Limits of the mandibular symphysis as a donor site for bone grafts in early secondary cleft palate osteoplasty.

With the assistance of computed tomography, the bone volume in the symphysis was assessed on 28 historic mandibles with mixed dentition, before the eruption of the canines. The quantification gave an average bone volume of 1.0 cm3, and the values fitted a normal distribution curve. Assuming that there were no appreciable differences in size between the historic and recent mandibles, the mandibular symphysis can theoretically be used as a donor site in early secondary osteoplasty in about 92% of cleft patients to augment a cleft volume of 0.5 cm3, in 50% for a cleft volume of 1.0 cm3, and in 18% for a cleft volume of 1.5 cm3. With cleft volumes larger than 1.5 cm3, the symphysis can hardly be considered. If, however, a safety margin of 5 mm from the apices of the front teeth is maintained, the chance that the mandibular symphysis will suffice decreases for a 0.5 cm3 volume to 64%, for a 1.0 cm3 cleft to 3.5%, and for a 1.5 cm3 cleft to 0%.