Pattern of change in force and moment according to amounts of labial tipping and material types of clear aligner: In vitro experiment with a six-axis mechanical sensor apparatus.

Objective: To investigate the pattern of change in force and moment according to the amounts of labial tipping and the material types of clear aligners (CA).

Methods: A 3D-printed maxillary typodont system, including crown, root, and periodontal ligament space, was constructed. Six groups were established based on the amount of labial tipping of #12 (0.3 mm and 0.6 mm), and the material types (Zendura [thermoplastic, one-layer, 0.75 mm], Trioclear [thermoplastic, three-layer, 0.5 mm], and Graphy TA-28 [direct printing, 0.5 mm]) (n = 6/group). A six-axis mechanical sensor apparatus was connected to the roots. Force and moment were measured after seating the CA in a 37°C water bath.

Results: When comparing 0.3 mm and 0.6 mm tipping, #12 showed an increase in labial inclination moment (Lab-inclination moment) in Zendura (P < 0.05); a decrease in labial force and an increase in Lab-inclination-moment in Trioclear (P < 0.05, P < 0.01); while a lingual force and Lab-inclination moment without significant change in Graphy (all P > 0.05). For 0.3 mm tipping, the amounts of labio-lingual forces and Lab-inclination moment did not differ among the three materials (all P > 0.05). However, at 0.6 mm tipping, Zendura exerted a greater labial force than Trioclear, while Graphy produced a lingual force (P < 0.01). Zendura and Trioclear generated a stronger Lab-inclination moment compared to Graphy (P < 0.01). Despite displaying unexpected force and moment directions, Graphy consistently exhibited the lowest absolute values among the groups.

Conclusions: Clinicians should select the appropriate aligner material based on the specific biomechanical requirements to prevent unexpected forces and moments.