Forces and moments delivered by novel, thinner PET-G aligners during labiopalatal bodily movement of a maxillary central incisor: An in vitro study

Abstract

Objective: To evaluate whether overloading of teeth can be avoided by utilizing aligners with reduced thicknesses of 0.4 mm or 0.3 mm. Materials and Methods: The experimental setup included an acrylic maxillary jaw model with tooth 11 separated and fixed via a 3-D force-moment transducer to a hexapod for experimental movement. Aligners tested were fabricated on duplicate stone models using commercially available polyethylene terephthalate glycol (PET-G) foils with thicknesses between 0.5 and 0.75 mm, and novel 0.4-mm-and 0.3-mm-thick foils. With the test aligner seated, 11 was bodily displaced in a labiopalatal direction in the range of 60.25 mm while all six force-and-moment components exerted on this tooth were registered. Results: With the thinnest commercially available 0.5-mm aligner, median forces of À7.89 N and 8.37 N were measured for the maximum 0.25-mm movement of 11 in a labial and palatal direction, respectively. In comparison, force values were 35% and 71% lower for the novel aligners with a thickness of 0.4 mm and 0.3 mm, respectively. Conclusions: Novel ''leveling'' aligners with reduced thickness may reduce overloading of individual teeth during aligner therapy. Due to form instability of 0.3-mm aligners, we suggest a novel sequence of 0.4-0.5-0.75 mm for aligner systems using several foil thicknesses for load graduation within single setup steps. This would combine low stiffness of the initial aligner and relatively constant load increases throughout the treatment. (Angle Orthod. 2016;86:883-890)

Forces and moments generated by aligner‐type appliances for orthodontic tooth movement: A systematic review and meta‐analysis

“…During mesiodistal rotation, forces were exceeding the suggested load of 20 Nmm . Similar findings were confirmed for intrusion, tipping and bodily movement …”

“…The thickness of plastic foil used for thermoforming PET‐G aligners ranged from 0.3 to 1 mm. The forces generated by the thinnest commercially available aligners of 0.5 mm resulted in significant overloading of the periodontal structures . When PET‐G aligners of reduced thickness, namely of 0.4 and 0.3 mm were used, the aforementioned forces were decreased by 35% and 71%, respectively .…”

“…The forces generated by the thinnest commercially available aligners of 0.5 mm resulted in significant overloading of the periodontal structures . When PET‐G aligners of reduced thickness, namely of 0.4 and 0.3 mm were used, the aforementioned forces were decreased by 35% and 71%, respectively . It has been reported that aligner thickness of 0.3 mm, may reduce rotational stiffness by 76% .…”

“…It has been reported that aligner thickness of 0.3 mm, may reduce rotational stiffness by 76% . Despite the fact that 0.3 mm PET‐G aligners seem to exert ideal forces, they are considered unsuitable for clinical use due to deformation . Thus, a sequence of aligners including 0.4, 0.5, 0.75 mm has been proposed in order to achieve low initial stiffness combined with a steady load.…”

“…Despite the fact that 0.3 mm PET‐G aligners seem to exert ideal forces, they are considered unsuitable for clinical use due to deformation . Thus, a sequence of aligners including 0.4, 0.5, 0.75 mm has been proposed in order to achieve low initial stiffness combined with a steady load. As for 0.625 and 0.75 mm PET‐G foils, findings indicate that both presented similar mechanical behaviour with respect to rotational moments during mandibular canine and maxillary central incisor rotation as well as labio‐lingual tipping and bodily movement .…”