Bone--special problems of the craniofacial region

The craniofacial region presents special problems for tissue engineering. First, the stresses and strains that engineered tissues will encounter are mostly unknown. Second, if tissue engineering is to be useful in ameliorating craniofacial anomalies, it will have to mimic the growth activity of the native tissues. These problems are interrelated in that bone growth responds to loading conditions.

Our work uses miniature technology to measure skull deformation during function in the miniature pig. Growth is quantified in the same animals by labeling replicating cells with bromodeoxyuridine and newly mineralized bone with fluorochromes. The mandibular condyle and the cranial sutures are both candidate areas for tissue engineering, and craniofacial periosteum is a promising graft material.

The condyle is compressed by the reaction load at the temporomandibular joint (TMJ). Cell divisions in the perichondrium are negatively correlated with bone strain. Craniofacial sutures deform during function much more than adjacent bones, and strains can be either tensile or compressive. In contrast to expectation, functional tension is not correlated with sutural growth rate. However, functional strain does predict sutural morphology, with compressed sutures showing complex interdigitation. Periosteum shows striking differences between resorptive and appositional surfaces. The resorptive medial side of the zygomatic arch is under pressure during function. Tensile strain perpendicular to the surface is probably greater on the temporal than on the zygomatic bone, thus correlating with more rapid periosteal apposition on the temporal.

Engineered implants may be more likely to succeed if their architecture suits the strain environment in which they will function.