High-resolution transmission electron microscopy is one of the few techniques where it is possible to investigate dental enamel at the individual crystallite level. By measuring interfringe spacings in lattice images of apatite crystallites during a through-focal-series, we were able to identify individual crystallites of fluorapatite from hydroxyapatite, even though their α-axis parameters differ by only 0.5%. We describe both an axial 3-beam and 7-beam method for determining α-axis parameters in apatite crystallites with a precision of < 0.1%. This provides a new method for investigating the interaction of fluoride with apatite crystallites in dental ename