High resolution TEM made it possible to study acid dissolution of biological and synthetic apatite crystals at the lattice pattern level. It was shown that acid dissolution starts at the dislocation level and proceeds more frequently according to lattice families with large d spacings, i.e., (100), (110), (101) and equivalents. Acid dissolution is preferential according to the c axis, due to the existence of dislocations and probably to variations occurring in the composition and organization of the solid phase. It was hypothesized that Mg ions could help organizing a nucleation phase remaining in the central part of mature crystallites and that incorporation of fluoride ions to the lattice, related to dislocations, could stop diffusion process and progress of dissolution.