You are required to:
• have a detailed knowledge of the sources and distribution of blood vessels and nerves supplying the mouth and associated structures (i.e. salivary glands, the musculature of the tongue, palate, floor of mouth, lips and cheeks, and the muscles of mastication), together with functional associations
• have good knowledge of the courses and distribution of the maxillary and mandibular divisions of the trigeminal nerve and also the central connections of the trigeminal nerve
• know the location of the major groups of lymph nodes draining orodental tissues and the tonsillar ring protecting the entrance to the pharynx.
(Note that physiological aspects of taste and thermosensation are dealt with in Chapter 5, in association with an account of the tongue. Mechanoreception in the oral cavity is covered in Chapter 15 in association with an account of the periodontal ligament, and oral pain is dealt with in Chapter 13 in relation to the pulpodentinal complex. Salivation is considered in Chapter 7.)
Blood supply to orodental tissues
Mandibular teeth and periodontium
The face is supplied mainly through the facial artery, a branch of the external carotid artery in the neck. The facial artery first appears on the face as it hooks round the lower border of the mandible, at the anterior edge of the masseter. It then runs a tortuous course between the facial muscles towards the medial corner of the eye. There is a rich anastomosis with the artery of the opposite side and with additional vessels supplying the face (transverse facial branch of the superficial temporal artery; infra-orbital and mental branches of the maxillary artery; dorsal nasal branch of the ophthalmic artery). The main arteries to the teeth and jaws are derived from the maxillary artery, a terminal branch of the external carotid, running in the infratemporal fossa. The alveolar arteries follow roughly the same course as the alveolar nerves.
The inferior alveolar artery, which supplies the mandibular teeth, is derived from the maxillary artery before it crosses the lateral pterygoid muscle in the infratemporal fossa. A mylohyoid branch is given off before the inferior alveolar artery enters the mandibular foramen in the ramus of the mandible. The inferior alveolar artery passes through the mandibular foramen to enter the mandibular canal and terminates as the mental and incisive arteries. Posteriorly, the buccal gingiva is supplied by the buccal artery (a branch of the maxillary artery as it crosses the lateral pterygoid muscle) and by perforating branches from the inferior alveolar artery. Anteriorly, the labial gingiva is supplied by the mental artery and by perforating branches of the incisive artery. The lingual gingiva is supplied by perforating branches from the inferior alveolar artery and by the lingual artery, a branch of the external carotid artery.
Maxillary teeth and periodontium
The middle superior alveolar artery, when present, arises from the infra-orbital artery (which is itself a branch of the third part of the maxillary artery in the pterygopalatine fossa). The middle superior alveolar artery runs in the lateral wall of the maxillary sinus, terminating near the canine tooth where it anastomoses with the anterior and posterior superior alveolar arteries.
The anterior superior alveolar artery also arises from the infra-orbital artery and runs downwards in the anterior wall of the maxillary sinus to supply the anterior teeth. Like the superior alveolar nerves, the superior alveolar arteries form plexuses. The buccal gingiva around the posterior maxillary teeth is supplied by gingival and perforating branches from the posterior superior alveolar artery and by the buccal artery. The labial gingiva of anterior teeth is supplied by labial branches of the infra-orbital artery and by perforating branches of the anterior superior alveolar artery. The palatal gingiva around the maxillary teeth is supplied primarily by branches of the greater palatine artery, a branch of the third part of the maxillary artery in the pterygopalatine fossa.
Palate, cheek, tongue and lips
The palate derives its blood supply from the greater and lesser palatine branches of the maxillary artery. The greater palatine artery anastomoses with the nasopalatine artery at the incisive foramen. The cheek is supplied by the buccal branch of the maxillary artery, and the floor of the mouth and the tongue by the lingual arteries. The lips are mainly supplied by the superior and inferior labial branches of the facial arteries.
Venous drainage of orodental tissues
Teeth and periodontium
The venous drainage of this region is extremely variable. The facial vein is the main vein draining the face. It begins at the medial corner of the eye by confluence of the supra-orbital and supratrochlear veins and passes across the face behind the facial artery. Below the mandible, it joins with the anterior branch of the retromandibular vein. This union is sometimes referred to the common facial vein.
