Description and Composition of the Smear Layer
- The smear layer is a thin layer of debris on dentinal walls after cavity preparation.
- It consists of organic and inorganic components, including collagen residues, glycosaminoglycans, dentine particles, residual pulp tissue, saliva, and bacterial components.
- There are two distinct layers of the smear layer: a loosely adherent layer covering the canal wall and a strongly adherent layer that occludes the dentinal tubules.
- The smear layer can be up to 5 micrometers thick and can hinder the penetration of disinfecting agents into dentinal tubules.
Effects of the Smear Layer
- The smear layer mechanically hinders bacterial invasion into dentinal tubules.
- Acid produced by microorganisms may dissolve the smear layer, allowing bacteria to pass into dentinal tubules.
- The smear layer acts as a protective diffusion barrier.
- Removing the smear layer improves the bond strength of certain sealer cements to dentin.
- Bacterial penetration into dentinal tubules can lead to various dental diseases.
Removal of the Smear Layer
- The smear layer should be removed to ensure effective bonding, disinfection, and obturation.
- Failure to remove the smear layer can compromise the bond strength and sealing ability of restorative materials.
- Various endodontic irrigation techniques, such as sodium hypochlorite, EDTA, and citric acid, are used to remove the smear layer.
- Paste lubricants and dentine conditioners can also aid in smear layer removal.
Smear Layer Removal Techniques
- Irrigation with 5% sodium hypochlorite followed by 17% EDTA effectively removes the smear layer.
- Scanning electron microscopy can be used to evaluate the effectiveness of smear layer removal.
- The use of 5.25% sodium hypochlorite alone is sufficient to remove the smear layer.
- In situ photo-polymerization and polymerization-shrinkage phenomena are involved in smear layer removal.
Influence of Smear Layer on Dentin and Microbial Efficacy
- Bacteria can invade dentinal tubules through the smear layer.
- Smear layer removal increases dentin permeability.
- The presence of the smear layer affects the adhesion of sealer cements to dentin.
- The smear layer does not impair the antimicrobial efficacy of root canal irrigants.
- AH sealer performs better than RS sealer in the absence of the smear layer.
In dentistry, the smear layer is a layer found on root canal walls after root canal instrumentation. It consists of microcrystalline and organic particle debris. It was first described in 1975 and research has been performed since then to evaluate its importance in bacteria penetration into the dentinal tubules and its effects on endodontic treatment. More broadly, it is the organic layer found over all hard tooth surfaces.
