Hypertension is a medical condition in which blood pressure is chronically 140/90 mmHg or higher and it is estimated to affect more than one billion people in the world and is defined as a persistent high systemic arterial blood pressure [1] [2] .

The worldwide prevalence of hypertension has increased two-fold from 1990 to 2019, to more than 30% for men and women aged 30 - 79 years old [3] . The prevalence of hypertension among American is 32% [4] , Chinese is 25.2% [5] , European is 22% [6] , African is 54% [7] , Congolese is 25.5% and is rapidly rising in DR Congo [8] .

The risk factors for high blood pressure are dependent such as age, sex, obesity, excessive alcohol consumption, smoking, diabetes, high dietary salt intake, physical inactivity and stress [9] - [19] . In addition, tooth loss is another risk factor that can lead to development of hypertension.

The viewing the mouth separately from the rest of the body must cease because oral health affects general health by causing considerable pain and suffering and by changing what people eat, their speech and their quality of life and well-being [20] .

Decline in masticatory function brings insufficient intake of vegetables and fruit and increased intake of fatty foods, which could cause obesity and the number of occluding pairs is an important indicator for oral health [21] .

Tooth loss may be seen as the worst-case scenario in oral health and its impacts on blood pressure is estimated to be significant. According to the interplay between tooth loss and hypertension, dental care appointments constitute an environment where blood pressure is commonly measured and therefore, might play a noteworthy responsibility in forwarding suspected undiagnosed hypertensive patients to seek proper care [22] [23] .

Numerous studies on tooth loss and hypertension have been carried out around the world, those conducted in high-income countries showed a great variation in study design, sample sources, and data analyses among population. Considering the differences in health care system, culture, genetic factors and health literacy, it is unclear whether the evidence generated from other countries is not generalizable to Congolese population.

With the present study, we intend to evaluate the impact of tooth loss on blood pressure measurements, on a large cross-sectional study from a national reference dental care clinic in DR Congo.

A cross sectional study was conducted from October 2019 to December 2023 among Congolese aged at least 30 years old reporting to the Congolese living in D R Congo (Kinshasa, Lubumbashi, Matadi, Nioki,Goma, Bukavu, Bunia, Butembo, Kananga, Likasi, Kolwezi, Boma, Mbandaka, Kimpese and Kikwit) ( Figure 1 ).

The National Center of Research in Oral Health Sciences (Democratic Republic of the Congo) granted ethics approval for this research under the following protocol CNRSBD1504.318. This cross-sectional study was performed following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines [24] .

In all, 25,396 participants were enrolled among Congolese population for this study. After oral examination, 13,421 were excluded for no tooth loss and 11,975 participants were selected.

Among 11,975 participants with tooth loss, 2207 were excluded among them 45 for diabetes, 23 for pregnant, 1026 smokers, 668 for consumption alcohol, 41 for obesity, 33 refusal and 371 aged less than 30 years old ( Figure 2 ).

The final sample consisted of 9768 participants, with an average of 46.2 (SD 6.2) years of age, and predominantly female 5402 (55.3%) and the mean of education level was high school 4521 (46.3%) ( Table 1 ).

The participants with tooth loss were divided into two groups: A group with hypertension (HTA group) and a group without hypertension (Non-HTA group) ( Figure 2 ).

Among all the participants, 2637 (26.9%) (HTA group) were diagnosed with hypertension had significantly more tooth loss (mean 11.06) than those without hypertension (Non-HTA group) (mean 6.09) (p < 0.001) ( Table 1 ).

Participants with severe tooth loss (>10) were older (p < 0.001) BP (p < 0.001). The prevalence of hypertension at examination was found higher, tooth loss participants (>10) (p < 0.001). In contrast, participants with normal blood pressure were more prevalent in participants with less than 6 teeth. We confirmed a consistent association of BP with tooth loss in Congolese participants. Additionally, older adults were more associated with severe tooth loss and higher measures of BP. There was evidence that the association between tooth loss and blood pressure (SBP and DBP) was mediated by age ( Table 2 ). A significant model was obtained when age was included as a mediator of the association between tooth loss and BP (Tooth loss, age p < 0.001; age BP, p < 0.001; and tooth loss, BP, p < 0.001).

