There are two ways of looking at this. Concerning the teeth, they might just be a useful medium to describe another worry you have eg. work you need to do but are afraid to start on etc or you could be worried about your teeth specifically - like have you had tooth ache or forgotten to brush them?
On the other hand, it could just be a mixture of other memories and events you are sorting through. Perhaps you had a big meal that day and felt a bit full afterwards and the breaking teeth was merely a manifestation of a worry of feeling full.
Either way, don't take it too much to heart. Dreams are a very dilute medium and I don't believe thay can be taken literally all of the time. Certainly don't worry unless you really do have tooth ache, and remember sometimes if you believe a thing very intensly you can convince yourself it's real when theres nothing to worry about.
The other dream sounds to me like a mixture of different stimuli combined into a single narrative. The want to go up a mountain and ride suggests you are an active person who wants to enjoy themselves. The fact that you found the school at the top could suggest that you feel your school is restricting you from doing what you really want. Or if not actually school itself then maybe another person or situation you are frustrated with.
That when you decided to dye your hair like everyone else, but found that your friends had left when you had finished could mean that you worry about being behind the times, and when presented with tha white horse but choosing the brown, you know your own mind and don't nessessarily want to take exactly whats presented.
Again, I wouldn't dwell too greatly on any of this. If you find what I've said helpful then I'm glad to have helped, but if any of it is worrying, always remember that this is merely my logical breakdown of the imagery. I might be completely off and it could all be random memories clumped together.
I had a dream a while back that I crashed my dad's jaguar (which he doesn't even have) and we stayed in a hotel only a room thick. This could reveal frustration on my part, but Im actually feeling ok right now, so never take anything at face value.
Hope I've been of help!