Hard to see what's going on here. The 3 (FDI 16) root filling looks OK but there is possible resorption of the mesial root and possible infection.
My first step would be to get a standard bitewing Xray so I can look at the tooth straight side-on. These PAs that you are showing do not always provide enough information on their own.
If the bitewing doesn't clarify the situation, then maybe get a CBCT (3D) Xray.
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