Objectives: Orthodontic tooth movement (OTM) requires 18-36 months of treatment, and may be longer in complex cases requiring temporary anchorage devices (TADs). Current methods to accelerate treatment are ineffective or transient. Previous studies indicate increased levels of RANKL accelerate OTM through increasing the number of osteoclasts. Our aim is to formulate microparticles to release RANKL in a sustained manner to increase OTM, which can be used in conjunction with TADs. We hypothesize a sustained, optimal dose of exogenous RANKL through injectable particulate formulations will increase osteoclast formation, thus may be used as a therapeutic to increase OTM.
Methods: Polylactic acid-co-glycolic acid (PLGA) is used to prepare 250-425µm-sized porous microparticles, using water-in-oil-in-water emulsion technique. RANKL is adsorbed by incubating microparticles with 40µg/mL of RANKL at 37°C for 1 hour. Microparticles are characterized for morphology with scanning electron microscopy, and for release behavior in phosphate buffer saline (pH 7.4). RANKL activity is tested with tartrate-resistant acid phosphatase staining after incubating microparticle releasates with mice osteoclast precursor cells (RAW 264.7).
Results: PLGA microparticles show a porous surface morphology and are 250-425µm in diameter. They show a burst release of 60% within the first hour, a subsequent linear release of 10µg/mL over 28 days. The incubation of RANKL releasates with RAW 264.7 osteoclast precursor cells shows an increase in the number of TRAP-positive osteoclast cells in vitro.
Conclusions: An exogenous source of RANKL supplied by an injectable PLGA formulation is effective at increasing the number of osteoclast cells in vitro in a sustained manner.