Why would you think the instruments are not sterile? If you have reason to believe your dentist does not use standard protocol why would you go to this dentist? Why do you not seek out a different dentist who does use standard practices and report this other dentist to the health board?
If the dentist did use instruments that were contaminated with blood from any prior patient with a blood borne illness yes there could be a risk of any illness transmitted by blood.
Are you in the United States?
This article from MedHelp.org provides information on who's at risk for Hepatitis C. It might help you sort out when you need to be concerned, and when you don't.