Teeth can have trouble meeting properly for several reasons. One reason is that teeth may have temporarily shifted. This can occur when there is a tooth infection or when inflamed maxillary sinuses are present. Another reason can be due to a recent trauma to the face. Localized trauma can result in a fracture of teeth, the mandible or maxilla and this can cause the teeth to not occlude properly. Still another reason can be an injury to the temporomandibular joint. If one condyle is not seating properly it can cause the bite to be off.
If your teeth do not meet properly for more than an hour, it is a good idea to contact your dentist to find out why. A dentist usually can usually ascertain the cause of teeth not meeting properly and can offer treatment or medicines that may alleviate the problem.