Figure 1.

Measurement and classification of the impacted third molars in cone-beam computed tomography [12]. The spatial relationship was subcategorized based on the angle between the long axis of the third molar and the adjacent second molar as follows (yellow lines and an asterisk mark): (1) mesioangular (11° to 79°), (2) horizontal (80° to 100°), (3) vertical (−10° to 10°), (4) distoangular (−11° to −79°), or (5) reverse, where the crown of the third molar was more root-oriented than horizontal. The depth was classified based on the line connecting the cementoenamel junction of the adjacent second molar (dotted blue line) as follows: (1) more than half of the third molar crown was above the CEJ of the adjacent second molar; (2) less than half of the third molar crown was above the CEJ of the adjacent second molar; (3) more than half of the third molar crown positioned superior to the mid-level of the adjacent second molar root; (4) the third molar crown level inferior to that mentioned above. The ramus relationship/space available was subcategorized based on the ratio between the distance from the ascending ramus to the distal of the second molar (a) and the diameter of the impacted third molar (b) (pink arrows). An eruption space (a/b) larger than two-thirds of the distance was defined as (1), between one-third and two-thirds—as (2), and smaller than one-third—as (3).