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': 'Average bond strength of second generation dentin bonding agents: \nSelect and explain. \nA. 2-5 MPA, B. 12-18 MPA, C. 20-23 MPA, D. 25-30 MPA', 'role': 'user'}, {'content': 'Answer: A \nExplanation: SECOND GEN - Contains halophosphorus esters of unfilled resins.\nMechanism of bonding Is by ionic bond to calcium by chlorophosphate groups.\nEg: scotchbond, bondlite.\xa0\nDisadvantages:\xa0\n\nAgain poor bond strength 2-5 MPA.\xa0\nHydrolysis of bond.\xa0\nBonds to smear layer.\xa0\xa0\n\nReference-Sturdevant 6th ed\xa0 Pg: 116', 'role': 'assistant'}]