Small veins from the teeth and alveolar bone pass into larger veins surrounding the apex of each tooth, or into veins running in the interdental septa. In the mandible, the veins are then collected into one or more inferior alveolar veins, which themselves may drain anteriorly through the mental foramen to join the facial veins or posteriorly through the mandibular foramen to join the pterygoid plexus of veins in the infratemporal fossa. In the maxilla, the veins may drain anteriorly into the facial vein or posteriorly into the pterygoid plexus. No accurate description is available concerning the venous drainage of the gingiva, though it may be assumed that the buccal, lingual, greater palatine and nasopalatine veins are involved; apart from the lingual veins which pass directly into the internal jugular veins, these veins run into the pterygoid plexuses.
Palate, cheek, tongue and lips
The veins of the palate are rather diffuse and variable. However, those of the hard palate generally pass into the pterygoid venous plexus, and those of the soft palate into the pharyngeal venous plexus. The buccal vein of the cheek drains into the pterygoid plexus. Venous blood from the lips drains into the facial veins via the superior and inferior labial veins. The veins of the tongue follow two different routes. Those of the dorsum and sides of the tongue form the lingual veins, which, accompanying the lingual arteries, empty into the internal jugular veins; those of the ventral surface form the deep lingual veins, which ultimately join the facial, internal jugular or lingual veins.
Lymphatic drainage of orodental tissues
As with the venous system, the lymphatic drainage is extremely variable.
Lymphatics from the lower part of the face generally pass through, or around, the buccal lymph nodes to reach the submandibular lymph nodes. However, lymphatics from the medial portion of the lower lip drain into the submental nodes.
The lymph vessels from the teeth usually run directly into the submandibular nodes on the same side, although lymph from the mandibular incisors drains into the submental nodes. Occasionally, lymph from the molars passes directly into the jugulodigastric group of nodes. The lymph vessels of the labial and buccal gingivae of the maxillary and mandibular teeth unite to drain into the submandibular nodes, although in the labial region of the mandibular incisors they may drain into the submental nodes. The lingual and palatal gingivae drain into the jugulodigastric group of nodes, either directly or indirectly through the submandibular nodes.
Lymphatics from most areas of the palate terminate in the jugulodigastric group of nodes. Vessels from the posterior part of the soft palate terminate in pharyngeal lymph nodes. Lymph from the floor of the mouth region can drain directly to the jugulodigastric nodes.
At the oropharyngeal isthmus lie the palatine tonsils between the pillars of the fauces and the lingual tonsils on the pharyngeal surface of the tongue. These tonsils form part of a ring of lymphoid tissue known as Waldeyer’s tonsillar ring. The other components are the tubal tonsils and adenoid tissue (pharyngeal tonsils) located in the nasopharynx.
Innervation of orodental tissues
Excepting regions around the oropharyngeal isthmus, the sensory innervation of the oral mucosa is derived from the maxillary and mandibular divisions of the trigeminal nerve. The trigeminal nerve also supplies the teeth and their supporting tissues (see Table 6.1
). Both the major and the minor salivary glands are supplied by secretomotor parasympathetic fibres from the facial and glossopharyngeal nerves.
Table 6.1 Nerves supply to the teeth and gingivae
||Greater palatine nerve
|Anterior superior alveolar nerve
||Middle superior alveolar nerve
||Posterior superior alveolar nerve
||Posterior superior alveolar nerve and buccal nerve
|1 2 3 4 5 6 7 8
||Tooth position (Zsigmondy system)
||Buccal nerve and perforating branches of inferior alveolar nerve
||Inferior alveolar nerve
|Lingual nerve and perforating branches of inferior alveolar nerve
The motor innervation of the muscles of the jaws and oral cavity is from the trigeminal, facial, accessory and hypoglossal nerves.
All three divisions of the trigeminal nerve are involved with the cutaneous innervation of the face:
• The ophthalmic division supplies the upper part of the face, forehead and scalp.
• The maxillary and mandibular divisions essentially supply the upper and lower jaw regions respectively.
Knowledge of these areas, and of the specific branches involved, is important clinically for assessing the effects of nerve damage and for an understanding of the successful anaesthetization of the buccal, infra-orbital and inferior alveolar (mental) nerves during dental treatment. The areas supplied by the three divisions of the trigeminal nerve also relate to aspects of the development of the face.
Inferior alveolar nerve
The inferior alveolar nerve courses through the mandible in a mandibular canal. Close to the premolar teeth, and after giving molar branches to the molar teeth, the inferior alveolar nerve divides into a mental branch and an incisive branch:
• The mental nerve is a sensory nerve to the skin and mucosa of the lower lip region.
• The incisive nerve supplies the anterior mandibular teeth.
