When dentin is exposed, the pulp and the oral environment communicate through the dentinal tubules. The density of the dentinal tubules is an important determinant in dentinal permeability. The purpose of this study was to investigate, with an indirect method, whether tubular density is higher on the axial or on the cervical wall in cavities in restorative dentistry. The results obtained indicated that density of tubules on the cervical wall was usually higher than that on the axial wall. Clinically, the cervical wall of restorations therefore warrants the same meticulous protection routinely provided to the pulpal wall.