Is this malpractice?

About a year ago, I went to this dentist to get my cavities filled. The cavity was either too big or he did it too rough, but when I got home I felt a jagged line running down the back of my tooth. I went back the next day and he told me "not to worry because it's just a crack in the enamel" and proceeded to smooth the tooth with a drill. Now the small crack became a cavity and the tooth is infected causing me pain. Is this an act of malpractice? Should I even try to sue him? Or would it be considered "my fault for not properly taking care of my teeth"? How would I even prove that it was his fault? Not to mention, one of the fillings fell out and almost every filling he did is a bit brown around the edges. Is it just discoloration or he just did a crap job and there's decay going on? I feel that it is his job as a dentist to inform of me of possible effects from a cracked tooth. I could've just paid him to fix it and not have to get a possible extraction or root canal and crown.