Purpose: Rhodium-plated orthodontic wires are utilized for esthetic purposes. However, the decline in the corrosion resistance of rhodium (Rh)-plated nickel-titanium (Ni-Ti) wires has been a concern. In this study, Rh-plated nickel (Ni) wires and Ni-Ti orthodontic wires were prepared via electroplating, and the microstructures of the plated layers were investigated.Methods: The surface microstructure and thickness of the plated layers were analyzed using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). The corrosion resistance was tested by immersion into an acidic solution in addition to applying plated and non-plated wires to the oral cavity or subcutaneous tissues of animals. Ni dissolution and distribution into the contacted oral mucosa and implanted subcutaneous tissues were visualized using synchrotron radiated X-ray fluorescence (SR-XRF).Results: In Ni wires, the 1-2 µm plated rhodium layer was formed in contact with the substrate. This layer suppressed the corrosion of the Ni wire in acidic solutions. However, in Ni-Ti wires, defects in the plated layer were observed and subsequently, Ni and Ti dissolution in the acidic solution was enhanced because of galvanic corrosion. In Ni-Ti wires, Ni and Ti could not be detected in the tissues because of their low contents.Conclusion: The plated Rh layer was homogeneously formed in contact with the substrate in Ni wire compared to the plated layer on Ni-Ti wires. For the clinical use in orthodontic treatment, it might be suggested that Rh-plated Ni-Ti wires should be more stable in oral cavity without ion dissolution, however, the effect of dissolved Ni and Ti from Rh-plated Ni-Ti wires would not be a concern due to their extremely lower contents.

Purpose: A radiopaque self-polymerizing adhesive resin was prepared by incorporating bismuth subcarbonate-poly(methyl methacrylate) prepolymerized composite (BS-PMMA) into an acrylic resin. The purpose of this study was to evaluate the radiopacity of prepared resins.Methods: As a radiopaque component, a composite containing 50% bismuth subcarbonate was used, and other metal compounds were adopted as controls. They were added to finely pulverized PMMA. Specimens were prepared from the powders, methyl methacrylate (MMA) monomer with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) and tri-n-butylborane derivative (TBB) by mixing. Radiographs of the specimens were taken together with tooth slices and aluminum step wedges. The density of the specimens was determined with a densitometer and was expressed in terms of the equivalent thickness of aluminum per 2.0 mm unit thickness of specimen. Results: The radiopacity value of BS-PMMA-based specimen was 3.7 mm Al / 2.0 mm specimen, which was nearly the same value as enamel (3.7) and exceeded the values of dentin (2.0). Conclusion: BS-PMMA composite and bismuth compounds are useful as a radiopaque additive for the acrylic resin.

Purpose: To explore the relationship between tooth sizes and configurations within a single dentition, the mesiodistal and buccolingual crown diameters were measured using a dentition model, and analyzed using statistical methods.Methods: A total of 96 maxillary dental casts were used. The mesiodistal crown diameter, buccolingual crown diameter, and crown area from the maxillary central incisor to the maxillary second molar were determined. The mean, standard deviation, median, coefficient of variation, and Spearman's rank correlation coefficients were determined. Hierarchical cluster analysis was performed to form clusters of maxillary dentitions with similar characteristics. Principal component analysis was performed to explore the characteristics of all 96 cases and each cluster. Furthermore, whether there was a difference between the clusters was asked.Results: Maxillary lateral incisor had a large coefficient of variation and did not show a high correlation coefficient with any of the other teeth. The maxillary dentition was classified into seven groups according to the size of the configuration teeth and the size of the teeth between the tooth types. Furthermore, among the seven groups, there was a group in which the size of the teeth constituting the dentition were in harmony, and a group in which the size of one tooth or tooth type tended to increase while the size of the other tooth or tooth type tended to decrease.Conclusion: The size of teeth in one maxillary dentition is observed within the same tooth type or between different tooth types, suggesting that they influence each other.