A common problem that occurs with some frequency is the mandibular second molar abutment that has tilted mesially into the space formerly occupied by the first molar. It is impossible to prepare the abutment teeth for a fixed partial denture along the long axes of the respective teeth and achieve a common path of insertion.
There is further complication if the third molar is present. It will usually have drifted and tilted with the second molar. Because the path of insertion for the fixed partial denture will be dictated by the smaller premolar abutment, it is probable that the path of insertion will be nearly parallel to the former long axis of the molar abutment before it tilted mesially. As a result, the mesial surface of the tipped third molar will encroach upon the path of insertion of the fixed partial denture, thereby preventing it from seating completely.
If the encroachment is slight, the problem can be remedied by restoring or recontouring the mesial surface of the third molar. However, the overtapered second molar preparation must have its retention bolstered by the addition of facial and lingual grooves.
If the tilting is severe, more extensive corrective measures are called for. The treatment of choice is the uprighting of the molar by orthodontic treatment.