Bottom of molar turning black but I brush my teeth... what the heck?

I dont understand. I brush my teeth twice a day. I dont floss like I should but many people dont and dont end up with their tooth decaying. On the other side a piece of my crown and actual tooth broke off but since I had a root canal it doesnt hurt. Im not trashy and brush my teeth. I NEVER drink cokes or other carbonated drinks and my sugar intake is very limited. I only chew sugar-free gum... I dont have dental insurance because I cant afford it and I am so scared to go to a dental school for reduced cost/free dental work because my brother had really bad results. My dad had really bad teeth - is this genetic? Help! Also, is there a way to keep the decay from spreading til I can get in to see a dentist?
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I'm glad you are not hurting, and you are right, since you had a root canal on that tooth you definately should not have any pain. However, you definately have a cavity. Here's the thing about crowns. There's a small ledge or lip where the crown meets the tooth. Bacteria that cause gum and tooth disease love to cling onto there, and that is a common area for decay. Even though you do not have pain there, the infection is there, and it will spread. Truely, there isn't any way to slow down the decay process once its begun. You could use an over the counter fluoride rinse like ACT for adults to keep your other teeth more resistant to decay. Here's the thing about cavities, once you have the bacteria in your mouth you have it for life. There's no way to sterilize the human mouth. Which brings me to your last question about heredity. The answer is babies are born without the cavity causing bacteria. It is in fact, tranmitted usually from a parent to baby from repetitive exposure from ,for example, tasting baby's food first to check temperature, or kissing baby. Cavities are actually a contagious disease, of which one day there will be a vaccination just like for Chicken Pox. People can be cavity prone if they eat things in high sugar, or acid contents. Also, sometimes has nothing to do with person's dietary habits, sometimes the person's salivary enzymes are not enough to protect the teeth. I rambled on a bit, but I hope I helped you. You do need to see a dentist to fix your tooth, as soon as possible.
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