Research the correlation between oral and systemic health. Is it a direct cause?

Research the correlation between oral and systemic health. Is it a direct cause? Correlation vs causation. Find issues in need of investigating such as whether or not certain systemic diseases stem from oral manifestations and diseases. Include oral risk factors that may impact systemic health or may need further investigating to see if they impact systemic health at all. Reference books, periodicals, scientific articles and the internet. Thorough instructions and one article I found interesting is attached.