Benign prostatic hyperplasia (BPH) is a common disease entity. The treatment of choice for BPH is surgery. Non-surgical treatment is of importance primarily in BPH patients who require therapeutic intervention but have relative contraindications to surgery. Non-surgical treatment currently under investigation include: medical therapy with alpha blockers, balloon dilatation and hypertheimia (HT). HT in BPH patients has been most frequently applied with microwaves at 915 MHz, utilizing a transrectal or transurethral (TUHT) approach. TUHT used in poor surgical risk BPH patients has been uniformly well tolerated without major toxicity. This treatment was applied on an outpatient basis without sedation or anesthesia. A major and long lasting objective and subjective benefit consistently exceeded 70% in patients with lateral lobes hyperplasia. In those patients with predominance of median lobe or median bar enlargement the efficacy was only 30%. TIJHT has shown to be very effective also in BPH patients presenting with urinary retention. A strong correlation between applied temperature and response was demonstrated. More work is needed to optimize TUHT technique and treatment schedule. A phase III prospective randomized trial is needed to define the role of this emerging treatment modality in BPH patients.

Serial changes occurring in the canine prostate were studied at 1 and 3 hours; 1, 2, 4, and 7 days; and 2, 3, 5, 7, and 20 weeks following transurethral laser prostatectomy using the Neodymium:YAG (Nd:YAG) laser which delivered 60 watts (W) of power for 60 seconds at 4 positions (2, 5,8, and 11 o'clock) through a Lateralase' 2.5-mmfiber. A well-demarcated sphere of thermal necrosis measuring 2.7 cm in diameter was present immediately which, within 24 hours, had begun liquefaction and was showing multiple areas of cavitation. At 1 week, the area of cavitation had coalesced to form a central cavity and within 5weeks, the ectatic cavity had been lined by transitional epithelium. These observations confirm our previous surgical and clinical impression of being able to satisfactorily perform an effective transurethral laser prostatectomy with reproducible and consistent results without using sophisticated monitoring devices.

We have used the Neo dymium:YAG laser to treat 30 patients with prostatic obstruction. Laser ablation is used as an alternative to traditional electro cautery resection. The department has a 15 month experience in this new technology for prostatic destruction. With a prototype delivery system (Lateralase TM) obstructing prostatic adenoma was removed. This delivery system comprises a 600 micron fibre with terminal gold alloy tip. Treatment is virtually bloodless, speedy and performed with a standard urological instrument under direct vision. There are some advantages over the conventional endoscopic resection. Laser ablation therapy of benign prostatic adenoma may be a practical alternative to transurethral resection.

It is widely known that treatment of prostate gland tumors by local microwave hyperthermia is helpful in many clinical cases. Applications of lasers for treating carcinoma of the prostate and benign prostatic hyperplasia have also been reported. However, there is no clear evidence as to which technique is better, so we compared both techniques in clinical investigations. In our studies we used a Thermex apparatus (Technorex, Israel) for microwave hyperthermal curing of prostate gland adenoma in 90 patients. We also used a laser to study how its radiation influences tumors in the prostate gland and which parameters of laser light provide the most efficient treatment. Results of these investigations are presented, along with the results of research in which we combined the techniques of microwave and laser hyperthermia in various ways. Possible avenues for further research and improvement of the techniques are briefly discussed.

Neodymium-Yag (Nd:YAG) laser irradiation for superficial bladder cancer is a valuable and safe treatment modality. The local recurrence rate is significantly reduced as compared to transurethral resection (TUR) alone (2.6 % versus 14.3 %). Remote recurrences can also significantly be reduced in solitary and multiple tumors if biopsies of the tumor are avoided. We state that the macroscopic appearance of a tumor is sufficiently reliable since only 0.67 % of the pathology proven Ti tumors were understaged macroscopically. The recurrence free interval for solitary tumors after Nd:YAG laser irradiation alone without biopsy was 19.i months as compared to i6 months after TUR with adjuvant intravesical instilations and in multiple tumors i3.6 months for Nd YAG laser irradiation alone without biopsies as compared to iO.4 months after TUR.

In order to develop new, easy, and safe treatment for urinary tract stricture, we investigated the laser plasty using a combination of an uv Ar laser for ablation and a novel multi-fiber catheter for laser delivery. To investigate the characteristics of the uv Ar laser ablation to ureteral tissue, the experiment in vitro was performed. The ureter was clearly ablated with sufficient thin coagulation layer. The proper laser power for the tissue ablation was about 0.5 W for 0.4 mm core-diameter fiber. The multi-fiber catheter (1.6 mm in outer diameter) consisted of 13 pixels of silica glass fibers (0.2 mm in core diameter) for laser delivery and a through lumen (0.9 mm in inner diameter) for guidewire. The catheter was inserted into a canine ureter under the general anesthesia. The ureter and urinary tract were irradiated using about 0.6 W of laser power at the catheter tip with 40s duration. The irradiated urinary tract tissues were histologically investigated. The ureter was ablated up to the submucosa layer. The urinary tract endotherium was eliminated by the laser ablation without the carbonization. No perforation was found at various irradiation conditions. To investigate the ureteral tissue damage of the uv Ar laser irradiation, the serosa temperature was measured by a thermocouple. The temperature elevation of the serosa could be restricted up to 60 degree(s)C, at which the protein was not coagulated. We concluded that the combination of uv Ra laser and multi-fiber catheter offered easy, reliable therapy for coronary structure.

The Holmium:YAG (Ho:YAG) laser operating at a wavelength of 2.1 micrometers with a maximum power of 15 watts (W) and 10 different pulse-energy settings was systematically evaluated on kidney, bladder, prostate, ureteral, and vasal tissue, and was used to perform various urologic surgical procedures (partial nephrectomy, transurethral laser incision of the prostate, and laser-assisted vasovasostomy) in the dog. By using the SurgiTome^TM 3- inch straight delivery system with an energy-pulse setting of 0.5 joules (J) at 20 Hz (10 W), partial nephrectomies required slightly longer operating times (15 minutes) than when similar procedures were performed using the Neodymium:YAG (Nd:YAG) laser and a free GI fiber at 59 to 83 W (4 - 7 minutes); however, the total energy required was considerably less. Hemostasis was excellent and no sutures were required to control bleeding. Transurethral incisions of the prostate using TV monitoring were made at the 4 and 8 o'clock positions extending from the colliculus seminalis through the vesical neck with an energy/pulse setting of 1.0 J at 15 Hz (15 W). Attempts at laser-assisted vasovasostomies were unsuccessful due to excessive thermal affect. The LaparoTome^TM Delivery System proved helpful in performing laparoscopic pelvic lymphadenectomy in the pig. Our investigations showed that the Ho:YAG laser possesses both excellent cutting and adequate hemostatic abilities even in a fluid medium. Although these results are preliminary, we believe that the Ho:YAG laser is well suited for urologic surgery and may well become the 'urologist's laser of the future.'

Tissue diagnosis and characterization are critically important to the development and applications of laser-based therapeutic procedures in urology (viz., laser lithotripsy and bladder cancer treatment). Recently, we demonstrated for the first time that the new technique of near-infrared laser excited Fourier transform (FT)-Raman spectroscopy can readily differentiate various types of renal stones and bladder cancer from normal kidney/bladder tissues. It has thus become possible to develop an FT-Raman-based fiberoptic sensor for clinical use in laser lithotripsy and bladder cancer treatment. The future development of such a diagnostic modality will allow a surgeon/physician to take real-time Raman spectra of urinary calculi or cancerous tissue via a flexible fiberoptic probe.

