Laser thrombolysis using long pulse frequency-doubled Nd:YAG lasers

BACKGROUND AND OBJECTIVE: Laser thrombolysis is a means for clearing blood clots in occluded arteries. Many researchers have studied the mechanisms of clot ablation, and research clinicians have used the technique to treat myocardial infarction with a number of different laser systems. Specifically, a 1-microsec pulsed dye laser has been used clinically to remove blood clots in coronary arteries. As a comparative study, the ablation characteristics of lasers with pulse durations in the ranges of 50-150 microsec and 2-10 msec were investigated. Two frequency-doubled Nd:YAG lasers at 532 nm were used in this study. Ablation threshold and ablation efficiency of gel phantoms and thrombus using these two lasers were measured and compared with the results of the pulsed dye laser. The pulsed dye laser in this study operated at 522 nm. STUDY DESIGN/MATERIALS AND METHODS: Gelatin samples with 150 cm(-1) absorption coefficient at 532 nm and animal clot were confined to 3-mm silicone tubes to measure ablation parameters. Additional samples with 150 cm(-1) absorption coefficient at 522 nm were prepared for use with the pulsed dye laser. A fluorescence technique and photographic bubble detection were used to determine ablation threshold. A spectrophotometric technique was used to determine ablation efficiency. RESULTS: The ablation threshold of the gel phantoms for all three lasers was determined to be 17 +/- 2 mJ/mm(2). Ablation efficiency for the gel phantoms was 1.7 +/- 0.1 microg/mJ. Clot had an ablation efficiency of 2.9 +/- 1.0 microg/mJ. CONCLUSIONS: Ablation threshold and efficiency are independent of laser pulse duration for 1-microsec, 50-150-microsec, and 2-10-msec pulses (P < 0.05).     

In vitro inactivation of endodontic pathogens with Nd:YAG and Er:YAG lasers

Both Nd:YAG and Er:YAG lasers have been suggested as root canal disinfection aids. The aim of this in vitro study is to compare both wavelengths in terms of irradiation dose required for microbial inactivation, to quantify these irradiation doses and to investigate the influence of certain (laser) parameters on the antimicrobial efficacy. Agar plates containing a uniform layer of Enterococcus faecalis, Candida albicans or Propionibacterium acnes were mounted perpendicularly underneath the laser handpieces (5?mm spot). The Er:YAG laser was operated in single-pulse mode. Pulse energies of 40–400?mJ and pulse lengths of 100, 300, 600, and 1,000?μs were tested. After incubation at 37°C for 48?h, growth on the plates was scored. The pulse energy yielding complete absence of growth over the entire spot area was taken as the total inhibition threshold (TIT). TITs were determined for every species and pulse length. The Nd:YAG laser was operated with pulse trains because single pulses were ineffective. Output power was 15?W and frequency was 100?Hz. Spots were irradiated for 5–120?s. After incubation, the diameters of the inhibition zones were measured. For the Er:YAG laser, TITs varied between 100 and 210?mJ, and differed significantly between species and pulse lengths. Using Nd:YAG irradiation, TITs were around 5,300?J/cm² for C. albicans and 7,100?J/cm² for P. acnes. No inhibition was observed for E. faecalis. Er:YAG irradiation was superior to Nd:YAG in inactivating microorganisms on agar surfaces.     

Effect of Er:YAG and Nd:YAG lasers on the mineral content of root canal dentin

Lasers in Medical Science - The aim of this study was to assess the effect of two different laser systems on the mineral content of root canal dentin. Thirty-six single canal-extracted mandibular...     

Laser treatment of keloids: a clinical trial and an in vitro study with Nd:YAG laser

Biochemical studies utilizing keloid fibroblast cultures revealed that Nd:YAG laser selectively suppressed collagen production by these cells. Based on these in vitro observations, eight patients with keloids were treated with Nd:YAG laser in a nondestructive manner. Results, with a 3-year follow-up, indicated flattening and softening of the lesions. Thus, the results suggest that Nd:YAG laser is an effective treatment modality for keloids, and its mechanism may involve bioinhibition of fibroblast functions.     

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.     

