I am a dentist. I came to know that the patient whom I extracted a tooth 1week back was HIV positive. Extraction was complicated one. What to do now?

HIV testing. Unfortunately it is too late to prevent infection if you were exposed. At 21 days you can get an HIV RNA test that will be very accurate as a test to see if you were exposed. But that said most health professionals i know practice universal precautions and are universally safe regardless of the procedures.
Get Tested. Start with an HIV test then have it repeated in 6 months. Discuss with infectious diseases doctor what the follow up should be. You should be able to visit center for diseases control in us to see treatment protocol for possible contact with virus. Good luck!
Universal Precaution. If you used universal precautions, and good sterilization techniques on every patient, and you did not stick yourself, you have very little to worry about. If not i would see my physician about getting tested, and if good sterilization techniques were not used, i would be worried about my patients too.