Osteopontin and RANKL Expression in Orthodontic Tooth Movement

Force induced tooth movement is frequently used in the treatment of malocclusions.  Objectives:  In order to systematically investigate the biology of orthodontic forces and their influence on bone remodeling we have developed a mouse model for lateral orthodontic tooth movement of the mandibular molar teeth using a bonded spring appliance.  Methods: Mice were treated with a pre-fabricated spring appliance of defined 9g-force for 3, 6, and 9 days.  Paraffin sections of the mandibles were stained for tartrate-resistant acid phosphatase (TRAP) positive cells or immunostained using monoclonal anti-RANKL or anti-OPN antibodies.  Mice were injected with tetracycline, alizarin red, and calcein blue on days 0, 3, and 6.  Undecalcified mandibles were imaged by synchrotron micro-CT, and ground sections were examined by fluorescent microscopy.  Real-Time PCR was used to examine gene expression of RANKL, OPN, IL-1b and COX-2.  Results: There was a gradual, 10-fold increase in the number of TRAP-positive multinuclear cells (osteoclasts) in the tooth movement group compared to control teeth from day 0 to day 9.  On the compression side, immunohistochemistry revealed significantly increased levels of RANKL in the PDL and OPN in the alveolar bone.  TRAP staining and histopathology documented significant increases in cementum and alveolar bone resorption on the compression side.  Real-time PCR demonstrated a 3-fold increase in RANKL and COX-2 expression and a 5-fold increase in OPN and IL-1b expression.  Conclusion: Our study documented altered gene expression in periodontal tissues together with an increase in osteoclastogenic factors and inflammatory mediators as a result of orthodontic force application.  Here we have established a predictable and repeatable model system for the study of the biological mechanisms of orthodontic tooth movement.  Funding for these studies was provided by NIH grant FDE 018298A to CGW and DE 15425 to TGHD.