Key points

Introduction

Management of impacted third molars constitutes a major portion of contemporary oral and maxillofacial surgery practice. It is a complex topic and controversial, particularly with regard to surgical techniques used and the management of systemic and disease-free teeth. Proper management of impacted third molars involves appropriate diagnosis using detailed clinical and radiographic examinations, treatment planning with emphasis on modifying risk factors that may be present, and appropriate surgical techniques to minimize the risks of complications and ensure an efficient procedure and optimal patient outcomes.

Classification of impacted teeth

There are a variety of classification systems available to categorize impacted teeth. Most of these systems rely on radiological assessment and clinical examination.

Classification of impacted third molars has often been used as a predictor regarding degree of surgical difficulty. However, this is not universally reliable. Other factors that can influence the surgical difficulty in removal of third molars may include dental-related factors and patient-related factors.

Dental-related factors may include:

• 1.

  Morphology of roots

• 2.

  Number of roots

• 3.

  Diameter of periodontal ligament

• 4.

  Presence or absence of a dental follicle

• 5.

  Proximity to adjacent teeth

• 6.

  Proximity to vital structures (ie, inferior alveolar nerve, lingual nerve, maxillary sinus)

Patient-related factors may include:

• 1.

  Bone density

• 2.

  Advanced age

• 3.

  Tongue size

• 4.

  Maximum interincisal opening

• 5.

  Size of oral aperture

• 6.

  Exaggerated gag reflex

• 7.

  Body mass index

• 8.

  Level of anxiety

• 9.

  Obstreperous behavior

• 10.

  Anesthetic management

The more common classification systems of impacted third molars analyze either the angulation of the long axis of the third molar or its degree of depth of impaction. These systems may provide a preliminary analysis of the potential surgical difficulty that may be encountered during removal of third molars. However, astute clinicians will also pay close attention to the other aforementioned factors.

Clinical evaluation

A clinical examination should start by obtaining the patient’s medical history. This evaluation usually begins by determining the patient’s chief complaint and then eliciting the history regarding the chief complaint or present illness. This information can give insight as to whether or not the patient is in pain or discomfort and is seeking urgent care versus being asymptomatic and seeking consultation regarding elective care.

The medical history should include a review of any existing systemic disorders, previous surgeries and hospitalizations, medications, allergies, and social history. Patients should be assessed for undergoing certain therapies such as radiation therapy or bisphosphonate therapy, which may have a detrimental effect on bone and soft tissue healing. Any previous anesthesia exposure should be discussed and an assessment of the patient’s level of anxiety should be performed.

Increasing age and systemic comorbidities have the potential of increasing the degree of difficulty associated with surgery. Therefore, a thorough medical history helps the surgeon determine the patient’s American Society of Anesthesiologists status and whether or not the patient is a candidate for surgery either as an outpatient or hospital inpatient. It also helps determine what type of anesthesia may be required for patient management.

Physical examination

Physical examination of the patient should include a thorough extraoral and intraoral head and neck examination.

Extraoral examination

This examination should note any abnormal size or asymmetry about the head and neck. Any suspicious masses or enlargements should be noted along with any changes in color, such as redness, paleness, or purpura. Extraoral palpation should be performed to detect any enlargement or tenderness of salivary glands, lymph nodes, or anatomic spaces. The presence of painful facial swelling or enlarged tender lymph nodes could indicate the presence of an active infection.

A temporomandibular joint (TMJ) examination should be included. The patient should be asked to open as wide as possible and close. The range of motion and maximum opening should be measured to determine normalcy or whether any trismus or deviation is present. At the same time, the size of the oral aperture can be appraised along with the laxity of the soft tissue of the lips and cheeks. As the patient opens and closes, the joints can be palpated to detect tenderness and observed for the presence of joint noises such as clicking, popping, or crepitus. This examination can help determine the existence of any preexisting TMJ disorders and may influence the surgical management of the patient.

