identify the predictors of EARR.

EARR severity demonstrated a progressive increase with greater retraction (group 1 < group 2 < group 3) (P <0.001). Retraction distance, apical displacement, appliance type, and miniscrew anchorage were independent predictors of root-to-crown ratio reduction (P <0.05). In descriptive analyses of movement patterns, greater resorption was observed with translation than with tipping. No significant association was found between skeletal pattern (ANB and MP-SN) and EARR.

Greater retraction of maxillary incisor is associated with an increased EARR in adult patients with premolar extraction treatment, and translation movement may elevate the risk more than tipping. Retraction magnitude and movement type should be considered when planning treatment aimed at facial profile improvement to minimize iatrogenic root damage. Appliance choice may also influence the risk of root resorption.