You are correct it is not good. The bible uses teeth to reference the gnashing of teeth which happens with God’s judgment (Psalm 3:7) or the enemy devouring people with his teeth (Psalm 124:6).
I think in this case because you are embarrassed and humiliated it has more to do with sharing your faith with others. Let me explain….
Paul talks about when you should be eating meat you are still drinking milk (1 Corinthians 3:2). Hebrews 5:12 also references the same thing. This has to do with spiritual maturity. You said you had retainers so these are in place to fix your teeth. These could be seen as your teachers,pastor, mentors. Once you removed the retainers your teeth are falling out which means you need them (mentors) as a support system.
One of two things, you’re either moving out too fast to share your faith with others or into ministry work and God is telling you to slow down you are not ready. If you proceed you will end up being embarrassed and humiliated. Or you actually are ready but you are afraid and God is using this to expose the spirit of fear to you. Only you know which one of these two scenarios fits the bill. Either way, you need to pray this through. Once you’ve prayed and put into action what you prayed correctly, I think you’ll stop having these dreams.
God Bless You.