microleakage in class ii composite restorations ... - ePrints@USM

However, (Tay and Pashley, (2005) stated that during the early stages of enamelbonding, few researchers understood that bur-cut tooth surfaces were covered by smearlayer. This layer masks the underlying enamel and could not be rinsed off with water.Resins applied to smear layer covered surfaces bonded relatively to weak smear layer,rather than to the underlying hard tissues. Therefore, the bond strength of the earlyadhesive systems was weak. As smear layers are acid labile, the occurrence of enamelsmear layer did not present a challenge in bonding that involves the use of phosphoricacid etching step. Nevertheless, the presence of enamel smear layer may become apotential problem when self-etch adhesives are applied on bur-cut enamel. This isrelated mainly to the acidity of self-etch adhesive used.Despite the lack of difference between bond strengths in grounded and intact enamelafter phosphoric acid etching, the ultrastructure of the resin-enamel interface inphosphoric acid-etched uncut enamel remains the most variable and by far the mostdifficult to interpret. This is due to the presence of aprismatic and prismatic etchingfeatures along the same interface (Tay and Pashley, 2005).2.2.3 Bonding to DentinBonding to dentin is more challenging than enamel, because of the complex andhydrated structure of dentin. Dentin is an intricate bonding substrate, and in order toobtain good bonding to dentin, an extended knowledge of the structure and compositionof the bonding substrate is indispensable. While enamel makes a uniform bondingsubstrate that consists of almost 90% inorganic material volume with a very smallamount of intrinsic water, dentin is a complex composite material with less than 50%inorganic material and high water content volume (21%). Moreover, the tubular buildup of dentin and the resulting outward pulpal water current in vital teeth turn dentin into21