How much root formation is complete when tooth erupts into the oral cavity?

 # How much root formation is complete when tooth erupts into the oral cavity?

A. 100%

B. 75%

C. 60%

D. 50%

 

The correct answer is B. 75%.

The eruption of a permanent tooth can be delayed if its primary predecessor is retained too long. When this happens, the obvious treatment is to remove the primary tooth. As a general guideline, a permanent tooth should erupt when approximately three-fourths of its root is completed. If root formation of the permanent successor has reached this point while a primary tooth still has considerable root remaining, the primary tooth should be extracted.

Reference: Contemporary Orthodontics, Fourth Edition, Proffit, Page 249

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