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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
awayfrom 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 July 2011
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.
No Sinus Approximation (NSA):

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