Primary teeth show less protecting factors against root resorption.

Background: Physiological root resorption differentiates primary from permanent teeth. The understanding of what protects and regulates root resorption might help to develop therapies to its control.

Aim: To verify the presence and distribution of ECRM and the expression of CK14, OPG, TRAP and COX-2 in the periodontal ligament (PDL) of human primary and permanent teeth. Design.  Eight primary teeth undergoing physiological or pathological root resorption and 4 permanent teeth were immunohistochemically processed for CK14, TRAP, COX-2 and OPG expression.

Results: PDL from primary and permanent teeth showed similar morphological features; however, fewer ECRM clusters and higher immunoreactivity to CK14 were found in primary PDL. In permanent teeth, ECRM were distributed along the entire PDL tissue. Howship's lacunae were found only in primary teeth, associated with the presence of TRAP-positive cells and increase in COX-2 expression. OPG expression in primary PDL was detected in nonresorptive cervical areas and in lacunae showing reparative tissue. It was observed higher expression of OPG in all permanent teeth when compared to primary specimens.

Conclusions: It may be concluded that PDL from primary teeth shows less ECRM clusters and lower expression of OPG. These features may be associated with lower protection against root resorption in primary teeth.