The Training and Safety Lecture Committee of the Japan Society for Laser Dentistry held the 4th educational seminar at the Health Sciences University of Hokkaido in 2016. This seminar was aimed at the first undergraduate training of the academic society, and combined lectures and hands-on training for the 5th grade of the dental school of the university. After completing the seminar, we conducted a questionnaire survey on the degree of understanding of the students and their interest in the laser. Forty-nine valid answers were collected （collection rate 100%）. The degree of comprehension of both lectures and practical training was 90% or more, and about 90% of students answered that they were interested in the clinical application of lasers in the future. Based on the results, the seminar was satisfying for the students, suggesting the effectiveness of undergraduate training in laser dentistry.
With the ultimate aim of newly developing an optimal dentin bonding system to Er:YAG-lased dentin, the adhesion-promoting effects of priming with hydrophilic monomers on the bonding performance of the resin-modified glass-ionomer adhesive system （RMGI） to laser-affected dentin were investigated. It was revealed that priming with 4-MET and HEMA following acid-conditioning with 10％ citric acid＋2％ ferric chloride solution might be very effective for improving the bond strength of RMGI to Er:YAG-lased dentin. This work was supported by JSPS KAKENHI Grant Number JP15K11138.
Objective; The aim of the present study was to investigate the effect of tip insertion depth on the extrusion of irrigating solution during Er:YAG laser-activated irrigation （LAI） in comparison with passive ultrasonic irrigation （PUI） and conventional syringe irrigation （SI）. Methodology; A root of an extracted human anterior tooth shaped to a working length of 15mm with apical size #40 and 0.06 taper was used. The root canal was then irrigated with water for 5 seconds with LAI, PUI or SI. In the LAI group, an Er:YAG laser unit （Erwin AdvErL, Morita） with a contact tip （R200T） was used at a power setting of 70mJ, 10pps. In the PUI group, an ultrasonic device （Piezon Master400, EMS） with a #20 file was used at the highest power setting. In the SI group, the canal was irrigated manually with a syringe and a 27G flat needle and 0.3ml of the irrigant. The tip insertion depth was set at 2, 5, or 10mm short of the working length in each group. Each irrigation was performed repeatedly seven times. To measure the actual volume of extruded irrigant, the root-end was covered with a piece of aluminum foil to collect the extruded irrigant, and the weight change of the aluminum foil was calculated using an electric balance （AE240, Mettler Toledo, Switzerland）. Data were analyzed by using one-way ANOVA and Games-Howell test at a significance level of p＝0.05. Results; Shorter insertion depth of the laser tip during LAI generated significantly less apical irrigant extrusion （p＜0.05）. When the tip was positioned at 2 and 5mm short of the working length, the mean volume of extruded irrigant solution was PUI＜LAI＜SI （p＜0.05）. When the tip was positioned at 10mm short of the working length, the mean volume of extruded irrigant solution was LAI＝PUI＜SI （p＜0.05）. Conclusions; Under the conditions of this study, the volume of extruded irrigant during LAI was significantly less than that during SI, and showed significant decreases with the decrease of tip insertion depth. When the insertion depth was set at 10mm short of the working length, the volume of extruded irrigant during LAI was similar to that during PUI.