Functional cranial analysis of the human maxillary bone: I, Basal bone

A morphometric analysis of the immature human infraorbital canal

PURPOSE

The importance of the infraorbital canal in the growth of the maxilla and associated mid-facial region has significance for innervation of this region as well as the associated dentition, yet little is known about the development of the canal. An analysis of its dimensions and morphology during the late prenatal and early postnatal periods was thus undertaken. The aim of this study was to describe changes in the morphology, size and branching pattern of the infraorbital canal during the late prenatal and early postnatal stages of human growth.

METHODS

Fifty human fetal and neonatal maxillae were analyzed. The sample included 27 late prenatal individuals (30 gestational weeks and birth) and 23 early postnatal individuals (birth and 1 year). Maxillae were scanned using a Nikon XTH 225 L micro-CT unit and analyzed using VG studiomax v3.2. Measurements included the maximum width, height and surface area of each foramen associated with the infraorbital canal and the total length of the canal, bilaterally.

RESULTS

All the measurements of the canal were greater in the early postnatal group than in the late prenatal group, while the walls and branching pattern of the canal were better developed in the postnatal group. Bone development occurred within the walls as development proceeded. Variations in the branching pattern of the canal were found.

CONCLUSION

The morphology of the infraorbital canal reflected the developmental stage of associated structures such as the dentition, maxillary sinus and orbit.

Morphometric study on the infraorbital foramen in relation to sex and side of the cranium in northeastern Brazil

Detailed knowledge of the possible anatomical and morphometric variations of the infraorbital foramen (IOF) is important for ensuring safe and successful regional anesthesia, and for avoiding iatrogenic nerve injuries during surgery on the middle third of the face. To conduct a morphometric study on the IOF, correlating this with sex and side of the cranium. Two hundred forty-two crania were used (148 male and 94 female). Measurements were made with the aid of digital calipers with precision to 0.01 mm. Presence of foramina and their multiplicity was also observed. The data were analyzed descriptively and analytically. Statistical significance was stipulated as 5% (P≤0.05). The IOF was found bilaterally in all the crania, and 26 of them presented multiplicity. The distance from the IOF to the anterior nasal spine was greater in males on both sides (P<0.001). Statistical differences between the sexes were also seen in relation to the following morphometric variables: height of the left IOF (P=0.007), width of the right IOF (P=0.004), and width of the left IOF (P=0.008), and the measurements were also larger among males. The IOF was present in all the crania and on both sides. It was morphometrically larger in males, on both sides.

Beyond the functional matrix hypothesis: a network null model of human skull growth for the formation of bone articulations

Craniofacial sutures and synchondroses form the boundaries among bones in the human skull, providing functional, developmental and evolutionary information. Bone articulations in the skull arise due to interactions between genetic regulatory mechanisms and epigenetic factors such as functional matrices (soft tissues and cranial cavities), which mediate bone growth. These matrices are largely acknowledged for their influence on shaping the bones of the skull; however, it is not fully understood to what extent functional matrices mediate the formation of bone articulations. Aiming to identify whether or not functional matrices are key developmental factors guiding the formation of bone articulations, we have built a network null model of the skull that simulates unconstrained bone growth. This null model predicts bone articulations that arise due to a process of bone growth that is uniform in rate, direction and timing. By comparing predicted articulations with the actual bone articulations of the human skull, we have identified which boundaries specifically need the presence of functional matrices for their formation. We show that functional matrices are necessary to connect facial bones, whereas an unconstrained bone growth is sufficient to connect non-facial bones. This finding challenges the role of the brain in the formation of boundaries between bones in the braincase without neglecting its effect on skull shape. Ultimately, our null model suggests where to look for modified developmental mechanisms promoting changes in bone growth patterns that could affect the development and evolution of the head skeleton.