My horse has suspected arthritis in his. Symptoms were reluctance to accept the bit when he used to open his mouth for it, so after a couple of bit changes and reaching a point where one day, he wouldn't drop it, I had a closer look and his incisors didn't line up. He is on bute (half a day), ridden in a hackamore and doesn't seem bothered by it now.
He has recently developed a diastema, not sure whether it is related or just coincidence.
No swelling, he did show some signs of quidding, but I can't be 100% sure it was connected and no headshaking but he was a bit 'off', not something anyone else would notice but I have had him for 17 years, so I know what is normal for him.