The purpose of present article was to review impacted mandibular third molar aetiology, clinical anatomy, radiologic examination, surgical treatment and possible complications, as well as to create new mandibular third molar impaction and extraction difficulty degree classification based on anatomical and radiologic findings and literature review results.
Literature was selected through a search of PubMed, Embase and Cochrane electronic databases. The keywords used for search were mandibular third molar, impacted mandibular third molar, inferior alveolar nerve injury third molar, lingual nerve injury third molar. The search was restricted to English language articles, published from 1976 to April 2013. Additionally, a manual search in the major anatomy and oral surgery journals and books was performed. The publications there selected by including clinical and human anatomy studies.
In total 75 literature sources were obtained and reviewed. Impacted mandibular third molar aetiology, clinical anatomy, radiographic examination, surgical extraction of and possible complications, classifications and risk factors were discussed. New mandibular third molar impaction and extraction difficulty degree classification based on anatomical and radiologic findings and literature review results was proposed.
The classification proposed here based on anatomical and radiological impacted mandibular third molar features is promising to be a helpful tool for impacted tooth assessment as well as for planning for surgical operation. Further clinical studies should be conducted for new classification validation and reliability evaluation.
In early 1954 Mead [
According to Elsey and Rock [
Third molar eruption and continuous
positional changes after eruption can be related not only with race
but also with nature of the diet, the intensity of the use of the
masticatory apparatus and possibly due to genetic background [
Impaction of mandibular third molars is a common condition related with different difficulty degree of extraction operation and risk of complications, including iatrogenic trigeminal nerve injury. The purpose of present article was to review impacted mandibular third molar aetiology, clinical anatomy, radiologic examination, surgical treatment and possible complications, as well as to create new mandibular third molar impaction and extraction difficulty degree classification based on anatomical and radiologic findings and literature review results.
Literature was selected through a search of PubMed, Embase and Cochrane electronic databases. The keywords used for search were mandibular third molar, impacted mandibular third molar, inferior alveolar nerve injury third molar, lingual nerve injury third molar. The search was restricted to English language articles, published from 1976 to April 2013. Additionally, a manual search in the major anatomy and oral surgery journals and books was performed. The publications there selected by including clinical and human anatomy studies.
Many theories have been proposed
owing to high incidence of mandibular third molar impaction. One
of the most popular theory is insufficient development of the retromolar
space [
Mandibular third molar is situated
at the distal end of the body of the mandible where is connection
with relatively thin ramus. There is the region of weakness and
the fracture can occur if excessive force will be applied during
impacted wisdom tooth elevation without preliminary and adequate
removing of surrounding bone [
The location and configuration of
impacted third molar, surrounding bone, mandibular canal and adjacent
tooth are important in imaging diagnosis for the proper surgical
operation planning. Periapical radiographs have been used for many
years to assess the jaws during impacted teeth surgery. Long cone
paralleling technique for taking periapical X-ray is the technique
of choice for the following reasons: reduction of radiation dose;
less magnification; a true relationship between the bone height
and adjacent teeth is demonstrated [
Nevertheless, the biggest concern
of periapical radiographs is that mandibular canal could not be
clearly identified in the third molar region. Furthermore, the angulation
of the periapical film can affect the perceived location of the
canal with respect to the bone crest [
When a specific region that is too
large to be seen on a periapical view, panoramic radiograph can
be the method of choice. The major advantages of panoramic images
are the broad coverage of oral structures, low radiation exposure
(about 10% of a full-mouth radiographs), and relatively inexpensive
of the equipment. The major drawbacks of panoramic imaging are:
lower image resolution, high distortion, and presence of phantom
images. These can artificially produce apparent changes thus may
hide some of important vital structures [
Cone Beam Computed Tomography (CBCT)
have been advocated as method of choice than there is need to have
a three dimensional view of the mandibular third molar and adjacent
anatomical structures [
According to the recommendations
of National Institute of Health (NIH) [
Following indications for mandibular
third molar extraction were highlighted by Koerner [
There are two main intraoral approaches
for surgical removal of impacted mandibular third molars: one through
the sublingual space and the other buccally through the entire mandibular
thickness. There is also extraoral method from the submandibular
space [
After mucoperiosteal flap elevation
excessive bone must be excised using bur before third molar extraction.
In most cases there will be necessary to remove buccal and distal
bone borders. In difficult cases the tooth should be sectioned with
a fissure bur in a high-speed handpiece. The wound should be irrigated
with cool sterile physiologic saline solution. After tooth extraction
using elevator or forceps it is necessary to clean operation area
and to suture the wound without tension [
The frequency and severity of untoward
events associated with surgical procedures are influenced by multiple
factors that may be related to the procedure, patient, and/or surgeon
[
The most serious and unpleasant iatrogenic
complication that arise from third molar surgery is inferior alveolar
and/or lingual nerve injury and neurosensory function disturbance.
The incidence of inferior alveolar nerve injury according to different
authors varies from 0.81% to 22% of cases [
Typical postoperative complications
are pain, swelling, bruising, trismus [
In order to minimise number of complications
during mandibular third molar extraction several classifications
have been developed that are assessing the difficulty of surgical
procedure and helping to create an optimal treatment plan. The most
popular are Winter’s [
Eruption status of the lower third
molar is important risk factor for inferior alveolar nerve injury.
Incidences of inferior alveolar nerve injury in fully erupted, partially
erupted and unerupted lower wisdom teeth were 0.3%, 0.7% and 3.0%,
respectively [
In general the proximity of the mandibular
third molar to the mandibular canal is considered a risk factor
for damage to the inferior alveolar nerve. This fact inspirited
further studies for the predictive radiographic parameters identification.
