Introduction to Third Molar Surgery: Part 3-Classification of Impaction

Classification of third molar impaction is done to facilitate the communication between clinicians, for record keeping that may be used for audit research purposes.    

Mandibular Third Molar Impaction  

The mandibular third molar impactions may be classified according to degree of impaction, angulation of the tooth or proximity to the inferior alveolar canal.  

Degree of Impaction: three types  

1. No Impaction-fully erupted 
    • (I) in functional occlusion 
    • (II) Non-functional  
2. Soft tissue impaction-
    • (I)partially erupted or 
    • (II)completely submerged   
3. Bony impaction-
    • (I)partially or 
    • (II)completely surrounded by bone  

Angulation of the tooth: four types  

  1. Vertical   
  2. Mesio-angular  
  3. Disto-angular  
  4. Horizontal  

All classes of impaction may further be divided into bucco- or linguo- version.  

Heterotopic impaction: In this class, the tooth is located in unusual places along the lower border of mandible or higher up the ascending ramus, mostly in an inverted position.  

Panoramic radiograph showing an inverted third molar associated with a radiolucent image in the left subcondylar region. (Courtsey


Proximity to the inferior alveolar canal: five types  

  1. No contact  
  2. Root apices in direct contact  
  3. Roots crossing the canal on one side only-no imprint of canal on the root surface  
  4. Roots partially encircling the canal-imprint of the canal clearly visible on the root surface.  
  5. Roots completely encircling canal- canal passes between the roots of the tooth  

Maxillary Third Molar Impactions  

The classification of the maxillary third molar is done based on how high up is the location of the tooth in relation to the maxilla. It may be divided into three classes:  

  1. First level  
  2. Second level  
  3. Third level  

First level: The tooth is partially or completely erupted  

Second level: The tooth has not erupted and is submerged in the maxilla. The crown margin of the tooth is below the level of the apices of the second molar tooth.  

Third Level: The margin of unerupted crown of the maxillary third molar tooth is above the apices of the adjacent maxillary second molar tooth.   

The third level of impaction poses the greatest surgical difficulty amongst all degrees of impactions.  

You can get MCQ practice paper HERE.

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