According to Edward H. Angle's classification of malocclusion, what is the defining characteristic of Class III malocclusion?

 # According to Edward H. Angle's classification of malocclusion, what is the defining characteristic of Class III malocclusion?

A) Normal relationship of the molars but malposed teeth

B) Lower molar distally positioned relative to the upper molar

C) Lower molar mesially positioned relative to the upper molar

D) Correct line of occlusion with rotated teeth

The correct answer is C. Lower molar mesially positioned relative to the upper molar.

Angle’s classification of malocclusion in the 1890s was an important step in the development of orthodontics because it not only subdivided major types of malocclusion but also included the first clear and simple definition of normal occlusion in the natural dentition. Angle’s 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. This statement, which 100 years of experience has proved to be correct except when there are aberrations in the size of teeth, brilliantly simplified normal occlusion.

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

Ref: Proffit, W. R., Fields, H., Msd, D. M., Larson, B., & Sarver, D. M. (2019). Contemporary Orthodontics, 6e: South Asia Edition-E-Book. Elsevier India.