I'm no expert on cysts, although that sounds like it's in a place that might cause discomfort so I'd probably get that done, tbh.
For the teeth, have you tried using a supplement? I've used PlaqueOff in the past, and it does work, but it's about £30 for a 180g tub. I have 6 dogs (including a 10 yo working cocker!) so I was going through a lot of it.
However.... if you go in to ebay and search for Plaque off, scroll down until you see a listing that says "Get the PLAQUE OFF dog's teeth, 150g plain packaging", it's £8.50 with free postage, and it's the same stuff - organic dried ground seaweed. The seller is dogsareus17 by the way, in case there's a few the same.
Start off just sprinkling a tiny tiny bit on his food, and then it increases to 1g a day. You'll notice a difference within a couple of weeks, sometimes the plaque just comes off by itself, other times it'll come off if you brush his teeth. It's quite satisfying if that happens, it comes off like a bit of shell!
Definitely worth a try anyway.
It should go without saying but I have no connection whatsoever to the ebay seller.