Relationship to Occlusal Plane
The depth of the impacted tooth compared with the height of the adjacent second molar provides the next classification system for determining the difficulty of impaction removal. This classification system was also suggested by Pell and Gregory and is called Pelt and Gregor)’ A, B, and C classification. In this classification the degree of difficulty is measured by the thickness of the overlying bone: that is, the degree of difficulty increases as the depth of the impacted tooth increases. As the tooth becomes less accessible and it becomes more difficult to section the tooth and to prepare purchase points, the overall difficulty of the operation increases substantially. A class A impaction is one in which the occlusal surface of the impacted tooth is level or nearly level with the occlusal plane ofthe second molar (Fig. 9-23). A class B impaction is an impacted tooth with an occlusal surface between the occlusal plane and the cervical line of the second molar (Fig. 9-24). Finally, the class C impaction is
Pel! and Gregory class 3 impaction. Impacted thirdmolar is completely embedded in bone of ramus of mandible.
Pel! and Gregory class A impaction. Occ’usal plane 01 impacted tooth is at same level as occlusal plane of second molar. Pile ill which the occlusal surface at” till’ impacted tooth is below the cervical line of the second molar (Fig. 9′:~SI.