Here's the problem with passing with just C's. You never know until you actually start dschool if dentistry is for you. There are people every year who find out that dentistry isn't for them or what they anticipated. By accepting just passing grades, you lower your GPA and make it more difficult to get into another program like med school, pharmacy, etc should you decide to drop out of dschool. I never thought I'd drop out of dental school in my 2nd yr. I did. Had I decided to take it easy that last semester of undergrad, I might not have got into dschool the 2nd time. Just saying.
Don't give up at this point.