THE SMEAR LAYER REVISITED

The smear layer is created on hard tissues of the teeth whenever they are cut with hand or rotary instruments. This thin (1-2 microns) layer of denatured cutting debris is very tenacious and is often the surface to which restorative materials are luted. The solubility characteristics, chemical reactivity and the structure-function relationships of this layer have not been well-defined. During creation of the smear layer, cutting debris is forced into variable distances into dentinal tubules. These so-called smear plugs, together with the smear layer decreases dentin permeability, dentin sensitivity and surface wetness. Bonding adhesive resins to smear layers appears to limit the theoretical bond strength unless the smear layers are loosened or partially removed. While confusion persists whether the smear layer should be kept or removed in restorative dentistry, removal of this layer is important for the success of endodontic treatment. Its removal is obtained using chemical solutions during root canal preparation such as Ethylene Diamine Tetra acetic acid (EDTA) preparations, combination of EDTA and sodium hypochlorite solutions, organic acids and lasers. The aim of this paper is to briefly review general concepts concerning the smear layer: its structure and composition, role of smear layer in restorative dentistry and endodontics.