The composite is a system composed of a mixture of two or more macromolecules which are essentially insoluble in each other and differ in form. The composite material’s properties are superior to those of its individual components, e.g., fiberglass has a resin matrix which is reinforced by glass fibers. The resulting composite is harder and stiffer than the resin matrix material, but less brittle than glass. Examples of natural composite materials are tooth enamel and dentin. Matrix is made of collagen, with hydroxyapatite crystals acting as fillers. Though the early composites were developed for restorative purposes their uses subsequently expanded to include provisional, restorations, luting, etc. One of the initial problems when resin restoratives were introduced was microleakage which resulted from the shrinkage of the resin while curing. The problem was overcome to a great extent by the introduction of the acid etch technique by Buonocore in 1955.