The purpose of this study was to evaluate the effect of Nd: YAG laser irradiation in non-vital tooth bleaching when the laser was combined with 30% hydrogen peroxide.140 human extracted permanent teeth which had been artificially stained withhematoporphyrin were used. The specimens were divided into 3 groups. In the controlgroup, a cotton pellet saturated with 30% hydrogen peroxide was placed in the pulp chamberfor 3 minutes. In the experimental groups, each pulp chamber was filled with 30% hydrogenperoxide and Nd: YAG laser (d-lase 300, American Dental Laser Co.) was irradiated eitheron the labial enamel surface or on the labial wall of the pulp chamber from a distance of10mm. The laser was irradiated under the condition of 1, 2, 3W, 30pps, defocused beam andtwo times irradiation for one minute with one minute-interval. The colour of each tooth before staining, before the treatment and after the treatment was recorded by photography andmeasured with a colourmeter in Region-1 (cervical third) and Region-2 (incisal third).Morophological changes and temperature rising on the irradiated tooth surface were examined with a scanning electron microscope and thermography.
1. Laser irradiation groups revealed more improvement of the discolouration than the control group by the examination. Promotion of the bleaching effect by laser was confirmedalso by the colourmeasuring.In the enamel-irradiation group, reduction of L* values (lightness) in Region-1 and 2 was obvious even with 1W and reduction of C* value (chroma) inRegion-1 and 2 was observed with 2 and 3 W. In pulp chamber-irradiation group, L* valuesin Region-1 reduced with 2 and 3W, those in Region-2 did with 1, 2 and 3W.C* value inRegion-1 and 2 reduced with 2 and 3W.
2. No morophological changes was observed on the irradiated enamel surface, howeverslight melting of dentin surfaces was found in the pulp chamber irradiated with 3W.
3. Temperature rising on the irradiated tooth surface were measured to be 4.1-21.6°C. Itseemed that temperature in Region-2 became higher than that in Region-1, and the reductionof L* and C* values was propotional to the temperature rising. It was concluded that thisbleaching method with Nd: YAG laser and 30% hydrogen peroxide was safe and effective to reduce the chair time for the treatment of non-vital discoloured teeth. (J. Jpn. Soc. Laser Dent.4: 9-19, 1993Reprint requests to Dr. Hirayama)
