When Should Unerupted Third Molars be Removed?
Surgical removal of impacted third molars (M3) is the single most commonly performed
operation by oral and maxillofacial surgeons.
As a result of uncertainty in prognosis, clinicians are
divided on whether asymptomatic impacted third molars should be extracted or left in
place. In their comprehensive review of 149 articles (available upon request from the OCR
Editor)on this controversial topic, Mercier and Precious suggest the issue is more a
question of management than treatment. They advocate the development of a systematic
clinical decision-making pathway that takes into account all known relevant risks and
benefits before the extraction of third molars is recommended to a patient (see Figure).
Risks of Non-Intervention
Most studies agree that it is impossible to predict if there
will be a lack of space for normal M3 eruption. Recent attempts to predict the positioning
of an M3 have been contradictory, and prophylactic extraction on those grounds is not
warranted. The issue of whether or not impacted M3 contributes to the crowding of teeth is
controversial, although some evidence now suggests that this may be the case. M3 removal
solely on the grounds of arch crowding, however, may not be justified.
Horizontally and mesio-angular impacted M3 may damage the
root of adjacent teeth in a small number of cases, although this effect is difficult to
document by x-ray. Most studies agree that M2 root resorption occurs in less than 2% of
such cases. Periodontal studies have found large differences in the periodontal status of
a mandibular M3. In some studies involving young adults, less than 1% had M3
periodontitis, while another study found more frequent periodontitis in all late erupting
M3s.
Dental hygiene is also a factor, with less periodontitis in
those with good oral hygiene.
Pericoronitis, an infection that can lead to abscess
formation, is most often seen in a vertically positioned mandibular M3 partially covered
with soft tissue or bone. It is one of the most common reasons for M3 extraction. The
development of cysts and tumors as a result of an impacted M3 is rare. Often cysts are
confused with enlarged follicular spaces, and there is some disagreement about the
frequency of their incidence. Tumors are found in less than 1% of cases.
Risks of Intervention
Minor complications found to be associated with M3 removal
include sensory nerve alterations, alveolitis, infection, trismus, hemorrhage, fractures,
periodontal injury and adjacent tooth injury. Alveolitis, or dry socket, is the most
common complication, and is more commonly seen in patients older than 25 years and in
women. It is also seen more often in patients who had their teeth removed therapeutically
as opposed to prophylactically. Alveolitis will occur in 1-5% of patients regardless of
the skill of the operator or surgical protocol. Sensory injuries are uncommon, but can
involve lingual and labial paresthesia.
Major complications include dysesthesia and infections.
Although most nerve injuries heal after a period of temporary dysfunction, permanent
injuries to the cranial nerves do occur; deficiency beyond six months is likely to be
permanent. These injuries are often, although not exclusively associated with deep
impaction. Although the bacteremia often seen after M3 removal is usually minor, infection
can occasionally lead to endocarditis, and brain, liver or heart abscesses.
Benefits of Non-Intervention
If benefits of non-intervention outweigh risks,
non-intervention should be chosen. Non-intervention allows the patient the full potential
for growth and development of the teeth and jaws, while full eruption and functional
position allows the maximum occlusal table. An M3 can also be used for transplant in the
case of premature tooth loss elsewhere in the arch. Non-intervention also avoids exposing
the patient to the risks of surgery.
Benefits of Intervention
The younger a patient is at the time of extraction, the less
morbidity is observed. A preventive approach to extraction involves germectomy in late
childhood, or lateral trephination and removal during adolescence. A curative approach
involves exposure of the crown if the tooth has good positioning, or ablation when there
is a lack of space for eruption. In addition, there are a number of useful therapeutic
measures that can be taken to ease the complications associated with extraction. These
include antibiotics for infection, tetracycline and lavage for dry socket, dexamethasone
during extraction for swelling and trismus, and NSAIDs post-operatively for pain and
swelling.
Treatment strategies
After reviewing the entire M3 literature, strategies for the
treatment of an unerupted mandibular M3, also based on whether good or poor oral hygiene
is practiced, have been proposed.1 Risks are assigned negative values, while benefits are
assigned positive values. Summing the risks and benefits provides the optimal strategy for
each patient. The best general approach to an impacted M3 appears to be extraction of some
teeth before the age of 14 and others before the age of 22 when the chances of eruption
are minimal. However, after the age of 22, the best strategy is to periodically examine
the patient, removing only symptomatic M3 teeth after fully informing the patient of all
the relevant risks and benefits.
Reference
1. Mercier P and Precious D. Risks and benefits of removal of impacted third molars: a
critical review of the literature. J Oral Maxillofacial Surg 1992; 21:17-27.