Hi cwilde,
It is hard to diagnose what treatment is necessary based on the x-ray alone. What we can tell from the x-ray is that there is a significantly deep filling on the tooth.
There are a couple of things that we need to see before we can make a diagnosis and recommend treatment.
1) Is there any symptoms on the tooth (pain on cold/hot, pain on biting/percussion)
2) A peri-apical X-ray to see if there is any active infection at the end of the root/tooth
With that information, we would be able to make an informed decision.
Please don't hesitate to ask anymore questions and hope that helps guide you!