Recent studies have shown spray cooling of the skin surface with millisecond cryogen spurts to be an effective method for protecting the epidermis from non-specific thermal injury during various laser mediated dermatological procedures. We have investigated the effects of ambient humidity level, spraying distance, and cryogen boiling point on the resulting radiometric surface temperature. Our findings indicate that: (1) decreasing the ambient humidity level results in less ice formation on the skin surface without altering the radiometric surface temperature during a cryogen spurt; (2) increasing the spraying distance to 85 mm lowers the radiometric surface temperature; and (3) boiling point of the cryogen does not directly affect the surface temperature in the geometries studied.

Aim of the study was the comparative investigation of cutaneous and subcutaneous vascular lesions. By means of color coded duplex sonography (CCDS), laser doppler perfusion imaging (LDPI) and infrared thermography (IT) we examined hemangiomas, vascular malformations and portwine stains to get some evidence about depth, perfusion and vascularity. LDI is a helpful method to get an impression of the capillary part of vascular lesions and the course of superficial vessels. CCDS has disadvantages in the superficial perfusion's detection but connections to deeper vascularizations can be examined precisely, in some cases it is the only method for visualizing vascular malformations. IT gives additive hints on low blood flow areas or indicates arterial-venous-shunts. Only the combination of all imaging methods allows a complete assessment, not only for planning but also for controlling the laser treatment of vascular lesions.

The purpose of this study was the evaluation of different combined cooling and compression techniques for the treatment of vascular disorders of the skin and subdermal layers. In combination with flashlamp pumped dye lasers, argon lasers and Nd:YAG-lasers the effectiveness of glass plates, a cooling chamber with a flexible membrane and continuous ice cube cooling were evaluated in vitro by temperature measurements with thermocouples and thermographic camera readings and in vivo by laser doppler flowmetry, color coded duplex sonography and comparison of photographic documents for effectiveness and occurrence of side effects. Experimental and clinical evaluations show excellent results for skin protection, effective treatment depth enhancement and minimalization of side effects as well as for pain perception.

CO₂ laser skin resurfacing devices are widely used in cosmetic surgery for the treatment of facial rhytides, acne scars and aging skin. This technique is also useful in the treatment of various benign and premalignant or multiple pathological skin conditions and disorders originating in the epidermal, dermal and skin appendages, vascular lesions, epidermal nevi, infected wounds and ulcers, and keloids. Various surgical techniques have been developed in our clinic using laser resurfacing in the treatment of more than 2,000 patients with various skin pathologic disorders. We describe our experience with the various techniques used. The precise depth control and ablation properties combined with the hemostatic and sterilizing effects of the CO₂ laser beam, reduction of the possibility of bleeding, infection and damage to healthy tissues, make the CO₂ laser resurfacing techniques the treatment of choice for cosmetic surgery and treatment of benign, premalignant and multiple pathologic skin conditions.

Different laser systems and techniques are used for the treatment of hypertrophic scars, keloids and acne scars. Significant criteria in selecting a suitable laser system are the scar's vascularization, age and diameter. Flashlamp- pumped dye-lasers, CO₂-lasers with scanner, Argon and Nd:YAG-lasers are used. Telangiectatic scars respond well to argon lasers, erythematous scars and keloids to dye-laser treatment. Using interstitial Nd:YAG-laser vaporization, scars with a cross-section over 1 cm can generally be reduced. For the treatment of atrophic and acne scars good cosmetic results are achieved with a CO₂-laser/scanner system, which allows a precise ablation of the upper dermis with low risk of side-effects.

Since the first application of CO₂ laser in skin photosurgery, various techniques such as laser pulsing, beam scanning and computer-assisted laser pulse generator have been introduced for the purpose of reducing tissue carbonization and thermal necrosis. Using a quite simple XY optical scanner equipped with two galvanometric driven mirrors and an appropriate software to process the scanning data and control the interaction time and energy density in the scanned area, we have obtained a device which can improve CO₂ laser application in cosmetic and aesthetic surgery. The opto-mechanical CO₂ laser scanner based on two total reflecting flat mirrors placed at 90 degree(s) in respect to the XY scanning directions and independently driven through a magnetic field provides a linear movement of the incident laser beam in the operating field. A DA converter supplied with scanning data by the software enables a scanning with linearity better than 1% for a maximum angular deviation of 20 degree(s). Because the scanning quality of the laser beam in the operating field is given not only by the displacement function of the two mirrors, but also by the beam characteristics in the focal plane and the cross distribution in the laser beam, the surgeon can control through software either the scanning field dimensions or the distance between two consecutive points of the vertically and/or horizontally sweep line. The development of computer-assisted surgical scanning techniques will help control the surgical laser, to create either a reproducible incision with a controlled depth or a controlled incision pattern with minimal incision width, a long desired facility for plastic surgery, neurosurgery, ENT and dentistry.

