In an effort to better understand the interrelationship of the growth and development pattern of the mandible and condyle, a sequential growth pattern of human mandibles in 38 embryos and 111 fetuses were examined by serial histological sections and soft X-ray views. The basic growth pattern of the mandibular body and condyle appeared in week 7 of fertilization. Histologically, the embryonal mandible originated from primary intramembranous ossification in the fibrous mesenchymal tissue around the Meckel cartilage. From this initial ossification, the ramifying trabecular bones developed forward, backward and upward, to form the symphysis, mandibular body, and coronoid process, respectively. We named this initial ossification site of embryonal mandible as the mandibular primary growth center (MdPGC). During week 8 of fertilization, the trabecular bone of the mandibular body grew rapidly to form muscular attachments to the masseter, temporalis, and pterygoid muscles. The mandible was then rapidly separated from the Meckel cartilage and formed a condyle blastema at the posterior end of linear mandibular trabeculae. The condyle blastema, attached to the upper part of pterygoid muscle, grew backward and upward and concurrent endochondral ossification resulted in the formation of the condyle. From week 14 of fertilization, the growth of conical structure of condyle became apparent on histological and radiological examinations. The mandibular body showed a conspicuous radiating trabecular growth pattern centered at the MdPGC, located around the apical area of deciduous first molar. The condyle growth showed characteristic conical structure and abundant hematopoietic tissue in the marrow. The growth of the proximal end of condyle was also approximated to the MdPGC on radiograms. Taken together, we hypothesized that the MdPGC has an important morphogenetic affect for the development of the human mandible, providing a growth center for the trabecular bone of mandibular body and also indicating the initial growth of endochondral ossification of the condyle.

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Early in the 20th century, a series of studies were initiated across North America to investigate and characterize childhood growth. The Craniofacial Growth Consortium Study (CGCS) combines craniofacial records from six of those growth studies (15,407 lateral cephalograms from 1,913 individuals; 956 females, 957 males, primarily European descent). Standard cephalometric points collected from the six studies in the CGCS allows direct comparison of craniofacial growth patterns across six North American locations. Three assessors collected all cephalometric points and the coordinates were averaged for each point. Twelve measures were calculated from the averaged coordinates. We implemented a multilevel double logistic equation to estimate growth trajectories fitting each trait separately by sex. Using Bayesian inference, we fit three models for each trait with different random effects structures to compare differences in growth patterns among studies. The models successfully identified important growth milestones (e.g., age at peak growth velocity, age at cessation of growth) for most traits. In a small number of cases, these milestones could not be determined due to truncated age ranges for some studies and slow, steady growth in some measurements. Results demonstrate great similarity among the six growth studies regarding craniofacial growth milestone estimates and the overall shape of the growth curve. These similarities suggest minor variation among studies resulting from differences in protocol, sample, or possible geographic variation. The analyses presented support combining the studies into the CGCS without substantial concerns of bias. The CGCS, therefore, provides an unparalleled opportunity to examine craniofacial growth from childhood into adulthood.

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