The influence of habitual tooth brushing frequency on individuals diagnosed with coronary artery disease
The present study was a retrospective analysis conducted on residents diagnosed with CAD in southwest China. The key findings were: (1) Only 51.4% of the participants reported brushing their teeth twice or more daily. (2) The prevalence of CAD among the general population was found to be 3.4%. Additionally, over a four-year follow-up period, the incidence rates of 3P-MACEs, new stroke, new MI, and CAD-caused mortality were observed to be 14.4%, 3.7%, 8.1%, and 5.0%, respectively. (3) Inadequate tooth brushing frequency may potentially increase the risk of 3P-MACEs.
Oral health promotion has attracted increased attention from the public in China43. However, approximately 19.3% of Chinese suffered from severe periodontal diseases in 201944. Our study found that the prevalence of periodontitis was 34.4%, and 13.7% of the residents who had missing teeth. This was only a rough investigation and analysis, the actual prevalence rate could be definitely higher than this, as some residents had never visited an oral medical institution. Besides, only less than 20% of Chinese adults had a good understanding of periodontal diseases, which revealed that the Chinese population’s cognition of oral health has not significantly developed over the years45. From another perspective, public health strategies regarding periodontal health remained insufficient45. Until 2021, in the primary care services of the public health department, the procedures for diagnosis and management of periodontal diseases were incomplete46. Curative and rehabilitation oral health care was still not covered in health benefits packages for Chinese citizens, only routine and preventive oral care was provided46.
It was recommended that tooth brushing more than twice per day was significant for preventing caries47, before bedtime and on other occasions48,49. According to the Adult Oral Survey 2021 in the UK, approximately 77% of adults (16 years and over) reported brushing their teeth at least twice daily, while 20% indicated they brushed once per day. Only 2% stated they brushed their teeth less frequently than once a day50. In the last 5 years, studies about Chinese citizens’ oral care, oral hygiene, and tooth brushing habits were limited. Therefore, according to newly published data from the 4th national oral health epidemiology survey in 2016, oral diseases remained highly prevalent in China43. Nevertheless, access to specialized dental care was limited for most citizens, and many individuals found it unaffordable because of restricted insurance coverage43. Although the study population was limited, our research observed that 78.8% of residents brushed their teeth in the morning, whereas 70.0% did so in the evening. Notably, nearly half of the respondents did not meet the recommended frequency for tooth brushing. This phenomenon exhibited residents’ neglect of oral health to some degree.
The incidence of CAD has rapidly increased over the past two decades, and the estimated number of CAD patients in China for the year 2022 was 11.39 million51, making it the second leading cause of death52,53,54. Consequently, this has imposed a substantial economic burden on society55,56. The main findings of our study align with the results documented in the existing literature, that a reduced daily frequency of tooth brushing may increase adverse cardiovascular outcomes29,57,58,59,60,61.
For instance, Oliveira et al. reported that CAD had the highest proportion of cardiovascular events caused by poor oral hygiene, they reported an HR for fatal CVD of 2.40 (1.50–4.00) for tooth brushing less than once a day within 8.1 follow-up years23. In addition, research by Zhuang et al.24 and Zhou et al.57 discovered that less tooth brushing frequency was associated with an increased risk of all-cause mortality. Similarly, Matsui et al.’s research proved that insufficient frequency and short duration of tooth brushing (< twice/day and < 2 min/procedure) were associated with a higher risk of major adverse cardiovascular events including acute MI, with an HR of 3.06 (1.24–7.63)15. A prior study by Chang et al. analyzed 206,602 individuals indicating that frequent tooth brushing (≥ 3 times/day) was associated with a reduced stroke risk (HR: 0.80; 95% CI 0.75–0.85; p < 0.001)58. Additionally, individuals who brushed their teeth more frequently were reported to have lower 10-year cardiovascular risk59. Moreover, a systematic review also highlighted a significant negative correlation between the frequency of tooth brushing and CVD risk35. These findings further support the link between poor periodontal health status and an elevated risk of CVD23.
In contrast, our study, which featured a 4-year follow-up period, demonstrated that CAD participants who brushed their teeth once daily had a significantly higher HR for new stroke events and CAD-related mortality, compared to those who brushed twice daily. Furthermore, those who brushed once daily exhibited an elevated risk of 3P-MACEs.
Conversely, although the group that brushes once daily has the highest incidence of new-onset MI (8.6%), our findings did not reveal that tooth brushing frequency had a remarkable influence on the incidence of new-onset MI among CAD residents. This may be attributed to the fact that our study population exclusively comprised CAD patients from southwest China, with MI cases limited to newly occurring events. Additionally, the CAD patient group may have exhibited a lower propensity to initiate and adhere to anti-platelet and lipid-lowering medications both at baseline and during follow-up after diagnosis. During the follow-up period, the research team may also provide additional medical advice to reduce the likelihood of progression to MI. However, this does not negate the potential benefits of regular oral hygiene behaviors such as tooth brushing.
