<prompt> In Angles classification for malocclusion, key tooth is:MB cusp of Permanent Max. 1st molarDB cusp of Permanent Max. 1st molarMB cusp of Permanent Max. 2nd molarMB cusp of Permanent Mand. 1st molar  <response>: Angles postulate was that the upper first molars were the key to occlusion and that the upper and lower molars should be related so that the mesiobuccal cusp of the upper molar occludes in the buccal groove of the lower molar. If the teeth were arranged on a smoothly curving line of occlusion and this molar relationship existed , then normal occlusion would result. Angle then described three classes of malocclusion, based on the occlusal relationships of the first molars:Class I: Normal relationship of the molars, but line of occlusion incorrect because of malposed teeth, rotations, or other causes.Class II: Lower molar distally positioned relative to upper molar, line of occlusion not specified.Class III: Lower molar mesially positioned relative to upper molar, line of occlusion not specified.Reference: Contemporary orthodontics, Proffit 6th ed page no 2 