I think teeth is the most likely culprit, but I would also wonder if he is going through any developmental stages? We had really bad developmental waking with dd2 at every stage: learning to sit, learning to roll, learning to crawl, learning to walk and now I think she is working on talking and that it disturbing his sleep.
I think that SA would be more likely to manifest at other times during the day - both of mine wouldn't let me leave the room when they were going through their SA periods (although it never caused any sleep problems!), so I think it is more common that they show anxiety every time you are out of sight.