Growth of the nasal bone in the rat

Age-related transversal changes in craniofacial sutures of the anterior viscerocranium in growing rats

Objective: To evaluate the dimensional changes that occur in the internasal and nasopremaxillary sutures, and related transverse craniofacial dimensions, of rats from 4 to 38-weeks of age. Methods: Four groups of twelve male Wistar rats were sacrificed at different ages [4-weeks (immature), 16-weeks (adolescent), 26-weeks (young adult), 38-weeks (adult)]. The rats were scanned with a high-resolution micro-computed tomography imaging device with 90 µm voxel size and 45 mm × 45 mm field of view (FOV) to obtain images of the viscreocranium, and with 10 µm voxel size and 5 mm × 5 mm FOV to obtain images of the internasal and left nasopremaxillary sutures. The nasal bone width, transverse width between the nasopremaxillary sutures and interzygomatic width were measured as craniofacial measurements. The endocranial, ectocranial and mean suture widths (cross-sectional area between endocranial and ectocranial borders/suture height), and suture height were measured at 5 frontal planes with 1.2 mm intervals. Outcomes were compared at different ages, and correlation coefficients were used to assess the relationship between craniofacial and suture changes. Results: All transverse craniofacial dimensions increased significantly from 4-16 weeks of age (p < 0.001). After 16-weeks of age, the only significant increase was observed in interzygomatic width (p = 0.02), between 26 and 38 weeks. In both the internasal and nasopremaxillary sutures, the endocranial suture mean widths decreased from 4-16 weeks (p < 0.001 and p = 0.002, respectively), but did not show any significant change after 16-weeks of age. The ectocranial internasal suture width decreased from 4-16 weeks (p < 0.001), increased until 26-weeks (p = 0.035), and subsequently decreased (p < 0.001). The nasopremaxillary suture widths decreased from 4-38 weeks to varying degrees in different frontal planes. Except for the internasal ectocranial suture width, all suture measurements were found highly and negatively correlated with the transverse craniofacial dimensions. The height of the sutures increased with time, with the most significant changes occurring between 4 and 16 weeks of age (p < 0.001). Conclusion: Although the internasal and nasopremaxillary endocranial suture widths nearly reach their final widths during adolescence, the changes in the ectocranial and mean suture widths continue into early adulthood. These results may serve as a reference for future studies aiming to evaluate the effects of functional demands on suture development and dimensional changes of the viscerocranium.

Studies on orthocephalization: growth behavior of the rat skull in the period 13-49 days as described by the finite element method

Rat cranial skeletal growth was studied, using a cross-sectional data set, for the period 13-49 days by the application of the concepts of continuum mechanics and the numerical techniques of the finite element method (FEM). In contrast to the methods of conventional craniometry (CM) and roentgenographic cephalometry (RCM) the FEM permits fine scale, reference frame invariant descriptions and analysis of growth behavior. This advantage was demonstrated by a numerical example of the use of FEM. The skull was discretized into a number of two-dimensional, triangular elements, whose enclosed areas corresponded closely to both specific skeletal structures and to related functional matrices. Since it was assumed presently that the growth behavior of all of the points enclosed within a given element was similar, the application of the functional matrix hypothesis permitted an integrated description of the growth of the skeletal structure and functional matrix related to each element. The principal locus of rotation of the facial skull, relative to the cranial base, is the inferior frontoethmoidal articulation, a motion that includes a rigid body rotation. Other active and passive skeletal and visceral growth events associated with orthocephalization were located and described. Finally it was shown that the morphogenetically important growth behavior of other portions of the rat head were not directly involved in orthocephalization.

Restricted growth at the frontonasal suture: alterations in craniofacial growth in rabbits

Apposition of bone at the sutural margin is generally thought to be a compensatory adjustment to growing soft-tissue organs such as the brain or eyes within the skull. The frontonasal suture which is located at the interface between the cranial and facial skeletons is a site of extremely active growth in the young rabbit. Recently, we showed that premature closure of a cranial suture, the coronal suture, can alter the growth not only at the adjacent frontonasal suture but also of the basicranium and midface. This study examines the effects of restricted growth at the frontonasal suture on both growth at adjacent cranial sutures and linear growth of the basicranium and midface. Thirty newborn New Zealand White rabbits were subdivided into experimental and sham-treated groups of equal size and distribution for sex and birth weight. At 9 days of age, the frontonasal suture of each experimental animal was immobilized by bilateral application of methyl-cyanoacrylate adhesive across the frontonasal suture. Growth and morphometric changes were monitored by radiocephalometric methods through 120 days of age by bilateral implantation of radiopague markers on each side of frontonasal, coronal, and anterior lambdoid sutures. Results indicate that restricted growth at the frontonasal suture results not only in a significant shortening of the midface but also in significant decreases in growth at the coronal and internasal sutures. Growth at the interfrontal and sagittal sutures is increased. Furthermore, growth at the anterior portion of the nasal bones is significantly increased, thereby offsetting a portion of the decreased nasal bone length resulting from frontonasal restriction.

Spatial position of the lateral semicircular canal in 14--60-day-old rat heads

During growth the rat skull straightens considerably due to flexions between skull parts and individual bones. This straightening is defined as orthocephalization. Orthocephalization might also be caused by a change in head posture during growth, i.e. it may be "apparent". In order to study the significance of this phenomenon, radiographs of dried skulls of male rats, 14, 30 and 60 d of age were subjected to angular measurements between the plane of the lateral semicircular canal and the plane of foramen magnum and of the basisphenoid bone, respectively. When the plane of the lateral semicircular canal is placed horizontally, the head is claimed to be in natural position. No changes in the angulation between the lateral semicircular canal and the basisphenoid bone could be revealed, whereas the foramen magnum was shown to rotate upwards and backwards in relation to the plane of the canal. This implies that the orthocephalization which takes place between 14 and 60 d is caused only by angular changes, and that no apparent changes occur due to changes in head posture.

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.