The effect of Nd:YAG and Er,Cr:YSGG lasers on the microhardness of human dentin

The current investigation determined the microhardness of dentin tissue irradiated with erbium, chromium-doped yttrium scandium gallium garnet (Er,Cr:YSGG) and neodymium-doped yttrium–aluminum garnet (Nd:YAG) lasers. Thirty non-carious human molars were used in this study. Dentin disks were prepared by horizontal sectioning of one third of the occlusal surface. Halves of dentin specimens were irradiated with 3.5- and 4.5-W Er,Cr:YSGG lasers and with a 2-W Nd:YAG laser. The remaining halves served as controls. The microhardness measurements were recorded with a Vickers surface microhardness tester. The results were statistically evaluated by paired t test and one-way ANOVA (p?=?0.05). Laser irradiation has significantly reduced the microhardness of dentin within each group compared to its control. Moreover, statistically significant differences were observed among the different groups (p?<?0.05). The 3.5-W Er,Cr:YSGG laser produced the greatest reduction in microhardness of dentin followed by 4.5 W and Nd:YAG laser. The differences between all the groups were statistically significant. It was concluded that both laser devices used in this study have resulted in significant thermal damage and subsequent reduction in dentin microhardness values.     

Comparison of dentin root canal permeability and morphology after irradiation with Nd:YAG, Er:YAG, and diode lasers

The aim of this study was to compare the effects of Nd:YAG, Er:YAG, and diode lasers on the morphology and permeability of root canal walls. The three laser wavelengths mentioned interact differently with dentin and therefore it is possible that the permeability changes caused will determine different indications during endodontic treatment. Twenty-eight human single-rooted teeth were instrumented up to ISO 40 and divided into four groups: group C, control (GC), non-laser irradiated; group N (GN), irradiated with Nd:YAG laser; group E (GE), with Er:YAG laser and group D (GD) with diode laser. After that, the roots were filled with a 2% methylene blue dye, divided into two halves and then photographed. The images were analyzed using Image J software and the percentage of dye penetration in the cervical, middle, and apical root thirds were calculated. Additional scanning electron microscopy (SEM) analyses were also performed. The analysis of variance (ANOVA) showed significant permeability differences between all groups in the middle and cervical thirds (p < 0.05). The Tukey test showed that in the cervical third, GN presented means of dye penetration statistically significantly lower than all of the other groups. In the middle third, GE and GD showed statistically higher dye penetration means than GC and GN. SEM analysis showed melted surfaces for GN, clean wall surfaces with open dentinal tubules for GE, and mostly obliterated dentinal tubules for GD. Er:YAG (2,094 nm) laser and diode laser (808 nm) root canal irradiation increase dentinal permeability and Nd:YAG (1,064 nm) laser decreases dentin permeability, within the studied parameters.     

Laser sclerostomy ab interno using a continuous wave Nd:YAG laser

We report the use of a continuous wave Nd:YAG (CW-YAG) laser focused through a sapphire crystal to create a filtering bleb by ab-interno sclerostomy. A 2-mm clear corneal incision was made in each eye of five anesthetized Dutch Belted rabbits, and the 30-mm-long sapphire crystal with a 0.2-mm focal tip was passed across the anterior chamber until it came in contact with the opposite angle. Between two and three pulses of 0.8 J were required to produce a filtering bleb in each of the 10 eyes. The overlying conjunctiva was not damaged; the procedure time was under five minutes. Histological examination revealed a surrounding area of scleral melting that extended an average of 0.06 mm from the sclerostomy. These data suggest that the CW-YAG laser may be useful in performing glaucoma filtering surgery with minimal damage to surrounding ocular tissues.     

Laser transmission through membranes using the Q-switched Nd:YAG laser

BACKGROUND AND OBJECTIVE: Many laser centres utilise various transparent membranes during treatment sessions with Q-switched lasers to prevent or reduce tissue splatter, thereby reducing the aerosolised biohazard of cellular debris to operator and laser. STUDY DESIGN/MATERIALS AND METHODS: We performed a series of experiments with the Q-Switched Nd:YAG laser, a selection of 11 varieties of membrane and a power meter in order to ascertain which of the membranes was the most effective protector concerning transmission of laser energy. Other mechanical properties such as transparency, strength, ease of application, and flexibility were taken into account. RESULTS: Tegaderm (overall average 94% transmission), Cling Film (93%), Bioclusive (89%), Opsite (91%), and Microwave Cling Film (87%) all consistently performed well in pure transmission terms, whereas other membranes tested such as Acetate (74%), Grades of Melinex (75%, 72%, 75%), 2nd Skin (74%), and Perspex (68%) were unsuitable as protection. CONCLUSION: Cling Film proved to be the best all round membrane. We recommend its use for operator and laser protection against the tissue spatter produced from the Q-Switched Nd:YAG laser.     