The laser lithotripsy of ureter stones with the Alexan Triptor was introduced into urology in 1989. Pulsenergy, pulsewidth, wavelength, fiber performance, and endoscope performance are important parameters for effective stone disintegration.

A long pulse XeCl excimer laser (200 ns) was used to induce fragmentation of human urinary stones and artificial models during 'in vitro' experiments. High UV energy fluences, up to 50 J/cm², could be delivered to the samples by means of silica optical fibers. Fragmentation thresholds of the different samples were observed in the range 5 - 20 J/cm², well within the energy capability of the fibers. Total fragmentation was always successfully achieved, requiring a variable number of pulses (10 - 100), depending on the pulse energy and the hardness of the sample. The effects of ultraviolet laser radiation on urinary stones are also compared with those of commercial Alexandrite and dye lasers.

The effect of long pulsed Nd:YAG laser (pulse duration 300 ns) with the fundamental and second harmonic wavelength on the fragmentation of different urological and gall stones has been investigated. With 200 and 400 micrometers fibers in a contact application, all types of stones could be fragmented with energies less than 120 mJ (400 micrometers fiber) or 45 mJ (200 micrometers fiber). By use of a double pulse-simultaneous application of second harmonic and fundamental radiation the efficiency of fragmentation could be increased and the energy threshold decreased.

The endoscopically controlled electrohydraulic shock wave lithotripsy (EISL) of salivary stones was performed on 29 patients with submandibular duct stones as a new non-surgical treatment of sialolithiasis. Under local anesthesia, a flexible fiberscope with an additional probe to generate shock waves is placed into the submandibular duct. Under endoscopic monitoring the fiberscope is advanced until the stone is identified. For stone disintegration, the probe must be situated 1 mm in front of the concrement. The fragmentation itself is performed by pressure waves generated by a sparkover at the tip of the probe. By means of the endoscopically controlled shock wave lithotripsy (EISL), it was possible to achieve complete stone fragmentation in 20 of 29 patients without serious side effects. In 3 patients only partial stone fragmentation could be achieved due to the stone quality. The endoscopically controlled electrohydraulic intracorporal shock wave lithotripsy (EISL) represents a novel non-invasive therapy for endoscopically accessible salivary gland stones. This therapy is performed on an outpatient basis with little inconvenience to the patient. The advantage in comparison to the endoscopically controlled laser lithotripsy will be discussed.

We discuss our experience using Nd:YAG contact fibers (both conical and hemispherical versions) for neurosurgical procedures involving 22 patients. These fibers represent important tools in the neurosurgical armamentarium, especially in deep lesions and near-eloquent brain regions. Handheld contact fibers are excellent surgical tools for incision, excision, hemostasis, and vaporization of lesions. These 'sculpted' contact fibers offer advantages over the sapphire tips previously used for incision and excision. In addition to their larger size, the sapphire tips had to be frequently replace due to damage from overheating; this lengthened the time required to perform an operative procedure. the introduction of sculpted fibers represents an improvement in laser delivery systems for neurosurgical use.

Low-power interstitial thermal therapy using a 1064 nm Nd:YAG laser and a newly designed fiberoptic transmission system, the ITT laser fiber, is a promising therapeutic approach in the treatment of cerebral tumors. After CT-guided stereotactic implantation of an applicator probe, we performed laser-induced interstitial thermal therapy in a patient with an astrocytomas WHO grade II under simultaneous magnetic resonance imaging (MRI) control. In order to assess the effects of the treatment a 2D-Flash sequence with an acquisition time of 15 sec was used. It could be demonstrated that laser-tissue interactions progressed with duration of irradiation depending on laser powers applied. There was a well-defined area of tissue necrosis with a maximum size of 17 mm in diameter in the center of the tumor and a small zone of transient perifocal edema. With regard to experimental studies, it seems to be possible to define between reversible and irreversible laser-tissue effects.

To meet the high accuracy demands of most brain lesion resection surgeries, surgeons are always looking out for new and more reliable guiding systems and methods. In this paper we are presenting a system that has been developed through many years of experience in brain surgery and hundreds of stereotactic brain lesion resection operations. The computer assisted system consists of a special designed software and hardware. The software starts by collect the data directly from different types of imaging systems, then using several modules of interactive 2D-3D graphic displays enables the surgeon to simulate, optimize, and plan the surgery. The hardware consists two main parts. The first part is a localizing unit with a set of instrument, that provide the reference system needed for the imaging data preoperatively and intraoperatively. The second part is an intraoperative automated image guided system for microscopic based resection cases.

The design and application of a temperature-tracking apparatus using a laser as heating source for electrophysiological preparation are presented. The apparatus provides the ability to follow a given temperature pattern at a local site. The studies were conducted to understand the mechanisms underlying thermal damage to ion channels in the frog nerve node of Ranvier. Main objectives of the temperature controller design are short temperature rise time and precise static temperature control. The temperature controller allows a minimum rise time of 150 ms with an accuracy of +/- 0.2 degree(s)C in the nerve membrane of nodes of Ranvier. The application of the device to nerve membrane thermal damage study showed that after a 5-second exposure to laser-induced hyperthermia at temperature of 48 - 54 degree(s)C, there was a differential suppression of Na and K currents in the nodal membrane currents. Potential applications of the temperature controller design can be found in other research areas in medicine and biophysics that require a stable high temperature heat source for local heating.

Digital nerve samples obtained from horses using a CO₂ laser for surgical excision at various power densities in both continuous wave (CW) and superpulse (SP) modes were examined histologically and using a scanning electron microscope. Preliminary data suggest that the lowest power density examined (637 W/cm²) in CW mode provided a wide zone of thermal change and the best tissue coagulation. Power densities of 15,924 and 31,847 W/cm² SP mode showed a narrower zone of thermal change, and a coagulated but much more disrupted excisional surface than that which was observed at lower power densities, or at the same power densities where CW mode was used. Clinical trials where equine palmer digital neurectomies have been done at 637 W/cm² (5 W, 1.0 mm spot size) CW and at 47,771 W/cm² (15 W, 0.2 mm spot size) SP have not been completed at this time. It has been observed that attempting the surgical procedure at 127,388 W/cm² (40 W, 0.2 mm spot size) CW was difficult for the surgeon to control and resulted in marked post surgical discomfort of the patient. For these reasons we eliminated power densities above 63,694 (20 W, 0.2 mm spot size) from our neurectomy studies.

While many colon cancers are curable, curability relates closely to stage. Once disease is spread beyond the confines of the colon and adjacent lymph nodes, cure is clearly the exception rather than the rule. Recently, surgical resection of solitary liver metastases has been effective in treatment of colon cancer, producing long term survival in approximately 20% of treatable patients. Surgery, however, is technically complex and there is a high perioperative morbidity and substantial perioperative mortality. For patients with multiple hepatic metastases in whom surgical extirpation is not possible, the outlook is dismal. Other modalities including chemotherapy have also resulted in limited success. Recently, a number of investigators have evaluated the effect of low power interstitial Nd:YAG laser irradiation for inducing hyperthermia and coagulative necrosis is hepatic tissue. In treating multiple or large hepatic metastases, the use of a lower power (1 - 5 watts), long duration (50 - 2400 seconds), single fiber laser delivery system has limitations. A computer controlled continuous wave Nd:YAG (1064 nm) laser system using a single fiber 'coupled' to a multiple array of fibers (4 to 6) has been developed for the delivery of low power laser irradiation to hepatic tissue. The advantage of laser energy being delivered simultaneously through multiple fibers is that it expands the area of tissue that can be treated over a given time. Through the use of interventional techniques including percutaneous ultrasound and/or CAT scan directed treatment, laser induced interstitial hyperthermia for large or multiple metastatic lesions could be initiated without the morbidity associated with open surgical procedures.

