Consult with Dentist ASAP
You need to check with your dentist ASAP because it could be as simple as cavity to pulpal infection(nerve infection) . Your dentist can determine exactly what will be right solution for you. Best of luck
Blackened Broken Tooth
It could be decay, it could be discoloration from an old silver filling or could result from a long term pulp issue. The only way to find out is to see a dentist promptly and have it checked. If you don't see a dentist and have it treated though, it will get worse no matter what the cause.