You could go to the vet for a consult and ask how much time you could risk (before tooth loss) to give the Petzlife a chance to work before doing a full-on dental. Petzlife makes some great claims, so I wonder if it could live up to what you need it for.
There is a new prodcut posted in Health by Gracie2006 that looks interesting too.
My guys' teeth are beautiful from feeding raw - but I think you've been down that road, right? Oddly, Wylie's teeth were at his worst during homecooking (vs. kibble). Then, they cleared up on their own once he was on raw. (which I didn't really expect)