Q-switched CTE:YAG (2.69 μm) laser ablation: Basic investigations on soft (corneal) and hard (dental) tissues

Ablative infrared lasers either show poor transmission in optical fibers (Er:YAG: 2.94 μm; ErCr:YSGG: 2.79 μm) or are characterized by potential relevant thermal side effects (Ho:YAG: 2.1 μm). The CTE:YAG laser (Cr,Tm,Er doted YAG) emits radiation at a wavelength of 2.69 μm. Efficiently high optical fiber transmission is accomplished (attenuation: < 8db/m for Low-Hydroxy-Fused-Silica (LHFS): 0.3 ppm). Since the laser can easily be run in the Q-switch mode (pulse duration: 0.5–2.5 μs) thermal side effects of tissue interaction were expected to be low. Laser tissue interaction was studied on soft (porcine and human cornea), as well as on hard (human dental) tissue. Histological and micromorphological examinations were performed by light microscopy and scanning electron microscopy. It was found that ablation rates in corneal tissue increased from 5 to 90 μm/pulse with increasing laser fluences (5.5–20 J/cm²). Collateral thermal damage reached as far as 20 ± 5 μm, and was higher (up to 50 μm) when craters where processed in the contact mode using LHFS-optical fibers. In comparison to soft tissue ablation, hard dental tissue ablation showed very little increase of ablation rate (1–3 μm/pulse) when higher fluences were applied. In dental tissue processing, the ablative effect was accompanied by a luminescence, indicating the presence of plasma. We conclude that the presented CTE:YAG laser can be considered as an effective tool for a variety of laser surgical applications where high power optical fiber delivery is required and where strong thermal side effects are not desired. © 1993 Wiley-Liss, Inc.     

Histologic Effect of a Variable Pulsed Er:YAG Laser

BACKGROUND: Carbon dioxide (CO2) lasers used for laser resurfacing produce significant thermal damage. Short-pulsed Er:YAG lasers provide significant control over depth of ablation with minimal thermal damage. Newer combined short-pulsed/long-pulsed Er:YAG lasers offer the potential for both precise control over depth of ablation and degree of chosen thermal damage. OBJECTIVE: To determine the correlation between the histologic effects of an ablative short-pulsed Er:YAG laser and/or a thermally damaging longer-pulsed Er:YAG laser and the findings chosen on the touch panel of such a machine. METHODS: In situ lasing of abdominoplasty specimens was undertaken. Various depths of ablation and/or thermal effect were chosen on the machine. The tissue was laser irradiated, histologically analyzed, and ablation/thermal depths of damage were analyzed by a blinded dermatopathologist. RESULTS: Postlaser histologic depths of ablation after short-pulsed Er:YAG laser resurfacing correlated well with those chosen on the machine. However, when a longer, thermally damaging Er:YAG laser pulse was chosen, chosen ablative and/or thermal depths of damage showed histologic correlation only for the first pass. With repeated passes, using the variable pulse width, the histologic depth of ablation and residual thermal damage do not match the settings on the machine. CONCLUSION: A dual-mode Er:YAG laser provides the histologic control over depth of ablation seen with all short-pulsed Er:YAG lasers. In addition, the histologic thermal effect desired from CO2 lasers could be observed when such a system is used with longer Er:YAG laser pulses. Good correlation between chosen laser parameters and histologic findings are seen with all chosen levels of short-pulsed Er:YAG laser parameters. Good correlation is seen between the chosen laser parameters and histologic findings after a first pass of either a longer pulsed thermal damaging Er:YAG laser alone or in combination with a shorter pulsed ablative Er:YAG laser. However, subsequent laser passes in these modes showed poor correlation between the chosen laser parameters and histologic effect. Such findings have important implications when such a laser is used clinically.     

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.     

