How Does Oral Health Status Correlate with Cognitive Decline in Individuals with Dementia and Alzheimer’s Disease: An Umbrella Review

1. INTRODUCTION

An increasing body of research is examining the connection between dental health and cognitive performance, which is a reflection of the growing understanding of the interdependence of neuronal and systemic health [1]. Dementia is a complex condition that is primarily characterised by progressive cognitive deterioration. It presents severe challenges not only to the sufferer but also to carers and health services worldwide [2]. In recent times, there have been increasingly more research scientists studying potentially modifiable risk factors for dementia about its onset and progression [3-6].

The state of the oral cavity, in most instances, matters a great deal to health and the overall quality of life. It is crucial for communication, nutrition, and a life free from pain. Oral infections leading to tooth loss, periodontal disease, or oral infection can cause or exacerbate systemic inflammation, poor glycemic control, and malnutrition—all known to have an effect on brain health [4-6]. Besides being a gateway to the body, the mouth may contain bacterial infections that induce systemic inflammatory responses, one of the proposed mechanisms that relates dental health to brain health [7]. A few observational studies are available that support the hypothesis that oral health is directly related to cognitive function [8-10]. In addition, due to decreased motor skills and forgetfulness caused by cognitive decline in dementia, poor oral hygiene often occurs, worsening the condition of both oral and cognitive health [9].

The relevant literature in this regard presents a mixed picture despite the probable biological causes and observational evidence. This is because different studies have examined different populations, defined oral and cognitive health in different ways, and employed different assessment procedures [10]. Although systematic reviews in this field have made an effort to compile the information that is currently accessible, it is difficult to reach firm conclusions because of variations in their methodologies and conclusions [11-13]. This heterogeneity underlines the need for an umbrella review, or a review of previous systematic reviews, that can provide a complete synthesis and evaluation of data related to the link between dental health and cognitive decline in dementia.

Therefore, the aim of this umbrella review is to critically appraise and summarize the findings of various reviews on the association between the status of oral health and cognitive deterioration in patients with dementia and, finally, to uncover any consensus or differences between studies.

2. MATERIALS AND METHODS

3. RESULTS

3.2. Bias Assessment Observations

As shown in Fig. (2), the bias assessment of the included reviews highlighted variability in methodological rigor and the presence of potential biases. Reviews by Hamza et al. [20] and Maldonado et al. [21], and to a lesser extent, Delwel et al. [18], demonstrated higher methodological quality, particularly in sampling, outcome assessment, and statistical analysis. Conversely, Ab Malik et al. [16] and Chalmers et al. [17] received lower scores, reflecting substantial potential biases. These biases primarily stemmed from limitations in inclusion criteria, inadequate handling of confounding factors, and insufficient descriptive information on comparator groups. Furthermore, issues with the validity of outcome measurements and follow-up durations were noted in many studies. However, Guo et al. [19] excelled in certain methodological criteria, notably in the comprehensive assessment of periodontal indices.

4. DISCUSSION

The scope and character of these relationships varied, despite the fact that all of the evaluations included [16-23] recognised a general pattern of worsening dental health in dementia patients and its possible influence on cognitive decline. For example, Ab Malik et al. [16] and Hamza et al. [20] were more concerned with the inflammatory component and proposed that cognitive issues were caused by systemic inflammation. On the other hand, periodontal disease as a risk factor for cognitive impairment was the subject of sound statistical investigations by Guo et al. [19] and Maldonado et al. [21]. Wu et al. [23] specifically emphasised the preventive potential of maintaining proper oral hygiene, while Delwel et al. [18] and Rejnefelt et al. [22] emphasised the gradual nature of oral health loss in dementia. The complex relationship between oral health and cognitive functioning in ageing populations is presented by this varied but related body of studies.

According to Ab Malik et al. [16], inflammation may play a part in dementia development, suggesting that inflammatory mediators linked to poor dental health may also play a role in cognitive decline. Similar findings were proposed by Hamza et al. [20], who also pointed out that a possible inflammatory pathway connecting periodontitis and neurodegeneration may be highlighted by the elevated inflammatory markers in Alzheimer's patients with poor oral health. Guo et al. [19] provided a robust statistical foundation with an odds ratio calculation, highlighting the fact that periodontitis provides a substantial risk factor towards cognitive impairment. Their findings were strikingly comparable to those of Maldonado et al. [21], who assessed the development of periodontal diseases in patients suffering from dementia and found substantial statistical evidence linking periodontal health to cognitive deterioration. In addition to Guo et al. [19] reporting significant variation in probing pocket depth, both publications highlighted periodontal disease as a critical factor in maintaining cognitive status; however, Maldonado et al. [21] did not address this.

According to Delwel et al. [18] and Rejnefelt et al. [22], dementia patients have a high rate of oral health issues. Rejnefelt et al. [22] documented longitudinal decline, while Delwel et al. [18] concentrated on the necessity of offering oral care support. Although Delwel et al. [18] also reported conflicting findings on periodontal health, which tend to imply less of a causal relationship than what Rejnefelt et al. [22] described, these studies were comparable in that they concluded that dementia causes a steady loss in oral health. By presenting conflicting results about the correlation between tooth count and cognitive decline and pointing out that better personal dental care was linked to less severe cognitive decline, Wu et al. [23] offered a nuanced perspective. This study stood out from others because it raised the possibility that maintaining proper dental hygiene could prevent cognitive decline, an idea that has not been fully explored in previous research.

