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Classification of 3rd Molar (Wisdom Teeth) Impaction
Systematic and meticulous classification of the position of impacted molar teeth helps in assessing the best
possible path of removal of the impacted teeth and also in encountered during removal.

Prediction of operative difficulty before the extraction of impacted third molars allows a design of treatment that
minimises the risk of complications.  Both radiological and clinical information must be taken into account.

Factors such as sex, age, position of the molar tooth in relation to the
occlusal plane and operative difficulty as
judged by the surgeon, have all been reported to be associated with a significantly increased duration of
postoperative recovery.  It seems likely that patients judged to be at higher risk for delayed recovery will benefit
from a more exhaustive postoperative follow-up and from specific post-operative measures to aid recovery.

Prediction of operative difficulty is therefore important for correct management.  Various methods have been
proposed for the pre-operative evaluation of difficulty but these have often been of limited validity.  To overcoming
the limitations of these systems, the classification systems can be used in conjunction with each other to
determine the difficulty of removal of the impacted tooth


Classification of Impacted Mandibular 3rd Molars

  • Based on the nature of the overlying tissues
  • Winter’s classification
  • Pell & Gregory’s classification


Based on the Nature of the Overlying Tissue

Based on the nature of the overlying tissue impaction, impacted lower wisdom teeth can be classified into:

  • Soft Tissue Impaction.  When the height of the tooth’s contour is above the level of the surrounding alveolar
    bone and the superficial portion of the tooth is covered only by soft (though this can be dense and fibrous)
    tissue.  Soft tissue impaction is usually the easiest of type of impacted tooth to remove.

  • Hard Tissue ('Bony') Impaction.  This is where the wisdom tooth fails to erupt due to being obstructed by the
    overlying bone.  This can be sub-divided into Partial and Complete Bony Impactions.

  • Partial Bony.  The superficial portion of the tooth is covered only by soft tissue but the height of the tooth's
    contour is below the level of the surrounding alveolar bone.  Apart from cutting the gingiva (gum) & possible
    bone removal from behind the tooth, the tooth's roots may need to be divided.

  • Complete Bony.  The tooth is completely encased in bone so that when the gingiva is cut and reflected back,
    the tooth is not seen.  Bone removal (large amounts) together with root sectioning will be needed to remove
    the tooth.  These are often the most difficult tooth to remove.


Winter's Classification

The classification is based on the inclination of the impacted wisdom tooth (3rd molar) to the long axis of the 2nd
molar
.

Mesio-Angular.  The impacted tooth is tilted toward the 2nd molar in a mesial direction.
Disto-Angular.  The long axis of the 3rd molar is angled distally / posteriorly away from the 2nd molar.
Horizontal.  The long axis of the 3rd molar is horizontal.
Vertical.  The long axis of the 3rd molar is parallel to the long axis of the 2nd molar.
Buccal / Lingual Obliquity.  In combination with the above, the tooth can be buccally (tilted towards the cheek) or
lingually (tilted towards the tongue) impacted.
Transverse.  This is where the tooth is in effect horizontally impacted but in a cheek-tongue direction.
Inverse.
Significance.  Each type of impaction has some definite path of withdrawl of the teeth.

Mesially impacted teeth are (can be) easier to remove whereas distally impacted teeth are (can be) the hardest
to remove.

Bucally positioned maxillary (upper) teeth are easier to remove as the bone covering the tooth is thinner whereas
the palatally positioned tooth requires bone removal and hence males the extraction difficult.


Pell & Gregory's Classification

This is based on the relationship between the impacted lower wisdom tooth (3rd molar) to the ramus of the
mandible
(lower jaw) and the 2nd molar (based on the space available distal to the 2nd molar).

Class A.  The occlusal plane of the impacted tooth is at the same level as the occlusal plane of the 2nd molar.  
(The highest portion of impacted 3rd molar is on a level with or above the
occlusal plane).

Class B.  The occlusal plane of the impacted tooth is between the occlusal plane & the cervical margin of the
2nd molar.  (The highest portion of impacted 3rd molar is below the
occlusal plane but above the cervical line of
the of 2nd molar).

