Since the laser was first developed by Maiman in 1960, its use for medical and photobiological applications has been investigated. High-energy lasers are useful in producing coagulation necrosis in target tissue with a subsequent reaction in the surrounding tissue. Various biostimulatory effects of low-energy laser irradiation have been reported that involve regeneration healing, fibroblast and chondral proliferation, collagen synthesis, and nerve regeneration. In particular, the acceleration of bone regeneration by laser treatment has been a focus of recent research.
In this paper, the application of low-energy laser for periodontal regeneration is discussed, based on scientific evidence from currently available basic and clinical studies.

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Laser ablation [Er: YAG (Erwin Adverl®, 60mJ/10pps), CO₂ (Topal®, 1W/0.3sec)] of dentin reduces the adhesive properties of resin bonding systems. The so-called “laser-etching” might not be effective in promoting adhesion. By TEM observations of non-decalcified specimens, such morphological changes as observed in the acid-etched dentin surface could not be detected in the subsurface layer of the lased dentin. It was mechanically weakened due to the formation of structural defects and heat-denatured layer, leading to considerably lower adhesive properties. Significantly lower bond strength was obtained in the wedge-shaped defects compared with the flat surfaces. The configuration factor (C-factor) might be an important factor especially for the adhesion to lased dentin.
However, high-energy laser ablation of dentin (Er: YAG: 250mJ/lOpps, CO₂: 3W/0.3sec) hardly reduced the bond strength. In the subsurface layer of low-power lased dentin (Er: YAG: 60mJ/1 pps, CO₂: 1W/0.3sec), TEM observations of decalcified specimens revealed that amorphous matrix substances containing denatured collagen fibers were generated (Er: YAG: 3-4μm, CO₂: 1-2μm). On the other hand, in the high power-lased dentin (Er: YAG: 250mJ/1pps, CO₂: 3w/0.3sec), such morphological structure that could hardly be distinguished from sound dentin (Er: YAG) or the subsurface dentin layer having both little amorphous matrix and torn collagen fibers with cross-striation (CO₂) was observed. The effects of high-energy laser ablation might be limited to the superficial layer.
It was concluded that laser-etching might not be effective in promoting adhesion, and that the amount of irradiation energy should be considered when evaluating the adhesive properties of resin bonding systems.

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[in Japanese]

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The aim of this study was to compare the pain relief effect after periodontal and endodontic surgeries between Er: YAG laser irradiation and the administration of anti-inflammatory drugs in the same patients using Visual Analogue Scale (VAS). Forty teeth in 10 patients were used in this study. The surgical procedure was as follows: the gingival flap was elevated, then root planing and bone defect debridement were done. In the experimental group (Exp) of 22 teeth in 10 patients, Er: YAG laser wa irradiated to root surfaces, bone defects and the inside of gingival flaps after root planing and bone defect debridement (1.0W, 30 seconds, 3 times). In addition, this laser was irradiated around the mucogingival junction immediately after surgery (1.5W, 1 minute, 3 times). In the control group (Coot) of 18 teeth in 10 patients, Er: YAG laser was not irradiated following surgery and antiinflammatory drugs were administered after surgery as early as possible. All patients were administerted some antibiotics. VAS was performed immediately after surgery, at 1, 2, 3, 4, 5 and 6 hours after surgery, and at 1, 2, 3, 4, 5 and 6 hours after getting up for the following two days. Healing was uneventful in all patients. The statistical analysis by the Wilcoxon signed-ranktest indcated that there was no statistical significance between the experimental group and control group for VAS values in this study. This study suggested that Er: YAG laser irradiation and anti-inflammatory drugs might have almost the same pain relief effect after periodontal and endodontic surgeries.

