<prompt> Orthodontic brackets attached directly to the tooth are retained by a:Compressive forceHydrostatic forceMechanical bondChemical bond  <response>: Bonding of resins bracket-adhesive to etched enamel is based on micromechanical interlocking produced by the resin tags that are formed by the penetration of the resin into micro-porosities created in the surface of the enamel after acid etching.The essential components of composite resin are a resin matrix, filler particles, a coupling agent and a curing system.Key comment:The chemical method of bonding tried using GIC failed to withstand the compressive, shear stress in orthodontic bracket bonding. Textbook of ORTHODONTICS Sridhar Premkumar 