In vitro preliminary study to evaluate the capability of Er,Cr:YSGG laser in posterior teeth root-canal preparation with step-back technique

This preliminary study was to investigate in vitro the Er,Cr:YSGG laser ablation capability, both range (enlargement aspects of laser tips corresponded to conventional endodontic files) and quality (removing of smear layer and opening of dentinal tubules) to clean and shape the root canal for final obturation step. The crowns of 15 extracted multi-rooted posterior human teeth were resected, and then 15 canals were prepared by an Er,Cr:YSGG laser up to 1.5 W (actual power output) using the step-back technique, while the other 15 canals (control) were enlarged conventionally by K-flex file. The results revealed that posterior root-canal preparation could be achieved by laser beam transmitted to the canal using endodontic tips. At a chosen significance level of α = 1%, the results showed no significant statistical difference between the two groups (P > 0.01). Considering the results of this current study, laser-based root-canal preparation still shows certain limitations, and further improvements are mandatory for higher achievement and better preparation outcomes.     

In vitro decalcification of aortic valve leaflets with the Er:YSGG laser,Ho:YAG laser,and the cavitron ultrasound surgical aspirator

This study was designed to compare the efficacy of the erbium: yttrium-scandium-gallium-garnet (Er:YSGG) laser and the holmium:yttrium-aluminum-garnet (Ho:YAG) lasers in debriding calcium from freshly explanted aortic valve leaflets and to compare the Er:YSGG laser with the Cavitron ultrasonic surgical aspirator (CUSA). Aortic valve leaflets were freshly explanted from patients undergoing aortic valve replacement for aortic stenosis. Initially, 4 leaflets each were debrided with the Er:YSGG and the Ho:YAG lasers to attempt removal of calcium deposits while preserving the underlying integrity of the leaflets and minimizing thermal damage. The Er:YSGG laser was more effective in doing so with less thermal and photoacoustic damage when compared with the Ho:YAG laser. Twelve more leaflets each were then debrided with the Er:YSGG laser and the CUSA. The Er:YSGG laser again proved less injurious to the underlying leaflet. The CUSA-treated leaflets demonstrated shattering and disruption of adjacent tissue as well as collagen fiber exposure. These changes were not seen with the Er:YSGG laser. Because of these properties, the Er:YSGG laser merits further evaluation as a tool for aortic valvuloplasty procedures in selected patients with senescent calcific aortic stenosis. © 1993 Wiley-Liss, Inc.     

Effect of different power parameters of Er,Cr:YSGG laser on human dentine

The aim of this work was to determine the optimal power setting of an Er,Cr:YSGG laser for cutting human dentine to produce a surface that remains suitable as a foundation on which to build and bond a dental restoration. The cutting efficiency and resulting microhardness of the dentine were evaluated for various laser power settings, and representative samples were examined by SEM. The microhardness of the dentine was significantly reduced by 30–50% (p < 0.05, paired t test) after laser irradiation, irrespective of the power setting used. The mean ablation efficiency increased in proportion to the power setting of the laser. Although the laser power setting did not affect the extent of reduction in microhardness, it did affect the microstructure of human dentine.     

An assessment following root canal preparation by Er,Cr:YSGG laser irradiation in straight and curved roots, in vitro

In the present study, the effectiveness of Er,Cr:YSGG laser in straight and curved root canal preparation was compared with that of the conventional canal preparation technique, in vitro. The degree of root curvature of 40 root canals was determined, and then 20 canals were prepared by an Er,Cr:YSGG laser of 2 W by using the crown-down technique, while the other 20 canals were shaped by K-file (control). The achievement degree of root canal preparation and debris score was investigated morphologically. The results indicated that straight root canals could be successfully prepared by Er,Cr:YSGG laser irradiation; a significant decrease of smear layer or debris was also recognized (P<0.01). However, canal preparation by laser device in curve root often leads to a ledge or zipped formation, perforation or over-instrumentation. The results demonstrated that further development in laser device and technique are required to ensure its success in root canal preparation, especially in curve root.     

