OBJECTIVES: To quantify differences in the etch quality of enamel within and between human teeth, which has not previously been attempted. MATERIALS AND METHODS: The buccal right and left halves of 27 extracted human teeth were randomly allocated to scanning electron microscopy (SEM) or micro-computed tomography (CT) for evaluation. The buccal surfaces were pumiced, etched with 37% phosphoric acid gel etchant for 15 seconds, rinsed, and air dried. Each tooth was divided into three regions (incisal, middle, and cervical) and viewed after etching at 1200 magnification with SEM. The CT scans were taken before and after etching to calculate apparent and material mineral densities. RESULTS: SEM showed greater aprismatic enamel and poorer etch quality (ie, significantly less percentage enamel) for the posterior than anterior teeth and for the cervical region than for the incisal and middle regions of all teeth. Although there were no density differences prior to etching, CT demonstrated that etching increased material density significantly more for the anterior than posterior teeth. Prior to etching, the enamel in the cervical regions was significantly less dense than the enamel in the middle or incisal regions. Etching significantly increased the material density of all three regions, which decreased initial regional differences. After etching, the apparent density of the cervical region remained significantly lower than the densities of the other two regions. CONCLUSIONS: Based on SEM and CT, there is greater aprismatic enamel and inferior etch quality in the cervical regions of all tooth types and is clinically significant in explaining the failure of sealant retention and the propensity for white spot lesions.