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

clinically undetectable passage of bacteria, fluids, molecules, or ions between a cavitywall and the restorative material applied to it (Kidd, 1976).Nanoleakage: occurs when the voids are so small that only water and some smallmolecules can pass. The difference between both types is somewhat arbitrary, since bothmay occur simultaneously (Dorfer et al., 2000).Many different laboratory techniques have been used to demonstrate microleakage.These techniques include the use of bacteria, compressed air, chemical and radioactivetracers, neutron activation analysis, artificial caries technique, scanning electronmicroscope, and perhaps the most common of all, dye penetration. Investigation ofleakage has been carried out both in vivo and in vitro, but the latter is more common. Invitro experiments can be divided into two categories, one that uses a clinical simulationand the other one that is purely a test of the behavior of materials (Kidd, 1976).2.1.2 Factors Contributing to MicroleakageSeveral factors can affect the integrity of the tooth-restoration interface and cancontribute to microleakage. Among these are:• Polymerization shrinkage and cavity configuration factor• Hydroscopic expansion• Light polymerization concepts and units• Thermal cycling and occlusal stresses2.1.2.1 Polymerization Shrinkage and Cavity Configuration FactorPhoto-polymerization is now a widely accepted initiation mode for the clinicalhardening processes with a wide range of biomaterials including dental adhesives andrestorations. The polymerization of dental composite resins is inevitably accompaniedby shrinkage. Due to this, molecular densification during the polymerization process of8