In the absence of evidence from randomised controlled trials, the indications for removal of third molar teeth are likely to remain the subject of debate. In some areas there is evidence for clear indications for removal, but it is important to recognise that these indications may be modified by the general health of the patient and local circumstances.

3.1 Strong indications for removal

3.1.1

There are a number of reasons for removal of third molars where there is pathology in and around the third molar. It is considered good practice and it is reasonable to assume that recurrent acute attacks of infection associated with third molars necessitate the early removal of the affected teeth. There is no evidence to suggest that leaving the teeth in situ makes surgery easier and there is strong evidence that morbidity increases with age.^{21, 30, 36} Evidence level III and IV

Removal of any symptomatic wisdom tooth should be considered, especially where there have been one or more episodes of infection such as pericoronitis, cellulitis, abscess formation; or untreatable pulpal/periapical pathology. 37, 38

3.1.2

If a second molar requires to be extracted it is sensible to remove the adjacent unerupted third molar unless the third molar could erupt into the position of the second molar. Similarly, it may be difficult to fill a carious impacted third molar and this tooth should be removed unless there is a very high risk of complications associated with the removal of that tooth. ^{39, 40} Evidence level III

Removal should be considered where there is caries in the third molar and the tooth is unlikely to be usefully restored, or when there is caries in the adjacent second molar tooth which cannot satisfactorily be treated without the removal of the third molar.

3.1.3

Where there is periodontal disease and pocketing between the third molar and the second molar, there is some evidence to suggest that if removal of the third molar is delayed beyond the age of 30 years then the condition may become irreversible. Removal of the third molar will result in repair of the injured periodontium and therefore early removal of the impacted third molar is beneficial. Untreated horizontal and mesio-angular impaction are particularly prone to cause bone loss distal to the second molar. Late removal of such impacted teeth has not been shown to improve the periodontal status of the adjacent second molar, but early extraction of the impacted wisdom tooth reduces periodontal damage. ^{41, 43} Evidence level III

Removal should be considered in cases of periodontal disease due to the position of the third molar and its association with the second molar tooth.

3.1.4

Dentigerous cyst formation and other related oral pathology are considered to be rare in association with third molars, but there is evidence of dentigerous cyst formation occurring in association with impacted third molars.⁴² In most cases there is a strong indication for removal of the third molar in order to prevent expansion or recurrence of a keratocyst.⁴³ Evidence level IIb and III

Third molar removal should be considered in cases of dentigerous cyst formation or other related oral pathology.

3.1.5

External resorption of the third molar or of the second molar is relatively rare. Root resorption occurs principally in the 21-30 year old age group. The incidence after the age of 30 has been shown to be remote.⁴⁴ Evidence level III

Third molar removal should be considered in cases of external resorption of the third molar or of the second molar where this would appear to be caused by the third molar.

3.2 Other indications for removal

3.2.1

Third molar removal may occasionally be indicated for orthodontic reasons. However there is evidence, including a single prospective randomised controlled trial,⁴⁵ that the removal of third molars in the lower arch will not prevent, limit, or cure imbrication of the lower anterior teeth.^{30, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57} Evidence level Ib and III

Removal of the third molar may be indicated prior to orthognathic surgery, e.g. when a sagittal split osteotomy is planned, removal of the third molar diminishes the risk of surgical complications with regard to that osteotomy.^{16, 18} Evidence level IV

Removal of the third molar may be indicated prior to orthognathic surgery.

There is no reliable evidence that third molar removal affects the growth of the mandible.

3.2.2

There are a number of other indications for removal of unerupted and impacted third molar teeth. These are all relative indications and are quite uncommon. These include the occasional use of the third molar tooth, when it is sound, for autogenous transplantation - usually to a first molar socket site. ³⁴ The low incidence of success with the procedure means it is not widely used except in special circumstances. Evidence level IV

Third molar removal may be considered for autogenous transplantation to a first molar socket.

3.2.3

The presence of a tooth in a fracture line increases the risk of infection in some cases, especially when that tooth has been displaced or rendered non vital.^{58, 59} A similar situation arises with tumour resection and irradiation of the tissues may lead to a reduction in the blood supply, infection, or osteoradionecrosis. Early removal of teeth at the site of the resection reduces the risk of infection. ^{34, 60} Evidence level IV

Removal may be considered in cases of fracture of the mandible in the third molar region or when a tooth is involved in tumour resection.

3.2.4

Rarely, an unerupted third molar may lie in an atrophic mandible and a careful choice needs to be made whether it is better to remove the tooth or leave it in situ. There is no clear evidence as to what is best to do and a degree of common sense must therefore prevail.⁷ Evidence level IV

Removal of an unerupted third molar in an atrophic mandible may be appropriate.

This situation needs to be carefully evaluated. In very elderly patients the third molar might be left but in a middle-aged patient where there is a risk of spontaneous fracture or where minor trauma might cause a fracture then prophylactic removal is appropriate.

3.2.5

In the presence of specific medical conditions such as cardiac valvular disease or in a situation when the patient may require radiotherapy it is clear that where there is a potential for infection, this should be eliminated. A partially erupted third molar tooth would come into this category, whereas a completely unerupted tooth which was never likely to erupt would not. In borderline situations, removal should be undertaken if symptoms are likely in the future. Other medical procedures such as organ transplantation, chemotherapy, or the insertion of alloplastic implants should be considered in a similar way.^{7, 34} Evidence level IV

Prophylactic removal of a partially erupted third molar or a third molar which is likely to erupt may be appropriate in the presence of certain specific medical conditions.

3.2.6

The situation with regard to facial pain of an atypical nature is a difficult one and removal of a completely buried tooth should only be considered as a last resort and only when the patient points to that area as the source of pain. In some cases this relieves the pain but there is no guarantee. It is not known why a completely buried third molar should cause pain.

Much more commonly, atypical facial pain is associated with temporomandibular joint dysfunction and this possibility must be eliminated. Signs of muscle spasm are normally present in dysfunctional situations. Confusion can arise when there is concomitant muscle pain associated with a clenching habit and local third molar pain.^{4, 61} Evidence level III

Atypical pain from an unerupted third molar is a most unusual situation and it is essential to avoid any confusion with temporomandibular joint or muscle dysfunction before considering removal.

3.2.7

Pain associated with the lower third molar tooth is commonly exacerbated by the upper third molar biting on the gum flap, causing pain and discomfort. If the upper third molar tooth is easy to remove and it is non functional then immediate removal of that tooth will often dramatically relieve the pain from the area. This is particularly useful where there is likely to be delay in the surgical removal of the lower third molar.

Acute exacerbation of symptoms occurring while the patient is on a waiting list for third molar surgery may be managed by extraction of the opposing maxillary third molar.

3.2.8

If the third molar tooth is close to the surface or has broken through the surface in relation to an upper or lower denture then it is appropriate to remove that tooth before or as soon as symptoms arise, as they are likely to persist and become more severe if the tooth is not removed.^{7, 31} Evidence level IV

Removal of a partially erupted or unerupted third molar close to the alveolar surface should be considered prior to denture construction or close to a planned implant.

There are virtually no controlled trials or rigorous studies in the situations described above, although the outcome of an American Association of Oral and Maxillofacial Surgeons five-year prospective multicentre international study may provide valuable information. In most cases, the individual situation is self evident and the line of treatment is obvious. However, where there is doubt, careful consideration should be given as to the risks and benefits of removal of third molars in these patients.