In this study, we examined the clinical characteristics of patients with dental malocclusion from an otolaryngologic perspective and evaluated the correlation between AR and dental malocclusion. The incidence of SPT (+) (79.7%), hypertrophied inferior turbinate (82.0%), and T&A hypertrophy (31.8%) in the orthodontic group exceeded the values observed in epidemiological studies in the general population [16–19]. We found a high prevalence of nasal symptoms and abnormal physical findings even in SPT (-) patients with dental malocclusion. Hypertrophied tonsils, adenoids, and inferior turbinates can cause mouth breathing by obstructing the nasal airway [20–22]. These physical findings should be considered as risk factors for dental malocclusion. However, the severity of symptoms was lower among patients in the orthodontic group than those in the AR group. The mean MCA of the nasal cavities measured using acoustic rhinometry was not significantly different between the two groups. These values are similar to those reported in the general population of the same age group in South Korea .
Our findings suggest that constitutional or structural problems seem to affect the development of dental malocclusions in patients undergoing orthodontic treatment, although not as much as in patients with AR. Upper airway obstruction that induces mouth breathing can lead to the development of malocclusion, by causing an imbalance between the forces from the cheeks and the tongue and an altered position of the mandible [24–25]. Upper airway obstruction and mouth breathing can be induced by many different factors which are responsible for the obstruction of air reflux inside the nasal cavity, deformities of the nasal septum, T&A hypertrophy, nasal polyposis, and AR [26, 27].
Asymptomatic AR is believed to lead to persistent inflammation of the nasal mucosa . As this minimal persistent inflammation (MPI) may contribute to co-morbidities of AR such as asthma, it is believed that the treatment strategy may need to include MPI management . For patients with subclinical AR, three major options may be used to treat MPI: antihistamines, anti-leukotrienes, and intranasal corticosteroids .
Untreated subclinical AR might contribute to the development of dental malocclusion. Our study suggests that early detection and treatment of subclinical AR, other rhinological problems, and structural abnormalities of the upper airway in patients with malocclusion may help us manage malocclusion from an otolaryngologic perspective.
Several studies have investigated the association between the type of occlusion and prevalence of malocclusion in children with nasal obstruction using cephalometric analysis. However, the results of these studies are inconsistent: the prevalence of malocclusion in children with rhinitis ranges from as high as 78.2% to as low as 3% . Furthermore, few authors have assessed the prevalence of AR and otolaryngologic features in children with dental malocclusion. Luzzi et al.  compared 125 patients with malocclusion with 150 healthy patients. They found that children with AR had a three-fold higher risk of developing one or more dento-skeletal alterations. Imbaud et al.  evaluated 89 patients who underwent orthodontic treatment and observed a higher prevalence of rhinitis and hypersensitivity to airborne allergens in SPT. However, previous studies, including those described above, did not assess the symptoms or structural abnormalities of AR using quantitative parameters. To our knowledge, this is the first study to compare an orthodontic group with an age- and sex-matched AR group using both subjective and objective quantitative parameters such as the SNOT-22 questionnaire and acoustic rhinometry.
However, the present study has some limitations. Acoustic rhinometry has not yet been accepted as a standard evaluation method because of its unstandardized results . In addition, the results of acoustic rhinometry might be inconsistent due to the nasal cycle, which is a physiological phenomenon that causes a periodic change in nasal airway patency. Thus, future studies must analyse nasal cavity structures using imaging techniques such as computed tomography. Furthermore, a prospective study evaluating the effect of treatment of AR on the development of dental malocclusion is needed to better understand the correlation between AR and dental malocclusion.