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Background/purpose: In orthodontic applications, NiTi wires are under continuous bending stress and exposed to fluctuations in temperature over long durations. The sensitivity of NiTi to temperature can have a considerable influence on its mechanical properties. This study investigated the effects of deflected NiTi wire, presented in stress-induced (detwinned) martensite microstructure, combined with thermal cycle on the microstructure and mechanical properties. Materials and methods: We tested four types of as-received orthodontic NiTi: (1) Nitinol Classic (3 M Unitek), (2) Sentalloy (Tomy), (3) 27 °C CuNiTi (Ormco) and (4) 40 °C CuNiTi (Ormco). Each group of specimens was subjected to three different testing conditions: (1) temperature fluctuations (5000 cycles) between 5 and 55 °C, (2) continuous three-point bending force and (3) combination of thermal cycling and bending stress. Results: The specimens that underwent thermocycling as well as loading exhibited a substantial narrowing in stress hysteresis, which may be attributed to crystallinity lower than that of as-received NiTi wires. Reduced crystallinity can manifest in a number of imperfections, such as dislocations and internal stress, as well as a less-organized structure. Micro X-ray diffraction (XRD) analysis revealed the existence of martensite phase in Sentalloy wires subject to thermal and stress conditions. Under loading conditions, stress-induced martensite of NiTi wires exposed to temperature fluctuations of 5–55 °C also induced cyclic changes in bending stress. In a simulated intra-oral environment, the stability of austenite↔martensite transformation decreased. Conclusion: This study determined that bending stress in conjunction with repeated temperature fluctuations can greatly affect the microstructure and mechanical properties of NiTi wires.

Background/purpose: The palate has become a popular site for the placement of temporary anchorage devices (TADs) owing to its bone quantity and quality. This study aimed to investigate total and cortical bone thicknesses in the whole palate as well as palatal width using a standard grid system and cone-bean computed tomography (CBCT) images. Materials and methods: The CBCT images of 43 samples were selected. The total bone and cortical bone thicknesses of the palate were surveyed on 64 points per patient. The palatal width was measured. The difference between the age and sex groups was analyzed. Results: The total palatal bone thickness in the adult group ranged from 9.85 ± 2.04 to 1.87 ± 0.79 mm. In the adolescent group, we found one-third of the incisor roots in the area 3 mm distal to the incisive foramen and 8 mm lateral to the mid-palatal suture. The cortical bone thickness in adults was significantly thicker in the posterior paramedian area than that in adolescents. Conclusion: The thickest vertical bone is located in the zone 3 mm distal to the incisive foramen and 4–8 mm lateral to the midpalate. The zone 6 mm posterior to the incisive foramen and 2–8 mm lateral to the midpalate exhibited optimal thickness and was away from the incisor roots. This region could be a safe zone for adolescent patients to place TADs. When TADs are to be inserted at the posterior palate, the 2-mm paramedian area should be the first region of choice.