HOW ODONTOBLASTS REACT ULTRA-STRUCTURALLY TO ORTHODONTIC INTRUSIVE FORCES.

Background: The purpose of orthodontic treatment is to move teeth as efficiently as possible with least damage to teeth and their supporting tissues. Previous studies have revealed that varying degrees of force magnitude, frequency, and duration of orthodontic forces express extensive macroscopic and microscopic changes on dental tissues. Aim of the work:The present work aimed to investigate the ultra-structural changes that might occur to odontoblasts in response to light and heavy intrusive orthodontic forces. Materials and Methods: Twenty-four vital maxillary first premolars from orthodontic extraction cases were allocated in three groups. Control group: premolars were not subjected to any force. Group I: light intrusive force was applied. Group II: heavy intrusive force was applied. Extraction was done after three weeks of force application. Coronal and radicular pulpal tissues were examined by transmission electron microscope (TEM). Results: Control, TEM revealed common cellular features regarding coronal and radicular odontoblasts. Evidence of affection of the odontoblasts could be manifested in both experimental groups as they expressed varies degrees of nuclear alterations, chromatin condensation, cytoplasmic organelles affection and loss of cellular junctions. Conclusions: Intrusive orthodontic force can induce ultra-structural changes in odontoblastic cells. Heavy intrusive have greater impact on odontoblastic cells than light force. Generally, radicular cells are more affected than coronal cells by the same magnitude of the intrusive force. Both coronal and radicular odontoblastic cells can transform into multinucleated odontoclastic cells under the influence of heavy intrusive orthodontic force. Light intrusive force could induce odontoclastic differentiation of radicular odontoblastic cells.