Chloroaluminum phthalocyanine tetrasulfonate was administered intravenously (1.0 mg/kg) to client owned cats and a dog with spontaneously occurring squamous cell carcinoma of head and neck. Light was delivered 48 hours post injection of the photosensitizer. An argon- pumped dye-laser was used to illuminate the lesions with 675 nm light delivered through a microlens fiber and/or a cylindrical diffuser. The light dose was 100 J/cm² superficially or 300 J/cm interstitially. Eleven photodynamic therapy treatments in seven cats and one dog were performed. Two cats received a second treatment in approximately sixty days after the initial treatment. The superficial dose of light was increased to 200 J/cm² for the second treatment. While the longest follow-up is twelve months, the responses are encouraging. The dog had a complete response. Among the cats, three showed complete response, three showed partial response and one showed no response. One cat expired two days post treatment. It is early to evaluate the response in two cats that received second treatments. Photodynamic therapy with chloroaluminum phthalocyanine tetrasulfonate was effective in treating squamous cell carcinoma in pet animals.

The effectiveness of one or two suture prothesis in performing laryngoplasty was compared. Forty-six horses treated for left laryngeal hemiplegia at North Carolina State University, College of Veterinary Medicine (NCSU-CVM) between January 1987 and April 1991 were included in the study. Thirty-seven of the horses were treated with two sutures, while nine were treated with one suture. All horses, after recovering from general anesthesia, were sedated the following day and were subjected to a transendoscopic neodymium: yttrium aluminum garnet (Nd:YAG) laser ablation of the left laryngeal ventricle. Ability to perform after treatment relative to before treatment, reduction or elimination of respiratory noise, owner or trainer satisfaction, were compared for the two suture prosthetic procedures using chi-squared test or Fisher's exact test. No statistical significant differences were found for performance, reduction of noise, and owner or trainer satisfaction. The use of one or two sutures seemed to have no effect on the effectiveness of prosthetic laryngoplasty procedure followed by Nd:YAG ventricular ablation.

A telephone survey was conducted to assess the efficacy of laryngoplasty surgery followed by Nd:YAG laser laryngeal ventricular ablation. Forty-three horses were included in the study that were treated at North Carolina State University, College of Veterinary Medicine (NCSU- CVM) January 1987 and September 1990. Questions asked of the owners or trainers of the horses related to complications that the horses may have had since leaving the hospital, ability to perform after treatment relative to before treatment, how respiratory noise after treatment related to before treatment, results of follow-up endoscopic exams, additional surgery that may have been performed, and owner satisfaction with the procedure. Wilcoxon signed rank test was used to determine the success of the procedure. Success was defined as a reduction of noise or improvement in performance ability. Results of the test indicated that the two procedures had an effect in reducing respiratory noise (p equals 0.0001) and increasing performance (p equals 0.0017).

Laparoscopic cholecystectomy has revolutionized the management of symptomatic cholelithiasis and cholecystitis. Although electrosurgery devices are used by a majority of surgeons, laser technology is a valued addition to the armamentarium of the skilled laser laparoscopist. A variety of fiberoptic capable wavelengths have been applied successfully during this procedure. Use of the CO₂ laser for this purpose has lagged due to difficulties encountered with free-beam and rigid waveguide dissections via the laparoscope. Recent developments in flexible waveguide technology have the potential to expand the role of the CO₂ laser for laparoscopic cholecystectomy and other procedures. Twelve laparoscopic cholecystectomies were performed using Luxar (Bothell, WA) flexible microwaveguides of various configurations. In each case, dissection of the gallbladder from the gallbladder bed was accomplished with acceptable speed and hemostasis. There were no complications. Shortcomings include coupling and positioning with an articulated arm and occasional clogging of some waveguide tips with debris. Modifications of this technology are suggested. Flexible waveguides make the CO₂ laser a practical alternative for surgical laparoscopy.

Broncho-pleural fistula is a difficult clinical problem without a simple solution. Laser-assisted solder techniques potentially offer a means to precisely fix tissue glues into the fistulae through a bronchoscopic approach. Using a canine model, secondary bronchi were sealed with cryoprecipitate made from solvent/detergent treated plasma (treated to inactivate membrane enveloped virus) mixed with indocyanine green (absorption 805 nm). Diode laser energy (emission 808 nm, 7.3 W/cm²) was applied to the solder until desiccation was observed. Leakage pressures ranged between 18 - 86 mmHg with a mean of 46 +/- 24 mmHg. Laser-assisted solder techniques provide a reliably strong seal over leaking bronchial stumps and use of dye enhancement prevents undesired collateral thermal injury to surrounding bronchial tissue. Solvent/detergent plasma, prepared by methods shown to inactivate large quantities of HIV, HBV, and HCV, is an effective source of cyroprecipitate and should allow widespread use of pooled human material in a clinical setting.

Spontaneous pneumothorax is a common disease in young people. Operative intervention has been done in most of the recurrent cases. Recently thoracoscopic treatment has been tested as a less invasive treatment modarity. We adopted carbon monoxide (CO) laser for thoracoscopic treatment of recurrent spontaneous pneumothorax. CO laser (wavelength; 5.4 micrometers ) could be delivered by chalcogenide glass (As - S) covered with a teflon sheath and ZnSe fiber tip. The sterilized flexible bronchoscope was inserted through the thoracoscopic outer sheath under local anesthesia. Shrinkage of blebs was obtained by non-contact method of CO laser irradiation. Laser power at the tip was 2.5 - 5 W and irradiation duration was 0.5 s each. Excellent shrinkage of bleb and bulla could be obtained by CO laser without perforation complication. Advantages of CO laser as a thoracoscopic treatment were: (1) capability of fiber delivery (flexible thoracoscopy was easy to operate and clear to visualize the blebs which were frequently found at the apical portion of the lung, and (2) shallow extinction length (good shrinkage of blebs, low risk of perforation, and thin layer of carbonization). In conclusion, our new technique of thoracoscopic CO laser irradiation was found to be a safe and effective treatment of spontaneous pneumothorax.

A new technique has been developed which enables the creation of an end-to-side anastomosis between arteries with zero or an extremely short occlusion time (2 min) of the recipient artery for ischemic sensitive areas. The feasibility of the technique was studied in a rabbit model. The right common carotid artery was connected with the exterior of the left common carotid artery. Through an artificial sidebranch, which was connected with the donor artery proximally from the anastomosis, a laser catheter was introduced in contact with the recipient arterial wall. The laser was activated to create a hole in this wall and the artificial sidebranch was subsequently occluded. Meanwhile no occlusion of the donor artery was necessary. In a series of 100 rabbits using a coated hemispherical contact probe (1.8 or 2.2 mm diameter) coupled to a Nd:YAG laser (one 0.5 s, 18 W pulse) a 95% patency rate was obtained. In a recent series of 20 rabbits an Excimer-laser (Technolas, XeCl 308 nm, 120 ns, 20 Hz, 25 mJ/pulse) was used. The hole was created with a custom designed multifibercatheter of 2.2 mm diameter consisting 140 laserfibers in a flat circular configuration. A patency rate of 100% was obtained. Scanning electron microscopy of the anastomosis site through eight weeks showed a perfect endothelialization. The advantage of the Excimer based multifiber catheter compared with the Nd:YAG-based contact probe, is the absence of thermal effects at the site of the anastomosis. A pilot study is in progress in a series of patients, where an extra- intracranial bypass is indicated.

