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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20本のヒト抜去歯を用い, 248nmのKrFエキシマレーザーを健全なエナメル質と象牙質及び齲蝕エナメル質に照射し, その形態学的変化を光学顕微鏡と走査型電子顕微鏡で調べた。また, エネルギー分散型X線マイクロアナライザーによって照射部と非照射部の元素分析の比較がおこなわれ, サーモグラフィーによって照射後の歯質の温度上昇が測定された。光学顕徴鏡所見では, 照射によって形成された小さな窩洞周囲には炭化も亀裂も生じていないことが示された。走査型電顕所見では, 照射部のエナメル質と象牙質の表層は粗造になっており, 溶解融合した結晶様構造物が観察された。齲蝕エナメル質では, 照射により軟化歯質が完全に除去され, 底部のエナメル質表層は溶解像を呈していた。X線マイクロアナライザー所見では, 照射部象牙質のCa・Pの値がわずかに上昇していることが示された。サーモグラフィーでは, このKrFエキシマレーザーは193nmArF, 308nmXeClエキシマレーザーより温度上昇が大きく, 8秒で47℃, 30秒で74.5℃を記録した。

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ラット頭蓋冠より分離, 株化した骨芽細胞様細胞 (MC3T3-E1) に短時間 (3分間, 5分間) のHe-Neレーザーを照射した時の細胞の増殖に与える影響と, 細胞の無機質形成能の変化を調べるために実験を行い, 次の結果を得た。
1) レーザー照射1日後, 3日後, 8日後の細胞の形態を光顕下で観察したところ, 非照射細胞のそれとの違いは見られなかった。
2) 非照射群, 3分間照射群, 5分間照射群に細胞の増殖能の違いは認められなかった。
3) レーザーを照射した細胞内外に蓄積したカルシウム量は, 非照射細胞のそれよりも有意に大きな値を示した。

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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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ヒトのエナメル質を35%リン酸およびNd: YAGレーザー (0.75W～1.00W, 15pps, 90秒) 照射の2つの異なる方法でエッチングしエナメル質の表面性状を比較検討した.エッチングされたエナメル質表面に両群共, 窩溝填塞剤であるDelton (J & J) を填塞しtag形成の状態を2群で比較した.その結果, Nd: YAGレーザーでエッチングしたエナメル質の場合より, リン酸でエッチングしたエナメル質に多量のmicroporosities (脱灰された小柱端末) がユニフォームに形成された.またtag形成についても, Nd: YAGレーザーで処置したエナメル質よりリン酸で処置したエナメル質において良好であることが示された.

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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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レーザー照射によるエナメル質表面の性状については, 従来よりNd: YAGレーザーによるものやCO2レーザーによる報告は見られるが, その効果については明らかにされていない.私は, 保存学的立場より, Er: YAGレーザーをエナメル質面に照射し, エッチング効果が生じるかどうかについて検討を行った.歯科領域にレーザーを使用する場合, 使用するレーザー光の波長によって吸収係数が異なるため, また光の到達深度も異なってくる.この場合, あらかじめ正確に歯質の吸収係数を測定し, 到達深度を見積もっておくことが必要であり, 適切なレーザーを選ぶに当たって, 臨床応用には重要なことの一つである.熊崎 らは, 第1回レーザー歯学研究会において, 歯質の光吸収係数を詳しく検討した結果を報告し, 日本レーザー歯学会誌第3巻第1号 (1992) に発表した.その結果, エナメル質, 象牙質の吸収係数は3μm前後と10μm前後に大きな吸収を認め, 使用するレーザーの選択に当たっては, この2つの波長を有するレーザーが有効と考えられる.
CO2レーザーについては, 日本歯科保存学会において熊崎らが既に発表を行ったので, 今回は3μm前後の波長を有するEr: YAGレーザーについてエナメル質の表面処理効果 (エッチング効果) の検討を行った.
実験方法: 牛下顎前歯エナメル質にEr: YAGレーザーを9段階のパワーで照射を行い, それぞれの段階において歯質表面処理後にレジン充填を施し, 引張強さを測定し, エネルギー密度と引張強さとの関係について攻究した.
さらに照射レーザービームの評価についてはSpiricon Type LMP32×32-81 (スピリコン社製) レーザービーム評価システムを用いて行った.
さらに各々の照射条件におけるSEM像との対比において最適条件を決定し, 臨床応用に一段と近づいたものと考えている.
実験結果: Er: YAGレーザーによる歯質表面処理効果 (エッチング効果) が生じることが, 引っ張り試験およびSEM像により明らかになった.牛歯エナメル質エッチングによる引張強さでは, エネルギー密度8.5J/cm2で139.7kg/cm2を示し, 酸エッチングの118.9kg/cm2より強い引張強さを示した.このことは明らかに表面にエッチング様変化が変こったものと考えられる.
また, SEM像においてもエッチングによる像によく似た状態が見られる.レーザーによる表面処理効果の発生が考えられた.

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