Peripheral Thermal Damage Research Articles

Use of lasers in gastrointestinal endoscopy: a review of the literature

Lasers emit highly directional light with consistent wavelengths, and recent studies have demonstrated their successful applications in gastrointestinal endoscopic therapy. Although argon plasma coagulators (APC) became the preferred treatment option due to improved safety profile and lower costs, advancements in laser and optic fiber manufacturing have reignited interest in laser treatment. Different laser wavelengths have distinct features and applications based on their tissue absorption coefficient. Lasers with shorter wavelengths are effectively absorbed by hemoglobin, resulting in a good coagulation effect. Near-infrared lasers have ability to ablate solid tumors, while far-infrared lasers can make precise mucosal incisions without causing peripheral thermal damage. Lasers have proven to be highly applicable to endoscopy devices such as endoscopes, endoscopic ultrasound (EUS), double-balloon enteroscopes (DBE), and endoscopic retrograde cholangiopancreatography (ERCP), making them a potent tool to enhance the effectiveness of endoscopic treatments with minimal adverse events. This review aims to help readers understand the applications and effectiveness of lasers in gastrointestinal endoscopy, with the potential to promote the development and application of laser technology in the medical field.

A new sealed RF-excited CO2 laser for enamel ablation operating at 9.4-μm with a pulse duration of 26-μs.

Several studies over the past 20 years have shown that carbon dioxide lasers operating at wavelengths between 9.3 and 9.6-μm with pulse durations near 20-μs are ideal for hard tissue ablation. Those wavelengths are coincident with the peak absorption of the mineral phase. The pulse duration is close to the thermal relaxation time of the deposited energy of a few microseconds which is short enough to minimize peripheral thermal damage and long enough to minimize plasma shielding effects to allow efficient ablation at practical rates. The desired pulse duration near 20-μs has been difficult to achieve since it is too long for transverse excited atmospheric pressure (TEA) lasers and too short for radio-frequency (RF) excited lasers for efficient operation. Recently, Coherent Inc. (Santa Clara, CA) developed the Diamond J5-V laser for microvia drilling which can produce laser pulses greater than 100-mJ in energy at 9.4-μm with a pulse duration of 26-μs and it can achieve pulse repetition rates of 3 KHz. We report the first results using this laser to ablate dental enamel. Efficient ablation of dental enamel is possible at rates exceeding 50-μm per pulse. This laser is ideally suited for the selective ablation of carious lesions.

Pathomorphological distinction between Er:YAG and diode lasers on the excisional biopsy of the oral mucosa

Background - In oral pathology, laser devices can provide important advantages, especially in the treatment of certain lesions. However, there is controversy about the use of some wavelengths in the analysis of suspected dysplastic or neoplastic lesions, raising doubt about the laser's suitability for use in biopsy procedures. The present pilot study evaluates the pathomorphological characteristics and suitability of Er:YAG and diode lasers for performing excisional biopsies in the oral mucosa with special emphasis on the extent of the thermal damage zone created. Material and Methods - 10 patients were randomly assigned to one diode or one Er:YAG laser groups. The Er:YAG laser(2940nm) was used in a pulsed wave mode 200mJ/35Hz with a power of 7 W. Power settings for the diode laser(810 nm) were 3 W in a pulsed mode. The thermal damage zone of the two lasers and intraoperative and postoperative complications were assessed and compared.All biopsy specimens were evaluated by optical microscopy by threeblinded pathologists. After establishing the pathomorphological diagnosis of the lesion assessed, the pathologists measured the maximal width of the peripheral thermal damage zone in the specimen in μm and classified it using appropriate index. Results - The peripheral thermal damage zone on the borders of the excisional biopsies was significantly smaller with the Er:YAG laser compared to the diode laser regarding values in μm or pathomorphological index scores. No postoperative complications occurred in any of the two groups. Conclusions - The Er:YAG laser seems to be appropriate for excisional biopsies of benign oral mucosal lesions. The Er:YAG laser offers clear advantages in terms of smaller thermal damage zones over the diode laser. Although in some samples thermal damage was minimally visible, in all samples histological evaluation was clearly possible. The study demonstrated that the Er:YAG laser can be safely used in oral biopsy investigations while ensuring a successful histological evaluation, which is fundamental to correct clinical management.

