2018 Volume 29 Issue 1 Pages 1-9
Introduction: Laser irradiation on living tissue have bilateral characters like HLLT and LLLT. It is possible to reduce pathogenic factors such as bacteria using Er:YAG laser in dental caries treatment as HLLT, while there is a possibility that Er:YAG laser can promote wound healing process of pulp tissue. Some literatures demonstrated that Er:YAG laser irradiation induced earlier and more frequent tertiary dentin formation compared with conventional rotary preparation. However, the mechanism of pulpal wound healing process using laser is still unclear.
We hypothesized that the dual effects of Er:YAG laser on bacteria and pulp tissue will be useful in the deep caries treatment. Therefore, this study investigated the effects of Er:YAG laser irradiation on the wound healing mechanism of pulp tissue using indirect pulp capping model.
Materials and methods: This study was carried out under the approval of the Animal Experiment Committee of the Osaka University Graduate School of Dentistry (Approval number: 29–006–0) and thirteen male Wistar rats (8weeks old) were used. A cavity was prepared in the mesial surface of first upper molar under rubber dam using a round burr without pulp exposure. Then, Er:YAG laser irradiation was performed towards the cavity floor followed by covered with GIC. No laser irradiation group was used as controls.
Immediately, 1, 3 and 7 days after the pulp capping, all specimens were observed by micro-CT. Histological analysis was carried out using the specimens immediately, 1 and 3 days after cavity preparation by H-E staining. Immunofluorescence staining against high mobility group box 1 (HMGB-1) and dentin sialophosphoprotein (DSPP) was performed using the samples of the day 3 and day 7 respectively. The day 7 specimen was observed by electron back scatter diffraction patterns methods (ESD) using scanning electron microscope (SEM).
Results and Discussion: Micro-CT analysis showed the depth of the prepared cavities was around half of dentin thickness in the all specimens. In the extracellular matrix deposition considered as a tertiary dentin was earlier observed in the Er:YAG laser irradiation group compared with control group by H-E staining. The observation by ESD using SEM showed more tertiary dentin formation was observed beneath the laser irradiation region compared to the area without laser irradiation. Additionally, the cells beneath the extracellular matrix considered as tertiary dentin showed DSPP expression by immunohistochemistry. Immunofluorescence staining of HMGB-1 showed a specific expression in Er:YAG laser irradiation group and this expression area was larger than control group (p<0.01). HMGB-1 was reported to associate with wound healing process and regeneration of the tissue. Thus, the result of HMGB-1 expression in this study indicated it might play an important role in the healing mechanism of pulp tissue and Er:YAG laser irradiation could be used as LLLT in the pulp capping procedure.
Conclusion: Er:YAG laser irradiation after cavity preparation without pulp exposure may induce earlier tertiary dentinogenesis compared with no-laser irradiation. Er:YAG laser irradiation possibly promote a wound healing process of pulp tissue and it can be applied for deep caries treatment and be useful for vital pulp therapy.