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     

Histopathological evaluation of pulpotomy with Er,Cr:YSGG laser vs formocresol

The purpose of this study was to histologically investigate whether pulpotomy with Er,Cr:YSGG laser is an acceptable alternative for formocresol. Pulpotomy of 48 dog’s primary canine teeth was performed with formocresol or Er,Cr:YSGG laser. Histological evaluations on hematoxylin and eosin-stained pulp tissues were made by an optical microscope 7 or 60 days later. Statistical analysis was performed with Fisher’s exact test, Mann–Whitney U test, and Student’s t test. Seven days after pulpotomy, samples treated with laser had significantly favorable histological features in the following measures: continuity of odontoblastic layer (P < 0.001), presence of hemorrhage (P < 0.008), amount of inflammation (P < 0.002), tissue necrosis (P < 0.001), internal resorbtion (P < 0.002), level of vascularization (P < 0.002), and size of abscess (P < 0.041). Similar results were observed 60 days after pulpotomy, except that the differences were not mostly significant due to natural exfoliation of 16 teeth. In conclusion, Er,Cr:YSGG laser system is an acceptable alternative for formocresol in pulpotomy of deciduous teeth.     

In vivo study of the healing processes that occur in the jaws of rabbits following perforation by an Er,Cr:YSGG laser

This study investigates the healing process that takes place in the bone and soft tissue of the maxilla and the mandible after perforation by an Er,Cr:YSGG laser device. The jaws of New Zealand white rabbits were irradiated with an Er,Cr:YSGG laser, forming wounds 0.4 mm in diameter. Irradiation parameters were as follows: repetition rate was 20 pulse/s, pulse duration was 140–200 s, power was 2 W, exposure time was 10 s, energy density was 80 J/cm². After sacrifice at 0–56 days post-surgery, gross observations and histological examinations were performed. Effective hemostasis was achieved after Er,Cr:YSGG laser surgery. There was a minimal delay before the healing began. After 56 days all of the bone defects had been completely replaced by new bone. In conclusion, the Er,Cr:YSGG laser allows precise surgical ablation with minimal thermal damage to adjacent tissues in vivo. The overall subsequent healing was favorable. This laser may potentially be used in minor oral surgery.     

A comparative SEM study between hand instrument and Er:YAG laser scaling and root planing

Scaling and root planing are one of the most commonly used procedures for the treatment of periodontal diseases. Removal of calculus using conventional hand instruments is incomplete and rather time-consuming. In search for more efficient and less difficult instrumentation, investigators have proposed lasers as alternatives or adjuncts for scaling and root planing. The aim of the present study was to compare the effectiveness of subgingival scaling and root planing with erbium: yttrium, aluminium, garnet (Er:YAG) laser and hand instrumentation in vitro. The mesial and distal surfaces of 15 periodontal loosed extracted teeth were treated randomly either by hand instrumentation or by Er:YAG laser irradiation. After choosing the “very long pulse mode” (pulse duration of about 700 μs), the output energy of 160 mJ with 920-μm beam diameter (RO7 Perio tip, Fidelis, Fotona, Slovenia) and frequency of 12 Hz were selected, both according to the best results of past studies. In addition, air water spray was used during the procedures. The morphology of the root surface was evaluated by three observers with a scanning electron microscopy in magnifications of 50× and 400×. The result of this setting showed that the rate of remained roughness on treated root surfaces in two groups of hand instruments and Er:YAG laser had a meaningful difference: The surface roughness in Er:YAG laser group was more than in hand instruments group. The present study could demonstrate the in vitro capability of the Er:YAG laser for scaling and root planing in periodontitis, although the effectiveness of this setting did not reach that achieved by hand instrumentation. It could be concluded that lower frequency and long pulse duration maybe more suitable for the micro-morphology of root surface after treatment. This theory is going to be tested with the same laser instrument in the next study.     

Adhesion after erbium, chromium:yttrium-scandium-gallium-garnet laser application at three different irradiation conditions

The aim of this study was to investigate whether distinct cooling of low fluence erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation would influence adhesion. Main factors tested were: substrates (two), irradiation conditions (three), and adhesives (three). A 750 μm diameter tip was used, for 50 s, 1 mm from the surface, with a 0.25 W power output, 20 Hz, energy density of 2.8 J/cm² with energy per pulse of 12.5 mJ. When applied, water delivery rate was 11 ml/min. The analysis of variance (ANOVA) showed that laser conditioning significantly decreased the bond strength of all adhesive systems applied on enamel. On dentin, laser conditioning significantly reduced bond strength of etch-and-rinse and one-step self-etch systems; however, laser irradiation under water cooling did not alter bonding of two-step self-etching. It may be concluded that the irradiation with Er,Cr:YSGG laser at 2.8 J/cm² with water coolant was responsible for a better adhesion to dentin, while enamel irradiation reduced bond strength, irrespective of cooling conditions.     

