Tuomo Kantomaa

Effect of Mechanical Forces on Chondrocyte Maturation and Differentiation in the Mandibular Condyle of the Rat

The effects of mechanical factors on the growth of the mandibular condyle were studied by monitoring the maturation of the mesenchymal cells in 55 rats. Thirty-five animals were fed normal pellet food, and 20 were fed a soft diet and their incisors were cut regularly. 3H-thymidine was injected intraperitoneally three days before death at 18, 23, or 33 days. Histologic sections showed the most advanced 3H-thymidine-labeled cells to occur deep in the cartilage, in the lower hypertrophic cell layer in anterior and posterior regions of the condyle, and in the upper hypertrophic cell layer in the superior region at the age of 18 days. A distinct difference in the maturation state of the labeled cells could also be observed between these regions. In animals fed a soft diet, maturation was slower in the superior region of the condyle and faster in the posterior region than in the normal rats. The rate at which cells stepped out of the proliferating cell pool was measured by use of monoclonal antibodies against proliferating cell nuclear antigen. The ratio between labeled cells in the proliferating cell layer and the number of labeled cells beneath it was greater in control animals than in the soft-diet animals. The rate of differentiation and maturation of mesenchymal cells into chondrocytes seems to be controlled by mechanical factors.

Comparison of amounts and properties of collagen and proteoglycans in condylar, costal and nasal cartilages.

In this study we compared the compositions of extracellular matrices of condylar, costal and nasal cartilages to characterize differences in growth patterns in relation to matrix composition. Condylar, costal and nasal cartilages of 25- and 35-day-old rabbits were extracted and subjected to bio- and histochemical analysis to determine total amounts of collagen and amounts and aggregating properties of proteoglycans. We found that proteoglycan content and aggregate formation were greatest in nasal cartilage, and lower in costal and markedly lower in condylar cartilage. The amount of proteoglycans increased by varying amounts in all samples with age. Collagen content was highest in costal cartilage. In 25-day-old rabbits the quantity of collagen in condylar cartilage exceeded that in nasal cartilage. In 35-day-old rabbits the quantities were nearly the same. It is suggested that collagen does not only provide tensile strength, but counteracts forces responsible for interstitial growth such as osmotic pressure. Based on the results, it seems that the amount of proteoglycans is greater in cartilages, which have greater independent growth potential. Variations in increase in amount of proteoglycans with age could reflect differences in the timing of growth of such cartilages.

Immunohistochemical localization of the matrix glycoprotein tenascin in the skull of the growing rat.

Tenascin is an extracellular matrix glycoprotein which interacts with other matrix molecules and with cells, and which appears to play important roles in growth and differentiation. The immunohistochemistry of sections of newborn, 5-day and 20-day-old rats showed that accumulation of tenascin was largely restricted to bones, cartilages and teeth. It was also present in the periosteal and endosteal surfaces of membrane bones, in perichondrium, and ion the dental pulp, but was absent from mature bone, cartilage and dentine. In nasal cartilage, tenascin was present only in the perichondrium, whereas in the condylar cartilage staining was observed in the proliferating and maturing cell layers but not in the hypertrophied cartilage. These differences may reflect differences in the growth mechanisms of primary and secondary cartilages. Accumulation of tenascin was particularly striking in areas where the periosteum or perichondrium was thickened such as sites of some muscle attachments, sutures and condylar cartilage. The restricted distribution of tenascin is unlike the patterns observed for other extracellular matrix molecules. Tenascin may have a unique role in bone growth and remodelling in the craniofacial region.

Mechanism of Adaptation in the Mandibular Condyle of the Mouse

The cranial base and whole mandible of 7-day-old mice were cultured for 1 or 2 weeks in a novel organ culture system that provided an articulating movement for the temporomandibular joints. The mandibles were articulating either in a closed or in an open position to simulate the in vivo mouth-breathing pattern. The reactions of the condylar processes were followed macroscopically and microscopically after osteoid or von Kossa staining. After 1 week of culture, small differences were found in the shape of the condylar processes between the two groups. After 2 weeks, significantly increased growth was observed superiorly in those condyles which had been working in a closed position and posteriorly in the condyles which had been working in an open position. Histologic analysis revealed that after 1 week calcification had proceeded faster in the posterior aspect of the condyles in the mandibles which had been working in a closed position as compared to the mandibles which had been working in an open position, and the difference was even more marked after 2 weeks. In the latter condyles calcification had proceeded markedly in the anterosuperior aspect. Osteoid staining showed that perichondrial mesenchymal cells had differentiated into osteoblasts in the posterior aspect of the condyles in those mandibles which had been working in a closed position. This led to a ceasing of expansive growth in the posterior aspect and thus to a more upwardly directed condylar growth. In mandibles which had been working in the open position to simulate the mouth-breathing pattern in vivo, chondrogenesis and thus expansive growth continued in the posterior aspect, leading to a more posteriorly directed condylar growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycosaminoglycan Synthesis in the Mandibular Condyle during Growth Adaptation

