Aim: An evaluation was made of the sterilizing effects of the Erbium:YAG laser at different power ratings upon dental structures in vitro. Design: An in vitro study was made of 47 single-root teeth removed for periodontal reasons in the Oral and Maxillofacial Surgery Teaching Unit (Department of Medicine and Orofacial Surgery, Madrid Complutense University Dental School, Spain). The teeth were divided into three laser irradiation groups (250, 350 and 450 mJ) and a non-irradiated control group. The teeth were then immersed in an enrichment medium for 72 hours under conditions of anaerobiosis, with visual controls after 24, 48 and 72 hours. Posteriorly, microbiological cultures were made in blood agar to confirm the results of the visual inspections. Results: Increased percentage sterilization of the samples was recorded with increasing irradiation power - statistically significant differences being observed between all irradiated groups versus the controls. Conclusions: The Erbium:YAG laser exerts a sterilizing effect upon dental structures in vitro. This effect increases with increasing laser power ratings.