Collagen formation and growth in the mandibular joint of the guinea pig as revealed by autoradiography with 3H-proline

Type II collagen expression in the mandibular condyle during growth adaptation: an experimental study in the rabbit

An experiment was designed to mimic orthopedic functional appliances in order to investigate the spatial and temporal characteristics of type II collagen secretion as a marker of cartilage maturation in the mandibular condyle of young rabbits. The position of the glenoid fossa in relation to the condyle was altered so that articulation now took place more posteriorly. Histological sections of the condyles of 15-, 20- and 30-day-old experimental and control animals were stained with toluidine blue and with an anti-type II collagen antibody. A widened progenitor cell layer was found posteriorly in the experimental condyles and a narrow layer was found anteriorly to the articulating region. The chondroblast layer was also widened posteriorly, whereas the hypertrophic cell zone was narrower; the opposite was seen anteriorly. The effect was marked in 15- and 20-day-old animals and weak in 30-day-old animals. Type II collagen stain and strong toluidine blue metachromasia were not observed in the progenitor cell zone until the chondroblasts had acquired a flattened, slightly hypertrophic morphology, which was found deeper in the experimental condyles than in the controls. This is interpreted as a slowing down of the differentiation of chondroblasts as a result of the force applied. The effect of masticatory function may also be explained in terms of delayed differentiation of chondroblasts and increased growth.

Cartilage matrix production and chondrocyte enlargement as contributors to mandibular condylar growth in monkeys (Macaca fascicularis)

In an attempt to determine the contributions to condylar growth of cartilaginous matrix production and chondrocyte enlargement, four prepubertal male monkeys (Macaca fascicularis) were used. Each animal received 1 mCi 3H-proline per kilogram of body weight 24 hours before death. From the left condyles, the anterior and central segments of the growth cartilage in the lateral and medial joint region were examined with the light microscope. Volumes of cells and extracellular matrix, as well as the intensity of radioautographic labeling, were estimated stereologically in four layers from the articular surface to the zone of endochondral ossification. On the assumption of a steady-state system, these data led to the conclusion that an average chondrocyte in the anterior segment of the growth cartilage contributed to condylar growth by about 3000 microns 3 of newly formed matrix and about 1000 microns 3 of increased cell size. The respective estimates in the central segment were about 3700 microns 3 and 2000 microns 3. Thus, unlike findings in the condylar cartilage of 20-day-old rats, matrix production in the simian condyle exceeded chondrocyte enlargement, although in varying ratios of about 3:1 anteriorly and 1.85:1 centrally. On the other hand, chondrocyte enlargement from the anterior segment to the central segment increased by about 100%, while the increase of about 25% in matrix production was outweighed by variation between individual animals. These findings suggest that the relative contribution of the two growth components varies considerably, on the one hand, with the species or possibly with the stage of condylar development examined and, on the other hand, between various anteroposterior locations within the condylar cartilage.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular stages in cartilage formation as revealed by morphometry, radioautography and type II collagen immunostaining of the mandibular condyle from weanling rats

The role played by cell addition, cell enlargement, and matrix deposition in the endochondral growth of the condyle was assessed in weanling rats by four approaches making use of the light microscope: morphometry, 3H-thymidine radioautography, 3H-proline radioautography, and immunostaining for the cartilage-specific type II collagen. From the articular surface down, the condyle may be divided into five layers made up of cells embedded in a matrix: 1) the articular layer composed of static cells in a matrix rich in fibers presumed to be of type I collagen, 2) the polymorphic cell layer including the progenitor cells from which arise the cells undergoing endochondral changes, 3) the flattened cell layer in which cells produce a precartilagenous matrix devoid of type II collagen while undergoing differentiation in two stages: a "chondroblast" stage and a short "flattened chondrocyte" stage when intracellular type II collagen elaboration begins, 4) the upper hypertrophic cell layer, in which cells are "typical chondrocytes" that enlarge at a rapid rate, actively produce type II collagen, and deposit it into a cartilagenous matrix, and 5) the lower hypertrophic cell layer, composed of chondrocytes at a stage of terminal enlargement while the cartilagenous matrix is adapting for mineralization. 3H-thymidine radioautographic results indicate that the turnover time of progenitor cells in the polymorphic cell layer is about 2.9 days. The time spent by cells at each stage of development is estimated to be 1.4 days as chondroblasts, 0.5 days as flattened chondrocytes, 2.3 days as the chondrocytes of the upper hypertrophic cell layer, and 1.1 days as those of the lower hypertrophic cell layer. Calculations referring to a 1 x 1-mm square-sided column extending from the articular surface to the zone of vascular invasion provide the daily rate of cell addition (0.0077 mm3), extracellular matrix deposition (0.0127 mm3), and cell enlargement (0.0302 mm3). Hence the respective contribution of the three factors to condyle growth is in a ratio of about 1:1.6:4. This result emphasizes the role played by cell enlargement in the overall growth of the condyle.

