The prevalence of dementia or cognitive impairment is becoming greater as the number of older adults increases, although the incidence of age-specific dementia has appeared to decrease.1 The main features of dementia are cognitive decline and functional impairment, which have negative impacts on systemic and oral health and nutrition.2, 3, 4, 5, 6, 7 The prevention and management of dementia is a major issue and has been regarded as a national healthcare priority.1 Increasing efforts and investments have been made based on the aetiology and risk factors elucidated in several previous studies.1,8, 9, 10 Multiple risk factors are known to be associated with dementia and can be classified into non-modifiable and modifiable categories; the former includes age, sex and genetic factors and the latter includes lifestyle and health conditions. To prevent dementia, it is crucial to recognise the risk of these modifiable factors throughout the life course and to reduce the potential risks by improving lifestyle, known as primary prevention. In addition to primary prevention, secondary prevention which aims at early treatment following early diagnosis to minimise the disease has been reported.11, 12, 13 Multiple interventions, such as education, nutrition or supplements, physical activity, and cognitive stimulation, are necessary for populations with subjective cognitive decline or mild cognitive impairment. 11, 12, 13 These studies suggest the potential roles of these interventions as secondary prevention, although they also noted the necessity of further longitudinal studies.

In general, poor oral health status has been identified in the older population and in people with dementia or cognitive impairment.4,6,14, 15, 16 This condition leads to compromised nutrition and a decline in central nervous system function.17 Previous studies have reported that periodontitis and its associated microorganisms are associated with dementia risk,18, 19, 20 and some underlying biological mechanisms have been suggested.21, 22, 23 In addition, several meta-analyses have concluded that tooth loss is a risk factor for cognitive decline and the development of dementia.24,25 Furthermore, declines in oral functions, such as maximum bite force,26 tongue pressure,27 and tongue-lip motor function (oral diadochokinesis),27,28 are associated with cognitive impairment. These findings suggest that improvement in oral condition may contribute to cognitive improvement. In recent years, an increasing number of studies have examined the effect of oral intervention on cognitive function. However, no review has been conducted on this topic.

This systematic review focused on whether oral care and rehabilitation can affect or improve cognitive function. This systematic review aimed to provide current information on the effects of interventional oral care and rehabilitation on cognitive function.