teeth
525
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Fig. 31.33 A decalcified
longitudinal section of a
tooth showing groups
of periodontal ligament
fibres (the alveolar
crest fibres and the
horizontal fibres) in the
region of the alveolar
crest. Van Gieson stain.
(With permission from A B
Berkovitz BKB, Holland
GR, Moxham BJ 2009
Oral Anatomy,
Embryology and
Histology, 4th ed.
Edinburgh: Mosby.)
Fig. 31.35 A decalcified section of a root of a tooth showing Sharpey’s
fibres from the periodontal ligament entering alveolar bone (A). The
Sharpey’s fibres in bone (thick arrows) are seen to be thicker, but less
numerous, than those entering the cementum (B) on the tooth surface
(thin arrows). Van Gieson stain. (With permission from Berkovitz BKB,
Holland GR, Moxham BJ 2009 Oral Anatomy, Embryology and Histology,
4th ed. Edinburgh: Mosby.)
Pulp cavity
Interdental
septum
Cancellous *
bone
Mandibular
canal Fig. 31.36 A bite-wing radiograph of teeth and surrounding bone. Note
the different radiopacities of enamel and dentine. In a healthy tooth, such
Compact as the first molar illustrated here, the lamina dura is complete and
bone appears as a radiopaque line. In the case of the adjacent second molar
tooth, in which the bulk of the crown has been lost due to dental caries,
Fig. 31.34 The anterior part of the left side of the mandible, with an abscess (*) has formed at the base of the tooth and, as a result, the
superficial bone removed on the buccal side to show the roots of a lamina dura has lost its continuity. (Courtesy of Ms Nadine White.)
number of teeth, some of which have also been sectioned vertically. Note
the cortical plate of compact bone lining the sockets of the teeth (the
lamina dura of radiographs; see Fig. 31.36), and the flat table of bone


surmounting the interdental bone septa. In this specimen, the mandibular In clinical radiographs, the bone lining the alveolus commonly
canal is widely separated from the roots of the teeth, a variable condition. appears as a continuous dense white line about 0.5–1 mm thick: the
lamina dura (Fig. 31.36). However, this appearance gives a misleading
impression of the density of alveolar bone; the Xray beam passes tan
gentially through the socket wall, and so the radiopacity of the lamina
body of the mandible or the maxilla (Fig. 31.34). Like bone in other dura is an indication of the quantity of bone the beam has passed
sites, alveolar bone functions as a mineralized supporting tissue, gives through, rather than the degree of mineralization of the bone. Super
attachment to muscles, provides a framework for bone marrow and acts imposition also obscures the Volkmann’s canals. Chronic infections of
as a reservoir for ions, especially calcium. It is dependent on the pres the dental pulp spread into the periodontal ligament, which leads to
ence of teeth for its development and maintenance, and requires func resorption of the lamina dura around the root apex. The presence of a
tional stimuli to maintain bone mass. Where teeth are congenitally continuous lamina dura around the apex of a tooth therefore usually
absent – as in anodontia, for example – it is poorly developed, and it indicates a healthy apical region (except in acute infections where
atrophies after tooth extraction, which can cause difficulties in the resorption of bone has not yet begun).
prosthodontic rehabilitation of patients. On the labial and buccal aspects of upper teeth, the two cortical
The alveolar toothbearing portion of the jaws consists of outer and plates usually fuse, and there is very little cancellous bone between
inner alveolar plates. The individual sockets are separated by plates of them, except where the buccal bone thickens over the molar teeth near
bone termed the interdental septa, while the roots of multirooted teeth the root of the zygomatic arch. It is easier and more convenient to
are divided by interradicular septa. The compact layer of bone that lines extract upper and lower teeth by widening the tooth socket in a buccal


the tooth socket has been called either the cribriform plate, on account direction due to its thinness. Anteriorly in the lower jaw, labial and
of its content of vascular (Volkmann’s) canals, which pass from the lingual plates are thin, but in the molar region the buccal plate is thick
alveolar bone into the periodontal ligament; or bundle bone, because ened as the external oblique line. Near the lower third molar, the lingual
numerous bundles of Sharpey’s fibres pass into it from the periodontal bone is much thinner than the buccal and it is important to realize that
ligament (Fig. 31.35). the lingual nerve is easily damaged by poor technique.


Oral cavity
526
4
NOitcES
VASCULAR SUPPLY AND LYMPHATIC Table 31.2 Innervation of the teeth and gingivae
DRAINAGE OF THE TEETH AND
Nasopalatine nerve Greater palatine nerve Palatal gingivae
SUPPORTING STRUCTURES Maxilla Anterior superior Middle superior Posterior superior Teeth
alveolar nerve alveolar nerve alveolar nerve
The main arteries to the teeth and their supporting structures are derived Infraorbital nerve Posterior superior alveolar nerve and Buccal gingivae
buccal nerve
from the maxillary artery, one of the two terminal branches of the
external carotid artery. The upper teeth are supplied by branches from 1 2 3 4 5 6 7 8 Tooth position
the superior alveolar arteries, and the lower teeth by branches from the Buccal nerve and perforating
Mental nerve branches of inferior alveolar Buccal gingivae
inferior alveolar arteries.
nerve
Mandible Incisive nerve Inferior alveolar nerve Teeth
Superior alveolar arteries
Lingual nerve and perforating branches of inferior Lingual gingivae
alveolar nerve
The upper jaw is supplied by posterior, middle and anterior superior
alveolar (dental) arteries. The posterior superior alveolar artery usually (With permission from Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral Anatomy, Embryology and
arises from the third part of the maxillary artery in the pterygopalatine Histology, 4th ed. Edinburgh: Mosby.)
fossa. It descends on the infratemporal surface of the maxilla, and
divides to give branches that enter the alveolar canals to supply molar
and premolar teeth, adjacent bone and the maxillary sinus, and other
branches that continue over the alveolar process to supply the gingivae. Venous drainage of the teeth
The middle and anterior superior alveolar arteries are branches from
the infraorbital artery.
Veins accompanying the superior alveolar arteries drain the upper jaw
The infraorbital artery often arises with the posterior superior alveo
and teeth anteriorly into the facial vein, or posteriorly into the pterygoid
lar artery. It enters the orbit posteriorly through the inferior orbital
venous plexus. Veins from the lower jaw and teeth collect either into


fissure and runs in the infraorbital groove and canal with the infra
larger vessels in the interdental septa or into plexuses around the root
orbital nerve. When the small middle superior alveolar artery is present,
apices and thence into several inferior alveolar veins. Some of these
it runs down the lateral wall of the maxillary sinus and forms anasto
veins drain through the mental foramen to the facial vein; others drain
motic arcades with the anterior and posterior vessels, terminating
via the mandibular foramen to the pterygoid venous plexus.
near the canine tooth. The anterior superior alveolar artery curves
through the canalis sinuosus to supply the upper incisor and canine
Lymphatic drainage of the teeth
teeth and the mucous membrane in the maxillary sinus. The canalis
sinuosus swerves laterally from the infraorbital canal and inferomedi
ally below it in the wall of the maxillary sinus, following the rim of the The lymph vessels from the teeth usually run directly into the ipsilateral
anterior nasal aperture, between the alveoli of canine and incisor teeth submandibular lymph nodes. Lymph from the mandibular incisors,
and the nasal cavity. It ends near the nasal septum where its terminal however, drains into the submental lymph nodes. Occasionally, lymph
branch emerges. The canal may be up to 55 mm long. from the molars may pass directly into the jugulodigastric group of
nodes.
Inferior alveolar artery
INNERVATION OF THE TEETH
The inferior alveolar (dental) artery, a branch of the maxillary artery,
descends in the infratemporal fossa posterior to the inferior alveolar The regional innervation of the teeth and gingivae is shown in Table
nerve. Here, it lies between bone laterally and the sphenomandibular 31.2. The teeth in the upper jaw are supplied by the superior alveolar
ligament medially. Before entering the mandibular foramen it gives off nerves, while those in the lower jaw are supplied by the inferior alveolar
a mylohyoid branch, which pierces the sphenomandibular ligament to nerve (Rodella et al 2012).
descend with the mylohyoid nerve in its groove on the inner surface of


