The purpose of this study was to investigate histopathologically the effects on dental pulp intentionally exposed by Er: YAG laser. A total of 139 teeth of adult dogs, which were administeved general anesthesia, were divided into two groups, laser and control groups. In the laser group, the dental pulp was exposed by an Er: YAG laser in which the output of irradiation was set at 100mJ/pulse (10pps), and the pulp was exposed by a rotary cutting instrument in the control group. Immediately after the exposure, the pulp tissues, which did not undergo any treatment were observed histopathologically in both groups. Seven and ninety days after the exposure, the pulp tissues of both groups which were directly capped with calcium hydroxide, were examined. The presence of microbes and tubular structures of dentin bridge were also investigated. Defects in the center of pulp tissues were evident, even though the exposed areas were small in the laser group. Round cell infiltration and delay of dentin bridge formation were prominent in the laser group on the 7th postoperative day. There was no significant difference in morphological changes of the tissues between both groups on the 90th postoperative day. From the results, it was suggested that pulp tissues may undergo a healing process when the tissues are exposed by an Er: YAG laser as well as those by a rotary cutting instrument.
