To elucidate empirical findings about the accelerated wound healing after soft laser irradiation, we examined how soft laser rays activated mouse normal fidroblasts with varying exposure conditions. Then, we observed interesting morphogical changes in the fibroblasts under the optimal exposure conditions.
We used a gallium-arsenide diode soft laser system with the mean output of 2mW emmiting a beam of 904nm wavelength. The cells tested were fibroblasts from mice. We evaluated various exposure conditions on the basis of the growth of mitochondria defined by MTT colorimetry 24 hours after exposure. Next, cellular exposure was made with the optimal exposure conditions, and compared cells with and without exposure to the soft rays immediately, 5, 10, 15 and 18 hours after exposure for their morphologic changes.
The optimal condition selected for the mouse fibroblasts was 4-minute A mode irradiation repeated three times. The morphologic exathination showed that those fibroblasts were originally spindle-shaped immediately after cell division in both groups. Five hours later the fibroblasts without exposure to the soft ray had changed from the spindle-shaped to polygons, while the exposed ones were spindle-shaped with long cytoplasmic filaments. Ten hours later the not exposed cells had changed to big polygonal bodies, while the exposed cells had changed to the spindle shape with several cytoplasmic filaments. Fifteen hours the not exposed cells remained the same polygonal shapes as before, while the exposed cells almost began to devide. Eighteen hours later the not exposed cells had changed in shape from polygonal to spindle-shaped, while the exposed cells had completed the cell division to be spindle-shaped with long cytoplasmic filaments. In summary, it was clearly demon strated that the soft laser rays directly act on the fibroblasts to accelerate their cell growth.
(J. Jpn. Soc. Laser Dent. 7: 1-5, 1996 Reprint requests to Dr. Takagi)

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Recently, the Er: YAG laser was invented for the hard tissue ablation. The Er: YAG was low noise, less vibration and less pain during procedure compared with conventional drilling machines. Above mentioned advantages of the Er: YAG laser was very useful in Pedodontics fields. The irradiation condition of the laser on the deciduous tooth becomes necessary for the clinical application of the laser on the pediatric patients.
The purpose of this study was to decide the most suitable laser irradiation condition in the deciduous tooth.
The extracted deciduous upper central incisors were used in this experiment. The energy of the laser was varied from 100mJ/pulse, 200mJ/pulse, 300mJ/pulse, 400mJ/pulse and 500mJ/pulse, the repetition rate was 8Hz and irradiation time was 5 seconds in each.
Then the morphological changes of the tooth structure were examined by the light microscope or the scanning electron microscope.
The conclusions from these results were as follows.
1) The laser irradiated area had clear margin with the surrounding tissues. The crater was occurred in this area. The depth of the crater was depend on the energy density of the laser.
2) Any smear layer was not seen at the laser irradiated dentin, but opening of the dentinal tubules were clearly observed.
3) This experiment showed that the optimum laser irradiation energy for cavity preparation of the deciduous tooth was 300mJ/pulse.
In this laser condition, little heat degenerative changes could be seen at the laser irradiated area and no degenerative changes were seen in surrounding tooch structures.
(J. Jpn. Soc. Laser Dent. 7: 6-11, 1996 Reprint requests to Dr. Moriya)

