You speak short, but the neck is not enough! This may be a dentist's problem or a mechanic's problem. The lingual neck edge of porcelain teeth is not covered properly. If the neck edge is worn, it will be sore, but you don't, and the chance of dental caries is very small. But you said the crown was loose. I don't know exactly how to loosen it, but if the inner crown has a thick layer of cement, it is a problem, which directly leads to the porcelain teeth falling off easily, because the thickness of cement is limited. If so, I suggest you do it again with the mold.