Root resorption: the possible role of extracellular matrix proteins

During maxillary permanent canine eruption, the deciduous canine root is selectively resorbed while the adjacent permanent lateral incisor root is left intact. An understanding of this selective resorption could provide insights into the cause of moderate to severe iatrogenic root resorption during orthodontic tooth movement. This study investigated the possible role of extracellular matrix (ECM) proteins in the selective resorption process. The spatial expression patterns of 2 ECM proteins, osteopontin (OPN) and bone sialoprotein (BSP), were assessed within the periodontal ligament (PDL) surrounding root surface areas of deciduous and permanent teeth. Intact and resorbed root surface areas from 14 deciduous roots and intact root surface areas from 12 permanent tooth roots were examined. In the deciduous roots, BSP and OPN were locally expressed in the cell layer adjacent to the root surface and most intensely concentrated in areas surrounding and within odontoclasts proximal to the resorptive lacunae. In contrast, BSP and OPN were expressed in a generalized pattern throughout the PDL of permanent roots. These preliminary findings suggest a differential expression of ECM proteins on deciduous versus permanent tooth roots, which could act as a signal for selective odontoclast adhesion to, and subsequent resorption of, deciduous root surfaces.