We have tested the strength and collagen concentration of high-risk anastomoses of the rat colon after endoscopic irradiation by He-Ne laser. Repeated He-Ne laser irradiation (1.9 J/cm²) increases the bursting strength of the anastomoses by almost 100% on the fourth postoperative day. This effect is not observed by increasing the radiation dose (6.4 J/cm²). Differences in collagen (hydroxyproline) concentration did not reach statistical significance. Our study suggests that repeated endoscopic irradiation with He-Ne laser enhances the early phases of anastomotic healing in high risk colonic anastomoses.

A Nd:YAG laser has been used since 1983, first on therapeutic research animals and fresh internal organs of the human body, and then clinically. This paper summarizes and analyzes the cases treated by using the endoscopic Nd:YAG laser from 1983 to 1990.

Intravascular and percutaneous irradiation of blood by low power light of He-Ne laser (wavelength 632.8 nm) is used for therapy of a wide range of diseases. Proof and optimization of photobiostimulation of human organism depends on the results of investigations in the following areas: (1) clarification of the physical and chemical mechanisms of biostimulation; (2) development of mathematical and physical methods of laser light dosimetry within tissues; and (3) accumulation of impartial clinical information. In the paper, a short survey of the hypotheses of red laser light biostimulating effect on blood is made, the problems of dosimetry during percutaneous laser treatment of blood are discussed and some results of clinical investigations are presented.

215 patients (86 males and 129 females, average age 60.3 years) suffering from musculoskeletal and neuromuscular disorders, both chronic and acute, were treated by low energy lasers. Most patients failed to improve in spite of the fact that different conventional treatment modalities were implemented. Some of them were unable to tolerate drugs because of allergy or gastrointestinal intolerance. The photobiostimulation system FABULIGHT^TM (IMM Inc., Canada) with adjustable output parameters for both red and infrared wavelength was used. Different modalities of LELBT were used: local and generalized stimulation of tender points and affected areas. Stiffness, swelling, range of motion and pain were assessed. 65% of symptoms improvement was obtained in average.

Recent studies of tissue fusion (welding) processes have reported temperature ranges but have not carefully analyzed critical exposure time data. Electron microscopic (EM) studies suggest that the fusion process in blood vessels may be dominated by random re-entwinement of thermally dissociated adventitial collagen fibrils (Type I) during the end stage heating and early cooling phases. At the light microscopic level, this bonding process is reflected by the formation of an amorphous coagulum of thermally coagulated adventitial collagen at the anastomotic site. We have constructed a numerical model of the vessel welding process, assuming CO₂ laser impingement, and used it to simulate quantitative histologic data obtained from successful welds of rat femoral and canine brachial arteries (unpublished data). The model estimates smooth muscle and collagen damage based on kinetic thermal damage analysis and water loss boundaries as a function of irradiation beam parameters and heating time. Both heating and cooling phases are simulated. The results illustrate the importance of the damage kinetics and local heat transfer phenomena to the weld characteristics realized.

In every surgical endeavor, the process of tissue repair should ideally result in the reapproximation of di''ided structures ith the restoration of anatomical tissue plane ind minimal scarring. Over the past to centuries, fine needle nd suture techniques have been used to accompliBh this; they have, however, fallen quite short of ideal repair. Ihe use of even fine suture for the reapproxirnation of arteries results in chronic inflammatory response that eventually lead to a neointimal hyperplasia, atherosclerosis, stenosis, and occIuion These problems the needle and suture led us to explore the use of thermal lasers for tissue repair.

Clinical use of laser tissue soldering with cryoprecipitate has been delayed by the fear of infecting recipients with donor viral products. Solvent-Detergent (S/D) treatment of human plasma is a technique for disrupting membrane enveloped viruses and rendering them noninfectious. Dual 6 cm incisions were created on the dorsum of nine rats and closed with either standard skin staples of with laser activated S/D cryoprecipitate. The animals were sacrificed at one of three time periods: 0, 2, and 4 days. The use of the laser tissue solder significantly improved tensile strength over standard skin closures at all time periods. Deactivation of viral particles during preparation of cryoprecipitate does not reduce the utility of this material as a solder during laser bonding. Reduced infectivity of S/D prepared products enhances their clinical utility.

In order to produce a solder for Laser-Assisted Tissue Bonding (LATB) with better tactile characteristics and shelf life, plasma-derived fibrinogen concentrate has been augmented with various additives, including anionic polysaccharides, anti-fibrinolytic agents, and preservatives. For comparison of this new, compounded 'solder' with the pure, plasma- derived fibrinogen concentrate an in vivo tissue 'weld' assay was devised. While further analyses must be done to assess more critical healing time periods and characteristics, this study is an affirmation that the plasma-derived, protein concentrates, with or without certain additives, offer effective alternatives to suture repair.

For the last two years we have been investigating the use of a 830 nanometer laser for low level laser therapy in chronic pain syndromes. This laser is of low energy and by definition is low level therapy (a laser output which does not exceed 100 milliwatts). This wave length has been carefully selected to be in the 'window' of wavelengths between 650 and 900 nanometers. At this level, the laser energy will penetrate the epidermis, the dermis and the subcutaneous layers to the deep tissue. The tissue effect of this laser energy is not thermal but rather a stimulation of micro-circulation with a secondary effect of blocking pain enzymes and activation of the synthesis of endorphin enzymes. We have experience with approximately 75 patients who have been treated with low level laser therapy. We have engaged in a double- blind study at several General Motors facilities in Michigan to determine the effectiveness of low level laser therapy in this inflammatory condition. Repetitive injuries in the work place have moved from 18% of industrial accidents in 1981 to 52% in 1989. Carpal Tunnel Syndrome is the number one economic problem in occupational medicine. It is true that 15% of the employees of American automotive plants have Carpal Tunnel Syndrome. This large number of patients have been treated in the past by standard physiotherapy treatment modalities and ultimately by surgery for failure of conservative therapy. Incidence of 'return to work activities' has been low. We intend to show that low level laser therapy may afford a positive solution to this problem not only therapeutically but prophylactically. Indications for treatment are Chronic Pain Syndrome and Carpal Tunnel Syndrome of mild to moderate degree.

A variety of fixatives and stains were examined for the ability to differentially stain the extracellular matrix components of thermal damage to the skin in an attempt to provide methods for examining the extent of thermal effects. This information is important in comparing different lasers and laser parameters. Four zones of thermal damage were identified including char and three zones of less extensive damage. The lower bounds of the damage with steady state conditions for these zones were 64 - 66 degree(s)C, 80 - 85 degree(s)C, and > 100 degree(s)C. The best choices based on this study include the following: fixative: Bouin's, overall stain: H & E, inner zone stain: Pinkus' acid orcein giemsa, middle zone stain: Movat's pentachrome, and outer zone stain: the modified elastic stain presented in the appendix of this paper.

