This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Orthodontic brackets attached directly to the tooth are retained by a: \nSelect and explain. \nA. Compressive force, B. Hydrostatic force, C. Mechanical bond, D. Chemical bond', 'role': 'user'}, {'content': 'Answer: C \nExplanation: 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.\nThe essential components of composite resin are a resin matrix, filler particles, a coupling agent and a curing system.\n\n\u200bKey comment:\nThe chemical method of bonding tried using GIC\xa0failed to withstand the compressive, shear stress in orthodontic bracket\xa0bonding.\xa0\nTextbook of ORTHODONTICS Sridhar Premkumar', 'role': 'assistant'}]