Greater Incisor Retraction Increases Risk of Root Resorption in patients undergoing premolar extraction: Study

A new study published in the American Journal of Orthodontics and Dentofacial Orthopedics showed that greater retraction of the upper (maxillary) incisors is linked to an increased risk of external apical root resorption (EARR) in adult patients after premolar extraction therapy.

Premolar extractions are often required during orthodontic therapy for adults in order to decrease excessive bimaxillary protrusion or alleviate severe crowding. In order to close newly formed voids and attain the ideal facial profile, anterior teeth undergo substantial incisor retraction after these extractions. However, orthodontically induced inflammatory root resorption (OIIRR), a harmful and permanent iatrogenic consequence, is closely linked to this crucial biomechanical stage.

Both the amount of retraction and the particular orthodontic movement pattern used have a direct impact on the severity of this apical root shortening. In contrast to regulated body translations, current clinical evidence indicates that prolonged, long-distance retractions and uncontrolled tipping motions result in increased stress concentrations at the root apex. Optimizing adult orthodontic results requires a thorough understanding of how these mechanical factors determine the likelihood of root resorption. In adult patients after premolar extraction, this study assessed the relationship between incisor retraction magnitude, movement pattern, and EARR.

Three groups were created based on the maxillary incisor retraction distance: <4 mm (group 1), 4-8 mm (group 2), and ≥8 mm (group 3) for a retrospective sample of 180 people (mean age, 24.73 ± 4.83 years) who had at least two maxillary premolar extractions. The Malmgren index and the relative root-to-crown ratio were used to measure EARR using panoramic radiographs. Skeletal change and tooth movement (translation vs. tipping) were described using cephalometric variables. The determinants of EARR were found using multivariable linear regression.

With increased retraction, EARR severity showed a gradual rise (group 1 < group 2 < group 3) (P <0.001). Root-to-crown ratio decrease was independently predicted by retraction distance, apical displacement, appliance type, and miniscrew anchoring (P <0.05). Translation was shown to have more resorption than tipping in descriptive assessments of movement patterns. EARR and skeletal pattern (ANB and MP-SN) did not significantly correlate. Overall, in adult patients after premolar extraction therapy, greater retraction of the maxillary incisor is linked to a higher EARR. 

Source:

Zhang, H., Jiang, Q., Wang, Y., Bajestan, M., Li, J., & Li, H. (2026). Effect of incisor retraction magnitude and movement pattern on root resorption after premolar extraction in adults. American Journal of Orthodontics and Dentofacial Orthopedics : Official Publication of the American Association of Orthodontists, Its Constituent Societies, and the American Board of Orthodontics. https://doi.org/10.1016/j.ajodo.2026.03.018