Histological in vitro evaluation of the effects of Er:YAG laser on oral soft tissues

In oral pathology, laser devices can provide important advantages, especially in the treatment of certain lesions. However, there is controversy about the use of some wavelengths in the analysis of suspected dysplastic or neoplastic lesions, raising doubt about the laser's suitability for use in biopsy procedures. In recent studies, the KTP and diode lasers have been used in biopsy procedures without histological artefacts. The aim of this in vitro study was to evaluate the exact extent of peripheral thermal damage to oral soft tissues caused by an Er:YAG laser (λ 2,940 nm) without water cooling. The study was performed on five swine cadaver tongues. Nine samples from each tongue were taken by the same operator using the Er:YAG laser with increasing energies (from 60 to 150 mJ) and fluencies (from 21 to 53 J/cm(2)). In addition to the laser samples, a specimen obtained using a scalpel was used as control. The samples were placed in 10% formalin solution and were examined by optical microscopy by two blinded pathologists who assigned a thermal damage score (from 0 to 3) to each sample. The Er:YAG laser produced less damage at 80 and 100 mJ and 28 and 35 J/cm(2) (intermediate parameters). Although in some samples thermal damage was minimally visible, in all samples histological evaluation was clearly possible. The study demonstrated that the Er:YAG laser can be safely used in oral biopsy investigations while ensuring a successful histological evaluation, which is fundamental to correct clinical management.

High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

CO(2) lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO(2) laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO(2) lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation.

Effects of KTP laser on oral soft tissues. An in vitro study

A biopsy is a surgical procedure performed to establish a clear diagnosis of a lesion in order to clarify a clinical diagnostic suspicion. During a biopsy procedure it is fundamental to maintain safe and readable cut margins in order to permit histological visualization of possible marginal infiltrations or malignant transformation of a lesion. The aim of this study was to evaluate the histological peripheral damage caused by application of a KTP (potassium titanium phosphate) laser during oral soft tissue biopsy procedures. A KTP laser (lambda 532 nm) at different power settings and fluences was used to obtain 45 samples from pig cadaver tongues. The samples were then subdivided into five groups of nine samples each. A final specimen was taken by scalpel as a control. All samples were put into test tubes containing 10% buffered formalin solution, and were examined separately under an optical microscope by two pathologists to evaluate the peripheral thermal damage induced by the laser. In all specimens the cut edges of the incision were free from histological artefacts, especially when lower settings were applied. Statistical analysis showed no differences among the groups. The KTP laser demonstrated surgical effectiveness and caused little peripheral damage to the cut edges, and therefore would always allow a safe histological diagnosis to be obtained.

Pulpal effects of enamel ablation with a microsecond pulsed lambda = 9.3-microm CO2 laser.

In vitro studies have shown that CO2 lasers operating at the highly absorbed 9.3 and 9.6-microm wavelengths with a pulse duration in the range of 10-20-microsecond are well suited for the efficient ablation of enamel and dentin with minimal peripheral thermal damage. Even though these CO2 lasers are highly promising, they have yet to receive FDA approval. Clinical studies are necessary to determine if excessive heat deposition in the tooth may have any detrimental pulpal effects, particularly at higher ablative fluencies. The purpose of this study was to evaluate the pulpal safety of laser irradiation of tooth occlusal surfaces under the conditions required for small conservative preparations confined to enamel. Test subjects requiring removal of third molar teeth were recruited and teeth scheduled for extraction were irradiated using a pulsed CO2 laser at a wavelength of 9.3 microm operating at 25 or 50 Hz using a incident fluence of 20 J/cm(2) for a total of 3,000 laser pulses (36 J) for both rates with water cooling. Two control groups were used, one with no treatment and one with a small cut made with a conventional high-speed hand-piece. No anesthetic was used for any of the procedures and tooth vitality was evaluated prior to treatment by heat, cold and electrical testing. Short term effects were observed on teeth extracted within 72 hours after treatment and long term effects were observed on teeth extracted 90 days after treatment. The pulps of the teeth were fixed with formalin immediately after extraction and subjected to histological examination. Additionally, micro-thermocouple measurements were used to estimate the potential temperature rise in the pulp chamber of extracted teeth employing the same irradiation conditions used in vivo. Pulpal thermocouple measurements showed the internal temperature rise in the tooth was within safe limits, 3.3+/-1.4 degrees C without water cooling versus 1.7+/-1.6 degrees C with water-cooling, n = 25, P<0.05. None of the control or treatment groups showed any deleterious effects on pulpal tissues and none of the 29 test-subjects felt pain or discomfort after the procedure. Only two test-subjects felt discomfort from "cold sensitivity" during the procedure caused by the water-spray. It appears that this CO2 laser can ablate enamel safely without harming the pulp under the rate of energy deposition employed in this study.

