The main assumption of the thesis that periodontitis affects the initiation and progression of atherosclerosis is the fact that the periodontal disease cause subtle systemic inflammation. The present study has revealed elevated levels of inflammation markers in the study group. Leukocytes count was 10.82 (± 3.87) 109/l, ESR 28.69 (± 17.62) mm/h, the levels of hsCRP 8.34 (± 18.72) mg/l, and fibrinogen 4.62 (± 1.09) g/L. In the conducted analysis, a correlation was revealed between the values of periodontal parameters attesting to the presence and the severity of a periodontal disease and the blood level of inflammation parameters. Moreover, there was an inverse correlation between the number of teeth and ESR (R=-0.31; p = 0.01). This may be due to the fact that periodontal inflammation is the main reason for teeth loss.
An increased level of systemic inflammatory response markers, such as leukocytes count, and the levels of hsCRP and fibrinogen, is significant in the pathogenesis of cardiovascular diseases. Determining the levels of these markers may be important in assessing the risk of an acute coronary syndrome. In the experimental models, the influence of CRP on the onset of endothelial dysfunction, increasing expression of adhesion molecules, and on the recruitment of monocytes into the vessel wall was demonstrated. Moreover, CRP contributes to the production of foam cells, formation of reactive oxygen species and to the proliferation and migration of smooth muscle cells [24]. The systematic review and meta-analysis of the study on the correlation between periodontitis and CRP levels conducted by Paraskevas et al. [25] demonstrated elevated CRP levels in blood serum of patients with periodontitis in comparison to healthy people. It was also shown that, among patients with stable coronary artery disease, elevated CRP level increases the risk of myocardial infarction, while in patients with myocardial infarction, it contributes to an increased risk of complications and worse prognosis [26, 27, 28]. A multicentre Stability Study showed a link between inflammation markers like hsCRP and interleukin-6 and periodontitis. In this study a large number of patients were collected, however, unlike the present study, the simplest indicator of periodontal disease, which is a tooth loss, was used [29]. In present study, hsCRP level correlated with the parameters attesting to the advancement of the periodontal disease, such as: PD (R = 0.28; p = 0.01), NoPD ≥ 4 mm (R = 0.24; p = 0.04); moreover, there was a positive correlation with the clinical attachment loss CAL (R = 0.27; p = 0.02). Different results were obtained by Górski et al., who did not demonstrate any correlation between CRP levels and periodontal markers [30]. However, Swaroop et al. [31], demonstrated in their study statistically significantly higher levels of inflammation markers, such as hsCRP and fibrinogen, among people with chronic periodontitis than among those with the healthy periodontium (p < 0.001); what is more, they proved positive correlations between hsCRP levels and fibrinogen and the measured periodontal parameters (PD, BI, CAL).
Another extremely important result of the present study is the relationship between periodontal disease and fibrinogen. Namely, a positive correlation between the values of the BI marker, indicating active inflammation of periodontium, with the level of fibrinogen (R = 0.36; p = 0.006). Fibrinogen is a protein synthesized by hepatocytes and fibroblasts in response to inflammation. The level of fibrinogen in the blood correlates with the severity of atherosclerotic lesions, the risk of an acute coronary syndrome, and mortality among patients with myocardial infarction. Fibrinogen participates in the thrombotic process; it is also pro-inflammatory, as it increases the expression of adhesion molecules and stimulates production of inflammatory mediators by endothelial cells [28, 32]. This has an additional significance in the studied group of patients with acute myocardial infarction, where prothrombotic hyperactivity is a key pathogenetic factor. The study by Bokhari et al. [33], in which 317 patients with coronary artery disease and periodontitis were examined, indicated correlation between BI and the level of fibrinogen. Also Górski et al. [30] documented positive correlation between the concentration of fibrinogen and the values of BI (p = 0.0587), as well as between the number of lost teeth and the level of fibrinogen (p = 0.0003). Seringec et al. [34], in turn, demonstrated considerably higher levels of hsCRP, fibrinogen, and globulins among patients with chronic periodontitis, as well as a higher tendency of erythrocytes to aggregate than in people with healthy periodontium.
