What are the chances of contracting HIV from a single exposure?
Your chances are exceptionally low. Your mouth would have to be actively bleeding, and he would have to be unmedicated and at a peak point in viral load for the infection risk to be significant. What you need for peace of mind may be completely different however, and you should get tested after a minimum of 30 days. HIV is not a highly contagious virus that exposure to automatically means seroconversion.