The Q-switched ruby laser has been demonstrated to provide selective photothermolysis of pigmented tissue at a wavelength of 694 nm and a pulsewidth of 40 nanoseconds. It was utilized to treat 15 patients with nevus of Ota involving the face with an age range of 6 - 52 years. Eleven of the 15 patients were Asian, 2 were Caucasian, 1 was Hispanic, and 1 was Indian. The energy fluence utilized varied between 6 and 10 J/cm², and the number of treatments ranged from 1 to 7. Significant lightening or clearing was noted at the higher energy ranges of 9 - 10 J/cm² with significantly less lightening noted at the lower energy range of 6 - 8.5 J/cm². No scarring was noted in any of the 15 patients, and some isolated hypopigmentation was noted in one of the subjects. Transient post-inflammatory hyperpigmentation was noted in only one patient. Complete clearing has been noted in four patients. Q-switched ruby selective photothermolysis appears to be an effective and safe method of lightening or removing nevus of Ota.

A method for quantitative characterization of port wine stain (PWS) is presented. Pulsed photothermal radiometry (PPTR) uses a non-invasive infrared radiometry system to measure changes in surface temperature induced by pulsed radiation. When a pulsed laser is used to irradiate a PWS, an initial temperature jump (T-jump) is seen due to the heating of the epidermis as a result of melanin absorption. Subsequently, heat generated in the subsurface blood vessels due to hemoglobin absorption is detected by PPTR as a delayed thermal wave as the heat diffuses toward the skin surface. The time delay and magnitude of the delayed PPTR signal indicate the depth and thickness of the PWS. In this report, we present an initial clinical study of PPTR measurements on PWS patients. Computer simulations of various classes of PWS illustrate how the PPTR signal depends on the concentration of epidermal melanin, and depth and thickness of the PWS. The goal of this research is to provide a means of characterizing PWS before initiating therapy, guiding laser dosimetry, and advising the patient as to the time course and efficacy of the planned protocol.

An opto-thermal study of in-vivo skin response to hydration and externally applied chemicals has revealed a high sensitivity to the solvent Dimethyl Sulfoxide (DMSO). Dependence on dose, individual and post-treatment recovery after washing were investigated. The measurements indicate that skin hydrates much more rapidly after treatment with DMSO, than normal skin.

Two-hundred and fifty-seven patients (136 adults and 121 children) with port-wine stains of the head and neck were treated with the flashlamp-pumped pulsed dye laser. The head and neck was subdivided into 8 anatomical regions (forehead/temple, periorbital, medial cheek, nose, upper cutaneous lip, lateral cheek, chin and neck) which were independently evaluated for response. Response to treatment was found to be associated with the anatomical location of the lesion; in both adults and children the mid-facial region (medial cheek, nose and upper cutaneous lip) responded less favorably to treatment than the other regions of the head and neck (periorbital, forehead/temple, lateral cheek, neck and chin). In adults and children, mean percent lesional lightening of the mid-facial regions was 70.7% compared to 82.3% of the other regions of the head and neck with an estimated difference of 11.6% (95% confidence interval: 8.7% - 14.6%). The mean number of treatments for adults was 3.7, while this number in children was 3.9. All side effects were transient, and included cutaneous depressions, hypopigmentation and hyperpigmentation.

A prospective, side-by-side comparison study of two different lasers for the treatment of solar- induced telangiectasia was carried out in 14 patients at the Beckman Laser Institute and Medical Clinic. The argon tunable dye laser (Coherent, Palo Alto, Calif.) was used in the method modified from Orenstein and Nelson to completely treat discrete telangiectasias on one cheek. Specifically, the argon tunable dye laser (ATDL) was set at 0.7 - 0.8 watts, 585 nm wavelength, shutter-pulsed at 0.1 second duration with a spot size of 0.1 mm, and individual vessels were 'traced out' with 4X loupe magnification. Each patient's opposite cheek was then treated in the standard fashion with the flashlamp pulsed dye laser (Candela, Natick, Mass.) using a technique similar to Polla's et al. Specifically, the flashlamp pulsed dye laser (FPDL) was set at 585 nm wavelength, pulsed mode of 450 microseconds pulse duration, spot size of 5 mm, overlapping 10 - 20%, with power densities of 5.5 to 6.5 joules/cm². All patients had symmetrical cheek telangiectasias of several years' duration. Patients were treated on day 0, and examined on weeks 2, 4, and 6. Photos were taken at each visit, and evaluation was done by questionnaire and direct observation, as well as by photographic slides later projected to an impartial panel. Final evaluation by the panel at week 6 showed 11/14 patients with excellent results (75 - 100% clearing) at sites treated with the FPDL, compared with 4/14 with the ATDL. In contrast, 4/14 FPDL sites were graded as fair to minimal improvement, and 9/14 as fair for the ATDL. The patients' self-evaluations graded the final results very similar to that of the panel. Most patients were bothered by the ecchymosis and hyperpigmentation associated with the FPDL, resulting in less than 50% of the patients preferring the FPDL despite its more impressive results. We conclude that the final results favor the FPDL over the ATDL for treatments of facial telangiectasia. However, non- ecchymosis producing methods of treating these lesions are an important option to be optimized in order to improve patient acceptance.

Cutaneous angiodysplasias are currently treated by Argon, CW-Dye or Pulsed Dye Lasers. Green light at 532 nm is highly specific for hemoglobin-laden vessels. Therefore, this wavelength was evaluated on different cutaneous angiodysplasias. One hundred thirty-five (135) patients with either port wine stains (94) or facial telangiectasia (41) were treated with a 532 nm laser coupled to an automatic delivery system. Treatments were performed using the minimal blanching technique. The average fluence was 17 J/cm^-2 for port wine stains and 15 J/cm^-2 for facial telangiectasia. Pathologic scars were not reported for any patient. Sixty percent (60%) of the patients with port wine stains achieved good or excellent results after a 12-month period of observations. Ninety percent (90%) of the patients with facial telangiectasia achieved good or excellent results after a 12-month period of observation.

We report histological changes in port-wine stains treated with illumination times of 3.3 ms (5 W) and 17 - 26 ms (2 W). A copper vapor laser is used and the spot diameter is 0.4 mm. The results show that using an illumination time of 3.3 ms there is more damage to the endothelial cells of the vessel walls and less damage to non vascular tissue. This is in agreement with the predictions of theoretical calculations.

The new method of combined surgical and therapeutic treatment by means of laser produced surface plasma is discussed. The first data on crater formation in tissue modelling samples as well as applications of such plasma in dermatology is presented. Pulsed TEA CO₂ lasers were used in the experiments and medical tests.

Ablation of hard biological tissue using XeCl-excimer lasers (wavelength 308 nm) yielded promising results. The 308 nm radiation was guided by tapered quartz fibers with core diameters of 400 - 1000 micrometers . Applying pulse energy of up to 70 mJ (pulse duration 28 ns, 60 ns, 300 ns) at different repetition rates, we found no noticeable thermal damage. The samples were immersed in water during irradiation. Bone specimens cut by the excimer laser did not show any melted hydroxylapatite crystals as described in the CO₂-cutting experiments performed by HORCH (4). The gross, histological, and scanning electron microscope examination of cuts and bore holes produced by excimer laser ablation of meniscus and bone tissue will be presented.