Intraoral examination

This examination should include soft and hard tissue evaluation. The soft tissue of the labial and buccal mucosa, soft and hard palate, gingiva, floor of mouth, tongue, and oropharynx should be inspected for any color changes, swelling, elevated or depressed lesions, masses, or ulcerations. These soft tissues should also be palpated to elucidate any tenderness, firmness, or fluctuance.

The hard tissues, such as teeth, alveolar bone, mandible, and maxilla, should be examined. The overall condition of the teeth should be assessed. Any missing, malposed, or supernumerary teeth should be noted. The alveolar bone, mandible, and maxilla should be evaluated for any asymmetry or enlargement. In addition, a more focused examination of the third molar area is performed.

Third molar focused examination

Examination of the third molars should determine the following:

• •

  Eruption status: erupted, partially erupted, completely unerupted

• •

  Position in the arch: any buccal, palatal, or lingual displacement

• •

  Functional status: in occlusion

• •

  Any presence of local infection or inflammation of soft tissue adjacent to third molar (pericoronitis)

• •

  Periodontal status of third molar and adjacent second molar, including probing depths, bleeding on probing, or the ability to detect the third molar with probing

• •

  Presence of caries, restorations, or resorption of third molar or adjacent second molar

• •

  Third molar impingement on second molar

• •

  Available access for surgery and oral hygiene maintenance

• •

  Any limited opening caused by TMJ disorder, small aperture, submucosal fibrosis, scarring

• •

  Thickness of overlying bone

• •

  Any orthodontic considerations

• •

  Any restorative considerations

• •

  Any prosthetic considerations

• •

  Any presurgical considerations

On completion of the clinical examination, any positive findings should be noted and considered during the decision-making process regarding removal or retention of the third molar. This process takes place following an adequate radiographic evaluation.

Radiographic evaluation

In addition to a thorough clinical examination, a radiographic evaluation is required to confirm whether disease is associated with the third molar and to assist in the formulation of an appropriate treatment plan. The radiographic images should provide information pertaining to the third molar, the adjacent teeth, the surrounding bone, and adjacent anatomic structures.

Oral surgeons have traditionally used conventional two-dimensional radiographic images such as bitewing, periapical, occlusal, cephalometric, and panoramic radiographs to diagnose and treat patients.

An advantage of an intraoral radiograph (ie, bitewing, periapical) is the sharpness of the image. It is higher than that of a panoramic image, and the magnification factor when using a paralleling technique is around 1.05 with minimal image distortion.

An intraoral periapical radiograph may be sufficient for the assessment of a third molar before surgical removal. The image should show the whole third molar, the size of the follicle, the adjacent second molar, the surrounding bone, and the relation to the inferior alveolar canal (IAC). If there appears to be overlap between the roots of the molar and the IAC, a modification of the tube shift method along the vertical plane can be implemented. This technique was described by Richards. The SLOB (same side lingual, opposite side buccal) rule can be applied.

An advantage of an intraoral occlusal radiograph is the capability to determine whether an impacted third molar is in buccal version or lingual version. This image may also identify the presence of additional roots.

However, there are potential disadvantages of intraoral radiographs. Positioning of the intraoral receptor may be difficult because of the size of the film or digital receptor. The film or receptor can be deflected by the soft tissue in the floor of the mouth. This deflection can cause gagging or discomfort for the patient. Another potential disadvantage is the inability to fully visualize a deeply impacted third molar. In about 25% to 36% of patients, the whole third molar and adjacent anatomic structures are not imaged by the intraoral imaging method. ^,

Thus, periapical radiographs tend to be used as a supplement to panoramic radiographs if indicated. They can provide more detailed imaging of caries, root contour, and alveolar bone height adjacent to the second molar.

Orthopantomography (OPG) is still the most common imaging technique for evaluating impacted third molars. It is readily available, inexpensive, and provides visualization of both the upper and lower jaw with minimal discomfort and at a low radiation dose.

