Enamel is the hardest mineralized structure in the body; designed perfectly by nature to endure the greatest of mechanical, thermal and chemical insults in the oral cavity. Man is yet to make a material similar to it. In addition to its aesthetic qualities, natural healthy enamel is superior to most of the restorative material available. Most of its noble features are undoubtedly related to the underlying "dentin cushion" on which it rests. Dentin is a unique biologic tissue, composed of near perfect combination of organic and inorganic constituents, along with "fluid" components that provides the right cushioning for enamel, the hardest tissue found in the human body. In fact dentin absorbs all the shock from a variety of insults that enamel is subjected to in the oral cavity. Studies have shown that unsupported occlusal enamel could be attached internally to a restorative material via bonding and thus reinforced. This invitro study was designed to test the ability of four restorative materials having chemical or micromechanical bonding to tooth structure, to reinforce undermined occlusal enamel.