It has not been elucidated whether the initiation of condylar development of the mandible is related with the periosteurn of the mandible, or if it derives from a separate programmed blastema not related with the mandible. Also, although the mandibular condylar cartilage is known to promote growth, few studies have dealt with molecular-biologic mechanisms such as the expression of specific genes according to the differentiation of the mandibular condyle.
To elucidate the unique cellular characteristics, development, and differentiation process of the mandibular condyle, an examination of expressions of genes characteristic of cartilage and bone were carried out using RT-PCR and mRNA in situ hybridization.
1. Type?collagen mRNA was detected with type Icollagen mR.NA in the differentiation and growth process of the cartilage of the mandibular condyle. Type llcollagen,mRNA was demonstrated in the whole resting and upper part of the proliferative zone, whereas type Ilcollgen rRNA was observed in the resting, proliferative and upper hypertrophic cartilage zone of the mandibular condyle.
2. The condylar cartilage rapidly increased in size due to the accumulation of hypertrophic chondrocytes as characterized by the expression of type II collagen mRNA during postnatal development.
3. Bl1P-4 mRNA was present in the anlage of the future condylar process and also in the ossifying mandibular body. 4. IHH mRNA was limited exclusively to the lower part of the proliferative zone and the upper part of the hypertrophic cartilage zone during condylar development
These findings were different from those in the growth-plate cartilage of the long bone, indicating characteristic feature of the differentiation of the chondrocytes in the condylar cartilage present in prenatal and postnatal development. Furthermore, it was also suggested that chondroblasts of condylar cartilage rapidly differentiate into hypertrophic chondrocytes with increased functional Load force such as muscle activity and mastication.
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