the ramus of the mandible. The mylohyoid artery ramifies superficially Superior alveolar nerves
on the muscle and anastomoses with the submental branch of the facial
artery. The inferior alveolar artery then traverses the mandibular canal
The teeth in the upper jaw are supplied by the three superior alveolar
with the inferior alveolar nerve to supply the mandibular molars and
(dental) nerves that arise from the maxillary nerve in the pterygopala
premolars, and divides into the incisive and mental branches near the
tine fossa or in the infraorbital groove and canal. The posterior superior
first premolar.
alveolar (dental) nerve leaves the maxillary nerve in the pterygopalatine
The incisive branch continues below the incisor teeth (which it sup
fossa and runs anteroinferiorly to pierce the infratemporal surface of
plies) to the midline, where it anastomoses with its fellow, although
the maxilla, at which point it is possible to perform a local anaesthetic
few anastomotic vessels cross the midline. In the canal, the arteries
block that will anaesthetize the pulps of the premolar and molar ipsi
supply the mandible, tooth sockets and teeth via branches that enter
lateral teeth; it then descends under the mucosa of the maxillary sinus.
the minute hole at the apex of each root to supply the pulp. The mental
After supplying the lining of the sinus, the nerve divides into small
artery leaves the mental foramen and supplies the chin; it anastomoses
branches that link up as the molar part of the superior alveolar plexus,
with the submental and inferior labial arteries. Near its origin, the
supplying twigs to the molar teeth. It also supplies a branch to the upper
inferior alveolar artery has a lingual branch, which descends with the
gingivae and the adjoining part of the cheek.
lingual nerve to supply the lingual mucous membrane. The pattern of
The middle superior alveolar (dental) nerve arises from the infra
branching of the inferior alveolar artery reflects that of the nerves of the
orbital nerve as it runs in the infraorbital groove, and runs downwards
same name.


and forwards in the lateral wall of the maxillary sinus. It ends in small
branches that link up with the superior dental plexus, supplying small
Arterial supply of periodontal ligaments
rami to the upper premolar teeth. This nerve is variable, and it may be
duplicated or triplicated, or absent.
The periodontal ligaments supporting the teeth are supplied by dental The anterior superior alveolar (dental) nerve leaves the lateral side
branches of alveolar arteries. One branch enters the alveolus apically of the infraorbital nerve near the midpoint of its canal and traverses the
and sends two or three small rami into the dental pulp through the canalis sinuosus in the anterior wall of the maxillary sinus. It curves
apical foramen, and other rami into the periodontal ligament. Inter first under the infraorbital foramen, then passes medially towards the
dental arteries ascend in the interdental septa, sending branches at right nose, and finally turns downwards and divides into branches to supply
angles into the periodontal ligament, and terminate by communicating the incisor and canine teeth. It assists in the formation of the superior
with gingival vessels that also supply the cervical part of the ligament. dental plexus and it gives off a nasal branch, which passes through a
The periodontal ligament therefore receives its blood from three minute canal in the lateral wall of the inferior meatus to supply the
sources: from the apical region; ascending interdental arteries; and mucous membrane of the anterior area of the lateral wall as high as the
descending vessels from the gingivae. These vessels anastomose with opening of the maxillary sinus, and the floor of the nasal cavity. It com
each other, which means that when the pulp of a tooth is removed municates with the nasal branches of the pterygopalatine ganglion and
during endodontic treatment, the attachment tissues of the tooth finally emerges near the root of the anterior nasal spine to supply the
remain vital. adjoining part of the nasal septum.


Salivary glands
527
13
rEtPaHc
Fig. 31.39 The
salivary glands of
the left side. The
cranial region of the
superficial part of
the submandibular
Accessory part of parotid gland
gland has been
excised and
Parotid gland mylohyoid has been
Parotid duct
cut and turned
down to expose a
portion of the deep
Buccinator
part of the gland.
Masseter
Mucous membrane
(cut edge) with Body of mandible
sublingual ducts
Lingual nerve Sternocleidomastoid
Digastric, posterior belly
Sublingual gland
Submandibular gland
(superficial part)
Hyoglossus
Stylohyoid
Digastric, anterior belly
Submandibular gland (deep part)
Mylohyoid
Platysma (cut edge) (turned down) Submandibular duct
Inferior alveolar (dental) nerve Pain sensation in teeth
The course of the inferior alveolar nerve in the infratemporal fossa is The teeth are supplied by nociceptors that generate pain sensation of a
described on page 551. Just before entering the mandibular canal, the very high order. The mechanism underlying this sensitivity is of con
inferior alveolar nerve gives off a small mylohyoid branch that pierces siderable clinical significance and is controversial. Currently, the most
the sphenomandibular ligament and enters a shallow groove on the widely accepted view is that fluid movements through the dentine
medial surface of the mandible, following a course roughly parallel to tubules stimulate nerve endings at the periphery of the dental pulp
its parent nerve. It passes below the origin of mylohyoid to lie on the (hydrodynamic hypothesis).
superficial surface of the muscle, between it and the anterior belly of
digastric, both of which it supplies. It gives a few filaments to supply Local analgesia
the skin over the point of the chin.
In the mandibular canal, the inferior alveolar nerve runs downwards Available with the Gray’s Anatomy e-book
and forwards, generally below the apices of the teeth until below the
first and second premolars, where it divides into terminal incisive and


mental branches. The incisive branch continues forwards in a bony SALIVARY GLANDS
canal or in a plexiform arrangement, giving off branches to the first
premolar, canine and incisor teeth, and the associated labial gingivae.
The lower central incisor teeth receive a bilateral innervation, fibres Salivary glands are compound, tubuloacinar exocrine glands whose
probably crossing the midline within the periosteum to reenter the ducts open into the oral cavity. They secrete saliva, a fluid that lubricates
bone via numerous canals in the labial cortical plate. food to assist deglutition, moistens the buccal mucosa, which is impor
The mental nerve passes upwards, backwards and outwards to tant for speech, and provides an aqueous solvent necessary for taste
emerge from the mandible via the mental foramen between and just and a fluid seal for sucking and suckling. Salivary glands also secrete
below the apices of the premolar teeth. It immediately divides into digestive enzymes, e.g. salivary amylase, and antimicrobial agents, e.g.
three branches, two of which pass upwards and forwards to form an immunoglobulin A (IgA), lysozyme and lactoferrin, into saliva. Condi
incisor plexus labial to the teeth, supplying the gingiva (and probably tions in which there is a significant decrease in the production of saliva
the periosteum). From this plexus and the dental branches, fibres turn (xerostomia) may result in periodontal inflammation and dental caries.
downwards and then lingually to emerge on the lingual surface of the An illustration of the position of the major salivary glands and their
mandible on the posterior aspect of the symphysis or opposite the ducts is given in Figure 31.39.
premolar teeth, probably communicating with the lingual or mylo The major salivary glands are the paired parotid, submandibular and
hyoid nerve. The third branch of the mental nerve passes through the sublingual glands. In addition, there are numerous minor salivary
intermingled fibres of depressor anguli oris and platysma to supply the glands scattered throughout the mouth.


