In the present study, we found that the number of teeth was associated with a lower risk of frailty. Older nursing home adults who brush their teeth have a lower risk of frailty than individuals who do not brush their teeth as part of their daily life. Our study emphasizes the importance of maintaining teeth and brushing teeth, which could reduce the risk of frailty among residents.
In our study, the prevalence of edentulism was 33.3% among older nursing home residents, which was higher than that in community-dwelling older adults reported in two previous studies (19.4% [23] and 23.5% [24]). The main reason for this discrepancy was that the mean age in our study was higher than that in the abovementioned previous study (87.6 years versus 77.2). When adults become aging, they often suffer from some oral disease, which leads to tooth loss [25]. A previous study conducted in the United States reported that the edentulism prevalence among participants aged 65–74 and ≥ 75 was 15% and 22%, respectively [26]. Nursing home residents with edentulism can easily develop frailty because of deficient nutrition intake [27].
Our study found that there was a significant association between tooth loss and a greater likelihood of frailty among older nursing home residents, which was in line with previous studies. In a study covering 903 community-dwelling older adults, the number of teeth was associated with frailty, with an OR = 0.98 (95% CI: 0.96–0.99) [17]. In addition, a cohort study with 3 years of follow-up among home-dwelling individuals aged 70 or older indicated that one additional tooth could lower the risk of frailty by 5.0% [14]. Although there are a growing body of studies consisting of cross-sectional or cohort studies investigating the association between tooth loss and frailty, to date, only one published study has investigated this association in a nursing home setting. In 2021, Saarela et al. conducted research to explore the association between oral health and frailty among older adults living in long-term care [18]. The results showed that the mean number of teeth between frail residents and nonfrail residents was not significantly different, with a figure of 9.7 (9.3) versus 11.0 (9.3), which was inconsistent with our study. There are a few reasons that could explain this difference between our current study and that of Saarela and colleagues. First, our study included a nationwide sample of nursing home residents, whereas theirs studied a single center; this might reduce selection bias. Second, the sample size in Saarela’s study was smaller than in ours, which might fail to reach enough statistical power to detect the difference. However, a large-scale study is needed to confirm the association between the number of teeth and frailty among older nursing home residents in the future.
Our study also found that the oral health indicator, brushing teeth regularly, could reduce the likelihood of frailty in nursing homes. One of the reasons for teeth loss among older adults was poor health behaviors, such as failing to brush regularly. A previous study conducted among older nursing home adults aged 75 years indicated that the proportion of oral cleaning habits was lower among frail dentate people than among those without frailty, with a figure of 52.7% versus 75.4%, which was similar to our present study [28]. In addition, in another study exploring the association between the oral environment and frailty, the results found that frailty tends toward a higher proportion of poor hygiene [29]. Regular toothbrushing can help maintain good hygiene and clean away harmful bacteria, which helps maintain good oral health, reducing the likelihood of frailty among older adults. However, we need to be cautious because frailty itself might also affect older adults’ ability to hold a toothbrush. Those frail older adults were more likely to have impaired health, declined performance in activities of daily living, and chronic disease, which contributes to poor oral behaviors and lower dental service use. A previous qualitative study indicated that institutionalized older adults suffered from poor oral health because they were disoriented or lacked support from family, friends, and society [30].
The mechanism of tooth loss in developing frailty has been well described before and involves three potential pathways: nutritional, psychological, and inflammatory factors [31, 32]. Older adults with tooth loss, especially edentulism without false teeth, have to ensure they have a varied diet and are more likely to have to eat soft food because of their decreased chewing ability [33]. When older adults endure this condition for a period of time, they may suffer from frailty through malnutrition. In addition, older adults with tooth loss might have less confidence when communicating with others, which leads to lower levels of physical activity [34] and a higher likelihood of depression [35], ultimately contributing to frailty. More studies need to confirm these three mechanistic pathways among older nursing home residents.
Our study has many clinical implications. Due to the results supporting the maintenance of natural teeth and consistent oral health care behavior and toothbrushing, strategies and interventions to help older nursing home residents maintain good oral health are warranted. For instance, interventions such as improving the knowledge and awareness of oral health benefit older adults to protect their natural teeth. In fact, in a previous review study that summarized the current evidence on interventions for improving oral health, the results supported that educational interventions, professional oral healthcare, and restorative treatment can improve oral health among older adults [36]. However, from the preventive perspective, nursing home staff and clinicians need to adopt strategies to prevent older adults from losing their teeth. In addition, for frailty, oral health interventions combined with a traditional effective program such as exercise and nutrition need to be explored in the future.
Our study has some strengths and limitations. First, this was the first study to explore the association between oral health (number of teeth and oral behaviors) and frailty among older nursing home residents from China based on a literature review. Second, our study employed comprehensive statistical analysis, such as full adjustment, generalized additive model analysis, and sensitivity analysis, making our results reliable and credible. Third, our study has significant clinical implications for maintaining oral health among this population—older nursing home residents. However, there were some limitations that need to be taken into account. First, due to the nature of cross-sectional studies, cause-and-effect associations cannot be determined; however, we performed a sensitivity analysis by deleting the worst 10% frailty scores from the total sample. The results showed similar findings, which could help reduce the risk of reverse causality. Second, in our study, we did not construct frailty based on Physical Frailty Phenotype according to the CLHLS; thus, we cannot compare our results with previous studies that used Physical Frailty Phenotype as an assessment tool. Third, some important factors that are closely related to frailty, such as malnutrition, were not included in the CLHLS, which might overestimate the results. Fourth, a previous study confirmed that oral hygiene affected frailty among older people. However, the original Public Data did not provide this important variable, which should be explored in future studies.