J.G.
Is the sun rising earlier lately? That might be a factor.
Good for you for not picking him up right away. It's a safe place for him to have his own quiet playtime. And it lets you listen to him giggle and talk and think 'Oh he is so adorable, so smart, so cute. I'm so thankful for him.' Put some books in his crib after he falls asleep at night, in the morning he'll have something to look through.
If you decide to change your bedtime routine, I think it's best to do so by 15 minute incriments, maybe pushing it all forward 15 minutes one week, then another 15 minutes the next week. This way, it's not a big difference.
Yes, it could be teeth. It could just be a phase. Like I said, it could be the sun. Are his naps longer lately? Maybe he's napping too long, so then not sleeping at night as long? I wouldn't worry. If you're tired, you might try going to bed a little earlier yourself so you can get your beauty-sleep. Sounds like you're doing a good job keeping things consistent with him (which kids love). I'm sure you'll make the right decisions with this too.