Human tooth decays more rapidly and is subject to severe cavities if not properly treated, but dentin still acts as a protective layer and supports the crown of the tooth. Dentin is a mineralized connective tissue with an organic matrix of collagenous proteins. Dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border. The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900 nm near the dentino-enamel junction. Although they may have tiny side-branches, the tubules do not
Smear layer Smear layer The smear layer is a layer of microcrystalline and organic particle debris that is found spread on root canal walls after root canal instrumentation. It was first described in 1975 and much research has been performed since then to evaluate its importance in assisting or preventing the penetration of bacteria into the dentinal tubules. More broadly, it is the organic layer found over all hard tooth surfaces. Early studies of dentinal walls after cavity preparation performed by Brännström and Johnson (1974) showed the presence of a thin layer of debris that was 2 to 5 micrometres thick. In