Influence of output energy and pulse repetition rate of the Er:YAG laser on dentin ablation

OBJECTIVE: We sought to improve the efficiency of dentin ablation with the Er:YAG laser by investigating the effects of output energy and pulse repetition rate on ablation. Background Data: The Er:YAG laser is superior to other lasers in ablating dental hard tissues. However, the factors affecting the efficiency of ablation with an Er:YAG laser remain unclear. METHODS: Fifty bovine root dentin plates were irradiated with an Er:YAG laser at an output power of 1.0 W, 1.5 W, or 2.0 W under a water spray while moving the plate at 1 mm/sec. After irradiation, the depth and volume of each ablated site were measured by laser microscopy and the ablated surfaces were examined by scanning electron microscopy. RESULTS: The output power showed a strong positive correlation with the depth and volume of ablation. The output energy had much more pronounced effects on the depth and volume of ablation compared to the pulse repetition rate. The shape of the ablated site varied with the output power, and no cracking or vitrification was observed under the irradiated dentin. The most effective parameters for dentin ablation were an output power of 2.0 W, with an output energy of 80 mJ/pulse at 25 pulses per second (pps) or 100 mJ/pulse at 20 pps. CONCLUSION: These findings suggest that the output energy is the main factor affecting the efficiency of dentin ablation with an Er:YAG laser. We propose that the efficiency of dentin ablation can be improved by choosing an optimal combination of output energy and repetition rate.     

Er:YAG Laser-Assisted Hair Transplantation in Cicatricial Alopecia

BACKGROUND: Autologous hair transplantation and its combination with flap or reduction procedures is a common surgical approach to cover defects in cicatricial alopecias. Due to the poor recipient conditions present in scar tissue, it is crucial to minimize the trauma exerted on implantation holes in order to achieve good transplantation results. OBJECTIVE: We sought to evaluate the "cold"-ablative properties of the Er:YAG laser for the generation of recipient holes in cicatricial alopecia. METHODS: Patients with cicatricial alopecia of diverse etiology were treated with Er:YAG laser-assisted hair transplantation. Mini- or micrografts were inserted into recipient holes ablated with a pulse energy of 900-1200 mJ and a spot size of 1.0-1.6 mm. RESULTS: A fluence of 80-120 J/cm2 and 8-12 pulses gave an almost ideal combination of minimal thermal damage and tissue ablation down to the subcutis. With an apparent mini- and micrograft survival of 95% we achieved good cosmetic results after two to five transplant sessions in all patients. CONCLUSION: The Er:YAG laser is a novel effective tool to ablate recipient holes for autologous hair transplantation in cicatricial alopecia.     

Residual heat deposition in dental enamel during IR laser ablation at 2.79, 2.94, 9.6, and 10.6 microm

BACKGROUND AND OBJECTIVE: The principal factor limiting the rate of laser ablation of dental hard tissue is the risk of excessive heat accumulation in the tooth. Excessive heat deposition or accumulation may result in unacceptable damage to the pulp. The objective of this study was to measure the residual heat deposition during the laser ablation of dental enamel at those IR laser wavelengths well suited for the removal of dental caries. Optimal laser ablation systems minimize the residual heat deposition in the tooth by efficiently transferring the deposited laser energy to kinetic and internal energy of ejected tissue components. STUDY DESIGN/MATERIALS AND METHODS: The residual heat deposition in dental enamel was measured at laser wavelengths of 2.79, 2.94, 9.6, and 10.6 microm and pulse widths of 150 nsec -150 microsec using bovine block "calorimeters." Water droplets were applied to the surface before ablation with 150 microsec Er:YAG laser pulses to determine the influence of an optically thick water layer on reducing heat deposition. RESULTS: The residual heat was at a minimum for fluences well above the ablation threshold where measured values ranged from 25-70% depending on pulse duration and wavelength for the systems investigated. The lowest values of the residual heat were measured for short (< 20 micros) CO(2) laser pulses at 9.6 microm and for Q-switched erbium laser pulses at 2.79 and 2.94 microm. Droplets of water applied to the surface before ablation significantly reduced the residual heat deposition during ablation with 150 microsec Er:YAG laser pulses. CONCLUSIONS: Residual heat deposition can be markedly reduced by using CO(2) laser pulses of less than 20 microsec duration and shorter Q-switched Er:YAG and Er:YSGG laser pulses for enamel ablation.     

