Role of the nasal septal cartilage in midfacial development

Abstract

<bold>University of Washington<bold> <bold>Abstract<bold> <bold>Role of the nasal septal cartilage in midfacial development<bold> Ayman Al Dayeh <bold>Chair of the Supervisory Committee: <bold> Professor Susan W. Herring Department of Orthodontics The role of the nasal septal cartilage in midfacial growth has been an ongoing intellectual dilemma. While some authors believe that the septal cartilage is the driving force for midfacial growth, others believe that the cartilage role in midfacial growth is passive and it acts as a vertical strut that supports the midface against masticatory loads. This dissertation evaluated the above hypotheses using a pig animal model to measure the in vivo growth and the mechanical deformation of the nasal septal cartilage during mastication. The in vivo growth of the nasal septal cartilage and nasofrontal suture was measured in real time using linear displacement transducers. In addition, cellular proliferation of the septal chondrocytes was evaluated. The results showed that the growth strain rate of the nasal septal cartilage (0.07 ± 0.03 % length/hour) was significantly higher than that of the nasofrontal suture (0.03 ± 0.02% length/hour) and that the growth of the cartilage tended to precede the separation of the suture. In addition, cellular proliferation analysis revealed that the septal chondrocytes are proliferating at a relatively high rate (22 ± 5.0% /24 hours). Deformation of the septal cartilage and nasofrontal suture during mastication was assessed utilizing linear displacement transducers. The results showed that the septal cartilage and the nasofrontal suture are compressed in an anteroposterior direction during mastication with the magnitude of deformation of the septal cartilage (1000 to 2700 µε) comparable to the deformation of the suture (2000 to 4000 µε). The orientation of the compressive strain is not consistent with a role of the septum as a vertical strut. The mechanical properties of the septal cartilage were evaluated. The results revealed that the septal cartilage is highly adaptable to compressive loading and that its stiffness is much lower than stiffness of surrounding bones. In conclusion, the results of this thesis support the hypothesized active role of the nasal septal cartilage in midfacial growth. On the other hand, the hypothesis that the septal cartilage acts as a vertical strut during mastication was not supported.