Unilateral nasal obstruction induces morphological changes of the mandibular condyle in growing rats

Purpose

Chronic nasal obstruction is known to decrease blood oxygen saturation. Mouth breathing in association with chronic nasal obstruction leads to the collapse of the buccinator mechanism and to a clockwise rotation of the mandible, which causes mandibular retrusion. This study aimed to investigate the influences of nasal obstruction on the morphological and histological changes of the mandible in growing rats.

Materials and methods

Thirty 8-day-old male Wistar rats were randomly divided into the control and experimental groups. The experimental group underwent unilateral nasal obstruction by cauterization of the external nostrils at 8 days of age. Pulse oxygen saturation (SpO₂) was monitored every week. Rats were sacrificed at 9 weeks of age. The mandibular changes were analyzed via lateral cephalometric radiographs and micro-CT scans. We utilized toluidine blue and tartrate-resistant acid phosphatase (TRAP) staining for histological analysis. Immunohistochemical staining of hypoxia induced factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), osteoprotegerin (OPG) receptor activator of nuclear factor kappa-B ligand (RANKL) were also performed to reveal the mechanism of the morphological changes.

Results

SpO₂ was significantly lower in the experimental than in the control group. In the experimental group, length, bone mineral density and cartilage layer thickness of mandibular condyle were decreased. The number of TRAP-positive cells in the condyle, HIF-1α-positive cells, VEGF-positive cells and RANKL-positive cells in the condylar cartilage was significantly increased. In contrast, a reduced expression of OPG protein was observed in the experimental group.

Conclusions

Our findings suggest that unilateral nasal obstruction in the growth period affects mandibular morphology.