Deformation of nasal septal cartilage during mastication

Abstract

The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals were (1) to determine whether the cartilage should be considered as a vertical strut supporting the nasal cavity and preventing its collapse, or as a damper of stresses generated during mastication and (2) to shed light on the overall pattern of snout deformation during mastication. Strains were recorded simultaneously at the septo-ethmoid junction and nasofrontal suture during mastication. A third location in the anterior part of the cartilage was added during masseter stimulation and manipulation. Contraction of jaw closing muscles during mastication was accompanied by anteroposterior compressive strains (around -1,000 muepsilon) in the septo-ethmoid junction. Both the orientation and the magnitude of the strain suggest that the septum does not act as a vertical strut but may act in absorbing loads generated during mastication. The results from masseter stimulation and manipulation further suggest that the masticatory strain pattern arises from a combination of dorsal bending and/or shearing and anteroposterior compression of the snout.

Fig. 1

Sagittal section of a pig skull illustrating location of nasal septal cartilage, its relations to surrounding structures, and the location of the DVRTs. E, perpendicular plate of ethmoid bone; F, frontal bone; FS, frontal sinus; M, maxilla; N, nasal bone; OR, rostral bone (os rostri); PM, premaxilla; PS, presphenoid bone; SC, septal cartilage; V, vomer; VG, vomerine groove which contains the lower portion of the septal cartilage. The DVRTs were implanted in the anterior cartilage (Ant DVRT), nasofrontal suture (NF DVRT) and the septo-ethmoid junction (SE DVRT). Note that the anterior DVRT was inserted after the pig was reanesthetized.

Fig. 2

Dorsal view of a pig skull illustrating surgical access windows (dashed boxes) and sensor locations. Ant, anterior; NF SG, nasofrontal suture strain gauge. Other abbreviations are as in Figure 1.

Fig. 3

Coronal sections of the snout (hematoxylin and eosin stain) showing the nasal septal cartilage (A) at the location where the anterior DVRT was implanted and (B) close to the septo-ethmoid junction where the posterior DVRT was implanted. Dorsally the cartilage splits into two parietotectal cartilages that underlie the nasal and frontal bones. (C,D) Enlargements of the boxed areas in B. The parietotectal cartilages are tightly connected to the overlying bones by fibrous tissue as seen in C. The ventral part of the cartilage lies on a pad of loose connective tissue in the vomerine groove as seen in D. The vomerine groove depth increases posteriorly (compare A and B). The break between the palate and the palatal mucosa in both A and B is artifactual.

Fig. 4

Recording from subject 401 during mastication illustrating EMG of right and left masseter and temporalis synchronized with the nasofrontal and septo-ethmoid DVRTs and nasofrontal strain gauge. The side of chewing is indicated at the top. Scale bars correspond to 30 mV for masseter and 100 mV for temporalis, 500 με for the DVRTs and strain gauge.