INTRODUCTIONComposite resins have provided an important esthetic alternative to amalgam restorations for over sixty years.1 An obstacle to this method of restoration is the phenomenon microleaks. Microleaks result from imperfect bonding, leaving a microscopic gap, allowing molecules and ions to flow between the tooth and the restoration interface.2 Lack of margin integrity has been implicated in complaints of tooth sensitivity. patients, the formation of secondary caries, corrosion of dental materials and aesthetic problems. staining at the margin.2 This article will discuss the basis and discovery of microleakage, the causes and effects of the phenomenon, including polymerization shrinkage, tooth whitening agents and some etching techniques, as well as methods prevention that the operator can use to minimize microleaks in the posterior composite. restorations. The study of microleaks dates back to 1912, when Dr. WE Harper first studied the phenomenon.3 Natural teeth were simulated in the study using steel matrices containing Class II preparations. A tube was then secured through the pulpal floor of the matrices and air pressure ranging from 3 to 30 psi was applied. The emergence of air bubbles from the margins indicates that a microleak has occurred.MATERIALS AND METHODSCure shrinkageA comparison of various composite resinsA research study comparing 17 different flowable and non-flowable composite resins was carried out.4 Parameters Measured include: shrinkage (vol%), contraction stress (Mpa) and tensile modulus (GPa). Figure 1 describes the materials tested. Shrinkage was measured by mercury dilatometry. Contraction stress measurements were obtained using a tensilometer device as shown in Figure 2. Each component ...... middle of paper ...... sin coating on the microleaks of the restorations of class V after treatment with carbamide peroxide in vitro. Opera Dent. 2010; 35(6):634-40.7. Ceballos L, Osorio R, Toledano M, Marshall GW. Microleaks in composite restorations after acid or Er-YAG laser cavity treatments. Tooth Mater. 2001; 17(4):340-6.8. Collins LZ, Maggio B, Gallagher A, York M, Schäfer F. Safety evaluation of a new whitening gel containing 6% hydrogen peroxide and a commercially available whitening gel containing 18% carbamide peroxide in a clinical study with exaggerated use. J Dent. 2004; 32 Supplement 1:47-50.9. Crim GA. Postoperative whitening: effect on microleaks. Am J Dent. 1992; 5(2):109-12.10. Da Silva Dominguez L, Martinez-Insua A, Rivera FG, Santana-Penin UA. Differences in bonding to acid-etched or Er:YAG laser-treated enamel and dentin surfaces. J Prosthesis Tooth. 2000; 84(3):280-8.