The anatomy of bifid mandibular foramina: a comprehensive review

Introduction Understanding the anatomy of pterygomandibular fossa is crucial for dentists since it is one of the target spaces for inferior alveolar nerve blocks prior to dental treatment. Failure of achieving adequate anesthesia was reported in 20% of inferior alveolar blocks [1]. The sphenomandibular ligament and the interpterygoid fascia are integral structures that define this area [2]. The borders of pterygomandibular fossa are parotid glandular tissue posteriorly and pterygomandibular raphe anteriorly which is made by the union of buccinator and superior pharyngeal constrictor muscles. The lateral border is defined by the mandibular ramus and the medial border is formed by medial and lateral pterygoid muscles [3]. Nerves passing through the pterygomandibular fossa include: lingual nerve, inferior alveolar nerve, and nerve to the mylohyoid. The inferior alveolar nerve (IAN) is the largest branch of the mandibular division of the trigeminal nerve [4]. The mylohyoid nerve branches off the IAN just before it enters into the mandibular foramen. Towards the anterior end of the mandibular foramen; the IAN branches into two main sensory nerves: mental nerve emerging from the mental foramen and the incisive nerve continuing its course anteriorly. The mental nerve supplies the skin of the chin and oral mucosa while the incisive nerve is responsible for providing sensory innervation for first premolar, canines and incisors. The IAN is also accompanied with inferior alveolar artery and vein. Inferior alveolar artery is a branch of the maxillary artery, although it has been reported that it can branch off the external carotid artery [5]. The IAN was found to be anterior to inferior alveolar artery in the majority of cadavers [6]. When administrating inferior alveolar block into the patient; there are many factors that should be taken into consideration including needle gauge, patient age and sex, as well as anatomical variation within the pterygomandibular fossa. Common anatomical variations that influence the success of mandibular anesthesia are: bifid mandibular foramina [7], accessory mylohyoid nerve, contralateral innervation of the anterior incisors and retromolar foramen [8]. The scope of this review is to focus on the anatomy, prevalence and relevance of bifid mandibular foramina.