Case• 25. Impacted lower third molars
A 24-year-old gentleman is referred to you in your oral surgery-orientated practice for a second opinion on the need to remove his lower third molar teeth. Is this the correct decision, and if it is, how should it be achieved?
The patient has no complaint at present but has been advised by his general dental practitioner to have his lower third molars extracted. He is very nervous about the extractions and requests a second opinion before deciding on treatment.
History of complaint
The patient has had two episodes of pericoronitis around the lower left third molar. The first was relatively mild but the second, about 3 months ago, was associated with inability to open the mouth and slight facial swelling and required a course of oral antibiotics.
The patient is fit and well. He has had a general anaesthetic previously to reduce and fix a compound fracture of his arm which has been permanently plated. He has had no problems with bleeding following trauma.
The left submandibular lymph nodes are palpable but not tender. There is no facial asymmetry.
▪ What particular features of the intraoral examination are important and why?
See Table 25.1.
|Interincisal opening||One feature determining access for surgical removal and affecting the difficulty of extraction. Trismus may also reflect infection or inflammation in the muscles of mastication.|
|Condition of rest of dentition||If the first or second molars have a poor prognosis through caries or are extensively restored, transplanting the third molars in their place might be considered.|
|Oral hygiene||Poor oral hygiene increases the risk of dry socket, soft tissue infection and delayed healing.|
|Position of lower third molars||The degree of eruption, angulation and proximity to the second molars are important. Partially erupted vertical or distoangular lower third molars are more at risk of pericoronitis than mesioangularly impacted ones.|
|Position of upper third molars||Nonfunctional upper third molars may overerupt and traumatize the operculum over the lower third molar or erupt buccally and traumatize the cheek. Both situations might contribute to symptoms.|
|Position of external oblique ridge||If this lies close behind or over the impacted tooth, access is poor and considerable bone removal may be required if the tooth is large or impacted.|
|Condition of lower second molars||The lower second molar is at risk of iatrogenic damage during surgical removal of the third molar. Crowns or large restorations, especially those involving the distal surface, will be at risk and may increase the difficulty of the extraction.|
|Presence of pericoronitis||Has the same effect as generalized poor oral hygiene except that the risk of adverse effects is higher. Surgery should not be performed in an infected field.|
|Miscellaneous features||Factors such as a pronounced gag reflex, poor patient compliance and anxiety may all affect treatment.|
In this case the patient has normal mouth opening, a full unrestored dentition without evidence of caries, periodontal disease or poor oral hygiene. The lower third molars are partially erupted and appear vertically orientated and there is mild inflammation of the attached gingivae surrounding both crowns. The upper third molars are overerupted and nonfunctional. The patient has a pronounced gag reflex when the teeth are examined.
▪ Would you take radiographs? If so, which views would you take and why?
Yes, radiographs are required to assess root morphology, degree of bone impaction, proximity to inferior dental nerve and the possibility of associated disease (e.g. cysts, hypercementosis and periodontal bone loss).
|Periapicals of upper and lower third molars||Provided the periapicals can be taken with a paralleling technique these are the ideal views. They provide a geometrically accurate projection with true relationships to the adjacent structures. They are also convenient for single extractions. These views are the first choice.||Unfortunately it may not be possible to obtain films using the paralleling technique because of patient tolerance. Placement of the film in the ideal position, showing the teeth and inferior dental nerve canal, is uncomfortable. If films are angled then a degree of distortion is inevitable.|
|Oblique laterals||Readily taken without specialized equipment. Show both upper and lower third molars without superimposition. Give a good view of the surrounding bone when adjacent lesions (e.g. cysts) are present. It is the second-best option.||Suffer a degree of distortion as the beam is angled upwards, so that the relationship to adjacent structures is not accurate.|
|Panoramic radiograph||Convenient survey film if equipment available. Gives a good view of the surrounding bone when adjacent lesions (e.g. cysts) are present. Though only third choice on technical merit, panoramic films are often used and in practice usually provide sufficient information to assess extractions.||Poor image quality because the view is a tomograph. In addition there is superimposition of the opposite angle of mandible over upper and lower third molars. The upward beam angle distorts the relationship between teeth and adjacent structures and the image is magnified. Root morphology often cannot be assessed on panoramic films.|
|Lower oblique occlusal||Useful when the lower third molar lies horizontally and is seen end-on in a periapical view. Provides information on buccolingual orientation. Useful if tooth lies out of the line of arch. Used only rarely.|
|Cone beam computerised tomography||Low dose computerised tomography available in a dental setting, high definition 3D imaging showing accurate relationships between tooth and ID canal and other structures. For example, see the final image in this problem.||Not yet widely available.|
There is little to choose between these radiographic views in terms of radiation dose, provided fast films and appropriate intensifying screens are used.
In this case the patient’s gag reflex prevented the taking of paralleling technique periapicals and so a panoramic radiograph was taken. It is shown in Figure 25.1.
▪ What does the radiograph show?
The patient is fully dentate with no restoration or caries visible on the film. The lower third molars are vertically orientated and impacted against soft tissue rather than the second molars. The impacted teeth are of normal size and the surrounding bone appears to be of normal density. The roots of both teeth appear to be closely related to the inferior dental nerve canal, there is darkening but no narrowing or deflection of the bony wall of the canal, suggesting that it does not contact or pass through the tooth root.