If ass. rests gloved hands on back ofchair, then handles dental instruments, can i get hcv, assuming chair isn't cleaned and she does it w/eachpatient?

No: Hcv is spread through contaminated blood. So what you describe would not be a way that the disease could be transmitted.

Very Doubtful: Dental offices/gloves are not sterile, they are clean...There's a difference. The instruments are sterilized b/t each patient's use, and disposable supplies are used wherever possible to the reduce any possibility of cross-contamination. All chairs, trays, counter-tops, drawer handles, etc are disinfected and/or barrier wrapped b/t each patient. That is osha and infection control protocol.