My dentist extracted my tooth and after a few minutes, he did bone grafting. now its very painful to open my mouth even slightly. why is it so? what should i do?

Advil (ibuprofen) or............: Take some otc pain medication such as advil, motrin, aleve, (naproxen) or what you would normally take for headache, follow the instructions given by your dentist and if you have any concerns, call your dentist for advice.

Timing of onset?: If pain on opening is something that started to occur right after the procedure, a common condition called trismus could be the answer. It is like a muscle cramp or cramping of the muscles of biting (mastication). Over-stretching of the mouth during the tooth extraction could have easily caused this. If it is indeed the case; moist heat, using anti-inflammatory drugs, a soft diet should correct it.

Infection: Go back to the dentist to get an evaluation to rule out dry socket. If grafting involved you should get antibiotics and Medrol (methylprednisolone) dose pack (a steroid and analgesic combination to treat swelling and pain).