Evaluation of Third Molars: Clinical Examination and Imaging Techniques

Third molars are thought to have once been a necessity for early human ancestors in order to efficiently chew and digest the cellulose that comprised the plant foliage, which was an integral part of the dietary intake. Due to evolutionary changes and societal advancements, human diets are less plant based, jaw size has become smaller, and the functional need for third molars minimal . Third molars, or wisdom teeth, however, are still present in the majority of people and often require removal to prevent or treat third molar–associated disease states. Critical to the determination of third molar management is the clinical examination and radiographic analysis.

Clinical evaluation

History

A complete history should be obtained before the physical examination, starting with a patient’s chief complaint and history of present illness, which guide the examination and ultimately the treatment. Furthermore, this step triages patients, differentiating elective from more urgent patients, such as one with an odontogenic abscess. For instance, does the patient have pain, drainage, or swelling or was the patient referred due to concerns of an orthodontist about third molar–associated anterior dentition crowding? As with any surgical patient, a patient’s past medical history, past surgical history, medications, allergies, and social history should be thoroughly obtained. A past anesthesia history should be discussed as well. Significant comorbidities, anticoagulation, specific medication allergies, and severe dental phobia may alter the treatment algorithm and is critical to patient safety and care.

Physical Examination

General

A thorough head and neck examination should be completed as part of the third molar evaluation. The temporomandibular joints should be assessed to evaluate for any pretreatment findings of temporomandibular disorders, such as clicking, popping, crepitus, laxity, and tenderness to palpation. Such information is of significant importance so as to take the necessary precautions if surgery is planned and to document pre-existing conditions and avoid attributing any temporomandibular disorders to the surgical removal of the third molars. Next, the examination should evaluate for signs of infection, such as edema, erythema, and asymmetry, and the neck should undergo palpation to assess for lymphadenopathy. Intraoral examination should include a global inspection of the oral cavity and well as a focal examination of the third molar areas. Furthermore, a directed anesthesia evaluation should address items, such as the Mallampati classification, neck range of motion, and thyromental distance.

Third molar specific

Clinical examination of the third molar areas should first assess for whether the third molars are visible in the oral cavity and whether the teeth are impacted or simply not present, because third molar agenesis occurs in up to 20% of patients . Once confirmed present and if not completely impacted, the examination should assess for potential disease states as well as difficulty of access and surgical removal of the third molar teeth.

Examination findings to note as related to third molars:

  • Periodontal disease

  • Dental caries

  • Pericoronitis

  • Second molar or adjacent tooth resorption

  • First or second molar caries as a predictor for development of third molar caries

  • Associated cysts or tumor growth

  • Crowding of anterior dentition

  • Presence of an oral prosthesis

Findings to note as related to surgical access and third molar surgery:

  • Body mass index

  • Trismus

  • Cheek laxity

  • Macroglossia

Radiographic analysis

The management of third molars consists of radiographic evaluation of dentofacial structures and the third molars in particular. Imaging is particularly important because it augments the evaluation by providing further information as to the size, shape, and position of the teeth and their relationship to the surrounding structures. Furthermore, the presence of associated pathology, which has been reported to occur in up to 10% of patients, may be determined . Also, technical considerations regarding the surgical removal may be addressed. Specifically, the relationship of the mandibular third molars to the inferior alveolar canal and the maxillary third molars to the maxillary sinus may be appreciated, providing teaching points for the patient and risk stratification regarding postoperative issues, such as nerve injury, jaw fracture, or oral-antral communications. In cases of impaction, which has been reported to occur in more than 50% of patients, imaging may be the only means to evaluate these teeth .

As for the imaging modality itself, some debate has developed over the use of CT versus the orthopantogram, which has been the standard imaging technique for evaluating third molars. The primary impetus behind the use of imaging other than the orthopantomogram is an effort to decrease the frequency of inferior alveolar nerve injury after third molar removal. Specifically, nerve injury associated with third molar extraction has been reported to occur in up to 7% percent of patients and it has been suggested that this can be greatly reduced, especially in high risk patients, via the use of 3-D, enhanced detail imaging, allowing for superior preoperative diagnostic assessment . Furthermore, accuracy of third molar angulation is of importance in surgical planning. Dudhia reconfirmed the presence of distortional inaccuracies with orthopantomograms or panoramic imaging secondary to projection geometry creating discrepancies in angular measurements. Simply, the panoramic image results in the mandibular third molars appearing less mesially inclined, which can have both treatment planning and surgical implications. Digital panoramic images offer significantly greater diagnostic precision over conventional panoramic images but ultimately create only a 2-D image of a 3-D anatomic area . As a result, studies, such as the one by Bouquet and colleagues , demonstrated the intuitive conclusion that CT offers increased anatomic precision over orthopantography but with a significant increase in radiation exposure and cost. The advent of cone- beam CT technology (CBCT) has resulted in imaging with decreased radiation exposures and intraoffice practicality versus the medical-grade CT scanners . Tantanapornkul and colleagues demonstrated the CBCT to be superior to panoramic imaging in predicting neurovascular bundle exposure during extraction of impacted third molar teeth ( Fig. 1 ). Specifically, CBCT scanners use narrow, collimated conical radiation beam geometry coupled to 3-D reconstruction algorithms. The result is the generation of an accurate and large volume of data in a short scanning interval . In addition, Ghaeminia and colleagues reported that CBCT elucidated the 3-D relationship of the third molar root to the mandibular canal and allowed for buccolingual appreciation of the inferior alveolar nerve (see Fig. 1 ). Furthermore, even MRI has been proposed by Tymoflyeva and colleagues as an alternative imaging option for impacted teeth because it results in volumetric morphology while eliminating ionizing radiation, which is especially important in younger patients.

