Herman S. Duterloo

Effects of compressive forces on proliferation and matrix synthesis in mandibular condylar cartilage of the rat in vitro

The cartilage from 4-day-old rats were exposed to continuous and intermittent compressive forces. Proliferative activity and matrix synthesis in vitro were determined by measuring the incorporation of [3H]-thymidine, [35S]-sulphate and [3H]-proline by autoradiography and liquid-scintillation counting. The findings suggest that a continuously-applied force of approx. 0.5 g stimulated proliferation in the condylar cartilage but reduced the synthesis of the sulphated glycosaminoglycans and collagen. A stimulatory influence on the synthesis of these matrix components, on the other hand, was observed when the condylar cartilage was exposed to an intermittent force (0.7 Hz) of approx. 0.5-1.0 g; this intermittent force, however, reduced the proliferative activity. It appears that, at least in vitro, the basic growth processes in the condylar cartilage can be regulated by compressive forces.

Growth and growth pressure of mandibular condylar and some primary cartilages of the rat in vitro

To compare the in vitro development of the secondary cartilage of the mandibular condyle with that of primary cartilages, several cartilaginous explants derived from 4-day-old rats were cultured in a serum-free culture system. The following cartilages were used: the mandibular condylar cartilage, the distal epiphyseal cartilage (including the growth plate) of the third metatarsal, a fragment of costal cartilage (including the osteochondral junction) of the fourth rib, the spheno-occipital synchondrosis and the chondroepiphysis of the femoral head. In addition, with a specially designed, in vitro pressure registration system, the maximal growth pressures for each of the explants, except the femoral head, were determined. The results show an independent growth potential for the primary cartilages of the epiphyseal and costal growth plates with a maximal growth pressure of 9.5 and 7.8 g/mm2, respectively. The primary cartilage of the spheno-occipital synchondrosis, on the other hand, although it possesses an independent growth potential, could exert a maximum growth pressure of only 1.5 g/mm2. The secondary cartilage of the mandibular condyle showed a limited intrinsic growth potential, as well as a low maximal growth pressure (2.6 g/mm2). If calculated per dividing and/or matrix synthesizing cell (cells mainly responsible for the cartilage growth), the cells of the condylar cartilage showed the least growth potency (0.08 mg/cell in comparison to 1.9, 1.5 and 0.3 for epiphyseal, costal, and synchondroseal cartilages, respectively.

An in-vitro system for studying the effect of variable compressive forces on the mandibular condylar cartilage of the rat

An in-vitro system enabled variable range of continuous and intermittent compressive forces to be applied to the cartilage of 4-day-old rats under serum-free culture conditions. A continuous compressive force below 3 g did not affect the growth of the cartilage; when the force exceeded 3 g, growth ceased. Under an intermittent compressive force up to 8 g, growth continued, but at a lower rate; over 8 g, growth ceased. When growth-restricting compression was removed or reduced, growth was reactivated until a new balance was achieved. The normal architecture of the different zones was altered in the non-compressed in-vitro controls, but not in cultured cartilage during the application of these compressive forces.

GROWTH OF THE MANDIBULAR CONDYLAR CARTILAGE OF THE RAT IN SERUM-FREE ORGAN-CULTURE

To evaluate the intrinsic capacity for growth, the mandibular condylar cartilage of 4-day-old rats was cultured in a serum-free, chemically-defined medium for 28 days and compared with the condylar cartilage cultured in a serum-supplemented medium and with the normal growth in vivo. Under the serum-free culture conditions, cell proliferation, differentiation into functional chondroblasts and matrix formation continued, but chondroclasia and osteogenesis were absent. This resulted, after 28 days of culture, in an enlarged condylar cartilage with altered proportions, a severe reduction of the prechondroblastic and the transitional zone and a considerable increase of the hypertrophic zone. It appears that the serum-free culture system is unfavourable for endochondral osteogenesis and lacks factors modulating the rate of proliferation, differentiation and maturation of the prechondroblasts. In the functional environment of the condyle, humoral or mechanical factors seem to exert this essential modulating influence on the condylar-cartilage growth.

THE INITIAL REACTION OF A MACERATED HUMAN SKULL CAUSED BY ORTHODONTIC CERVICAL TRACTION DETERMINED BY LASER METROLOGY

Tensile forces were applied to the maxilla of a macerated human skull in a backward direction 10 degrees below the occlusal plane. The skull was fixed to a heavy metal support at the occipital and parietal bones. These forces were applied near the first permanent molars via a rigid stainless steel bar, which was fitted to a cast-metal splint attached to the palatal surface and buccal region of the maxillary arch. Forces were increased step by step from 2.0 N (1N = 100 grams) to 7.25 N per side. Using a holographic configuration with two 5 mW HeNe lasers, double-exposure holograms were made from the frontal and from the left lateral sides. Fringe shifts in different points of the hologram were measured and the x, y, and z components of the displacement were calculated for eight points located on various bones of the skull. Viewed from the frontal, force application to the maxilla resulted in a downward and backward rotation. The zygomatic bone was also rotated downward and backward with a small rotation in a transverse direction. Other craniofacial structures were also affected. With a force of 7.25 N per side, a deformation of the temporal bones and zygomatic arches occurred.

THE INITIAL EFFECTS OF ORTHOPEDIC FORCES - A STUDY OF ALTERATIONS IN THE CRANIOFACIAL COMPLEX OF A MACERATED HUMAN SKULL OWING TO HIGH-PULL HEADGEAR TRACTION

The initial reaction of components of the craniofacial skeleton of a macerated human skull was studied after high-pull headgear traction. The applied forces were increased step by step from 0.5 N to 3.25 N per side (1N = 100 grams). Laser holography was used for measuring displacements in three dimensions in seventeen indicator points on the skull. These points were located near sutures or on the outer surface of individual bones. The skull was observed from the right frontal and from the left lateral side. Results indicate that displacements range from 0 micrometer to 17.0 micrometers, depending on force magnitude and on the location of the observed point. Individual components of the craniofacial skeleton were mostly displaced in a horizontal backward direction when the skull was viewed from the frontal aspect. Various compression and shearing patterns were observed in the craniofacial sutures, apparently depending on their spatial locations and intersutural surface morphology.

Initial displacements and variations of eight human child skulls owing to high-pull headgear traction determined with laser holography

In this study eight macerated, human child skulls (dental age approximately 9.5 years) were subjected to a standardized high-pull headgear traction system. Tensile forces from 0.5 to 3.5 N (1 N = 0.1 kgf) per side were produced to the maxillae. Displacements of skeletal components were determined at 22 indicator points per skull by means of laser holography. Coordinated displacements and variations in amount and direction were established in all skulls. The overall amount of displacements was primarily a characteristic of an individual skull, not of a particular displacement. On the average, the maxillae were displaced in a slightly downward and posterior direction almost parallel to the occlusal plane. No deformations of skeletal components were seen. Results indicated that initial displacements of the maxillae and other skeletal components are not in the same direction as the direction of applied forces.

Translative and transformative growth of the rat mandible

The growth of the rat mandible was studied during a period from 14 to 30 days of age. Roentgencephalometric and alizarin vital staining techniques were employed. Growth in length doubles the growth in breadth; the angle between the mandibular halves decreases slightly. Bone remodeling patterns were revealed with the alizarin technique. Posteriorly facing surfaces and the anterior end of the incisal process show apposition. Lateral facing surfaces of the posterior part of the mandibles were resorptive. A medio-posterior growth direction of these parts were found. The intermandibular articulation plays no role in the translative growth movements, in contrast to other articulations between skull bones as sutures and synchondroses, but serves primarily during biting and chewing.