Well almost every night. I'm not even looking for solutions, because frankly I think we've tried everything, but wondering if anyone else has been here?
I don't think it's teeth or discomfort of any kind (because it happens so frequently) - I think it's just his sleep cycle. He'll wake up sometime between 1:30 and 2:30am, and it'll take an hour to get him back to sleep. Generally he's not that upset - just kind of moans on. We've tried leaving him/not leaving him/patting him/cuddling him/co-sleeping (which incidentally generally makes things worse as he seems to think it's playtime and then gets really upset when he realises it's not).
Hell, it's knackering.