Bone ablation with Er:YAG and CO2 laser: study of thermal and acoustic effects.

A pulsed Er:YAG laser at 2.94 microns and a superpulsed CO2 laser at 10.6 microns are used to investigate bone ablation applications in otolaryngology. Quantitative measurements of mass removal and the ablation depth of cat skull bone and rat femur are presented with the Er:YAG laser at fluences of 9-117 J/cm2. Histological results show that the minimal thermal injury zone from the edge of the lesion is 5-10 microns. Comparison of the photoacoustic and thermal effects during the ablation process indicates that the temperature rise from the 10.6-microns light was higher than that from the 2.94-microns light but that the photoacoustic wave amplitude produced with the Er:YAG laser was higher than that with the CO2 laser. The fluence used for the efficient ablation of bone tissues produces a photoacoustic wave ranging from 100 to 120 dB. The ear can tolerate this level for a short time period. Results of this study suggest that the Er:YAG laser can be an important surgical tool in otolaryngology.     

The ablation threshold of Er:YAG and Er:YSGG laser radiation in dental enamel

. The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the ablation threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the ablation threshold of an Er:YAG laser (λ=2.94 μm) and an Er:YSGG laser (λ=2.79 μm) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2–40 J/cm². The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of τ_P(FWHM)≈150 μs and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the ablation threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9–11 J/cm². The range for the Er:YSGG laser was slightly higher at 10–14 J/cm². Paper received 15 May 2001; accepted after revision 14 January 2002. Correspondence to: Dr Christian Apel, Department of Conservative Dentistry, Periodontology and Preventive Dentistry, University of Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany. Tel.: +49 241 8089088; Fax: +49 241 8888468; e-mail: capel@post.klinikum.rwth-aachen.de     

Er:YAG laser ablation of cerebellar and cerebral tissue

. With the availability of suitable fibres, the Er:YAG laser has become an indispensable tool for invasive neurosurgical applications as a source of precise ablation. The aim of this study was to investigate the ablative effects of the Er:YAG laser on brain tissue. The response of neuronal tissue to 2.94 μm Er:YAG laser irradiation was investigated on excised rat brain specimens. Ablation craters were created in cerebral and cerebellar tissues using 0.3, 0.5 and 1.0 J single pulses of 150 μs duration. The corresponding average irradiances were 37.7 J/cm², 62.9 J/cm² and 125.8 J/cm², respectively. Craters were checked qualitatively, crater dimensions were measured and compared, and volume of ablated tissue was estimated. Laser-induced crater dimensions were found to be significantly different at different energy levels applied. Moreover, dimensions of craters on cerebral and cerebellar tissues were significantly different in terms of dimensions. We observed that with the Er:YAG laser ablation craters were created with practically no thermal damage to adjacent tissues. The differences observed in the response of cerebral and cerebellar cortical tissues were dependent on the anatomical and chemical differences. Paper received 3 August 1999; accepted after revision 26 June 2000.     

Cavity preparation using a superpulsed 9.6-microm CO2 laser--a histological investigation

BACKGROUND AND OBJECTIVES: The superpulsed 9.6-microm CO(2) laser is an effective laser for ablating dental tissues and decay. This histological study compares laser class V preparations with conventional treatment to evaluate the resulting formation at the cavity walls. STUDY DESIGN/MATERIALS AND METHODS: Four class V preparations (one made with a diamond drill and three with the CO(2) laser (9.6 microm, 60 microseconds pulse width, 40 mJ pulse energy, 100 Hz, integrated scanner system, water cooling) were performed on ten extracted teeth. The cavities were filled with a composite resin partly including enamel and dentine conditioning. RESULTS: After laser preparation, no cracks or signs of carbonisation were detected. The results were comparable to those attained with conventional treatment. Following cavity filling without prior conditioning, gaps were noted at the cavosurface indicating a lack of adhesion. Dentinal bonding decreased gap formation significantly. CONCLUSION: The 9.6-microm CO(2) laser is an effective tool for cavity preparation.     

