Tooth feels thinner at the bottom & appears translucent after dentist filled a cavity at the top of tooth. Why did this happen?

Tooth feels much "thinner" at the bottom & appears translucent after dentist filled a cavity at the top of the tooth. There was no reason for him to mess with the bottom of my tooth and he claims that he didn't. However it was NOT like this before I went to him. I am very upset because I take very good care of my teeth, they are (well were) beautiful. What can have caused this and what can I do to try to fix his mistake? Note: it is causing the inside of my upper lip to hurt and swell.