We investigated the effect of a free-running 2.01 micron pulsed Tm:YAG laser on bovine knee joint tissues. Ablation rates of fresh fibrocartilage, hyaline cartilage, and bone were measured in saline as a function of laser fluence (160 - 640 J/cm²) and fiber core size (400 and 600 microns). All tissues could be effectively ablated and the ablation rate increased linearly with the increasing fluence. Use of fibers of different core sizes, while maintaining constant energy fluence, did not result in significant difference in ablation rate. Histology analyses of the ablated tissue samples reveal average Tm:YAG radiation induced thermal damage (denatunalization) zones ranging between 130 and 540 microns, depending on the laser parameters and the tissue type.

A Ho:YAG laser system operating at a wavelength of 2.1 microns has recently been introduced for use in arthroscopic surgery. The acceptability of this new tool will be determined not only by its ability to resect tissue, but also by its long term effects on articular surfaces. In order to investigate these issues further, we performed two studies to evaluate the acute and chronic effects of the laser on cartilaginous tissue. We evaluated the acute, in vitro effects of 2.1 micron laser irradiation on articular and fibrocartilage. This included the measurement of ablation efficiency, ablation threshold and thermal damage in both meniscus and articular cartilage. To document the chronic effects on articular cartilage in vivo, we next performed a ten week healing study. Eight sheep weighing 30 - 40 kg underwent bilateral arthrotomy procedures. Multiple full thickness and partial thickness defects were created. Animals were sacrificed at 0, 2, 4, and 10 weeks. The healing study demonstrated: (1) no healing of full or partial thickness defects at 10 weeks with hyaline cartilage; (2) fibrocartilaginous granulation tissue filling full thickness defects at two and four weeks, but no longer evident at ten weeks; (3) chondrocyte necrosis extending to greater than 900 microns distal to ablation craters at four weeks with no evidence of repair at later dates; and (4) chondrocyte hyperplasia at the borders of the damage zone at two weeks but no longer evident at later sacrifice dates.

Previous studies have recorded the reduction of caries-like lesions in extracted human teeth that have been irradiated with CO₂ laser. Other studies have shown a decrease in dissolution rate of enamel that has been irradiated with CO₂ laser and acid resistance. This study was conducted to evaluate the effects of Argon laser irradiation on acid resistance and demineralization of dental enamel. Human enamel was laser irradiated with approximately 60 J/cm² and 120 J/cm². The amount of demineralization was determined in a rotating disk assembly (0.1 M acetate buffer, pH-4.5) for 24 hours and the results determined and plotted against the nonlased control using microradiographs and computerized imaging. The amount of dissolution of tooth structure lost to demineralization in 4.5 pH acid bath in a 24 hour period was reduced from approximately 140 micrometers to approximately 70 micrometers . This study show that demineralization is reduced when human enamel is exposed to Argon laser irradiation.

Root canal preparation was performed on 20 extracted human teeth. After opening the coronal pulp, the root canals were prepared by 308 nm excimer laser only. All root canals were investigated under SEM after separation in the axial direction. By sagittal separation of the mandibles of freshly slaughtered cows, it was possible to get access to the tissues and irradiate under optical control. Under irradiation of excimer laser light, tissue starts to fluoresce. It was possible to demonstrate that each tissue (dentin, enamel, bone, pulpal, and connective tissue) has a characteristic spectral pattern. The SEM analyses showed that it is well possible to prepare root canals safely. All organic soft tissue has been removed by excimer laser irradiation. There was no case of via falsa. The simultaneous spectroscopic identification of the irradiated tissue provides a safe protection from overinstrumentation. First clinical trials on 20 patients suffering of chronical apical parodontitis have been carried out successfully.

The interaction of two short pulse excimer lasers with dentin has been evaluated using 193 nm radiation from a 15 ns ArF and 308 nm pulses from a 15 ns XeCl. Temperature changes of the ablated surfaces were monitored and correlated to scanning electron microscope studies. While surface temperatures during irradiation with the XeCl laser rose significantly higher than those due to exposure to the ArF pulses, heat penetration into the tooth was minimal in both systems and did not perturb the vicinity of the root canal. The dependence of the dentin thermal response on changes in the beam spot size was investigated as well. Surface temperatures were found to be linearly dependent on spot size in both lasers. Scanning electron microscopic observations of the ablated surface showed that although temperature changes at low pulse repetition rates and at low fluence were minimal in both lasers, localized melting of dentin was observed in both lasers. In the case of the XeCl laser, sufficient amount of melted dentin was generated to induce flow and partial sealing of existing cracks in the dentin structure. Only minimal amount of dentin melting was generated by the ArF laser, but a very thin (approximately equals 1 micrometers ) coating of exposed tubules was observed at lower fluences. Surface morphology was found to depend strongly on the fluence levels used but was relatively insensitive to the laser pulse repetition rates.

Lasers are certainly a major expectation to improve the quality of endodontic preparation. Very little research has been published in the field of interaction between a laser beam and the dentin walls of a root canal. CO₂ lasers have been used to sterilize the periapical areas during apical surgeries. Dederich has demonstrated that the exposure of the dentin wall with a Nd-YAG laser beam gives a closure of the dentinal tubules and leads to a reduction in the permeability of the dentin walls to fluids or bacteria. The latest study has demonstrated that it was possible to enlarge a root canal with a Nd-YAG laser beam driven through a fiber optic. This technique improved the cleanliness of the canal after laser cleaning and shaping. This research demonstrated the interest in using a fiber optic during the canal preparation. Another interesting finding was the fact that the silica fiber was shortening itself during the endodontic procedure. The purpose of this study was to determine through an electron microscopic examination the interaction between the components of the fiber optic and canal walls during canal preparation.

An important indicator to prove the effectiveness of laser radiation and to control the side effects are histological studies of dental hard tissues. In our study, different pulsed, rare earth doped YAG-laser systems in the range from 1 micrometers to 3 micrometers were investigated. An improved plastic embedding technique based on a penetrating uv-activated PMMA-medium was developed to cut undecalcified sections of 15 micrometers thickness. The Nd:YAG laser showed wide zones of necrosis but little carbonization. The radiation of Holmium and Thullium-doped YAG lasers causes strong but well-defined zones of carbonization comparable to those of pulsed (ms) CO₂ lasers. The Erbium-doped YAG-laser was the most effective system. As predominant side effects, residual zones of debris and microcracks were observed. In deeper cavities, the zones of damages increase. The side effects of the pulsed infrared laser types seem to be mainly influenced by the physical or chemical properties of the dental tissues and not by the selected laser parameters.

Conventional cleaning and shaping of root canal systems employs hand and/or rotary instrumentation to remove the contents of the canal and shape the canal to receive a filling material. With the advent of the Nd:YAG laser system another method of accomplishing proper cleaning and shaping is evaluated. Single rooted teeth were radiographed bucco- lingually and mesio-distally and were divided into 2 groups. The first group was accessed and the root canal systems cleaned and shaped with a step back technique utilizing hand files and gates glidden burs. At completion of the procedure the teeth were again radiographed at the same positions as those prior to the procedure. The teeth were split longitudinally and examined under scanning electron microscopy to assess cleaning. The second group of teeth were accessed, and cleaning and shaping was accomplished using the Nd:YAG laser in combination with hand files and rotary instruments. These teeth were subjected to the same analysis as those in the first group. The before and after radiographs of each group were subjected to image analysis to determine effectiveness of the two methods in shaping the canal systems. We will discuss the ability of Nd:YAG to clean and shape root canal spaces and remove smear layer and organic tissue remnants from those areas.

