The Role of RANKL and Involvement of Cementum in Orthodontic Root Resorption

Orthodontic root resorption (ORR) is an unintended side effect of orthodontic treatment, and severe ORR can affect treatment outcome. Receptor activator of nuclear factor kappa-B ligand (RANKL) has been detected in the resorbed cementum and periodontal (PDL) tissues exposed to excessive orthodontic forces. Recent studies have demonstrated that PDL cells and cementoblasts express RANKL that may play a role in ORR during orthodontic tooth movement. It is known that the hardness of cementum in human maxillary premolars differs among individuals. Furthermore, this difference has been reported to be attributed to differences in the calcium (Ca)/phosphorus (P) ratio. A correlation was observed between the Vickers hardness and Ca/P ratio of the cementum in the apical region. These findings suggest that cementum hardness and the Ca/P ratio may be indirectly involved in ORR caused by orthodontic forces. In this review, it aims to identify the role of RANKL and involvement of cementum in ORR.