Effects of aging procedures on the molecular, biochemical, morphological, and mechanical properties of vacuum-formed retainers.

The influence of intraoral exposure procedures on the physical characteristics of thermoplastic vacuum-formed retainers (VFRs) is still unclear. The effects of thermoforming and intraoral use on the molecular, chemical, morphological, and mechanical properties of thermoplastic VFRs were investigated. VFRs with a 0.8-mm-thick thermoplastic PETG sheet acquired from 48 patients were investigated with two aging procedures, including vacuum forming and intraoral exposure, for 2-week and 6-month. Eight evaluating sites for thermoplastic VFRs were assessed with seven analytical techniques. LM, SEM, and AFM microscopic findings showed that the surface characteristics increased with increasing in vivo exposure time (a four-fold increase) and varied depending on the sites evaluated (an occlusal surface). Raman and EDX spectroscopic findings showed that aging procedures led to a significant change in the molecular composition of VFRs, leading to a decrease in the composition rate of carbon (C) and the presence of silicon (Si), phosphorus (P), and calcium (Ca). Compressive strength and tensile tests showed that aging procedures led to a significant increase (P<0.01) in ultimate tensile strength, elastic modulus, the stored energy at a 6-mm deflection (u6 mm), and the compressed load at a 3-mm deflection (σ3 mm). Thermoforming led to a smoother surface and no crystallization of PETG sheets. Intraoral exposure accelerated changes in surface morphology, tensile strength, and elastic modulus of VFRs. This change was site-specific and enhanced with an increase in intraoral exposure time. Therefore, thermoforming and in vivo oral exposure procedures led to the molecular, morphological, and mechanical properties of thermoplastic VFRs.

Anterior Decompensation Using Segmental Osteotomy for Patients With Mandibular Asymmetry.

To obtain sufficient correction of facial asymmetry by orthognathic surgery, precise and sufficient dental decompensation during preoperative orthodontic treatment is needed. Facial asymmetry often includes complicated 3-dimensional dental compensation in the anterior alveolar region, which can limit the treatment options and lengthen the treatment time. As an alternative, anterior decompensation using segmental osteotomy (ADSO) with the patient under local anesthesia could be a reasonable approach, as it represents an effective, selective, and relatively safe method for correcting lower anterior disharmony during preoperative treatment. Furthermore, ADSO can quickly eliminate anterior compensation and move the teeth to their proper positions such that the basal bone supports them beyond the anatomic limits. Precise evaluation and diagnosis using data obtained from 3-dimensional computed tomography should be performed for accurate ADSO. The present report describes the versatile use of ADSO for 2 patients with different types of severe facial asymmetry. In the first case, ADSO was performed to correct the anterior dentoalveolar yaw and in the second, to change the vertical positioning and inclination of the anterior teeth. In both cases, sufficient elimination of anterior compensation using ADSO guaranteed successful improvement of the facial asymmetry and stabilization of occlusion after orthognathic surgery. The use of ADSO during preoperative treatment can quickly and effectively correct lower anterior disharmony and facilitate surgical correction of facial asymmetry.