Smear Layer
A thin layer of grinding debris—comprising disrupted collagen, hydroxyapatite crystals, and oral bacteria—deposited on a prepared dentine surface by rotary instruments.
Full Definition
The smear layer is generated whenever a bur or other cutting instrument contacts dentine, producing a 1–5 µm thick amorphous coating that occludes dentinal tubule orifices (smear plugs) and reduces dentinal permeability. Its management is pivotal in adhesive dentistry: total-etch systems remove it completely with phosphoric acid, self-etch adhesives dissolve it and incorporate it into the bond interface, and some glass ionomer systems condition rather than remove it. The smear layer's presence or absence profoundly influences bond strength and post-operative sensitivity outcomes. Editors should be aware that 'smear layer' is a two-word open compound and should not be hyphenated.
Usage
Usage note: Write as two unhyphenated words: 'smear layer'. Distinguish 'smear layer' (surface coating) from 'smear plug' (the portion occluding tubule openings).
In Context
- "Self-etch adhesives modify rather than remove the smear layer, incorporating its components into the bonding interface." — Adhesive systems review article
- "Complete removal of the smear layer by phosphoric acid was confirmed by SEM before bonding procedures commenced." — Laboratory methods section