Hello You should be using Sensodyne only for a limited period as its a medicated tooth paste taking care of your sensitivity issue. If the tooth requires RCT which can be diagnosed after clinical and X Ray evaluation then no use of applying sensitive tooth paste then the answer is to get RCT done for that tooth followed by full restoration crown. Point to be remembered of it's an initial cavity which is left untreated then a filling should be done. So most important is the correct diagnosis.