Should the "envelope of discrepancy" be revised in the era of three-dimensional imaging?

Since their introduction in the field of orthodontics, temporary anchorage devices (TADs) have been widely applied in the treatment of cases that have proven difficult to treat using conventional methods. Although TADs have broadened the scope of orthodontic treatment by modifying the envelope of discrepancy, whether they represent the ultimate solution in all cases remains controversial. Cone-beam computed tomography (CBCT) has recently been used to obtain three-dimensional images of the craniofacial skeleton and teeth. Thus, CBCT has clarified the three-dimensional morphology/configurations of structures that cannot be appropriately visualized using conventional imaging (i.e., cephalometric and panoramic radiographs). These structures include the incisive canal and maxillary sinus. In this review, I highlight the importance of understanding the mutual relationship between the roots of the maxillary teeth and these structures for diagnosis and treatment planning, as well as potential need to revise the envelope of discrepancy.