Association Between Oral Hygiene Behaviours and Cognitive Decline in Adults: A Systematic Review and Meta-Analysis.

Aim: To evaluate the association between oral hygiene behaviour and cognitive decline in adults. The outcomes include changes in global cognitive function, visual attention, task switching and the risk of dementia.

Design: We conducted a systematic review following the preferred reporting items for systematic reviews and meta-analyses guidelines.

Data Sources: A systematic search of 11 databases and grey literature sources was conducted from inception to January 2024. We included interventional trials or cohort studies that investigated the effect of oral hygiene behaviours (e.g., toothbrushing, mouth washing, flossing, using toothpicks and cleaning dentures) on cognitive decline in adults.

Methods: Data extraction and risk of bias assessment were performed by two independent reviewers with expertise in conducting systematic reviews. Meta-analyses were conducted using random-effects models, and heterogeneity was assessed with the I statistic and χ test.

Results: A total of eight studies (six intervention studies and two cohort studies) met inclusion criteria, including 261,772 participants. Follow-up periods ranged from 30 days to 48 months for interventions and 9 to 18 years for cohorts. Toothbrushing was associated with a significantly slower decline in global cognitive overtime. Toothbrushing in older adults with moderate/severe dementia could achieve significant changes in cognitive decline. There was no significant difference between the effectiveness of toothbrushing performed by professionals and caregivers. Other oral hygiene behaviours, including dental flossing, using mouthwash, using toothpicks and cleaning dentures, were not associated with the risk of dementia.

Conclusions: Toothbrushing is linked to a decreased risk of dementia and improved global cognitive function. Promoting toothbrushing at least twice daily may significantly reduce the risk of cognitive decline and dementia.

Impact: These findings highlight the urgent need for programmes that encourage daily toothbrushing, particularly in nursing home settings and among older adults with moderate-to-severe dementia.