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 an indication of onlay cast restoration? \nSelect and explain. \nA. Width of the lesion exceeds ½ the intercuspal distance, B. Strong, self-resistant cusps are there, C. Occlusal surfaces are not to be changed, D. The tooth is not to be used as an abutment', 'role': 'user'}, {'content': 'Answer: A \nExplanation: MOD Onlay\n\nAn indirect restoration, which is partly intracoronal and partly extracoronal that covers all the cusps of a posterior tooth.\nOnlay has cuspal protection as the main feature.\nThe use of an onlay keeps the stresses at a low level and creates no hazard to the remaining tooth structure.\n\nIndications\n\nIf the width of the lesion is 1/3 to 1/2 the intercuspal distance - cuspal protection is to be considered.\nWidth of the lesion exceeds 1/2 the intercuspal distance - cuspal protection is mandatory.\nIf the length : width of the cusp is more than 1:1, but not exceeding 2:1 - cuspal protection is to be considered.\nIf the length : width of the cusp is more than 2:1 - cuspal protection is mandatory.\nWhen there is need to change the dimension, shape and inter relationship of the occluding tooth surfaces.\nAbutment teeth for RPD and fixed prosthesis.\nWhen wear facets that exceed the cusp tips and triangular ridge crests facially / lingually are to be included.\n\nMDS Prep Bytes (Cast Restoration – Inlay)', 'role': 'assistant'}]