We investigated the transmission of Nd: YAG laser through human dentin and reported the results on the Journal of Japanese Society for Laser Dentistry VOL.7, No 1.
In this report, we further investigated the transmission of GaAlAs semiconductor laser through human dentin. The materials and methods were in accordanse with the previous report, but GaAlAs semiconductor laser equipment used in this study was DSL-1000 (Morita). The irradiation conditions of GaAlAs semiconductor laser were normal pulse, 700 mW, 810 nm and 2-second duration.
Three measurements of the intensity of transmitted laser light (T-light) through dentin of approximately 1 mm thickness were performed by a power monitor (Ophir Optics Ltd). And the power monitor was transferred 2 mm perpendicularly from the center of laser light (C-L). And then the measurment of the intensity of scattered laser light (S-light) was trebled. And then the power monitor was further transferred 4, 6, 8, 10 and 12 mm from C-L and the measurment of the intensity of S-Light was trebled at each displacement from C-L.
Then the thickness of dentin (DTh) was stepwise decreased with the interval of approxi mate 100 μm, 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 6 mm, but no significant relationship was found if the distance from C-L exceeded 8 mm.
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.
4. The extent of scattering of S-light through human dentin was greater on GaAlAs semiconductor laser than that on Nd: YAG laser.
(J. Jpn. Soc. Laser Dent. 8: 1-6, 1997 Reprint requests to Dr. ZENNYU)

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The purpose of this study was to examine the depth into penetration of the tissue and the circulatory structure of the microvasculature after irradiation the Nd: YAG laser on the lingual dorsum of a 9-week-old male wistar rat.
The Nd: YAG laser was irradiated against the tongue of rats under the following condition; the energy level; 1, 2 and 3-Watts for 1.0, 2.0 and 3.0 seconds.
Wounds of tongue were observed macroscopically, microscopically and also examined by SEM. The following results were obtained; Microscopical findings: The penetration was observed until the lamina propria in 1W1S and 1W2S groups
The penetration of 1W3S, 2W2S and 3W1S groups were observed still superior tranversus linguae layer and also were observed in the muscle layer for 3 second group.
SEM findings: The capillary loops of the papillae and the lamina propria venure networks were damaged in 1W1S and 1W2S groups.
Irradiation wounds disappeared in the capillary loops of the papillae and the lamina propria venure networks.
In 1W3S, 2W2S and 3W1S groups, and also disappeared in the capillaries of muscle layer in 3 second groups.
(J. Jpn. Soc. Laser Dent. 8: 7-15, 1997 Reprints request to Dr. MATSUMOTO)

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The irradiation effects and the mechanisms of Er: YAG and Nd: YAG lasers on LPS (lipopolysaccharide) were evaluated. LPS was irradiated by Nd: YAG and Er: YAG lasers at 100mJ (1.5W). Also, the combustive experiment was performed using mild and hard flames with a gas burner. Several proteins with molecular weights of 10 to 40kDa were recognized as quantitative change on SDS-PAGE after the irradiation of Er: YAG laser.
The electrophoretic pattern of LPS after the exposure to Nd: YAG laser was similar to that of the LPS burned by the hard flame. The hexosamine content, which was surmised from the value of the amino acid analysis of LPS after the irradiation by Nd: YAG laser showed a marked difference compared to that of other samples. The amino acid composition of LPS after the irradiation by Er: YAG laser was almost similar to that of the control and the mild flame.
(J. Jpn. Soc. Laser Dent. 8: 16-22, 1997 Reprint requests to Dr. Yamaguchi)

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ently, many studies on the application of Er: YAG laser in the dental field have been reported. Er: YAG laser can ablate dental hard tissues with small thermal damages, and is clinically applied for removal of dental caries. However, there are few studies on apicoectomy using Er: YAG laser. The purpose of this study was to compare apicoectomy using Er: YAG laser and the conventional cutting method in vitro.
Extracted single-rooted human teeth were used in this experiment. Root resection was performed with Er: YAG laser (output energy: 70mJ10pps) or a fissure bur mounted to a micro-motor. Resected root surfaces were evaluated with scanning electron microscopy.
In addition, cutting efficiency of both methods and dye penetration of the cut surface were compared. After removing the tooth crown of 10 extracted single-rooted human teeth, root canals were cleaned, shaped and obturated. Then, the samples were randomly divided into two groups. Root resection by Er: YAG laser or micro-motor was perfOrtned, and working time was counted and the cut surface area measured. Then, all the root surfaces were sealed with nail polish except the resected surface. All roots were placed into 0.1% methylene blue dye for 7 days, rinsed and air-dried. Finally, they were split and the dye penetration from the resected surface was measured and statistically analyzed.
The results were as follows:
1. There were no smear layer or debris left on the resected surface cut by Er: YAG laser, and the shape of the cut surface was irregular. On the other hand, both smear layer and debris were observed on the surface cut by the conventional method, and the cut surface was smooth.
2. The cutting efficiency of Er: YAG laser and micro-motor was 14.8 (±7.3) sec./mm² and 4.4 (±1.7) sec./ram², respectively. Cutting by Er: YAG laser significantly needed more time than that by micro-motor (t-test, P<0.05).
3. Dye penetration length in the Er: YAG laser group and micro-motor group from the resected surface was 0.95 (±0.37) mm and 1.07 (±0.70) mm, respectively. There was no significant difference between the two groups.
(J. Jpn. Soc. Laser Dent. 8: 23-30, 1997 Reprint requests to Dr. EBIHARA)

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The purpose of this study was to examine morphological and histopathological changes of the cervical enamel and root dentin of the treated cavity after root caries ablation using an Er: YAG laser. The prepared surfce using the Er: YAG laser was compared with that of conventional mechanical treatment. Ten extracted human teeth with root caries were used. Half of the carious lesion in each tooth was ablated with the Er: YAG laser, and the other was removed with a steel bur mounted on a low-speed micromotor. Er: YAG laser treatment was carefully performed under water spray using a combination of contact and non-contact irradiation modes. SEM and histopathological observations were performed for each treatment. The Er: YAG laser was able to ablate root carious lesion effectively without major thermal damage to the surrounding dental hard tisssues. However, the treated cavity margin tended to be irregular and unclear. Due to the careful irradiation technique, the irregularity of the cavity floor was relatively small and the residual structural change of the lased dentin was generally minimal except for the scarce highly-damaged area. The super ficial layer of the lased dentin showed deep staining with hematoxylin in the histological observation and typical microirregularities in the SEM examination. On the lased enamel, however, large microcraks and microirregularities were noted in the SEM evaluation.
In order to perform effective caries removal and cavity preparation using the Er: YAG laser, further studies are required on the irradiation conditions and techniques, and on the conditioning of the lased surface for adhesive restorations. Especially, structural changes and finishing of the marginal enamel of the lased cavity should be investigated more minutely.
(J. Jpn. Soc. Laser Dent. 8: 31-37, 1997, Reprint requests to Dr. AOKI)

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