Non-clast cells start orthodontic root resorption in the periphery of hyalinized zones

Abstract

Previous research has indicated that orthodontically-induced root resorption is regularly associated with local trauma, most often with over-compression of the periodontal ligament (PDL). Recent research has revealed that the initial root resorption occurs in the periphery of the necrotic PDL, where mononucleated cells not stained by tartrate resistant acid phosphatase (TRAP), are the first cells to penetrate the root surface. The aim of the present transmission electron microscopic (TEM) investigation was to study in more detail the root surface during the initial penetration of cells into precementum and mineralized cementum. In 21 Wistar rats (age 40–45 days) the maxillary first molar was moved mesially by a closed coil spring for 6 and 12 hours, 1, 2, 3, 4, and 5 days. The results clearly indicate a role for mononucleated non-clast cells in the initial local removal of precementum and mineralized acellular cementum in the periphery not only near, but also at some distance from the compressed PDL.