IMPORTANCE OF THE CRITICAL-SIZE BONE DEFECT IN TESTING BONE-REGENERATING MATERIALS

A substantial interest exists in developing substitute materials and h uman recombinant bone-inducing factors to enhance bone regeneration bo th in the craniofacial complex and in other parts of the skeleton. A p ersistent problem has been to find an animal model that allo-tvs for t he comparison of different osteopromotive materials. The purpose of th is investigation was 1) to determine whether a 5-mm calvarial defect i n adult rats fulfilled the requirements of a critical-size bone defect and 2) to discuss the use of this animal model in assessing bone repa ir in the craniofacial region. Bilateral full-thickness calvarial defe cts were trephined in the calvarial bone of 56 5- to 6-month-old Wista r rats. Except for minor amounts of bone formation limited to the marg ins of the defect, none of the defects revealed any signs of spontaneo us bone regeneration 6 and 12 months after surgery. The full-thickness 5-mm calvarial defects thus fulfill the criteria for a critical-size bone defect. This animal model allows for an experiment with a paired design, it avoids inclusion of the sagittal suture in the osseous defe ct, and it thereby minimizes morbidity by reducing the risk of damagin g the midsagittal sinus. An adequate experimental model has been devel oped to evaluate the efficiency of osteopromotive materials in the hea ling of bone defects in the craniomaxillofacial region.