Very good question! The answer to your question is really based on the anatomy of your jaw bone, where your sinuses are located and where you lower nerves are positioned. Based on the positions of the above-mentioned structures and the length of your jaw bone, this dictates how far back in your mouth teeth may be placed. Its all engineering and equations that are determined in your mouth and in the dental laboratory. If the implants are placed further apart and further back in your jaw bone then YES you can have second molars. If this is not the case then 1st molars would be it. If 2nd molars were placed and they violated our principles for designing the All-On-Four restoration,your prosthesis and/or implants could fracture