The influence of Er:YAG laser pulse fluence and duration on temperature profile development, coagulation depth and the ablation threshold in skin resurfacing is analyzed using an original 1D numerical model. The model is focused on the role of mechanical properties of the treated tissue, such as elastic modulus and tensile strength. It combines a thermodynamic model of overhead tissue water with the response of surrounding elastic medium to the resulting pressure increase. Diffusion of dissipated heat is treated in one dimension for the case of isolated tissue surface. Additionally, the nonlinear protein denaturation process is modeled as usual. The results show how the pulse duration influences the depth of heat-affected layer in mid-IR laser skin resurfacing.

The work reports studies aimed at determining the pain and sensitivity thresholds of human skin surface induced by an intense radiation of IR laser. The pain and sensitivity thresholds of skin surface and their dependence on such characteristics of laser radiation as pulse duration, energy density, and laser spot diameter were obtained.

In the past ten years partial coherence interferometry and optical coherence tomography have been developed for high precision biometry and tomography of the human eye in vivo. The longitudinal resolution of the optical coherence tomography technique depends on the spectral bandwidth of the light source used and on the dispersion of the media to be measured. In nondispersive media the resolution is approximately equal to the coherence length of the light used, which is inversely proportional to the width of the emission spectrum. Hence, a broad emission spectrum yields a short coherence length and consequently a good resolution. However, if the tissue under investigation is dispersive, the coherence envelope of the signal broadens leading to a decrease in resolution and interference fringe contrast. This effect becomes predominant if measurements through the dispersive media of the eye to the retina are performed with source bandwidths larger than approximately 25 nm. In order to achieve optimum resolution of OCT by applying a light source with a broad emission spectrum, the dispersion of the object to be measured, i.e. in this case of the ocular media, has to be compensated. Within the scope of this work we demonstrate the resolution improvement that is obtained by compensating the dispersive effects of the ocular media and using broadband light sources. Furthermore, we present the first optical coherence tomogram recorded with this technique in the retina of a human eye in vivo with an axial geometrical resolution of approximately 6 micrometers which is a two-fold improvement compared to presently used technology.

Pulsed laser ablation of corneal tissue at the typical operative fluences of Argon-Fluoride photorefractive keratectomy produces stress waves propagating into the eye. Temporal and spatial evolution of these pressure pulses during propagation were measured directly in porcine eyes with a needle hydrophone. Beside diffraction effects that give rise to a bipolar shape of the pressure pulse with a positive compression peak followed by a marked rarefaction phase, we found a significant focusing of the stress wavefront caused by the spherical shape of the cornea, that increased for larger irradiation spot diameters.

In this study the ablation characteristics and the wound healing process of rabbit cornea irradiated with a Q- switched Er:YAG laser was evaluated. The laser, emitting at 2.94 micrometers wavelength, has a pulse width of 100 ns. The spot size on the corneal surface was 1 mm in diameter at a fluence of 750 mJ/cm². The laser beam was applied by a `flying spot' mode, performing refractive ablations of -7 to -8 dpt. As a biological model, the corneas of 9 rabbits were irradiated. The post-treatment follow-up was as long as 39 days. The treated corneas were investigated by light and electron microscopy. The wound healing on rabbit cornea of the Q-switched Er:YAG laser radiation in corneal tissue processing resembles to what is known from ArF- excimer laser application. To shorten the pulse width by means of Q-switching is one major key to the successful application of the Er:YAG laser for PRK.

Laser thermokeratoplasty (LTK) is a minimally invasive method to correct hyperopia and astigmatism. A cw mid-IR laser diode emitting at wavelengths around 1.86 micrometers was used to perform LTK on a first clinical trial. The coagulations were applied to the cornea by means of a specially designed focusing handpiece which was introduced into a corneal application mask fixed by a suction ring. Coagulation patterns consisting of 8 spots per ring were performed with a laser power between 100 - 150 mW and an irradiation time of 10 seconds both on single and on double rings. Significant refractive changes up to 19 D could initially be achieved followed by a strong regression within the first month. Three months post LTK, refractive changes achieved with the single and double ring have stabilized, yielding 1.2 and 1.8 D on the average, respectively. The method reveals only little adverse effects limited to the first days post-op. Force measurements were performed on corneal stripes, which were submerged for 10 s into an oil bath of constant temperature in order to investigate the absolute temperatures required for corneal collagen contraction. Only temperatures exceeding 90 degree(s)C induced a significant force. Analyzing the clinically used LTK parameters by temperature calculations revealed that only a small part of the heated stromal volume experienced sufficient high temperatures to induce significant collagen shrinkage.