The present study has demonstrated correlation between the leukocytes count and the parameters indicating the severity of the periodontal disease, such as PD (R = 0.27; p = 0.02), NoPD ≥ 4 mm (R = 0.28; p = 0.02), as well as %PD ≥ 4 mm (R = 0.28; p = 0.01). Numerous epidemiological studies showed positive correlation between leukocytes count and the risk of coronary artery disease. In a prospective NHAHES I epidemiological study, a group of people with the leukocytes count < 6600 cells/mm³ was compared with a group with the leukocytes count > 8100 cells/mm³; it was found that increased leukocytes count is linked to an increased risk of coronary artery disease among white males (RR = 1.31; 95% CL 1.07–1.61) and white females (RR = 1.31; 1.05–1.63) aged 45–74, taking into account other cardiovascular risk factors [35]. In the meta-analysis of seven most important studies regarding the correlation between the leukocytes count and coronary artery disease, which encompassed 5,337 participants with ischemic heart disease, the difference between the leukocytes count below or equal to 2800 cells/mm³ was connected to the total RR of 1.4 [36].
Bearing in mind the main purpose of the research, indicating the correlation between periodontical markers and myocardial injury and heart failure indicators was the most important. Univariate analysis has been demonstrated a significant relationship between BI and the level of BNP in the study group (R = 0.29; p = 0.02). Linear regression analysis using backward elimination showed that a significant predictor of BNP is only CAL. As the CAL increases by one unit, the BNP value increases by 31.33 units. For the left ventricle ejection fraction prediction, none of the analyzed models were statistically significant (F < 1.62; p > 0.210) and none of the analyzed variables were a significant predictor of left ventricle ejection fraction (p > 0.05). BNP is recognized as a prognostic marker in patients with acute coronary syndromes. It is believed that BNP inhibits the growth of cardiomyocytes and fibroblasts, impairs collagen synthesis in relation not only to the myocardium but also to periodontal tissues [37]. The increase in BNP is influenced by factors such as smoking, stress, diabetes, and age [38]. These are also risk factors for periodontal disease. Increased serum BNP levels are observed in patient with periodontitis compared to those without periodontitis. Studies by Leira et al. have shown that increased destruction of periodontal correlates with a higher serum BNP level [39]. On the other hand, in patients with coexisting heart failure and periodontidis professional periodontal treatment can contribute to a decrease in the values of BNP [40]. As a potential mechanism linking periodontal disease with heart failure, cross-reactivity between periodontal and myocardial antigens mediated by chronic Toll-like receptor activation is suspected [41]. Current results seem to confirm the thesis that periodontitis is associated with the biochemical features of heart failure in the course of myocardial infarction. It probably depends on the size of heart injury, as it was asserted by Marfil-Alvarez. This author indicated the correlation between periodontitis and the size of myocardial infarction. This observation is reflected by the higher level of troponin and myoglobin depending on the extent of the myocardial injury [42]. This observation in patients with myocardial infarction is extremely important from a prognostic point of view. Perhaps, an unfavorable prognostic factor in patients with myocardial infarction is not only classic and well-established BNP level but also periodontitis. However, this requires validation studies dedicated to this issue.
An interesting observation is the relationship between the severity of periodontitis and TnI levels. Linear regression analysis showed that significant predictors of the level of TnI are API and BI. With 1% increase in API, TnI levels decrease by 0.3 units, while with 1% BI increase, TnI levels increase by 0.26 units. The present research is consistent with the results obtained by Marfil-Alvarez et al., who found a significant correlation between BI and TnI level (R = 0.21, p < 0.025) [43]. Moreover, hierarchical linear regression has showed that the TnI concentration was positively associated with indicators of the extent and severity of chronic periodontitis. Interestingly, the relationship between chronic periodontitis severity and TnI was mediated by the total leukocytes count. On the contrary, current results for patients with acute myocardial infarction are quite different from the data presented by Vedin et al. [29]. Indeed, they found no relationship between periodontal disease, which a simple index was the loss of teeth, and the level of troponin. It should be noticed, however that this study focused on patients with stable coronary heart disease. In earlier studies these authors showed no relationship between tooth loss and myocardial infarction in this population [43].
