Multibracket appliance therapy based on edgewise appliances by Dr. E. Angle have evolved in terms of thier base materials, design, and application method over the past 100 years. For orthodontic therapy using multibracket appliances, bracket bonding adhesives and elastic ligutures containing fluoride have been used in order to prevent enamel demineralization, although the actual effects in clinical situations are unknown. In orthodontic practice, the concept of skeletal anchorage using miniscrews and miniplates has been accepted worldwide. Recently, the clear aligners, fabricated by a series of 3D-printed setup models and thermoplastic materials with vacuum forming, have become very popular. Moreover, custom-made orthodontic brackets and wires for individual patients, fabricated by a scanned 3D model and cone beam computed tomography (CBCT) data, have been developed.

On diagnosis by dental X-ray, it was necessary to observe the mandible and teeth in three dimensions, but there were problems such as the radiation dose, resolution, and size of the equipment. These matters were resolved by a small radiation field and high-resolution dental cone-beam CT (CBCT). In orthodontic treatment, a wider field of view and lower radiation dose were required. However, expansion of the field of view and lower exposure show a reciprocal relationship. Even in cases of CBCT under low radiation-dose conditions, the dose is 10 times that of normal cephalography, so care must be taken. A hybrid device with CBCT and panoramic radiography was developed. It has become possible to cover all the imaging methods required for orthodontic treatment with one device. Integration with other digital equipment, selection of lower radiation dose conditions, and merging of three-dimensional image information are considered the most important.

The degradation of mechanical properties of Ni-Ti superelastic orthodontic alloy wire induced by fluoride in the oral cavity is reviewed here from the viewpoint of hydrogen absorption accompanied by corrosion. The alloy is subjected to general corrosion and absorbs a large amount of hydrogen in acid fluoride solutions in a short time, thereby causing the degradation of mechanical properties, i.e., hydrogen embrittlement. In neutral fluoride solutions, active path corrosion occurs before hydrogen embrittlement. The degradation markedly depends on environmental factors, such as the fluoride content and pH, and material factors, such as hydrogen states and martensite. Hydrogen embrittlement of the alloy is essentially dominated by the formation and accumulation of damage induced by dynamic interactions between stress-induced martensite transformation and hydrogen. One of the countermeasures to inhibit hydrogen absorption in fluoride solutions is to shift the noble direction of the corrosion potential by adding a small amount of hydrogen peroxide.

Research conduced over the past ten years (from 2010 to 2019) on orthodontics that was reported in academic meetings of the Japanese Society for Dental Materials and Devices (JSDMD), the Journal of JSDMD, and Dental Materials Journal was investigated. In this review, I would like to briefly discuss the results of these investigations and future expectations regarding the innovation of materials in orthodontics.

The study examined the effect of storage conditions on the shear strength and shear elastic modulus of dual-cured self-adhesive resin cements. Three commercially available dual-cured self-adhesive resin cements ［G-CEM ONE (GC), BeautiCem SA (Shofu), and RelyX Unicem2 Clicker (3M Japan)］ were used in the study. Each specimen was immersed in deionized water (Wet), stored under dry conditions with silica gel (Dry), or subjected to thermal cycling up to 10,000 cycles (TC). The shear strength of the specimens was also measured one hour after the start of cement mixing as the baseline strength. In addition, specimens with or without light irradiation were prepared for each storage condition. The shear strengths were determined using the punch tool in the universal testing machine (n＝10 for each condition). The shear strengths of specimens with light irradiation were greater than those without light irradiation. A trend was found whereby Dry specimens showed weaker strength than Wet and TC specimens. The shear elastic moduli of Dry specimens tended to be greater than those of Wet and TC. It was suggested that the specimen storage conditions affected both the shear strength and shear elastic modulus of the dual-cured self-adhesive resin cements examined.