Recently, we presented a new research instrument to perform dynamic light scattering measurements in each section of the eye axis from the cornea to the retina. Using this instrument, a set of in vivo measurements of static scattered light at the scattering angle of 174 degree(s) on different ocular tissues has been performed. From these measurements the Rayleigh ratio has been evaluated. The motivation for the present study is the complete lack, in literature, of this important scattering parameter for ocular tissue. Rayleigh ratio is important to evaluate a- priori the predetection signal achievable by scattering probes from different ocular tissues. In vivo measurements have been performed on thirty normal subjects aged 16 - 73 years, and Rayleigh ratio has been evaluated as a function of the measuring position and subjects age.

A compact fiber optic probe developed by Ansari et al. for fluids experiments in the challenging conditions of a microgravity environment on-board a space shuttle orbiter has been applied to obtain `cataractograms' in transgenic mice to study early onset of cataractogenesis. Cataractograms are topographical contour maps of the lens which are obtained non-invasively by scanning the eye with the probe in three-dimensions (x, y, and z directions). This new method provides a visual means, in false color, for quantitative detection and monitoring of cataracts in the entire lens. The portion of lens mapped is only limited by the degree of pupil dilation. The dilated pupil is about 1 mm for the transgenic mice system reported in this study.

A 3D finite element model is developed to study the conduction and convection heat transfer due to an argon laser iridectomy in the human eye. The objective is to explain the appearance of two important postoperative complications reported by ophthalmologists: corneal burns and lens opacities. Contraction burn is studied using simple shot of 1 s in duration, 0.5 mm in size, 0.4 W in power and double laser shot of 0.5 s in duration, 0.5 mm in size, 0.4 W in power and 0.5 s of relaxation time. Iris tissue pyrolisis temperature threshold is included as onset of tissue removal. Two laser spot positions on the iris circumference are considered. The phenomena of cornea and lens overheating for both normal and pathological human eyes are presented and discussed.

Measurement of refraction distribution in the human eye opens new opportunities to make photorefractive surgery more accurate due to accounting imperfections not only of the cornea, but of the eye as an optical system. To calculate the to-be-ablated cornea layers, mathematical relations must be found between measured coordinates of retina ray tracings and transfer function of an eye. A new concept for modeling eye optical system is proposed using four phase transparencies, each of them exercising its own function: accommodation (equivalent to varifocal system), image focusing on the retina (optical system with constant optical power), regular aberrations (spherical and chromatic, astigmatism), and irregular phase distribution. It is shown, how the parameters, necessary for phase transparencies description, can be derived from direct and indirect measurements. Results of modeling experiment with simplified set of test points showed good sight correction. Investigated methodology proved to be fruitful even with limited number of test points and restricted length of polynomial approximation. In our refraction mapping system, transfer function reconstruction will use initial information from 65 points.

A modified double-pass wave model is proposed being a wave diffraction model of the secondary coherent field formed due to double pass of light in the human eye system. The modification takes into account: cornea contribution into total eye refraction, coherent nature of light reflection from the retina, and non-additive character of the cornea and lens aberrations. Irreversibility and anisoplanatism of the optical eye system follow from this study concurrently with the fact that the coherent point-spread function of double pass is not the autocorrelation of single-pass point- spread function. We used Hartmann-Shack wave front sensor and found it to be a promising technique for eye aberrations study: refraction map of the whole eye aperture can be reconstructed from a single-pulse information, presenting essential advantage as compared with point-by-point measurements. TV image of spot pairs can be got with CCD camera, its lens being replaced with lenslet array. Image processing consists in distance calculation between corresponding spot pairs. We use two-pulse exposure for this purpose: one--for producing a reference set of spots, the second one--for getting the spots produced by a distorted wave front. The sensitivity of this technique is estimated to be of the order of several percents.

