page_title: Dentine bonding agents
section_title: Smear layer and its role in bonding
hierarchical_section_title: Dentine bonding agents / Dentin Bonding / Smear layer and its role in bonding
caption_attribution_description: English: Scanning electron micrograph of a smear plug blocking the entrance of a dentinal tubule. SP, smear plug. (From Sturdevant Art and Science of Operative Dentistry, 7th edition, p155)
context_page_description: Also known as a "bonderizer" bonding agents are resin materials used to make a dental composite filling material adhere to both dentin and enamel.
  Bonding agents are often methacrylates with some volatile carrier and solvent like acetone. They may also contain diluent monomers. For proper bonding of resin composite restorations, dentin should be conditioned with polyacrylic acids to remove the smear layer, created during mechanical treatment with dental bore, and expose some of the collagen network or organic matrix of dentin. Adhesive resin should create the so-called hybrid layer. This layer is an interface between dentin and adhesive resin and the final quality of dental restoration depends greatly on its properties.
  Modern dental bonding systems come as a “three-step system”, where the etchant, primer, and adhesive are applied sequentially; as a “two-step system”, where the etchant and the primer are combined for simultaneous application; and as a “one-step system”, where all the components should be premixed and applied in a single application.
context_section_description: Smear layer refers to a layer of debris on the inorganic surface of substrate which comprises residual inorganic and organic components. This layer is produced whenever the tooth structure undergoes a preparation with a bur.
  Smear layer will fill the orifices of the dentinal tubules, hence forming smear plugs. These smear plugs decrease dentin permeability by 90% and the smear plug alone can prevent adhesive resin penetration into dentinal tubules. The thickness of smear layer can range from 0.5-2 µmeter and for the smear plug, 1 to 10 µmeter.
  Smear layer poses some threat for optimal bonding to occur. That is why it needs to be removed. For example, smear layer needs to be removed prior to bonding by etch-and-rinse (total etch) adhesives.  This will lead to thicker hybrid layer and long, denser resin tags which results in better bond strength.
caption: Scanning electron micrograph of a smear plug blocking the entrance of a dentinal tubule. SP, smear plug. (From Sturdevant Art and Science of Operative Dentistry, 7th edition, p155)
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