Variant Inferior Alveolar Nerves and Implications for Local Anesthesia.

A sound knowledge of anatomical variations that could be encountered during surgical procedures is helpful in avoiding surgical complications. The current article details anomalous morphology of inferior alveolar nerves encountered during routine dissection of the craniofacial region in the Gross Anatomy laboratory. We also report variations of the lingual nerves, associated with the inferior alveolar nerves. The variations were documented and a thorough review of literature was carried out. We focus on the variations themselves, and the clinical implications that these variations present. Thorough understanding of variant anatomy of the lingual and inferior alveolar nerves may determine the success of procedural anesthesia, the etiology of pathologic processes, and the avoidance of surgical misadventure.

Anatomical relationships within the human pterygomandibular space: Relevance to local anesthesia.

A thorough understanding of the anatomy of the pterygomandibular space is fundamental to the successful administration of inferior alveolar nerve (IAN) blocks, which are frequently used in dentistry for mandibular anesthesia. However, the nature and extent of anatomical variations and relationships within this space are not well documented, and descriptions vary within the literature. This study analyzed the anatomical patterns and relationships of structures in the pterygomandibular space of 56 human cadaver hemi-heads, with both left and right sides from 10 individuals being available, and described the range of variability. In most cases, the IAN was anterior to the inferior alveolar vasculature with the inferior alveolar vein(s) being closest to the bone. On average, there were two veins per specimen. The position of the inferior alveolar neurovascular bundle expressed as the ratio of its distance from the anterior border of the ramus to the total anteroposterior length of the ramus was 0.60 (standard deviation [SD] = 0.07). The distance of anterior and medial displacement of the lingual nerve to the IAN was 7.3 mm (SD = 2.4 mm) and 3.9 mm (SD = 1.6 mm), respectively. The direct distance between the IAN and lingual nerve was 8.5 mm (SD = 2.4 mm). The sphenomandibular ligament always appeared dense and fibrous, medial to the neurovascular bundle. This anatomical study highlights the extent of variations in the positioning of anatomical structures directly relevant to IAN blocks, and reassesses the rationale for the direct approach, which is currently taught and practiced throughout many countries.

Anatomical variations and clinical implications of the artery to the lingual nerve.

The pterygomandibular space is a critical anatomic area for the delivery of local anesthesia in the practice of dentistry. The neurovascular contents of this area are subject to trauma and its resultant local and systemic complications. This study of 202 cadaveric specimens reaffirms the literature as to the percent distributions of the superficial and deep routes of the maxillary artery and details for the first time the anatomic variations of the artery to the lingual nerve. This artery courses through the pterygomandibular space placing it at risk for injection trauma along with the other neurovascular contents. It has been uncommonly identified and referred to in the literature, yet it may be the first artery encountered when entering the space with a needle or during surgical intervention in the area.

[Morphometric study of chorda tympani-derived fibers along their course in the lingual nerve].

The topographical organization of chorda tympani-derived fibers (Ch-fibers) was investigated macroscopically and histologically along their entire course through the lingual nerve in 81 adult Japanese cadavers (113 sides), in order to obtain basic data to explain the taste disturbance occurring after oral anesthesia. Ch-fibers frequently (approx. 80%) merged and intermingled with nerve bundles composed of fibers of the lingual nerve proper (L-fibers) above the level of the mandibular foramen (intermingled type). However, on 23 sides (20.4%) the Ch-fibers could be separated under a stereomicroscope from the L-fiber bundles during their course behind the oral cavity (separated type). Moreover, on 12 of the 23 sides, the Ch-fibers were clearly separated from the L-fibers, since the Ch-fibers formed an independent nerve bundle attached to the surface of the L-fiber bundles throughout almost their entire course to the tongue. Irrespective of whether they were intermingled or separated, however, the Ch-fibers traveled downward, maintaining their superficial and posterolateral topographical organization in the lingual nerve. In 8 of the 12 clearly separated cases, the perimeter of the myelinated fibers was analyzed at three levels: the hard palate, the mandibular foramen and immediately above the angle of the mandible. At each level, the perimeter spectrum of Ch-fibers was significantly smaller (mean: 16.6 +/- 5.4 microns, e.q. at the level of the mandibular foramen) than that of the L-fibers (mean: 20.2 +/- 6.2 microns, at the same level) (p < 0.01). Moreover, the lingual nerve consistently had 2-3 buccal branches supplying the lining of the oral cavity posterior to the internal oblique line of the mandibular ramus. These buccal branches did not contain Ch-fibers, but were composed of only L-fibers, possibly including pain fibers. These observations suggest that physicians performing nerve block to and around the mandibular foramen tend to regard the inferior alveolar nerve and the lingual nerve as targets of the block, irrespective of whether or not this is intended, since the buccal branch of the lingual nerve should also be anesthetized in such cases. Moreover, local anesthetics seem to have a rapid effect on Ch-fibers, because of their superficial position in the lingual nerve and their smaller diameter than L-fibers. Consequently, Ch-fibers along the lingual nerve seem to be easily damaged by local anesthesia of the oral region. Greater care should therefore be exercised to avoid producing a taste disturbance when performing oral anesthesia in clinical practice.

[Supplementary innervation of lower teeth. Review of the literature]. / Contribuição ao estudo da inervação suplementar dos dentes inferiores - uma revisão bibliográfica.

When pain persists after a successful injection of the inferior alveolar nerve, the professional must think on the possibility of supplementary nerve supply of the region. This review updates the current knowledge of this supplementary innervation. Not every patient will require this kind of anesthesia, however, the dentist must be aware of its existence.