Immunohistochemical Localization of Root-resorption-protecting Factors in Primary Human Periodontal Ligament

A primary tooth suffers physiological root resorption leading to its exfoliation and eruption of a succedaneum permanent element, being that feature which differentiates deciduous from permanent teeth. Osteoprotegerin (OPG) inhibits differentiation and stimulates apoptosis of clastic cells. Epithelial cell rests of Malassez (ECRM) are thought to be resting cells that may be involved in periodontal ligament (PDL) space maintenance and protection against root resorption. OBJECTIVES: the aim of this study was to verify the presence and distribution of ECRM clusters as well as the expression of OPG, TRAP and COX-2 in the PDL of human primary and permanent teeth. METHODS: 4 deciduous teeth undergoing physiological root resorption, 4 primary teeth undergoing pathological inflammatory root resorption as a consequence of caries progression and 4 permanent teeth (root resorption negative controls) were collected and immunohistochemically processed for CK14, TRAP, COX-2, and OPG expression. RESULTS: PDL tissues from primary and permanent teeth showed similar morphological features. However, fewer ECRM clusters and higher immunoreactivity for CK14 of these agglomerates were found in primary PDL, mainly in cervical areas. In permanent specimens, ECRM clusters were distributed within the PDL tissue along the entire root surface. Howshipxs lacunas were found only in deciduous specimens, always associated to the presence of TRAP-positive cells and increase in COX-2 expression, independent of the type of ongoing resorption. OPG expression in primary PDL was located only in non-resorptive cervical areas or in lacunas showing reparative tissue. It was observed higher expression of OPG in all permanent specimens when compared to primary teeth. CONCLUSION: it may be concluded that PDL from deciduous teeth shows less ECRM clusters and lower expression of OPG. ECRMs in primary PDL showed higher immunoreactivity for OPG. These features may be associated to lower protection against root resorption in deciduous teeth when compared to permanent teeth.