skin of the lower lip and chin. Branches of the mental nerve also com Approximately 0.5 l of saliva is secreted per day. Salivary flow rates
municate with terminal filaments of the mandibular branch of the are typically 0.3 ml/min when unstimulated, and rise to 1.5–2 ml/min
facial nerve. when stimulated. Flow rate is negligible during sleep. In the unstimu
Variations in the fascicular organization of the inferior alveolar nerve lated state, the parotid gland contributes 20%, the submandibular
are clinically important when extracting impacted third molars. The gland 65%, and the sublingual and minor salivary glands 15% of the
nerve may appear as a single bundle lying a few millimetres below the daily output of saliva. When stimulated, the parotid contribution rises
roots of the teeth, or it may lie much lower and almost reach the lower to 50%.
border of the bone, so that it gives off a variable number of large rami
that pass anterosuperiorly towards the roots before dividing to supply
the teeth and interdental septa. Only rarely is it plexiform. The nerve PAROTID GLAND
may lie on the lingual or buccal side of the mandible (slightly more
commonly on the buccal side). Even when the third molar tooth is in The parotid gland is the largest salivary gland and is almost entirely
a normal position, the nerve may be so intimately related to it that it serous. The parotid duct runs through the cheek and drains into the
grooves its root. Exceptionally, the nerve may be similarly related to the mouth opposite the maxillary second permanent molar tooth. The
second molar. parotid gland is described in detail on page 504.


Oral cavity
527.e1
13
rEtPaHc
The failure of complete anaesthesia to the mandibular teeth follow The lingual nerve passes across the surface of the periosteum lin
ing an inferior alveolar nerve block, which is meant to anaesthetize the gually to the lower wisdom tooth, separated from the tooth only by a
nerve before its entrance into the mandibular canal, indicates that there cortical plate of bone no thicker than an eggshell. Damage to this nerve
are alternative pathways for sensory nerves to the teeth. Knowledge of results in altered sensation (paraesthesia) to the ipsilateral side of the
these alternative pathways is important in helping clinicians to obtain tongue and floor of mouth.
complete dental anaesthesia. These alternative pathways involve ana A major problem when extracting mandibular third molar teeth,
tomical variation in the distribution of the inferior alveolar nerve, the especially if they are impacted, is possible damage to the inferior alveo
buccal branch of the mandibular nerve, the mylohyoid nerve, the lar nerve. Indeed, surgical treatment may only necessitate the removal
lingual nerve, the deep temporal nerves and the cervical plexus. of the crown, leaving behind the roots (after suitable root filling). Max
The inferior alveolar nerve may give multiple branches before enter illary third molars are only rarely impacted because they erupt postero
ing the mandibular canal, one or more of which may escape anaesthesia inferiorly. A clear radiograph is required before any tooth extraction is
following inferior alveolar nerve block. They may then reenter the undertaken in order to alert the dental surgeon to any problems that
mandible via small accessory foramina in the retromolar region to may be encountered. For example, although the inferior alveolar nerve
supply sensation to the molar teeth. and its accompanying vessels generally lie beneath the roots of the third
The buccal branch of the mandibular nerve, which supplies the permanent molar in the mandibular canal, the neurovascular bundle
buccal gingivae of the molar teeth, may also possess a branch that may occupy a higher position, close to the roots, and may even run
passes through a small retromolar foramen to supply the molar teeth. between the roots. This may be evident in routine periapical or ortho


Occasionally, mandibles may present with retromolar foramina. pantomograph radiographs as a constriction or deviation of the man
Although primarily a motor nerve supplying mylohyoid and the dibular canal or as a radiolucent canal overlying the roots of the third
anterior belly of the digastric, the mylohyoid nerve carries some sensory molar (Fig. 31.37). In this situation, the inferior alveolar nerve is at risk
fibres that may enter the mandible via one or more small retromental during extraction of third molars; damage to the nerve may result in
foramina in the vicinity of the genial tubercles to supply some sensation paraesthesia in the distribution of the mental nerve, with consequent
to the anterior teeth. altered sensation or numbness in the lower lip. The root of a mandibu
Communications exist between the inferior alveolar and lingual lar premolar may occasionally be unusually long and may be in close
nerves. If the lingual nerve is not anaesthetized during an inferior alveo relationship to the mental nerve, which may then be at risk during
lar nerve block, this pathway could account for any remaining sensation extraction of this tooth.
in the teeth. Routine radiographs are no longer considered satisfactory for reveal
Although the deep temporal nerves are primarily motor, it has been ing the close relationship of the inferior alveolar nerve to the third
suggested that terminal branches may pass from the substance of tem molars; cone beam computed tomography (CBCT) is the method of
poralis to enter the mandible through foramina in the retromolar choice to show this relationship in three dimensions. CBCT is also
region to supply some sensation to molar teeth. routinely used prior to insertion of a dental implant to determine not
In the cervical plexus, the great auricular nerve, formed by the anter only the exact position of the inferior alveolar nerve and its mental
ior primary rami of the second and third cervical spinal nerves, supplies branch but also the topography of the surrounding bone, to establish
skin over the angle of the mandible (p. 442). It is possible that this whether it is suitable for receiving a dental implant.
nerve may provide a branch that penetrates the mandible to supply one
or more of the cheek teeth.
If a successful inferior alveolar nerve block does not completely


anaesthetize teeth in a jaw quadrant, additional local injections of
anaesthetic solution around the tooth in question may be necessary to
block the alternative pathways described above. In addition, there is the
possibility of overlap across the midline involving the incisive and
mylohyoid nerves. In children, there is evidence to suggest that the
lingula is variable in position and its position from the occlusion plane
increases with age. It is therefore not considered an appropriate land
mark for inferior alveolar nerve block (Ezoddini Ardakani et al 2010).
Impacted mandibular third molars In many subjects, there is a
disproportion between the size of the teeth and the size of the jaws,
such that there is insufficient space for all the teeth to erupt. As the third
mandibular molar teeth (the wisdom teeth) are the last to erupt, they
are often impeded in their eruption and either become impacted or
remain unerupted deeply within the jaw bone. If the tooth is completely
covered by bone and mucosa, it is very unlikely to cause any symptoms,
and the subject remains unaware of its presence unless the tooth is seen
on a routine dental radiograph. Very rarely, the surrounding dental fol
licle may undergo cystic degeneration, which can ‘hollow out’ the jaw,
usually the mandible, to a considerable degree. The developing cyst may
displace the tooth as it expands and the tooth may end up as far away
as the condylar neck or coronoid process.
More commonly, the erupting wisdom tooth erupts partially before
impacting against the distal aspect of the second molar. When this
occurs, symptoms are common due to recurrent soft tissue inflamma
tion and infection around the partially erupted tooth caused by food
impaction. This condition is known as pericoronitis and, if the infecting
Fig. 31.37 A radiograph indicating that the mandibular canal containing
organism is virulent, the infection may rapidly spread into the adjacent
the inferior alveolar canal and its contents (arrow) are closely related to
tissue spaces as described elsewhere. The tooth only merits surgical
the roots of the impacted permanent mandibular third molar. (With
removal if the patient suffers a severe bout or multiple bouts of peri
permission from Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral


coronitis. Surgery is not immediately indicated because it is associated
Anatomy, Histology and Embryology, 4th ed. Edinburgh, Mosby.)
with a degree of morbidity: the lingual and inferior alveolar nerves,
which are often in close proximity to the tooth, may be damaged during
its removal.


