Anesthesia is one of the most important inventions made by man. It is hard to imagine a world where there is no way to deal with the pain caused by surgery and other related medical procedures. Complicated medical procedures such as surgery require the application of appropriate anesthetic. But even with expert knowledge about anesthesia and the skills necessary to perform complex dental procedures, the patient can still suffer from unbearable pain if the dentist does not understand the complex nature of dealing with the inferior alveolar nerve or IAN. It is the responsibility of the dentist or surgeon to be familiar with these anatomical variations.
The IAN is a mixed nerve and the main reason why people have the ability to have sensory perception in the lower teeth, lower lip and buccal mucosa (Sandoval, Lopez, & Suazo 51). The IAN is the largest branch of the mandibular nerve (Pai, Swamy, & Prabhu 93). It represents a direct continuation of its posterior trunk and carries sensory and motor fibers (Lang 119). The IAN descends behind and positions itself lateral to the lingual nerve in the interpterygoid fascia between the pterygoid muscles (Lang 119). The IAN enters the mandibular foramen through the pterygomandibula space (Lang 119).
In addition, the IAN “supplies the mandibular teeth, a portion of its fibers exiting at the mental foramen as the mental nerve (Lang 119). This is the basic description of the IAN. But it is common knowledge among experts that the IAN can be observed as having different anatomical variations. These variations can have significant implications when it comes to oral healthcare especially in the context of surgery and other complex dental works.
Anatomical Variations
The IAN may form a single trunk with the lingual nerve and this extends as far as the mandibular foramen (Bergman, Afifi, & Miyauchi, 18) In another type of variation, the IAN can be separated from the lingual nerve by an accessory ligament that extends “from the lateral pterygoid plate and spine of the sphenoid to the lateral side of the pterygospinous ligament” (Bergman, Afifi, & Miyauchi, 18). In another case the IAN can be perforated by the internal maxillary artery (Manikandhan, Naveenkuma, & Anantanarayanan 185). In another kind of variation, the IAN may have accessory roots connected to the mandibular nerve.
In another type of variation, the IAN mylohyoid branch can be the reason why there is a branch that goes through the mylohyoid muscle and joins the lingual nerve. In other cases, it was observed that these branches that arise from the mylohyoid branch and communicates with the depressor anguli oris as well as parts of the platysma (Sandoval, Lopez, & Suazo 51). It is interesting to note that this section is usually supplied by the facial nerve but in this case the IAN figured prominently in how the person perceives pain if the dentist fails to appreciate the variations that exist in the relation to this particular nerve and where its anatomical branches are located.
In other cases it was discovered that the IAN formed several connections with the auriculotemporal nerve (Bergman, Afifi, & Miyauchi, 18). But in a rare case that was documented, the roots of the third lower molar tooth surrounded the IAN (Sandoval, Lopez, & Suazo 52). It has to be made clear that the infratemporal fossa “consists of two pterygoid muscles, maxillary vessels and mandibular nerves and its branches (Pai, Swamy, & Prabhu 93). It is the site where surgery is usually performed. Therefore, it is of primary importance that surgeon, neurosurgeon, maxillofacial surgeon and even radiologist must be aware of the fact that variations do exist. Specialists may be unaware of the variation or simply could not accept the fact that the occurrence may not be as rare as they thought.
In another type of variation, researchers were able to discover the close interrelationship of the lingual nerve and IAN. Due to the variation, researchers were able to establish that these two types of nerves were able to communicate to each other (Sandoval, Lopez, & Suazo 51). This was made possible because according to the report, the IAN was “origin by two roots and the second portion of the maxillary artery passed through the two roots of the IAN (Sandoval, Lopez, & Suazo, 51). This conclusion was partly based on the findings made by other researchers. After examining the lingual nerves in 48 hemisectioned human heads, they were able to discover that there were communications or bridges between the lingual nerve and IAN (Sandoval, Lopez, & Suazo, 52).
A more detailed explanation was given by the researchers and they wrote: “The maxillary artery was observed along the nerve juncture produced between the IAN and the lingual never and the nervous bridge between the two, located 5.4mm from the foramen ovale, passing between the lingual nerve and the IAN (Salvador, Lopez, & Suazo, 52). It is of grave importance that healthcare providers must be aware of the details pertaining to the infratemporal fossa and the common variations especially when it comes to the IAN.
