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Biomedical subjects

R Hibst

Publications and source records attributed to R Hibst.

30 records · Page 2Linked to original sources
PubMed1994

Thermal side effects of fiber-guided XeCl excimer laser drilling of cartilage.

We examined thermal effects during ablation of human joint cartilage using two XeCl excimer lasers with pulse durations of approximately 20 ns and 60 ns. An increase in radiant exposure or repetition rate caused a rise in tissue temperature up to 82 degrees C at a 100-microns distance. With increasing distance from the crater edge, the temperature dropped exponentially. Radiant exposures higher than 1.8 J/cm2 and repetition rates above 20 Hz lead to a formation of hot gaseous products escaping from the laser crater. When osteoarthritic cartilage is irradiated, these gases spread inside the tissue causing a temperature rise of > 50 degrees C at a distance of 1 mm from the crater edge. In the contact mode, we found a linear rise of ablation rate with increasing repetition rate both in air or saline. But ablation rates in saline were only half the rates achieved in air. Both phenomenons can be explained by additional thermal effects of excimer lasers working in the range of higher repetition rates and pulse energies.

Cartilage, Articular↗
PubMed1994

Cutting and skin-ablative properties of pulsed mid-infrared laser surgery.

BACKGROUND: Pulsed mid-infrared lasers allow a precise removal of soft tissues with only minimal thermal damage. OBJECTIVE: To study the potential dermatosurgical usefulness of currently available systems at different wavelengths (2010-nm Thulium:YAG laser, 2100-nm Holmium:YAG laser, 2790-nm Erbium:YSGG laser, and 2940-nm Erbium:YAG laser) in vivo on pig skin. METHODS: Immediate effects and wound healing of superficial laser-abrasions and incisions were compared with those of identical control lesions produced by dermabrasion, scalpel incisions, or laser surgery performed by a 1060-nm Nd:YAG and a 1060-nm CO2 laser (continuous and superpulsed mode). RESULTS: Best efficiency and least thermal injury was found for the pulsed Erbium:YAG laser, leading to ablative and incisional lesions comparable to those obtained by dermabrasion or superficial scalpel incisions, respectively. CONCLUSION: In contrast to other mid-infrared lasers tested, the 2940-nm Erbium:YAG laser thus provides a potential instrument for future applications in skin surgery, especially when aiming at a careful ablative removal of delicate superficial lesions with maximum sparing of adjacent tissue structures. However, in the purely incisional application mode pulsed mid-infrared lasers, though of potential usefulness in microsurgical indications (eg, surgery of the cornea), do not offer a suggestive alternative to simple scalpel surgery of the skin.

Aluminum Silicates↗
PubMed1993

[Comparative study of ab-externo sclerostomy with the excimer and Er:YAG laser].

The specific ablative effect of pulsed 308 nm XeCl-excimer laser radiation (4 mJ 80 Hz) on the tissue has proved its worth in clinical use in glaucoma patients. However, the cytotoxic and mutagenic photochemical reactions induced by intraocular ultraviolet irradiation could theoretically be cataractogenic and retinotoxic. Unlike the excimer laser technique, ab externo sclerostomy with the Er:YAG laser (2940 nm/11 mJ, 7 Hz) excludes these risks. Histological and scanning electron microscope analysis of pig eyes showed thin, and smoothly limited zones of necrosis and only minimal irritation of the adjacent tissue and a slightly wavy surface. A newly developed handpiece for the Er:YAG laser enables energy transport via zirconium fluoride fiber and coupling to a quartz fiber tip with a core diameter of 320 microns. Er:YAG laser sclerostomy has so far been performed on 16 eyes in which the average preoperative IOP was 29 mmHg. The procedure took only a few minutes and the patients reported feeling no pain although retrobulbar anesthesia was not induced. The postoperative average IOP was less than 20 mmHg after 6 weeks and for the rest of a maximum observation period of 12 weeks. Reoperation was necessary in 2 cases. Er:YAG laser ab externo sclerostomy could be another alternative for the operative therapy of glaucoma.

Aged↗
PubMed1992

Mechanical effects of erbium:YAG laser bone ablation.

When intending to use pulsed erbium:YAG laser radiation for the ablation of small bones, e.g., the ossicular chain or footplate, not only temperature and thermal damage, but also mechanical side effects become important. In studies on desiccated bone the total recoil momentum caused by laser ablation was measured using a sensitive pendulum. The momentum depends linearly on the radiant energy of the laser pulse with a slope of 10(-4) kg m s-1/J. The temporal course of the recoil force during ablation observed by means of a piezoelectric transducer is nearly proportional to the laser pulse intensity. By evaluating recoil momentum and mass loss data, the average initial velocity of the plume was calculated to be 230 to 280 m s-1. The kinetic energy is approximately 1% of the input energy. The measurements support to the hypothesis of a thermally induced explosive process.

Animals↗
PubMed1991

[Pulp reactions during Erbium YAG laser irradiation of hard tooth structure].

