Possibility of root canal preparation by Er:YAG laser.

OBJECTIVE: The purpose of this study was to evaluate the cutting efficiency and morphological changes of root dentin irradiated by an Er:YAG laser in vitro. STUDY DESIGN: Thirty-two root dentin blocks were divided into 4 groups. The irradiation conditions were as follows: Group 1 (G1): 30 mJ, 10 pps, 1 mm/s, 20 times; Group 2 (G2): 30 mJ, 10 pps, 1 mm/s, 10 times; Group 3 (G3): 30 mJ, 10 pps, 2 mm/s, 20 times; and Group 4 (G4): 30 mJ, 25 pps, 1 mm/s, 10 times. After being irradiated, the blocks were observed by mu-CT and their width and depth were measured. Moreover, SEM observations were performed. RESULTS: There were significant differences between G1 and G2, between G1 and G3, between G2 and G4, and between G3 and G4 for both width and depth (P < .05). The SEM observations showed that no smear layer was present on the surface of any of the samples. CONCLUSION: These results show that the Er:YAG laser operated under the conditions used in this study is an effective tool for root canal preparation.

Evaluation of cariogenic bacteria.

OBJECTIVES: The evaluation of Mutans streptococci (MS) is one of the index for caries risk. Dentocult(TM) and CRT(TM) are commercial kits to detect and evaluate MS, conveniently. However, the evaluation of MS has also been carried out simply using an instruction manual. But the instruction manual is not easy to use for evaluation of MS. The aim of this study was to examine the utility of modified Mitis-Salivalius Bacitracin (MSB) agar medium compared with MSB agar medium and commercial kits, and to establish a convenient kit (mMSB-kit) using modified MSB agar. METHODS: The MS in stimulated saliva from 27 subjects were detected by MSB, modified MSB agar medium and commercial kits. Laboratory and clinically isolated strains of MS were similarly evaluated. The ratios of MS in detected bacteria were compared by ELISA. RESULTS: The scores using an mMSB-kit on the basis of modified MSB agar medium were tabulated. Saliva samples showed different levels of MS between culture methods and the commercial kit. Some samples which were full of MS were not detected by the commercial kit. The detection of MS by modified MSB agar medium and mMSB-kit were significantly higher when compared with MSB agar medium,CRT(TM), (P< .01) and Dentocult SM(TM) (P<.05). CONCLUSION: The sensitivity for detection of MS is higher for modified MSB agar medium when compared with MSB agar medium. The mMSB-kit can be used simply, and can be an important contributor for the evaluation of MS as a caries risk factor.

Effects of intracanal carbon dioxide laser irradiation on cultured human fibroblasts.

OBJECTIVE: The purpose of this study was to evaluate, under various conditions, the damage that might occur to viable cells after CO2 laser irradiation of the root canal. STUDY DESIGN: A laser tip was placed within the root canal of extracted human teeth that were positioned above cultured fibroblasts (NB cells), and then irradiation was applied. The irradiation modes used were either pulse (40 pps) or super-pulse (151 pps). The laser energy was set at 32 J in both modes, and the tip of the laser beam was positioned to a point 2 mm from the fibroblasts. RESULTS: When the pulse mode irradiation was applied, there was significant difference (P < .05) in the percentage of viable cells between teeth with closed apical foramen (1-mm wall between root canal and root apex) and the #15 group (No. 15 K-file used), #30 group (No. 30 K-file), or #50 group (No. 50 K-file). The difference between the #30 group and the #50 group (P < .05) was also significant. The larger the diameter of the apical foramen became, the lower was the percentage of viable cells. CONCLUSION: If a CO2 laser irradiates a root canal system enlarged to within 1 mm of the root canal length, little damage to the periapical tissues would be expected to occur.