The goal of this observational study is to develop better ways to detect and predict major oral diseases, including oral cancer, gum disease, and tooth decay. This study will collect detailed oral health information and biological samples from adults with different oral health conditions and healthy participants to identify markers that may help doctors detect diseases earlier and predict how diseases may change over time. The main questions this study aims to answer are whether biological markers from saliva, mouth rinse samples, blood, or oral tissue samples can help identify people with oral diseases, whether these markers can predict future disease changes such as worsening gum disease, new or progressing tooth decay, or recurrence and spread of oral cancer, and whether combining clinical information with biological markers can improve disease detection and risk prediction. Participants will receive a standard oral health examination, provide information about their health history and oral health behaviors, provide biological samples when appropriate, and be followed over time through clinical visits, questionnaires, and health information collection. Researchers will compare findings among people with different oral health conditions and healthy participants to better understand disease-related changes and develop tools for earlier detection and prediction of oral disease outcomes.