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Three types of laser: the Nd: YAG laser, CO₂ laser and Er: YAG laser, have been used for various dental treatments since July 1996 in Comprehensive Dentistry, Niigata Hospital, The Nippon Dental University. In this study, the frequency of using each laser was examined for each category of dental diseases between July 1996 to June 2004. They were used in a total of 1, 158 cases, with a mean age of 49.5 years (range 12 to 81 years). The frequency of use of the Nd: YAG laser (Pulse Master 600 LE, Denics International), CO₂ laser (Opelaser 03S, Yoshida Dental Mfg. Co.), CO₂ laser (Opelaser 03S II SP, Yoshida Dental Mfg. Co.) and Er: YAG laser (Erwin, Morita Co.) were 605 cases (52.2%), 301 cases (26.0%), 249 cases (21.5%) and 3 cases (0.3%), respectively. Based on the results of this survey, various factors such as wavelength characteristics, specifications of equipment, the light guide system and operative ability had significant influences on the selection of laser equipment for each clinical treatment. It is important for effective and safe use of lasers in dental treatment to understand the characteristics of each type of laser equipment.

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Recently, a laser is begun to use for gingival retraction instead of an electrosurgical knife when the gingiva cover up the margin of abutment tooth. We have been using CO₂ laser and Er: YAG laser for gingival retraction for the few years. One of the advantages of gingival retraction using laser is that the patients feel a few pains. However, the research referred to the pain when laser was irradiated to the gingival isn't found. In the present study, we experimented about the pain to feel for the patients when irradiating CO₂ laser and Er: YAG laser to gingiva. As a result, under the irradiation condition using for usual gingival retraction, the subjects felt few pains in irradiating Er: YAG laser than CO₂ laser, Hemostatic effect of Er: YAG laser is low compared with CO₂ laser, however operating time of gingival retraction using Er: YAG laser is relatively long. Therefore, when using laser for gingival retraction, we should choose suitable laser according to the situation of marginal gingiva.

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Angiogenesis is an important and interesting subject in dentistry. However, few studies on angiogenesis by low power laser irradiation have been performed in vivo.
In this study, the effects of low power laser irradiation on angiogenesis of human endothelial cells were investigated in vitro. The behavior of angiogenetic factors was examined by ELISA and confocal laser scanning microscopy.
Growth factors (VEGF, angiopoietin-1, angiopoietin-2) localized at endoplasmic reticulum in the endothelial cells and their receptors (Flt-1, KDR/Flk-1, Tie-2) appeared on cell membranes. In addition, adhesive molecules (VE-cadherin, beta-catenin) were visible at regions of cell to cell contact.
After the irradiation, their expressions were enhanced except angiopoietin-2. Each of the amounts of the proteins increased compared to the control. VEGF-VEGFR, VE-cadherin and beta-catenin, and Angiopoietin-Tie were activated by the laser irradiation. Cell proliferation, mitogen, adhesion and vessel formation were promoted.
These results suggest that low power laser irradiation promotes angiogenesis to activate not only the endothelial cells but also expressions of growth factors and adhesive molecules.

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The aim of this study was to compare the gingival surface anesthetic effect of Nd: YAG, Er: YAG laser irradiation and a surface anesthetic using Visual Analogue Scale (VAS) in a short time interval.
Ten adult volunteers participated in this study. The subjects were divided into 3 groups (Nd: YAG laser, Er: YAG laser, control). The irradiated sites were gingival and buccal areas of mandibular incisors. Each laser was irradiated for 1 minite, 3 times at 1.5W. A surface anesthetic was used for the control group. The change of VAS and the depth pierced by a cartridge needle were measured immediately after the laser irradiation, and at the following 1, 2, 3, 4, and 5 minutes. For the control group, these measurements were performed from 3 minutes after the laser irradiation with the same interval. The results were subjected to the Kruskal-Wallis test and Mann-Whitney test.
The results of this study indicated that the VAS value of the Er: YAG laser group was significantly higher than that of the Nd: YAG laser group and control group at immediately after the laser irradiation and was significantly higher than that of the Nd: YAG laser group at 2, 4, 5 minutes after the laser irradiation. However, there was no significant difference between the three groups in the measurement of pierced depth.
This study suggested that Nd: YAG laser is almost equal to a surface anesthetic and that Er: YAG laser is not so effective as Nd: YAG and a surface anesthetic.

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