The distribution of nerves to the mandibular premolars and molars is variable, dental branches coming either directly from the inferior alveolar nerve by short or long branches or indirectly through several alveolar branches. In rare instances, the nerve to the mandibular third molar may arise from the inferior alveolar nerve before it enters the mandibular canal. Communications between the inferior alveolar nerve and nerves from the temporalis and lateral pterygoid muscles have been described, the nerves penetrating the mandible through foramina in the region of muscle attachments. It has been suggested that such nerve connections might explain why, in approximately 5% of patients, the teeth may not be anaesthetized after the main trunk of the inferior alveolar nerve has been blocked at the mandibular foramen by the injection of local anaesthetic solution. It is said that, in any one individual, the mandibular canal remains in a relatively fixed position with respect to the lower border of the mandible. The canal is often closely related to the roots of the mandibular molars. Indeed, the roots of lower third molars may even be perforated by the mandibular canal.
In the premolar region, the main trunk of the inferior alveolar nerve divides into mental and incisive nerves. The mental nerve runs for a short distance in a mental canal before leaving the body of the mandible at the mental foramen to emerge on to the face. In about 50% of cases, the mental foramen lies on a vertical line passing through the mandibular second premolar. In an adult with a full dentition, the mental foramen usually lies midway between the upper and lower borders of the mandible. During the first and second years of life, as the prominence of the chin develops, the opening of the mental foramen alters in direction, from facing forwards to facing upwards and backwards. As well as supplying the skin of the lower lip, the mental nerve provides fibres to an incisor plexus, which innervates the labial periodontium of the mandibular incisors.
The incisive nerve runs forwards in an intraosseous incisive canal. This nerve primarily supplies the incisors and canines but may also supply the first premolar. In some instances, the canine may be supplied directly from the inferior alveolar nerve.
Superior alveolar nerves
Supplying the maxillary dentition there are usually three superior alveolar nerves.
The posterior superior alveolar nerve arises from the maxillary nerve in the pterygopalatine fossa, whence it passes through the pterygomaxillary fissure to descend on the posterior wall (tuberosity) of the maxilla. The dental branches of the nerve enter the maxilla and run in narrow posterior superior alveolar canals above the roots of the molar teeth. A gingival branch does not enter the bone, however, but runs downwards and forwards along the outer surface of the maxillary tuberosity. The dental branches of the posterior superior alveolar nerve may arise from a common nerve trunk within the bone or on the tuberosity before entering bone, or alternatively may appear as separate nerve trunks from the main trunk of the maxillary nerve in the pterygopalatine fossa.
The middle superior alveolar nerve is found in about 70% of subjects. It generally arises from the infra-orbital nerve in the floor of the orbit/roof of the maxillary air sinus, although it may arise from the maxillary nerve in the pterygopalatine fossa. The nerve may run in the posterior, lateral or anterior walls of the maxillary sinus. It terminates above the roots of the premolar teeth.
The anterior superior alveolar nerve arises from the infra-orbital nerve within the infra-orbital canal, generally as a single nerve, but occasionally as two or three small branches. The nerve leaves the infra-orbital canal near its termination and then, diverging laterally from the infra-orbital nerve, runs in the anterior wall of the maxillary sinus. It terminates near the anterior nasal spine after giving off a small nasal branch.
Note that the posterior superior alveolar nerve has an extrabony course that permits anaesthesia of the nerve trunk(s) as it passes across the maxillary tuberosity, whereas the middle and anterior superior alveolar nerves are entirely intrabony in their course and cannot be ‘blocked’ with an anaesthetic injection. The superior alveolar nerves form a plexus above the root apices of the maxillary teeth. From this plexus nerves pass to the teeth, although it is difficult to trace the precise innervation of the teeth from specific superior alveolar nerves. As a general rule, however, the incisors and canines are supplied by the anterior nerve, the molars by the posterior nerve, and intermediate areas by the middle nerve.
Sensory nerves to oral cavity
The sensory nerve supply to the palate is derived from the maxillary division of the trigeminal nerve via branches of the pterygopalatine ganglion. A small area behind the incisor teeth is supplied by terminal branches of the nasopalatine nerves. These nerves emerge onto the palate at the incisive foramen. The remainder of the hard palate is supplied by the greater palatine nerves emerging onto the palate at the greater palatine foramina. The soft palate is supplied by the lesser palatine nerves emerging onto the palate via the lesser palatine foramina. Although the maxillary division of the trigeminal nerve supplies most of the palate, there is evidence to suggest that some areas supplied by the lesser palatine nerves may also be innervated by fibres from the facial nerve. The posterior part of the soft palate and the uvula are also supplied by the glossopharyngeal nerve, pr/>
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