Urinary calculus fragmentation during Ho: YAG and Er:YAG lithotripsy

BACKGROUND AND OBJECTIVES: We tested Ho:YAG and Er:YAG laser ablation of human urinary calculi to determine if Er:YAG is a more efficient lithotripsy device. STUDY DESIGN/MATERIALS AND METHODS: Ablation efficiency of Ho:YAG and Er:YAG lasers was tested at varying energy settings, ranging from the damage threshold to clinical energy setting associated with Ho:YAG laser. Stones of known composition (calcium oxalate monohydrate (COM), cystine, and uric acid (UA)) were irradiated. Crater width, depth, and ablation volumes were determined using an optical coherence tomography (OCT). RESULTS: For all stones and energy settings, the Er:YAG laser produced deeper craters and larger ablation volumes than Ho:YAG laser. The Ho:YAG laser created wider craters during the multiple pulse process and the shape of craters was irregular. CONCLUSIONS: The Er:YAG laser is more efficient than the Ho:YAG laser for lithotripsy. The deeper craters produced by the Er:YAG laser is attributed to the high absorption of energy at its wavelength.     

Histologic analysis of the effect on dental pulp of a 9.6-microm CO(2) laser

BACKGROUND AND OBJECTIVE: Both patients and dentists would like a replacement of the dental drill. During the last decade, lasers have been investigated as a possible replacement. For lasers to be accepted, studies must show that their effect on the dental pulpal tissues is equal to or less noxious than those effects caused by the dental handpiece (drill). STUDY DESIGN/MATERIALS AND METHODS: In this study, two laser systems were used; the first was a breadboard CO(2) laser and the second a prototype clinical CO(2) laser system both emitted 60-micros-long pulses of 9.6-microm radiation. On the delivery system of both lasers, a scanner moved the focussed beam in a circular pattern and a water spray system served to cool the ablation site. Both lasers were used to create holes of similar dimensions in canine teeth. The treated teeth were then restored and harvested at either 4 days or 4 weeks. The teeth were decalcified, sectioned, and stained for examination via light microscopy. RESULTS: The histologic examination revealed normal pulpal tissues in the canine teeth treated with both CO(2) lasers. Some histologic sections showed an increase in the predentin layer, 28 days after laser treatment. While many histologic sections showed normal pulpal architecture following handpiece treatment, some sections showed total disruption of the normal pulpal histology. CONCLUSIONS: Histologic evaluation revealed that the lasers produced no noticeable damage to the dental pulpal tissue and appear to be a safe method for removing dental hard tissues. From this study, it appears that 9.6 microm CO(2) laser does not cause damage to the dental pulpal tissues in dogs.     

Urologic dosimetry studies with the Nd:YAG and CO2 lasers: bladder and kidney

Dose recommendations for the use of the Nd:YAG and CO2 lasers have been accepted with little laboratory analysis. We have examined both endoscopic and open applications in the bladder and open applications on the kidney with the lasers over a variety of power and pulse duration settings. In addition, we have studied the effect of varying the temperature of the tissue and irrigation solution on the depth of penetration. We found that with the Nd:YAG laser, the maximum depth of penetration in our animal model was only 2.62 mm in the bladder. This occurred during an endoscopic treatment with settings of 50 W at 4 seconds with irrigation solution of 25 degrees C. The depth of penetration using current recommendations of 40 W for 2 seconds was less than 1 mm at all temperatures. Room temperature irrigation solution may be the ideal compromise, but higher-power long-pulse durations or repeated treatments to the same area may be necessary to achieve penetrations of 3-5 mm. In open applications on bladder and kidney, the maximum depth of penetration in our animal model was 2.75 mm, which was found during a treatment with settings of 60 W at 4 seconds with the kidney parenchyma at 25 degrees C. Using the CO2 laser on open applications of bladder strips, we obtained a maximum depth of penetration of 1.75 mm at 30 W of power for 1/2 second at 85 degrees C tissue temperature. Unfortunately, penetration by the CO2 laser is accompanied by vaporization of tissue, leaving a large crater. Minimal injury exists beyond this area. In the kidney, we obtained a maximum depth of penetration of 1.75 mm at 30 W of power at 25 degrees C and 20 W of power at 2 degrees C each for 1/2 second.     

