Torus mandibularis affects the severity and position-dependent sleep apnoea in non-obese patients

Objective: Various anatomical structures of upper airway and physical differences are known to be risk factors for obstructive sleep apnoea (OSA). Torus mandibularis is a structure that can appear on the inside of the mandible. Therefore, it is possible for tori to influence airway volume by occupying the space for tongue and cause sleep apnoea. The purpose of this study is to investigate the effect of torus mandibularis on the severity of OSA as one of the craniofacial risk factors.

Design: Retrospective case-control study.

Setting: University-based tertiary medical centre.

Participants: Adult patients over 19-years-old who visited outpatient clinics with complaints of sleep-disordered breathing symptoms between January 2010 and December 2017 were investigated.

Main outcome measures: The presence of torus mandibularis in oral cavity was confirmed by physical examination or CT image. We analysed demographic findings including age, sex, medical history, previous operation history, physical findings of upper airway and result of polysomnography. To evaluate the effect of torus mandibularis on OSA, polysomnography data of the two groups according to presence or absence of torus mandibularis were compared and analysed.

Results: Two-hundred and thirty-two OSA patients with BMI <25 were divided into two groups, according to either the presence or absence of torus mandibularis. We analysed 138 patients of control group and 94 of torus mandibularis group. Apnoea-hypopnoea index (AHI) was 18.8 ± 14.9 in control group and 25.1 ± 18.4 in torus mandibularis group (P = 0.006). Respiratory disturbance index (RDI) was 23.1 ± 14.7 in control group and 27.9 ± 18.4 in torus mandibularis group (P = 0.035). Supine AHI showed 26.6 ± 20.3 in control group and 32.5 ± 22.6 in torus mandibularis group (P = 0.039). Patients with torus mandibularis had a trend of increase in proportion according to the severity of sleep apnoea, such as AHI (P = 0.007) or RDI (P = 0.034).

Conclusions: We newly found that the presence of torus mandibularis affects not only severity of OSA and also position-dependent OSA. These results support the necessity of torus mandibularis evaluation in OSA patients, and further study is also required to investigate its consequence in the surgical outcome.