Classification of impacted mandibular third molar

Pell and Gregory's Classification

A. Relation of the tooth to the ramus of the mandible and the second molar:

 

Class I: There is a sufficient amount of space between the ramus and the distal surface of the second molar for the accommodation of the mesiodistal diameter of the crown of the third molar.

Class II: The space between the ramus and the distal surface of the second molar is less than the mesiodistal diameter of the crown of the third molar.

 

Class III: All or most of the third molar is located within the ramus.


B. Relative depth of the third molar in bone:

Position A: The highest portion of the tooth is at level with or above the occlusal line.

Position B: The highest portion of the tooth is below the occlusal plane, but above the cervical line of the second molar.

Position C: The highest portion of the tooth is below the cervical line of the second molar.


C. The position of the long axis of the impacted mandibular third molar in relation to  the long axis of the second molar. This is included from Winter’s classification.

Winter's Classification

1. Vertical: The long axis of the impacted tooth is parallel to the long axis of the second molar.

2. Horizontal 

 3. Inverted

4. Mesioangular

5. Distoangular

6. Buccoangular

7. Linguoangular

All of these may occur in

a. Buccal version

b. Lingual version

 

c. Torsion

Based on the nature of the overlying tissue:

i. Soft tissue impactions: Dense, fibrous tissue overlying the teeth sometimes prevent eruption.
ii. Hard tissue impaction: (e.g. when tilted teeth interfere with eruption)
iii. When eruption is prevented due to overlying bone.