Apical External Root Resorption and Repair in Orthodontic Tooth Movement: Biological Events

Table 2

Classification of degree of external root resorption (based on [4, 7, 23, 24]).

Mild	Apical root resorption less than 2 mm of the original root length
Moderate	Apical root resorption greater than 2 mm but less than one-third of the original root length
Severe	Root resorption exceeding 4 mm or one-third of the original root length