The authors have demonstrated that a normal pulsed Nd: YAG laser was the most suitable among the lasers to produce resistance against acid decalcification of human tooth enamel, and a combined treatment of laser irradiation and fluoride application onto the enamel obtained most remarkale acid resistance.
It is interest to determine whether the use of laser and fluoride in combination is a more effective procedure for incipient caries prevention.
Artificial caries-like lesions were made on human enamel, and the enamel was then treated with laser irradiation and APF (acidulated phosphate fluoride). The laser used in this study was a normal pulsed Nd YAG laser which has 0.3 msec pulses with a pulse energy of 0.2 J/pulse. The tooth enamel was lased at a repitition rate of 20pps and total enegy density of 40J/cm².
The acid resistance of the enamel was determined by the amount of dissolved calcium from the enamel surface in the acidic solution. Fluoride uptake in the enamel was examined by mean of EPM (electron probe microanalyzer). Remineralization of the enamel was measured by microradiographic technique and microhardness test. The following results were obtained.
1) An increment in acid resistance of enamel was caused by laser irradiation alone and also fluoride treatment after laser irradiation.
2) In the case of fluoride treatment after laser irradiation, the fluoride uptake into the surface and subsurface enamel was higher than in the cases of fluoride treatment alone.
3) The remineralization was remarkable in the cases of laser irradiation and fluoride treatment after laser irradiation groups. The extent of remineralization was seen from the surface to the bottom of the lesion area.

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Recently the laser doppler velocimeter has been developped as aids in evaluation of microcircuratory flow in a variety of human tissue. We have used this instrument to measure viability of the flaps which were transplanted to the reconstruction of maxillo-facial region.
The blood circulation of D-P flaps and Abbe flap were measured by laser doppler verocimeter. The analog data of the blood circulation was analyzed by using personal computer. The software for data analysis was developped by ourselves.
The laser doppler verocimeter is a non-invasive instrument capable of instantaneous and continuous evalation of local flow in tissue microcirculation. It is fit to monitor viability of flaps used oral and maxillo-facial surgery.

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The purpose of this study was to investigate the changes of the tongue by ArF excimer laser irradiation.
ArF excimer laser was irradiated on the surface of the rat's tongue under the following irradiation conditions: wave length; 193 nm, output; 0.12 W, pulse repetition rate; 10 Hz, spot size; 1.0×3.3 mm, irradiation time; 60 seconds. We examined the thermal change on the tongue during laser irradiation by thermographs. The elevation of temperature on the surface of the tongue during laser irradiation was minimal. The maxium temperature rise was 33.8°C after 6 seconds. Histopathological and scanning electron microscopical studies were performed immediately, forty eight hours, one week and one month after the irradiation. Immediately after irradiation, the wound showed cleancut margins with little coagulation and necrosis tissue. Total removal of the epithelium was effected and, the superficial connective tissue and muscle fiber bundles had also been removed. Forty eight hours after irradiation, there was a clearly defined ulcer associated with bacterial infection. One week after irradiation, normal architecture and thickness of the epithelium was seen. Moreover, SEM findings revealed signs of recovery of the lingual papillae. One month after irradiation, rege nerated lingual papillae were observed over the surface of the wound. Neither inflammatory cell infiltration nor abnormality could be observed.
Because ArF excmer laser dose not demonstrate thermal injury, this finding seems to suggest a focarable condition for the healing process of wounds. The effectiveness of this laser can be attributed to the photoablation of tissues. However, there is much uncertainty about ultraviolet lasers, therefore more studies should be directed toward thes newtypes so it may be used in the clinical field in the future.

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