An experimental model in calvaria to evaluate bone therapies.

The clinical therapeutic application of experimental strategies requires extensive preclinical experimentation in appropriate animal models. Thus, a valid model must be established. The aim of the present study was to determine the critical size defect (CSD) of rat calvaria that is unable to undergo spontaneous bone regeneration. Forty Sprague Dawley female rats (body weight (bw): 250 +/- 20 g) were distributed in two groups. Circular surgical defects, 3 mm (Group A) and 5 mm (Group B) in diameter, were produced in the parietal bones. The animals were left untreated and sacrificed 1, 2, 3 and 6 weeks after surgery. Group A showed bone formation at the experimental site, increasing from 1 week (4.5%) to 6 weeks (46%). However, Group B showed scarce bone formation (less than 10%) throughout the experimental period. We may conclude that a defect 5 mm in diameter is a critical size defect (CSD) because it is the minimum bone defect size that requires treatment to heal. Thus, a circular defect 5 mm in diameter in rat calvaria would be an appropriate experimental model to study bone therapies.