Oral cavity
527.e2
4
NOitcES
It is technically possible to achieve profound regional anaesthesia by M
depositing local anaesthetic solution adjacent to the trigeminal nerve
trunks or their branches within the infratemporal fossa. These injec
tions can either be performed transorally – posterior superior alveolar
nerve block, maxillary nerve block, inferior alveolar nerve block, lingual
nerve block and mandibular nerve block – or, more rarely, by an exter
nal route through the skin of the face – maxillary nerve block, inferior
alveolar nerve block and mandibular nerve block.
In the case of the mandible, the anterior teeth can be anaesthetized
by simple diffusion techniques, as the bone is relatively thin. However,
this is not adequate for the cheek teeth due to the increased thickness
of the bone. In this case, the inferior alveolar nerve has to be anaesthe
tized before it enters the inferior alveolar canal. The needle has to be
placed within the pterygomandibular space to achieve a successful in
ferior alveolar nerve block. The lingual nerve is also usually blocked, as
it lies close to the inferior alveolar nerve. Because of the other structures
within the infratemporal fossa, it is important for the operator to have
a detailed knowledge of the anatomy in this region in order to under
stand, and therefore try to avoid, the complications that may arise. Any
damage to blood vessels in the infratemporal fossa – generally, the
pterygoid venous plexus – can lead to haematoma formation. In
extreme cases, bleeding can track through the inferior orbital fissure,
resulting in a retrobulbar haematoma, which can lead to loss of visual
acuity or blindness. Intravascular injection of local anaesthetic solution
(which usually contains adrenaline (epinephrine)) can have profound
A
systemic effects, and for this reason an aspirating syringe is always used
to check that the needle has not entered a vessel prior to injection
M
(vessels in this area that theoretically may be entered include the maxil
lary and internal carotid arteries). If the needle is placed too medially,
it may enter medial pterygoid; if directed too laterally, it may penetrate


temporalis. In either case, there will be a lack of anaesthesia, followed
later by trismus. If the needle is placed too deeply, anaesthetic solution
may cause a temporary facial nerve palsy due to loss of conduction from
the facial nerve in the region of the parotid gland. Local anaesthetic
solution may enter the orbit via the inferior orbital fissure and give
orbital symptoms, the most likely being a temporary paralysis of the
abducens nerve with loss of activity of lateral rectus.
The root apices of the maxillary cheek teeth are close to, and may
B
even invaginate, the maxillary sinus. The permanent tooth most com
monly involved is the second molar, followed by the first molar; less
frequently, premolars and the third molar may be involved. The likeli Fig. 31.38 A, A routine orthopantomogram showing the roots of the
hood of cavitation of the maxillary sinus increases significantly after permanent maxillary molar teeth and the maxillary sinus (M). The precise
relationship of the root apices to the floor of the maxillary sinus is not
tooth extraction. During removal of fractured root apices in this region,
clear. B, Cone beam computed tomography of the same patient shown in
care must therefore be taken to ensure that the root fragment is not
A; the image in the sagittal plane clearly shows the two buccal root
pushed into the sinus. Similarly, during root canal treatment, care must
apices (arrow) of the permanent maxillary second molar tooth invaginating
be taken to ensure that any filling material is not pushed into the sinus.
into the maxillary sinus (M). (Courtesy of Dr J Davies.)
When routine radiographs fail to provide sufficient definition of the
close relationship between the floor of the maxillary sinus and root
apices, CBCT may be necessary to provide additional detail (Fig. 31.38).


Oral cavity
528
4
NOitcES
SUBMANDIBULAR SALIVARY GLAND submandibular ganglia, close to salivary parenchymal cells and blood
vessels (Tosios et al 2010). The sympathetic root is derived from the
The submandibular gland is irregular in shape and about the size of a plexus on the facial artery and consists of postganglionic fibres from
walnut. It consists of a larger superficial and a smaller deep part, con the superior cervical ganglion that traverse the submandibular ganglion
tinuous with each other around the posterior border of mylohyoid. It without synapsing. These fibres are vasomotor to the blood vessels of
is a seromucous (but predominantly serous) gland. the submandibular and sublingual glands. Sensory fibres derived from
the lingual nerve may also pass through the ganglion.
Superficial part of the submandibular gland
Submandibular duct
The superficial part of the gland is situated in the digastric triangle,
where it reaches forwards to the anterior belly of digastric and back to The submandibular duct is about 5 cm long and has a thinner wall than
the stylomandibular ligament, by which it is separated from the parotid the parotid duct. It begins from numerous tributaries in the superficial
gland. Above, it extends medial to the body of the mandible. Below, it part of the gland and emerges from the medial surface of this part of
usually overlaps the intermediate tendon of digastric and the insertion the gland behind the posterior border of mylohyoid. It traverses the
of stylohyoid. This part of the submandibular gland presents inferior, deep part of the gland, and then passes at first up and slightly back for
lateral and medial surfaces, and is partially enclosed between two layers approximately 5 mm, this sharp bend over the free edge of mylohyoid
of deep cervical fascia that extend from the greater cornu of the hyoid being known as the genu of the duct. It then runs forwards between
bone. The superficial layer is attached to the lower border of the man mylohyoid and hyoglossus, passing between the sublingual gland and


dible and covers the inferior surface of the gland. The deep layer is genioglossus to open in the floor of the mouth on the summit of the
attached to the mylohyoid line on the medial surface of the mandible sublingual papilla at the side of the frenulum of the tongue (see Figs
and covers the medial surface of the gland. 31.4, 31.10). It lies between the lingual and hypoglossal nerves on
The inferior surface, covered by skin, platysma and deep fascia, is hyoglossus but, at the anterior border of the muscle, it is crossed lat
crossed by the facial vein and the cervical branch of the facial nerve. erally by the lingual nerve, terminal branches of which ascend on its
Near the mandible, the submandibular lymph nodes are in contact with medial side. As the duct traverses the deep part of the gland, it receives
the gland and some may be embedded within it. small tributaries draining this part of the gland. It has been suggested
The lateral surface is related to the submandibular fossa on the previously that the genu of the duct predisposes to the stasis of saliva
medial surface of the body of the mandible and the mandibular attach and thereby encourages salivary stone (sialolith) formation, but this is
ment of medial pterygoid. The facial artery grooves its posterosuperior somewhat controversial and largely unproven.
part, lies at first deep to the gland and then emerges between its lateral Like the parotid gland, the duct system of the submandibular gland
surface and the mandibular attachment of the medial pterygoid to reach can be visualized by sialography (Fig. 31.40).
the lower border of the mandible.
The medial surface is related anteriorly to mylohyoid, from which it
SUBLINGUAL SALIVARY GLAND
is separated by the mylohyoid nerve and vessels and branches of the
submental vessels. More posteriorly, it is related to styloglossus, the
stylohyoid ligament and the glossopharyngeal nerve, which separate it The sublingual gland is the smallest of the main salivary glands; each


