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': 'Which of the following is the best indication of the appliance given in the color plate? \nSelect and explain. \nA. Posterior crossbite and finger sucking habit, B. Skeletal posterior crossbite, C. Rapid maxillary expansion, D. Space maintainer', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In children with ﬁnger/thumb sucking habit and posterior crossbite, quad helix is one of the most\xa0useful appliances to intercept the habit and correct the posterior crossbite.\nQuad helix is made of two anterior and two posterior helices; the anterior helices are adapted close to the maxillary palatal\xa0mucosa and in this way, it reduces the space in the oral cavity. When child tries to place the thumb or ﬁnger into the oral cavity, it will touch the helices and it will cause an unpleasant sensation and reaction\xa0in the child. This acts as a reminder for the child.\nAt the same time, this appliance tips the posterior teeth in labial direction and corrects the posterior\xa0crossbite, which is caused by the altered buccinator mechanism.', 'role': 'assistant'}]