A possibility of the He-Ne laser application for human dental plaque control was investigated. Twenty adult volunteers participated in this experiment. One of the premolar teeth on one side of a subject was irradiated by the He-Ne laser for 3min., once a day, for 3 days, at an output power of 20mW, while one of the premolar teeth on the other side was left unirradiated as a control. The number of cultivable plaque bacteria was found to be reduced by He-Ne laser irradiation when dental plaque was stained with methylene blue-based plaque-disclosing dye. No similar decrease in cultivable bacteria was observed when the laser irradiation or the plaque-disclosing dye alone was used. From these results, the photodynamic killing mediated by He-Ne laser irradiation was shown to affect oral bacteria in vivo, and the potential application of this new modality for dental plaque control is discussed.

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The clinical phase III trial of photodynamic therapy (PDT) was performed using the excimer dye laser (PDT EDL-1) and the photosensitizer PHE (Photofrin II) for endoscopical early stage lung cancer (25 cases/281 esions), gastric cancer (18cases/181esions), and esophageal cancer (5 cases/51 esions) in 6 hospitals from September 1990 to March 1992. The exposure energy densities of the laser beam were 100J/cm² or more for lung cancer and 60J/cm² or more both for gastric and esophageal cancers, Photofrin II was 2mg/kg. The complete response (CR) due to the therapeutic effect of PDT was 81.5%(22/27) for lung cancer, 88.9%(16/18) for gastric cancer and 100%(5/5) for esophageal cancer. Complete cures were obtained for lesions that seemed less invasive with respect to surface size, depth and endoscopic appearance. Recurrence was 6.0%(3/50), probably due to insufficient penetration of the laser beam. The main complications (≥WHO grade 2) of PDT were dermatitis (2.1%), sunburn (2.1%), symptoms due to obstructive pneumonitis (4.3%) and gastrodynia due to ulceration (2.1%), all of which were transinent and none of which were serious.
Photodynamic therapy with PDT EDL-1. and Photofrin II is an effective therapy through which complete cure can be achieved for cancers evaluated endoscopically as early stage, though some restriction in size.

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Bipolar laser forceps (BLF) were developed by the application of fiber coupler method in order to divide one laser beam into two transmissions.
Divided laser fibers were attached to each tip of a pair of forceps; then Nd: YAG lasers were irradiated from different directions through these forceps grasping an object.
After the irradiation activity was confirmed by means of fundamental investigations, BLF were applied to several clinical operations. Bio-physical studies revealed the possibility of laser beam division. The energy loss from division was 6% and the difference in power output between both laser fibers 2%. The conventional laser system was applicable to this method if the fiber coupler was connected to.
As a basic experiment, coagulation and cutting were attempted on the renal vessels of rats. As a result, the vessels were completely transected at an energy output of 14.5 J. An histological examination revealed a localized thermal damage around the irradiation area.
BLF were then applied to several urological operations for the clinical evaluation. At a low power output, bipolar laser irradiation demonstrated excellent coagulating and cutting effect during the surgical procedure.
According to the present experience, therefore, it was suggested that the use of BLF would be indicated for a greater area including endourology.

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We have used potassium titanyl phosphate (KTiOPO₄: KTP) laser in various craniotomies, and evaluated its efficacy. The KTP laser has a wavelength of 532nm, which is just a half wavelength of neodymium: yttrium-alminum-garnet (Nd: YAG) laser. Its energy is easily absorbed in hemoglobin because the wavelength is very close to that of maximum absorption to hemoglobin. This evidence is beneficial for the hemostatic cutting. The KTP laser light is delivered through a flexible quartz fiber to the operative field. The visible green laser light allows the surgeon to set the target precisely. With the light bayonet hand piece, the laser could be introduced even through a minimun opening to the deep seated skull base tumors. The laser was used in both contact and non-contact methods with simply cleaving the tip of the fiber, whenever polluted. The tissue damage caused by laser irradiation was investigated with brain tumors as well as rat cereberum. It was disclosed that the thickness of thermal damage was no more than 1.5mm when the laser mode was set for the usual tumor evacuation. These features of the KTP laser apparatus in considered to be powerful advantage for using in microneurosurgery.