Class C.  The impacted tooth is below the cervical margin of the 2nd molar.  (The highest portion of impacted 3rd
molar is below the
cervical line of the of 2nd molar).

Class 1.  There is sufficient space available between the anterior border of the ascending ramus & the distal
aspect of the 2nd molar for the eruption of the 3rd molar.

Class 2.  The space available between the anterior border of the ramus & the distal aspect of the of the 2nd
molar is less than the
mesio-distal width of the crown of the 3rd molar.  It denotes that the distal portion of the
3rd molar crown is covered by bone of the
ascending ramus.

Class 3.  The 3rd molar is totally embedded in the bone of the anterior border of the ascending ramus because of
the absolute lack of space.  It is obvious that
Class 3 teeth present more difficulty in removal as a relatively large
amount of bone has to be removed and there is a risk of
damaging the ID nerve or fracturing the mandible (or
both).
Last Updated 13th January 2020
Classification of Impacted Maxillary 3rd Molars

The classification of impacted maxillary 3rd molars is similar to those used for mandibular 3rd molars.


Pell-Gregory Classification

Class A.  The occlusal plane of the impacted tooth is at the same level as the occlusal plane of the 2nd molar.  
(The lowest portion of impacted 3rd molar is on a level with or above the
occlusal plane).

Class B.  The occlusal plane of the impacted tooth is between the occlusal plane & the cervical margin of the
2nd molar.  (The lowest portion of impacted 3rd molar is below the
occlusal plane but above the cervical line of
the of 2nd molar).

Class C.  The impacted tooth is below the cervical margin of the 2nd molar.  (The lowest portion of impacted 3rd
molar is below the
cervical line of the of 2nd molar).

There is are no
Classes 1 - 3 (as in the mandibular classification).

Winter's Classification

  • Vertical
  • Horizontal
  • Mesio-Angular
  • Disto-Angular
  • Inverted
  • Bucco-version
  • Linguo-version
  • Transverse


These classifications have been revised / tweaked / conflated by Archer (1975) & Kruger (1984).
Relationship of the Maxillary 3rd Molar to the Maxillary Sinus / Antrum

Sinus Approximation (SA):

No bone or thin partition of bone twixt the impacted
maxillary 3rd molar & the maxillary sinus / antrum.
Useful Books:


Winter, GB.  
Impacted Mandibular Third Molar.  St Louis, American Medical Book Co., 1926.

Pell GJ, Gregory BT.  
Impacted mandibular third molars: classification and modified techniques for removal.  
Dent Digest 1933; 39: 330 – 338.

Parant M.  
Petite Chirurgie de la Bouche.  Paris: Expansion Scientifique, 1974.

Archer, WH.  
Oral & Maxillofacial Surgery, 5th Edition.  Saunders, Philadelphia, PA.  1975.

Kruger, GO.  
Oral & Maxillofacial Surgery, 6th Edition.  Mosby, St Louis, Mo.  1984.

MacGregor AJ.
 The Impacted Lower Wisdom Tooth. Oxford: Oxford University Press; 1985.

Pedersen, GW.  
Surgical Removal of Teeth.  In Pedersen, GW.: Oral Surgery, Saunders, Philadelphia, pp. 47 –
82.  1988.

Peterson LJ.  
Principles of management of impacted teeth.  In: Peterson LJ, Ellis E III, Hupp JR, Tucker MR,
eds. Contemporary Oral and Maxillofacial Surgery, 3rd Edition. Philadelphia: CV Mosby, 1998.




Useful Article:


J Oral Maxillofac Res 2013.  Mandibular 3rd Molar Impaction - Review of Literature & a Proposal of a
Classification

J Pharm Sci Res 2014.  Third Molar Impaction - A Review

Health Renaissance 2015.  Tooth Impaction - A New Variable in Difficulty Index of Third Molar Extraction
No Sinus Approximation (NSA):

> 2mm of bone twixt the impacted
maxillary 3rd molar & the maxillary sinus / antrum.