If you have a cavity in one of your lower right back teeth that is kind of big will the dentist be able to fill it with a filling?

I had a root canal on my back tooth that was supposed to be crowned, but i didn't get around to it, and because the tooth became brittle it broke ( a chunk actually came out of it). My dentist said he'd try and fill it and see how it held up. That was 5 1/2 years ago. It's fine, and has never bothered me. I guess it may depend on the location. My tooth broke in half and part of the middle came out, but the tooth was dead, so i didn't experience any pain or problems.