Effects of Er:YAG and Er,Cr:YSGG lasers on dentine hypersensitivity. Short-term clinical evaluation

Dentine hypersensitivity (DH) is a painful condition and is a clinical challenge due to the different treatment strategies available. High-intensity lasers have been studied as a possible option. The aim of this randomized, controlled, double-blind clinical study was to evaluate the effects of Er:YAG and Er,Cr:YSGG lasers on DH. The study group comprised 28 subjects who met the inclusion criteria. A visual analogue scale was used to quantify sensitivity before treatment as baseline, immediately before and immediately after treatment, and 1 week and 1 month after treatment. Teeth were assigned to four groups: group 1 control (no treatment), group 2 Er:YAG laser treatment (2 Hz/32.4 mJ/5.9 J/cm(2)), group 3 Er,Cr:YSGG laser treatment (0.25 W/4.4 J/cm(2)), and group 4 Er,Cr:YSGG laser treatment (0.50 W/ 8.9 J/cm(2)). Data were collected and submitted to statistical analysis for both evaporative (air) and mechanical (probe) stimulation. For both the air and probe stimulation no differences were observed between the pretreatment sensitivities. With the evaporative stimulus, the pain level immediately after treatment was reduced; however, after this the values remained stable. Irradiation with the Er:YAG laser was associated with the lowest level of pain. With the mechanical stimulus, group 4 showed the most pronounced decrease in pain immediately after treatment; however, by the end of the study, pain levels had increased. Groups 1, 2 and 3 showed a reduction in pain that was significantly different from that in group 4 after the 4 weeks of clinical follow up. Based on the results and within the limits of this study, it can be concluded that none of the laser treatments studied was capable of completely eliminating pain, but the Er:YAG and Er,Cr:YSGG lasers are suitable for the treatment of DH.     

The efficacy of Er,Cr:YSGG laser supported periodontal therapy on the reduction of peridodontal disease related oral malodor: a randomized clinical study

Background

This study aims to evaluate the efficacy of Er,Cr:YSGG laser assisted periodontal therapy on the reduction of oral malodor and periodontal disease.

Methods

Sixty patients with chronic periodontitis were included in the study and allocated into two groups each containing 30 patients. The study was planned in a double blind fashion. Conventional periodontal therapy was performed in group 1 and conventional periodontal therapy was performed in association with Er,Cr:YSGG application in group 2. Periodontal parameters of probing depth, clinical attachment level, plaque index and bleeding on probing were measured with a periodontal probe. Quantitative analysis of volatile sulphure compunds (VSCs) were measured with a calibrated halimeter at baseline level and at post-treatment 1st, 3rd and 6th months. P values <0.05 were accepted as statistically significant.

Results

There was a statistical significant reduction in VSC values in group 2 at post-treatment 3rd and 6th months (p?<?0.05). Pocket depth values at post-treatment 1st month and bleeding on probing values at post-treatment 3rd and 6th months were significantly decreased in group 2 (p?<?0.05). Intragroup statistical analysis revealed that there were statistically significant differences for all parameters (p?<?0.01).

Conclusions

Er,Cr:YSGG laser assisted conventional periodontal therapy is more effective in reducing oral malodor and improving periodontal healing compared to conventional periodontal therapy alone.

     

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.     

A split-face,evaluator-blind randomized study on the early effects of Q-switched Nd:YAG laser plus Er:YAG micropeel (combined therapy) versus Q-switched Nd:YAG alone in light solar lentigines in Asians

Solar lentigines are a common sign of aging in Asians, who often asked for treatment. Various lasers, including Q-switched Nd:YAG and Er:YAG, have been adopted, but the results are not always satisfactory, especially for those who are relatively light in color. Our objective was to compare the early effects as well as side effects of Q-switched Nd:YAG laser plus Er:YAG micropeel (combined therapy) with those of Q-switched Nd:YAG laser (QSNY) alone in light solar lentigines in Asians. This was a split-face, evaluator-blind, randomized controlled study. A single session of treatment was performed on Asian patients with light facial lentigines. A combined treatment with QSNY and Er:YAG micropeel was allocated to one half of the face, and QSNY alone to the other half. The response to therapy was evaluated by two independent dermatologists, with standardized photographs taken 2 weeks and 1 month after the laser treatment. Patients’ satisfaction and preference in treatment were also assessed. Fifteen patients completed the study and were analyzed. Overall, a reduction in pigment was observed with both treatment arms during the study period. The degree of pigment reduction following combined therapy and QSNY alone was similar at 2 weeks’ follow-up (P?=?0.433). However, due to the higher incidence of postinflammatory hyperpigmentation (PIH) with combined therapy (73.3 vs 40 %), the degree of pigment reduction in the combined side of the face was found significantly lower than that of the QSNY-alone side at 1-month follow-up (P?=?0.014). Although our study results show that both combined therapy and QSNY alone are capable of reducing pigmentation, QSNY alone is considered to have more favorable qualities than combined treatment for light solar lentigines in Asians.     

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.