Low level laser therapy (LLLT) is gaining popularity in a variety of clinical applications. The lasers used in dental applications for LLLT are such as the He–Ne laser, the semiconductor laser and others. Low level laser light is reported to alleviate pain and trigeminal nerve paresthesia, to accelerate wound healing, to have a positive effect on inflammatory processes, the prevention and treatment of radiotherapy-induced oral mucositis in oral cancer. However, the biochemical reactions by low level laser irradiation are not fully understood. This paper presents the efficacy of LLLT and cautions when applying clinical in use.

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The research which tries to use the laser to join the dental prosthesis has been done for about 40 years. It turned out to be able to use the laser welding to join the dental prosthesis effectively from results of a lot of researches. As a result, the laser welder for dental use is developed now and they has come to be used for clinical widely. However, the problem of the laser welding has begun to be worried as use spreads. The welding deformation and the welding defect accompany the laser welding. These problems were pointed out from early time and the improvement of these has come to be requested as a clinical application spreads. Efforts are being turned to the improvement of these problem in the laser welding now. The welding deformation is caused by the coagulation and heat shrinkage of the weld. The shape of fusion zone greatly influences the welding deformation. The deformation is small when diameter of fusion zone is small and melted shape is near the column form. The existence of the element which forms the eutectic with low melting point greatly influences about the crack generation. Sulfur, phosphorus and carbon increase the occurrence of the solidification crack. The welding method for preventing deformation and the alloy design for preventing crack generation being examined. Porosity often generation by remaining of the keyhole. Pulse shaping is effective to porosity. The research on pulse shaping might be advanced further by the appearance of the laser welder with pulse-shaping function. As a result, a better laser welding can be expected to become possible.

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In the application of laser to the area of endodntics, we have the problem that the object of laser treatment is narrow area. Especially to treat a root canal, we have the difficulties on both the guide of laser beam and the irradiating direction of laser. Moreover during the irradiation of laser beam at an apical area, if we applied the laser beam to the apical tissue through the apical foramen, the apical tissue was wounded. Then the patient will feel the pain. Although the laser treatment has these problems on the area of endodntics, we will get the development on the promotion of care and the establishment of painless treatment. But if we can't exhibit the cause of disease, we should not do the aimless laser irradiation to avoid the spreading of pain.

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Treatment methods in pediatric dentistry must be painless, safe, and relatively short to avoid fear in the patient and allow convenient postoperative healing. Laser treatment satisfies these criteria, making it very effective for pediatric patients. Low level lasers such as the He-Ne laser, diode laser and Nd:YAG laser are currently used for pulp therapy to accelerate pulp wound healing, whereas the CO₂ laser and Nd:YAG laser are used for dental caries prevention by making enamel acid resistant. The CO₂ laser is mainly used for soft tissue problems because hemostasis can be achieved rapidly during surgery and the patient experiences good wound healing with little or no postoperative pain. The Er:YAG laser allows preparation of a cavity without pain by ablation of dental hard tissue. In this paper, we discuss the effectiveness of laser therapy for pediatric patients in clinical procedures from deciduous dentition to permanent dentition.

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The optical applications have been tried in caries diagnosis that is an old practice.
In recent years, we can new usefulness dental caries diagnosis laser and optical devices in dental trea^™ ent with advances of optical devices, computer and combined of both technologies. These optical devices will be the mainstream of caries diagnosis in this century. In this report, we present of the summary and future direction of the laser and optical caries diagnosis devices.

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In order to perform exact medical treatment, first, exact diagnosis is indispensable, and if the simple and exact diagnostic technique independent of a measurement person's skill is acquired, it will be thought that the efficiency and reliability of medical treatment can be raised by leaps and bounds. If early detection of a disease can be performed by improvement in diagnostic technology, a serious disease can be prevented and medical treatment can be suppressed to the degree of minimum. In this paper, laser diagnostic techniques used with dentistry, i.e., autofluorescence diagnosis, photodynamic diagnosis, and optical coherence tomography are described.

