Histomorphometric study on growing condyle of rat.

The purpose of this study was to carry out the histomorphometric assay on the mandibular condylar tissue of the growing rats. Male rats of the Wistar strain at the age of 3, 4, 6, 8 and 10 weeks were used. All rats were injected intravenously with tetracycline and calcein, respectively. They were killed 12 hours after calcein injection. Before embedding in acrylic resin, 3 reference points were marked directly on each condyle to establish the reference plane for the histomorphometry on the ground section. After preparing the ground section, the growth rate of the condyle was obtained by measuring the distance of the two different fluorescent labeling lines. Furthermore, the age-related changes of the relative distribution of the bone, calcified cartilage and prebone (uncalcified bone matrix) were measured under a light microscope by using a grid on the eyepiece reticle. The number of osteoblasts and osteoclasts were also calculated in the same specimen. The following results were obtained: The thickness of the cartilaginous layer and the growth rate of the endochondral bone formation decreased with age. The relative ratio of the bone area in the subchondral tissue increased constantly with age.