OPG can provide information regarding angulation of teeth, number of roots, morphology of roots, and associated hard tissue disorder. It can detect the presence (or absence) of third molars and supernumerary third molars. It can also show the relationship of upper third molars to the maxillary sinus and the proximity of the lower third molar to the IAC, albeit in a two-dimensional view. This evaluation is essential because the anatomic relationship between the mandibular third molar and the IAC may be the most predictable risk factor for inferior alveolar nerve (IAN) injury.

Rood and Shehab found 3 radiological diagnostic signs to be significantly related to IAN injury:

• 1.

  Darkening of the roots, which has been attributed to impingement of the canal on the tooth root causing a loss of density of the root ( Fig. 13 A). Darkening of the roots has also been attributed to thinning or perforation of the lingual cortex by the roots when evaluated by cone beam computed tomography (CBCT) imaging.

  

  Darkening of roots, diversion of IAC, and interruption of white line of IAC. ( A ) Diagram of darkening of roots. ( B ) Section of a pantomograph of a lower right third molar with 2 roots showing overlap of the IAC, darkening of roots, and diversion of the canal. Green arrows show diversion of canal. Yellow arrow shows darkening of roots. ( C ) Inferior alveolar canal diversion. ( D ) Interruption of white line of IAC. ( E ) Section of a pantomograph of a lower right third molar showing interruption of the superior white line of the IAC. Yellow arrows show inferior border of IAC. Superior border of IAC appears absent in between the orange arrows.

  ([ A, C, D ] From Rood JP, Shehab BA. The radiographic prediction of inferior alveolar nerve injury in third molar surgery. Br J Oral Maxillofac Surg. 1990;28(1):22; with permission.)

• 2.

  Diversion of the IAC. If the IAC changes its direction as it crosses the mandibular third molar, then it is considered to be divergent ( Fig. 13 C).

• 3.

  Interruption of the white lines of the IAC ( Fig. 13 D). Interruption of the cortical roof and floor of the IAC may indicate either deep grooving of the root if it appears alone or perforation of the root if the interruption is seen in conjunction with narrowing of the inferior alveolar canal.

Additional studies seem to confirm that darkening of the roots and interruption of the white lines are the most frequently observed signs of risk of injury to the IAN and most strongly associated with contact between the tooth and the canal.

These high-risk signs identified by OPG images are significantly associated with the absence of cortication between the mandibular third molar and the IAC. However, the absence of these signs does not guarantee a lack of close contact.

Another panoramic radiographic marker viewed by clinicians as an indicator of a close relationship between the third molar and the IAC is the vertical relationship between the IAC and the roots of the third molar ( Fig. 14 ). The risk of IAN injury is increased significantly in a class I vertical relationship where the superimposition of the third molar roots extend beyond the inferior border of the IAC or when the canal is superimposed over more than one-half of the root. ^, It is suspected that the risk of injury increases because of the increased surface area of contact between the third molar and the IAC.

Section of a pantomograph of a lower left third molar postcoronectomy. There is a class 1 vertical relationship between the IAC and the roots of the third molar. The complete canal is superimposed by the third molar roots; the apex lies beneath the inferior border of the IAC. Orange arrows indicate superior border of IAC. Yellow arrows indicate inferior border of IAC. Green arrows indicate apex of root structure of third molar.

Therefore, when a traditional two-dimensional image reveals 1 or more of these high-risk signs, it may be beneficial to assess the relationship via a three-dimensional evaluation using CBCT, especially if the apices appear to be touching or crossing the inferior border of the canal or floor of the maxillary sinus. CBCT can provide information in the axial, coronal, and sagittal planes and has been shown to be more accurate than panoramic images in identifying direct contact where there is no bony separation between the third molar and the IAC. ^, It can also identify absence of cortication between maxillary roots and the maxillary sinus.

