Biomechanical Analysis of En-Masse Versus Alternate Anterior Retraction for Anterior Teeth With Clear Aligners: A Three-Dimensional Finite Element Study.

OBJECTIVE

This study aimed to investigate the biomechanical effects of en-masse versus alternate retraction during aligner treatment in premolar-extraction cases.

METHODS

Four finite element analysis models of maxillary first premolar extraction were created: Group I (en-masse retraction), Group II (canine distalization), Group III (incisor retraction) and Group IV (alternate retraction). Various aligner torque compensations (0°, 1°, 2°, 3°) were applied on the anterior teeth. Tooth displacement tendencies, labiolingual inclination, mesiodistal tipping and stresses on the periodontal ligaments were analysed.

RESULTS

Group I and IV showed comparable retraction (0.13 vs. 0.14 mm) and lingual inclination (0.48° vs. 0.49°) of central incisors, while Group III exhibited greater retraction (0.19 mm) and lingual inclination (0.68°). Group II demonstrated slight labial inclination of incisors and significant distal movement of canine (0.25 mm). Group I, II and IV exhibited similar incisor extrusion (0.06 mm), whereas Group IV resulted in more canine extrusion compared to other groups. The sub-steps of alternate retraction led to less mesial tipping of posterior teeth; however, overall alternate retraction exhibited more mesial tipping of posterior teeth compared to en-masse retraction. Bodily movement of the central incisor was achieved with a torque compensation of 1.6° in both alternate and en-masse retraction and 2.2° for incisor retraction.

CONCLUSION

The sub-steps of alternate retraction showed superior anterior retraction and posterior anchorage protection. However, overall alternate retraction demonstrated similar retraction and vertical control of incisors compared to en-masse retraction; but provided weaker vertical control of canines and less protection for posterior anchorage teeth. Further clinical research is required to confirm these findings.