Is the mandible intrinsically different in Apert and Crouzon syndromes?

Relative mandibular prognathism is an observed finding in Apert and Crouzon syndromes. This imbalance in the facial profile is generally attributed to the diminished growth of the maxilla, thereby increasing the disparity between maxilla and mandible with increasing age. What is not known is whether the mandible is, indeed, normal. Previous work by Kreiborg with Crouzon syndrome led to the conclusion that the mandible, although somewhat smaller, grew in a "normal" pattern. Our own observations, which used a greater variety of mandibular measurements on patients with both Apert and Crouzon syndromes, corroborated Kreiborg 's conclusions but go further to suggest a syndrome-specific mandibular malformation. Ramal height was found equal to the norm and sometimes greater. Mandibular body length was significantly shorter, thereby producing a distinctly different ramus/body length ratio, particularly in older patients. These findings become significant in the planning of reconstructive procedures. They also raise the question as to whether the shape of the mandible is genetic in origin or is an adaptation to the increasing derangements of the cranial base, maxilla, and occlusion observed with maturation in these patients. The possibility of interactive genetic and environmental factors affecting growth of the mandible emerges from the data.