from the pharynx. In its intermediate part, the medial surface is related gland is narrow, flat, shaped like an almond, and weighs approximately
to hyoglossus, from which it is separated by styloglossus, the lingual 4 g. The sublingual gland lies on mylohyoid, and is covered by the
nerve, submandibular ganglion, hypoglossal nerve and deep lingual mucosa of the floor of the mouth, which is raised as a sublingual fold
vein (sequentially from above down). Below, the medial surface is (see Fig. 31.4). The anterior end of the contralateral sublingual gland
related to the stylohyoid muscle and the posterior belly of digastric. lies in front, and the deep part of the submandibular gland lies behind.
The mandible above the anterior part of the mylohyoid line, the sub
Deep part of the submandibular gland lingual fossa, is lateral, and genioglossus is medial, separated from the
gland by the lingual nerve and submandibular duct.
The sublingual glands are seromucous but predominantly
The deep part of the gland extends forwards to the posterior end of the
mucous.
sublingual gland. It lies between mylohyoid inferolaterally, hyoglossus
and styloglossus medially, the lingual nerve superiorly, and the Vascular supply, innervation
hypoglossal nerve and deep lingual vein inferiorly (see Figs 31.10,
and lymphatic drainage
31.39).
Vascular supply and lymphatic drainage The arterial supply is from the sublingual branch of the lingual artery
and the submental branch of the facial artery. Innervation is via the
submandibular ganglion. Lymphatic drainage is to the submental
The arteries supplying the gland are branches of the facial and lingual
nodes.
arteries. The lymph vessels drain into the deep cervical group of lymph
nodes (particularly the juguloomohyoid node), interrupted by the sub
mandibular nodes.
Innervation
The secretomotor supply to the submandibular gland is derived from
the submandibular ganglion. The vasomotor supply is derived from the
superior cervical ganglion.


Submandibular ganglion
This small, fusiform body is a peripheral parasympathetic ganglion. It
lies on the upper part of hyoglossus, superior to the deep part of the
submandibular gland and inferior to the lingual nerve, to which it is
connected by several filaments. The posterior filament is the motor,
parasympathetic root. It conveys preganglionic fibres from the superior
salivatory nucleus in the brainstem via the facial, chorda tympani and
lingual nerves to the ganglion, where they synapse. Five or six postgan
glionic secretomotor branches from the ganglion supply the sub
mandibular gland and its duct, and the sublingual and anterior lingual
glands, by travelling either through the anterior filaments that connect
the submandibular gland to the lingual nerve or along adjacent blood Fig. 31.40 A sialogram showing a normal submandibular duct (long
vessels to their targets. Neuronal cell bodies and small ganglia have arrow). Unusually, a sublingual duct is also evident (short arrow).
been described in the interlobular connective tissue stroma of human (Courtesy of Dr N Drage.)


Salivary glands
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Sublingual ducts MICROSTRUCTURE
The sublingual gland has 8–20 excretory ducts (see Fig. 31.10). Smaller Salivary glands have numerous lobes composed of smaller lobules sep
sublingual ducts open, usually separately, from the posterior part of the arated by dense connective tissue that is continuous with the capsule
gland on to the summit of the sublingual fold (a few sometimes open of the gland, and contains excretory (collecting) ducts, blood vessels,
into the submandibular duct). Small rami from the anterior part of the lymph vessels, nerve fibres and small ganglia. Each lobule has a single
gland sometimes form a major sublingual duct (Bartholin’s duct), duct, whose branches terminate at dilated secretory ‘endpieces’, which
which opens with, or near to, the orifice of the submandibular duct. are tubular or acinar in shape (Fig. 31.42). Their primary secretion is
This duct may be visualized occasionally in a submandibular sialogram modified as it flows through intercalated, striated and excretory ducts
(see Fig. 31.40). into one or more main ducts that discharge saliva into the oral cavity.
They contain a variable amount of intralobular adipose tissue; adi
Ranula pocytes are particularly numerous in the parotid gland.
The secretory endpieces of the human parotid gland are almost
exclusively serous acini (Fig. 31.43A); mucous tubules or acini are rare.
If the ducts draining any salivary gland become obstructed, the gland
In the submandibular gland, secretory units are predominantly serous
itself is at risk of developing a retention cyst where the retained secre
acini, with some mucous tubules and acini (Fig. 31.43B). Mucous
tions dilate the gland itself rather like a balloon. This phenomenon is
tubules are often associated with groups of serous cells at their blind
seen mostly in the minor salivary glands that line the lips and oral
ends, appearing as crescentshaped serous demilunes in routine histo


cavity, where it is known as a mucocele. Trauma, such as persistent lip
logical preparations. However, this appearance is a fixation artefact, as
biting, results in scarring of the overlying oral mucosa and obstruction
tissue prepared by rapid freezing methods lacks serous demilunes and
of the small drainage duct. When trauma occurs in the floor of the
the serous secretory cells align with mucous cells around a common
mouth and obstructs the drainage duct/s of the sublingual gland, the
lumen (Yamashina et al 1999). In the sublingual gland, mucous tubules
resulting retention cyst is known as a ranula. (Ranula is the Latin name
and acini predominate (Fig. 31.43C) but serous cells also occur, as acini
for a frog and is used here because the tense cystic swelling is said to
or as serous demilunes.
resemble the throat of a croaking frog.)
Serous cells are approximately pyramidal in shape. Their nuclei vary
A ranula usually presents as a large, tense, bluish swelling anteriorly
in shape and position, but are more rounded and situated less basally
in the floor of the mouth just to one side of the midline, which often
than in mucous cells. Apically, the cytoplasm is filled by proteinaceous
displaces the tongue (Fig. 31.41). Occasionally, the developing reten
secretory (zymogen) granules with high amylase activity. Additionally,
tion cyst herniates through a midline dehiscence where the two mylo
serous cells secrete kallikrein, lactoferrin and lysozyme, an antibacterial
hyoid muscles fail to meet in the midline anteriorly, and then the
enzyme whose synthesis has been localized in particular to the serous
ranula may present as a submental swelling or as a combined submen
demilunes of the submandibular and sublingual glands, and which is
tal and floorofmouth swelling, a ‘plunging’ ranula (Harrison et al
important in the defence against oral pathogens. In the human parotid
2013). The treatment for a ranula is excision of the sublingual gland


and submandibular glands, zymogen granules also show a positive
responsible.
periodic acid–Schiff staining reaction, which indicates the presence of
polysaccharides, and some texts refer to these cells as seromucous.
MINOR SALIVARY GLANDS Mucous cells are cylindrical and have flattened, basal nuclei. Their apical
cytoplasm is typically packed with large, palestaining and electron
translucent secretory droplets. The histological appearance of serous
The minor salivary glands of the mouth include the labial, buccal,
and mucous cells will vary according to the stage in the secretory cycle.
palatoglossal, palatal and lingual glands. The labial and buccal glands
contain both mucous and serous elements. The palatoglossal glands are
Ducts
mucous glands and are located around the pharyngeal isthmus. The
palatal glands are mucous glands and occur in both the soft and hard
palates. The anterior and posterior lingual glands are mainly mucous. Intercalated, striated (both intralobular) and extralobular collecting
The anterior glands are embedded within muscle near the ventral ducts lead consecutively from the secretory endpieces. The lining cells
surface of the tongue and open by means of four or five ducts near the of intercalated ducts are flat nearest the secretory endpiece but become
lingual frenulum, and the posterior glands are located in the root of cuboidal. Intercalated ducts function primarily as a conduit for saliva
the tongue. The deep posterior lingual glands are predominantly serous. but, together with the striated ducts, may also modify its content of
Serous glands (of von Ebner) occur around the circumvallate papillae; electrolytes and secrete IgA. Striated ducts are lined by a low columnar
their secretion is watery, and they probably assist in gustation by spread epithelium and are so called because their lining cells have characteristic
ing taste stimuli over the taste buds and then washing them away. basal striations. The latter are regions of highly infolded basal plasma
membrane, between which lie columns of vertically aligned mitochon
dria. The nuclei are consequently displaced by the basal striations from


