Teeth serve a purpose for chewing food and also for appearance. When teeth are rotting and falling out, it can send a message to the dreamer they are worried about their survival that may also be due to their external appearance; how they appear to the general public.
When rotting teeth affect language and communication, the dreamer needs to pay attention to what he or she is saying and how they are portraying their message to the world. Are they saying something that should be kept silent instead? Are they speaking “rotten” words instead of something encouraging and based in truth rather than emotion?