The effects of pulsed ultraviolet and infra-red lasers on dental enamel.

To evaluate micromorphological changes seen in enamel following irradiation with pulsed lasers, extracted human teeth were treated with a TEA-CO2, an Er:YAG and an ArF laser systems. Light and scanning electron microscopic studies demonstrate that the Er:YAG laser produces a zone of microcracks in the subsurface area. While TEA-CO2 laser irradiation results mostly in surface melting, the Er:YAG laser produces a roughened enamel surface. After ArF laser irradiation a retentive surface appears, accompanied by some melting effects and an increased porosity. The observed results of all the employed laboratory type lasers varied over a wide range due to the widespread biologic differences in tooth structures.

The excimer laser in orthopaedics.

This review details clinical and laboratory experience with the 308 nm XeCl excimer laser. This ultraviolet laser is not approved yet for use in arthroscopy, but has been shown to be extremely proficient for debridement of degenerate articular cartilage and meniscus. It has fewer advantages than conventional techniques for synovectomy, meniscectomy, and lateral release. Preliminary in vitro and in vivo studies were performed to investigate the character of laser-irradiated articular cartilage and to search for evidence of regeneration. A model of arthritis was created in rabbits to test the effects of the laser. Partial-thickness cuts in articular cartilage also were irradiated to test for cartilage regeneration. In vitro results indicated that the cartilage was sealed, with only a negligible loss in thickness. The results of live rabbit studies initially showed a similar sealing under scanning electron and light microscopy; however, it tended to break down in time. The results of autoradiographic and histologic studies showed no evidence of cartilage regeneration. Recent evidence suggests that the laser may adversely affect chondrocyte vitality in a region beyond the region of visible damage. There is no evidence to suggest that the laser is mutagenic.

Excimer lasers in dentistry: future possibilities with advanced technology.

The thermal side effects of carbon dioxide and neodymium:yttrium-aluminum-garnet lasers limit their clinical applications. These high-powered, infrared lasers result in zones of charring and carbonization even in soft tissues and the bone. In contrast, the pulsed, ultraviolet radiation emitted by excimer lasers causes limited thermal, denaturative damage to surrounding tissues. Therefore, treatment of dental tissues with the nonthermal process of photoablation with excimer lasers may present alternatives to traditional dental practice. Possible future applications of the excimer laser include selective caries removal, the conditioning of tooth surfaces, and cleaning of root surfaces; the zones of necrosis are small, so that there is no residual debris.

[Laser-induced photoacoustic effects in the dentin]. / Laserinduzierte photoakustische Effekte im Dentin.

To study photoacoustic effects in dentin caused by UV-laser ablation, laser-induced shockwaves were measured using piezoelectric PVDF films. Above the tissue-specific energy threshold for photoablation the amplitude of the acoustic shock waves is proportional to the applied laser energy density. Laser energy densities of 2 J/cm2 cause pressure amplitudes of 50 bar, densities of 20 J/cm2 cause pressure amplitudes of 1000 bar. To avoid microcracks in dentine the maximum laser energy density to prepare dentin should be limited to approximately 20 J/cm2.

[Laser technology in dentistry]. / Lasertechnik in der Zahnheilkunde.

Although dental laser treatment is receiving great attention in basic and clinical research, only very few clinical applications have emerged as accepted standard methods. The most promising range of possible applications includes diagnostics and surgery. Most laser systems developed for therapeutic use are heat-producing units, i.e. they convert electromagnetic energy into thermal energy. These systems are employed above all in oral surgery for vaporization, cutting or coagulation of soft tissues and in prosthodontics for welding. More recently, new types of lasers have been developed allowing non-thermal modes of tissue interaction. A great number of technical and biological problems will have to be solved, however, before these laser systems will be practically applicable in such clinical fields as, for instance, caries therapy. In the near future, laser systems are expected to complete and supplement conventional methods in diagnosis and treatment, but not to replace them.

[Root canal preparation using Excimer lasers]. / Aufbereitung von Wurzelkanälen mit Excimer-Lasern.

As an alternative in endodontics to mechanical methods for root canal treatment, the use of a XeCl-excimer laser to prepare the canal wall was studied. In a light microscopic investigation undecalcified sections of laser-treated extracted human teeth showed that it was not possible to remove dentine in the root canal. Pulpal tissues remained in all wall areas. The available energy densities of this laser type seem to be not sufficient to ablate pulpal tissues or wall dentine.

Lasers in dentistry: new possibilities with advancing laser technology?

Although there are a considerable number of published papers on the role of laser treatment in dentistry, a critical review shows that laser technology is used only by specialists in a small therapeutic field. Most lasers are heat-producing devices converting electromagnetic energy into thermal energy. These lasers find uses in oral surgery for cutting or coagulating soft tissues or in the welding of dental prostheses. More recently, new types of lasers have offered non-thermal modes of tissue interaction, called photoablation, photodisruption and photochemical effects. Basic and clinical research is being carried out into the application of these devices in dentistry. However, much development will be required before lasers can replace conventional surgical methods for treating oral cancer or indeed replace the conventional bur for excavating carious lesions.