For the treatment of prostate anew instrumentation set is built. This allows an ambulant resection of the prostate by using a combination method of laser and radio frequency (RF). Both instrumentations were combined in a new laser RF resectoscope which consists of a shaft and two working elements; one for the laser fiber and one for the RF loop. The treatment first coagulates the prostate tissue with laser by using a simple bare fiber that irradiates lateral. Since the fiber can be moved manually in axial direction by means of the laser fiber carrier all sections of the prostatic tissue can be systematically covered by the laser beam. Thus substitutes costly and sophisticated systems, i.e. side firing fibers. Further benefits are given; so the instrumentation can also be used for bladder tumors, urethral strictures and bladder neck incisions.

Conventional diagnostics fail to trace dysplasias and early cancers of the colon. By means of Laserlight Induced Fluorescence Diagnostics (LIFD) macroscopically not visible malignant tumors and dysplasias of the colon can be detected. The main side effect of systemically applicated photosensitizers is a general photosensibilization of the organism which provokes an increased photosensitivity of the body. Local application of (delta) -aminolevulinic acid (ALA) reduces systemic uptake without impairment of the quality of investigation. Colorectal cancer in male wistar rats was induced by weekly subcutaneous (s.c.) injections of 1,2- dimethylhydrazine (DMH) for 17 weeks. After s.c. DMH injection the wistar rats (n equals 25) developed in average 5.6 macroscopically visible colon carcinomas. 80% of these tumor were detected by LIFD after photosensibilization with Photofrin II intravenously (i.v.), 29% after application of mTHPC (i.v.), 13% after ALA (i.v.), 20% after intraperitoneal application of ALA (i.p.) and 57% after local application of ALA in the colon. LIFD is a capable method for the detection of macroscopically not visible dysplasias and colon carcinomas of the rat induced by DMH. The applied PS and the method of application influences the detection of carcinomas and dysplasias. Systemic photosensibilization of the whole organism can be avoided by the local application of ALA without limiting the quality of investigation.

LIFD and PDT are based on the selective uptake of photosensitizers resp. the selective metabolism of their precursors in malignant tissue. Excitation with laserlight results in fluorescence or phototoxic reactions which can be used for the detection or destruction of colorectal carcinoma and dysplasia. General photosensibilization resulting in an increased photosensitivity of the whole body represents the main side and necessitates avoidance of daylight for days up to weeks. Local application of (delta) - aminolevulinic acid (ALA) may reduce systemic uptake. Rats with DMH induced colorectal cancer were photosensitized for LIFD by oral, intravenous or local application of ALA. Urine concentrations of ALA and porphobilinogen (PBG) representing systemic photosensibilization were determined by two-column chromatography. Local colon application of ALA not only increases the quality of LIFD of colorectal cancer, it also provokes three times lower concentrations of PBG in comparison to oral or intravenous administration and reduces in consequence general photosensibilization.

The Paterson lamp is a convenient, low cost, portable, alternative light source to lasers for PDT. A multi- wavelength capability enables the clinician to vary the photosensitizer used. The Paterson lamp has been applied in the field of dermatology using a liquid light guide with distal optics for surface application. We now describe distal optics suitable for use with this light guide for intraluminal applications in the oesophagus and colorectum. The geometry of the site (oesophagus and colorectum) requires distal optics such as a cylindrical diffuser or a side fire diffuser. We have designed new cylindrical probes that diffuse light radially from the guide axis (cylindrical diffusion). The tips have a frosted glass surface that scatters and effectively couples light radially into the tissue. An acrylic spacer is placed over the diffuser to position the tissue at a constant diameter from the probe. This is held in position by a silicone sheath placed over the distal one meter. For use in the oesophagus, a channel, to facilitate intubation over a guide wire, is included. The diameter of the entire probe is 8.4 mm and the power output can be adjusted from 0 - 500 mW.

Authors compared Nd:YAG laser and the transrectal microsurgery in the treatment of large sessile polyps of distal rectal stump. Disadvantages of using of the laser technique is necessity to repeat laser sessions and impossibility of the correct histology specimens of all adenomatous polyps. Necessity of general or spinal anesthesy, great diameter of operative rectoscope in contrast of the relative narrow optical field restricted usability of transrectal microsurgery in the treatment of large sessile adenomatous polyps of the rectum. Greatest advantage of laser treatment is using of the standard colonoscopy device in the outpatient procedure in contrast of the expensive transrectal microsurgery device which need special training of the medical staff. In conclusion authors considered Nd:YAG laser of the method of choice in the treatment of large sessile adenomatous polyps of distal rectal stump.

