There is a fairly new product out there the help the edentulous patient; it is the all on 4 implant retained denture. This is put in and not removable by the patient. The denture is attached to the 4 implants and does not press on the delicate lining of the mouth. The denture does not move around. Most patients are very happy with this treatment. The downside, it is costly. Even if you have dental insurance, it will cover only $2,000 out of approximately $22,000 per arch. The expectation is that the implants will last forever, the denture has a metal framework with a lifetime guarantee.....but the plastic teeth on the denture will need to be reset periodically. Most of the cost is upfront. It really is a quality of life issue. This treatment is so much better than the traditional denture .
In answer to your sore gums.....try to wear the denture as little as possible....hardly a great answer, but a common problem, with no great inexpensive solution.
The depth of the decay and the sensitivity or pain the patient is in, are the factors in determining whether a tooth needs a root canal