Decontamination of deep dentin by means of erbium, chromium:yttrium-scandium-gallium-garnet laser irradiation

The aim of this in vitro study was to evaluate the depth of effectiveness of erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation on microorganism reduction. From human roots, dentin slices of 100 μm to 1,000 μm thickness were prepared. These specimens were sterilized and then inoculated with 1 μl of Enterococcus faecalis suspension. The backs of the specimens were then irradiated with Er,Cr:YSGG radiation at a pulse energy of 3.13 mJ, delivered at an incidence angle of 5° to the dentin slice surface. A control group was left without irradiation. The remaining bacteria were collected in 1 ml sterilized NaCl solution, serially diluted and seeded in Columbia-Agar plates. Despite the low pulse energy of 3.13 mJ, the Er,Cr:YSGG laser irradiation resulted in significant bacterial reduction up to a dentin thickness of 500 μm (P < 0.05). Scanning electron microscopy (SEM) micrographs of the contaminated and irradiated surfaces showed the absence of a smear layer and opened dentinal tubules.     

Evaluation of mineral content of dentin prepared by erbium, chromium:yttrium scandium gallium garnet laser

Laser etching has an effect on the mineral content of dentin. The aim of this study was to evaluate the mineral content of dentin prepared at three different power settings with an erbium, chromium:yttrium scandium gallium garnet (Er,Cr:YSGG) laser. The enamel of five, lower, wisdom, molar teeth was removed to expose the dentin surface. Four dentin slabs were obtained, then each tooth was randomly divided into four portions (groups 1 W, 2 W, 3 W and control) so that we could evaluate the effect of laser treatment. The Er,Cr:YSGG laser used for the study had a pulse duration of 140 μs, a pulse repetition rate of 20 Hz and a power output range of 0 W to 6 W. Laser energy was delivered through a fiberoptic system to a sapphire tip terminal 6 mm long and 600 μm in diameter, using a non-contact mode. The levels of five elements: magnesium (Mg), phosphorus (P), calcium (Ca), potassium (K), and sodium (Na), in each slab were measured by inductively coupled plasma–atomic emission spectrometry (ICP-AES). There were significant differences between the groups (1 W, 2 W, 3 W and control) for Ca, Mg, Na, P and Ca/P ratio (P < 0.05); however, there were no significant differences for K (P = 0.43). Laser treatment at 1 W significantly affected the mean percentage weight of all element groups except K. Scanning electron microscopy (SEM) photographs indicated that the surface irregularities increased with increasing power setting.     

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.     

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.     

One-year clinical results of Er,Cr:YSGG laser application in addition to scaling and root planing in patients with early to moderate periodontitis

In 30 patients with periodontitis, a total of 278 teeth exhibiting bleeding on probing, subgingival calculus, and a probing depth between 3–6 mm were examined. For each participant, two treatment types were alternatively applied on the contralateral quadrants: scaling and root planing (SRP) as control, and SRP followed by Er,Cr:YSGG laser application (SRP+laser), as a test method. Five clinical parameters: plaque level, bleeding on probing, probing depth, gingival recession and clinical attachment level were examined at baseline and at 2, 3, 6, 12 months after treatment. Of the total of 1,668 sites examined in all patients, 1,088 sites were found with a probing depth of 3–6 mm. In these sites, differences in clinical parameters between SRP and SRP+laser-treated quadrants were analyzed, assuming the level of p < 0.05 as significant. After 2 months from baseline, the mean probing depth reduction and the clinical attachment level gain were significantly greater in SRP+laser than in SRP quadrants, and remained so throughout the study (p < 0.001). A marked reduction of the bleeding scores occurred in all examined sites, irrespective of the treatment method. However, after 12 months, significantly less teeth exhibited bleeding on probing in SRP+laser quadrants than in SRP quadrants (p < 0.001). The mean plaque and gingival recession levels did not differ between the SRP and SRP+laser quadrants neither before nor after the treatment. The periodontal procedures either using Er,Cr:YSGG laser after SRP or SRP alone, lead to significant improvements in all clinical parameters investigated. However, laser application, as an adjunct to SRP, appeared to be more advantageous.