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Therapeutic light has been increasingly used in clinical dentistry for surgical ablation, disinfection, bio-stimulation, reduction in inflammation, and promotion of wound healing. Photodynamic therapy (PDT), a type of phototherapy, has been used to selectively destroy tumor cells. Antimicrobial PDT (a-PDT) is used to inactivate causative bacteria in infectious oral diseases, such as periodontitis. Several studies have reported that this minimally invasive technique has favorable therapeutic outcomes with a low probability of adverse effects. PDT is based on the photochemical reaction between light, a photosensitizer, and oxygen, which affects its efficacy. Low-power lasers have been predominantly used in phototherapy for periodontal treatments, while light-emitting diodes (LEDs) have received considerable attention as a novel light source in recent years. LEDs can emit broad wavelengths of light, from infrared to ultraviolet, and the lower directivity of LED light appears to be suitable for plaque control over large and complex surfaces. In addition, LED devices are small, lightweight, and less expensive than lasers. Although limited evidence exists on LED-based a-PDT for periodontitis, a-PDT using red or blue LED light could be effective in attenuating bacteria associated with periodontal diseases. LEDs have the potential to provide a new direction for light therapy in periodontics.

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Recently, the Er:YAG and CO(2) lasers have been applied in periodontal therapy. However, the characteristics of laser-irradiated root cementum have not been fully analyzed. The aim of this study was to precisely analyze the alterations of root cementum treated with the Er:YAG and the CO(2) lasers, using non-decalcified thin histological sections. Eleven cementum plates were prepared from extracted human teeth. Pulsed Er:YAG laser contact irradiation was performed in a line at 40 mJ/pulse (14.2 J/cm(2)/pulse) and 25 Hz (1.0 W) under water spray. Continuous CO(2) laser irradiation was performed in non-contact mode at 1.0 W, and ultrasonic instrumentation was performed as a control. The treated samples were subjected to stereomicroscopy, scanning electron microscopy (SEM), light microscopy and SEM energy dispersive X-ray spectroscopy (SEM-EDS). The Er:YAG laser-treated cementum showed minimal alteration with a whitish, slightly ablated surface, whereas CO(2) laser treatment resulted in distinct carbonization. SEM analysis revealed characteristic micro-irregularities of the Er:YAG-lased surface and the melted, resolidified appearance surrounded by major and microcracks of the CO(2)-lased surface. Histological analysis revealed minimal thermal alteration and structural degradation of the Er:YAG laser-irradiated cementum with an affected layer of approximately 20-µm thickness, which partially consisted of two distinct affected layers. The CO(2)-lased cementum revealed multiple affected layers showing different structures/staining with approximately 140 µm thickness. Er:YAG laser irradiation used with water cooling resulted in minimal cementum ablation and thermal changes with a characteristic microstructure of the superficial layer. In contrast, CO(2) laser irradiation produced severely affected distinct multiple layers accompanied by melting and carbonization.

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BACKGROUND AND OBJECTIVES: Blue light has been employed or investigated in both the medical and dental fields. Many studies have so far been reported a bactericidal effect of blue light emitting diodes (LED). However, it is still unclear whether exposure to blue LED kills or inhibits the growth of bacteria. We therefore investigated the effect of blue LED irradiation on the growth of Porphyromonas gingivalis compared with the effects of red LED. MATERIALS AND METHODS: P. gingivalis cell suspensions were irradiated with blue or red LED (135 J/cm2) anaerobically, incubated for various lengths of time, and then the total RNAs were isolated. The RNA degradation and gene expression levels of stress-related proteins in blue or red LED-irradiated samples were examined using the RNA integrity number (RIN) and RT-PCR, respectively. Quantitative RT-PCR was done to investigate the gene expression profiles associated with chromosome replication and cell division. RESULTS: Exposure to blue LED delayed the growth of P. gingivalis, while red LED did not. The RIN value indicated no RNA degradation in either the blue or red LED-irradiated samples. In addition, the gene expression levels of stress-related molecules remained either constant or increased 15 minutes after the blue LED irradiation compared to that before irradiation, thus suggesting that blue LED may not kill P. gingivalis cells. However, the blue LED irradiation did lead to a remarkably decreased expression of genes associated with chromosomal DNA replication and cell division after 5 minutes; exposure to the red LED did not. CONCLUSION: The inhibition of the growth of P. gingivalis by blue LED may therefore be induced not by a bactericidal effect, but instead due to a bacteriostatic effect mediated by the suppression of the genes associated with chromosomal DNA replication and cell division at the transcriptional level.

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