RESUMO
INTRODUCTION: This study aimed to evaluate the effects of varying auxiliaries on tooth movement and stress distribution when maxillary central incisors were torqued 1° with a clear aligner through finite element analysis. METHODS: Three-dimensional finite element models, including maxillary alveolar bone, periodontal ligament, dentition, and clear aligner, were constructed. According to the auxiliaries designed on the maxillary central incisor, 5 models were created: (1) without auxiliaries (control model), (2) with the power ridge, (3) with the semi-ellipsoid attachment, (4) with the horizontal rectangular attachment, and (5) with the horizontal cylinder attachment. The tooth movement and periodontal ligament stress distribution after a palatal root torque of 1° were analyzed for each of the 5 models. RESULTS: With 1° torque predicted, the maxillary central incisor without auxiliaries showed a tendency of labial tipping, mesial tipping, and intrusion. The rotation center moved occlusally in the power ridge model. The labiolingual inclination variation increased in the semi-ellipsoid attachment model but decreased in the power ridge model. The maxillary central incisor is twisted in the distal direction in the power ridge model. The maxillary central incisor of the horizontal rectangular attachment and the horizontal cylinder attachment model behaved similarly to the control model. Periodontal stresses were concentrated in the cervical and apical areas. The maximum von Mises stresses were 11.6, 12.4, 3.81, 1.14, and 11.0 kPa in the 5 models. The semi-ellipsoid attachment model exhibited a more uniform stress distribution than the other models. CONCLUSIONS: Semi-ellipsoid attachment performed better efficacy on labiolingual inclination, and power ridge performed better efficacy on root control. However, a distal twist of maxillary incisors could be generated by the power ridge.
RESUMO
OBJECTIVES: The objectives of this retrospective clinical study were to evaluate the efficacy of clear aligners on upper-incisor torque control, with the expectation of providing guidance for clinics. MATERIALS AND METHODS: Pretreatment (T0) and posttreatment (T1) cone-beam computed tomography (CBCT) scans of 47 patients with a nonextraction treatment using clear aligners were obtained and 120 upper-incisors with torque ≥5° were selected. Voxel-based superimpositions were performed using Dolphin imaging software and achieved movements were then measured. Difference between achieved and predicted movement (DAPM) and the efficiency for upper-incisor torque were used to evaluate the torque control efficacy. RESULTS: The achieved torque movement with clear aligners was lower than predicted significantly, as the mean efficiency was 46.81±33.95%. Additionally, the achieved incisor movement of the crown and root differed significantly from the predicted movement, especially root movement. CONCLUSIONS: Clear aligners struggle to control upper-incisor torque, particularly root movement. In that case, overcorrection is necessary to prevent torque loss. CLINICAL RELEVANCE: Clear aligners remain a limitation on torque control and overcorrection should be considered.
