Pattern of change in force and moment according to amounts of labial tipping and material types of clear aligner: 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 ( < 0.05); a decrease in labial force and an increase in Lab-inclination-moment in Trioclear ( < 0.05, P < 0.01); while a lingual force and Lab-inclination moment without significant change in Graphy (all > 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 > 0.05). However, at 0.6 mm tipping, Zendura exerted a greater labial force than Trioclear, while Graphy produced a lingual force ( < 0.01). Zendura and Trioclear generated a stronger Lab-inclination moment compared to Graphy ( < 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.