The CO₂ laser has been used in medicine for nearly three decades. Although it had many advantages in the field of oral and maxillofacial surgery, it had limited applications because of its bulky articulated-arm delivery system and so on. Recent improvements such as new flexible fibers and tiny handpieces, however, now allow easy access to any part of the mouth. Nowadays we pay attention to its excellent hemostasis and non-contact surgery in the management of patients with infectious diseases.
For the purpose of progressing clinical applications, open and closed wounds which were intended to mimic those produced in clinical oral surgery were created by CO2 laser at rabbit tongue. Then macroscopic and histopathological observations were performed on the healing process of these wounds. And moreover they were compared with scalpel wounds.
The results were as follows. Although laser wounds heal slower than scalpel wounds, there is no essential difference in healing process. There is also no difference in the healing process detween open and closed wounds even if the tissue damage extends to the muscle layer.

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The penetrative sensitivity of Ga-Al-As semi-conductor laser (790nm, 60mW, continuous wave) in living tissue were evaluated the amount and the distribution of the laser beam on the penetrative side were quantified. Tissues used in this study consist of mandi bular cortical bone derived from human or ox, masseter muscle and fat tissue from ox, white meat of chicken and human venous blood which were all collected on the same day of mesurement. Five samples of each tissue were investigated in fresh status the transmittance and the attenuance of each sample were calculated, and finally following results were indicated.
1. Contact irradiation was more effective for the reduction of energy loss on tissue surface than incontact method.
2. Percent transmittance of either human or ox mandibular cortical bone in 1.0mm thickness reached approximately 50%. The distribution of the beam power on the penetrative side showed remarkable scattering and some absorption through the same sample.
3. The transmittance of masseter muscle and fat tissue from ox close to cortical bone but chicken white meat showed high transmittance of 75% in 1.0mm thickness. In the analysis of the distribution of energy on penetrative side of these three soft tissues, resemble patterns produced under the mixed effects of absorption and scattering were observed.
4. Human venous blood indicated low level of the transmittance as compared with other tissues. According to the results of analysis on power distribution, the laser beam seemed to be attenuated by absorption rather than by scattering.
5. Attenuation of the laser beam in accordance with the thickness was similar to the graph which was led to Kubelka-Munk's formula for the attenuation of scattering light.

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We present a case of oral malignant melanoma, which was treated by CO₂laser surgery and radiation, and which has been controlled over seven years after the treatment.
A 78-year-old female visited our hospital with a complaint of a black tumor in the upper molar region, September 20th, 1985. She noticed a swelling 2 months ago. At the first visit we observed a well defined pigmented mass, 20×30mm in size, in the left upper molar alveolar region, and several pigmented spots in the median part of the hard palate and the left buccal mucosa. We made a diagnosis of malignant melanoma and began a linac X-ray irradiation. When the radiation dose was 26Gy, we excised and vaporized the lesion including the bone of alveolar process and palate, pigmented spots of the palate and buccal mucosa using CO₂ laser. Then we continued the radiotherapy and finished it total 60Gy. There is no recurrence or metastases over seven years after the treatment.

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[in Japanese]

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[in Japanese]

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This study was carried out to clarify the effects of low-energy laser, diode laser (wavelength: 890nm, output power: 0.339mW) irradiation on osteoblastic cell activity. In addition, we investigated the influence of presence of the implant body on osteoblastic cells.
We used the human osteoblastic cells (HUO9, O9N2, YT-48). These cells were cultured in a RPMI-1640 medium supplemented with 2mM ascorbic acid, 2mM α-glycerophosphate and 10% fetal calf serum. Irradiation time (density) were 1min (0.6mJ/cm²), 2min (1.2mJ/cm²), 3min (1.8mJ/cm²), 5min (3.0mJ/cm²), 7min (4.2mJ/cm²), 10min (6.0mJ/cm²), 12min (7.2mJ/cm²), 15min (9.0mJ/cm²).
As the result, proliferation of these cell were not stimulated by the laser irradiation, but the presence of the implant body were not inhibited them. Alkaline phosphatase activity of HUO9 and O9N2 were decreased by laser irradiation (irradiation density, more than 6.0mJ/cm²). But YT-48 was not inhibited.

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A laser as stimulated optical radiation was first described by Maiman in 1960, and since that time the application of the laser in dental and medical clinics has extended from diagnosis to treatment. On the other hand, a potential danger exists if an error is made during the irradiation procedure. However, the extent of retinal damage after exposure to a soft laser is still far from clear.
For demonstration of damage due to laser irradiation, ophthalmoscopic and light and electron microscopic studies were made on the hooded (pigmented) rat retina after the irradiation at therapeutic (peak power 20W) and experimental (peak power 80W) levels with a Ga-Al-As diode pulse laser (904nm) apparatus. And the features observed were compared with the retinal damage induced by argon laser photocoagulation (20mW for 0.02 sec and spot size of 50μm was used).
The following results were obtained.
1. In ophthalmoscopic observation, exposure of the retina to soft laser irradiation did not reveal any problems such as retinal damage and degeneration which were seen after photocoagulation.
2. Light and electron microscopical examination did not indicate any pathological changes in the retina throughout the observaion period, except for distention of choroidal vessels by 24 hours after the exposure at the experimental level.

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The etching pattern for the enamel surface of human teeth was compared using 35% phosphoric acid and the use of the Nd: YAG laser with potency varying from 0.75w to 1.00w, and 15pps during 90 seconds. The formation of tags was also observed in two groups, one treated with 35% phosphoric acid and the other with Nd: YAG laser, and both received DELTON (J&J) pit and fissure sealant. The samples were examinated by scanning electron microscopy (SEM), which showed that the patterns obtained by the phosphoric acid etching were uniform presenting a great quantity of microporosities thus being considered superior to the pattern obtained by the Nd: YAG laser etching, either by 1.00w or 0.75w. The formation of tags showed better results in the group treated by the phosphoric scid than in that treated with Nd: YAG laser.

