I have heard crest toothpaste with whitening mixed with betadine works well. I have never had to treat, but I have heard from a few people who have treated with that with excellent results. Though I suppose it depends what type of sarcoid as well...
There is something else that is actually meant for treating them that works well, but I can't think of what it is called...
ETA: Now that I'm thinking about it, the horse specific cream was actually vet prescribed unfortunately.
Here's a photo of Faith's sarcoid. I've read that it's the fluoride in the toothpaste that is thought to affect it, so am using a fluoride mouthwash in a spray bottle twice a day. We've been hit or miss with it for a week, but she's getting over her hissy fits about it, so hope to be religious about it from now on.