This patient's recent dental procedure, new heart murmur, and the observed vegetations on the aortic valve suggest infective endocarditis. The identified gram-positive cocci in clusters is indicative of Streptococcus viridans, a bacteria known for causing such a condition and is associated with dental procedures.

While group A strep can lead to various CVS problems, the bacterium is gram-positive and grows in chains, not clusters. In addition, this patient's recent dental procedure points more towards staphylococcal endocarditis.

S. mutans can indeed cause infective endocarditis, especially after dental procedures, but they are gram-positive cocci in chains, not clusters.

Staph aureus can cause infective endocarditis, but usually following a skin breach such as in intravenous drug use. In this case the person has had dental procedures carried out which makes it more likely to be infective endocarditis due to Streptococcus viridans