Importance of Understanding Anatomical Variations
Any variation in the IAN can give rise to “neurovascular compression causing numbness, regional pain and headache” as a direct result of the inadequate application of anesthesia (Manikandhan, Naveenkuma, & Anantanarayanan 185). But the root cause is the inability to deal correctly with the effect of the variations in the IAN and other related nerves and artery. Consider for instance the impact of the following discovery when an adult male cadaver, who was about forty years old, was dissected. During the dissection, the ramus was excised above the mandibular foramen and this is what the researchers found out:
In the right infratemporal fossa, the inferior alveolar nerve was seen to emerge from three different roots instead of a single root from the posterior division of the mandibular nerve. These variant roots emerged from the posterior division of the mandibular nerve, and the lingual nerve (Pai, Swamy, & Prabhu 93).
Based on these findings, specialists urged one another to keep in mind the impact of variations in the IAN. One practical application of this discovery is the need to determine how to deliver the correct dosage when it comes to the use of anesthesia. In another case, the variation of the IAN was made possible by the rare variation in the inferior alveolar artery. This is significant because the IAN descends into the mandibular foramen together with the inferior alveolar artery. Thus, the researcher who discovered this anomaly made a report regarding their find as they completed their examination of a 63-year old cadaver (Khaki et al. 345). After they detached the coronoid process and removed the ramus of the left mandible of the said cadaver, they found out that the inferior alveolar artery originated from the external carotid artery (Khaki et al. 345). In addition it was also discovered that the location of the artery was 3.5 cm inferior to its terminal bifurcation into the maxillary and superficial temporal arteries (Khaki et al. 345).
This variation is significant because the dentist has to be aware of these anomalies when it comes to dental, oral and maxillofacial surgery. Since the IAN is the largest branch of the mandibular nerve, it is the target in the event of dental procedures and the goal is to achieve mandibular anesthesia (Khaki et al. 346). Therefore, there is potential hazard to cause vascular trauma. It has been reported that arterial penetration can reach as high as 20% and so the variation can negatively affect the health of the patient.
Another example of variation was discovered when doctors attempted to perform surgery on a 20 year old Indian female. The specialists wanted to operate on the said individual because she was diagnosed with hemifacial microsomia but they found out that the IAN perforated the ramus of the mandible “with a very short intra-bony course and exiting laterally” (Manikandhan, Naveenkuma, & Anantanarayanan 185). This again is another proof that variations come in different forms but the more important thing to remember is that it occurs frequently.
Conclusion
In the case of dental or maxillofacial, the specialist must not underestimate the importance of variation. In most anatomical variations of the IAN, the obvious consequence is the failure of the anesthesiologist when it comes to pain management. But in other forms of variation, such as those that are brought about by variations in other major artery or nerve the consequence can be as simple as vascular trauma or death. It is therefore important that healthcare providers must be knowledgeable about this particular anatomical variation.
Works Cited
Bergman, Ronald, Adel Afifi, and Ryosuke Miyauchi. Illustrated Encyclopedia of Human Anatomic Variation. IA: University of Iowa Press, 1996. Print.
Khaki, Amir et al. “A Rare Variation of the Inferior Alveolar Artery with Potential Clinical Consequences.” Folia Morphology 64.4 (2005): 345-346. Print.
Lang, Johannes. Clinical Anatomy of the Masticatory Apparatus Peripharyngeal Spaces. New York: Thieme Publishers, 1995. Print.
Manikandhan, R., J. Naveenkuma, and P. Anantanarayanan. “A Rare Variation in the Course of the Inferior Alveolar Nerve.” International Journal of Oral & Maxillofacial Surgery 39.2 (2010): 185-187. Print.
Pai, Mangala, Ravindar Swamy and Latha Prabhu. “A Variation in the Morphology of the Inferior Alveolar Nerve with Potential Clinical Significance.” Biomedical International 1 (2010): 93-95. Print.
Sandoval, Catherine, Bernarda Lopez, and Ivan Suazo. “An Unusual Relationship Between the Inferior Alveolar Nerve, Lingual Nerve and Maxillary Artery.” International Journal of Odontostomatol 3.1 (2009): 51-53. Print.