Several studies have indicated that contact between the IAC and the mandibular third molar seems to occur more frequently when the IAC is positioned on the lingual side of the impacted tooth. ^, The degree of this proximity or contact between the IAC and the mandibular third molar also seems to be related to the shape of the IAC as seen on a CBCT image. ^,

Canal shapes can be described as round, oval, teardrop, or dumbbell. The dumbbell shape has been referred to as invagination, narrowing, or flattening of the canal, presumably caused by intimate contact with the mandibular molar. These dumbbell-shaped canals are seen more frequently on the lingual side of the lower third molar roots and are at high risk of IAN injury. ^,

Overall, there seems to be a significant association between the lingual position of the IAC and an increased risk of IAN injury following third molar removal. ^{, , , ,} There is also a significant correlation between narrowing/flattening of the IAC at the contact area of the third molar and an increased risk of IAN injury following third molar removal. ^{, ,}

In summation, CBCT images that are associated with higher risk of IAN injury show:

• 1.

  Direct contact between the IAC and the roots

• 2.

  Absence of IAC cortication

• 3.

  Lingual position of the IAC relative to the roots ( Fig. 15 A)

  

  Coronal views of CBCT showing shape and anatomic position of IAC. ( A ) Lingual dumbbell-shaped IAC. Coronal CBCT image. Yellow arrow indicates a lingual dumbbell-shaped IAC between third molar roots and lingual cortex of mandible. ( B ) Interradicular IAC. Coronal CBCT shows an impacted mandibular right third molar with an interradicular position of the IAC. Yellow arrow indicates inferior alveolar canal is between the mesiobuccal and mesiolingual roots ( orange arrows ) of a 3-rooted impacted mandibular right third molar. Orange arrows indicate mesiobuccal and mesiolingual roots.

• 4.

  Dumbbell shape/narrowing of the IAC (see Fig. 15 A)

• 5.

  Interradicular position of the IAC ( Fig. 15 B)

Additional advantages of CBCT imaging compared with OPG include:

• 1.

  More reliability in detecting multiple roots of mandibular third molars ( Fig. 16 B, C) and detecting supernumerary third molars ( Fig. 17 B, C) ^{, ,}

  

  Impacted mandibular right and left multirooted third molars. ( A ) Cropped panoramic image showing impacted mandibular right and left third molars. ( B ) Coronal CBCT image showing lingual version and multiple roots of the mandibular right and left third molars. ( C ) Coronal CBCT image of the mandibular left third molar showing 3 roots with the IAC positioned interradicularly between a mesiobuccal and mesiolingual root. Yellow arrow points to IAC. Orange arrows show 3 separate roots. Superior orange arrow points to distal root.

  

  Impacted maxillary right and left supernumerary third molars and supernumerary mandibular left third molar. ( A ) Pantomograph showing evidence of maxillary right, left, and possibly mandibular left supernumerary third molars. ( B ) Multiplanar reconstruction (MPR) of CBCT. Yellow arrows indicate maxillary right supernumerary third molar. Orange arrows indicate maxillary left supernumerary third molar. ( C ) MPR of CBCT. Green arrows indicate supernumerary mandibular left third molar.

• 2.

  Better assessment of the relationship between the maxillary sinus and molar root apices ( Fig. 18 B, C )

  

  High impacted maxillary right and left third molars. ( A ) Pantomograph showing high impacted maxillary right and left third molars. Upper right third molar is superimposed by the maxillary sinus. Upper left third molar is horizontally inclined. ( B ) Coronal CBCT image of maxillary right third molar appears to indicate the tooth is alongside the posterior wall of the sinus. ( C ) Sagittal CBCT view confirms the maxillary right third molar is alongside the posterior wall of the maxillary sinus ( arrow ).

• 3.

  Confirmation of pathosis either at the distal surface of the second molar or in association with the third molar (ie, internal or external resorption, marginal bone loss, cyst formation) ( Figs. 19 B and 20A )

  

  Imaging of high impacted maxillary right and left third molars. ( A ) Pantomograph showing high impacted maxillary right and left third molars. Uncertainty regarding possible presence of cyst associated with upper left third molar or whether the third molar is in the maxillary sinus. ( B ) Sagittal CBCT image of maxillary left third molar. Orange arrow identifies associated cyst with impacted third molar. Extremely thin sinus floor separates third molar from the sinus cavity.