Re-establishment of the oesophageal lumen is the main focus of care in patients with inoperable oesophageal carcinomas. The self-expanding metal mesh stents (MMS) are increasingly being used. 51 patients aged 44 - 89 with inoperable oesophago-gastric carcinomas were intubated with MMS. 18 of these patients had endoscopic laser therapy (ELT) as primary palliation. 25 patients required follow-up endoscopy at variable intervals after stent insertion. 17 patients were found to have significant tumor growth (9), overgrowth (4) and both (4). All these patients were treated with Nd:YAG or diode laser for maintenance of satisfactory swallowing. 4 patients being treated with Nd:YAG laser developed deformity of MMS. This complication was not encountered with diode laser. The reblockage of MMS due to ingrowth or overgrowth of tumor is a not uncommon complication. The timing of the stent insertion should be carefully chosen since the longer the stent is in situ, the greater is the likelihood of tumor ingrowth or overgrowth. ELT can effectively deal with tumor ingrowth and overgrowth. Nd:YAG laser can cause melting of MMS. Overall the combination of ELT and MMS may offer the best palliation, particularly when patient survival of several months is anticipated.

The objective of this study was to evaluate and compare the safety and efficacy of the KTP 532 laser to direct vision internal urethrotomy (DVIU) in the management of urethral strictures. A total of 32 patients were randomized prospectively in this study, 14 DVIU and 18 KTP 532 laser. Patients were evaluated postoperatively with flowmetry and in the case of recurrence with cystourethrography at 3, 12, 24 weeks. With the KTP 532 laser complete symptomatic and uredynamic success was achieved in 15 (83%) patients at 12 and 24 weeks. Success rate was lower in the DVIU group with 9 (64%) patients at 12 weeks and 8 (57%) patients at 24 weeks. Mean preoperative peak-flow was improved from 6 cc/s to 20 cc/s at 3, 12 and 24 weeks with the KTP laser. With DVIU mean preoperative peak-flow was improved from 5.5 cc/s to 20 cc/s at 3 weeks followed by a steady decrease to 13 cc/s at 12 weeks and to 12 cc/s 24 weeks. No complication was observed in either group of patients. Our results confirm that stricture vaporization with the KTP 532 laser is a safe and efficient procedure. The better results after laser surgery make it also a valuable alternative in the endoscopic treatment of urethral strictures. These findings suggest a favorable influence of laser surgery on wound healing with less wound contraction and scarring. The lack of contraction of laser wounds might be related to the absence and the lack of organization of myofibroblasts in laser induced lesions.

From November 1, 1992 to January 31, 1997, 227 patients with inoperable esophageal and cardial carcinomas were treated with Nd:YAG laser therapy and prosthesis intubation. The retrograde technique was used in most cases. The tumor involved in 75 pts the Cardia, in 65 the middle thoracic esophagus, in 47 pts the lower thoracic esophagus, in 23 in the upper thoracic esophagus and in 17 in the cervical esophagus. The indications for palliative Nd:YAG laser and prosthesis intubation were a locally advanced or metastatic tumor in 146 pts (64.4%) and poor surgical risk in 81 pts (35.6%). The quality of palliation was evaluated according to the ability to swallow. The mean survival rate of the patients during the follow up was 22 weeks for the laser therapy and 16 weeks for the prosthesis intubation.

From November 1, 1992 to January 31, 1997, we treated 189 pts: 113 males and 76 females, of mean age 67 yrs. 148 pts were affected with colo-rectal cancer and 41 pts with extensive carpet benign tumors. Tumor location was: rectum in 115 pts, recto-sigmoid joint in 31 pts, colo-rectal anastomosis in 25 pts, sigmoid colon in 15 pts, descending colon in 2 pts and cecum in 1 pt. 26 pts were treated with diathermo-therapy, 15 pts with dilatation, 12 pts with radiotherapy, 5 pts with chemotherapy, 1 pt with chemotherapy and radiotherapy. Yag-laser palliation gave good results in 90% (170 - 189) with an average survival of 24 weeks; there were complications due to the treatment in due pts (1%) without hospital mortality.

