<s>[INST] I have several teeth on the bottom that are turning black at the gum line, what is causing this and what can I do to fix it?  I am only 44 years old and I am afraid I either need several root canals or they will tell me to put dentures in but I'm only 44.  I brush my teeth twice a day and use mouth wash also. [/INST] helloo...the black line if present on tooth surface it can be either due to staining or it can be caries...if caries u can get it filled based on depth if its staining it can be removed by scaling...if black colour is in gum..then it can be due to subgingival calculus which can be removed by scaling...so nothing to be worried meet a dentist and get ur problem solved...according to symptoms said by u i dont feel u have chances of denture now.....be cool..hope ur benefitted something by this reply..have a healthy day!!! </s>