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     

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.     

Ablation of polymethylmethacrylate by Ho:YAG,Nd:YAG,and Erb:YAG lasers

Ho:YAG, Nd:YAG, and Erb:YAG laser ablation of Polymethylmethacrylate (PMMA) was investigated under in vitro and simulated clinical conditions. Ablation rates were measured for all lasers and after ablation, macroscopic and microscopic appearance of the ablation site was investigated. The mean ablation rates of the Erb:YAG, Ho:YAG, and Nd:YAG laser increased from 8 μm per pulse at 100 mJ to 44 μm per pulse at 300 mJ from 100 μm per pulse at 200 mJ to 222 μm per pulse at 800 mJ and from 28 μm per pulse at 100 mJ to 189 μm per pulse at 800 mJ, respectively. Macroscopic investigation exhibited melting of bone cement for the Ho:YAG and Nd:YAG lasers and pulse-to-pulse vaporization for the Erb:YAG laser. The width of thermal alteration, however, was comparable for all lasers used. Removal of cement from bone specimens under simulated clinical conditions showed good detachment of cement when the fiber was used parallel; in case of perpendicular use, remainders of cement and carbonization of bone could be observed upon histological investigation. © 1993 Wiley-Liss, Inc.     

Comparison between laser-induced photoemissions and phototransmission of hard tissues using fibre-coupled Nd:YAG and Er3+-doped fibre lasers

During pulsed laser irradiation of dental enamel, laser-induced photoemissions result from the laser-tissue interaction through mechanisms including fluorescence and plasma formation. Fluorescence induced by non-ablative laser light interaction has been used in tissue diagnosis, but the photoemission signal accompanying higher power ablative processes may also be used to provide real-time monitoring of the laser-tissue interaction. The spectral characteristics of the photoemission signals from normal and carious tooth enamel induced by two different pulsed lasers were examined. The radiation sources compared were a high-power extra-long Q-switched Nd:YAG laser operating at a wavelength of 1,066 nm giving pulses (with pulse durations in the range 200-250 μs) in the near infrared and a free-running Er(3+)-doped ZBLAN fibre laser operating at a wavelength near 3 μm with similar pulse durations in the mid-infrared region. The photoemission spectra produced during pulsed laser irradiation of enamel samples were recorded using a high-resolution spectrometer with a CCD array detector that enabled an optical resolution as high as 0.02 nm (FWHM). The spectral and time-dependence of the laser-induced photoemission due to thermal emission and plasma formation were detected during pulsed laser irradiation of hard tissues and were used to distinguish between normal and carious teeth. The use of these effects to distinguish between hard and soft biological tissues during photothermal ablation with a pulsed Nd:YAG laser or an Er fibre laser appears feasible. The real-time spectrally resolved phototransmission spectrum produced during pulsed Nd:YAG laser irradiation of human tooth enamel samples was recorded, with a (normalized) relative transmission coefficient of 1 (100%) for normal teeth and 0.6 (60%) for the carious teeth. The photoemission signal accompanying ablative events may also be used to provide real-time monitoring of the laser-tissue interaction.     

Er:YAG laser ablation of tissue: measurement of ablation rates

The ablation of both soft and hard tissue using the normal-spiking-mode Er:YAG laser has been quantified by measuring the number of pulses needed to perforate a measured thickness of tissue. Bone is readily ablated by 2.94 microns radiation; however, at per pulse fluences greater than 20 J/cm2, plasma formation decreases ablation efficiency. At low fluence, desiccation can prevent efficient ablation of bone. The ablation efficiency for aorta and skin is higher than for bone. The ablation efficiency, 540 micrograms/J, and the ablation depth per pulse, greater than 400 microns, for skin are too high to be readily explained by simple models of ablation and thus provide evidence for a more complex explosive removal process.     