Background: The oxygen utilization, and therefore the metabolic state, of a distinctive area of the retina may be calculated from the diameter of the supplying artery and vein, the haemoglobin oxygenation, and the velocity of the blood. The first two parameters can be determined by imaging spectrometry at the patients ocular fundus. This technique enables the simultaneous measurement of reflectance spectra of neighboring locations at the fundus, e.g. across retinal vessels. However, the reflected light emerging from a vessel is determined by different mechanisms of reflection and backscattering. The following most significant light fractions, contributing to the measuring signal, are considered: Light which is backscattered from deeper fundus layers and transmitted once or twice through the vessel, light which is backscattered from the blood column inside the vessel, and light which is specular reflected at the vessel wall. Goals are the investigation of the contribution of the single fractions to the vessel profile and its approximation by an analytical function which can be used to compensate specular reflection at in vivo measured profiles. Method: To evaluate the contribution of the different pathways we set up a Monte Carlo model of radiative transport inside the ocular fundus as a layered structure containing a vessel with circular cross section. The developed software is able to distinguish photons contributing to the simulated vessel profile which penetrated the blood column once, twice, or never. Experimentally determined absorption and scattering parameters of the fundus tissues were used in the simulation. Results: Considering retinal vessels with diameters of 25 micrometers to 200 micrometers we found the reflection from a thin vessel to be determined by the single and double transmission of light at 559 nm. The backscattering from the blood column determines the reflectance in the case of a thick vessel. However, both components are in the same order of magnitude. Discussion: The spectra measured even at the center of retinal branch vessels are composed from light which is backscattered from the blood column inside the vessel and from transmitted light fractions which were reflected behind the vessel. Since the latter is influenced also by the absorption of melanin and haemoglobin in the choroid, care must be taken in the calculation of the oxygen saturation of blood in retinal vessels from this spectra. The reconstruction of an in vivo measured vessel profile which is distorted by specular reflexes is possible by the use of a polynomial of sixth degree.

Previous studies have recorded the reduction of caries-like lesions or demineralization in extracted human teeth that have been irradiated using CO₂, Nd:YAG and Argon lasers, with CO₂ or Argon showing up to 40 - 50% reduction. By adding a chemical inhibitor, such as DAC or fluoride to lasing procedures, the demineralization can be reduced 60 - 80%. Studies have demonstrated the laser safety for Argon and CO₂ laser in these procedures. Clinical trials are being initiated to evaluate acid resistance of enamel exposed to laser radiation. This presentation will review prior results and present our current findings.

Root canal treatment is still a problem in dentistry. Very often the conventional treatment fails and several treatment sessions are necessary to save the tooth from root resection or extraction. Application of lasers may help in this situation. Bacteria reduction has been demonstrated both in vitro and clinically and is either based on laser induced thermal effects or by using an ultraviolet light source. Root canal cleansing is possible by Er:YAG/YSGG-Lasers, using the hydrodynamic motion of a fluid filled in the canals. However root canal shaping using lasers is still a problem. Via falsas and fiber breakage are points of research.

Recently it has been shown that bacterias can be sterilized by Er:YAG laser irradiation. By optical fiber transmission the bactericidal effect can also be used in endodontics. In order to explore potential laser parameters, we further investigated sterilization of caries and measured temperatures in models simulating endodontic treatment. It was found out that the bactericidal effect is cumulative, with single pulses being active. This offers to choose all laser parameters except pulse energy (radiant exposure) from technical, practical or safety considerations. For clinical studies the following parameter set is proposed for efficient and safe application (teeth with a root wall thickness > 1 mm, and prepared up to ISO 50): pulse energy: 50 mJ, repetition rate: 15 Hz, fiber withdrawal velocity: 2 mm/s. With these settings 4 passes must be performed to accumulate the total dose for sterilization.

From previous studies it could be demonstrated that an efficient ablation of dental calculus is possible using an Er:YAG laser with a special contact fiber tip. After improving of the design and the efficiency of light transmission of the contact tip laser treated tooth root surfaces were investigated due to morphological changes in comparison to conventional root scaling and planing. Surface modifications were observed histologically under the light microscope and by means of a Scanning Electron Microscope. During laser treatment the intrapulpal temperature increase was measured. The results show that the improved contact tip a microstructured surface can be generated, which shows no signs of thermal effects even when a laser pulse repetition rate of 15 Hz was used. Temperature increase was limited to 4 K at a repetition rate of 10 Hz and to 5.5 K at a repetition rate of 15 Hz.

This study compares bond shear strength between hard dental tissues and composite resin filling material after a classical acid etching treatment procedure and Er:YAG laser surface conditioning. The retention of composite resin was evaluated for three cases: (1) the flat dental substrate without any conditioning, (2) the classical drilling machine prepared surface with acid etching and (3) the Er:YAG laser conditioning of enamel and dentin. None significant differences between bond shear strength of the classical drilling machine prepared surface with acid etching in comparison with the laser radiation conditioning were found.

