UCSF

Post-orthodontic relapse is the phenomenon in which teeth move back towards their original position after orthodontic tooth movement. This provides a challenge for clinicians and patients in maintaining results and benefits from orthodontic treatment. The exact mechanism of relapse is unclear, but bone resorption is required to allow teeth to move. Current relapse prevention relies on patient compliance with wearing appliances. However, past studies have looked at methods that target biological pathways associated with bone remodeling. Osteoprotegerin fusion protein (OPG-Fc) has been shown to reduce relapse with limited systemic effects. A past study found that a single, localized injection could reduce relapse to just 30% of initial tooth movement. However, bolus OPG-Fc has a limited half-life (6-7 days), and with a single dose, the effects of OPG-Fc decrease significantly within a week. These studies raise the question of whether OPG-Fc could be even more effective with long-term, sustained release. Our study examined the efficacy of a slow- release long-term delivery system to deliver OPG-Fc. This study tested polyethylene glycol dimethylacrylate (PEGDMA) microparticles as a sustained delivery system. First, OPG-Fc-loaded PEGDMA microspheres were shown to deliver 1.6μg of OPG-Fc over 24 days in vitro. The particles were then tested in an in vivo rat model of orthodontic tooth movement. Effectiveness of this slow-release long-term delivery system were inconclusive due to lack of statistical power.