The goal of this observational study, called OMICA (Oral Microbiome in Carotid Atherosclerosis), is to learn how bacteria living in the mouth may influence the development and stability of plaques in the carotid arteries, which supply blood to the brain. Plaque buildup in these arteries can lead to stroke. Researchers want to understand whether certain oral bacteria are linked to plaque vulnerability, meaning a higher chance that the plaque will rupture and cause a stroke. The study will include a cohort of adults scheduled for carotid endarterectomy at Semmelweis University. Participants will be enrolled in the Semmelweis University Carotid Biobank project. The main questions the study aims to answer are: Do people with more severe gum disease or tooth infection have a higher number of bacteria in their carotid plaques, and are those plaques more likely to rupture? Are the bacteria found in vulnerable plaques different from those in stable plaques? Are similar bacteria found in the mouth, gut, and plaques, suggesting that bacteria may travel through the body? What participants will do: Have their oral health checked before surgery, including an exam of gum disease and tooth infections. Provide microbiome samples from the mouth, anus, urine, and carotid plaque (taken during surgery). Have preoperative photon-counting computed tomography (CT) performed to assess plaque stability and study eligibility. All samples and imaging data will be analyzed to identify bacterial species and their relationship to plaque type. The study does not involve any experimental treatment or medication. Participation adds no significant medical risk beyond standard care. Researchers will compare bacterial patterns between people with vulnerable plaques and those with stable plaques to identify microbial signatures linked to carotid plaque instability. The results may help create future microbiome-based risk models for detecting people at higher risk of stroke or severe atherosclerosis.