Dentin hypersensitivity is considered to be a consequence of the presence of open dentin tubules on the exposed dentin surface. Various methods and materials used in the treatment of this disease are directed to achieve a tubule's occlusion. The purpose of this study was to evaluate under scanning electron microscopy and clinical method the sealing effects of CO₂ laser on dentin tubules of human teeth without any damages of the surrounding tissues. Samples of freshly extracted noncarious 3^rd molars were used. The teeth were randomly divided in to two groups A and B. The samples of group A were exposed to laser beam in cervical area, directed parallel to their dentin tubules. The teeth of group B were sectioned through a hypothetical carious lesion and lased perpendicularly or obliquely of the dentin tubules. The CO₂ laser, at 10.6 micrometers wavelength, was operated only in pulse mode and provided 6.25 - 350 mJ in a burst of 25 pulses each of 250 microsecond(s) time duration with a 2 ms time interval between successive pulses (repetition rate up to 500 mH). Melting of dentin surface and partial closure of exposed dentin tubules were found for all specimens at 6.25 to 31.25 mJ energy. Our results indicated that using CO₂ laser in a parallel orientation of laser beam with dentin tubules, the dentin sensitivity can be reduced without any damages of pulp vitality.

To compare ablation quality of Er:YAG and Er:YSGG laser the surface quality, crater shape, mass loss, and temperature development were determined using the same fiber transmission system and handpiece. Similar crater depths for both lasers but greater diameters for the Er:YAG laser were measured. Also mass loss per pulse of the Er:YAG laser exceeds that of the Er:YSGG laser. Temperature development while ablation of dentin is more pronounced for the Er:YSGG laser. The observed minor ablation quality of the Er:YSGG laser can be explained by the lower absorption coefficient of dental hard substances compared to the Er:YAG laser.

Using the pendulum method the recoil momentum on dentin samples after pulsed irradiation (pulselength 80 - 100 microsecond(s) ) with a medical CO₂-laser (Sharplan 40C, 10.6 micrometers ) was measured. Therefore a Laser-Doppler-vibrometer was used to deliver the velocity and the direction of movement. Because of known masses of the samples and measurement of the ablated masses the velocity of the ablated particles was calculated. As a second method to measure the velocity of the ablated particles the vibrometer was used in a time of flight experiment. Both methods delivered the same results at a mean power of 0.5 Watt. The velocity of the ablated particles was 50 - 60 m/s. At higher mean powers the thermal behavior of the tooth material leads to higher velocities.

Influence of water-spray cooling on the efficiency of erbium laser ablation of hard dental tissues is investigated experimentally. Consecutive pulses from a dental Er:YAG laser system are applied to dentin and enamel surface in vitro. Depths and diameters of the resulting craters, obtained with and without the use of a pressurized air/water spray, are compared at single-pulse fluences from 10 to 140 J/cm². Similar measurements are performed also with direct drilling of enamel with a fiber tip. The results show that direct interaction of the cooling water with the laser radiation increases the ablation efficiency for enamel, especially in fiber-tip drilling.

The problem of jaw-face traumatism is actual in surgical stomatology and fracture of lower jaw make up about 90% from all types of traumas. Number of approaches that include non- specific stimulation of immune system by intravenous laser irradiation were used to raise efficacy of treatment of above indicated fractures. But the application of laser beam irradiation must be controlled by independent biochemical and immunological methods. In particular it is considered the necessity of preliminary analysis of immune system state to determine dose loading of this factor. In dependence on immune system activity the laser beams can promote treatment or reduction of its efficiency. In this report the experimental data about necessity of such control in case of usage of laser beam irradiation are demonstrated. The levels of thymic serum activity (TSA), inhibitors TSA (ITSA) and sub-fractional distribution of substances in blood serum were analyzed in two groups of patients with the fracture of lower jaw: (1) with ordinary treatment and (2) with additional inclusion of number of procedures of laser irradiation. The total quantity of investigated patients was 16. It was shown that: (1) at the irradiation of patients with the normal original TSA level in blood plasma: (a) TSA decreased; (b) ITSA appeared; (c) laser-correlation spectrums changed that indicated about increase of level of substance with less translation mobility and (d) the overall term of recovery increased for 1 day; (2) when the original TSA was lower, above mentioned parameters changed into opposite direction as it is indicated in point 1. So, low intensive laser radiation can have both positive and negative effect in dependent on original organism state.

