Hello, Once the (pulp)nerve of the tooth gets involved by infection, RCT should be done depending on the condition of the tooth. After the rct is done the tooth becomes non vital and tend to fracture during mastication (chewing food) as the nerves which provide nutrients to the tooth like any other organ or body part is removed in the process of root canal. So its always advisable that after rct once the tooth gets stable ( you don't feel any pain or any other discomfort in the rc treated tooth) go for crown. This also add life to the damaged tooth