Effects of unilateral nasal obstruction on the characteristics of jaw-closing muscles in growing rats

Objectives: Mouth breathing caused by nasal obstruction (owing to abnormal pressure of masticatory muscles) affects craniofacial growth and development. The influence of unilateral nasal obstruction on jaw-closing muscles was investigated in rats to reveal one of the etiologic mechanisms. Materials and Methods: Forty 8-day-old male Wistar rats were used in this study. Experimental rats were subjected to left-sided nasal obstruction by burning the external nostril tissue at the age of 8 days. Pulse oxygen saturation was recorded each week. Morphologic changes were evaluated by staining with hematoxylin and eosin (to assess the cross-sectional area) and by adenosine triphosphatase activity staining (to assess the myosin heavy chain isoform composition). Immunohistochemical and reverse transcription quantitative real-time polymerase chain reaction analyses of tumor necrosis factor-alpha and glucose transporter 4 were carried out at 5 and 9 weeks of age. Results: The cross-sectional area of the jaw-closing muscles was lower in the experimental group at 9 weeks of age. The percentage of myosin heavy chain-2a in masseter muscles was increased in the experimental group compared with the control group. An increase in the tumor necrosis factor-alpha messenger RNA and protein levels and a decrease in the glucose transporter 4 messenger RNA and protein levels at 5 and 9 weeks of age in the jaw-closing muscles in the experimental group were noted. Conclusions: Unilateral nasal obstruction could affect the morphology and contractile characteristics of jaw-closing muscles during growth in rats.