Many types of lasers have been used to treat a variety of diseases and conditions in the oral cavity including dental caries, periodontal disease and peri-implantitis. The use of lasers in dentistry is widespread and growing steadily. To date, most laser applications use high power to ablate tissues as opposed to low-level laser therapy (LLLT) applications, which use low power to alter cellular function. The clinical and biological effects of ablative laser therapy on hard and soft tissues have been reported with histological findings. However, there have been few studies reporting the histological changes in bone following low-level laser irradiation. The purpose of this study was to histologically evaluate the effects of low-level laser therapy from Er:YAG laser on bone healing in rat tibiae. Materials: A total of thirty adult female rats (age 9 weeks) were used in this study. A bone defect (1 mm in diameter) was created in each tibia, with a dental burr under profuse irrigation, for a total of two defects per animal. One side was treated with low-level laser therapy (1.0 W/cm2, 50 mJ, 20 Hz) every day until sacrifice while the other side served as the control (i.e., no laser therapy). Animals were sacrificed at 3, 7 and 14 days (ten per time interval). Tibiae were removed and fixed in 10% neutral formalin. Half of the specimens were prepared for histological evaluation. Tissues were decalcified with EDTA and embedded in paraffin for serial sections and staining with hematoxylin and eosin (HE). The other half of the specimens were prepared for micro CT evaluation. Results: All specimens demonstrated good healing of the osseous defect. On day 3, scattered inflammatory cell infiltration was observed in the healing bone defects of both the laser treated and control specimens. On day 7, new bone formation was observed in the defects of both groups. The volume of new mineralized bone structure in the laser treated defects was significantly greater (38±0.49%) than in the control defects (28±1.34%), p<0.01. On day 14, the newly formed bone tissues appeared mature. The volume of mineralized bone tissue in the laser treated defects was significantly greater (59±1.15%) than in the control group (54±0.59%), p<0.01. A horizontal tomogram with micro CT scanner revealed that mineralized bone formation in tibia treated with laser was strongly increased in comparison with that in the control group on day 7 and 14. Conclusion: The findings of the present study demonstrate that LLLT from Er:YAG laser stimulates bone formation during the early healing period and suggest that low-level laser therapy may be an effective tool to enhance bone regeneration.
The aim of this study was to visualize the fluid dynamics in a root canal model during Er:YAG laser-activated irrigation. After high-speed imaging together with particle image velocimetry (PIV) in a transparent canal, an analysis was conducted using fluid-analysis software. The laser was irradiated in canals of two different sizes and using laser tips with two different diameters, under the following conditions: group 1, canal size #80+tip size 200 µm; group 2, canal size #80+tip size 400 µm; group 3, canal size #140+tip size 200 µm; and group 4, canal size #140+tip size 400 µm. The tip was located 15 mm from the bottom of the canal. The ratio of areas where active flow occurred in the canal decreased in order of group 2, group 4, group 1, and group 3. Furthermore, the activation of irrigant in group 3 was statistically lower than that in other groups (p<0.05). In conclusion, Er:YAG laser might produce different streaming in a root canal, depending on the canal size and tip diameter. Irrigation efficiency might decrease when a thin laser tip is used in greatly enlarged root canals.
The aim of this study was to compare the efficacy of three irrigation techniques: laser-activated irrigation, ultrasonic irrigation, and conventional syringe irrigation, in removing debris and smear layer from the root canal wall. Bovine root dentin was used. The canal surface was ground with a carbide bar to make a smear layer. Thereafter, the specimens were set at an apical area of the simulated root canal model. As irrigation solution, sodium hypochlorite and EDTA were used in this order. By scanning electron microscopy, laser-activated irrigation and ultrasonic irrigation samples showed effective smear layer removal and open dentinal tubules. In contrast, smear plugs and debris remained in the syringe irrigation samples. In conclusion, irrigant activation using laser and ultrasonic devices might contribute to root canal cleanliness.
Wound healing in the oral mucosa, which covers the whole area of the oral cavity, is generally fast and the residual scar is minimal. Mucosal wound healing proceeds in the same manner as a cutaneous wound through the same stages, including hemostasis, inflammation, proliferation, and remodeling of collagen matrix. It is well known that ideal wound healing should be achieved by primary closure. On the other hand, the secondary intention of wound results in scar contracture. From the perspective of wound healing, the thermal damage created by a CO2-laser or YAG laser should be taken into consideration. In this article, we describe the process of normal wound healing and residual scar contracture in both skin and oral mucosa. Furthermore, we present the factors of abnormal wound healing.
Photoactivation, also known as photobiomodulation, is recognized as one effect of laser/tissue interactions. This phenomenon, which is induced by low-level laser irradiation, was reported by Mester in the late 1960s. The therapeutic method with photoactivation was defined as low-reactive level laser therapy (LLLT) by Ohshiro in 1988. Today, various clinical applications using LLLT have been reported in the field of wound healing, pain attenuation, musculoskeletal injuries and so on. This introductory review covers the fundamentals of laser/tissue interactions and the basic mechanism of photoactivation to provide a better understanding of LLLT for wound healing.
It is well known that a wound in the oral cavity heals faster without severe scar formation or contraction by scarring compared with a skin wound. However, there is a large potential risk of inducing various severe dysfunctions. As the variations of treatment modalities have increased as lasers have prevailed in the dental field, the principles of treatment and the basic knowledge about wound healing are needed. We should be able to predict the site of the scar and reconsider laser treatment in the dental field, while comparing the current consensus on wounds. With good knowledge of the characteristics of various types of laser, we should reevaluate the use of lasers considering the treatment goals and predicted postoperative state.