I have owned many pitbulls and lost them all too early; one at 9, one at 10 and one at 12: in my experience they are not a long lived breed :-(
I kept my pitbulls teeth clean in two ways; I got a dental tool for two bucks from the drugstore and scraped gunk and tartar off - particularly at the base of the gum line. I also fed raw, meaty bones. Actually my male didn't like his bones raw, so I toasted them in the oven at 350 for half an hour, so the meat roasted up but the bone was still raw. You want to feed non-weight bearing bones - so NO soup bones or shank bones or the hard bones that are tube shaped and hollow inside; no marrow bones. I got beef rib bones and beef neck bones. These bones do not bear weight so are softer, they gnaw down and grind down rather than splintering, and the interesting shape of the bones allow them to be worked deep in the mouth so the dog can really use them to scrape teeth. If your boy is not used to eating fresh roasted bones feed them for half an hour and then take away; try this for 1 week and supervising while he is gnawing on the bone for that half hour. If he is breaking chunks off into smaller bits, pick up the smaller bits. Some dogs find these bones so yummy they swallow the smaller bits; they tend to barf them right back up, so pick them up to avoid cleaning up a mess later. I do find if my dogs can keep the bone bits down they have not caused any impaction and they don't splinter so no punctures in the gut - again mostly they barf them up - [so you know what to expect].
The pain and arthritis may be helped by adding 2 tables spoons of the raw, unpasturized and unfiltered Apple Cider Vinegar to the water or to his food twice per day.
The cysts and tumours may be helped with Essiac Tea - there are many posts by Om about this tea, so be sure to read up on Essiac and look for Om's posts on the subject.