The determination of the thermal effects of Nd:YAG laser energy on enamel and dentin is critical in understanding the clinical applications of caries removal and surface modification. Recently extracted non-carious third molars were sterilized with gamma irradiation. Calculus and cementum were removed using scaling instruments and 600 grit sand paper. The smear layer produced by sanding was removed with a solution of 0.5 M EDTA (pH 7.4) for two minutes. Enamel and dentin surfaces were exposed to a pulsed Nd:YAG laser with 150 microsecond(s) pulse duration. Laser energy was delivered to the teeth with a 320 micrometers diameter fiberoptic delivery system, for exposure times of 1, 10 and 30 seconds. Laser parameters varied from 0.3 to 3.0 W, 10 to 30 Hz and 30 to 150 mJ/pulse. Other conditions included applications of hot coffee, carbide bur in a dental air-cooled turbine drill and soldering iron. Infrared thermography was used to measure the maximum surface temperature on, and thermal penetration distance into enamel and dentin. Thermographic data were analyzed with a video image processor to determine the diameter of maximum surface temperature and thermal penetration distance of each treatment. Between/within statistical analysis of variance (p <EQ 0.05) determined a difference existed between enamel and dentin in thermal effects from the Nd:YAG laser. Enamel had lower maximum surface temperatures than dentin for all laser powers and times. The surface temperature ranged from 34 +/- 1 degree(s)C to 110 +/- 4 degree(s)C on enamel and 62 +/- 5 degree(s)C to 392 +/- 82 degree(s)C on dentin. As power and time of exposure increased, both the maximum surface temperature and thermal penetration distance increased. The greatest length of thermal effect on the surface (11.0 +/- 0.9 mm) and thermal penetration distance (4.7 +/- 0.4 mm) recorded were caused by the air-cooled turbine drill on dentin. Surface temperatures were much higher for the Nd:YAG laser applied to enamel and dentin than those of the air-cooled turbine drill with carbine bur. Although temperatures created with the laser were higher, the diameter of the hot spot on the surface and the thermal penetration distance in the pulpal direction were significantly less than those of the dental drill. Therefore, the pulsed infrared Nd:YAG laser, with 320 micrometers fiber optic delivery, can be applied to enamel and dentin without detrimental thermal pulpal effects.

Historically, many techniques have been attempted in the search for a satisfactory and consistent treatment of inflamed, painful, hyperemic pulpal tissue. Present techniques attempting to achieve profound local anesthesia in such tissue, have not been satisfactory. Local anesthesia techniques acceptable to the patient with painful hyperemic pulpal tissue, has eluded previous technology. The subsequent treatment of hyperemic tissue without sufficient anesthesia primarily involves undesirable invasive mechanical/surgical procedures. Described in this clinical trial is a technique using free running (FR) pulsed, Nd:YAG laser energy to ablate soft tooth pulpal tissue--a technique employed after conventional endodontic methods failed. A free running pulsed, FR Nd:YAG dental laser was successfully used at 20 pulses per second and 1.25 watts to photovaporize endodontic pulpal tissue (pulpectomy) to allow a conventional endodontic file to extirpate the remaining soft tissue remnants and access the root apex. Also described in this paper is the 'hot-tip' effect of contact fiber laser surgery. This clinical trial achieved the immediate, short term objective of endodontic soft tissue removal via photovaporization, without pain reported by the patient. The pulsed FR Nd:YAG dental laser used as described in this clinical report appears to be a very safe and very effective technique; offers a treatment alternative to traditional therapy that suggests high patient acceptance; and is significantly less stressful for the doctor and staff than traditional treatment options. Long-term, controlled scientific and clinical studies are necessary to establish the safety and efficacy of both the helium-neon energy for visualization and the low-watt pulsed FR Nd:YAG energy for photovaporization of soft endodontic pulpal tissue within the root canal. Research is especially needed to understand the effects of a low-watt, pulsed FR, Nd:YAG laser on the activity of osteoclasts and odontoclasts and identify risks for developing external and/or internal resorption after intracanal application of pulsed FR Nd:YAG laser energy.

Formation of dystrophic calcification deposits within the root canal of a tooth, have historically been difficult clinical endodontic complications. Presently, removal of such tissue, mineralized through the deposition of calcareous materials in a root canal (a 'calcified canal'), remains resistant to conventional endodontic techniques. The subsequent treatment primarily involves undesirable surgical procedures and/or loss of the tooth. Described in this clinical trial is a technique using free running (RF) pulsed, Nd:YAG laser energy to ablate hard calcified tissue which obstructed mechanical access of the root canal and root apex--a technique employed after conventional endodontic methods failed. This paper discusses the 'plasma' effect, 'spallation', canal illumination and transillumination using the helium-neon (HeNe) aiming beam. A free running pulsed, FR Nd:YAG dental laser was successfully used at 20 pulses per second and 1.75 watts to photovaporize and photodisrupt enough calcified tissue obstruction, to allow a conventional endodontic file to pass the canal blockage, and access the root apex. This clinical trial achieved the immediate, short term objective of endodontic hard tissue removal via photovaporization and photodisruption. The pulsed FR Nd:YAG dental laser used as described in this clinical report appears to be a very safe and very effective technique; offers a treatment alternative to traditional therapy that suggests high patient acceptance; and is significantly less stressful for the doctor and staff than traditional treatment options. Long-term, controlled scientific and clinical studies are necessary to establish the safety and efficacy of both the helium-neon energy for visualization and the low- watt pulsed FR Nd:YAG energy for photovaporization and photodisruption of hard calcified tissue within the root canal. Research is especially needed to understand the effects of low- watt, pulsed FR, Nd:YAG laser on the activity of osteoclasts and odontoclasts and identify risks for developing external and/or internal resorption after intracanal application of pulsed FR Nd:YAG laser energy.

Nowadays after the long-term efforts of physicists and dantists we came up to the creation of very important device for human life - laser drilling machine. However the problem of laser choice for this machine has not been solved yet. In table 1 are represented the earlier published data of main lasers — candidates on the role of "drill" [1-5]

Although there has been interest in lasers in dentistry since lasers were first developed in the early 1960's, this interest was limited until recently. Over the past five years there has been a flurry of interest to find the most effective wavelength and parameters of treatment. With this interest has come clinical and experimental reports. This project is a pilot study to investigate laser effects on dogs teeth. Multiple teeth from 2 dogs (n equals 40) were treated using either a CO₂, Nd:YAG, or an Er:YAG laser, or slow-speed rotary instrumentation. One dog died after treatment and was not used in this study. The second dog was sacrificed four days after treatment with the lasers and the teeth were decalcified and processed for light microscopy. The dentin and pulpal tissues were then evaluated for changes from their normal histologic patterns. The purpose of this study was to first determine if the dog would be a good model for in-vivo histologic testing of lasers and second to evaluate the histologic effects of different lasers on dog's teeth. Our findings suggest that each laser causes a different degree of effect to the treated teeth. The specifics of these effects are discussed herein.

