if you're looking for an affordable dentist I'd like to recommend Studio dentistico Benedettini; I found this dentist through Groupon (offer is still – or perhaps it's again as I was there first time over a month ago – valid, the link is further below; I don't know what's your experience with Groupon deals – as to me, sometimes I'm satisfied, sometimes I'm not, and this time I was).
Besides the excellent Groupon deal, at the end of the first visit the dentist provided me with a really outstanding cost estimate in order to fix a certain dental problem of mine, and I accepted it happily and thus returned.
Full disclosure: I'm a resident here, so I'm actually eligible to access the Italian national healthcare's (ASL) dentist services. However, due to some not-so-good experiences with the ASL dentists, I prefer to pay a bit more and receive better dental care. I've tried also other dentists through Groupon; nothing to complain but with the other dentists I had no reason to return.
If you want to take a look, the link to Dr. Ciocie's Groupon offer is here: Protected content
The downside might be that the dentist studio isn't very close to city center but it seems to be relatively close to underground stops Bande Nere and Primaticcio (I move by bike!).