Three months after I got a block of 4 crowns installed, the gum receded and I have a hole that is very sensitive to the cold?

I have a block of four crowns installed on my molars and pre-molars on the lower jaw. It hurt my last molar quite a lot but the pain subsided after two months. Another couple of months later, however, my gum receded slightly on that same tooth and I have a kind of hole there, that is very sensitive to the cold. In fact, I can't eat anymore on that side. My dentist waves it off as irrelevant and doesn't want to do anything. What should I do, are there any options?

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