Masticatory Dysfunction by Extensive Tooth Loss as a Risk Factor for Cognitive Deficit: A Systematic Review and Meta-Analysis

Abstract

Background: An amount of cognition decline is normal with aging; however, intrinsic and extrinsic risk factors may exacerbate it, affecting social and occupational tasks. Masticatory dysfunction (MD), as a general term, refers to an impairment in the masticatory function triggered by a structural factor, such as tooth loss; functional factors, such as weaker bite force or a poorer masticatory performance; or both factors. MD acting as a source of chronic stress, promotes functional and morphological changes on the hippocampus, a brain area crucial for learning and memory abilities. This study aimed to synthesize evidence on the association between MD and cognitive deficit (CD), and demonstrate whether might be adequately considered as a risk factor. Methods: Observational studies were screened in seven online databases; the search strategy (PECO) was focused in observational studies with humans as a population (P), presenting groups exposed (E), and non-exposed (C) to tooth loss, in which cognition parameters were measured and compared between groups (O). The final selection included only those studies comparing the effect in cognition between subjects having ≥20 remaining teeth and <20 remaining teeth, considering the latter as a structural factor triggering MD by the literature. Searching and data extraction were conducted following PRISMA guidelines. Qualitative and risk of bias evaluations were performed. The meta-analysis (MA) was constructed including the odds ratio (OR) and its 95% confidence interval (CI) comparing two groups—with/without MD. The level of evidence was rated by Grading Recommendations Assessment, Development and Evaluation (GRADE) approach. Results: In total, 5,666 citations were identified, 14 accomplished our eligibility criteria, and nine were include in the MA. The MA demonstrates that individuals with MD had 46% higher chance to presented CD (OR 2.24 [1.73, 2.90], p < 0.00001, I 2 = 46%). The level of evidence was rated as low by GRADE. Conclusion: Despite the low certainty in evidence, according to our MA, MD is positively associated with increased risk of CD. However, more studies including other factors underlying MD and similar measurements should be conducted to obtain a strong estimate of the risk.

Association of Oral Hypofunction with Frailty, Sarcopenia, and Mild Cognitive Impairment: A Cross-Sectional Study of Community-Dwelling Japanese Older Adults

“…There have been a few studies showing that cognitive function was associated with poor oral hygiene and occlusal force assessment using the number of teeth. A recent meta-analysis [ 35 ] reported that masticatory dysfunction was positively associated with an increased risk of cognitive deficit, while Fukushima et al [ 36 ] reported in animal studies that the reduction in masticatory stimuli affect memory and learning function. However, dementia patients struggle to follow test directions, making it difficult to determine proper results or to perform objective measurement using machines.…”

The impact of tooth loss on cognitive function

“…The possible etiologic role of edentulism in the development of MCI and dementia has attracted the attention of researchers in recent years [15][16][17]. Possible mechanisms supporting this relationship, as reviewed elsewhere [18], include the following: (1) the inflammation/infection mechanism: Porphyromonas gingivalis, a well-known periodontopathogen, may induce the local release of proinflammatory cytokines [19] and subsequently increase both the peripheral circulation [20] and brain accumulation of amyloid-β [21]; (2) the masticatory mechanism: preclinical and clinical studies have demonstrated the negative effect of impaired masticatory function on the incidence of cognitive performance [22]; (3) the diet and nutrition mechanism: this is strongly related to the masticatory one, since tooth loss may influence dietary patterns, which can have a deleterious effect on intraoral food preprocessing before deglutition, leading to a reduction in the intake of nutritional components that have a neuroprotective effect and also promote obesity [23].…”

Oral health diseases among the older people: a general health perspective

“…Beyond aesthetic considerations, edentulism can greatly hinder chewing ability, which can in turn lower one's quality of life through a deterioration of physical function, an increased risk of disease, and even cognitive impairment [78][79][80][81]. Note that tooth loss is also viewed by many as a sign of economic impoverishment [82,83].…”