IL-1α AND TNF-α EXPRESSION DURING EARLY PHASES OF EXPERIMENTAL ORTHODONTIC TOOTH MOVEMENT An immunohistochemical study

Remodeling of the periodontium after application of mechanical forces constitutes the basis of clinical orthodontics. Orthodontic tooth movement causes bone resorption in the pressure area and bone deposition in the tension side with various immunoregulatory molecules being involved in the above mentioned biological bone remodeling processes. The proinflammatory cytokines IL-1α and TNF-α are prominent examples of such molecules due to their involvement in bone resorption. The aim of this study was to investigate the expression of IL-1α and TNF-α during early phases of experimentally induced orthodontic tooth movement. Eight-teen male Wistar rats were used. All maxillary right first molars were moved orthodontically with a force of 0.5 N for 3 hours, 1 day and 3 days (6 rats for each time period). The contra-lateral sides served as untreated controls. Parasagittal sections of the maxillary molars and the surrounding tissues were subjected to immunohistochemical staining for IL-1α and TNF-α. The mesial aspect of the distal root, the distal aspect of the mesial root, the gingiva and the periodontal ligament mesially and distally to the first molars, as well as the pulp tissue were evaluated using light microscopy. IL-1α and TNF-α were expressed in both the mesial aspect of the distal root and the distal aspect of the mesial root (compression and tension zones respectively) of the experimental sides. The TNF-α expression began as early as 3 hours after force application, whereas IL-1α showed increased expression after 1 day. Increased intensity of staining for both cytokines was observed in the 1-day and 3-days groups. The compression zone exhibited heavier staining than the tension zone for both IL-1α and TNF-α. Moreover, these cytokines were expressed in the gingiva of both control and experimental sides. Nevertheless, the orthodontically moved teeth demonstrated heavier gingival staining than the controls. Minor changes in the expression of these cytokines were seen in the pulp tissue.