Mid-infrared laser ablation of the cornea: a comparative study.

The ablation thresholds and patterns of collateral damage in cornea produced by Er:YAG (2.94 microns) and Er:YSGG (2.79 microns) lasers were measured. Two different pulse durations, 200 microseconds (normal spiking mode) and 100 ns (Q-switched mode), were used at both wavelengths. In the normal spiking mode, damage zones of 16 +/- 2 microns and 39 +/- 7 microns and ablation thresholds of 250 +/- 20 mJ/cm2 and 420 +/- 35 mJ/cm2 were measured at 2.94 microns and 2.79 microns, respectively. In the Q-switched mode, damage zones of 4 +/- 2 microns and ablation thresholds of 150 +/- 10 mJ/cm2 were found irrespective of the laser used. The similarity between the results using the Er:YAG and Er:YSGG lasers in the Q-switched mode suggest that either laser can be used with equal effectiveness for corneal trephination.     

Transmission of Q-switched erbium:YSGG (λ=2.79 μm) and erbium:YAG (λ=2.94 μm) laser radiation through germanium oxide and sapphire optical fibres at high pulse energies

The erbium:YSGG and erbium:YAG lasers are used for tissue ablation in dermatology, dentistry and ophthalmology. The purpose of this study was to compare germanium oxide and sapphire optical fibres for transmission of sufficient Q-switched erbium laser pulse energies for potential use in both soft and hard tissue ablation applications. Fibre transmission studies were conducted with Q-switched (500 ns) Er:YSGG (=2.79 m) and Er:YAG (=2.94 m) laser pulses delivered at 3 Hz through 1-m-long, 450-m germanium oxide and 425-m sapphire optical fibres. Transmission of free-running (300 s) Er:YSGG and Er:YAG laser pulses was also conducted for comparison. Each set of measurements was carried out on seven different sapphire or germanium fibres, and the data were then averaged. Fibre attenuation of Q-switched Er:YSGG laser energy measured 1.3±0.1 dB/m and 1.0±0.2 dB/m for the germanium and sapphire fibres, respectively. Attenuation of Q-switched Er:YAG laser energy measured 0.9±0.3 dB/m and 0.6±0.2 dB/m, respectively. A maximum Q-switched Er:YSGG pulse energy of 42 mJ (26–30 J/cm²) was transmitted through the fibres. However, fibre tip damage was observed at energies exceeding 25 mJ (n=2). Both germanium oxide and sapphire optical fibres transmitted sufficient Q-switched Er:YSGG and Er:YAG laser radiation for use in both soft and hard tissue ablation. This is the first report of germanium and sapphire fibre optic transmission of Q-switched erbium laser energies of 25–42 mJ per pulse.     

Study of visible and mid-infrared laser ablation mechanism of PMMA and intraocular lenses: experimental and theoretical results

Laser–polymer interactions have attracted extensive attention both for understanding the inherent basic ablation mechanism and for development of tissue simulators in several biomedical laser applications such as in human ophthalmology. Ablation experiments were performed on polymethylmethacrylate used as cornea tissue simulator and PMMA intraocular lenses. The polymer–ablation mechanism was examined with two different wavelengths and pulse durations. The experiments were conducted with Nd:YAG and Er:YAG solid-state lasers, and the ablation rates were simulated by a mathematical model in each case. Furthermore, to investigate the role of tissue hydration during laser ablation, we performed a set of experiments in which Er:YAG laser ablation of hydrophilic acrylic intraocular lenses, with different H₂O and D₂O concentrations, was studied. The hydrophilic acrylic lenses with the higher concentration of H₂O gave the most satisfactory results regarding both the ablation efficiency and the quality of the ablated craters.     

