2011 Volume 22 Issue 2+3 Pages 100-107
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.
