Jason Jamali, Antonia Kolokythas, and Michael Miloro
Department of Oral and Maxillofacial Surgery, College of Dentistry, University of Illinois Chicago, Chicago, Illinois, USA
An understanding of the anatomical relations within the region of intervention is critical to minimize surgical complications. Radiographic imaging assists in the assessment of anatomical variation and allows for risk stratification and predictable treatment outcomes.
The lingual nerve provides sensation to the anterior two-thirds of the tongue. The lingual nerve is at risk for injury with the extraction of third molars and with procedures involving the floor of the mouth. Within the third molar region, the lingual nerve is located, on average, 3.0 mm apical to the crest of the alveolar ridge and 2.0 mm medially from the lingual cortical plate. In 17.6% of the population, the lingual nerve is at or above the crest of the alveolar bone. In 22% of the population, the lingual nerve contacts the lingual cortex adjacent to the third molar region. Within the second molar region, the lingual nerve is located, on average, 9.5 mm inferior to the cementoenamel junction (CEJ). Within the first molar and second premolar regions, the average vertical distances from the CEJ lingually are 13.0 mm and 15.0 mm, respectively. The lingual nerve begins to course toward the tongue between the first and second molar regions.
As the inferior alveolar nerve (IAN) descends from the base of the skull, it traverses the pterygomandibular space and enters the mandibular foramen approximately 1.5–2.0 cm inferior to the sigmoid notch. Within the corpus of the mandible, the course of the mandibular canal in the buccal-lingual dimension tends to follow one of three general patterns:
- Type 1: in the majority of the population (approximately 70%), the canal follows the lingual plate within the ramus–body region.
- Type 2: in 15% of the population, the canal initially runs within the middle of the ramus when posterior to the second molar, and then follows the lingual plate as it passes through the region of the second and first molars.
- Type 3: in 15% of the population, the canal is positioned in the middle to lingual third of the mandible along its entire course.
- In approximately 80% of the population, the inferior alveolar artery courses above the nerve within the bony canal.
- Older patients have been shown to have less distance between the buccal cortex of the mandible and the lateral aspect of the canal.
- In relation to impacted third molars, the inferior alveolar canal is located:
- Lingual to the third molar in 49% of the population
- Buccal to the third molar in 17% of the population
- Inferior to the third molar in 19% of the population
- Interradicular in 15% of the population.
In general, the risk of exposure of the inferior alveolar canal during third molar removal is greater in patients with lingual, rather than buccal, canal positioning. Among molars in the posterior mandible, the distance from the buccal cortex to the canal tends to be greatest within the region of the second molar.
The mental foramen typically lies between the first and second premolars in line corresponding with a vertical reference from the infraorbital foramen. Variability in the vertical distance of the foramen may be problematic in edentulous mandibles with excessive alveolar bone resorption. The mental nerve courses superio/>