5 Removal of unerupted teeth
Most patients attending hospital with impacted teeth are referred because of pain and infection, associated with partially erupted teeth (Fig. 5.2); however, many impacted or displaced teeth are unerupted and asymptomatic and therefore an incidental finding following radiographic examination. Occasionally, unerupted wisdom teeth, in the absence of any obvious infection, can give rise to discomfort (often described by patients as ‘pressure’ at the back of the mouth). It is important to exclude other possible causes such as temporomandibular joint pain and pulpitis/periapical abscess from another tooth.
Intraoral anatomical factors that may influence surgical access include size of the tongue and degree of mandibular opening. The position of the impacted wisdom tooth should be noted (unerupted, partially erupted or erupted but non-functional), together with any signs of infection (e.g. caries, pericoronitis). Probing the distal aspect of the second molar will confirm whether the buried tooth is in communication with the mouth.
Pericoronitis may be defined as an infection involving the soft tissues surrounding the crown of a partially erupted tooth. It is usually caused by streptococci and anaerobic bacteria, and may be classified clinically as acute (the features of acute inflammation developing over hours to days, possibly with systemic involvement) or chronic (some redness and/or discharge of pus with few acute symptoms, lasting over weeks or months). It may be associated with poor oral hygiene, stress and upper respiratory tract infection.
Signs and symptoms of pericoronitis include swelling, soreness, erythema of the overlying soft-tissue operculum, trismus, facial swelling, raised temperature, regional lymphadenopathy and general malaise. The disorder may be precipitated by trauma from an over-erupted upper wisdom tooth or entrapment of food debris and bacterial infection of the operculum.
Pericoronitis may be treated by removal of the upper wisdom tooth (if this is traumatizing the operculum overlying the lower wisdom tooth), irrigation under the operculum with chlorhexidine, the careful application of a medicament such as trichloroacetic acid beneath the operculum, hot salt-water mouthwashes and analgesics (e.g. ibuprofen). If there is systemic involvement, then antibiotics are indicated (e.g. amoxicillin or metronidazole). Severe infections may require admission to hospital as they can spread through the fascial planes and compromise the airway (see Ch. 7).
The radiographic examination of choice is a panoramic radiograph such as an OPT (Fig. 5.3), although periapical or oblique lateral views of the mandible may be taken as an alternative. When referring a case for treatment all recent relevant radiographs should be included to avoid further exposure to ionizing radiation.
Fig. 5.4 (a) Orientation of third molar: (i) towards second molar; (ii) away from second molar. (b) Increased depth of crown of right third molar (i) from occlusal plane compared to left third molar (ii). (c) Distance between anterior ramus and distal aspect of second molar compared with width of third molar crown: increased surgical access for right third molar (i) but reduced access for left third molar (ii).
From the clinical and radiographic examination, a decision on whether to remove the impacted third molar needs to be made (discussed below). If there is pain/discomfort, the cause (e.g. caries) should be identified and treated. Trauma to the operculum of the lower third molar may be eliminated by either extracting or grinding down the cusps of the maxillary third molar. Pericoronitis may require irrigation with chlorhexidine, antibiotics (if systemic involvement) and analgesics. The decision whether to prophylactically remove non-diseased third molars is discussed below in greater detail, although in general their removal is not indicated because they are usually symptomless.
The US National Institutes for Health (NIH) consensus on indications for removing wisdom teeth (published in 1980) (see also SIGN 2000 and NICE 2000) listed the following points as definite indications for removal:
Fig. 5.10 A severely resorbed mandible. The horizontal third molar and impacted second molar occupying the full depth of the mandible show an increased risk of jaw fracture. (Note retained roots in the maxilla.)
Thus patients should be warned to expect pain, swelling, bruising, difficulty in opening the mouth and possible damage to the lingual or inferior dental nerve (‘numbness in the tongue or lip’). Effects on ‘quality of life’ issues that may occur (interference with eating, socializing) and time off work, if applicable, should also be mentioned.
Lower third molars may be impacted mesioangularly (Fig. 5.3, right), vertically (Fig. 5.6), distoangularly (Fig. 5.3, left), horizontally (Fig. 5.10) or ectopically placed.
One simple method of determining the type of impaction involves comparing the distance between the roots of the third and second molar (a) with the distance between the roots of the second and first molars (b) (Fig. 5.11). If (a) is greater than (b) it is a mesioangular impaction; where (a) is less than (b) it is a distoangular impaction; where (a) is equal to (b) it is a vertical impaction. If the first molar is missing, the impaction can be determined by comparing a line drawn down the long axis of both the second and third molars: if parallel, it is vertical; if lower 8 leans towards lower 7 it is mesioangular; if the lower 8 long axis diverges from that of the 7, then it is a distoangular impaction.
The difficulty associated with removing distoangularly impacted teeth should not be underestimated. Although their impaction may appear mild, the path of withdrawal towards the ramus is often associated with more bone removal and reduced surgical access. Horizontal impactions are more difficult to deal with than mesioangular impactions.
A horizontal tooth (i.e. where the line down the long axis of the tooth is roughly parallel with the occlusal plane) usually has its crown facing the second molar but occasionally lies buccolingually (Fig. 5.12). An occlusal view can be taken to identify which way the crown lies. Pell and Gregory (1933) have classified the position of the impacted lower wisdom tooth according to (1) distance between distal surface of lower second molar and anterior aspect of ramus and (2) depth of the occlusal surface of the wisdom tooth in comparison to the occlusal plane of the second molar.
Once the decision has been made that a patient will benefit from removal of a wisdom tooth, the difficulty of the surgery should be assessed in order to determine who should perform it, to select the mode of anaesthesia and to advise the patient concerning the likely outcome. The following method allows the operation to be planned in reverse as the flap size and shape will depend upon the bone removal, which depends upon the position of the tooth. A radiograph is essential before such assessment, and should show the whole tooth and its association to neighbouring structures (e.g. ID canal, adjacent teeth and preferably the lower border of the mandible).