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To evaluate the efficacy of laser-assisted vascular anastomosis (LAVA) for the wound healing, collagen content, non-collagenous protein content and collagen concentration were measured at 1 hour and 7, 15, 30, 60 and 90 days after anastomosis of canine common carotid artery. The dye-binding method was employed, Results were compared to conventional suture vascular anastomosis (CSVA) with 7-0 polypropyrene.
In LAVAs, collagen content and conecntration rapidly increased and hit a peak at 15 days, then, after 30 days, returned to the same value as at 1 hour. In CSVA, they were gradually increased and maintained high level even 60 days after surgery.
From these results, we concluded that LAVAs gained better and more rapid healing than CSVAs.

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The influence of 70% hepatectomy on the healing process of arterial anastomosis was investigated in rats who underwent arterial reconstruction by the microscopic surgical techniques of laser-assisted vascular anastomosis (LAVA) and conventional sutured vascular anastomosis (CSVA). In bursting pressure and incidence of aneurysm formation at the anastomotic site, there was no significant difference between LAVA and CSVA. Incidence of calcification at the anastomotic site was significantly lower in LAVA than in CSVA. It was concluded that LAVA would be a useful option in vascular anastomosis, even during extended hepatectomy.
Anastomosed vessels, especially for liver transplantation, are often different in diameter, wall thickness or nature. These specific situation are problematic and its investigation is mandatory for the clinical application of LAVA.

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Low energy Nd-YAG laser was utilized to make vascular welding with contact method. After success and good patency for vascular welding in canine experience, sixty three patients with 4 ischemic heart disease, 2 coarctation complex, 39 peripheral occlussive disease and 18 chronic renal failure were received laser vascular welding. these weldings successed in all cases except one and patency rate was excellent. The anastomotic sites of the aorta in infants were growable. Late patency rate was also excellent because of 77% seven years later.

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End-to-end anastomosis of the external iliac artery was performed in 4 young mongrel dogs using an argon laser and interrupted suteres. The time needed for the procedure by each technique and, after growth of the animals, the degree of stenosis, complications, growth rate, and histological changes at the anastomosis site were compared. Laser anastomosis was made with an argon laser system (PC, HGM Medical) equipped with a 0.3mm optic fiber distribution system at an electoric output of 0.35 watts, a spot size of 0.066cm², and an exposure time of about 3 seconds/cm². The mean time needed for anastomosis was 9 minutes by the laser technique and 15 minutes with interrupted sutures. The patency of the vessel immediately after completion of anastomosis was satisfactory by both techniques. After 5 months, all animals were sacrificed, and the vessels from the aorta to the external iliac artery were excised.
Angiography showed that all vessel specimens were patent with no complications such as aneurysms. The growth rate of the external diameter at the anastomosis site was 65% in the laser group and 56% in the interrupted suture group. Histologically, the anastomosis site was nearly completely cured in the laser group, and although there was a relatively wide defect in the muscle layer, the intima was repaired with no signs of hyperplasia.
In the interrupted suture group, marked scars were observed on thevascular wall at the sites of anastomosis, foreign body reactions persisted, and intimal hyperplasia was noted. Based on these observations, we conclude that vascular anastomosis by means of an argon laser is more advantageous than the conventional procedure with interrupted sutures espetially in growing vessels.

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The aim of this study was to evaluate anavailability of vascular anastomosis by laser tissue welding. For this study CO₂laser was applied for tissue welding, because of minimized tissue reaction, Optimal conditions of laser vascular anastomosis were 20-40mW in output and 6-12sec/mm in irradiation time.
Based on the excellent experimenatal studies, CO₂laser was employed for 110 patients with intermittent claudication, renal failure and anginal attack. There are no complications for laser irration. From these findings, technique of the tissue welding by laser might be used in vascular surgery especially for small-caliber vessels.

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