Ceramic brackets are an esthetic substitute for conventional stainless steel brackets in orthodontic patients. However, ceramic brackets are more brittle and have higher bond strengths which can lead to bracket breakage and enamel damage during debonding. It has been demonstrated that various lasers can facilitate ceramic bracket removal. One mechanism with the laser is through the softening of the bracket adhesive. The high energy density from the laser on the bracket and adhesive can have a resultant deleterious thermal effect on the pulp of the tooth which may lead to pulpal death. A theoretical computer model of bracket, adhesive, enamel and dentin has been generated for predicting heat flow through this system. Heat fluxes at varying intensities and modes have been input into the program and the resultant temperatures at various points or nodes were determined. Further pursuit should lead to optimum parameters for laser debonding which would have minimal effects on the pulp.

The aim of this investigation was studying the regularities of the strain distributions around in- bone implants of various shapes: cone, cylinder, tube, and blade-vent. Secondly, it was to study the force parameters of the cortical and porous bone substance when blade-vent implants of various size which are the distal supports of the bridge-shaped dentures are introduced into the planting bed. By means of the histological radiology method we carried out a study of the upper and lower jaws architectures on the basis of jaw segments investigation. A study was carried out by means of holographic interferometry of compression and tension areas distribution in the skull bones, the upper and lower jaws and temporo mandibular joint area under load. A laser holographic set-up used to obtain interference patterns covering strained and deformed jaws containing introduced implants consisted of a He-Ne laser, mirrors, lenses, a hologram, a VC, a TV monitor, and loading device.

Research has shown that low levels of CO₂ laser irradiation raise enamel resistance to sub-surface demineralization. Additionally, laser scanned fluorescence analysis of enamel, as well a laser and white light reflection studies, have potential for both clinical diagnosis and comparative research investigations of the caries process. This study was designed to compare laser fluorescence and laser/white light reflection of (1) non-lased/normal with lased/normal enamel and (2) non-lased/normal with non-lased/carious and lased/carious enamel. Specimens were buccal surfaces of extracted third molars, coated with acid resistant varnish except for either two or three 2.25 mm² windows (two window specimens: non-lased/normal, lased/normal--three window specimens: non-lased/normal, non-lased carious, lased/carious). Teeth exhibiting carious windows were immersed in a demineralizing solution for twelve days. Non-carious windows were covered with wax during immersion. Following immersion, the wax was removed, and fluorescence and laser/white light reflection analyses were performed on all windows utilizing a custom scanning laser fluorescence spectrometer which focuses light from a 25 mWatt He-Cd laser at 442 nm through an objective lens onto a cross-section >= 3 (mu) in diameter. For laser/white light reflection analyses, reflected light intensities were measured. A HeNe laser was used for laser light reflection studies. Following analyses, the teeth are sectioned bucco-lingually into 80 micrometers sections, examined under polarized light microscopy, and the lesions photographed. This permits comparison between fluorescence/reflected light values and the visualized decalcification areas for each section, and thus comparisons between various enamel treatments and normal enamel. The enamel specimens are currently being analyzed.

It is well known that enamel and dentin fluoresce when illuminated by short-wavelength optical radiation. Fluorescence emission from carious and non-carious regions of teeth have been studied using a new experimental scanning technique for fluorescence analysis of dental sections. Scanning in 2 dimensions will allow surface maps of dental caries to be created. These surface images are then enhanced using the conventional and newer image processing techniques. Carious regions can be readily identified and contour maps can be used to graphically display the degree of damage on both surfaces and transverse sections. Numerous studies have shown that carious fluorescence is significantly different than non-carious regions. The scanning laser fluorescence spectrometer focuses light from a 25 mW He-Cd laser at 442 nm through an objective lens onto a cross-section area as small as 3 micrometers in diameter. Microtome prepared dental samples 100 micrometers thick are laid flat onto an optical bench perpendicular to the incident beam. The sample is moved under computer control in X & Y with an absolute precision of 0.1 micrometers . The backscattered light is both spatial and wavelength filtered before being measured on a long wavelength sensitized photomultiplier tube. High precision analysis of dental samples allow detailed maps of carious regions to be determined. Successive images allow time studies of caries growth and even the potential for remineralization studies of decalcified regions.

Previous oral medicine research has insufficiently quantified and correlated laser effects on calcified/soft-tissue combinations. The purpose of this study was to explain lasing effects on outcome variables (pulp response and enamel condition). Vital animal molars were irradiated using several mediums, with predetermined energy densities serving as independent variables. Predetermined safe-tissue thresholds, including pulp/enamel conditions, can be demonstrated to display linear relationships using several laser systems.

The employment of photoablative effect on coronary artery angioplasty has been a new exciting field as a treatment option. Guided by good results in the literature, our group decided to study the laser/tissue interaction on carotid arteries with the intent of a less invasive treatment of intracranial and extracranial obstructed disease in vascular neurosurgery. We studied human cartoid arteries from ten male autopsy specimens with an average age of 53 years (34 - 37 years old) which a total of 22 laser applications were performed. Using the same repetition rate and energy, 20 Hz and 30 mJ, we compared the effect of the laser energy on 'normal' and 'pathologic' areas of the carotid arteries. The pathologic specimens, presenting calcified and non-calcified plaques, the same as the macroscopical 'normal' specimens, were submitted to the energy of the Excimer Laser with 308 nm wavelength. The laser beam was delivered perpendicularly through continuous flushing of saline on the targeted artery wall varying from 200 to 400 pulses. Histological studies were done and statistical analysis was performed. The results showed that the depth of penetration varied from 113 micrometers to 1200 micrometers , with a width of the lesion ranging from 150 micrometers - 1500 micrometers . In our study we found that the range between non-effective and destructive effect caused by the laser was around 400 pulses. We encountered minimal degree of carbonization while lasering on calcified plaques. We concluded that Excimer laser is a feasible and secure tool to prevent thermical complications of laser treatment, which will allow neurosurgeons in the future athermic laser angioplasty. Progress in this field must rely on further in vitro and in vivo research, before it can be clinically applied as well as improvements in delivery systems.

We report on the new technique of interstitial laser coagulation of the prostate (ILCP) in the treatment of benign prostatic hyperplasia (BPH). Basic experiments by use of a Nd:YAG laser in combination with a newly designed fiber tip homogeneously distributing the laser irradiation have been performed in potato, muscle, liver, and surgically removed human BPH-tissue to determine the volume of coagulation. The coagulation zone surrounding the probe was well defined and homogeneous. The size was dependent on laser power and irradiation time. Carbonization was never present except in darker tissues irradiated with high energy. Volume and time resolved measurements correlated well with the size of coagulation. 10 W and 5 minutes, for example, resulted in a coagulation zone of 17 X 15 mm. Comparable results have been seen in in-vivo experiments in surgically exposed canine prostates. Specimen for macroscopic and microscopic examination were taken immediately after treatment and after 5 and 35 days. The well demarked coagulation necrosis of the early stage resulted in cystic degeneration and fibrosis in the later stages. This was combined with shrinkage and reduction in volume. The urothelium of the urethra, the external sphincter and the rectum showed no damage. Until now, 15 patients suffering from obstructive symptoms due to BPH have been treated with interstitial laser coagulation. The probes were inserted from the perineum into the center of each lateral lobe of the prostate by transrectal ultrasound guidance, while the median lobe was treated by urethroscopic guidance, while the median lobe was treated by urethroscopic control. Dependent on the size of the prostate irradiation, time was 5 to 10 minutes per lobe at a power setting of 5 to 10 W.