For the overall sample, when considering a crude model (Model 1) the presence of hypertension (OR = 2.64, 95% CI: 1.50 - 4.29) was associated with the number of tooth loss ( Table 3 ). Then, multiple linear regression analyses investigated the linear relationship between SBP and DBP with age and tooth loss for the overall sample ( Table 3 ).

Model 1: univariate; Model 2: adjusted for sex and age; Model 3: adjusted for age, sex, education level.

The goal of our study was to determine the impact of tooth loss on blood pressure among Congolese population.

This cross-sectional study found that the number of tooth loss more than ten teeth may have a positive association with the risk of development of hypertension. Individuals having greater tooth loss exhibiting a high prevalence of hypertension and high blood pressure. In our study, the prevalence of hypertension was 26.9%. This study has confirmed the key reported traditional lifestyle factors associated with high BP in DRC [8] [28] . The reason is that tooth loss causes a decrease in masticatory function and decreased consumption of vegetables and fruits, and higher consumption of high energy food, tend to cause obesity compared to those with adequate mastication [29] - [32] . Tooth loss may lead to alterations of dietary patterns, such as low intake of citrus fruit, beta-carotene, folate, vitamin C and fiber. These undesirable eating habits are closely related to the development of high blood pressure via many factors. Another reason is that the reduction in chewing leads to a decrease in diet-induced thermogenesis and inactivation of neuronal histamine, which may consequently lead to obesity [33] - [35] . According to previous studies, 20 natural teeth is used as a criterion for severe tooth loss. Sheiham et al. reported that individuals with ≥21 natural teeth can optimize nutritional intake. The cut-off point in the number of teeth in our study was similar to that of Sheiham et al. [36] . However, the cut-off in the number of teeth differed among all studies. Having 20 or more teeth is enough for masticatory function [21] . Therefore, the association between tooth loss and high blood pressure may be explained by nutritional intake [37] .

The present study suggests that tooth loss is associated with an increased risk of hypertension and higher systolic blood pressure. Our results are similar to other previous study [38] . This association was also observed in younger participants than 65 years [39] . Another study reported that tooth loss was related to severe hypertension in participants aged 50 years or more in China [40] . Hye-sun-shin study involving the Korean population showed that a decrease in the number of teeth may be independently associated with hypertension [41] . Our results are similar to those of these previous studies and provide additional information on the positive association between tooth loss and an increase in the risk of developing hypertension in a longitudinal study.

Other studies have shown a differential association of gender in the relationship between severe tooth loss and blood pressure. German studies found this association to be significant only in males [42] . The same investigators also argued that higher degrees of osteoporosis in women may lead to early tooth extraction, thus reducing the risk of long-lasting periodontitis. Other studies including only women have found an association between severe tooth loss and hypertension [43] .

Additionally, older adults were more associated with severe tooth loss and higher measures of SBP and DBP. We assessed the distribution of blood pressure according to the number of tooth loss. Interestingly, mean systolic blood pressure increased gradually as the number of teeth decreased, whereas diastolic blood pressure showed a non-linear pattern that increased to teeth and then decreased in cases of <20 teeth [44] [45] .

In other observational studies, a strong association between tooth loss and hypertension was observed after controlling for a number of confounding variables. A cross sectional study in Indian adults indicated that participants with partial tooth loss had 1.62 times (95%, higher OR of developing hypertension after adjusting for all confounders, compared to those with no tooth loss [46] . Moreover, the study of Peres et al. observed that edentulous people have an 8.3 mmHg higher SBP compared to individuals with more than 10 teeth in both arches after adjustment [47] . In South African, Ayo-Yusuf et al., found that total tooth loss was significantly associated with hypertension [48] .

