Revisiting the link between cognitive decline and masticatory dysfunction

Abstract

Age-related decline in cognitive functions and dementia are major challenges in geriatric healthcare. Accumulating evidence from clinical, epidemiological and animal research suggests that tooth loss may be a risk factor for the decline of cognitive functions. This issue highlights the role of the brain-stomatognathic axis in geriatric medicine. Whether input from the stomatognathic apparatus can affect the brain remains an open debate. By revisiting the evidence published in the past five years, we argue that the hypothesis regarding the association between cognitive decline and masticatory dysfunction should be carefully interpreted. Most of the available clinical and epidemiological studies present only cross-sectional data. With respect to the prospective studies, important confounding factors, such as nutritional and physical conditions, were not fully controlled for. Animal research has revealed that hippocampal deficits may play key roles in the observed cognitive decline. However, experimental intervention and outcome assessments may not capture the condition of human subjects. Brain neuroimaging research may be suitable for bridging the gap between clinical and animal research, potentially contributing to (a) the clarification of the brain network associated with mastication, (b) the identification of brain imaging markers for exploring the mechanisms underlying long-term changes in masticatory functions, and (c) the elucidation of interactions between mastication and other cognitive-affective processing systems. Three potential models of the brain-stomatognathic axis and relevant hypotheses are summarized, focusing on the sensory feedback mechanisms, the compensation of motor control, and cerebellar deficits. Finally, we highlight four critical aspects of study and experimental design that should be considered in future research: (a) the refinement of the considered behavioral assessments, (b) the inclusion of baseline changes in mental and physical conditions, (c) a prospective experimental design with longitudinal observations, and (d) a precise determination of the effect size of the association between cognitive decline and masticatory dysfunction.Electronic supplementary materialThe online version of this article (10.1186/s12877-017-0693-z) contains supplementary material, which is available to authorized users.

Meta‐analysis of brain mechanisms of chewing and clenching movements

“…Therefore, synthesising the loci commonly activated during teeth occlusion would be a critical step in establishing imaging markers for brain representation related to orofacial sensorimotor functions. Finally, accumulating evidence has shown that the brain and the stomatognathic system engage in bidirectional communication . A hotly debated issue is whether an association exists between declining masticatory function and declining cognitive function .…”

“…Finally, accumulating evidence has shown that the brain and the stomatognathic system engage in bidirectional communication. 15 A hotly debated issue is whether an association exists between declining masticatory function and declining cognitive function. 56,57 A potential application of fMRI is to explore the neural mechanisms underlying this potential association and to identify, for example, the relationship between chewing-related S1/M1 representations (an index of oral function) and changes in hippocampal/prefrontal activation (an index of cognitive function).…”

“…Masticatory dysfunction is associated with interruption of the S1/M1 or the CMA . In human subjects, the association between the sensorimotor cortex and mastication has been investigated using fMRI . Recent evidence shows that repeated clenching tasks would induce a neuroplastic effect on the corticomotor control of the masticatory muscles .…”

“…14 In human subjects, the association between the sensorimotor cortex and mastication has been investigated using fMRI. 15 Recent evidence shows that repeated clenching tasks would induce a neuroplastic effect on the corticomotor control of the masticatory muscles. 16 Such a training-related change of oromotor function may be associated with M1 neuroplasticity.…”

Prediction of Frailty and Dementia Using Oral Health Impact Profile from a Population-Based Survey

“…There has been growing evidence suggesting that poor oral health is associated with cognitive impairment in older adults. The issue highlights the role of the brain-stomatognathic axis in geriatric medicine [50]. Previous studies have demonstrated that suboptimal dentition (<20 teeth) and poorer mastication are associated with a higher risk of dementia or cognitive decline [20,51].…”