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': 'Ugly duckling stage affects \nSelect and explain. \nA. Maxillary anterior teeth, B. Mandibular anterior teeth, C. Both maxillary and mandibular teeth, D. Vertical height of face', 'role': 'user'}, {'content': "Answer: A \nExplanation: The Broadbent's Phenomenon - Ugly Duckling Stage (8-11 years)\nAround the age of 8 years, a midline diastema is commonly seen in the upper arch, which is usually misinterpreted by the parents as a malocclusion. Crowns of canines in young jaws impinge on developing lateral incisor roots, thus driving the roots medially and causing the crowns to flare laterally. The roots of the central incisors are also forced together, thus causing a maxillary midline diastema. The period from the eruption of lateral incisor to canine is termed as the Ugly Duckling stage.\xa0It is an unaesthetic metamorphosis, which eventually leads to an aesthetic result. With eruption of canines, the impingement from the roots shifts incisally, thus driving the incisor crowns medially, resulting in closure of the diastema.\nTextbook of Orthodontics, Gurkeerat Singh, 2nd Ed, pg-46", 'role': 'assistant'}]