The direction of He-Ne laser beam propagation in enamel is studied while the laser radiation was aimed on to enamel surface of flat longitudinal and transversal teeth slices. The slices with hypermineralized and transparent enamel (so called opalescent enamel) have been examined. The patterns of side-scattering of light have been detected by CCD camera. The scattering (Tyndall effect) and refraction of radiation have been observed. The data obtained explain some features of teeth exterior under increasing of enamel transparency and may be used for right choice of necessary hue of composite during tooth esthetic restoration.

The effect of redistribution of halogen light source intensity by hard dental tissues is presented. The study was performed on extracted intact molars. Commercially available lamp for light-cured materials was used as halogen light source. The spatial distribution of radiation was registered by CCD camera. The effect of redistribution of halogen light source intensity is caused by waveguide-scattering properties of dentin. This effect may be observed in case of irradiation of light-cured material through hard dental tissues.

For the very first time it is represented a study of filling material edge bordering upon root channel cavity modified with a laser. As a filling material it is used a glass ionomer cement. It is demonstrated that Nd:YAG laser radiation effects on increase of grade of edge bordering on the average of 20 - 30% at temperature rise of no more than 2 - 3 degrees in periodontium area in a period of operation.

We present a new technique, scanning laser retinoscopy, to spatially resolve in two dimensions the optical aberrations and refractive power of the ocular media. For this purpose, the Maxwellian view of a confocal scanning laser ophthalmoscope (SLO) is configured to scan simultaneously the posterior and the anterior segment of the eye at different levels of prefocussing. This set-up allows retinal imaging and psychophysics through different optical zones of the cornea and lens. In addition, the size of the anatomical pupil can be dynamically controlled by adjusting the colinear infrared and visible light intensities of the illuminating system. In retinoscopic images we can see a part of the retina superimposed by distinctive patterns of shadows in the pupillary area. The variable patterns of shadows in the retinoscopic images change with the level of prefocussing of the SLO. The patterns are the result of local variations in refraction or wavefront aberrations within the lens and cornea. In cases of excimer laser refractive surgery, for example, scanning laser retinoscopy is able to distinguish between a treated central area, transition zone and peripheral cornea. As a corollary, we can document differences between excimer laser delivery systems and also correlate the retinoscopic images with the subjective complaints of refractive surgery patients. These include monocular diplopia, glare, loss of contrast sensitivity besides reduced visual acuity.

Introduction: Laser ablation of the prostatic tissue or laser prostatectomy, is used as an alternative method to traditional endoscopic resection of the prostate. The usual side-firing Nd:YAG laser fiber for the treatment of obstructive symptoms has operational difficulties, a high cost and often poor early results. Materials: We describe the laser coagulation of the prostate using a 600-um bare fiber inserted in a modified Albarran bridge which included at the tip, a new gold-plated deflectable reflector. The complete device passes through a 21Fr.rigid cysto- urethroscope. The system and the fiber can be used for several dozen treatments. The dosimetry was 2000 J per 1 cc of prostatic tissue. Methods: VLAP using the prostascope was performed on more than 70 men in one institution, and 150 in a second one, for obstructive symptoms due to benign prostatic hyperplasia. The parameter included AUA symptom score, flow rate, residual volume and complications. Data were obtained preoperatively and 1, 3, 6 and 12 months after treatment. Discussion: According to our data VLAP with this system is a save, minimal invasive and effective treatment. Results are comparable to other non-contact laser devices. As the gold-plated reflector is inexpensive and the standard bare fiber can be used repeatedly, the cost is less than of an usual side-firing laser fiber.

The Holmium-YAG is a versatile laser with multiple soft- tissue applications including tissue incision and vaporization, and pulsed-laser applications such as lithotripsy. At 2140 nanometers, the wavelength is highly absorbed by tissue water. Further, like CO2 laser, the Holmium produces immediate tissue vaporization while minimizing deep thermal damage to surrounding tissues. It is an excellent instrument for endopyelotomy, internal urethrotomy, bladder neck incisions and it can be used to resect the prostate. The Holmium creates an acute TUR defect which gives immediate results like the TURP. More than 50 patients were treated from Jan. 1996 to Jan. 1997 for obstructive symptoms due to benign prostatic hyperplasia, bladder neck stricture, urethral stenosis, and superficial bladder tumors.

In vivo experimental results of hydroxyapatite coated real dental prostheses in unloaded conditions are presented. Implants were covered by method of laser ablation. Coated and reference prostheses were implanted into jaw of minipigs. Osseointegration and quality of new bone formation were studied.