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The aim of this study was to histopathologically investigate the effects of pulsed Nd: YAG laser irradiation on the periradicular tissues when applied in the root canal of the dog.
Six adult mongrel dogs were anesthetized and the tooth pulps of the upper and lower premolars were extirpated. Each root canal was cleaned and shaped to a final apical file size #55. Non-irradiated root canals were served as control.
The laser irradiation (100mJl0pps, 100mJ20pps, 100mJ30pps, 200mJ10pps and 200mJ20pps) was performed under an up-and-down motion in the root canal between the apical and cervical portion with an optical fiber (∅=400μm) for 30 sec. After the irradiation, a small cotton pellet soaked with formalin cresol was placed in the pulp chamber and the access cavity was filled with glass ionomer cement. The animals were sacrificed at 7 and 28 days postoperatively.
The results were as follows:
1. At 7 days postoperatively, no histopathological difference was found between the control and 100mJ10pps group. On the other hand, carbonization and defects of the root canal wall were observed in all laser-treated groups except the 100mJ10pps group.
2. At 28 days postoperatively, alveolar bone resorption was often observed again in all laser-treated groups except the 100mJ10pps group. Furthermore, in the 100mJ20pps group, dentoalveolar ankylosis was observed in the periradicular tissues, and severe external root resorption was frequently seen in the 200mJ20pps group. However, in the 100mJ10pps group, the degree of inflammation in the periradicular tissues was similar to the control.
3. It was concluded that pulsed Nd: YAG laser with irradiation energy less than 100mJ10pps could be used safely in the root canal of the dog.
(J. Jpn. Soc. Laser Dent. 7: 12-21, 1996 Reprint requests to Dr. SEKINE)

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To elucidate the in vivo effect of low power diode laser irradiation on mineralization in molar tooth germ, we examined the effect of the laser on the development of mandibular first and second molars in neonatal mouse. In a newborn mouse, the mandibular first molar showed differentiated odontoblast, differentiated ameloblast, slight dentin and enamel formation. The second molar was an early bell stage. In a two day-old neonatal mouse, the developmental stage of the second molar corresponded to the stage of the first molar in a newborn mouse. The laser (50mW, 5min/day) was irradiated to the mandibular tooth germ at twice and the chemical and histological changes in these molars were examined. In the second molar showing an early developmental stage (cell proliferation and differentiation), the laser irradiation increased alkaline phosphatase activity, calcium content and the formation of both dentin and enamel. Also, in the first molar showing a late developmental stage (additional mineralization), the laser irradiation also increased the mineralization in both dentin and enamel. From the in vivo experiment, we confirmed that diode laser irradiation accelerated tooth formation and mineralization at all developmental stages observed in the present study.
(J. Jpn. Soc. Laser Dent. 7: 22-29, 1996 Reprint requests to Dr. Okumura)

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Previously, we demonstrated the suppressive effect of low power laser (He-Ne laser) irradiation on mineralization in molar tooth germ using the organ culture system. In the present study, we examined the in vivo effect of the laser on the development of mandibular first and second molars in neonatal mouse. The laser was irradiated at developmentally different stages and the chemical and histological changes in these molars were examined. At an early developmental stage of tooth germ showing cell proliferation and differentiation, the laser irradiation caused decreases of alkaline phosphatase activity, of calcium content and the formation of dentin and enamel in tooth germ. However, at a late developmental stage of tooth germ showing additional mineralization, these decreases were not observed at the time of the laser irradiation. From the in vivo experiment, we confirmed that He-Ne laser irradiation suppressed tooth formation and mineralization at an early developmental stage.
(J. Jpn. Soc. Laser Dent. 7: 30-36, 1996 Reprint requests to Dr. Tsuboi)

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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)

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Clinical application of the Er: YAG Laser for dental caries and periodontal treatment has been developed. In clinical use, the effect of mis-irradiation of the Er: YAG Laser on the surrounding tissues should be considered. The purpose of this study was to examine the effect of the Er: YAG Laser on soft tissues supposing the side effect of mis-irradiation. The Er: YAG Laser was irradiated against the tongue of rat under following various conditions; the energy level: 50, 150, 300mJ/pulse, pulsing time: 1 and 10 pulses, irradiation distance: 0, 5, 10 and 20mm, and irradiated field: wet or dry. Wounds on tongue were observed macroscopically at 0, 1, 3, 7 and 14 days after laser irradiation. Some specimens were also examined by SEM. The following results were obtained: contact irradiations caused limited damages to tongue regardless of water irrigation; however, the depth of wounds depended upon the pulsing time and power level of the laser, while, non-contact irradiation showed a little or no effect against tongue. Moreover, the use of water irrigation decreased their damages effectively. With respect to wound healing, all cases were shown as normal process. Clinically, most of mis-irradiations are supposed to happen with non-contact irradiation under water spray. These results indicate that the Er: YAG Laser application for intraoral usage would be safe for the surrounding soft tissues within the usual power setting in dental treatment.
(J. Jpn. Soc. Laser Dent. 7: 46-57, 1996 Reprint requests to Dr OHNO)