An equally important and original result of the study is the significant association of periodontitis with risk of myocardial infarction. The logistic regression analysis showed that API and BI are significant predictors of myocardial infarction. With the increase in API by 1%, the probability of myocardial infarction increases by 8% (OR = 1.08), while with a 1% increase in BI, the probability of myocardial infarction decrease by 7% (OR = 0.93). The current findings are consistent with the results of the PAROKRANK study of 805 people [44]. A relationship has been demonstrated between moderate to severe periodontitis, objectively confirmed by radiological bone loss, and the first myocardial infarction. Stability Study is a study dedicated to similar topics [29, 43]. In contrast to the our study in PAROKRANK study showed no association with periodontal disease and the onset of the first myocardial infarction. However, while various aspects of cardiovascular risk were assessed in this study, including myocardial infarction, all analyzes were based on a single but very simple indicator of periodontitis which is the number of teeth preserved. Since this was a multicenter observational study, the application of a general parameter that periodontal disease is justified. Remaining in this aspect in a sharp contrast to the present study, it also highlights its originality and methodical credibility. First, it emphasizes the comprehensiveness and diversity of periodontological data collected in the current study. Secondly, it concerns the acute phase of myocardial infarction, which the nature of the disease justifies the difficulties in obtaining so many periodontological data. The fact that the increase in the BI ratio by 1% is accompanied by a reduction in the risk of heart attack by 7%, also requires comment. Of course, higher BI indicates a greater severity of periodontitis. It should be remembered, however, that during the dental examination, patients in accordance with acute coronary syndromes treatment standards were already on dual antiplatelet therapy, which undoubtedly increases the risk of bleeding [20, 45]. Moreover, the severity of bleeding may be a clear evidence of the effectiveness of antiplatelet therapy, while it might be a problem in dental treatment in the period after acute coronary syndromes [46]. The explanation for this apparently unexpected relationship can therefore be seen in that - it is a net effect of the severity of periodontitis and the increased bleeding tendency associated with dual antiplatelet therapy. On the basis of the conducted analyses, it may be concluded that periodontitis is a condition which may affect the risk of the development of ischaemic heart disease as well as its complications in the form course of myocardial infarction, as it causes a mild systemic inflammatory response. Undoubtedly, social awareness of the possible clinical implication of periodontitis is insufficient. Considering the prevalence of the ischaemic heart disease, high mortality resulting from cardiovascular diseases, and the ubiquity of periodontitis in the Polish society, the periodontal health of the patients with ischemic heart disease should be taken into account and appropriate preventive and curative measures ought to be introduced. Moreover, patients with periodontitis should have their cardiovascular risk assessed. Focusing on any possible correlation between periodontal inflammation and the occurrence of ischaemic heart disease is of utmost importance due to the fact that this may be a modifiable risk factor. The importance of chronic periodontitis should be taken into account in both primary and secondary prevention of cardiovascular disease [47, 48]. What is more, even a single additional tooth brushing episode per day in healthy adult patients can reduce the incidence of atherosclerotic cardiovascular disease events [3]. However, the available literature does not provide sufficient evidence to support or refute the potential benefit of periodontitis treatment in secondary prevention of cardiovascular disease [48, 49]. Undoubtedly, further trials are necessary to conclude whether or not the periodontal disease treatment can help prevent the occurrence or recurrence of cardiovascular disease [60]. According to the recently consensus report published in 2020, patients with periodontitis should be informed about the higher risk for cardiovascular diseases, such as myocardial infarction or stroke, and as such, they should actively manage all their cardiovascular risk factors (smoking, exercise, excessive weight, blood pressure, lipid and glucose management, and sufficient periodontal therapy and periodontal maintenance) [48].
5.1. Strength and Limitations
The obvious and permanent limitation of studies with extensive research methodology is a relatively small number of patients. For two reasons, the undoubted indubitable limitation is also used pharmacotherapy for two reasons. Firstly, the use of statins, which is a known anti-inflammatory agent, may modify the severity of the systemic inflammation. However, patients with acute myocardial infarction have not yet used statins in most cases, and blood samples were taken before the drug was started. In turn, antiplatelet drugs may by their nature increase bleeding, including those associated with stomalotological assessment. The more that periodontal examination was performed 24 hours after the onset of myocardial infarction and thus anti-platelet activity was fully developed. For ethical reasons, however, this restriction cannot be eliminated because it is not possible to delay the treatment of myocardial infarction for periodontal assessment. It should be emphasized, however, that both in the case of statins and antiplatelet drugs the limitation resulting from their use loses some strength due to the fact that almost all patients had the same treatment. It proves the pharmacological uniformity of the examined group, which increases the reliability of the results. Another limitation is also possible coexistence of other inflammatory processes in patients from the study group. To this end, special care was taken to exclude from the study patients who, at the time of inclusion in the physical examination or in additional examinations, had additional, beyond the periodontium, detectable foci of inflammation.
An undoubted advantage of the study is the extensive dental methodology using many periodontological indices. Both the detailed assessment of the periodontal status and the multitude of periodontal indices applied in the study can guarantee an increased reliability of statistical analysis of the obtained results. These studies can increase the interest in the prevention and treatment of periodontal disease in order to improve both the periodontal status and the prevention of cardiovascular diseases in the population.