  

  Imaging and surgical removal of a maxillary second molar with buccal root resorption caused by impacted third molar. ( A ) Section of a panoramic image showing superimposition of roots of the maxillary second molar by the mesioangular impacted third molar. The image does not clearly depict any resorption of the second molar. ( B ) Extracted second molar with obvious buccal root resorption.

OPG images may be sufficient in most cases before removal of impacted third molars. However, preoperative assessment using CBCT images may be justified in high-risk cases where a more accurate assessment of the anatomic relationship between the third molar and vital structures is warranted. If this additional information can influence the surgeon’s decision-making process and ultimately change the treatment or the treatment outcome for the patient, then it may be deemed beneficial.

Until recently, the use of CBCT did not seem to reduce the number of neurosensory disturbances after surgical removal of mandibular third molars. ^{, ,} In addition, the cost associated with this imaging was estimated to be 3 to 4 times the cost of panoramic imaging. ^, The CBCT radiation exposure of the mandible was also estimated to be 4 to 5 times higher than OPG imaging. ^, If CBCT imaging were to become routine before surgical removal of mandibular third molars, it has been projected that the annual cancer risk would increase 0.46-fold. Therefore, CBCT should be used only when necessary. The potential benefits need to be weighed against the potential risks of exposure to additional ionizing radiation.

Several recent studies have shown evidence that the use of CBCT can alter the treatment or surgical approach before surgical intervention of mandibular third molars. ^{, , ,}

However, as yet, there are no standard eligibility criteria that necessitate the use of CBCT examination before removal of third molars. Ultimately, further studies and randomized clinical trials will be needed to determine whether CBCT imaging decreases the incidence of complications following the removal of impacted third molars compared with two-dimensional imaging.

Treatment planning

On completion of the history, clinical, and radiographic examinations, the clinician should determine whether the patient is symptomatic. If symptomatic, are the symptoms related to the third molars? Is there a presence or absence of disease related to the third molars?

Whether the patient is symptomatic or not, if a disease or aberrant condition is noted, the clinician should strive to make an evidence-based decision regarding what treatment option is most appropriate for management of the third molar or molars in question. The treatment option should be reasonably effective and the patient should be informed of the potential risks and complications associated with treatment versus no treatment.

In addition, any potential effects on health-related quality-of-life issues and any costs that may be incurred need to be reviewed. If there are any reasonable alternative treatment options, then those too should be discussed.

In most cases, the management of third molars is predicated on the presence or absence of symptoms and disease ( Boxes 1 and 2 ).

In an effort to facilitate the clinical decision-making process, Dodson developed an intuitive and useful classification system ( Table 1 ).

Via this system, a patient’s symptoms are designated as either present (S+) or absent (S−). Likewise, clinical or radiographic evidence of disease is designated either present (D+) or absent (D−).

It is recommended that the probing status of the third molar be evaluated during the clinical examination. This evaluation is done to assess the periodontal health status of the third molar and adjacent second molar because clinical evidence of periodontal disease may be subtle at times, especially if the third molar is not visible. If it is not visible, but can be detected on probing, this may indicate that the tooth is chronically contaminated with oral flora and prone to developing inflammatory disease. A probing depth (PD) greater than or equal to 4 mm in the third molar region is an indicator of chronic oral inflammation and incipient periodontal disease.

Management of group A patients: symptoms present (S+) and disease present (D+)

Management of these patients is fairly straightforward. The associated disease is determined by clinical, radiographic, and laboratory data. The cause may be one of the more common disorders, such as pericoronitis, caries, or periodontal disease. Less frequent disease entities may be related to root resorption of the adjacent second molar, the presence of an odontogenic cyst or tumor, or traumatic ulceration of buccal mucosa caused by a buccally malpositioned third molar. Treatment depends on the diagnosis, eruption status, and anatomic location of the third molar, associated risk factors, cost, and patient preference. Treatment may range from oral hygiene care to restorative treatment, periodontal therapy, coronectomy, or extraction.

Management of group B patients: symptoms present (S+) and disease absent (D−)

Patients presenting with symptoms purportedly related to third molars but showing no evidence of related disease are seen less frequently than patients in groups A, C, and D. Management of these patients can be perplexing.

