Prevention is the key to avoid problems like yours. The prevention is both patient care and design of restoration by the dentist.You need to have all decay removed from the tooth, if necessary you could need pulpal treatment or root canal therapy. It may be possible to save the veneers or they may need to be replaces with crowns. You want an experience cosmetic/ restorative dentist who understand the intricacies retrofitting matching restorations.I would always prefer to do the first restoration of a mouth over correction of problems. Patients prone to decay are often better served with wrap around veneers or 3/4 crowns to standard veneers. In my practices I want to create answers to immediate problems, but also long term solutions for 5 years, 10 years and lifetime results. Sometimes this means waiting on final crowns until a healthy state is achieved. When possible I like 2 visits for standard crowns and at least four visits for cosmetic makeovers.Step 1. Models, Bite, Photos for creation of diagnostic wax-up. This is the master plan.Step 2. Preparation and transfer of diagnostic wax-up to patients mouth. Also impression and bite.Step 3. Patient returns few days later to evaluate and make changes to insure the final result is what the patient is looking for. This step can be repeated to insure meeting patient expectations.Step 4 Delivery of final restorations.This is based on a health patient without major decay or gum disease or bite issues. Full mouth reconstructions are more complicated but can also be done utilizing the same steps.Ira L Shapira DDS, D,ABDSM, D,AAPM, FICCMOChair, Alliance of TMD OrganizationsThinkBetterLife.com