In order to apply laser to endodontics, it is necessary to use a narrow fiber to irradiate the laser in the canal. Recently, a new type of optical fiber of diameter 150 micrometers has been developed. This size is comparable with the tip diameter of a #25 file. Accordingly, the fiber is supposed to reach the apical portion of a fine canal. The objective of this study was to investigate the application of 150-micrometer-diameter fiber to endodontics. Cantilever bending testing of the fiber and a stainless steel K file was performed to measure the bending load at 2.4 mm deflection in the loading process. Then, dentin plates were prepared from a bovine tooth crown. The surfaces of the plates were irradiated by a Nd: YAG laser with 5% TiO2 solution for 5 seconds. The laser energy was 200, 300 and 350mJ with a pulse frequency of 20 pps. The fiber was moved parallel to the dentin surface at a speed of 1mm/s during lasing. Then, the irradiated surfaces were observed by digital microscopy and confocal laser microscopy. The width and depth of the laser irradiated surfaces were evaluated (n=4). Moreover, scanning electron microscopic observation was performed. Carbonization of the irradiated dentin surfaces was not observed by digital microscopy. The widths of 200, 300, and 350mJ laser-irradiated surfaces were 77, 227, and 193 micrometers, respectively. The depths of 200, 300, and 350 mJ laser-irradiated surfaces were 11, 32, and 35 micrometers, respectively. Melted dentin was observed by scanning electron microscopy. In clinical settings, this fine fiber has a possibility to enlarge the narrow apical portion of the canal. Our results suggest that the fiber tested might be useful for root canal preparation.
The purpose of this study was to evaluate the effects of CO2 laser irradiation on penetration of constricted canals. Root canals of human extracted teeth were opened by the usual method, and penetration of constricted canals to the apical foramen was performed with #15k-files. Fifteen canals, including eight incisors and seven premolars that could not be penetrated, were selected as the constricted specimens (n=15). These specimens were irradiated by a CO2 laser (E16, 9W, 0.5sec). After the irradiation, penetration to the apical foramen with #15 k-files was attempted. After the laser irradiation, the rate of penetration to the apical foramen was evaluated. The root surface temperature was also measured by an infrared thermometer before, during, and after the irradiation. Ten canals (67%) could be penetrated to the apical foramen. The root surface temperature increased during the irradiation. The CO2 laser irradiation could penetrate to the apical foramen; the mean rate of the penetration distance was 0.78±0.39mm (n=15). This study suggested that CO2 laser irradiation can penetrate a constricted root canal to the apical foramen.
Soldering has been the most common method to join metallic pieces for a long time. Problems in soldering are use of an investment material and heat, as well as a flax which has potential risk of corrosion and allergy. Laser welding can be performed directly on a working model and produces accurate fitting of a dental prosthesis. Laser welding enables saving of working time and cost for laboratory work. Also, this technique is considered essential to increase the use of titanium, which has high biocompatibility in the dental field. Thus, laser welding has many merits in prosthetic dentistry. Regarding the history of laser welding in the dental field, in 1968, Dr. Gordon et al. of the United States conducted the first experiment on laser welding of dental alloys using a Nd: Glass laser. In Japan, in 1971, the author started basic studies on laser welding using a Nd: YAG laser, and further the author has performed various clinical applications. In 1978, Dr. Van Benthem et al. of Germany started laser welding using a Nd: YAG laser, and he has reported many results. A dental laser welder was developed in Germany about ten years ago, and since then approximately 350 laser welders have been imported into Japan from Germany, and they are currently used in the dental clinics and laboratories. In this article, the author reports the transition and clinical progress of laser welding in dentistry through 34 years.