Real-time near IR (1310 nm) imaging of CO_2 laser ablation of enamel

The high-transparency of dental enamel in the near-IR (NIR) can be exploited for real-time imaging of ablation crater formation during drilling with lasers. NIR images were acquired with an InGaAs focal plane array and a NIR zoom microscope during drilling incisions in human enamel samples with a lambda=9.3-microm CO(2) laser operating at repetition rates of 50-300-Hz with and without a water spray. Crack formation, dehydration and thermal changes were observed during ablation. These initial images demonstrate the potential of NIR imaging to monitor laser-ablation events in real-time to provide information about the mechanism of ablation and to evaluate the potential for peripheral thermal and mechanical damage.

Adhesion of composite to enamel and dentin surfaces irradiated by IR laser pulses of 0.5–35 μs duration

The characteristics of laser-treated tooth surfaces depend on the laser wavelength, pulse duration, spatial and temporal laser beam quality, incident fluence, surface roughness, and the presence of water during irradiation. Ablated surfaces are most commonly restored with adhesive dental materials and the characteristics of the ablated surfaces influence adhesion of restorative materials. Previous studies suggest that high bond strengths can be achieved using shorter laser pulses that minimize peripheral thermal damage. In this study, Er:YSGG, Er:YAG, and CO(2) lasers were used at irradiation intensities sufficient to simulate efficient clinical caries removal to uniformly irradiate bovine enamel and human dentin surfaces using a motion control system with a microprocessor-controlled water spray. The degree of spatial overlap of adjacent pulses was varied so as to investigate the influence of irradiation uniformity and surface roughness on the bond strength. Composite resin was bonded to the irradiated surfaces and shear bond tests were used to obtain bond strengths in MPa. The highest results were obtained using the Er:YAG pulses with pulse durations less than 35 mus without the necessity for postirradiation acid etching. Some of these groups were not significantly different from nonirradiated, acid-etch-only positive control groups.

Rapid and conservative ablation and modification of enamel, dentin, and alveolar bone using a high repetition rate transverse excited atmospheric pressure CO[sub 2] laser operating at λ=9.3 μm

Transverse excited atmospheric pressure (TEA) CO(2) lasers tuned to the strong mineral absorption of hydroxyapatite near lambda=9 microm are well suited for the efficient ablation of dental hard tissues if the laser pulse is stretched to greater than 5 to 10 micros to avoid plasma shielding phenomena. Such CO(2) lasers are capable of operating at high repetition rates for the rapid removal of dental hard tissues. The purpose of this study was to test the hypothesis that stretched lambda=9.3-microA CO(2) laser pulses can produce lateral incisions in enamel, dentin, and alveolar bone for dental restorations and implants at repetition rates as high as 400 Hz without peripheral thermal damage. The single pulse ablation rates through enamel, dentin, and bone were determined for incident fluence ranging from (1 to 160 J/m(2)) for laser pulses from 5 to 18 mus in duration. Lateral incisions were produced in hard tissue samples using a computer-controlled scanning stage and water spray, and the crater morphology and chemical composition were measured using optical microscopy and high-resolution synchrotron radiation infrared spectromicroscopy. The residual energy remaining in tooth samples was measured to be 30 to 40% for enamel and 20 to 30% for dentin without water cooling, under optimum irradiation intensities, significantly lower than for longer CO(2) laser pulses. The transmission through 2-m length 300-, 500-, 750-, and 1000-microm silica hollow waveguides was measured and 80% transmission was achieved with 40 mJ per pulse. These results suggest that high repetition rate TEA CO(2) laser systems operating at lambda=9.3 microm with pulse durations of 10 to 20 micros are well suited for dental applications.

Dissolution studies of bovine dental enamel surfaces modified by high-speed scanning ablation with aλ = 9.3-µm TEA CO2 laser

