It is not uncommon to place a restoration on an upper second molar and have the contact open over time. The new crown is checked diligently at the seat appointment, and the contact flossed to ensure that it has the proper tension. The patient presents on an emergency because they are packing food, or at a routine hygiene exam and the open contact is detected. This can be frustrating and disconcerting for both the patient and the dentist. So why does this happen? As with many things in dentistry it is most likely multi-factorial, but one of the first things I check is the occlusion.
Often when this happens I find I have introduced a distalizing contact on the new crown or filling. Intercuspal position contacts that land on the mesial incline of a cusp will cause the tooth to be forced to the distal. If the contact is also slightly high and the tooth has no tooth holding it on the distal this can open the contact. In addition to MIP contacts Excursive interferences can create a distalizing force on the last tooth. For patients that parafunction this increased load and an excursive interference will compound each other. Another occlusal indication to look for is the first point of contact in centric relation, or what I refer to as a seated condylar position. Using a leaf gauge or bimanual guidance ( bilateral manipulation) check for the first point of contact. Often we have introduced a new FPC, and it can distalize the tooth.
In my office when I have found either of these occlusal issues on a tooth where a contact opened I simply adjust the occlusion and we wait and see what happens. Commonly, the contact will close again and the second molar will drift mesial into its original position. My guess is there are also other causes, and perio involvement is a complicating factor. However I have yet to see one of these happen in my patients where I could not identify an occlusal cause.