External root resorptions and orthodontic forces: correlations and clinical consequences.

Orthodontically induced root resorption is the most frequent unwanted side effect of orthodontic tooth movement that is unavoidable. This is due to the fact that both bone remodelling and root resorption are based upon a sterile inflammatory process, initiated by force application. In addition to individual factors that have a bearing on the amount of resorption, the type and magnitude of orthodontic forces play a major role. In animal and human experiments it could be shown that continuous forces, as produced by materials with pseudo- elastic characteristics, seem to produce more resorptions than discontinuous forces. Recent research shows that the magnitude of the orthodontic force up to 200cN is probably not decisive for root resorption.