Transmission of Nd: YAG Laser through Human Dentin

Transmission of Nd: YAG laser through human dentin, whose thickness was stepwise decreased, was measured. Four human molars stored in saline solution were used. Dentin specimens with the thickness of approximate 1mm were created by cutting the teeth crossectionally using a diamond disc, followed by being polished by #600 silocone carbide paper and a whetstone. Average dentin thickness (DTh) of each specimen was calculated from five measurements each using a micrometer. Nd: YAG laser equipment used was Dent Lase DCL 8 (S.L.T Japan). An experimental laser tip made of quartz and an experimental gold-plated specimen holder having a central hole were employed. The irradiation conditions of Nd: YAG laser were normal pulse, 170mJ, 20pps and 2-second duration.Three measurements of the intensity of transmitted laser light (T-light) through dentin of approximately 1mm thickness were performed for each specimen by a power monitor (Ophir Optics Ltd). And the power monitor was transferred 2mm perpendicularly from the center of laser light (C-L). And then the measurement of the intensity of scattered laser light (S-light) was trebled. And then the power monitor was further transferred 4, 6, 8, 10 and 12mm from C-L and the measurement of the intensity of S-light was trebled at each displacement from C-L.Then DTh was stepwise decreased with the interval of 100μm, and T-light and S-light was repeatedly measured in the same manner described above.Relationship between DTh and T-light or S-light, and the relationship between the distance from C-L and T-light or S-light were analyzed by regression analysis.The following results were obtained;1. T-light was found to decrease with increasing the thickness of dentin and an exponential relationship was found between DTh and T-light.2. An exponential relationship between DTh and S-light was found when the distance between C-L was within 2mm, but no significant relationship was found if the distance from C-L exceeded 4mm.3. S-light was found to decrease with increasing the distance between C-L and a linear relationship was found between the distance from C-L and S-Light irrespective of DTh.(J. Jpn. Soc. Laser Dent. 7: 37-45, 1996 Reprints request to Dr. Zennyu)