Fig. 1
( Upper ) 2-D orthopantomogram demonstrating wisdom teeth. ( Lower ) 3-D CBCT with particular emphasis on the inferior alveolar can and its relationship to the third molar mandibular teeth.
( Courtesy of Queensland X-Ray, Queensland, Australia; with permission.)

Radiographic Assessment of Surgical Difficulty of Removal of Impacted Third Molars

  • Orthopantogram specific :

  • Root number

  • Root morphology

  • Tooth position

  • Second molar relation

  • Size of follicular sac

  • Periodontal ligament space

  • Panoramic radiographic risk factors for inferior alveolar nerve injury :

  • Diversion of the inferior alveolar canal

  • Darkening of the third molar root

  • Interruption of the cortical white line

Radiographic analysis

The management of third molars consists of radiographic evaluation of dentofacial structures and the third molars in particular. Imaging is particularly important because it augments the evaluation by providing further information as to the size, shape, and position of the teeth and their relationship to the surrounding structures. Furthermore, the presence of associated pathology, which has been reported to occur in up to 10% of patients, may be determined . Also, technical considerations regarding the surgical removal may be addressed. Specifically, the relationship of the mandibular third molars to the inferior alveolar canal and the maxillary third molars to the maxillary sinus may be appreciated, providing teaching points for the patient and risk stratification regarding postoperative issues, such as nerve injury, jaw fracture, or oral-antral communications. In cases of impaction, which has been reported to occur in more than 50% of patients, imaging may be the only means to evaluate these teeth .

As for the imaging modality itself, some debate has developed over the use of CT versus the orthopantogram, which has been the standard imaging technique for evaluating third molars. The primary impetus behind the use of imaging other than the orthopantomogram is an effort to decrease the frequency of inferior alveolar nerve injury after third molar removal. Specifically, nerve injury associated with third molar extraction has been reported to occur in up to 7% percent of patients and it has been suggested that this can be greatly reduced, especially in high risk patients, via the use of 3-D, enhanced detail imaging, allowing for superior preoperative diagnostic assessment . Furthermore, accuracy of third molar angulation is of importance in surgical planning. Dudhia reconfirmed the presence of distortional inaccuracies with orthopantomograms or panoramic imaging secondary to projection geometry creating discrepancies in angular measurements. Simply, the panoramic image results in the mandibular third molars appearing less mesially inclined, which can have both treatment planning and surgical implications. Digital panoramic images offer significantly greater diagnostic precision over conventional panoramic images but ultimately create only a 2-D image of a 3-D anatomic area . As a result, studies, such as the one by Bouquet and colleagues , demonstrated the intuitive conclusion that CT offers increased anatomic precision over orthopantography but with a significant increase in radiation exposure and cost. The advent of cone- beam CT technology (CBCT) has resulted in imaging with decreased radiation exposures and intraoffice practicality versus the medical-grade CT scanners . Tantanapornkul and colleagues demonstrated the CBCT to be superior to panoramic imaging in predicting neurovascular bundle exposure during extraction of impacted third molar teeth ( Fig. 1 ). Specifically, CBCT scanners use narrow, collimated conical radiation beam geometry coupled to 3-D reconstruction algorithms. The result is the generation of an accurate and large volume of data in a short scanning interval . In addition, Ghaeminia and colleagues reported that CBCT elucidated the 3-D relationship of the third molar root to the mandibular canal and allowed for buccolingual appreciation of the inferior alveolar nerve (see Fig. 1 ). Furthermore, even MRI has been proposed by Tymoflyeva and colleagues as an alternative imaging option for impacted teeth because it results in volumetric morphology while eliminating ionizing radiation, which is especially important in younger patients.

Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Evaluation of Third Molars: Clinical Examination and Imaging Techniques
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