Natsuki Sano

Electric current induced in teeth by electromagnetic fields from electric toothbrushes and curing lights

Abstract Purpose The purpose of this study was to examine the electric current induced in teeth and tooth-bonded brackets by electromagnetic fields from electric toothbrushes and the curing lights used for photo-activating light-cured resins. Materials and methods Curing lights-generated low-frequency magnetic fields (1–2000 Hz) were measured with a spectrum analyzer. Temperature changes induced in the enamel and pulpal dentin surface of extracted upper premolar teeth (with or without a stainless steel or zirconia bracket) by electric toothbrushes and curing lights were estimated using an infrared thermometer. Electric current induced in these extracted teeth by electric appliances was estimated using a digital multimeter. Results Curing lights generated low-frequency magnetic fields. Irradiation of the tooth surface by curing lights elevated the temperature of the enamel and pulpal dentin surfaces, but there were no differences between curing lights. About electric current induced in extracted teeth (with or without a bracket) by electric toothbrushes and curing lights, the highest current was induced in teeth to which a zirconia bracket was bonded, whereas the lowest current was in unmodified teeth. Intermediate currents were generated in teeth bonded to stainless steel brackets. Conclusion The low-frequency magnetic fields induced by electric toothbrushes and light curing units induce electric current in tooth tissue, irrespective of whether these teeth are bonded to stainless steel or zirconia brackets.

Development of a compact induction-heated autoclave with a dramatically shortened sterilization cycle in orthodontic clinics

Abstract Purpose This article reviews the development of a compact autoclave with a dramatically shortened running time that did not compromise the quality of its sterilization properties including orthodontic appliances, orthodontic mini-implants (anchor screws), instruments and other dental items. Materials and methods Induction heating (IH) mechanisms were employed to produce a more compact machine and shorten sterilization sufficiently so that it could be used at chair-side. Intravessel pressure was estimated by a pressure gauge mounted in the lid of the sterilization vessel. A digital multimeter with a K thermocouple set in the lid of the vessel was used to monitor this intravessel temperature. The level of sterilization achieved with a conventional autoclave and an IH autoclave was quantified by the biological indicator containing vials of Geobacillus stearothermophilus bacteria in growth media. Results We found that the minimum effective sterilizing time after reaching the operating pressure was 25, 15, 12.5, 10 and 5 min at 0.20, 0.25, 0.30, 0.35 and 0.50 MPa with a compact IH mechanism, respectively. Combining the values with (i) the time taken to achieve the operating pressure and (ii) ∼2–3 min for cooling and removal of sterilized items gave the total sterilization cycle time, which were, on average, 30, 22, 19, 18 and 13 min at 0.20, 0.25, 0.30, 0.35 and 0.50 MPa, respectively. Conclusions IH mechanism is useful for compact and speedy autoclave, which reduce total sterilisation time by 40–80% compared with conventional autoclaves.

Modification of metallic materials for a white appearance without coating and plating

Abstract Purpose The purpose of this study was to develop white-colored metals for metal injection moldings, and white-colored surface preparation for metals to satisfy the esthetic demands of patients. Materials and methods Two methods for white coloration of metals were developed for two kinds of metals. For white-colored silver metal, silver powder was baked at 700 °C for 15 min with or without the alumina plate. For white-colored surface preparation, titanium wire, orthodontic brackets and dental implants were baked at 1000 °C for 15 min. Two kinds of white-colored specimens were used for evaluation of coloration, mechanical strength and the components. Results Treated silver metal was visually white, and closed to the color of white porcelain panel evaluated by a colorimeter. From the results of load-deflection tests, the mechanical strength of white-colored silver metal was almost same as that of non-treated one. Surface prepared titanium objects were also visually white, and closed to the color of white porcelain, and thickness of white color layer was 10–50 μm. Load-deflection tests revealed that white-colored titanium metal was fragile compared to non-treated one. The component of white-colored silver metal was approximately 100% Ag. On the other side, the surface component of white-colored titanium metal was titanium dioxide. Conclusion Two methods of white coloration for metals were developed. One method is use of injection molding especially for prevention of crushing of ceramics when combined with them. The other is a white-colored surface preparation for dental appliances, including orthodontic appliances.