Bonding is a procedure for ‘gluing’ a composite resin filling material with tooth structure. The steps usually involve creating an etched surface on the tooth enamel and sometimes dentine to increase the surface area for adhesion and this creates micro tags for miromechanical retention of the filling material. Once the enamel is etched a bonding agent is applied to the tooth cavity and set with a blue light. The cavity or tooth surface is now ready to take the filling which once applied and shaped has the blue light on it to cause the material to set hard. This is an adhesive restoration and means that usually there is less drilling because the cavity can be shaped with minimal destruction of sound tooth structure. With a metallic (amalgam) fillings, the cavity needs to be undercut i.e. the bottom of the cavity needs to be wider than the top to create mechanical retention; a white filling is chemically bonded to the tooth structure.