Biomechanical effects of aligner trimline design and intrusion protocol on mandibular anterior teeth: a finite element study.

OBJECTIVE: This study employed finite element analysis to evaluate the biomechanical effects of different aligner trimline designs (scalloped vs. high trimline) and intrusion methods (sequential vs. simultaneous) during mandibular anterior teeth intrusion. METHODS: A finite element analysis model was developed to evaluate stress distribution and displacement patterns. Two trimline designs (scalloped and high trimline) and two intrusion protocols (sequential and simultaneous) were compared. Parameters measured included initial tooth displacement, root stress, periodontal ligament (PDL) stress, and stress concentration patterns. RESULTS: Finite element analysis demonstrated that sequential intrusion with scalloped trimline aligners produced greater initial displacement (0.062-0.108 mm in central incisors) and a more favorable stress distribution compared to simultaneous intrusion. The scalloped design showed superior performance by generating 13-40% lower root stress (0.053-0.060 MPa) compared to high trimline aligners. Stress concentration patterns differed notably between intrusion methods. Sequential intrusion localized stress at the lingual cervical third of the central incisors, whereas simultaneous intrusion shifted peak stress to the canines and increased PDL stress three-fold (0.005-0.006 MPa). Posterior anchorage control was also better preserved with sequential intrusion protocols. CONCLUSION: This study confirms that sequential intrusion using scalloped trimline aligners is biomechanically optimal for mandibular anterior intrusion. This method provides greater displacement efficiency and reduced stress on dental structures. The findings offer clinically relevant evidence supporting the preference for scalloped trimline designs over high trimlines. Moreover, sequential protocols are recommended over simultaneous intrusion in managing deep overbites with clear aligners. These results enable clinicians to make informed decisions regarding intrusion mechanics, potentially enhancing treatment outcomes and minimizing adverse effects.