Comparison of Er:YAG and 9.6-microm TE CO(2) lasers for ablation of skull tissue

BACKGROUND AND OBJECTIVE: Craniotomy by using a drill and saw frequently results in fragmentation of the skull plate. Lasers have the potential to remove the skull plate intact, simplifying the reconstructive surgery. STUDY DESIGN/MATERIALS AND METHODS: Transverse-excited CO(2) lasers operating at the peak absorption wavelength of bone (lambda = 9.6 microm) and with pulse durations of 5-8 microsec, approximately the thermal relaxation time in hard tissue, produced high ablation rates and minimal peripheral thermal damage. Both thick (2 mm) and thin (250 microm) bovine skull samples were perforated and the ablation rates calculated. Results were compared with Q-switched and free-running Er:YAG lasers (lambda = 2.94 microm, tau(p) = 0.5 microsec and 300 microsec). RESULTS: The CO(2) laser produced ablation rates of up to 60 and 15 microm per pulse for thin and thick sections, respectively, and perforated thin and thick sections with fluences of less than 1 J/cm(2) and 6 J/cm(2), respectively. There was no discernible thermal damage and no need for water irrigation during ablation. Pulse durations > or =20 microsec resulted in significant tissue charring, which increased with the pulse duration. Although the free-running Er:YAG laser produced ablation rates of up to 100 microm per pulse, fluences of 10 J/cm(2) and 30 J/cm(2) were required to perforate thin and thick samples, respectively, and peripheral thermal damage measured 25-40 microm. CONCLUSIONS: In summary, the novel 5- to 8-microsec pulse length of the TE CO(2) laser is long enough to avoid a marked reduction in the ablation rate due to plasma formation and short enough to avoid peripheral thermal damage through thermal diffusion during the laser pulse. Furthermore, in vivo animal studies with the TE CO(2) laser are warranted for potential clinical application in craniotomy and craniofacial procedures.     

Er:YAG laser osteotomy for removal of impacted teeth: clinical comparison of two techniques

BACKGROUND AND OBJECTIVES: In contrast to many techniques currently employed for osteotomy, like saws, drills or modulated ultrasound, lasers offer non-contact and low-vibration bone cutting. Therefore, this report examines the benefits to laser osteotomy in oral surgery using two different short-pulsed Er:YAG laser systems. MATERIALS AND METHODS: Er:YAG lasers, using either a fiber-optic delivery system and an articulated arm delivery system, were used to remove impacted teeth in 30 patients. In 15 patients an Er:YAG laser utilizing a fiber-optic delivery system was applied for cutting bone, with a pulse energy of 500 mJ, a pulse duration of 250 microseconds and frequency of 12 Hz (energy density 177 J/cm(2)). The other 15 patients were treated with an Er:YAG laser utilizing an articulated arm delivery system, with a pulse energy of 1,000 mJ, a pulse duration of 300 microseconds and a frequency of 12 Hz (energy density 157 J/cm(2)). RESULTS: In all cases the lasers allowed precise bone ablation without any visible, negative, thermal side-effects. Since the laser tip was used in a non-contact mode and could be positioned freely, unrestricted cut geometries were feasible. Adjacent soft tissue structures could be preserved and were not harmed by the laser beam. However, osteotomies were time consuming, especially if teeth had to be separated. The level of water irrigation limited the use of the laser. In 20% of the cases in which the articulated arm delivery laser was used to section teeth, it was necessary to use a conventional dental drill to finish the procedure. CONCLUSION: This bone ablation technique, using short Er:YAG laser pulses and water spray, produced good clinical results without any impairment to wound healing. However, for now, the lack of depth control and the time required to perform the necessary osteotomy limit routine clinical application.     