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Studies of the light properties of hard tooth tissue established the infrared and Ultraviolet regions the spectrum which are absorbed by dentin (1981, the Japan Society of Conservative Dentistry). These studies show that dentin and enamel absorb light in the regions of the spectrum around 3 μm and 101 μm. Water also absorbs light in the 3 μm region. The Er:YAG laser is effective in the 3 μm region and the CO₂ laser in the 10 μm region. However, the CO₂ laser has a clinical drawback: it causes heating which cracks the tooth surface. This makes the Er:YAG the best possibility for clinical applications (1990, The Japan Laser Dental Society). In has also been show that the Er:YAG laser removes hard tooth tissue through the micro-explosive reaction of the OOH-Stem of the hydroxy apatite the hydration shell inside the crystal is instantly vaporized (1993, The Japan Laser Dental Society). Our laboratory is getting good results with the clinical application of the Er:YAG laser deliverad with a special contact tip developed here. The complete abscess of pain during the procedure is especially noteworthy. Considering the increasing population of senior citizens and the need to prevent caries of the tooth root, we measured the light absorption for cementum using Fourier transformation infrared spectroscopy (FTIR) and found it to be 9.38 μm. Furthermore we found that laser irradiation with a free electron laser (FEL) at 9.38 μm, which is within the range of a molecular vibration laser, caused the maximum absorption wavelength to shift and become shorter. This shows that the cementum tended to crystallize to a considerable degree, which would make it more durable.

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Lasers are widely used in the oral and maxillofacial region surgeries such as removal of benign and malignant lesions, excisional and incisional biopsies, frenectomics, and so on. The CO₂ laser has been used successfully in the treatment of diseases that occur in soft tissue because of its excellent excision and hemostatic abilities, and good results have been obtained. It also can be used for procedures such as evaporation. The Nd:YAG laser light has an affinity for pigmented tissues and penetrates soft tissues more deeply than the CO₂ laser. Using these characteristics, hemangiomas and vascular malformations can be treated with Nd:YAG laser. In this paper, current status of oral and maxillofacial laser surgery are reported with some case presentations.

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The main etiologic factor of periodontitis is the dental biofilm in the periodontal pockets. Biofilm is formed by the glycocalyx structure. Recently, the fundamental studies of photodynamic therapy (PDT) which used laser devices and photosensitizers to periodontal treatment have been reported. The advantage of PDT is that it can only affect the target tissue by combination of laser light with a specific wavelength to activate a photosensitizer and this photosensitizer does not have any toxicity. Therefore, the heat effect from laser device to other tissues becomes weak. Additional, it may be possible to destroy biofilm in the pocket where the laser fiber can not reach and evade side effects such as antibiotic. In this paper, the various clinical studies of photodynamic therapy (PDT) which have been reported until now and our studies are introduced. The possibility of application to periodontal treatment of PDT is also discussed.

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In recent, various lasers have been employed to treat dental hard tissue lesions, and many descriptions have been reported on those effects. The authors have also been reported effects of laser application on examination and diagnosis of dental caries, enhancing acid resistance of tooth structures, fluorides uptaking of tooth, fusing of apatite crystals to tooth surface, caries tooth structure removal and resin bonding. The present report reviews mainly our studies on laser examination and diagnosis of dental hard tissue lesions and modification of tooth structures that accelerate prevent of dental diseases. This report may also suggest the future development of laser applications on new era dentistry.

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Since the laser was developed in 1960,its applying to optical communication and medical practice has been investigated well. There are many kinds of dental laser and more than twelve of them are used in Japan. 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 it acts on regeneration healing, fibroblast and chondral proliferation, collagen synthesis, nerve regeneration. It is used in odontotherapy for diseases of hard tissue and soft tissue, periodontitis and peri-implantitis. The usage rate of a dental laser is 30% of dental clinics in Japan and 60% of them use a laser with carbon dioxide gas. In this paper, we describe the carbon dioxide whether promote the wound healing or not. The laser is used for a lot of medical treatments now. Moreover, the laser is used for not only the treatment; its usage also has been increased for diagnosis and prevention of the disease. Especially, its research and development progress rapidly due to applying to the odontology for medical treatment.

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The main objective of periodontal treatment is to remove supra- and subgingival biofilm and, as a consequence, alters the subgingival ecologic environment and suppresses periodontal destruction. This has traditionally been done using mechanical scaling and root planing combined with effective supragingival plaque control. Application of laser on these process would be more effective in clinical outcomes and promote the wound healing compared to the conventional methods. This paper reviews the author's experience with Er:YAG laser in periodontal treatment during the last 20 years, together with views on clinical applications of Er:YAG laser from scientific consideration.

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