a typical ductal basal position to a central or even apical location (see
Fig. 31.43). Infolding of the basal plasma membrane and local abun
dance of mitochondria are typical features of epithelial cells that actively
transport electrolytes. Here, the cells transport potassium and bicarbo
nate into saliva; they produce a hypotonic saliva by reabsorbing sodium
and chloride ions in excess of water. Striated ducts modify electrolyte
composition and secrete IgA, lysozyme and kallikrein. IgA is produced
by subepithelial plasma cells and transported transcytotically across the
epithelial barrier to be secreted, once it has been dimerized by epithelial
secretory component, into the saliva (Garrett et al 1998). This is also a
function of serous acinar cells and other secretory epithelia, notably the
lactating breast. The intralobular ductal system of the sublingual gland
is less well developed than that of the parotid and submandibular
glands.
Collecting ducts are metabolically relatively inert conduits that run
within interlobular connective tissue septa in the glands. They transport
saliva to the main duct, which opens on to the mucosal surface of the
buccal cavity. The lining epithelium of collecting ducts varies. It may be
pseudostratified columnar, stratified cuboidal or columnar in the larger
ducts, and has a distinct basal layer. It becomes a stratified squamous
epithelium near the buccal orifice.
Fig. 31.41 A ranula (arrow) in the floor of the mouth, caused by trauma
Myoepithelial cells
that damaged the floor of the mouth and the sublingual gland. (With
permission from Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral
Anatomy, Histology and Embryology. 4th ed. Edinburgh: Mosby. Courtesy Myoepithelial cells (see Fig. 31.42) are contractile cells associated with
of Dr JD Harrison.) secretory endpieces and with much of the ductal system (Ogawa 2003).


Oral cavity
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4
NOitcES
Serous demilune
(as seen in routine
histological preparations)
Serous
secretory
end-piece
Junctions between cholinergic axons
and intercalated duct cells
Junction between
striated duct cell and
cholinergic axon
Myoepithelial
cell
Complex arborization
Striated of adrenergic and
(intralobular) cholinergic axons
duct around secretory unit
accompanied by Intercalated Water or ‘end-piece’
non-myelinated ducts Salts
Neutral
postgangl aio xn oi nc N Ca l−+ W Saa ltt ser g Sl iy ac loo mpr uo cte inin ss M enu dc -o pu ies
c
s eecretory
α-amylase Sulphomucins
Peroxidase
To interlobular Immunoglobulin Proline-rich
excretory ducts proteins Adrenergic
Lysozyme nerve
Kallikrein terminals
K+
Arteriole
accompanied by
adrenergic axons
Fig. 31.42 The architecture of a generalized salivary gland. Solid black arrows indicate the direction of transport of salivary components, and the open
white arrow the direction of salivary flow. The innervation of the ducts, secretory units and arterioles is shown.
They lie between the basal lamina and the epithelial cells proper. They CONTROL OF SALIVARY GLAND ACTIVITY
extend numerous cytoplasmic processes around serous acini and are
often termed basket cells. Myoepithelial cells associated with ducts are The observed wide and rapid variation in the composition, quantity
more fusiform in shape and are aligned along the length of the duct. and rate of salivary secretion in response to various stimuli suggests an
Their cytoplasm contains abundant actin microfilaments, which elaborate control mechanism. Secretion may be continuous but at a low
mediate contraction. resting level, and may also occur spontaneously. It is mainly a response
Although stimulated by the autonomic nervous system, the precise to the drying of the oral and pharyngeal mucosae. A rapid increase can
functional role of myoepithelial cells in salivary secretion awaits clari be superimposed on the resting level, e.g. during mastication or when


fication (Garrett 1998). Functional studies clearly indicate that myoepi stimulated by the autonomic innervation. The controlled variation in
thelial activity can accelerate the initial outflow of saliva, reduce luminal the activity of the many types of salivary effector cells (serous, sero
volume, contribute to the secretory pressure, support the underlying mucous and mucous secretory cells, myoepithelial cells, epithelial cells
parenchyma, reduce backpermeation of fluid and help salivary flow to of all the ductal elements and the smooth muscle of local blood vessels)
overcome increases in peripheral resistance (although, if this is exces affects the quantity and quality of saliva. There is no clear evidence that
sive, it may lead to sialectatic damage of striated ducts, thereby increas circulating hormones evoke secretion directly at physiological levels but
ing overall permeability). they may alter the response of glandular cells to neural stimuli.
The control of salivation depends on reflex nerve impulses. The
Basal cells afferent inputs to the reflex arc pass to brainstem salivatory centres,
especially from taste and mechanoreceptors in the mouth. A variety of
other sensory modalities in and around the mouth are also involved,
A population of basal cells is present in the striated and collecting ducts
e.g. smell, for certain aspects of submandibular secretion in humans.
(Riva et al 1992). They are sparsely distributed in the striated ducts and
The afferent input is integrated centrally by the salivatory centres, which
more densely distributed in the collecting ducts, in which they form a
are themselves influenced by higher centres. The latter may provide
continuous layer as the ducts pass further towards the hilum. A small
facilitatory or inhibitory influences, which presumably explains why the
population of basal cells is found on the abluminal surface of ductal
mouth becomes dry under stress. The efferent drive to the glands passes
cells associated with both striated and collecting ducts. These cells can
via parasympathetic and sympathetic outputs from the centres. Rela
be distinguished from other parenchymal cells by a combination of
tively little is known about the connections of the preganglionic para
their morphology, their coexpression of cytokeratin 14 and the anti


sympathetic neurones in the salivatory centres, and virtually nothing is
apoptotic factor cl2, and a proliferative index of about 3%, which is
known about either the central location of the sympathetic pregangli
the highest of any cell in the region. Basal cells have been implicated
onic neurones, or the output pathways. No peripheral inhibitory mech
as potential stem cells during turnover and/or cell regeneration in sal
anisms exist in the glands (Garrett et al 1999).
ivary glands and during metaplasia, when oncocytes and sebaceous cells
The typical pattern of innervation is shown in Figure 31.42, but
may appear. However, some cell division is seen in all parenchymal cell
details vary in different glands and with age. Only the more constant
types, including myoepithelial cells, and all these cells may be involved
features are illustrated and described here. Cholinergic nerves often
in salivary gland regeneration.
accompany ducts and arborize freely around secretory endpieces, but
adrenergic nerves usually enter glands along arteries and ramify with
Lymph nodes
them. The main secretomotor nerves are predominantly unmyelinated
axons; the few myelinated axons that have been seen are presumably
Lymph nodes are situated both on the surface and within the parotid either preganglionic efferent or visceral afferent. Within the glands, the
gland, but are not found within the other salivary glands. nerve fibres intermingle, such that cholinergic and adrenergic axons


