Hard tissue ablation with a spray-assisted mid-IR laser.

The objective of this study was to understand the dominant mechanism(s) for dental enamel ablation with the application of water spray. A free-running Er,Cr:YSGG (yttrium, scandium, gallium, garnet) laser was used to ablate human enamel tissue at various radiant exposures. During dental ablation, distilled water was sprayed on the sample surface, and these results were compared to ablation without a spray (dry ablation). In order to identify dominant ablation mechanisms, transient acoustic waves were compared to ablation thresholds and the volume of material removed. The ablation profile and depth were measured using optical coherence tomography (OCT). Irregular surface modification, charring and peripheral cracks were associated with dry ablation, whereas craters for spray samples were relatively clean without thermal damage. In spite of a 60% higher ablation threshold for spray associated irradiations owing to water absorption, acoustic peak pressures were six times higher and ablation volume was up to a factor of 2 larger compared to dry ablation. The enhanced pressure and ablation performance of the spray-assisted process was the result of rapid water vaporization, material ejection with recoil stress, interstitial water explosion and possibly liquid-jet formation. With water cooling and abrasive/disruptive mechanical effects, the spray ablation can be a safe and efficient modality for dental treatment.

Topographical characteristics and shear bond strength of tooth surfaces cut with a laser-powered hydrokinetic system.

STATEMENT OF PROBLEM: Erbium lasers, specifically Er;YAG and Er, Cr;YSGG that emit in the near red wavelengths, cut both enamel and dentine. Bonding to these cut surfaces with composites has not been assessed for all laser systems. PURPOSE: This investigation assessed the shear bond strength of composite bonded to tooth structure treated with an Er,Cr;YSGG-powered hydrokinetic system (HKS, Millennium system) and then was compared with surfaces treated with a carbide bur. MATERIAL AND METHODS: Extracted human molars were cut into enamel and dentin with both systems. Nonetched and acid-etched subgroups were evaluated. Shear bond strength was measured with an Instron test machine with a knife-edge loading head. In addition, SEMs were evaluated. RESULTS: There were no significant differences in shear bond strength between etched bur cut (23.3 +/- 2.5 MPa), etched laser-cut enamel (23.7 +/- 4.5 MPa), and nonetched laser-cut enamel (20.5 +/- 2.8 MPa). For nonetched enamel, bond strength values for laser-cut surfaces were significantly higher than the bur-cut surfaces (8.7 +/- 4.3 MPa). Bond strength differences for dentin between bur (14.3 +/- 1.7 MPa) and laser cuts (11.5 +/- 4.3 MPa) were not significant (P =.03). SEM revealed that laser cutting of enamel did not cause formation of a smear layer. CONCLUSION: There were no significant differences in shear bond strength between etched bur-cut, etched laser-cut, and nonetched laser-cut enamel. With nonetched enamel, bond strength values for nonetched laser-cut surfaces were significantly higher than for the bur-cut surfaces. No bond strength differences between bur and laser cutting existed for dentin. Similar topography was observed for bur and laser prepared surfaces of etched enamel and nonetched dentin.

Pulpal thermal responses to an erbium,chromium: YSGG pulsed laser hydrokinetic system.

