Er,Cr:YSGG laser -dentine interaction: micromechanical and microscopic characterisation

Methods: Twenty extracted human premolar teeth with an exposed flat occlusal surface were cut transversally to prepare twenty dentine disks with 2 mm thickness. After mounting on a plastic support, all specimens were wet polished by using 500 grit SiC paper. They were divided into four experimental groups according to the power setting of Er,Cr:YSGG laser applied to the dentine surface; namely 3W, 3.5W, 4W and 4.5W. The focus length between the laser tip and dentine surface was 1 mm and the exposure time was 1 min. The depth of dentine removed by laser application was investigated by using a 3D laser scanning surface profiler. The microhardness values were measured by using a Martens microhardness tester before and after laser irradiation. Representative specimens were examined microscopically by SEM.

Results: The mean ablation depth (SD) of each experimental group was 0.15 (0.02), 0.28(0.10), 0.33(0.07) and 0.42(0.14) respectively. The mean value of irradiated dentine hardness (SD) was 42.89(16.39), 30.27(11.94), 40.41(19.52), 41.27(9.15) and which was significantly lower than the baseline dentine hardness which ranged from 60.85(8.39)to66.18 (5.12). Linear regression analysis showed a significant relationship between increasing power setting of the laser and the ablation depth of the irradiated dentine (R² = 0.61 ,p< .05). There was no relationship between power setting and hardness. The dentine hardness decreased significantly when treated with Er,Cr:YSGG laser (Pair t-test, p<.05). SEM examinations revealed the differences in dentinal tubule morphology with different power settings.

Conclusions: Increasing the power setting resulted in increasing ablation depth dentine. Laser irradiation may cause a reduction in the hardness of the dentine and changes of dentine structure.