Innervation and blood supply of the teeth
The innervation and blood supply of the maxillary and mandibular teeth are dependant on the blood vessels and the nerves that supply the upper and lower jaws. As the maxilla is deemed part of the midface and the mandible part of the lower face respectively, it is logical to assume that they have separate neurovasculature. While it is true that within the alveolar bone the maxillary and mandibular nerves and vessels mirror one another, there are anatomical differences with extra branches and adjacent structures, such as the mental foramen of the mandible or the greater palatine foramen of the hard palate. This article will highlight the main neurovasculature that supplies both the maxilla and the mandible, including the venous drainage of the teeth and will finish by explaining the pathological implications when a tooth undergoes trauma and this supply is cut off.
Innervation of the Maxillary Teeth
The maxillary nerve, which is the second division of the trigeminal nerve (CN V/II) carries sensory fibers to the teeth. It runs laterally to the cavernous sinus and exits the skull via the foramen rotundum in the middle cranial fossa, leading into the pterygopalatine fossa. Here it divides into four major branches including the infraorbital nerve, which is the main continuation of the maxillary nerve and forms a plexus with the posterior superior alveolar nerve by bifurcating further into the anterior superior alveolar nerve and the middle superior alveolar nerve. The other branches of the maxillary nerve are the ganglionic branches, the posterior superior alveolar nerve and the zygomatic nerve.
Before we continue to the branches that directly innervate the teeth, a few words must be said about the infraorbital nerve. It continues from the pterygopalatine fossa through the inferior orbital fissure and into the orbit. It leaves the orbit via the inferior orbital groove and the infraorbital canal anteriorly and finally emerges on the face via the infraorbital foramen. Here it divides into three branches which are the nasal, the inferior palpebral and the superior labial. These branches supply the alar cartilage of the nose, the dermis of the lower eyelid and the upper lip respectively.
The posterior superior alveolar nerve turns laterally into the pterygomaxillary fissure and into the infratemporal fossa. It descends via the infratemporal surface of the maxilla to form the posterior portion of the superior dental plexus and innervates the posterior aspect of the maxillary sinus as well as the maxillary molars.
The middle superior alveolar nerve varies upon its path and as it descends to form the middle portion of the superior dental plexus it innervates the medial and lateral aspects of the maxillary sinus and the premolars. It may, in some cases, also innervate the mesiobuccal root of the first molar, if it is not covered by the posterior superior alveolar nerve.
Lastly, the anterior superior alveolar nerve descends to form the anterior portion of the superior dental plexus. It innervates the anterior aspect of the maxillary sinus as well as the incisors and the canines.
Blood Supply and Venous Drainage of the Maxillary Teeth
From the external carotid artery arises the maxillary artery which supplies both the maxillary and mandibular teeth. The maxillary arch is supplied by a plexus of three arterial branches which include the anterior superior alveolar artery, the middle superior alveolar artery and the posterior superior alveolar artery.
The posterior superior alveolar artery stems from the third division of the maxillary artery. It arises in the middle cranial fossa before the maxillary artery enters the pterygopalatine fossa. It continues on and enters the infratemporal surface of the maxilla to supply the maxillary sinus, the premolars and the molars.
The middle superior alveolar artery arises from the infraorbital artery as does the anterior superior alveolar artery. Sometimes however this artery is not present. If it is, it arises within the infraorbital canal where it descends to supply the maxillary sinus and the plexus at the level of the canine.
The anterior superior alveolar artery also arises at the level of the middle superior alveolar artery and runs with it to supply the anterior portion of the maxillary arch, the maxillary sinus and the anterior teeth.
As for the venous drainage, the posterior superior alveolar vein, the middle superior alveolar vein and the anterior superior alveolar vein drain into the pterygoid venous plexus.
Innervation of the Mandibular Teeth
The mandibular teeth are supplied by four major nerves. The first and largest is the mandibular nerve, which is the third division of the trigeminal nerve (CN V/III). It carries fibers that are both sensory and motoric due to the merger of its large sensory and small motor roots just after it exits the skull via the foramen ovale. It enters the infratemporal fossa and immediately gives rise to a meningeal branch, a superior and an inferior division. The anterior division is smaller and motoric, save the buccal branch which remains sensory. The other branches include the masseteric nerve, the anterior and posterior deep temporal nerves, the medial pterygoid nerve and the lateral pterygoid nerve. The posterior division is the larger of the two and has the exact opposite ratio of motoric and sensory branches than the anterior division. The singular motoric branch is that of the mylohyoid nerve, whereas the sensory branches are the auriculotemporal nerve, the lingual nerve and the inferior alveolar nerve.
The inferior alveolar nerve is the largest of the mandibular branches and it descends to the lateral pterygoid muscle before running between the sphenomandibular ligament and the ramus of the mandible and finally entering the mandibular foramen and running through it to the level of the second premolar, where just like the inferior alveolar artery, it terminates on the corresponding mental and incisive nerves. It innervates all of the mandibular teeth, the periodontal ligaments and the gingiva from the premolars anteriorly to the midline.
The mental nerve supplies the chin, the lower lip, the facial gingiva and the mucosa from the second premolar anteriorly.
The incisive nerve supplies the teeth and the periodontal ligaments from the first premolar anteriorly.
Blood supply and Venous Drainage of the Mandibular Teeth
The maxillary artery gives rise to a single branch to supply the mandibular teeth which is known as the inferior alveolar artery. It descends inferiorly along with the inferior alveolar nerve and enters the bone via the mandibular foramen. At the level of the second premolar, it terminates into the branches of the mental and incisive arteries after it has supplied all of the mandibular teeth.
The mental and incisive arteries supply the labial gingiva of the anterior teeth and the anterior teeth themselves respectively.
The inferior alveolar vein is the sole collector of the blood pumped around the mandible and it drains into the pterygoid venous plexus.
When a tooth undergoes trauma, such as being knocked during a fall or a sports tournament, several degrees of injury may occur, from a simple concussion, to a fracture and all the way up to a subluxation or even avulsion. Any of these injuries may cause trauma to the apex of the tooth, where the neurovasculature enters and, when this happens, the tooth may likely die. As a result, the tooth becomes discoloured and looks grey. On an x-ray, the pulp cavity can be seen to calcify and, when this happens, a root canal is needed to prevent internal resorption. If the tooth is still sound within the alveolar bone, a simple veneer or a crown after a successful root canal treatment will restore the dentition.