Prenatal growth of the human mandibular condylar cartilage.

The question of whether the condylar cartilage possesses a growth potential like that of the long bone growth plates has been the subject of contrasting viewpoints. We have recently established that the thickness of the human tibial growth plate progressively decreases during the second half of the fetal period, but that the changes in the total human condylar thickness do not correlate with fetal age or weight. The present study examined the change in the thickness of the human mandibular condyle layers during the fetal growth of the mandible. Mandibles were obtained from autopsy of 19 human fetuses ranging in fetal age from 18 to 41 weeks. The total length of the mandible, the lengths of the mandibular body and of the ramus were measured, as well as the gonial angles. The total thickness of the condyle, and the thickness of the articular, progenitor, cartilage, chondroblast, and hypertrophic chondrocyte layers were measured on the central segment of central sagittal sections of the mandibular condylar cartilage. The total mandible, the corpus and the ramus lengths increased linearly with the age of the fetus and they all correlated strongly with fetal weight. However, changes in the total condylar thickness and in the thickness of the cartilage layer (chondroblast plus hypertrophic chondrocytes) did not correlate with fetal weight or mandibular length. The thickness of the articular layer increased with weight, but changes in the progenitor layer were independent of corporal and mandibular growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential spatiotemporal expression of E- and P-cadherin during mouse tooth development.

Changes in E- and P-cadherin (E- and P-CD) expression during embryonic mouse first molar development were analyzed by immunohistochemistry. During the induction and morphogenesis stages (bud, cap and early bell stages), E-CD was expressed in the cells of the invaginating epithelial tooth bud and in the cells of the outer enamel epithelium, stellate reticulum and stratum intermedium, suggesting a role for this molecule in the maintenance of enamel organ architecture. On the other hand, P-CD was strongly expressed in the inner enamel epithelium suggesting its participation in the processes of mesenchymal induction. during the cytodifferentiation stage (late bell stage), E-CD was expressed in polarizing preameloblasts, but cadherin expression was restricted to the basal and apical poles of differentiated secretory ameloblasts, where the zonula adherens type of cell-cell junctions is located. The present study demonstrates for the first time the spatiotemporal expression of cadherins during tooth development and suggests differential and specific roles for E-CD and P-CD during the morphogenesis and cytodifferentiation processes of this organ.

The role of the condylar cartilage in mandibular growth. A study in thanatophoric dysplasia.

A new approach to evaluate the role of the condyle in mandibular growth could be its study in chondrodysplasias. The growth of the condylar cartilage and the mandible has not previously been reported in thanatophoric dysplasia (TD), a lethal osteochondrodysplasia. We have studied the light microscopic, histomorphometric, and radiologic findings in four infants affected by TD and in four control infants. The diagnosis was made on the basis of clinical, radiographic, and pathologic criteria. All the measured radiographic parameters of the patients' mandibles showed a normal longitudinal growth in TD, despite the severe disturbance of the condylar cartilages. The lesions in the chondroblastic cells and the extracellular matrix were similar to those observed in growth plate cartilages in TD. Marked membranous ossification spread from the cartilage canals of the condyles. The articular and prechondroblastic layers were histologically normal. Histomorphometry demonstrated that condylar cartilages were twice as thick as normal in TD, mainly because of the thickening by the chondroblastic layer. Present results support the hypothesis that condylar cartilage is a secondary growth site instead of being a primary growth center.