Significant post-surgical relapse is a common occurrence after many orthognathic surgical procedures (for example, advanced mandibles often relapse 50% or more). This study will examine systematically the capacity of two therapies, alone and in combination, to reduce skeletal relapse in a rodent osteotomy site (unilateral mandibular advancement) that has been shown previously to relapse (32-45% of the advancement) as it heals under a complex admixture of, tensile, compressive, and torsional stresses. Treatments will be applied in an attempt to decrease relapse through either an acceleration of healing of the osteotomy site (direct current stimulation) or a reduction of soft tissue generated forces on the osteotomy site (pre-surgical stretching of soft tissues). It is hypothesized that the more rapidly an osteotomy site heals, the less susceptible it will be to deforming forces. It is further hypothesized that pre-surgically stretched soft tissues will produce less relapsing force on an osteotomy site. A 4 mm mandibular advancement will be performed, unilaterally, on adult (6- 8 month old) male Sprague Dawley rats and the osseous segments will be united with chromic gut suture. An experimental treatment or combination of treatments aimed at reducing relapse will be applied. Lateral cephalograms, transcranial radiographs of the condyle, and metallic implants will make it possible to measure both the surgical advancement of the mandible and subsequent relapse over the next 6 weeks. In addition, the callus will be examined histologically and its microscopic morphology characterized. Elimination of skeletal relapse after orthognathic surgical procedures is the ultimate goal of this experiment. Were relapse minimal, the outcome of surgery would become more predictable and the number of patients that either are or should be re-operated will be reduced. Indeed, because mst of the present treatments have already been used clinically (albeit in other contexts), it is assumed that the results of the present investigation will have immediate clinical impact.
