Objectives: Manufacturers report that treatment of carious tooth structure with Er:YAG laser energy results in preservation of sound tissue and reduction of bacterial bioburden. However, in an earlier in vitro study, whose method we replicate here, investigators found that laser energy stimulated bacterial growth. The current study investigates the ability of different Er:YAG laser pulse energies to affect bacterial bioburden from extracted, noncarious, permanent human molar teeth. Methods: Ten samples were divided randomly into two control groups and two treatment groups based on the following laser parameters: 290mJ/20Hz and 310mJ/20Hz. All teeth but the negative controls were then inoculated with pure isolates of Streptococcus mutans and Lactobacillus caseii. After five days of anaerobic incubation at 35C, treatments were conducted using a sterile 600 µm 80° quartz cutting tip attached to an Er:YAG laser. After laser ablation of occlusal fissures, vigorous scrubbing with sterile microbrushes collected residual bioburden. Each microbrush was placed into a sterile vial containing 0.5mL sterile deionized water and vortexed for 15 sec. Serial dilutions were poured onto separate TSA plates and anaerobically incubated for 48h at 35C. Results: Results indicate that both Er:YAG laser treatments reduced bacterial levels compared to positive controls, contradicting earlier findings. Energy setting 290mJ/20Hz was 10 times more effective at reducing S. mutans than the higher energy level. Whereas, energy setting 310mJ/20Hz was 10 times more effective at reducing L. caseii than the lower parameter. Conclusion: Therefore, Er:YAG laser treatment may reduce bacterial levels from the occlusal fissures of human molar teeth, but in a species-specific manner. Thus, the clinician should be aware that a given pulse of laser energy may reduce the concentrations of particular bacterial species more so than other species populating a bacterial biofilm.

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