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The purpose of this study was to evaluate the effects of Er: YAG laser irradiation on human extracted root surfaces in vitro, and to compare with Nd: YAG and CO₂ laser irradiation. Twelve 5mm×5mm human root slices were prepared for this study. Two areas with 2mm×3mm were marked at both sides to the tooth axis in each slice. One area was irradiated with water cooling and the other without cooling. Three slices were randomly assigned to each of the following 4 different treatment groups: 1) Er: YAG laser treatment; 2) CO₂ laser treatment; 3) Nd: YAG laser treatment; 4) Nd: YAG laser treatment to the root surface coated with black stain. Non-lased surfaces served as controls. The pulsed Er: YAG and Nd: YAG laser irradiations were performed for 10 seconds with an energy level of 50mJ at 10pps in the contact mode, holding the 0.6mm contact handpiece at 45 degree angulation to the root surface. The CW CO₂ laser was irradiated with an energy level of 0.5W in the non-contact focus mode. After laser irradiation, the specimens were examined with stereoscope and scanning electron microscope. Root surfaces irradiated by Er: YAG laser featured scaly like appearances. Surfaces received CO₂ laser irradiation without water cooling exhibited distinct carbonization and many cracks. With the Nd: YAG laser irradiation, charing, melting and lava-like appearance were observed when the laser was irradiated to the black stained surface without water cooling. The results of this study showed that three kinds of laser application to root surfaces resulted completely different morphological changes. We should consider the characteristics of laser and their effects to root surface, using any laser for periodontal treatment such as scaling, root conditioning, and killing of periodontopathic bacteria.
(J. Jpn. Soc. Laser Dent, 7: 58-66, 1996 Reprint requests to Dr. ANDO)

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Broad tunability and the unique pulse structure provided by Free Electron Laser (FEL) technology provided new possibility for laser dentistry. Using the FEL tuned to phosphoric acid ion (9.4μm) which is an absorption maximum in infrared region on dentine, we investigate the irradiation effect on dentine.
As a result, it was observed that irradiated dentine surface which was amorphous changed to the recrystalized structure. This result indicates that 9.4μm-FEL irradiation caused selective ablation of phosphoric acid ion and annealing.
(J. Jpn. Soc. Laser Dent. 7: 67-71, 1996 Reprint requests to OGINO)

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Acupuncture to the meridian point of “Gekan” has been used to treat the patients of temporomandibular joint disorder. In recent studies (Arao et al 1990, 1991, 1992, 1994), instead of using a needle, the author irradiated several times with a low power laser (Nd: YAG at 350mW) for the Type I, Type II and Type III patients with closed-lock. This relieved the pain somewhat, but since the treatment results were determined by the subjective judgement of the patient, the authors evaluated the results objectively. We used thermography to evaluate symptomatic change, and using the Laser Doppler Flowmeter (LDF), we measured the surface blood flow of the skin in the area of the temporomandibular joint.
In this study, for the Type IV patients, we used the low power laser. Each patient was treated by low power laser for “Gekan” for 15 minutes from the first examination. After the pain of the temporomandibular region was remedied, we manipulated the mandible. The results were that in several months, the symptoms of temporomandibular disorder ceased. But from the MRI findings, the disk position and the shape of mandibular head did not change.
These results suggest that the low power laser treatment for the patients of temporomandibular joint disorder is useful not only for the Type I, Type II, Type III parients with closed-lock patients, but also for Type IV patients.
We suggest that it is necessary to continue this line of research for a long period, and to treat a greater number of cases.
(J. Jpn. Soc. Laser Dent. 7: 72-82, 1996 Reprint requests to Dr. Arao)

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