PROBLEM: Laser systems are known to raise pulpal temperatures when applied to tooth surfaces. Dental biocalcified tissues can be cut with an erbium,chromium:yttrium-scandium-gallium-garnet laser-powered hydrokinetic system. This device is effective for caries removal and cavity preparation in vitro. Pulpal monitoring of temperature changes during hard tissue cutting by a hydrokinetic system have not been reported. OBJECTIVES: This study compared the effects of hydrokinetic system, dry bur, and wet bur tooth cutting on pulpal temperature. STUDY DESIGN: In vivo thermocouple intrapulpal measurements were made on cuspid teeth in anesthetized beagle dogs. In vitro measurements were made on extracted human molar teeth preserved in high-salt solution and later rinsed in phosphate-buffered saline (pH 7.4) to simulate in vivo conditions. The hydrokinetic system was compared with conventional air-turbine-powered bur cutting. The hydrokinetic system cuts and bur preparations were randomly made on the buccal surfaces at the cervical one third of the crown and extended until exposure of the pulp was confirmed clinically. RESULTS: Pulpal temperatures associated with the hydrokinetic system either showed no change or decreased by up to 2 degrees C. Wet bur preparations resulted in a 3 degrees to 4 degrees C rise. With dry bur preparations, a 14 degrees C rise in temperature was recorded. CONCLUSIONS: Under the conditions of this study, the erbium,chromium:yttrium-scandium-gallium-garnet laser-powered hydrokinetic system, when used for cavity preparation, had no apparent adverse thermal effect as measured in the pulp space.

Pulpal response to cavity preparation by an erbium, chromium:YSGG laser-powered hydrokinetic system.

The near red-pulsed erbium, chromium:yttrium-scandium-gallium-garnet laser hydrokinetic system, or Er,Cr:YSGG laser HKS, is effective in cutting dental hard tissues. In this longitudinal study, the authors studied the continuously erupting open-apex incisors of New Zealand albino rabbits and the constricted apex teeth of beagles to determine the effects of HKS-produced lesions at various energy levels and of preparations produced by a tapered fissure bur on dental pulp. No pulpal inflammatory responses could be identified either immediately or 30 days after surgery in HKS preparations that removed enamel and dentin without pulp exposure.

Effects of an erbium, chromium: yttrium, scandium, gallium, garnet laser on mucocutanous soft tissues.

OBJECTIVES: Lasers are effective tools for soft tissue surgery. The erbium, chromium: yttrium, scandium, gallium, garnet laser is a new system that incorporates an air-water spray. This study evaluates the cutting margins of this laser and compares healing with laser and conventional scalpel and punch biopsy-induced wounds. STUDY DESIGN: New Zealand white rabbits were divided into serial sacrifice groups; the tissues were grossly and microscopically analyzed after laser and convential steel surgical wounding. RESULTS: Wound margins were found to show minimal edge coagulation artifact and were 20 to 40 mm in width. Laser wounds showed minimal to no hemorrhage and re-epithelialization and collagenization were found to occur by day 7 in both laser and conventional groups. CONCLUSIONS: The new laser system is an effective soft tissue surgical device; wound healing is comparable to that associated with surgical steel wounds. The minimal edge artifact observed with this laser system should allow for the procurement of diagnostic biopsy specimens.

Pressure waves in root canals induced by Nd: YAG laser.

Recently, root canal preparation using Nd:YAG laser has been introduced. Laser interaction with matter may generate cavitation and subsequent pressure waves. This study characterized the pressure waves induced in root canals by either Nd: YAG laser, sonically vibrated files, or ultrasonically vibrated files. The root canals of 14 single-rooted teeth were prepared conventionally and filled with water. In 12 teeth, a pulsed Nd:YAG laser was activated in the canal using optical fibers of various diameters and various power settings. In the remaining two teeth, either a sonic or ultrasonic file was activated. The pressure waves induced in the canals were detected by a piezoelectric transducer. The results were analyzed using correlation coefficient and coefficient of variation. Laser irradiation resulted in pressure waves with amplitudes varying from 35.78 to 79.26 mV, being positively correlated with the laser power density (R2 = 0.870). Sonic and ultrasonic vibrations resulted in pressure waves with mean amplitudes of 60.51 mV and 7.02 mV, respectively. It was concluded that Nd:YAG laser irradiation induced pressure waves, with different characteristics from waves induced by freely vibrating sonic and ultrasonic endodontic instruments when applied to water-filled root canals.

Preliminary investigations on the utility of an erbium, chromium YSGG laser.