Sometimes patients in group B report vague pain associated with an erupting third molar. Occasionally, mild inflammation is seen. Typically, there is no evidence of disease radiographically and there appears to be enough dental arch space to accommodate eruption of the tooth into a normal occlusion. In this situation, the discomfort may be attributed to a teethinglike pain. Management may include reassurance, analgesics, perhaps an antimicrobial mouth rinse, and observation.

Other clinical disorders that may be associated with symptomatic, disease-free patients are TMJ disorders, myalgia, and atypical facial pain. Another scenario involves pain referred from an adjacent carious or periodontally compromised tooth.

Ideally, a proper diagnosis is established and then the appropriate treatment can be rendered. If the clinician is unable to identify the source of the symptoms, then observation may be warranted to see whether the source eventually presents itself. Otherwise, the clinician needs to thoroughly review the possible benefits and alternatives to third molar removal and inform the patient of the possibility that the symptoms may not resolve if the third molar is removed.

Management of group C patients: symptoms absent (S−) and disease present (D+)

Management of the patients in group C is similar to the management of patients in group A, mainly because the existence of disease associated with the third molar has been established. Therefore, the goal is to treat the disease. Periodically, the use of the term asymptomatic has been ambiguous in the literature. Asymptomatic does not necessarily mean disease free. A patient can be asymptomatic but still have evidence of third molar–associated disorder.

For example, periodontal disorder can be associated with asymptomatic third molars.

Twenty-five percent (82 of 329) of enrolled asymptomatic healthy patients in a 30-month longitudinal study had at least 1 PD equal to or greater than 5 mm on the distal aspect of a second molar or around a third molar. The mean age of the patients was 25 years. PD equal to or greater than 5 mm was also associated with periodontal attachment loss of at least 1 mm in every patient and 2 mm in 80 of 82 patients.

White and colleagues examined the microbial complexes in subgingival plaque taken from the distal surfaces of all second molars in 295 young, periodontally healthy patients with asymptomatic third molars. Periodontal pathogenic orange and red complex microorganisms were detected at levels of at least 10 ⁵ more often if the patients had a PD of at least 5 mm with periodontal attachment loss at the distal of second molars or around third molars at baseline.

These clinical findings of increased periodontal PDs and periodontal attachment loss, coupled with colonization of periodontal pathogens, support the concept that clinical and microbial changes associated with the initiation of periodontitis may manifest first in the third molar region of young adults.

Caries can also be associated with asymptomatic third molars. Prospective studies of occlusal caries in patients with asymptomatic third molars have reported an increasing frequency of caries with age and erupted third molars. At baseline, 28% of 303 asymptomatic patients had at least 1 third molar with occlusal caries (39% in patients ≥25 years old). Lower third molars were affected more often than upper third molars. Less than 2% of third molars had occlusal caries if first molars and second molars were without caries.

Another study that examined the progression of third molar occlusal caries in 211 patients with asymptomatic third molars found that 33% had third molar caries compared with 29% at baseline. This finding was at a median 2.9-year follow-up. The increase in caries occurred primarily in the mandible. Only 1% of the third molars had occlusal caries if the first molars and second molars were caries free.

The incidence of cysts or tumors related to an impacted third molar is low (2.77%–3.1%). ^, However, it is common for these patients to be asymptomatic and learn of presence of a pathologic entity during a routine radiographic examination. This situation is another example of being symptom free but disease present.

Management of group D patients: symptoms absent (S−) and disease absent (D−)

Management of patients in group D remains controversial. Patients in group D typically report no symptoms and there is no clinical or radiographic evidence of disease present. Clinical examination may reveal that the third molar is completely erupted, functional, in occlusion, and has PDs less than 4 mm.

Examination could also reveal that the third molar is impacted, cannot be seen, cannot be probed, and PDs are less than 4 mm.

Erupting, disease-free third molars with potentially adequate space to accommodate a functional tooth can also be included in this group ( Box 3 ).

Box 3

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