Salivary Gland Hypofunction in Aging
Epidemiology
Epidemiologic studies have revealed increases in the prevalence and incidence of dry mouth with age [29], [30]; however, in most studies aging per se is not indicated as the cause or a major risk factor for dry mouth.
It has been hypothesized that this is due to the reserve functional capacity of the salivary glands usually compensating for the loss of acinar tissue that is associated with aging changes in the glands [29].
In contrast to this finding, a recent paper by Smith et al. examined a 1-min stimulated flow collection of whole saliva from three different age groups (n = 180 per group) and did find that with aging (≥70 years) there was a significantly decreased flow rate [31]. This paper is noteworthy in that the stringent exclusion criteria ensured that individuals with medical conditions and/or medications that could impact salivary flow were excluded from participating.
Related Reading: Geriatric Dental Care: Older Adults and Oral Conditions
Effects of Salivary Hypofunction
Reduced salivary flow has many detrimental effects on oral health including increasing the risk of dental erosion, demineralization, dental caries, periodontitis, and intra-oral infections such as candidiasis [13], [14], [32].
Halitosis, burning mouth, oral soreness, difficulty in mastication, speech dysfunction, dysgeusia (taste disturbance) and dysphagia (difficulty swallowing) have all been linked to this finding [33], [34].
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Causes of Hypofunction
Salivary gland hypofunction (SGH) may result from many conditions directly or indirectly affecting the salivary glands [16], [35], [36]. Such hypo-function may signal the presence of serious underlying systemic diseases such as Sjogren’s syndrome [37] and by itself can have overwhelming effects on the oral health that may be observed in both the hard and soft tissues of the mouth [34].
The oral mucosa may become atrophic predisposing the individual to frequent ulcerations and trauma and the teeth can become carious as a result of the shift in the acid/base balance or pH of the saliva, thereby diminishing its buffering capacity. Changes in the concentration of immune-proteins especially when they are related to radiation therapy can also be found [38], [39].
Salivary Hypofunction Flow Values
The cut-off salivary flow values in individual glands for a diagnosis of SGH are based on the following flow rates: unstimulated submandibular/sublingual (sm/sl) or parotid saliva flow of <0.05 mL/min; stimulated sm/sl or parotid saliva flow <0.15 mL/min [40], [41], [42].
As has been previously mentioned, Xerostomia is the subjective sensation of oral dryness. When it does correlate with clinical findings of salivary hypofunction, typically the salivary flow has decreased by more than 40–50% from its usual rate [41], [43].
Risk Factors for Either Salivary Hypofunction or Xerostomia
Female sex is another known risk factor for dry mouth. Epidemiologic studies have demonstrated that female patients have a higher prevalence of the perceived symptoms of a dry mouth sensation or Xerostomia than males do at all ages [30].
Even though female patients are likely to take more medications than the male patients, the prevalence of Xerostomia was still high in non-medicated females compared to their male counterparts [30], [44]. However, in the study by Smith et al. healthy females did not differ significantly from healthy males in the same age group when stimulated salivary flow was measured objectively [31].
Common habits such as smoking, alcohol use (including its topical use such as in mouthwashes) and the drinking of caffeine containing beverages such as coffee and soft drinks can result in a clinical finding of oral dryness. In these instances dry mouth is reversible by avoiding or reducing the habit or consumption of the implicated products [25].
Other causes of dry mouth include heavy snoring, mouth breathing, upper respiratory tract infections, dehydration and fear [45].
Salivary gland atrophy will result in decreased salivary flow and can occur when there are prolonged periods of autonomic denervation such as liquid diet feeding, thus reducing the salivary flow reflex; or salivary duct ligation, which may be done to decrease or eliminate drooling. However, with intact autonomic innervation, there is regenerative capacity in the glands and they regain normal function upon removal of the ligation or reintroduction of feeding by mouth [46].
Various conditions can lead to a major reduction in secretion of saliva (e.g. Sjogren’s and radiation therapy) but it is also a frequent occurrence as a side effect of multiple medications.
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About the Authors
The article, “Dry mouth: A critical topic for older adult patients,” was authored by Phuu Han, Piedad Suarez-Durall, and Roseann Mulligan, Director Geriatric Dentistry Master and Certificate programs at the Herman Ostrow School of Dentistry of USC, and was originally published by Elsevier in the Journal of Prosthodontic Research.
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