Treatment of dental caries as one of the most economically relevant human disease can rely only on the understanding of the caries progress through dentin. As it can be seen from the frequency of tooth decay among different animals, its existence and progress strongly depend on the mineral part arrangement, especially on the orientation of the hydroxyapatite (HA) crystals, which resist the mechanical and chemical stress very anisotropically. It is therefore not surprising that different attempts have been made to unravel the mystery of dentin growth and HA crystals arrangement. By dentin irradiation with gamma-rays, very stable CO3 − radicals are generated within HA crystals which due to the anisotropic magnetic coupling enable detection of their orientational distribution via angular-dependent electron paramagnetic resonance spectroscopy. The latter can be significantly enhanced if the whole angular dependence can be fitted simultaneously within certain dentin structural models. As shown in this work, even subtle information like the orientation of the tubules relative to the pulp or the orientation of HA crystals relative to the tubules can be extracted. The sensitivity to different sample geometry is discussed to provide the best possible characterization.