tissue spaces around the jaws
531
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endpieces but their activity is also under neural control. Adrenal aldos
terone promotes resorption of sodium and release of potassium into
saliva by striated ductal cells, as it does in kidney tubules. Myoepithelial
contraction is stimulated mainly by adrenergic innervation but there
may be an additional role for cholinergic axons.
Age changes in salivary glands
A wide range of age changes has been documented in salivary glands.
*
In neonates, acini and ducts are immature and widely separated by
abundant vascular connective tissue. After the age of 6 months, glandu
lar structure is more compact and there are numerous lymphocytic foci
(Scott 1979). Over the age of 50 years, the amount of glandular tissue
decreases and the amount of fibrous tissue, adipocytes, inflammatory
cells and oncocytes increases. An increase in duct volume has also been
described, although it may in part reflect shrinkage of acini, giving the
A appearance of ductlike forms (Scott 1986).
With such a significant loss of parenchyma (in both major and
minor glands), it might be assumed that there would be a reduction in
the amount of saliva produced in the aged population, giving rise to
the clinical condition of xerostomia (dry mouth). However, in healthy,
unmedicated individuals, this is not the case. This could be interpreted
as the result of salivary glands being able to produce more saliva than
is needed, but is more likely to be a secondary effect related to the
increased use of medication (many drugs depress salivary production
and many, such as antidepressants and antihistamines, are anticholin
* ergic). Saliva is important in the maintenance of oral health; decreased
secretion from the salivary glands results in an increased incidence in
oral conditions such as periodontal disease, dental caries and candidal
infections (‘thrush’).
TISSUE SPACES AROUND THE JAWS
The dissemination of infection in soft tissues is influenced by the
B
natural barriers presented by bone, muscle and fascia. However, the
tissue spaces around the jaws are primarily defined by muscles, princi


pally mylohyoid, buccinator, masseter, medial pterygoid, superior con
strictor and orbicularis oris (Fig. 31.44). None of these ‘spaces’ is
actually empty and they should merely be regarded as potential spaces
that are normally occupied by loose connective tissue. It is only when
inflammatory products such as hyaluronase destroy the loose connec
tive tissue that a definable space is produced.
The spaces are paired except for the submental, sublingual and
palatal spaces.
POTENTIAL TISSUE SPACES AROUND
THE LOWER JAW
The important potential tissue spaces of the lower jaw are the submen
tal, submandibular, sublingual, buccal, submasseteric, parotid, pterygo
mandibular, peritonsillar, parapharyngeal and retropharyngeal spaces
C (see Fig. 31.44) (Langdon et al 2002).
The submental and submandibular spaces are located below the
inferior border of the mandible beneath mylohyoid, in the suprahyoid
Fig. 31.43 The microstructure of the salivary glands. A, The parotid
gland. B, Mixed secretory units of the submandibular gland. C, Mucous region of the neck. The submental space lies beneath the chin in the
acini in the sublingual gland. Asterisks indicate the lumen of a striated midline, between the mylohyoid muscles and the investing layer of
duct. (Courtesy of Mr Peter Helliwell and the late Dr Joseph Mathew, deep cervical fascia. It is bounded laterally by the two anterior bellies
Department of Histopathology, Royal Cornwall Hospitals Trust, UK.) of the digastric muscles. The submental space communicates posteriorly
with the two submandibular spaces. The submandibular space is situ
ated between the anterior and posterior bellies of the digastric muscle
and communicates with the sublingual space around the posterior free
often lie in adjacent invaginations of one Schwann cell. Secretion and border of mylohyoid. The sublingual space lies in the floor of the


vasoconstriction are mediated via separate sympathetic axons. A single mouth, above the mylohyoid muscles, and is continuous across the
parasympathetic axon may, through serial en passant terminals, induce midline; it communicates with the submandibular spaces over the pos
vasodilation, secretion and myoepithelial contraction. terior free borders of the mylohyoid muscles, helped by the submandib
Secretory endpieces are usually the most densely innervated struc ular gland’s slight extension over this edge.
tures in the gland; individual cells often have both cholinergic and The remaining tissue spaces are illustrated in Figure 31.44B. The
adrenergic innervation. Secretion of water and electrolytes, which buccal space is located in the cheek, on the lateral side of buccinator.
creates the foundation for the volume of saliva secreted, is the outcome The submasseteric spaces are a series of spaces between the lateral
of a complex set of processes that is largely induced by parasympathetic surface of the ramus of the mandible and masseter; they are formed
impulses. Secretion of protein is an ongoing constitutive process wher because the fibres of masseter have multiple insertions on to most of
ever it occurs. The regulated exocytosis of prepackaged proteins, which the lateral surface of the ramus. The pterygomandibular space lies
is the principal source of protein secretion into saliva, depends on the between the medial surface of the ramus of the mandible and medial
relative levels of activity in sympathetic and parasympathetic fibres. pterygoid, and the parotid space lies behind the ramus of the mandible,
The ductal elements of salivary glands can markedly modify the in and around the parotid gland. The parapharyngeal space is bounded
composition of saliva. They are less densely innervated than secretory by the superior constrictor of the pharynx and the medial surface of


Oral cavity
532
4
NOitcES
B
Parapharyngeal space
Parotid space
A
Maxillary air sinus
Pterygomandibular space
Peritonsillar space
Submasseteric space
Buccal space
(filled with buccal pad fat)
Fornix vestibuli
Buccal tissue space Submental tissue space
Submandibular
Buccinator tissue space
C
Mylohyoid
Geniohyoid
Submandibular gland in
Digastric, anterior belly
submandibular space
Sublingual gland in
sublingual tissue space
Fig. 31.44 Potential tissue spaces around the jaws. A, A coronal section showing the sublingual and submandibular spaces in the floor of the mouth and
the possible routes for the spread of infections from periapical dental abscesses (left). B, A horizontal section through the mandibular molar region
showing the associated tissue spaces. C, An inferior view of the floor of the mouth (suprahyoid region of the neck) showing the position of the
submandibular and sublingual tissue spaces. (B and C, With permission from Berkovitz BKB, Moxham BJ 2002 Head and Neck Anatomy. London:
Martin Dunitz.)
medial pterygoid. It is restricted to the infratemporal region of the head because the labial bone is thin, abscesses generally appear as a swelling
and the suprahyoid region of the neck, and communicates with the in the labial sulcus, above the attachment of mentalis. The abscess may
retropharyngeal space, which itself extends into the retrovisceral space open below mentalis, when it will point beneath the chin. If an abscess
in the lower part of the neck (the tissue spaces of the neck are described from a lower postcanine tooth opens below the attachment of buccin
on p. 446, and those of the pharynx on p. 578). The peritonsillar space ator, the swelling is in the face; if it opens above, the swelling is in the
lies around the palatine tonsil between the pillars of the fauces, and is buccal sulcus of the mouth. If an abscess opens lingually above mylo


part of the intrapharyngeal space. It is bounded by the medial surface hyoid, the swelling is in the lingual sulcus; if it is below, the swelling
of the superior constrictor of the pharynx and its mucosa. is in the neck. Third molar abscesses tend to track into the neck rather
than the mouth because mylohyoid ascends posteriorly and the termi
nation of its attachment is variable, sometimes terminating before the
POTENTIAL TISSUE SPACES AROUND position of the third molar and thereby allowing relatively unhindered
THE UPPER JAW access into the tissue spaces of the neck.
Apart from canine teeth, which have long roots, abscesses on upper
The tissue spaces of the upper jaw are usually associated with spread of teeth usually open buccally below, rather than above, the attachment
infection from the teeth. They are the canine (infraorbital), palatal and of buccinator. Because its root apex is occasionally curved towards the
infratemporal spaces. The canine (infraorbital) space associated with palate, abscesses of the upper lateral incisors may track into the palatal
the canine fossa lies between levator labii superioris and the zygomati submucosa. Abscesses of upper canines often open facially just below
cus muscles. The palatal space is not truly a tissue space in the hard the orbit. Here, the swelling may obstruct drainage in the angular part
palate, since the mucosa there is firmly bound to the periosteum. of the facial vein, which has no valves, and it is therefore possible for
However, inflammation can strip away some of this periosteum to infected material to travel via the angular and ophthalmic veins into
produce a wellcircumscribed abscess. The infratemporal space is the the cavernous sinus, potentially causing a cavernous sinus thrombosis.
upper extremity of the pterygomandibular space. It is closely related to Abscesses on the palatal roots of upper molars usually open on the
the maxillary tuberosity and therefore the upper molars. palate. Upper second premolars and first and second molars are related
to the maxillary sinus. When this is large, the root apices of these teeth
may be separated from its cavity solely by the lining mucosa. Sinus


