Biomechanical evaluation of a 3D-printed activator-type mandibular advancement clear aligner: a comparative finite element analysis

Clear aligner (CA) technology has rapidly expanded to include mandibular advancement appliances, yet their biomechanics remain insufficiently understood. This study investigates the biomechanical effects of thermoformed and 3D-printed mandibular advancement CAs. A comprehensive skeletal Class II bimaxillary model was constructed, incorporating craniofacial sutures, temporomandibular joint disc, and the four primary muscles of mastication (six functional components). Finite element analysis (FEA) evaluated the skeletal and dental effects of two conventional thermoformed CA designs—thermoformed wing-type and thermoformed TB-type—alongside a novel 3D-printed activator-type CA. For preliminary clinical evaluation, four growing patients with skeletal Class II malocclusion were treated with the 3D-printed activator-type CA. Under the present finite element assumptions, posterior mandibular displacement after appliance insertion was predicted for all three CA designs, with smaller displacement in the TB-type and 3D-printed activator-type designs than in the wing-type design. Occlusal forces concentrated stress at the intermaxillary connector regions of CAs, predicted to cause undesired tooth movement patterns: wing-type appliances and TB-type were predicted to produce molar intrusion, buccal inclination and mandibular molar mesial tipping, while 3D-printed activator-type produced mandibular incisor labial tipping. To address these, optimizing wing morphology reduced molar intrusion and mandibular molar mesial tipping in wing-type appliances, while vertical overcorrection partly reduced the predicted molar intrusion in TB-type appliances. For the 3D-printed activator-type CA, increasing anterior-segment thickness partially reduced, but did not eliminate, the predicted labial tipping of mandibular anterior teeth. In the pilot case series, exploratory observations over a mean time of 3.00 ± 0.82 months to the predefined early treatment endpoint were directionally consistent with the FEA-predicted tendencies, including overjet reduction of 4.50 ± 2.05 mm, overbite reduction of 2.15 ± 0.84 mm, and near-complete establishment of a Class I molar relationship, all interpreted as exploratory clinical observations. Under the present finite element assumptions, all three mandibular advancement CA designs showed the potential to maintain mandibular advancement positioning, but each design also produced undesirable dental side effects in simulation. The activator-type CA showed design-dependent biomechanical characteristics that may be further optimized through the manufacturing flexibility enabled by direct 3D printing. However, these findings remain hypothesis-generating and require validation in larger prospective clinical studies.