Antimicrobial photodynamic therapy （a-PDT） has garnered attention as an adjunct to conventional mechanical debridement for controlling bacterial infections in periodontal disease. The clinical application of a-PDT using red light is widely practiced, while in recent years, there have been an increasing number of studies demonstrating the efficacy of the antibacterial effect of a-PDT using blue light. Although basic and clinical studies of a-PDT using blue light are still limited, this method is expected to be shown to be an effective approach for the treatment and prevention of periodontal disease.

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Violet light with a wavelength of around 405nm is widely applied in industry. It is also being tried in various ways in the medical and dental fields. This article presents the attempts to apply light-emitting diodes （LEDs） and laser diodes with wavelengths in the violet to blue-violet region in the field of dentistry, particularly in preventive dentistry, cariology and oral and maxillofacial surgery.

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Nowadays, light wavelengths in the violet to blue range have been increasingly applied in the medical and dental fields. These emitted wavelengths, particularly blue-violet light, are efficiently absorbed by porphyrins, which are compounds associated with proteins like hemoglobin, myoglobin, and melanin pigments, while not being absorbed by water. Due to these absorption characteristics, we found in ex vivo or in vivo experiments in the mid-2000s, that the blue-violet diode laser could be used for soft tissue incision and coagulation at low power density, with minimal to no carbonization. This capability opens possibilities for precise, minimally invasive procedures that may reduce healing time and tissue damage. Recently, many studies indicate that the blue diode lasers also have a higher ablation efficiency and less thermal damage to tissues than conventional near-infrared diode lasers. In addition to surgical applications, it has been recognized that blue-violet and blue light absorbed by porphyrins have a bactericidal effect on bacteria, due to an increase in reactive oxygen species （ROS）. There is also the possibility of low-level laser therapy （LLLT）. As a laser with a wide range of applications, this wavelength band laser will continue to be a focus of attention.

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