There is no oral cavity in the world which is with teeth but without bacteria.
If pre-surgical procedures of oral prophylaxis, oral mouth washes & pre-extraction medication has been used then post extraction medication may be avoided.
there are many bacteria that have been known to cause systemic disease. Please visit link..
http://cmr.asm.org/cgi/content/full/13/4/547
So giving antibiotics prior to any oral surgical procedure is important. We as dentist will never know if 6 months after an extraction the patient suffers a heart attack / stroke following any septal defect due to the bacteraemia caused by the oral bacteria.