Quantification of laser-induced cartilage injury by confocal microscopy in an ex vivo model

BACKGROUND: The application of lasers in orthopaedic surgery is increasing. However, some investigators have reported that osteonecrosis may occur after laser meniscectomy. The objective of the present study was to evaluate the effect of laser wavelength and energy on cartilage injury in an ex vivo model. METHODS: Fresh bovine articular cartilage was exposed to either holmium:yttrium-aluminum-garnet (Ho:YAG) or erbium:YAG-laser (Er:YAG) irradiation. Both lasers were operated in a free-running mode and at a pulse-repetition rate of 8 Hz. The effect of laser treatment at several energy levels (Er:YAG at 100 and 150 mJ and Ho:YAG at 500 and 800 mJ) was examined. For each light source and energy level, ten cartilage samples were assessed by conventional histological analysis and by confocal microscopy. Thermal damage was assessed by determining cell viability. RESULTS: The extent of thermal damage demonstrated by confocal microscopy was much greater than that demonstrated by histological analysis. The extent of thermal injury after Ho:YAG-laser irradiation was much greater than that after Er:YAG-laser irradiation, which was associated with almost no damage. In addition, the ablation depth was greater after treatment with the Er:YAG laser than after treatment with the Ho:YAG laser. CONCLUSIONS: In the present study, histological analysis underestimated thermal damage after laser irradiation. In addition, our findings highlighted problems associated with use of high-power settings of Ho:YAG lasers during arthroscopic surgery.     

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.     

Histological and SEM analysis of root cementum following irradiation with Er:YAG and CO2 lasers

Recently, the Er:YAG and CO₂ lasers have been applied in periodontal therapy. However, the characteristics of laser-irradiated root cementum have not been fully analyzed. The aim of this study was to precisely analyze the alterations of root cementum treated with the Er:YAG and the CO₂ lasers, using non-decalcified thin histological sections. Eleven cementum plates were prepared from extracted human teeth. Pulsed Er:YAG laser contact irradiation was performed in a line at 40 mJ/pulse (14.2 J/cm²/pulse) and 25 Hz (1.0 W) under water spray. Continuous CO₂ laser irradiation was performed in non-contact mode at 1.0 W, and ultrasonic instrumentation was performed as a control. The treated samples were subjected to stereomicroscopy, scanning electron microscopy (SEM), light microscopy and SEM energy dispersive X-ray spectroscopy (SEM-EDS). The Er:YAG laser-treated cementum showed minimal alteration with a whitish, slightly ablated surface, whereas CO₂ laser treatment resulted in distinct carbonization. SEM analysis revealed characteristic micro-irregularities of the Er:YAG-lased surface and the melted, resolidified appearance surrounded by major and microcracks of the CO₂-lased surface. Histological analysis revealed minimal thermal alteration and structural degradation of the Er:YAG laser-irradiated cementum with an affected layer of approximately 20-μm thickness, which partially consisted of two distinct affected layers. The CO₂-lased cementum revealed multiple affected layers showing different structures/staining with approximately 140 μm thickness. Er:YAG laser irradiation used with water cooling resulted in minimal cementum ablation and thermal changes with a characteristic microstructure of the superficial layer. In contrast, CO₂ laser irradiation produced severely affected distinct multiple layers accompanied by melting and carbonization.     

Potential applications of the erbium:YAG laser in endourology.

The holmium:YAG laser has become the laser of choice in endourology because of its multiple applications in the fragmentation of kidney stones, incision of strictures, and coagulation of tumors. This paper describes the potential use of a new laser, the erbium:YAG laser, for applications in endourology. Recent studies suggest that the Er:YAG laser may be superior to the Ho:YAG laser for precise ablation of strictures with minimal peripheral thermal damage and for more efficient laser lithotripsy. The Er:YAG laser cuts urethral and ureteral tissues more precisely than does the Ho:YAG laser, leaving a residual peripheral thermal damage zone of 30 +/- 10 microm compared with 290 +/- 30 microm for the Ho:YAG laser. This result may be important in the treatment of strictures, where residual thermal damage may induce scarring and result in stricture recurrence. The Er:YAG laser may represent an alternative to the cold knife and Ho:YAG laser in applications where minimal mechanical and thermal insult to tissue is required.