The bactericidal effects of an Nd:YAG laser by using a reaction mediator of TiO₂ are described. The laser beam was irradiated to the TiO₂ suspension through a quartz optical fiber, and the generated induced dynamic stress was observed in the TiO₂ particles which were absorbed by the laser beam. Our previous study demonstrated the bactericidal effect of an Nd:YAG laser due to thermal and induced dynamic stress. The aim of this study was to investigate the effect of different conditions of the Nd:YAG laser on induced dynamic stress. A pulsed Nd:YAG laser (STREAK-I ALTEK Co., Tokyo) and rutile type of TiO₂ powder (TIO12PB Kojundo Chemical Lab. Co., Ltd., Saitama) were used. Streptococcus mutans ATCC 25175 was used for this experiment. Bacterial cell suspensions of the strain were irradiated by Nd:YAG laser with several different pulsed energies and times of exposure, then the samples were subjected to SEM investigation. After these treatments, the viable cell count was estimated in each sample under different conditions. Regarding the bactericidal effects of the Nd:YAG laser in the presence of TiO₂, there was a significant reduction such as 90-99.9% of viable cells of S. mutans. SEM (JSM-6390LV JEOL Ltd. Tokyo) investigations revealed morphological damage according to the pulse energies and exposure times applied. It is suggested that the bactericidal action occurred as a result of the dynamic stress induced by the Nd:YAG laser irradiation and TiO₂ as a reaction mediator.

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The chemo-mechanical method of removing caries is safer and less painful than conventional caries treatment with rotary instruments, but takes longer. Therefore, a prototype of a new caries removal reagent was developed to solve this disadvantage. This reagent (BO reagent) consists mainly of bromelain and orange oil, and removes caries approximately 2 minutes faster than Carisolv, but still takes longer to remove caries completely than the conventional method. To reduce the time further, we evaluated the effects of using this BO reagent with an Nd:YAG laser. Forty-five extracted human permanent teeth with caries were used in this study and were divided into nine groups with various laser irradiation conditions (60, 80, 100, and 120 mJ) with air-cooling or without air-cooling, and no laser irradiation. The time required for caries removal was measured for all specimens. To evaluate the temperature rise, thermal changes were also measured by thermometer during laser irradiation. After caries removal, each cavity was filled with composite resin and a micro-leakage test was performed. Then, all samples were transversely bisected with a diamond saw disc, and observed by stereomicroscopy. The mean time for the group with BO reagent without Nd:YAG laser irradiation was 388 seconds. For the groups irradiated by Nd:YAG laser, the times were 132 to 205 seconds on average and were statistically shorter than for the non-irradiated group. However, there was no statistical difference between the groups with and without air-cooling. The measured temperature rise was 2.1°C (80 mJ) to 4.4°C (120 mJ) for the groups without air-cooling, but was less than 2°C for all the groups with air-cooling. The rate of temperature rise and the time required for caries removal were similar for the 100 and 120 mJ-irradiated groups. In the micro-leakage test, there were no statistical differences among all groups. From these results, the BO reagent with Nd:YAG laser and air-cooling is a new candidate method for caries removal instead of conventional caries removal with rotary instruments. Especially, BO reagent with Nd:YAG laser irradiation of 100-120 mJ and air-cooling might be an effective and safe method of removing caries.

