Cutting efficiency of a mid-infrared laser on human enamel.

In this study, the cutting ability of a newly developed dental laser was compared with a dental high-speed handpiece and rotary bur for removal of enamel. Measurements of the volume of tissue removed, energy emitted, and time of exposure were used to quantify the ablation rate (rate of tissue removal) for each test group and compared. Cutting efficiency (mm3/s) of the laser was calculated based on the mean volume of tissue removed per pulse (mm3/pulse) and unit energy expended (mm3/J) over the range of applied powers (2, 4, 6, and 8 W). The specimens were then examined by light microscopy and scanning electron micrographs for qualitative analysis of the amount of remaining debris and the presence of the smear layer on the prepared enamel surface. Calculations of the cutting efficiency of the laser over the range of powers tested revealed a linear relationship with the level of applied power. The maximum average rate of tissue removal by the laser was 0.256 mm3/s at 8 W, compared with 0.945 mm3/s by the dental handpiece. Light microscopy and scanning electron micrograph examinations revealed a reduction in the amount of remaining debris and smear layer in the laser-prepared enamel surfaces, compared with the conventional method. Based on the results of this study, the cutting efficiency of the high-speed handpiece and dental bur was 3.7 times greater than the laser over the range of powers tested, but the laser appeared to create a cleaner enamel surface with minimal thermal damage. Further modifications of the laser system are suggested for improvement of laser cutting efficiency.

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).

Evaluation of the antibacterial effects of intracanal Nd:YAG laser irradiation.

Fifty canals of extracted single-rooted teeth were prepared to a size 50 master apical file, sterilized in ethylene oxide, and inoculated with a known quantity of Bacillus stearothermophilus spores. Five groups of 10 canals each were used. The control group received no treatment. The four treatment groups were exposed to pulsed Nd:YAG laser radiation or 0.5% NaOCl alone and in combination. The root canals were flushed with sterile distilled water to recover spores, and serial dilutions were incubated on blood agar and the number of colony-forming units recovered was determined. Analysis of the data indicated a 2-log reduction in colony-forming units among the four treatment groups as compared with the controls; however, no significant differences were observed among the treatment groups. In none of the treatment groups were the root canals sterilized.

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.

Evaluation of thermal cooling mechanisms for laser application to teeth.

Experimental cooling methods for the prevention of thermal damage to dental pulp during laser application to teeth were compared to conventional treatment in vitro. Pulp temperature measurements were made via electrical thermistors implanted within the pulp chambers of extracted human third molar teeth. Experimental treatments consisted of lasing without cooling, lasing with cooling, laser pulsing, and high-speed dental rotary drilling. Comparisons of pulp temperature elevation measurements for each group demonstrated that cooling by an air and water spray during lasing significantly reduced heat transfer to dental pulp. Laser exposures followed by an air and water spray resulted in pulp temperature changes comparable to conventional treatment by drilling. Cooling by an air water spray with evacuation appears to be an effective method for the prevention of thermal damage to vital teeth following laser exposure.

Current endodontic instruments, materials, and drugs, and new techniques for their application.

Technical improvements in endodontic instruments, materials, and drugs and the development of new techniques for their application present a problem for dental practitioners in the selection of materials and methods appropriate to their needs. Claims of "superior" products and "state-of-the-art" treatments only add to the confusion. A review of the dental literature reveals that there is seldom a consensus of opinion on any given subject. Preferences among individuals may reflect a desire for a less complicated, more rapid approach to endodontic treatment. Trends in thought among researchers may offer some direction in the choice between changing concepts and traditional methodology.

Thermal effects of continuous wave CO2 laser exposure on human teeth: an in vitro study.

The thermal effects of continuous wave carbon dioxide laser irradiation on human teeth were investigated. Internal temperature changes were monitored by means of electrical thermistors implanted within the pulp chambers of 20 extracted, unerupted human molar teeth. One-hundred test exposures at various powers and durations were obtained. Linear regression/correlation analysis of the data suggests a direct relationship between the independent variable, exposure energy (joules), and the dependent variable, internal temperature, under the conditions of this study.

The laser apicoectomy: endodontic application of the CO2 laser for periapical surgery.

This article describes the development of a surgical technique employing a carbon dioxide laser for endodontic periapical procedures. The advantages of laser application for sterilization and removal of the infected root apex, as well as enhanced hemostasis, are cited. A case in which the "laser apicoectomy" technique was performed successfully for treatment of secondary apical abscess is presented.