Feature analysis of salivary glands under ultrasonography

Background: Oral frailty, an ageing-associated decline in oral conditions in terms of oral motor and sensory abilities, contributes to reduced swallowing ability and speech clarity. Salivary glands, which are physiologically responsible for secretion of saliva, deteriorate in the course of ageing, which in turn alters the quantity and composition of saliva. Deterioration of salivary glands is one of the causes of oral frailty, increasing dental caries and causing 'dry mouth' conditions, thereby resulting in reduced efficiency of mastication and bolus formation in oral preparatory phase of swallowing. The latter is one of the core symptoms of oral frailty. The concept of oral frailty has been explored by longitudinal and cohort studies on orthodontic aspects, yet findings remain preliminary and fragmented. This research investigated quantitative and qualitative changes of salivary glands during ageing, with aims to elucidate the ageing process and lay a universal definition on oral frailty. Methods: Ten young adults aged 18 to 60 years and ten older adults aged ≥60 years were recruited. All were screened with the 3-oz water swallowing test and were confirmed to be non-dysphagic. Anatomical presentations of three sets of salivary glands (sublingual, submandibular, and parotid) were captured using B-mode ultrasound with a linear-shaped transducer. Images were processed using the Computer Vision Annotation Tool. Cross-sectional areas of individual salivary glands were measured, and then the features of echogenicity, homogeneity, number of hypoechogenic areas, hyperechogenic reflection, and clearness of gland borders were reviewed. Comparisons were made between the young adults and older adults. Results: The feature of border clearness significantly differed between the two groups. Conclusion: Gland size differences and quality differences between groups potentially contribute to reduced salivary flow rate during the ageing process. Ultrasonographic examinations on salivary glands may be included as part of the clinical bedside instrumental swallowing assessment to determine the functional decline in swallowing ability.