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Abstract:Objective: The purpose of this study is to make use of scanning electron microscopy in order to comparatively analyze the morphological alterations to human and bovine enamel and dentin. Earlier data: Many a morphological study involving Er:YAG laser can be found in the literature. Still, not a single study comparing the effects of this infrared laser in human and bovine teeth has been reported. Materials and Methods: Thirtytwo slices of human and bovine enamel and dentin were evenly divided into four groups. With the exception of the control group, the samples were irradiated with Er:YAG laser, focused at a distance of 12 mm and 10-hertz frequency, with 150, 250, and 350 mJ of output energy per pulse for 10 seconds. After irradiation all specimens were observed under a scanning electron microscope. Results: There was practically no morphological difference for those samples that underwent the 150 mJ/pulse irradiation. The dentin exposed to 250 mJ had few open dentinal tubules. These were seen in enamel after a 350 mJ irradiation, in which the energy was able to reach the dentin. Conclusions: The breadth of this study allows us to state that the pattern between the species grew more heterogeneous as the energy density was increased and that irradiation with 150 mJ/pulse resulted in greater likeness in human and bovine enamel and dentin. Z1 Z2 Z3Sketching of the classification proposed by Lizarelli and Bagnato [6], in which Z1 -center of the micro-cavity, the ablated area; Z2 -intermediate zone that may or may not exist; Z3 -region unaffected by irradiation