Expression of Osteoprotegerin (OPG) and Receptor Activator of Nuclear Factor-kB Ligand (RANKL) on root surface after different extra-oral dry times

Background: The current International and National Guidelines recommend that avulsed teeth be replanted as soon as possible to prevent desiccation and subsequent necrosis of the periodontal membrane. The extra-alveolar time prior to replantation has been found to be the most significant factor in determining the type of periodontal healing following this injury. Similar to orthodontic tooth movement and primary root resorption, it is assumed that periodontal healing is regulated by the molecular signalling system of osteoprotegerin (OPG) and receptor activator of nuclear factor-kB ligand (RANKL). The aim of this study was to investigate the expression and distribution of OPG and RANKL on root surfaces of teeth after exposure to different extra-oral dry times. Methods: Human teeth were extracted, left to air-dry for <5, 30 and 60 minutes prior to fixation. Immunohistochemistry was then performed on decalcified, paraffin-embedded longitudinal sections using antibodies raised against human OPG and RANKL. Secondary antibody horseradish-peroxidase labelling with haematoxylin as counterstain was used to visualise the expression of these antigens at the cervical, middle and apical regions of the root under light microscopy. Results: OPG was detected in the cementoblasts and periodontal ligament fibres with no statistical significance across the different dry times and regions (p>0.05). Five of the 8 specimens in the 60 minutes group had reduced or no RANKL immunoreactivity compared to the <5 or 30 minutes groups although this was not significant (p>0.05). Median RANKL scores were lower than that for OPG, with statistical significance noted at the apical region in the 60 minutes group (p<0.05). Conclusion: The expression for RANKL was consistently weaker than that for OPG at all dry times and locations. While OPG immunoreactivity did not differ significantly in all dry time groups and regions, RANKL expression decreased after 60 minutes of extra-oral dry time at the apical region.