Prenatal development of the human mandible

Abstract

Human embryos and fetuses ( n=25) ranging from 12 to 117 mm CRL (crown-rump-length) were serially sectioned and the mandibles were reconstructed in 3D. In addition, characteristic areas of apposition, resorption and resting zones were projected onto the surface of the mandibular reconstructions after histological evaluation of the remodeling processes. Furthermore, morphometric data were taken to describe growth processes in horizontal views. In this way the changing outlines as seen in 3D could be correlated with the remodeling patterns and with the changes in growth. In these stages the mandible showed a general appositional growth, but resorption areas were found at the posterior margins of the mental foramen and at the lateral and medial posterior bony planes at concave surfaces. The bulging of bone underneath and over Meckel's cartilage could be recognized as active appositional growth areas. Meckel's cartilage itself lay in a trough which could be characterized by less apposition and even resorption. Questions were raised in how much the gap between our present knowledge of genetic expression of signaling molecules and the precise morphologic description of the mandibles can be bridged.

Making Space for Permanent Molars in Growing Baboon (Papio anubis) and Great Ape (Pan paniscusandP. troglodytes) Mandibles: Possible Ontogenetic Strategies and Solutions

“…A 3D study of the developing human mandible described the first ossification centre not far from dm1, in the position of the future mental foramen and other small centres inferior to the posterior ends of Meckel's cartilage [40]. Also, the development of Meckel's cartilage initiates in a similar area of the molar tooth bud region [41].…”

Mapping the Mandibular Lingula in Pierre Robin Sequence

“…43 Given this abnormal anatomy and the fact that muscular function can affect the development and growth of the craniofacial skeleton, 50 it is conceivable that prenatal mandibular movement in PRS is also abnormal and further contributes to reduced mandibular size and increased gonial angle. In addition, since the mental foramen appears with the first ossification of the mandible, 47 it is subject to the remodeling that occurs in the following weeks. As a result, there are many prenatal and postnatal variables that could explain the diverse morphology of Pierre Robin mandibles.…”

“…45,46 In utero, the mandible undergoes resorption and remodeling. 47 Starting week 8 of fertilization, the mouth opens and moves. This movement is primarily induced by tongue musculature rather than masticatory muscles, which mature later in development.…”

Morphometric growth relationships of the immature human mandible and tongue

“…The attachment of the genioglossus muscle, first observed on the inferior side of the anterior portion of Meckel's cartilage, reattaches to the trabeculae of the mandibular symphysis by the end of the eighth week . During the sixth week, the primary ossification centre of the mandible is first observed near the mental foramen . The trabeculae of the mandible then extend radially towards the future mandibular symphysis, alveolar bone, mandibular body, and coronoid process .…”

“… considered the sequential growth pattern of the human mandible and observed the radiating expansion of the mandible from the primary growth centre as early as the fifth week of development . The ossification of the mandible commences at the sixth week of development with insular cartilages observed between weeks 10 and 14 near the posterior region of Meckel's cartilage. The mandible alters its morphology to accommodate the development of the deciduous dentition and the increase in mastication between 30 wk of gestation and 3 yr of age .…”