Laser surgery in general is becoming more and more common, and there are now several types of lasers used for middle ear surgery. However, surgeons can only depend on their own clinical experience when selecting which type of laser to use because there is almost no basic research to which they can refer. We have therefore analyzed the light absorption spectra for temporal bone and the ossicles of the middle ear in order to find which type of laser is best for treating these tissues. We found that the auditory ossicles had three light absorption peaks: first at 3.03 μm, second at 6.10 μm and third at 9.83 μm. We therefore selected the CO₂ laser (λ : 10.6 μm) and Er:YAG laser (λ : 2.94 μm) to irradiate the incus. The hole made by the CO₂ laser was relatively shallow with rounded edges, and there was carbonization on the surrounding surfaces. Also, the irradiated surface was rough and covered with many micro-cracks. On the other hand, the hole made by the Er:YAG laser was deeper and free of carbonization, and the irradiated surface was smooth without irregularities or micro-cracks. These results strongly suggest that the Er:YAG laser is better suited for treatment of the auditory ossicles.

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For a proper understanding of the interactions of tissue with lasers, it is essential to absolutely estimate optical constants of hard dental tissue, such as absorption coefficient (μ_a) and reflectance (R). The absorption coefficient is an important physical constant that characterizes laser-tissue interactions. In order to estimate the absorption coefficients of human and bovine enamels in the mid-infrared (MIR) region, we have established a KBr-FTIR method in which a pellet consisting the powder mixture of KBr and dental enamel is spectroscopically observed by a Fourier Transform Infrared Spectroscopy (FTIR). The optical absorptions of human and bovine enamels were determined using the proposed KBr-FTIR method. The absorption coefficient for human enamel (17324±12% [cm^-1]) was found to be about two times higher than that for bovine enamel (7701±12% [cm^-1]) at the maximum absorption peak (=9.6 μm). The bovine samples are widely used as a model substance of human samples. Therefore, we must consider the difference in absorption property between human and bovine enamels and pay careful attention to the laser parameters employed in clinical practice.

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Lasers are applied in various fields, including medicine. Lasers are also applied in the dental field, and basic studies and clinical reports for the purpose of their clinical application to soft or hard dental tissues have been presented extensively. As for current caries treatment, it is necessary to develop a device enabling a reduction of the load on a patient, such as a new cutting device which enables, as much as possible, the suppression of pain, reduces the uncomfortable sounds of the cutting device and employs a simply operable medical examination method with a high accuracy.
In a basic study on dental caries diagnosis applying a semiconductor laser conducted by our department, we reported that the diagnosis with the laser utilizes a clinically simple device for detecting caries and an effective examination method for diagnosing caries. The safety of the dental pulp when the Er:YAG laser is applied to the dentine has been confirmed. However, the adhesive power of the thickness and denatured layer of a laser-cut face is weak. Thus, we conducted a study on an elimination method of the thickness and denatured layer, and clarified that recovery of the adhesive power is obtained. Compared with a rotation cutting device, the laser has received attention as a new cutting device with less noise and vibration, a reduced unpleasant sensation and a reduction of pain-elimination methods.
From the above findings, repair treatment applying a laser has been advancing day by day and will ultimately be used extensively as a more clinically useful device through future studies.

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The use of lasers is getting popular year by year among Japanese dental practitioner. Oral soft tissue and cavity preparation uses are becoming more common in dental offices. This article summarizes the new trend of laser application in endodontics, especially, measurement of pulpal blood flow by laser Doppler flowmetry, application of lasers to direct pulp capping, pulpotomy, pulpectomy, disinfection of root canal, root canal shaping, and apicoectomy. Additionally, we discuss the problem with the laser irradiation in the root canal.

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Due to various advantageous characteristics such as ablation or vaporization, hemostasis, and bactericidal effect, laser treatment serves as an alternative or adjunctive therapy to conventional mechanical instrumentation in periodontal therapy. Lasers are effective tools for the treatment of periodontitis, which is a chronic inflammatory disease caused by bacterial infection. Recent development of the Er:YAG laser has increased laser applications in periodontal therapy. As it is applicable to both soft and hard tissues, the Er:YAG laser has become a promising laser in periodontics. In this communication, the application of Er:YAG laser for periodontal therapy such as esthetic management of gingival tissue, periodontal pocket treatment including calculus removal, periodontal surgery, and implant therapy are discussed, based on scientific evidence from currently available basic and clinical studies.

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PDT (Photodynamic therapy) is a relatively new treatment modality for cancer, having the advantage of selective destruction of malignant tumor cells. It is expected that patients with oral cancer also would be good candidates for the modality, and we have been investigated clinical applications. In this paper, we report superficial and interstitial PDT for treatment of oral cancer and ALA mediated PDT for treatment of premalignant lesions.

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Pediatric Dentistry requires methodology for fearless, painless, safe treatment with less time and convenient postoperative care. Laser treatment satisfies these conditions, making it very effective for the pediatric patients. Presently He-Ne laser has the high ability of healing the wound so that it is being used for pulp therapy. CO₂ laser or Nd:YAG laser is being used for dental caries prevention, which gives the acid resistance to the enamel. Moreover CO₂ laser is being mainly used for soft tissue problems; because the haemostasis can be immediately achieved during the surgery and the patient experience good wound healing with little or no pain post operation. Er:YAG laser has made it possible to prepare the cavity without pain by ablation of dental hard tissue. Hence all these modes offer a high quality treatment for child patients.

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[in Japanese]

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The uses with lasers in dentistry are becoming more common in dental offices. These include replacement of the dental drill with lasers, laser dental decay prevention, and laser decay detection. The essential question is whether a laser can provide equal or improved treatment over conventional care. With the availability and future development of different laser wavelengths and methods of pulsing, much interest is developing in this growing field. In this article, the interactions of dental hard tissue with lasers are divided into two; (1) chemical modification for decay prevention and (2) hard tissue ablation for cavity preparation. In order to clinically use treatments by means of these interactions, an appropriate choice of a laser wavelength and a peak power density is essentially required. This article reviews the role of lasers in hard tissue therapy and diagnosis from a basic point of view, and introduces a new technique for cavity preparation using transmitting liquid.

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