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Objective: The usefulness of laser irradiation for socket preservation in clinical cases has recently been reported, and the effective laser irradiation conditions for healing of the extraction wound have also been investigated. It was reported by our laboratory that HLLT and LLLT therapies using a CO₂ laser for extraction sockets resulted in characteristic new bone formation and the maintenance of a high alveolar crest in rats. However, the mechanism of healing promotion by CO₂ laser irradiation remains unclear, so we investigated the emergence of myofibroblasts (α-smooth muscle actin (α-SMA)) involved in granulation tissue scar contracture in extraction wounds and changes in the expression of transforming growth factor-beta 1 (TGF-β1) associated with myofibroblast differentiation and apoptosis.
Subjects and Methods: Seventy-two 5-week-old male Wistar rats were used. The first molar was extracted to prepare an extraction socket model. The rats were divided into CO₂ laser-irradiated and non-irradiated (control) groups and pathologically compared. In the CO₂ laser-irradiated group, HLLT was performed immediately after tooth extraction, followed by LLLT after one day, corresponding to clinical cases. The irradiated tissue including the extraction socket was excised 6 hours and 3, 5, 7, 10, and 21 days after treatment, fixed in 4% paraformaldehyde, decalcified in 10% EDTA solution, and paraffin-embedded employing the standard method, and serial sagittal sections were prepared. Granulation tissue of the superficial layer of the extraction socket was immunohistologically investigated using anti-α-SMA and anti-TGF-β1 antibodies. The number of α-SMA-positive cells and TGF-β1-positive area were measured, and the significance of differences was tested.
Results: On immunostaining with anti-α-SMA antibody, there were many α-SMA-positive cells in the non-irradiated group at 3 and 7 days, whereas significantly fewer positive cells were noted in the CO₂ laser-irradiated group (p < 0.05). On immunostaining with anti-TGF-β1 antibody, TGF-β1-positivity was not marked in the CO₂ laser-irradiated group, compared to that in the non-irradiated group, and a significant difference was noted 5 days after treatment (p < 0.05).
Conclusion: The combination of CO₂ HLLT and LLLT for the extraction sockets inhibited scar formation in the sockets, and the involvement of TGF-β1 was suggested.

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The purpose of this study was to investigate the kinetics of root fractures produced by root-end cavity preparation and the fracture resistance following root-end cavity preparation using an Er:YAG laser and ultrasonics. Twenty-seven roots of extracted human anterior teeth were prepared, laterally condensed with guttapercha, and the root-end was resected. Root-end cavities of 3 mm in depth, were prepared using an Er:YAG laser (Erwin AdvErL, Morita, Kyoto, Japan, 140 mJ 10 pps) with water cooling, an ultrasonic device (Piezon Master400, EMS, Switzerland) at the highest power setting with or without water cooling, or at the lowest power setting with water cooling. After the preparation, presence or absence of fracture and morphological change were observed with a microscope and a micro CT. Then, obturation materials in the root canal were vertically loaded using a universal testing machine. Fracture loads and fracture patterns were analyzed by ANOVA and Tukey comparison, and Kruskal-Wallis test and Steel-Dwass test (p = 0.05), respectively. In microscopic and micro CT observations, fractures were found in the ultrasonic group at the highest power setting, while no fracture was observed in the Er:YAG laser group and the ultrasonic group at the lowest power setting. There were significantly more fractures in the ultrasonic group at the highest power setting compared to the Er:YAG laser group and the ultrasonic group at the lowest power setting with water cooling. Carbonization and fusion were found in the ultrasonic group at the highest power setting without water cooling. Fracture patterns showed no significant differences among the groups (p > 0.05). The ultrasonic preparation at the highest power setting without water cooling group (11.10 kgf ± 4.73) had a significantly lower fracture load than the Er:YAG laser group (28.85kgf ± 7.53), ultrasonic preparation at the highest power setting with water cooling group (21.9 kgf ± 3.38) and ultrasonic preparation at the lowest power setting with water cooling group (29.20 kgf ± 2.65) (p < 0.05). There were no significant differences among the Er:YAG laser group, the ultrasonic preparation at the highest power setting with water cooling group and the ultrasonic preparation at the lowest power setting with water cooling group. Within the limitations of this in vitro experiment, fractures caused by Er:YAG laser irradiation under water cooling for root-end cavity preparation were minimal. However, there were no significant differences in the resistance and vertical root fracture patterns between the Er:YAG laser group and the ultrasonic group.

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