Ablation of composite resins using Er:YAG laser--comparison with enamel and dentin

OBJECTIVES: The purpose of this work is to investigate comparative ablation rate between composite resins and dental hard tissues (enamel and dentin) after Er:YAG laser irradiation to verify possible development of an ultra-conservative dentistry to with minimum effect for the teeth tissue. METHODS: We have used 11 extracted or exfoliated primary anterior and posterior teeth and six extracted permanent molar teeth. Three different types of composite resin were chosen (microfiller, hybrid, and condensable) in terms of chemical and structural composition. Composite tablets and the teeth were irradiated with a Er:YAG laser at different laser beam energy level per pulse (100, 200, 300, and 400 mJ). Diameter and depth of each resulted microcavity were measured and the material removed volumes were calculated. The resulted values were plotted and fitted to allow a comparative observation of the material removed as a function of energy level per pulse. RESULTS: While the idea of ultra-conservative dentistry seems to apply well for enamel of primary and permanent teeth, at the present stage it does not apply well for primary or permanent dentin. For dentin, the composition and content of water makes the Er:YAG laser ablation equal or superior in rate compared with the three used resins. SIGNIFICANCE: This work presents of a comparative study of Er:YAG laser ablation, allowing to analyze the possible selective ablation between composite resin placed and cured and dental hard tissues, with the goal to propose a new clinical technique: differential ablation for composite resin restorations using Er:YAG laser.     

Er:YAG laser ablation of enamel and dentin of human teeth: determination of ablation rates at various fluences and pulse repetition rates.

A pulsed Er:YAG laser (2.94 microns) was used to determine ablation depths per pulse of laser energy at 2 Hz and 5 Hz in human teeth cross sections of enamel and dentin. Ablation depths per pulse at 2 Hz in enamel of intact human teeth were measured and compared to ablation depths per pulse determined in enamel cross sections at 2 Hz. Close correlation was observed for ablation depths per pulse of laser energy between teeth cross sections and intact teeth for enamel. Photographs of lased holes at 2 Hz and 5 Hz indicated minimal thermal effects in enamel at fluences below 80 J/cm2. Minimal thermal effects in dentin were noted below 74 J/cm2. Scanning Electron Microscopy (SEM) pictures of lased dentin showed an irregular serrated surface. Results of this study suggest that the Er:YAG laser can effectively ablate enamel and dentin with minimal thermal effects at 2 Hz and 5 Hz.     

Cytologic and DNA-cytometric follow-up of oral leukoplakia after CO2- and Er:YAG-laser assisted ablation: a pilot study

BACKGROUND AND OBJECTIVES: The aim of the present pilot study was to determine therapeutic responses to Er:YAG- and CO(2)-laser ablation in patients with oral leukoplakia as evaluated by means of exfoliative cytology (EC) and DNA-image-cytometry (DNA-I). STUDY DESIGN/MATERIALS AND METHODS: Ten patients exhibiting a total of 16 lesions affecting a variety of intraoral sites were randomly treated with either (1) an Er:YAG laser (300 mJ/pulse, 10 Hz, defocused mode) (ERL), or (2) an CO(2) laser (4-6 W, 20-50 Hz, focused mode) (CO). Brush (B) and incisional (I) biopsies were obtained from the respective lesions immediately before treatment (B, I) as well as 24-96 weeks postoperatively (B). In cases, in which EC revealed suspicious cells, nuclear DNA-contents were measured using a TV image analysis system. RESULTS: Both treatment approaches resulted in a complete (C) or partial (P) remission of all investigated lesions. In particular, ERL exhibited C(3), P(5), and CO C(5), P(3). However, in the CO group, two of eight lesions showed a recurrence 32-48 weeks following treatment. Among all investigated lesions, both histological and EC/DNA-I diagnosis revealed no sign of malignancy or dysplasia before or following laser assisted ablation. CONCLUSIONS: Within the limits of the present study, it may be concluded that both treatment approaches seem to have limitations to achieve predictable eradication of oral leukoplakia.     