Structure and growth activities of the mandibular condyle in monkeys (Macaca fascicularis): I. Intracondylar variations

Eight condyles of four growing monkeys (Macaca fascicularis) of estimated ages between 1.6 and 3.6 years (minimum and maximum) were analyzed using radioautographic, histometric, and stereologic techniques. The aim of the study was to examine the relationship between intracondylar variations in structure and growth activities. The animals received 3H-proline (1 mCi/kg body weight) and 3H-thymidine (0.5 mCi/kg body weight) 24 and 3 hours, respectively, prior to sacrifice. The perichondral and chondral layers of the condylar articular covering as well as the subchondral zone of erosion were examined at different sampling sites distributed systematically in the antero-posterior and lateromedial dimension of the articulating surface. Intracondylar variations observed with respect to morphometric and radioautographic parameters suggest the following biologic mechanisms contributing to mandibular growth in a superior-posterior direction. Greater mitotic activity at the central and posterior sites of the condylar perichondrium generates a population of progenitor cells that is larger in these than in other regions. On the other hand, the rate of differentiation of these progenitor cells into chondroblasts and chondrocytes, i.e., the "migration" into and through the chondral layers of the articulating covering, seems to be enhanced in the same superior and posterior areas. Additionally, while "migrating" faster, these cartilage cells become larger and produce greater amounts of extracellular matrix than those in the anterior parts of the condyle. Finally, enhanced resorptive activities in the superior and posterior regions of the subchondral zone of erosion provide an increased "loss" of degenerated chondrocytes, thereby establishing the basis for a cartilaginous drift in the superior-posterior direction.

Application of morphometrical methods in studies of the mandibular condyle

Two mandibular condyles of a growing monkey (Macaca fascicularis) were used for developing and testing a morphometrical model system suitable for generating quantitative data about the structure of and the growth activities in the articulating surface layers. The animal received 3H-proline (1 mCi/kg body weight) 24 h and 3H-thymidine (0.5 mCi/kg body weight) 3 h prior to killing. Using standardized conditions, 1-2 microns thick histological sections were processed for autoradiography. The morphometrical analysis was carried out using light microscopy at two levels of magnification. Sampling of tissue fields was performed at twenty-four (level I) and twelve (level II) different sites, respectively. These sites were distributed systematically in the anteroposterior and lateromedial dimension of the cartilaginous condylar covering. Using a multivariate analysis of variance, a parameter comparison revealed significant differences between single sampling sites in the anteroposterior as well as in the lateromedial direction, suggesting that the articulating condylar surface is inhomogeneous with respect to both structures and growth activities. The sampling mode eventually arrived at in this study was shown to be sufficient for the recording of gradients within the condylar surface layers. The model system presented permits simultaneous quantitative characterization of structure and growth activities such as mitotic cell division and extracellular matrix production of the condylar cartilage including the zone of its replacement by bone.

Matrix formation in the mandibular condyle of the rat (35S) - sulfate incorporation studies

The matrix formation activity of the mandibular condylar cartilage was investigated using radioactive sulfate incorporation. The condylar cartilage was studied at various developmental stages; as an autotransplant, in situ and on a chemically defined medium. An initial decrease in the cpm/DNA was followed by an increase, until a maximum was attained for all groups, between the 14th and 17th days. Thereafter, the matrix formation activity decreased. There was a surprising likeness in the patterns of activity for all the samples investigated. This tends to support the hypothesis that cartilagenous growth seem to be regulated, at least to some extent by one or more humoral factors.

Thickness of the soft tissue layers and the articular disk in the temporomandibular joint

Out of 115 right temporomandibular joints from Swedish subjects aged 1 day to 93 years, 48 joints without any gross sign of arthrosis or deviation in form were examined histologically. The joint components were cut sagittaly, each into four parts. Histological sections were made of the condyle, the temporal component and of the articular disk. The total thickness of the soft tissue layers was measured in decalcified sections, cut from the medio-central and lateral parts of the condyle and the temporal component and from the medial, medio-central, latero-central and lateral regions of the disk. In the medio-central sections from the condyle and temporal component the thickness of the fibrous connective tissue layer i.e. the surface layer was also registered. The soft tissue layers were thickest in the condyle superiorly, about 0.4-0.5 mm, in the temporal component on the postero-inferior slope of the articular tubercle, about 0.5 mm, and in the disk posteriorly about 2.9 mm. In the roof of the fossa it was only 0.1 mm. The soft tissue layers on the condyle as well as the disk were thinner laterally while the corresponding tissue in the temporal component was thicker laterally. The thickness of the soft tissue layers seem to reflect the growth and functional load to which the joint is exposed.