Resin composite restorations are becoming have had a significant increase in popularity over the last few decades, and have become the patient’s preferred choice in filling material, due mainly due to their enhanced esthetics when compared to other restorations, as well as their ever-increasing durability. These factors have led to a large increase in demand from patients.1 As patient demand for this restorative material increases, so too do patient expectations for comfort and longevity in these restorations. An idyllic filling material would combine these effects with a perfect marginal seal, leaving no gap between the tooth structure and the restoration.2
According to a study by Stockton et al., “Imperfect bonding leaves a microscopic gap that allows the infiltration of bacteria, fluids, molecules and ions between the restoration and the tooth structure, commonly referred to as micro-leakage.”2 This gap is created by way of composite shrinkage during the process of polymerization, or “from mismatches between either the coefficients of thermal expansion of the tooth and the composite or between the elastic moduli of the tooth and the composite.”2 Most composite restorations will result in some level of micro-leakage, however the pulp of the tooth can withstand a small amount of leakage and remove the ions and fluid that make it through by way of the tooth’s own blood flow. If the leakage is significant enough, however, sensitivity, marginal discoloration3, and secondary caries can result, leading to possible failure of the restoration.2,
CAUSES OF MICROLEAKAGE
As previously stated, micro-leakage is mainly caused by shrinkage of the composite during polymerization. Bulk curing of composite results in a greater level of shrinkage.3 Along with shrinkage, several other factors contribute to micro-leakage. One such factor is where the restoration is being placed. Restorations with enamel margins tend to have a better seal, which usually results in a lower level of micro-leakage than restorations with margins purely in the dentin or cementum.4 For the same reasons, occlusal restorations had lower amounts of leakage than fillings at or apical to the cementoenamel junction (CEJ). Unfortunately, placement of composite apical to the CEJ is, at times, unavoidable. In such locations, it is difficult to polish the restoration and keep it completely isolated from oral fluid.2 Failure to do the latter can cause the bond to fail, resulting in micro-leakage. Failure may also be due to over-etching and drying, which both cause collagen fibril collapse, causing an incomplete bond.
Other factors leading to micro-leakage are operator error and pre-operative home whitening. New bonding and etching systems, each significantly different from the other, are released at an astounding rate. This has made it difficult for dentists to become proficient in each of these new systems.5 When used incorrectly, these systems become less effective, and the result...