Intermittent parathyroid hormone treatment enhances guided bone regeneration in rat calvarial bone defects

This study investigates the effects of intermittent parathyroid hormone (PTH(1-34)) treatment on bone regeneration and mechanical strength of critically sized rat calvarial bone defects covered with expanded membranes. A full-thickness bone defect (diameter 5 mm) was trephined in the central part of the parietal bones in 20-month-old female Wistar rats. The bone defects were covered with an exo-cranial and an endocranial expanded polytetrafluoroethylene membrane. The animals were killed 35 days after operation. 60 mug PTH(1-34)/kg was administered daily during the healing period, and control animals with calvarial bone defects were given vehicle. Mechanical testing was performed by a punch out testing procedure by placing a steel punch (diameter 3.5 mm) in the center of the healed defect. After mechanical testing, the newly formed tissue inside the defect was removed and the dry weight and ash weight were measured. PTH(1-34) increased dry weight by 48%, ash weight by 51%, and ash concentration by 26%. PTH(1-34) also augmented the mechanical strength of the new bone formed inside the defect by increasing ultimate stiffness by 87%. No differences in body weight were found between the vehicle-injected and the PTH-treated animals during the experiment. The experiment demonstrates that intermittent PTH(1-34) treatment increases bone deposition and enhances mechanical strength of healing rat calvarial defects covered with expanded polytetrafluoroethylene membranes.