According to a review of the literature, those who have dementia typically have poor dental health [24-26]. The state of oral health is not substantially impacted by the type of dementia, such as vascular dementia or Alzheimer's disease [24, 27, 28]. However, poorer oral hygiene, which is characterised by increased plaque accumulation and more common oral illnesses, seems to be associated with a higher degree of cognitive impairment [24-29]. In the study by Srisilapanan et al. [30], there was a noteworthy deviation from the norm. The patients were attending a memory clinic that also included dental care, which resulted in comparatively better oral health results when compared to the general dementia population.

The way of life of people with dementia also affects their dental health; there are conflicting findings about whether living in a nursing home or the community has an impact on oral health outcomes [31, 32]. According to some research, there are no appreciable variations in oral health based on where a person lives [33-35], but other studies have found that residents of nursing homes have poor oral health [33, 36], which may be related to the higher levels of cognitive and functional impairments observed in these environments [37].

The capacity to maintain oral hygiene is impacted by cognitive decline in dementia because normal dental care tasks become more difficult due to worsening executive functions, working memory, attention, and motor abilities, including apraxia and diminished hand grip strength [38-40]. Increased plaque accumulation is frequently the outcome of this [41, 42], and it is a major cause of gingivitis and can develop in periodontitis [43]. Maintaining oral health in people with dementia is essential for both dental and general health reasons, as periodontitis has been linked to systemic disorders, such as cardiovascular illnesses and type 2 diabetes mellitus [4].

A useful point of reference is provided by the results of Lin CS et al. [44], who also conducted an umbrella review on the more general subject of oral-cognitive linkages. The intricacy and diversity of variables influencing the relationship between dental health and cognitive performance were acknowledged by the authors of both our review and the study by Lin CS et al. [44]. Periodontal disorders are mentioned as a significant risk factor for cognitive impairment in both reviews. Similar to Lin CS et al., we discovered that, as shown in the research by Guo et al. [19] and Maldonado et al. [21], a significant deterioration in dental health was one of the most important factors linked to cognitive decline.

By concentrating on dementia patients, our evaluation provided a more concentrated examination of the effects of dental health on this demographic. The study by Lin CS et al. [44], on the other hand, was more comprehensive, taking into account a variety of cognitive dysfunctions and elements, such as masticatory function and the oral microbiome that were not the main focus of our review. Additionally, the statistical analysis and longitudinal data in our research brought to light the progressive loss in oral health among dementia patients, a feature that Lin CS et al. [44] did not fully address. The review was able to go further into specifics on specific disease mechanisms because of its focused emphasis. For example, Ab Malik et al. [16] and Hamza et al. [20] highlighted inflammation pathways, while Wu et al. [23] discussed the protective benefits of keeping good oral hygiene. A slight but significant advantage over the widely utilised strategy taken by Lin CS et al. [44] is that this attention allowed for a more precise delineation of prospective treatment and preventive interventions that are more closely targeted to the demands of a dementia patient.

A more specific examination of periodontal health as a risk factor for dementia and cognitive decline was provided by Asher et al. [26], who carried out a targeted evaluation of the long-term effects of poor periodontal health on cognition. Their findings, which show links between poor periodontal health and higher risks of dementia and cognitive decline, are consistent with our review's finding that periodontal disease is a major contributor to cognitive impairment. In addition to the more general findings from our umbrella review, their specificity—especially when stratifying the analysis by degree of tooth loss—offers a deeper understanding of how different impacts of periodontal deterioration on cognitive health might occur at different degrees of this deterioration. This major challenge is further highlighted by Asher et al.'s [26] critical evaluation of the quality of the evidence and reverse causality, which shows that even in this field, improved research methodologies were underplayed compared to what would be considered appropriate, necessitating significant improvement.

Skallevold et al. [34] expanded the talks to include a wider range of mental illnesses, such as dementia, where it would appear that oral health is related to each of the conditions listed. The consideration of our review of inflammatory pathways is consistent with the findings of Skallevold et al. [34], which emphasise systemic inflammation and microbial imbalance as underlying processes. In addition to supporting our demand for comprehensive dental care methods in dementia management, this larger viewpoint highlights the necessity for interdisciplinary approaches in addressing these disorders and supports the biological plausibility of the link between oral health and cognitive decline.

Our umbrella review did not particularly address the practical aspects of oral health care for older adults with dementia living in the community, but Ho BV et al. [37] did. Our findings about the increasing decline of oral health in dementia are consistent with their recognition of the dearth of accessible, specialised oral health care interventions and the limited services that are currently offered. In contrast to the theoretical connections offered in the preceding steps, the solutions developed by Ho BV et al. [37], such as the mobile dental programs and caregiver-supported oral hygiene, can be regarded as tangible manifestations of how oral health interventions could be put into practice.

CONCLUSION

Our research showed an association between poor oral health and deteriorating mental functions at all times. The data revealed that problems, such as periodontitis and tooth loss, were often associated with the risk of mental impairments. The literature review indicated that inflammation may be a common underlying factor for the relationship between deteriorating oral health and worsening brain health. Although there were some differences in the study approaches and their results, it was broadly agreed that good oral hygiene could help mitigate some decline of mental abilities in dementia sufferers. Since most of the studies we looked at were observational and differed in their approach, it is hard to tell whether one causes the other. Nonetheless, these findings highlight the importance of thorough oral care in managing dementia, suggesting that such care could be a practical way to lessen some mental decline.

REFERENCES