The aim of this in vitro study was to assess the thickness of secondary dentin separating dental pulp from the occlusal surface in equine incisors. The dentin thickness was measured in 41 horse incisors by cone bean computed tomography and in 10 incisors by radiovisiography with an instrument introduced into the pulp space. The mean thickness of subocclusal secondary dentin was 8.38 mm ± 2.62 (range of 4.2-13.9). Owing to great variation in the thickness of subocclusal secondary dentine between individual incisors, great care should be taken when grinding equine incisors.