ETCHING AND ITS IMPORTANCE IN ADHESIVE DENTISTRY

Adhesion to tooth structure by composite restorations is achieved by means of acid etching.Acid etching causes roughening of the surface leading to formation of microporosities into which the composite will bond micromechanically.However it is important that we do not forget the significance of this acid-etching and the correct method of doing so. Here are a few things to keep in mind while acid etching.

Acid etching of tooth surface is achieved by applying PHOSPHORIC ACID on the required tooth surfaces. This acid used is of 37%conc. and applied for 15 seconds since any amount of time beyond this would produce the same amount of roughness.Nowadays instead of the liquid etchant gel etchants are widely available which are more viscous and more user friendly.After gel application the surfaces should be thoroughly washed n dried to achieve a frosty appearance.

The most important thing that one should remember is that though many dentinal adhesives are now available, etching dentin is not as reliable as etching enamel because:
*Dentin is a dynamic tissue.
*It consists of considerable amount of organic tissue compared to enamel.
*It has close proximity to pulp tissue
Hence one must be very careful when etching dentin.As far as possible etching must be restricted to enamel, this is because too much etching or drying can lead to collapse of the collagen fibrils present in the tubules, this further can lead to failure of the restoration due to microleakage and hence secondary caries.

A guideline for the critical steps in dentin bonding would be:
-Adequate isolation to avoid salivary contamination and interference in the micromechanical bonding.
-Adequate pulp protection especially in deep cavities.
-Acid etching for optimum time of 15 secs with 37%conc. phosphoric acid.
-Avoid over-drying of the dentinal tubules.
-Appropriate application of selected bonding agent.