The violet laser diode was developed in 1996, and is now widely used as a light source for high-speed multilayer recording systems such as Blu-ray discs and HD-DVD systems. These lasers also show promise for medical applications, such as cutting soft tissue, laser acupuncture, tooth whitening, and detection of dental caries. The wavelength of the violet laser diode (approx. 405nm) may be suitable for hardening light-cured dental materials combined with some alternative photo-initiators. This article examines the light-curing efficiency of some commercial and three experimental dental resins by GaN-based violet laser diode determined in terms of ultimate micro-tensile strength, in comparison with curing by various commercial LED light-curing units. The spectral characteristics of the transmittance of contemporary dental adhesives and the emission of several commercially available light-curing units are also presented. The results revealed that violet laser diodes can be used as a light-curing source to initiate the polymerization of light-cured dental resins.

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Photodynamic therapy (PDT) is a medical treatment for cancers and infections with light irradiation and photosensitizers, which are excited by being exposed to light of a specific wavelength. Recently, PDT is applied to the treatment of periodontal disease. In this study, we investigated the bactericidal effect against Porphyromonas gingivalis, which is a periodontopathogenic bacteria, by white LED (light-emitting diode) irradiation with a higher visibility in the oral cavity. P. gingivalis (ATCC33277) was anaerobically cultured in brain-heart infusion (BHI) media, adjusted to an optical density of 0.3 using a photoelectrometer, and was then used as the bacterial solution for this experiment. After the bacterial solution was dispensed into a 96-well, clear, flat-bottom plate at 100 μL/well, the samples were irradiated with a white LED (irradiation intensities: 10, 20, 30 J/cm², irradiation distance: 15 mm). The bacterial solutions were diluted and anaerobically cultured on blood agar at 37°C for 7 days. Then, the colony forming units (CFU) were counted and compared to that of the control group (LED non-irradiation) to determine the bactericidal effect. Irradiation with the white LED resulted in a statistically significant decrease in CFU, with the number of CFU decreasing as the irradiation intensity increased. In the second part of the study, we examined two photosensitizers: Protoporphyrin IX and Fluorescein, for use in PDT with white LED as a light source. The irradiation intensity of white LED was set at 20 J/cm², and the concentration of each of the photosensitizers was set at 100 μM. A photosensitizer group (addition of the bacterial solution with photosensitizer and LED non-irradiation), an LED-irradiated group (bacterial solution alone and LED irradiation) and a combination group (addition of the bacterial solution with photosensitizer and LED irradiation) were compared to a control group (bacterial solution alone and LED non-irradiation), with the bactericidal effect evaluated by CFU measurements as described above. Neither of the photosensitizers affected the bactericidal effect. On the other hand, CFU of the combination group showed a statistically significant decrease compared to that of the LED-irradiated group. These results indicate that white LED irradiation has a bactericidal effect against P. gingivalis, and suggest that PDT with a combination of white LED irradiation and Protoporphyrin IX or Fluorescein added as a photosensitizer increase the bactericidal effect more than white LED irradiation alone.

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This study was performed in order to investigate the effects of Nd:YAG laser irradiation on human gingival fibroblasts (Gin-1), as represented by cell proliferation activity rate and TGF-β1 and Type I collagen production rate, as well as HSP47 expression.
Gin-1 cells were irradiated for 10 seconds at laser outputs of 2W (5pps/400mJ, 100pps/20mJ) and 7.2W (40pps/180mJ, 90pps/80mJ), at irradiation distances of 10mm or 20mm. Culture supernatant was recovered after 3 and 5 days of culture following laser irradiation and investigated for cell proliferation rate (modified MTT), and TGF-β1 and Type I collagen production rate (ELISA method). Gin-1 was also subjected to immunofluorescent staining after 3 hours of culture following laser irradiation, and observed for HSP47 expression by confocal laser scanning microscopy.
On the 5th day of culture, both of the groups irradiated by 2W at 10mm exhibited significantly higher cell proliferation rates than controls, and on the 3rd day of culture the group irradiated by 7.2W (90pps/80mJ) at 10mm exhibited significantly higher TGF-β1 production rates than controls. Among the 10mm irradiation groups on the 3rd day, both of the 7.2W groups exhibited significantly higher Type I collagen production rates than controls. Intracytoplasmic HSP47 expression was found in all groups.
Thus, high-output laser irradiation with an increased irradiation distance exerts a cell activating effect without harmful heating, similar to that of low-output laser irradiation.

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