Force comparison between Perfitalign 4D aligners and thermoformed aligners for mandibular incisor retraction: an in vitro study.

OBJECTIVES: To quantitatively compare the orthodontic forces exerted during mandibular incisor retraction by Perfitalign 4D aligners and thermoformed aligners over a 60-hour dynamic monitoring period, assess tooth movement trends, and investigate the effects of shape-memory properties on force characteristics. MATERIALS AND METHODS: Three groups of aligners were designed for mandibular incisor retraction. Group A aligners were fabricated using Erkodur foils (ERKODENT Erich Kopp) via thermoforming, while Groups B and C were fabricated using DCA resin (LuxCreo) via 3D printing. Groups A and B possessed a step size of 0.15 mm, whereas group C had a step size of 0.20 mm. Force data were monitored on a mandibular model for 60 h using a multi-axis transducer at 4-hour wear intervals. Groups B and C underwent thermal reactivation after every 12 h of cumulative wear, with recordings taken immediately before and after each activation. RESULTS: All groups exhibited high repeatability (ICC > 0.9). Perfitalign 4D aligners exhibited significant force recovery after thermal reactivation, though the recovery degree slightly decreased with repeated activations. Vertical forces markedly fluctuated but increased after thermal reactivation. Intergroup comparisons revealed significantly lower lingual forces in groups B/C compared to group A (P < 0.05). For mesiodistal and vertical directions, forces in groups B/C showed no significant reductions compared to group A. Residual stress analysis revealed rapid initial decay in group A, which decelerated subsequently, while groups B and C exhibited cyclic characteristics of "decay-thermal reactivation-induced recovery-decay". At 0 h, moment-to-force ratios (Mx/Fy) for mandibular incisors were significantly lower in groups B/C (- 3.3 to - 8.7 mm) than in group A (- 8.0 to - 10.7 mm). CONCLUSION: Perfitalign 4D aligners enable cyclic force recovery via shape-memory properties, independent of step size (0.15/0.20 mm). Despite larger steps, their lingual forces remained significantly lower than those of thermoformed aligners. A trend closer to bodily movement was observed with Perfitalign 4D aligners, although clinical studies are needed to validate movement efficiency and the long-term effects of elevated mesiodistal/vertical forces.