The connective tissue fibers of the layer of the dermis are extensively interwoven with those of the layer to stabilize the position of the skin and bind it to the underlying tissues.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.

the answer to your question is tooth decay.