porcelain onlay process

[feelingbetter]

Hi, my dentist is proposing I have porcelain onlays which I have never had before, although I have a crown. As I understand it, it doesn't involve too much drilling of the actual tooth - presumably they have to get the old fillings out though. I am asking because I am wondering whether I need IV for it (which I do have for extractions and would have for an RC). If it is relatively uninvasive that would save the expense and the faff. Any experiences please?