The Er:YAG Laser is an effective tool for removing hard tooth structure without causing any measurable degree of thermal damage. In view of the fact that the process of ablation basically depends on thermal effects, pulpal microcirculation was studied by Laser-Doppler flowmetry during Er:YAG Laser irradiation. Rat incisors were used to demonstrate that pulp damage can be avoided if correct laser parameters are used for preparing enamel and dentin.

Animals↗
PubMed1990

Pulsed 2.94-microns erbium-YAG laser skin ablation--experimental results and first clinical application.

In the present study we compared skin-ablative effects produced by 2.94-microns pulsed erbium-YAG radiation on pig skin with those of the pulsed 308-nm UV excimer laser, continuous-wave CO2 laser, electrocautery and cold-knife surgery. Pulsed 2.94-microns radiation led to clean ablation craters and precise cuts with only minimal adjacent tissue damage followed by excellent healing without apparent scarring. These experimental results are consistent with those obtained from first clinical applications in the treatment of epidermal naevi and tattoos. However, since coagulation was insufficient to prevent bleeding and because of low repetition rates provided, the Er-YAG lasers currently available seem as yet of limited value for effective removal of deeper or larger lesions.

Adult↗
PubMed1989

Pulsed Er:YAG- and 308 nm UV-excimer laser: an in vitro and in vivo study of skin-ablative effects.

Using a pulsed XeCl excimer laser (308 nm) and a pulsed Er:YAG laser (2,940 nm), we investigated skin ablation as a function of pulse number, radiant energy, and repetition rate. In vitro analysis of lesions performed in freshly excised human skin were consistent with in vivo results obtained from experiments on pig skin. Pulsed 308 nm laser radiation caused considerable nonspecific thermal tissue injury followed by an inflammatory reaction and impaired healing of lesions in vivo. These findings were especially pronounced with higher repetition rates, which would be required for efficient destruction of larger lesions. On the other hand, the 2.94 microns Er:YAG laser radiation produced clean and precise lesions with only minimal adjacent injury. In vivo skin ablation caused intraoperative bleeding with deeper penetration. The Er:YAG laser offers a promising surgical tool for careful removal of superficial epidermal lesions, if higher repetition rates, and an appropriate laser beam delivery system are available for clinical use.

Animals↗
PubMed1989

Experimental studies of the application of the Er:YAG laser on dental hard substances: I. Measurement of the ablation rate.

Up to now lasers have not achieved any practical importance in dentistry for drilling teeth because of considerable damage to the surrounding tissue. We studied the application of pulsed 2.94 microns Er:YAG laser radiation in vitro on extracted teeth to remove enamel, dentin, and carious lesions. The depth and diameter of laser-drilled holes were measured as a function of pulse number and radiant exposure. The tissue removal is very effective both for dentin and enamel.

Dental Caries↗
PubMed1989

Experimental studies of the application of the Er:YAG laser on dental hard substances: II. Light microscopic and SEM investigations.

Many studies have been undertaken trying to use various laser systems as optical drills on dental enamel and dentin, but the high radiant exposure needed and subsequent high temperature rises lead to fractures of the hard substances and possible damages to the pulp. Compared to the other laser systems, the use of the Er:Yag laser has given encouraging results. Optical and scanning electron microscopy showed only minimal if any damage of the surrounding tissue.

Carbon Dioxide↗
PubMed1989

[Ablative effect of an Er:YAG laser on enamel and dentin].

The effectiveness of a pulsed infrared Er:YAG laser beam at a wavelength of 2.94 micron in removing hard tooth structure was studied. The defects produced by the laser beam were evaluated quantitatively and morphologically as a function of energy and pulse frequency. The use of this instrument allows the efficient removal of enamel and dentin while sparing the surrounding tissues.

Dental Cavity Preparation↗
PubMedDate not supplied

Silicon cast method for quantification of photoablation.

BACKGROUND: Topometry and measurement of photoablation patterns are key questions for keratorefractive photoablation. Ablation rates have been determined previously by either tissue perforation or by micrometry performed on histologic sections. METHODS: A three-dimensional cast of cornea after irradiation was made by using a two-component silicon gel that polymerizes within minutes, thus preserving the corneal topography immediately after photoablation. Polymerization is athermal and nontoxic. The resulting silicon blocks were cut perpendicularly to the anterior surface and measured by calibrated light microscopy. RESULTS: The silicon surface is extremely smooth and the accuracy of the cast is better than 0.25 micron. Reproducibility and long-term stability were demonstrated for casts of photoablated polymethylmethacrylate. Thus, ablation rates and profile, volumetry, and topometry can be determined following laser ablation. The method has been applied for 193-nanometer excimer laser in vitro irradiation of the human cornea. Ablation rates in Bowman's layer and stroma for various radiant energies and distinct pulse numbers were found to be in agreement with published data, and an incubation effect for the first laser pulses could be demonstrated. CONCLUSIONS: The method is nondestructive, accurate, inexpensive, practical, and reduces requirements for laboratory animals.

Animals↗