Owing to the inherent limitations of the research design, it was not feasible to provide a detailed description of the oral hygiene characteristics of the population or to adjust for relevant confounding factors. Individuals with varying tooth brushing frequencies exhibit differences in demographic, social, psychological, economic, and physical conditions. Nevertheless, based on the aforementioned literature and our study findings, multi-factor correction analyses were conducted across different regions and populations, yielding consistent conclusions. Particularly, in our subgroup analysis, most subgroups demonstrated that less frequent tooth brushing was associated with 3P-MACEs, suggesting this was not a random occurrence. Therefore, we posit that reduced frequency of tooth brushing is likely to constitute a significant potential risk factor for adverse cardiovascular events.
The exact physiological mechanisms linking tooth brushing frequency to cardiovascular events are not yet fully understood. Nevertheless, there were researches revealing that insufficient tooth brushing frequency was closely associated with periodontitis60,61.
In Cho et al.’s study60, the frequency of tooth brushing made a significant impact on the classification of periodontal conditions. Compared with the healthy group, participants with severe periodontal disease showed a higher incidence of 26% for acute MI (HR: 1.26, 95% CI 1.13–1.42)60. During 10 years, acute MI presented more in people with severe periodontal conditions than people with no severe periodontal conditions (healthy or moderate periodontal conditions): 1.0% vs. 0.7%60.
Current evidence indicates that chronic bacteremia and low-grade systemic inflammation associated with periodontitis may significantly contribute to the development of atherosclerosis and related CVDs62. Elevated levels of CRP are strongly correlated with the incidence of cardiovascular metabolic diseases and have adverse effects on individuals with pre-existing cardiovascular conditions63. Systemic inflammation or immune responses elicited by periodontal infections can result in increased concentrations of white blood cells, CRP, and pro-inflammatory cytokines, thereby exacerbating the inflammatory state and potentially increasing the risk of cardiovascular events29,64. Moreover, periodontal pathogens can directly adhere to endothelial cells and colonize atherosclerotic plaques, leading to plaque instability and possibly triggering thrombotic events associated with atherosclerosis64. Research has demonstrated that enhancing oral hygiene practices can reduce levels of inflammatory markers such as CRP, further inhibiting the role of oral bacteria in driving systemic inflammation63,65.
Our research indicates that individuals who brush their teeth once daily exhibit a higher prevalence of periodontitis and tooth loss, suggesting suboptimal oral hygiene practices. We hypothesize that these individuals might have elevated levels of inflammatory mediators in their blood, although this could not be confirmed through blood tests in this present study. Furthermore, those with less frequent brushing habits tend to have lower educational attainment and income levels, this demographic is also less likely to engage in healthy lifestyles. Lastly, despite the established protective effects of lipid-lowering drugs against cardiovascular events66,67, these patients present relatively higher cholesterol levels and lower utilization rates of lipid-lowering medications, thereby diminishing the potential protective benefits. In conclusion, these hypotheses may elucidate the observed association in our study population between less frequent tooth brushing among CAD patients and an increased risk of 3P-MACEs.
Study strengths
We are one of the limited number of studies that have examined the prognosis of CAD residents with varying tooth-brushing habits in Southwest China. Our data sources are robust and the follow-up duration is substantial (4 years). While no direct interventions were implemented, this study has facilitated awareness among residents regarding the significance of proper oral hygiene. Furthermore, it has provided healthcare professionals with valuable insights to assist CAD patients in modifying unhealthy lifestyles.
Limitations
Despite the significant contributions of our research, several limitations should be acknowledged. (1) The study sample, although derived from a large epidemiological dataset, was confined to patients with a definitive diagnosis of CAD in the southwest region of China, resulting in a relatively limited sample size and geographical scope. Consequently, further large-scale, multi-regional studies are warranted to validate our findings. (2) This study adopted a retrospective design rather than a prospective one. Although we endeavored to adjust for confounding factors influencing cardiovascular prognosis based on existing literature, inherent limitations of retrospective studies may still introduce biases. Factors such as the event rate, sample size, and unmeasured covariates could potentially affect the results. (3) Our analysis focused solely on tooth brushing frequency, unable to consider other important aspects such as brushing technique, duration, or quality, nor did it examine the diagnosis and treatment of oral diseases. The absence of this information might introduce bias into our results. Additionally, unlike some other studies that included individuals with zero tooth brushing frequency as a reference group, our study lacked such a cohort due to the nature of our sample. Therefore, future research should aim to address these limitations through carefully designed prospective studies involving diverse populations.
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