Morphologic changes correlating to different sensitivities of Escherichia coli and enterococcus faecalis to Nd:YAG laser irradiation through dentin.

BACKGROUND AND OBJECTIVE: Previous studies demonstrated the disinfecting potential of Nd:YAG laser irradiation on the root canal system from an overall quantitative viewpoint. The aim of this study was to evaluate the specific effect of irradiation through dentin on gram-negative and gram-positive bacteria with regard to their cell structure. STUDY DESIGN/MATERIALS AND METHODS: Sterile dentin samples of standardized size were divided into two sets of four groups with eight samples each. The first set was inoculated with Escherichia coli as the gram-negative test strain, the second set was inoculated with Enterococcus faecalis, which served as the gram-positive test organism. The samples were then irradiated on the bacteria-free side in contact mode under constant scanning movement at an angle of 10 degrees by use of the fiber optic of the Nd:YAG laser. Upon laser treatment they were critical point dried and subjected to SEM investigation. Another two sets of samples were prepared and irradiated in the same manner and evaluated by standard microbiological procedures to verify whether the observed morphologic alterations correlated to cell death. RESULTS: SEM investigations revealed damage pattens that increased with the amount of energy applied. Whereas the gram-negative test organism showed immediate structural injury, the gram-positive test organism required repeated application of irradiation. The microbiological examination showed reduction of both bacterial strains, yet to different extents. CONCLUSION: Our study demonstrates the different morphologic impact of Nd:YAG laser irradiation through dentin on representatives of the two main groups of bacteria. It shows that the construction of the cell wall is crucial for their individual sensitivity to laser treatment.

Effects on oral soft tissue produced by a diode laser in vitro.

BACKGROUND AND OBJECTIVES: This investigation determined incision characteristics and soft-tissue damage resulting from standardized incisions using a wide range of laser modes and parameters of a diode laser at 810 nm. STUDY DESIGN/MATERIALS AND METHODS: Histologic examinations were performed to verify vertical and horizontal tissue damage as well as incision depth and width. RESULTS: Incision depth and width correlated strongly with average powers, but not with laser parameters or the used tips. No laser damage was visible to the naked eye in the bone underlying the incisions in the range between 0.5-4.5 W. CONCLUSION: The remarkable cutting ability and the tolerable damage zone clearly show that the diode laser is a very effective and, because of its excellent coagulation ability, useful alternative in soft-tissue surgery of the oral cavity.

The bactericidal effect of Nd:YAG, Ho:YAG, and Er:YAG laser irradiation in the root canal: an in vitro comparison.

OBJECTIVE: The aim of this study was to compare the antibacterial effectiveness of the Nd:YAG, the Ho:YAG, and the Er:YAG laser in infected root canals. SUMMARY BACKGROUND DATA: Lasers are gaining increasing importance in the field of endodontics. Numerous studies have shown the beneficial effects of laser treatment in disinfecting root canals. METHODS: In our in vitro experimental setup, 40 extracted and endodontically treated teeth were inoculated with a suspension of Escherichia coli and Enterococcus faecalis and then irradiated at standardized power settings. The disinfecting efficacy of each laser was proved by classical microbiological examination. RESULTS: This article highlights that all three lasers substantially decreased the bacterial population with only minimal differences in their microbicidal efficacy. At 1.5 W, the best results were obtained by the Er:YAG laser achieving a mean bacterial elimination of 99.64%, followed by the Nd:YAG laser (99.16%), and the Ho:YAG laser (99.05%). CONCLUSION: Our findings indicate that all three lasers act as strongly effective microbicides without causing unfavorable temperature rises at the settings used. They can thus be considered a valuable tool for root canal treatment.