[Spectroscopically controlled preparation of hard tooth structures using a UV laser]. / Bearbeitung von Zahnhartgeweben mit einem UV-Laser unter spektroskopischer Kontrolle.

During preparation of hard tooth structures with a 193nm-(ArF)*-excimer laser, the laser beam produces a specific fluorescent light whose spectrum is governed by the structure of the specimen. These fluorescence spectra allow an analysis of the removed tissues. The data thus obtained may be used to control the laser system so that only specific structures, such as carious tissue, are removed: reproducible fluorescence spectra were established by means of standardized samples (pure synthetic hydroxyl apatite ceramics, enamel, dentine and carious dentine) and the characteristic absorption bands (peaks) for the different substances were measured. With the aid of electronic data processing these reference spectra could be compared with the fluorescence spectra obtained during preparation. When a spectrum differed from the predefined limits of relative intensities, preparation was stopped. Since ablation per pulse is only to a small depth (0.04-4 microns) with the 193nm-(ArF)*-eximer laser, this feedback system of ablation and fluorescence spectroscopy allows decisions as to continuing or stopping the preparation process to be taken within the range of a few microns.

[Thermal effects in the dental pulp caused by laser radiation from various laser types]. / Thermische Effekte bei der Präparation von Zahnhartgeweben mit verschiedenen Lasersystemen.

In this in vitro study the temperature rises occurring in the dental pulp during laser irradiation were measured. Infrared laser radiation (CO2 and Nd: YAG) had great thermal effects on the pulp tissues. At an average power output level of 5 W temperature rises of approx. 40 degrees C within 100 s were observed. The effect of a cooling system was negligible. Radiation from an ArF excimer laser (193 nm) at an average output of 5 W caused only slight thermal changes, when an airstream was used to remove the fragments of photoablative decomposition of the dental tissues. The temperature in the pulp chamber increased by approx. 5 degrees C after 6 min. This result leads to the conclusion that only ArF excimer lasers may be effectively used in the mouth without producing inacceptable thermal effects in the dental pulp.

[Surgical laser in dentistry in 1989]. / Le laser chirurgical en odontologie en 1989.

After many years of microscopie, cellular and molecular studies, the use of Laser rays progressively developed in dentistry. This therapeutical "tool" is now well established in numerous dental fields: cariology, pathology of oral mucosa, periodontics... The Europeans have great advance in this research area and current progress is the clear proof of their work efficiency.

[Preparation of hard tooth structure with Excimer lasers. In vitro study]. / Bearbeitung von Zahnhartgeweben mit einem Excimer-Laser. Eine In-vitro-Studie.

The present study will show, that caries removal and conditioning of tooth surfaces by an (ArF)*-Excimer-Laser is an alternative to conventional preparation methods without thermal and mechanical irritations. This promises caries removal without pain to the patient. The photoablative process leads to retentive surfaces of the treated cavities. These findings promise good results in adhesive techniques. In vitro studies show, that photoablation of dental tissue is effective enough to make clinical usage possible.

[Preparation of hard tooth structure with Excimer lasers]. / Bearbeitung von Zahnartsubstanzoberflächen mit einem 193 nm-ArF-Excimer-Laser.

In this study the possible application of photoablation with an Excimer UV laser for the creation of retentive surfaces was studied as an alternative to conventional enamel conditioning methods using acids. Surfaces of untreated enamel and of prepared cavities were irradiated with an argon fluoride Excimer laser at a wavelength of 193nm and evaluated in a scanning electron microscope. The bond strength of composites to these surfaces was measured in tear tests. "Laser conditioning" left the surfaces similarly roughened as chemical etching. The variable extension of the laser field allows a sharp delineation of the area to be conditioned. The tear tests with human tooth enamel showed bond strength values corresponding to approx. 75% of those obtained by acid etching techniques. The question if these bonds are durable is the subject of current studies.

Mass spectroscopic analysis of excimer laser ablated material from human corneal tissue.

The clinical feasibility of photorefractive keratectomy depends on the surface structure of the ablated cornea. Two factors that influence the remodeled surface are the homogeneity of the energy distribution and the properties of the laser source (energy and wavelength). Currently, the homogeneity of the beam is difficult to control. The second factor, laser source properties, was the focus of this study. We investigated the effect of laser wavelength and energy by analyzing the reaction products of photoablation. We monitored the fragments produced by UV-laser ablation of human corneas using mass spectroscopy in the range of 0 to 100 atomic mass units. At 248 nm (KrF), average photon energy was 5 mJ/cm2, increased to 90 mJ/cm2 by intervals of 5 mJ/cm2. At 193 nm (ArF), photon energy was increased by the same interval from 5 mJ/cm2 to 80 mJ/cm2. Our experiments showed that there was a fluence threshold of approximately 40 mJ/cm2 at 193 nm (ArF) and 50 mJ/cm2 at 248 nm (KrF). Exceeding this threshold led to sudden increases in the number and relative intensity of fragment peaks in mass spectroscopy. This indicates the onset of multiple-photon processes and effective photochemical breakdown. There was a significant difference between both wavelengths in the distribution of mass peaks, indicating higher ionization power at 193 nm.