Previous studies have demonstrated that lasers can be used to modify the chemical composition of dental enamel to render the mineral phase more resistant to acid dissolution with minimal peripheral thermal damage. Transverse excited atmospheric (TEA) CO(2) lasers tuned to the strong mineral absorption of hydroxyapatite (HAP) near lambda = 9 microm are well-suited for the efficient ablation of dental hard tissues if the laser-pulse is stretched to greater than 5-10 microseconds to avoid plasma shielding phenomena. Moreover, TEA CO(2) lasers can be operated at very high repetition rates and are inherently less expensive and more versatile than Er:YAG and Er:YSGG solid-state lasers. In this study a lambda = 9.3-microm TEA CO(2) with a pulse duration of 8 microseconds and a repetition rate of 300 Hz was used to uniformly treat bovine enamel surfaces at ablative irradiation intensities. We hypothesized that a uniform surface layer of modified enamel of improved crystallinity and CaP phase composition would be formed with an enhanced resistance to acid-dissolution in the ablated areas at higher scanning rates used with the water spray. Such a modified layer of enamel formed at the base and walls of a cavity preparation under the irradiation conditions employed in this study have the potential to inhibit secondary caries under sealants and restorations. The surfaces of bovine enamel blocks (3 x 3 mm(2)) were rapidly scanned across the laser beam at rates of 2, 3, and 6 mm/second with and without a water-spray at an incident fluence of 30 J/cm(2). The resistance to acid dissolution was evaluated using controlled surface dissolution experiments on laser-irradiated and control samples. The groups irradiated at a fluence of 30 J/cm(2) with a repetition rate of 300 Hz and a high scan rate of 6 mm/second with and without water-cooling significantly reduced the overall surface dissolution rates (P < 0.001). At low scan rates (2-3 mm/second) excessive heat deposition resulted in the formation of an outer layer of asperities containing non-apatitic CaP phases that were more susceptible to acid-dissolution. At a scanning rate of 6 mm/second even without the water spray a layer of purer phase HAP was formed without thermal damage, indicating that a high scanning rate can be used to avoid excessive thermal damage during ablation. The best results (80% inhibition) were attained for the higher scanning speed 6-mm/second combined with a water spray. This study demonstrates that an enamel surface with enhanced resistance to acid dissolution is produced after ablation with lambda = 9.3-microm TEA CO(2) laser pulses delivered at high-repetition rates if sufficiently high scanning rates are used with or without a water-spray.

Optimization of the Erbium:YAG laser for precise incision of ureteral and urethral tissues: in vitro and in vivo results.

Tissue damage during endoscopic treatment of urethral and ureteral strictures may result in stricture recurrence. The Erbium:YAG laser ablates soft tissues with minimal peripheral damage and may be a promising alternative to cold knife and Holmium:YAG laser for precise incision of urological strictures. Optimization of the Er:YAG laser was conducted using ex vivo porcine ureteral and canine urethral tissues. Preliminary in vivo studies were also performed in a laparoscopic porcine ureteral model with exposed ureter. Laser radiation with a wavelength of 2.94 microm, pulse lengths of 8, 70, and 220 microseconds, output energies of 2-35 mJ, fluences of 1-25 J/cm2, and pulse repetition rates of 5-30 Hz, was delivered through 250-microm and 425-microm core germanium oxide optical fibers in direct contact with tissue. Ex vivo perforation thresholds measured 2-4 J/cm2, with ablation rates of 50 microm/pulse at fluences of 6-11 J/cm2. In vivo perforation thresholds were approximately 1.8 J/cm2, with the ureter perforated in less than 20 pulses at fluences greater than 3.6 J/cm2. Peripheral thermal damage in tissue decreased from 30 to 60 microm to 10-20 microm as the laser pulse length decreased from 220 to 8 microseconds. Mechanical tissue damage was observed at the 8 microseconds pulse duration. The Er:YAG laser, operating at a pulse duration of approximately 70 microseconds, a fluence greater than approximately 4 J/cm2, and a repetition rate less than 20 Hz, is capable of rapidly incising urethral and ureteral tissues with minimal thermal and mechanical side-effects.

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.

Carbon dioxide laser resurfacing of the aged face.

Aging of the skin of the face consists of an intrinsic aging process that is genotypically inherent and inevitable, which accounts for the thinness of tissue that is lax and redundant. It can include benign and premalignant neoplasms [1, 2]. While photoaging or extrinsic aging is environmentally mediated and is characterized by fine and deep facial skin wrinkling; it can be characterized by thickened, coarse, yellow, sallow skin, that is studded with telangiectasia, macules of hyper-and hypopigmentation, benign, premalignant and malignant neoplastic lesions [1, 3—6]. There are many ways to rejuvenate aged skin, which include topical treatments with vitamin A acid [7,8], alpha and beta hydroxy acids [9, 11] and various types of skin resurfacing either by chemical peelings of glycolic, trichloracetric or phenolic acids for superficial, medium to deep depth resurfacing respectively [12, 13], or by performing a mechanical dermabrasion [14, 17]. This presentation will highlight rejuvenating the photodamaged and aged skin of the face by the currently most popular modality of resurfacing, which is using a high energy carbon dioxide laser that is either pulsed or flashscanned [18—23].