Tooth loss may be certainly a risk factor for hypertension by the result of an indirect influence, which is highly remote from physiological point of view. Oral diseases such as dental caries and periodontal disease may participate in this mechanism, as they are the main responsible for tooth loss [49] .

In our study, the participants had an average of 11 missing teeth, comparable to the findings from large national oral health surveys using clinical examination data in China, in which adults aged 60 - 74 years had an average of 10 missing teeth [50] . Tooth loss and hypertension are both common among older adults, it is possible that the association between hypertension and tooth loss is bidirectional among those with significant tooth loss those who lost >10 teeth [51] .

In addition, education can be considered a modifying factor of health outcomes, influencing health knowledge, behaviors, employment, social beliefs, standing, and networks [52] .

Moreover, the periodic dental appointment reduced the chance of tooth loss in individuals with chronic disease. Although the barriers of access to oral health care services were not fully assessed in our investigation, it is suggested that this event occurs due to cost, availability of oral health care services in DR Congo and the fear of dentists. Dental services have low acceptance among the population, this fact is a consequence of individual and community factors.

The reality of our study shows the necessity of expanding the available primary

care, treating these individuals in a holistic way. Moreover, it would be necessary to reinforce the importance attached to general and oral health services, including a periodic schedule of evaluation for interdisciplinary team-based care.

Considering the relationship between hypertension and tooth loss, dental care appointments constitute an environment where BP is commonly measured and, therefore, might play a noteworthy responsibility in forwarding suspected undiagnosed hypertensive patients to seek proper care. As in Machado et al. study, these results validate dental units as potential primary care locations for detecting cases of undiagnosed hypertension and, possibly, expanding to other clinical situations (such as diabetes and oral cancers) [53] .

Despite these limitations, this study provides, for the first time in a large national representative sample, useful information on tooth loss as a risk indicator for hypertension, while controlling for multiple risk factors.

The strengths of our study are the relatively large sample size for a study of such scale. We adjusted for relevant confounders sequentially in our three models.

However, the study has certain limitations. Firstly, hypertension is known to be a punctual measurement so that the absence of years of hypertension of an individual may be a disadvantage. Secondly, it is better to use inadequate dentition with individuals with fewer than 20 teeth to categorize tooth loss. Thirdly, the place, as a study conducted in urban cities, participants have a higher level of education than other areas in the DR Congo. Therefore, the study findings may not be generalizable to the wider older population in the Congo. Finally, our findings were based on a cross-sectional study; therefore, we were only able to examine the association between tooth loss and hypertension.

Longitudinal and prospective cohort studies are needed to further elucidate the causal association between tooth loss and hypertension.

Among Congolese adults, we observed a strong association between tooth loss and high blood pressure. Low numbers of remaining teeth might be considered as an impact factor for high blood pressure among the population. This study demonstrated that the loss of 10 or more teeth was associated with a higher risk of developing hypertension.

We thank all participating Oral Health Experts (referred to as Oral Health Section Working Team) for their time and valuable contributions including C. Mbantshi, A. Mutombo, C. Musawu, A. Mufwar, V. Kaseka, G. Bimpe, C. Nkongolo, G. Nguala, G. Nyanguile, E. Ngalula, E. Mafuta, G. Mbumba, G. Shako, I. Luboa, B. Kabungu, D. Bokele, D. Nsumbu, F. Kayembe, P. Ekili, A. Cilambu, F. Mbumba, J. Dihulu, A. Katende, F. Salumu, V. Mukendi, J. Yamba, C. Mutombo, E. Mukenge, P. Mandiangu, D. Bwalungu, A. Kizangula, R. Kankolongo, I. Kalolo, F. Ndaya, J. Mawa, M. Mwayuma, B. Kazadi, CR. Mopamboli.

Authors ELT, AMM, FNB, DKM, DKM, EKK, JKB, FBM contributed to the conception, design of the study, acquisition of data, interpretation of data, and manuscript revisions. GPL, PMM, STM, PKN, GBB, JPK, JJMK, JRMK contributed to the writing.