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': 'Carex is a fluoride containing varnish with the following characteristics except- \nSelect and explain. \nA. 0.3 - 0.5  ml of varnish equivalent to 6.9-11.5 mg F is required to cover the full dentition, B. Application is done first on the lower arch and then on the upper arch, C. Contact between varnish and tooth surfaces for about 2 hours is maintained for  prolonged  interaction  between fluoride and enamel, D. Before carex application, teeth are dried but not isolated with cotton rolls', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Carex\xa0 is another\xa0 fluoride varnish and contains a lower fluoride concentration than Duraphat (1.8% fluoride) and has efficacy\xa0equivalent to that of Duraphat as a caries -preventive agent.\xa0\nTechnique of varnish application :\n\nAfter prophylaxis, teeth are dried, but not isolated with cotton rolls since varnish sticks to cotton.\xa0\nA\xa0 total of 0.3\xa0- 0.5\xa0 ml of varnish equivalent to 6.9-11.5 mg F is required to cover the full dentition.\xa0\nApplication is done first on the lower arch and then on the upper arch, using a single tufted\xa0 small brush, starting\xa0 with the\xa0proximal surfaces.\xa0\nAfter application, the patient is made to sit with the mouth open for 4 minutes before spitting to let Duraphat set on teeth which is\xa0 further\xa0 enhanced\xa0 by\xa0 saliva. (FIuorprotector sets faster than Duraphat).\xa0\nPatient is asked not to rinse or drink anything at all for one hour and not to eat anything\xa0 solid\xa0 but take\xa0 liquids\xa0 and\xa0semisolids only till the next morning, so that contact between varnish and tooth surfaces for about 18 hours is maintained\xa0for\xa0 prolonged\xa0 interaction\xa0 between fluoride and enamel.', 'role': 'assistant'}]