Dentin bonding refers to process of bonding a resin to conditioned dentin, where mineral component is replaced with resin monomers to form a biocomposite comprising dentin collagen and cured resin. The adhesive-dentin interface forms a tight and permanent bond between dentin and composite resins.
It can be accomplished by either etch-and-rinse (total etch) or self-etch adhesives. In etch-and rinse, acid will dissolve the minerals to a certain depth and leaves the highly porous dentinal collagen network suspended in water. Then, the collagen network is infiltrated with resin monomers. After chemical polymerization of these monomers happen, activated by light cure, it will result in a polymer-collagen biocomposite, commonly known as the hybrid layer:
The mechanism of action is explained below:
a) Application of acid to dentin will result in partial/total removal of smear layer and demineralization of the dentin.
b) Acid will demineralize the intertubular and peritubular dentin, and then open the dentinal tubules while exposing the collagen fibres, hence increasing the microporosity of intertubular dentin.
c) Dentin will be demineralized by up to approximately 7.5 µmeter, depending on the type of acid used, time of application and concentration.
d) Primer system is designed to increase critical surface tension of dentin, which gets decreased after etching of acid.
e) Bonding mechanism is when:
# When primer and bonding resin are applied to etched dentin, they penetrate the intertubular dentin, forming hybrid layer.
# They also penetrate and polymerize in open dentinal tubules, forming resin tags.
Moist bonding technique has been shown repeatedly to enhance bond strengths of etch-and-rinse adhesives because water preserves the porosity of collagen network for monomer interdiffusion.