Condylar growth was studied after an operation simulating functional orthodontic appliances. Twenty-five rabbits underwent a surgical operation for the induction of premature synostosis to displace the glenoid fossa posteriorly during growth. Twenty-five control rabbits underwent sham operations. At the age of 15 days, 10 experimental and 10 control animals and, at the age of 20 days, 5 experimental and 5 control animals were killed. Their mandibular condyles were organ-cultured for 3 h in the presence of radiolabelled sulphur. The condyles were used for autoradiographic purposes. Digital image analysis of autoradiograms of histological sections showed synthesis of glycosaminoglycans to have increased from the anterior to the posterior direction. This increase was more marked in experimental animals than in the condyles of control animals. Ten experimental and 10 control animals were killed at the age of 15 days, and mandibular condyles were organ-cultured for 1, 4 and 7 days. Differentiation of proliferating prechondroblasts into hypertrophied chondrocytes continued under organ culture conditions. A marked decrease in the proliferating cell layer was noticed, especially in control condyles. Hypertrophy was faster and came closer to the surface of the condyle in the anterior region of the condyle. This was most marked in the condyles of experimental animals. The results indicate that a procedure carried out on the glenoid fossa with the same effect as functional appliances increases the synthesis of extracellular matrix in the posterosuperior region of the mandibular condyle.

Relation of glenoid fossa morphology to mandibulofacial asymmetry, studied in dry human Lapp skulls.

Asymmetry in the shape and location of the temporomandibular joint and its associations with mandibulofacial asymmetry were studied in 40 Lapp skulls by a method in which the configuration of the fossa is clearly defined. The results show a general directional temporomandibular asymmetry. The glenoid fossa on the right was on average more laterally and distally placed than on the left when studied in the axial view. The mandible was more often longer on the left than on the right in the frontal view. The temporomandibular asymmetry found here was associated with skull base characteristics and left-right differences in mandibular length. The basic reason for the asymmetric relationships may lie in the reciprocal interaction between the developmental aspects of the skull base and impaired directional function.

Effect of altered loading on condylar growth in the rat

The aim of this investigation was to ascertain whether lessening of function by feeding rats a soft diet and cutting their incisors can change the growth of the condyle. Sixty Wistar rats were divided into two groups; a control group fed whole pellets and a soft-diet group fed ground pellets. At the age of 21 days the upper and lower incisors of the soft-diet group were shortened by cutting with a wire cutter twice a week. Ten control rats and 10 soft-diet rats were injected with alizarin red (200 mg/kg) intraperitoneally at the age of 22, 30, or 40 days and killed at the age of 30, 40, or 50 days, respectively. The heads were freed of soft tissues, and the growth of the condylar process and the mandible was measured. The height growth of the condylar process was significantly greater in the soft-diet group by 30 and 40 days, and its length growth was greater in the soft-diet group by 50 days. It is concluded that the change in the amount of chewing force and the place of articulation of the condyle alters the growth of the condylar process. Lessening of the load increases condylar growth until a new balance is achieved.

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

SummaryAn 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.

Weaning and the Histology of the Mandibular Condyle in the Rat

Eighty-eight Long Evans/Turku rats were used in the study. The effect of the articulatory function on the mandibular condyle was observed histologically during normal growth, when the rat is changing its diet from milk to whole pellets as a part of weaning. Six animals each were killed at the age of 10, 15, 20, 25, 30, 35, 40 and 50 days for histological tissue processing. For further information, 30 animals were fed a soft diet (6 animals each were killed at the age of 25, 30, 35, 40 and 50 days), and 10 animals were fed hardened pellets (2 animals each were killed at the ages of 25, 30, 35, 40 and 50 days). An even and regular transition from mesenchymal cells via immature chondroblasts into mature chondroblasts and hypertrophied chondrocytes was found at 10, 15 and 20 days during normal growth and also at 25, 30, 35, 40 and 50 days when animals were fed a soft diet. This maturing process appeared to be disturbed at the age of 25, 30, 35 and 40 days in the superior aspect of the condyle in animals fed ordinary pellets. The density of the mesenchymal cell layer was decreased, and the amount of intercellular matrix seemed to be evaluated in mesenchymal and intermediate cell layers. These features were later manifest deeper in the cartilage as acellular regions and as cell clusters. The changes were similar but more severe when the animals were fed hardened pellets.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in biologic response of the mandibular condyle to forward traction or opening of the mandible An experimental study in the rat

The effect of different mandibular postures on the growth of the mandible was studied. A total of 60 female Wistar rats were divided into 3 groups, and all the animals were anesthetized for 6 h daily from the age of 30 days onwards. The first group served as controls. The second had the mandible maintained in a protracted position, and the third had the mandible in an open position during the anesthesia. Macroscopic measurements showed the growth of the mandibular condyle to be increased in a posteroinferior direction and also in a superior direction in the animals with the mandible in an open position. The cartilage layer containing collagen type II was significantly thinned, whereas cell proliferation had significantly increased in the posterosuperior region. In association with mandibular protrusion the thickness of the cell layer containing collagen type II had increased, and cell proliferation in the posterosuperior region had significantly decreased. Significant differences in the growth of the condylar process were observed histologically and histochemically between the experimental animals, implying that the most rewarding aspect of the regulation of condylar growth seems to be the possibility to regulate the maturation rate of the cartilage cells.