Porphyromonas gingivalis is a Gram-negative oral anaerobe that is involved in the pathogenesis of periodontitis and is a member of more than 500 bacterial species that live in the oral cavity. This anaerobic bacterium is a natural member of the oral microbiome, yet it can become highly destructive (termed pathobiont) and proliferate to high cell numbers in periodontal lesions: this is attributed to its arsenal of specialized virulence factors. The purpose of this review is to provide an overview of one of the main periodontal pathogens—Porphyromonas gingivalis. This bacterium, along with Treponema denticola and Tannerella forsythia, constitute the “red complex,” a prototype polybacterial pathogenic consortium in periodontitis. This review outlines Porphyromonas gingivalis structure, its metabolism, its ability to colonize the epithelial cells, and its influence upon the host immunity.

Over the last two decades, the amount of evidence corroborating an association between dental plaque bacteria and coronary diseases that develop as a result of atherosclerosis has increased. These findings have brought a new aspect to the etiology of the disease. There are several mechanisms by which dental plaque bacteria may initiate or worsen atherosclerotic processes: activation of innate immunity, bacteremia related to dental treatment, and direct involvement of mediators activated by dental plaque and involvement of cytokines and heat shock proteins from dental plaque bacteria. There are common predisposing factors which influence both periodontitis and atherosclerosis. Both diseases can be initiated in early childhood, although the first symptoms may not appear until adulthood. The formation of lipid stripes has been reported in 10-year-old children and the increased prevalence of obesity in children and adolescents is a risk factor contributing to lipid stripes development. Endothelium damage caused by the formation of lipid stripes in early childhood may lead to bacteria penetrating into blood circulation after oral cavity procedures for children as well as for patients with aggressive and chronic periodontitis.

Type 1 diabetes mellitus is a chronic metabolic disease of an autoimmune origin with early manifestation predominantly in the childhood. Its incidence has been rising in most European countries. Diabetes has been intensively studied by all branches of medicine. There were a number of studies investigating oral consequences of diabetes; however, unambiguous conclusions were drawn only for the relationship between diabetes and periodontal impairment. Many studies confirmed higher plaque levels and higher incidence of chronic gingivitis both in adults and in children with diabetes. Juvenile periodontitis is rare both in healthy subjects and in those with type 1 diabetes. Yet certain findings from well-conducted studies, for example, differences in oral microflora or the impact of metabolic control of diabetes on periodontal health, indicate a higher risk of periodontitis in children with type 1 diabetes. As for the association of diabetes and dental caries, the results of the studies are inconsistent. However, it was found that some risk factors for dental caries are either more or less prevalent in the diabetic population. Despite an extensive research in this area we have to acknowledge that many questions have remained unanswered. There is a need for continued, thorough research in this area.

The determination of biomarkers in saliva is becoming an important part of laboratory diagnostics and the prediction of not only periodontal, but also other tissue and organ diseases. Biomarkers in saliva (e.g., enzymes, protein markers, or oxidative stress markers) can be used for activity determination and for periodontal disease prognosis. Saliva also contains many markers which can predict the risk of certain diseases (e.g., diabetes mellitus, cardiovascular, oncology, endocrinology, and psychiatric diseases). The study of salivary components proteomics clearly shows the relationship of periodontal diseases and diseases of distant systems, organs, or tissues.

CRP is a plasma protein that reflects a measure of the acute phase response to inflammation and is one of the markers of choice in monitoring this response. CRP can be used for the prediction and early detection of periodontal disease. The aim of this study was to compare and evaluate the systemic levels of CRP in the peripheral blood samples of patients with chronic and aggressive periodontitis, gingivitis, and gingival recessions and compare them with periodontal clinical parameters. All patients (N = 158) were examined prior to the initiation of periodontal treatment. Patients were divided into four groups. Group A consisted of 26 patients with aggressive periodontitis, Group B consisted of 111 patients with chronic periodontitis, Group C consisted of 13 patients with gingivitis, and Group D consisted of 8 patients with gingival recessions. Our study results indicate that CRP levels increase subsequently with the severity of the periodontal disease and that the bleeding on probing index showed much better positive correlation with the CRP levels compared to the pocket depth index in both periodontitis patients groups, especially in aggressive periodontitis patients.