An apparatus for measuring a surface topography of a patient's teeth may include an optical probe, a light source configured to generate incident light, and focusing optics configured to focus one or more wavelengths of the incident light to a fixed focal position external to the optical probe, wherein the fixed focal position is fixed relative to the optical probe. The apparatus may further include a light sensor configured to measure a characteristic of returned light generated by illuminating the patient's teeth with the incident light and a processing unit operable to determine the surface topography of the patient's teeth based on the measured characteristic of the returned light.