Analysis of hyperpigmentation and hypopigmentation after Er:YAG laser skin resurfacing

BACKGROUND AND OBJECTIVES: Pigmentary disorders--such as hyperpigmentation and hypopigmentation, are devastating complications of erbium:yttrium-aluminum-garnet (Er:YAG) laser resurfacing. This study was undertaken to assess the clinical and histopathologic features of hyperpigmentation and hypopigmentation following Er:YAG laser resurfacing, especially in darker skin. STUDY DESIGN/MATERIALS AND METHODS: One hundred and ninety patients (skin phototypes III and above), treated with Er:YAG lasers--short-pulsed and modulated (variable-pulsed and dual-mode) Er:YAG lasers--for skin resurfacing were recruited. The clinical features of hyperpigmentation and hypopigmentation were evaluated retrospectively using medical charts and serial photographs. For histopathologic examinations, skin biopsies were performed in three patients at hyperpigmentation sites and in four patients at hypopigmentation sites. RESULTS: Hyperpigmentation was observed in 38.4% of the patients. Mean onset and duration were 3.5 and 7.2 weeks, and then it has faded away within 16 weeks in 93.2% of cases. Hypopigmentation was observed in 13.7% of the patients; its mean onset was 2 months after treatment, and it faded within 1 year in 85% of cases. The incidences and mean durations of these side effects were more intense and longer in patients treated with short-pulsed, variable-pulsed, and dual-mode Er:YAG lasers, in increasing order. In terms of histopathologic examinations, melanin amounts in the epidermal basal layer were observed to vary. CONCLUSIONS: Hyperpigmentation and hypopigmentation are frequent complications of Er:YAG laser resurfacing. Long pulse duration-induced thermal damage seems to be the most important factor in terms of the induction of pigmentary disorders.     

Effects of Er:YAG and Nd:YAG laser irradiation on radicular dentine permeability using different irrigating solutions

BACKGROUND AND OBJECTIVES: To evaluate the effect of Er:YAG and Nd:YAG laser on radicular dentine permeability when using distilled and deionized water and 1% NaClO as irrigating solutions. STUDY DESIGN/MATERIALS AND METHODS: Thirty human maxillary canines were divided randomly into six groups. The root canals were instrumented with K files and the step-back technique. Group I, irrigation with distilled and deionized water; Group II, irrigation with 1% NaClO; Group III, irrigation with distilled and deionized water and Er:YAG laser application (140 mJ input, 61 mJ output 15 Hz, 300 pulses, and 42 J); Group IV, irrigation with 1% NaClO and Er:YAG laser application (same parameters as Group III); Group V, irrigation with distilled and deionized water and Nd:YAG laser application (150 mJ, 15 Hz, 2,25 W); Group VI, irrigation with 1% NaClO and Nd:YAG laser application (same parameters as Group V). During laser application the teeth were always filled with the irrigating solution. The tip was withdrawn gently in helicoidal movement from the apex to the cervical portion. The teeth were processed for histochemical evaluation. RESULTS: The Tukey test showed that the cervical and middle thirds were statistically similar (P > 0.05) and significantly greater than the apical third (P < 0.05). The Scheffé test showed significantly greater dentine permeability in root canals in which water and Er:YAG laser were used and were significantly different from the other treatments (P < 0.05). CONCLUSIONS: The use of distilled and deionized water and Er:YAG laser showed the greater increase of dentine permeability. The use of 1% NaClO with Nd:YAG laser, distilled, and deionized water with Nd:YAG laser and the use of water increased dentine permeability less than the other groups. The use of 1% NaClO with and without Er:YAG laser application were positioned intermediately among the treatments.     

Effects of Er:YAG laser and Nd:YAG laser treatment on the root canal dentin of human teeth: a SEM study

The objective of the study was to observe the morphological changes on root canal dentin after Er:YAG laser and Nd:YAG laser treatment. Twenty-one teeth biomechanically prepared were divided into three groups with seven teeth of each. Group A was unlased as a control. In group B, Er:YAG laser and in group C, Nd:YAG laser was applied to the root canal dentin. The roots were split longitudinally and examined using a scanning electron microscopy for the evaluation of debris, smear layer, and recrystallization. There was no statistically significant difference between the groups. This study indicates that laser beam is not effective in removing debris and smear layer.     