A variety of laser systems are under investigation as potential tools in dentistry. Most of these systems have been shown to be efficacious for soft tissue surgery of the mucous membranes; however, cutting bone and dental hard tissues has only recently been possible. In this report from the University of California at Los Angeles School of Dentistry, a review of laser applications in dentistry is discussed. The utility of a new laser system using an erbium YSGG medium with air water spray to cut soft tissues, bone, enamel and dentin is under investigation and preliminary research findings are presented.

Effects of Nd:YAG laser on the permeability of root canal wall dentin.

The effects of a thermally cooled pulsed Nd:YAG laser on the permeability and structural appearance of the root canal wall were investigated in vitro. Twenty specimens of freshly extracted human teeth were prepared by conventional methods. The teeth were randomly divided into two groups. Group 1 teeth were prepared conventionally but not lased. Group 2 specimens received three 15-s laser exposures totaling 45 s duration within the root canal via optical fiber delivery. Laser parameters were set at 5 W, 50 Hz, using a simultaneous air/water coolant spray of 10 psi air and 2 psi water. The external surfaces of the teeth were sealed with acrylic and placed in 2% methylene blue dye for 24 h. The teeth were then sectioned, photographed, and compared under light microscope for the extent of dye penetration. The specimens were subsequently prepared for scanning electron microscopy for correlation of permeability measurements with surface modifications. The combined use of scanning electron microscopy and dye permeability measurements revealed a sealing of the dentinal wall by deposition of glass-like material and, in one specimen, the bridging of a lateral canal that partially occluded the canal. Based on statistical comparisons, permeability of laser-treated teeth was significantly less than untreated specimens (alpha = 0.005).

Histologic effects of a thermally cooled Nd: YAG laser on the dental pulp and supporting structures of rabbit teeth.

The histologic response of the pulp, periapical tissues, supporting periodontal ligament, and alveolar bone adjacent to the incisor teeth of adult rabbits was compared after laser treatment (etching) or drilling with a high-speed dental rotary handpiece (enamelplasty) on the buccal enamel surface. Observations were made at four time periods, 2 days, 14 days, 60 days, and 180 days after treatment. Block sections were removed, and serial sections were prepared and examined by an independent veterinary pathologist for occurrences of histopathologic changes with untreated control teeth used for comparison. Under the conditions of this study, there were no differences between either the laser-treated or the drilled specimens compared with the untreated control teeth on the basis of the histologic appearance.

The efficiency of bone ablation with an Nd:YAG laser beam delivered with a cooling spray: an in vitro study.

This investigation studied the ablation of cortical bone with a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser and how an air and water cooling spray effectively reduced the amount of heat transferred to the surrounding tissue. A 600-microns-diameter optical fiber and a 400-microns-diameter optical fiber were used to deliver an Nd:YAG laser beam to the cortical bone of two rabbit tibiae while a continuous air and water cooling spray provided cooling and irrigation to the tissue site. Different power settings and energy densities were used on 6 groups of 10 holes each. The holes were then prepared for scanning electron microscope examination and average and standard deviations were calculated for each group of collected data. The results showed that the Nd:YAG pulsed laser beam with an experimental cooling irrigation system ablated bone efficiently with minimal thermal damage.

A comparison of dentin permeability after bur and laser apicoectomies.

This investigation compared the permeability of dentinal tubules after laser beam and conventional bur apicoectomies. Twenty roots were rountinely instrumented and obturated with laterally condensed gutta-percha. A bur was used to cut the apexes of 10 teeth, while the remaining 10 were cut with a laser beam carried through an optic fiber. A 35-W pulsed Nd:YAG laser system capable of cooling the irradiated area with an air and water spray supplied the power. Except for the apex, the teeth surfaces were coated with a blue wax. The samples were stored for 36 hours in a 2.5% methylene blue solution and were washed, split, and measured for dye penetration. Linear penetration in series 1 averaged 2.4 mm, while series 2 measured 0.9 mm. The laser apicoectomy appears to reduce the permeability of dentinal tubules.