Rood and Shehab [
Iatrogenic injury to the lingual
nerve may happen during third molar surgery due to the anatomical
proximity of the cortex region of the molar to the nerve, being
separated from it by the periosteum alone [
New mandibular third molar impaction
and extraction difficulty degree classification based on anatomical
and radiologic findings and literature review results is suggested
(
Mandibular third molar impaction classification
Position of the mandibular third molar | Risk degree of presumptive intervention (score) | |||
---|---|---|---|---|
Conventional (0) | Simple (1) | Moderate (2) | Complicated (3) | |
|
||||
|
Crown directed at or above the equator of the second molar | Crown directed below the equator to the coronal third of the second molar root | Crown/roots directed to the middle third of the second molar root | Crown/roots directed to the apical third of the second molar root |
|
Sufficient space in the dental arch | Partially impacted in the ramus | Completely impacted in the ramus | Completely impacted in the ramus in distoangular or horizontal position |
|
||||
|
Tooth is completely erupted | Partially impacted, but widest part of the crown (equator) is above the bone | Partially impacted, but widest part of the crown (equator) is below the bone | Completely encased in the bone |
|
≥ 3 mm to the mandibular canal | Contacting or penetrating the mandibular canal, wall of the mandibular canal may be identified | Contacting or penetrating the mandibular canal, wall of the mandibular canal is unidentified | Roots surrounding the mandibular canal |
|
||||
|
Closer to buccal wall | In the middle between lingual and buccal walls | Closer to lingual wall | Closer to lingual wall, when the tooth is partially impacted or completely encased in the bone (A2 or A3) |
|
||||
|
Vertical (90°) | Mesioangular ≤ 60° | Distoangular ≥ 120° | Horizontal (0°) or inverted (270°) |
IAN = inferior alveolar nerve; LN = lingual nerve.
Classification of mandibular third molar impaction and extraction difficulty degree enables the clinician to determine the difficulty in removal of the impacted tooth, to choose optimal treatment and to avoid the majority of possible complications. This classification describes wisdom tooth relation to the adjacent anatomical structures: mandibular ramus, second molar, alveolar crest, mandibular canal, and the spatial position of the tooth. Wisdom tooth position assessment should be performed clinically and using CBCT and panoramic radiographic images. The tooth position according to the all aforementioned landmarks has been not completely classified yet. Proposed classification is determining mandibular third molar mesiodistal position (in relation to the second molar - M and the mandibular ramus - R), apicocoronal position (in relation to the alveolar crest - A, and the mandibular canal - C), buccolingual position (in relation to mandibular lingual and buccal walls - B) and spatial tooth position - S.
Risk degree of presumptive intervention is scored as follows:
conventional extraction is determined, when all parameters are equal to score 0;
simple, when at least one parameter is equal to score 1 and surgical extraction with coronectomy and/or sectioning of roots is determined;
moderate, when at least one parameter is equal to score 2 and surgical extraction with coronectomy and/or sectioning of roots is determined;
complicated, when at least one parameter is equal to score 3 and surgical extraction with coronectomy and/or sectioning of roots is determined. Extraoral approach can be indicated.
To make the classification more informative,
each component of the indices (M,R,A,C,B and S) is described independently.
For example, position, extraction difficulty degree of tooth 48
and risk of trigeminal nerve damage during surgery is described
as following: M1,R1,A2,C2,B1,S3 (
A = Tooth No. 48 is classified as M1,R1,A2,C2,B1,S3 on the ortopantomograph.
B = Impaction in horizontal spatial position index (S3) predicts complicated surgical extraction.
There are some new approaches in
assessing different anatomical and radiological parameters in the
present classification. For example, the depth of tooth impaction
in Pell and Gregory’s [
A = On orthopantomograph close contact between impacted right mandibular third molar and mandibular canal is suspected.
B = More detailed view on the CBCT images reveals tooth penetration through the mandibular canal wall (C2) and moderate risk of inferior alveolar nerve damage.
Roots of tooth No. 48 are ≥ 3 mm away from the mandibular canal (C0) on the orthopantomograph. There is no risk to damage inferior alveolar nerve during surgical extraction.
Mesiodistal position is defined in
relation to the second molar and the mandibular ramus. It is important
to assess impacted tooth relationship to the second molar in order
to avoid iatrogenic tooth traumatisation. The impaction degree of
mandibular third molar in the ramus of mandible is associated with
extraction operation difficulty score and postoperative complications
manifestation. For example, high risk degree is registered when
tooth is completely impacted in the mandibular ramus in distoangular
or horizontal position (
Tooth No. 38, completely impacted in the mandibular ramus in distoangular position and classified as A3 and R3 according to the relation to alveolar crest and mandibular ramus, is noticed on the orthopantomograph. Complicated surgical extraction is anticipated.
Buccolingual third molar position
in relation to mandibular lingual and buccal walls is reflecting
risk of lingual nerve injury. It was discussed previously that iatrogenic
injury to the lingual nerve may happen during third molar surgery
due to the anatomical proximity of the cortex region of the molar
to the nerve [
Spatial mandibular third molar position is reflecting extraction difficulty degree especially in combination with other indices. For example distoangular or horizontal impacted tooth position in combination with deep impaction in the mandibular ramus, can be complicated case even for experienced clinician.
There are selected only the most informative parameters in presented herein classification, because it is impossible to reflect all important parameters, such as periodontal ligament width, soft tissue condition, patient characteristic, clinician’s experience, and et cetera in one classification which should be useful in daily practice. The classification proposed here based on anatomical and radiological impacted mandibular third molar features is promising to be a helpful tool for impacted tooth assessment as well as for planning for surgical operation. Further clinical studies should be conducted for new classification validation and reliability evaluation.
The authors report no conflict of interest related to the present study.