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Osteoclasts isolated from 3-4 days rats were cultured on laser irradiated bovineroot dentin to determine the behaviour of the osteoclasts, especially the cell adhesion as well as the resorption of dentin. Methods were as follows.
. The cells were stained by FITC-marked phalloidin and observed under fluorescence microscopy.
2. The cells were stained with TRAP and observed under microscopy.
3. The cells were observed under SEM.
Following results were obtained.
Osteoclasts and resorption pits were observed on the unirradiated dentin, however, they were not seen on the laser irradiated dentin. Laser exposure to dentin seemed to inhibit the adhesion of osteoclasts.

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The purpose of this study was to examine the morphlogical changes and the thermal effects of the CO2 laser irradiation on dentin. For this study, eighteen extracted hu man molars were used. In the experiment examining morphological changes, the irradiation power was 1 to 10 watts, the pulse times were 10 to 500ms and the irradiation frequency was 1 to 20 times. On the dentin surface irradiated by CO2 laser under various conditions, the carbonized area became wider, if the irradiation energy increased.
But the depth and width of the cavity was the same, when the irradiation power was con stant. the irradiation energy densities were less than 153J/cm2, the dentin surface changed without making any cracking.
In the experiment examining thermal effects, dentin blocks, 1.0 and 2.0mm in thickness, of extracted molars were prepared. These were lased by the CO2 laser using 1 to 5 watts at 10ms pulse mode for 30 seconds.
The thermal increase transmitted from the lased surface was measured with the thermoco uple. The results indicate that the thermal increase depends on the dentin thickness and is in inversely proportional to the square of the dentin thickness. For example the thermal in crease should not rise more than 5 degrees for 10 seconds, when the dentin thickness is more than 2mm and the irradiated power is less then 2 watts. This result suggests that this laser irradiation may be successfully used in clinical situation as one of dentin treatment tech niques after further clarification of thermal effects on dental pulp.

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It is generally known that infrared lasers have thermal side effect, which cause damage to the soft and hard tissues. The extent of thermal damage can be controlled by a choice of laser wavelength irradiance and exposure duration. Recently, it has been demon strated that soft and dental hard tissue can be removed by a long-pulse TEA CO₂ laser irra diation with minimal thermal damage. However, there are few studies about the effects of the TEA CO₂ laser on the bone tissue.
The purpose of this study was to investigate the changes of the bone structure induced by TEA CO₂ laser irradiation. The rat's mandibula in, in vitro (extripated) and in vivo condi tions were used. The bone surface was irradiated with TEA CO₂ laser beam under the fol lowing conditions: wave length; 10.6μEm, output; 95m J/pulse, pulse repetition rate; 1Hz, irradiation time; 7.5μEs/shot, spot size; 0.8×1.5mm, energy density; 7.9J/cm². Histological and scanning electron microscopical studies were performed. The same results were ob tained in the both cases (in-vitro and in-vivo). TEA CO₂ laser beam produced defect with clean-cut margins. Histological examinations revealed presence of the thin basophilic line at the bottom and along the walls of defects. There was the superficial melting of the bone which is smeared by scanning electron microscopical findings. Although we found that the thermal damage at the bottom and along the sides of defects in bone was minimal, it was still observed. However, undesirable thermal effects like surface-cracking and carbonization were not observed. These findings suggested that it is possible to remove the bone tissue by TEA CO2 laser irradiation with minimal thermal changes. Therefore, further investigations have to be done to prove TEA CO2 laser for possible applications in dentistry.

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The purpose of this study was to evaluate histopathologically and clinically, the effects of the pulsed Nd: YAG laser irradiation on the apical seat of root canals after vital pulp extirpation, using dogs and human teeth. First of all, the histopathological examina tion was conducted to estimate the clinical effects and safety of laser irradiation. 192 vital teeth of 18 dogs were instrumented up to #40 by the conventional method and divided into lased and control groups. In the lased group, the fiber of pulsed Nd: YAG laser (d-Lase 3 0 0; American Dental Laser Co., USA) was introduced to the apical seat and the laser was ir radiated under the condition of 1, 2 and 3W, 15 and 20PPS and 0.5, 1, 2, 3 and 4sec. Then, the access cavity of both groups was sealed with guttapercha and amalgam. Histopathological study of the two groups was carried out after 1, 2 and 4 weeks. The following results were obtained;
1. Debris in the apical seat could be removed depending on the condition of the laser irra diation.
2. Irradiation of higher energy output in case of 2 W-2 sec and 3 W-2 sec often produced carbonized dentin and periapical chronic inflammation including root resorption.
3. Irradiation under the condition of 1 W-2 sec, 2 W-1 sec and 3 W-0.5 sec was acceptable to the apical seat and periapical tissues.
Sixty human pulp extirpated teeth were divided into lased and control groups and immedi ately root canal filling were carried out. Under the consideration of the safety to the perio dontal ligament, the condition of lased group in the clinical study was determined as 1 W (1 5 PPS)-1 sec irradiation at the apical seat. Clinical examination up to 3 weeks revealed that significant reduction of post-treatment discomfort or pain in lased group was comfirmed with the 5% level according to the Chi-Square analysis. Irradiation under the condition of 1 W-1 sec at the apical seat was safe and useful in case of an immediate canal filling after vital pulp extirpation. The mechanism of laser effects was considered hemostasis and removal debris and remunant pulp at the lased potion.

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[in Japanese]

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