OBJECTIVETo measure the orthodontic forces exerted on the upper right central incisor with the increase of the distance of tooth movement and the thickness of the aligner.

METHODSThe labial movement of upper right central incisor at various distances (0.3, 0.6, 0.9, 1.2, 1.5, 1.8 mm) was designed and the stereolithography model (2 times bigger than the original model) was created with 3-D scanning and tomography output. These models were used to fabricate the aligners with different thicknesses (0.8, 1.0, 1.5 and 2.0 mm) of the thermoplastic materials (6 samples for various distances of tooth movement and thicknesses). Orthodontic forces exerted on the upper right central incisor were measured with the micro-stress sensor measurement system.

RESULTSThe orthodontic forces increased with the increase of the thickness of the aligner at the same distance of tooth movement (P < 0.05). The orthodontic force was (1.237 ± 0.082), (1.543 ± 0.059), (3.602 ± 0.102), (6.734 ± 0.063) N when the labial movement of upper right central incisor was 0.3 mm with the aligner of 0.8, 1.0, 1.5, 2.0 mm. The orthodontic forces also increased with the increase of the distance of the tooth movement at the same thickness of the aligner(P < 0.05). The orthodontic force of the aligner of 0.8 mm were (1.354 ± 0.039), (1.288 ± 0.037), (1.479 ± 0.031), (1.799 ± 0.039) N when the upper right central tooth labial movement at 0.6, 0.9, 1.2, 1.5 mm.

CONCLUSIONSThe orthodontic forces increased with the increase of the distance of tooth movement and the thickness of the aligner.