Observations on the simultaneous use of CO2 and Nd:YAG lasers in neurosurgery

Seven cases of cerebral tumors (four deep-seated sovratentorial gliomas located in motor area, occipital region, parietal region and frontal region; one deep-seated cystic cerebellar spongioblastoma; one sphenoidal wing meningioma, and one spinal cord intradural tumor) were simultaneously irradiated in the same area with two sources (CO₂ and Nd:YAG). Using CO₂ and Nd:YAG simultaneously, a larger and deeper lesion was obtained. The main bulk was irradiated with two sources free hand. The implant with the two sources was connected to the operating microscope. The rise in temperature, 3 mm from the border of the lesion, was similar to that obtained with Nd:YAG alone. Hemostasis was not impaired. In comparison with the single sources, this method allows a more rapid demolition of the tumor without additional damage to the surrounding tissues.     

Influence of water-layer thickness on Er:YAG laser ablation of enamel of bovine anterior teeth

Different ideas have been presented to describe the mechanism of augmented laser ablation of dental enamel with different shapes by adding water to the working environment. In this study, the influence of water–laser interaction on the surface of enamel during ablation was investigated at a wavelength of 2.94 μm with different distances between the laser tip and the enamel surface. A motion-control system was used to produce linear incisions uniformly on flat enamel surfaces of bovine anterior teeth, with free-running Er:YAG laser very short pulses (pulse length = 90–120 μs, repetition rate = 10 pulses per second). Four different output energies (100, 200, 300 and 400 mJ) were radiated on samples under distilled water from different distances (0.5, 0.75, 1, 1.25, 1.75 and 2.00 mm). The tooth slices were prepared with a cutting machine, and the surfaces of the ablated areas were measured with software under a light microscope. The average and standard deviation of all cut areas in different groups were reported. There was no significant difference when using a different pulse ablation speed (cm³/J) and a water-layer thickness between the tip and enamel surface of 0.5–1.25 mm with energy densities of 30–60 J/cm² (200–400 mJ). However, using an output energy of 15 J/cm² (100 mJ) and a thicker water layer than 1 mm, a linear ablation did not take place. This information led to a clearer view of the efficiency of Er:YAG laser in the conditions of this study. There are several hypotheses which describe a hydrokinetic effect of Er,Cr:YSGG. These basic studies could guide us to have a correct attitude regarding hydro-mechanical effects of water, although the wavelength of 2.78 μm has a better absorption in hydroxyl branch of water molecules. Therefore, our results do not directly interrupt with the series of investigations done with Er,Cr:YSGG. Water propagation and channel formation under water are investigated during the ablation of tooth enamel with the Er:YAG laser from different distances. Comparing the results of this study with the same research done with water/air spray concludes that the bubble formation and channel propagation in water with this wavelength leads to a more symmetric (linear) ablation process with cavity-preparation-recommended parameters.     

Holmium:YAG laser ablation of vascular tissue

The ablation of atherosclerotic lesions without collateral thermal or shock wave damage is thought to be a key element for successful laser angioplasty. This study evaluated the effectiveness of pulsed holmium:YAG laser (2.1 microns wavelength) for this application. Fresh normal tissue (n = 139) and arteriosclerotic canine arteries (n = 21) as well as formalin-preserved normal canine (n = 31) and atherosclerotic human arteries (n = 177) were irradiated under saline via a 600 microns diameter fiber placed perpendicular to the intimal surface with 0-10 gm of force. The laser was operated in the free running mode (FRM; 250 microseconds pulsewidth, 5 Hz, 30-7,100 mJ/mm2) and in the Q-switched mode (QSM; 200 nsec pulsewidth, 6 Hz, 30-1,100 mJ/mm2). Following the experiments, the samples were prepared for histologic and morphometric analysis. Ablation thresholds in the FRM were 60 and 180 mJ/mm2 in fresh and preserved canine tissue, respectively. Ablation thresholds in the QSM for fresh and preserved canine tissues were 75 and 180 mJ/mm2, respectively. Thresholds for human atherosclerotic tissue were dependent on the amount of calcification. In the QSM and FRM, there were no samples that could not be penetrated at 1,100 mJ/mm2 and above. Histologic examination of the FRM samples revealed confined columns of tissue ablation, with approximately 55-250 microns and 70-140 microns zones of thermal effect being apparent in the fresh and formalin-preserved samples, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)