Oral disease is a common human disease and the World Health Organization has listed oral health as one of the top ten criteria for human health. At present, as the transformation of the medical pattern and the concept of Healthy China continues to grow, oral health has become an important part of people's pursuit of health, and the oral health of older adults is closely related to their overall health. The fourth national oral health epidemiological survey in China showed that the current oral health status of the elderly in China is not optimistic, with the serious prevalence of caries and periodontal disease [37], and these poor oral health conditions may increase the risk of cognitive impairment in the elderly.
However, research on the relationship between oral health status and MCI is currently limited, which is constrained by the conventional views that "dental disease is not a disease" and "losing teeth is normal aging". This study assessed the relationship between oral health indicators and MCI, the results of the subjective and objective examination revealed that gender, education, economic level, dental caries, chewing ability, oral and maxillofacial pain, self-perceived oral health status, and the OHRQoL were all correlated with cognitive status in older adults. Further regression analysis showed that the oral health assessment index was negatively associated with cognitive status, and poorer OHRQoL in older adults was an independent risk factor for MCI.
In research by Jensen et al. [38] which aimed to investigate OHRQoL-related factors in community-disabled older adults using OHIP-14, the OHRQoL was associated with poor cognitive status. In the study by Lee et al. [39] on older adults using GOHAI, people with lower levels of cognitive function had poorer OHRQoL and impaired cognitive ability had a negative impact on OHRQoL. This is the first study to find that poorer OHRQoL is an independent risk factor for MCI. OHRQoL is a reflection of oral health physiological function, pain and discomfort, and psychosocial function and is closely related to oral physiological dysfunction such as tooth loss, dental caries, and decreased chewing ability, which may be an indicator of true oral health problems.
Oral diseases are the main influencing factors of OHRQoL, and older adults with poor oral examination results have low OHRQoL [40]. Functional dentition and dental caries are two important factors contributing to poor oral OHRQoL in older adults [41]. Batista et al. [42] found that tooth loss was associated with damage to OHRQoL and that the location and distribution of missing tooth affected the severity of the damage. de Medeiros et al. [43] found that the tooth loss and dentures had an impact on the masticatory function, and poor masticatory function also negatively affected the OHRQoL of older adults. In addition, the physical, psychological and social problems of periodontitis can reduce OHRQoL [44]. Overall, low OHRQoL predicts oral problems in older adults and may influence cognitive function through physiological function.
Oral diseases not only affect the physiological function of oral but also damage the harmony and aesthetics of the face [45], which restricts the social activities of the elderly and can have a detrimental effect on their mental health level [46]. The OHRQoL reflects the impact of oral health on the psychology of older adults while also has a direct psychological impact [47]. Previous studies have shown that poor OHRQoL can lead to loneliness [48], depression [49], and restriction of mobility and social participation [50]. Meanwhile, psychological problems are an important risk factor for cognitive decline. Loneliness [51], depression [52], and reduced social activities [53] have been associated with cognitive decline in older adults. The psychological influence of oral health or the negative psychological impact of OHRQoL on older adults can also affect cognitive function. Therefore, identifying and managing OHRQoL in older adults can help to relieve discomfort, improve oral problems, reduce psychological stress, and also improve cognitive status in older adults with MCI.
In the regression analysis, oral problems such as tooth loss, dental caries, and mastication impairment have not been found to be associated with MCI in older adults, which may be related to factors such as the sample size used and the assessment method. Obviously, the impact of poor oral health on the OHRQoL of older adults has a negative effect on cognitive function. Oral health is an easily identifiable and modifiable risk factor. The MCI stage, where older adults retain good mobility and can take care of their oral health, is the best stage for interventions for poor oral health in older adults with cognitive disorders. The OHRQoL of older adults enables the detection of oral problems, which will help to slow down the decline in cognitive function. The objective examination of oral health often has special requirements, and GOHAI is a more comprehensive and subjective evaluation system that reflects the new medical model and view of health. GOHAI can be used by a variety of researchers to assess the OHRQoL and to improve poor oral conditions, healthcare behaviors, and habits promptly, which is important for the overall health and QoL of older adults. Therefore medical workers can adopt targeted interventions to create proper oral awareness and establish proper oral habits in older adults, which may improve their OHRQoL and improve cognitive performance.
A limitation of this study is the study design, as our study was designed as a cross-sectional study, it is difficult to draw conclusions about the causal relationship between oral health status and MCI. In subsequent studies, there is a need to refine the classification indicators, expand the sample size and reduce confounding factors to further improve the study design, preferably through longitudinal studies to clarify the causal relationship between various oral health indicators and MCI.