We would need to see radiographs (x-rays) to better determine the problem. Your gum line on this crown is at a similar level, as tooth 25. There are a few possibilities at work. If the crown is impinging in the gingiva, which would be called a biologic width invasion, then this inflammation will remain for a very long time. The gingiva and bone might remodel in an unhealthy way and you may end up with periodontitis, or gum and bone loss in this area. Many dentists do not recognize when they should have had you see a periodontist for a procedure called crown lengthening. There are periodontists in Germany, although this specialty is not as common in Europe, as it is in the US. A gum graft is done to add tissue, which might have helped and still might help on 23, although closer pictures could help us decide on that. 23 could stand to have a mm or two of new tissue for root coverage. Allergies to crown metal are very rare. There also may be cement left behind by your dentist. Leaving cement around a crown margin is a guaranteed way to have inflamed gingiva and can cause the periodontal disease I mentioned earlier. But, I would get with your dentist and ask to go over the radiographs and see if the crown margin is impinging.
