Aim: The aim of this study was to examine the extent to which the ratio of the endochondral growth components cell volume increase to matrix production was subject to age-dependent and animal-specific changes per cell in the condylar cartilage of the domestic pig. In addition, it was to be investigated whether the cell distribution in the condylar cartilage and thus the tissue differentiation changes as one aspect of the aging process and whether the differentiation differs from that of primary hyaline cartilage.
Material and methods: The tissue specimens available were hematoxylin/eosin-stained section series from the cartilage of the condylar process of six domestic pigs (0-24 months) of the genus Suis scrofa. Using a special squared measuring grid in the optical path of a microscope, the following histomorphometric primary parameters were ascertained in the cartilage zones under investigation: the average section area of the cartilage cells and the number of cut cells per unit area. From these figures, the cell volume and the extracellular matrix volume per cell were calculated using the stereological calculation algorithm for ellipsoids of revolution in accordance with Weibel and Gomez. Quantitative analysis of the cell distribution pattern was based on two methods used in stochastic geometry: calculation of the dispersion index DI, and performance of the chi(2) adaptation test.
Results: It was shown that, in this species of experimental animal, the relative proportion of cell volume increase in the complete process of endochondral growth is predominant until the juvenile stage at 11 months. In late puberty, volume gain as a result of matrix synthesis then exceeds cell volume increase. Comparisons with other stereological growth studies show that the investigated ratio in the condylar cartilage of the domestic pig has a similar aging behavior to that in the rat. By contrast, the matrix synthesis is predominant in the monkey. The cell clustering typical of mature hyaline cartilage in other joints was not observed at any stage in the development of the condylar cartilage. This suggests that the differentiation process is adapted in a special way to the stress-strain relationship in the temporomandibular joint.
Conclusion: The methods used successfully in the present study for measuring and evaluating uninfluenced cartilage growth in the condylar process of the domestic pig is suitable for more extensive basic studies into the influence of orthodontic treatment on joint development.