Oral Dysfunction and Cognitive Decline: A Review of Nutritional and Brain Structural Pathways Linking Tooth Loss, Oral Frailty, and Solitary Eating to Dementia.

Dementia is a growing challenge for aging societies, and effective prevention depends on identifying risk factors that can be addressed early, before cognitive decline becomes clinically apparent. Declining oral and dental function, particularly tooth loss, is increasingly recognized as one such factor, and its effect on the brain extends well beyond a reduced ability to chew. This review synthesizes current evidence linking impaired oral function to cognitive decline and dementia, with a focus on nutritional and structural brain pathways. We propose that tooth loss affects the brain through two partly independent routes. The first is nutritional: tooth loss shifts the diet away from fiber- and micronutrient-rich plant foods, which may injure the brain through oxidative stress, inflammation, and gut microbiota changes; the hippocampus, a key memory region, appears especially sensitive to nutritional status. Eating alone adds a social dimension: it is associated with lower diet quality and with reduced volume in memory-related regions, an association only partly explained by diet, since the medial temporal difference persists after dietary adjustment. The second is sensory-neural: the loss of natural teeth removes sensory input from the periodontal ligament and reduces chewing, weakening signaling to the brain and its capacity for plasticity. Importantly, atrophy of the medial temporal lobe and adjacent memory-related regions, together with increased white matter damage, is detectable even in cognitively healthy older adults, and a revised Oral Frailty Five-item Checklist can identify these presymptomatic changes. Because these structural brain changes persist despite denture use and after adjusting for diet, preserving natural teeth may be an especially valuable preventive target. Overall, maintaining oral function is a promising, accessible target for dementia prevention that warrants confirmation in prospective trials.