DENTAL ABSCESS infections may stimulate the nerves entering the teeth, simulating
toothache in the ipsilateral premolars and molars; this phenomenon is
Abscesses developing in relation to the apices of roots ultimately pen known as referred pain. Upper first premolars and third molars may be
etrate the surrounding bone where it is thinnest. The position of the closely related to the maxillary sinus.
resultant swelling in the soft tissues is largely determined by the rela With loss of teeth, alveolar bone is extensively resorbed. Thus, in the
tionship between muscle attachments and the sinus (the path taken by edentulous mandible, the mental nerve, originally inferior to premolar
the infected material) in the bone. Thus, in the lower incisor region, roots, may lie near the crest of the bone. In the edentulous maxilla, the


533
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Key references
sinus may enlarge to approach the oral surface of the bone. Both of and may need surgical removal before satisfactory dentures can be
these facts are of importance when planning surgery in this area. fitted.
Occasional bony prominences, termed the torus mandibularis, torus Severe systemic infections during the time the teeth are developing
maxillaris and torus palatinus, may lie lingual to the lower premolars may lead to faults in enamel, which are visible as horizontal lines
or molars, or the upper molars. They lie in the midline of the palate (cf. Harris’s growth lines).
Bonus e-book images
Fig. 31.11 A, B, Entire nerve maps of an Fig. 31.24 Two supernumerary teeth related to the roots of the impacted
adult human tongue, Sihler’s stain. overlying the permanent central incisors. permanent mandibular third molar.
Fig. 31.15 The primary dentition. Fig. 31.25 A child with mixed dentition Fig. 31.38 A, A routine orthopantomogram
showing hypodontia and microdontia (small showing the roots of the permanent
Fig. 31.23 An orthopantomogram showing conical-shaped teeth). maxillary molars, molar teeth and the
supernumerary teeth in the upper incisor maxillary sinus. B, Cone beam computed
region preventing the exfoliation of the Fig. 31.37 A radiograph indicating that the tomography of the same patient.
upper primary central incisors and impeding mandibular canal containing the inferior
the eruption of the upper permanent central alveolar canal and its contents are closely
incisors.
KEY REFERENCES
Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral Anatomy, Histology and A chapter that describes the tissue spaces in the floor of the mouth and how
Embryology, 4th ed. Edinburgh: Mosby. they become involved in the spread of infection.
A textbook that describes in detail the gross morphology, histology and
Reid DJ, Dean CM 2006 Variation in modern human enamel formation
development of human teeth.
times. J Hum Evol 50:329–46.


Garrett JR 1998 Myoepithelial activity in salivary glands. In: Garrett JR, A paper that describes variations in the formation times of modern teeth
Ekström J, Anderson LC (eds) Glandular Mechanisms of Salivary Secre from two populations (South Africa and Northern Europe) using
tion. Frontiers in Oral Biology, vol. 10. Basel: Karger, pp. 132–52. incremental lines in enamel.
A paper that discusses the activity of myoepithelial cells in the secretory
Renton T 2011 Minimising and managing iatrogenous trigeminal nerve
process.
injuries in relation to dental procedures. In: Birch R Surgical Disorders
Garrett JR, Ekström J, Anderson LC (eds) 1999 Neural Mechanisms of Sal of the Peripheral Nerves. Berlin: Springer. Ch. 11, pp. 501–25.
ivary Secretion. Frontiers of Oral Biology, vol. 11. Basel: Karger. A chapter that describes surgical techniques for avoiding damage to
A book that contains much basic information concerning the role of nerves branches of the mandibular nerve during tooth extraction.
in the secretory process of salivary glands.
Scott J 1986 Structure and function in aging human salivary glands. Geron
Harrison JD, Kim A, AlAli S et al 2013 Postmortem investigation of mylo tology 5:149–58.
hyoid hiatus and hernia: aetiological factors of plunging ranula. Clin A paper that gives quantitative information on changes that occur in the
Anat 26:693–9. parenchyma of the major salivary glands with age, and discusses the results
A paper that describes the anatomy of the mylohyoid muscle in relation to in terms of xerostomia.
the aetiology of ranulas.
Yamashina S, Tamaki H, Katsumata O 1999 The serous demilune of the rat
Langdon J, Berkovitz BKB, Moxham BJ 2002 Infection and the infratemporal sublingual gland is an artificial structure produced by conventional fix
fossa and associated tissue spaces. In: Langdon J, Berkovitz BKB, ation. Arch Histol Cytol 62:347–54.


Moxham BJ (eds) Surgical Anatomy of the Infratemporal Fossa. London: A paper that describes the steps needed to avoid fixation artefacts when
M. Dunitz, pp. 77–99. studying the histological appearance of salivary glands.


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rEtPaHc
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A textbook that describes in detail the gross morphology, histology and National Institute for Health and Clinical Excellence 2005 Division of anky
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(eds) Development, Function and Evolution of Teeth. Cambridge: Cam 383–408.
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Ezoddini Ardakani F, Bahrololoumi Z, Zangouie Booshehri M et al 2010 The times. J Hum Evol 50:329–46.
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Garrett JR 1998 Myoepithelial activity in salivary glands. In: Garrett JR, branches of the mandibular nerve during tooth extraction.
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A paper that discusses the activity of myoepithelial cells in the secretory 55:Suppl:115–24.
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Garrett JR, Ekström J, Anderson LC (eds) 1999 Neural Mechanisms of Sali Schroeder HE, Listgarten MA 1997 The gingival tissues: the architecture of
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A book that contains much basic information concerning the role of nerves Scott J 1979 Qualitative and quantitative changes in the histology of the
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overview of the literature. ISRN Pediatr 2013:956269.


CHAPTER Infratemporal and pterygopalatine fossae
32
and temporomandibular joint
inferior alveolar nerves emerge below its inferior border, and the deep
INFRATEMPORAL FOSSA
temporal nerves and vessels emerge from its upper border. A venous
network, the pterygoid venous plexus, lies around and within lateral
The infratemporal fossa lies deep to the ramus of the mandible. It com- pterygoid and is important in the spread of infection.
municates with the temporal fossa superiorly deep to the zygomatic
arch, the orbit anteriorly through the inferior orbital fissure, and the
BONES
pterygopalatine fossa medially through the pterygomaxillary fissure. It
also communicates with the middle fossa through the foramina ovale
and spinosum. The major structures that occupy the infratemporal fossa The sphenoid bone, the paired maxillae and temporal bones, the pala-
are the lateral and medial pterygoid muscles, the mandibular division tine bones and the mandible collectively provide the skeletal framework
of the trigeminal nerve, the chorda tympani branch of the facial nerve, to the infratemporal and pterygopalatine regions. The mandible and the
the otic parasympathetic ganglion, the maxillary artery and the ptery- two temporal bones articulate at the right and left temporo mandibular
goid venous plexus. joints. The disarticulated maxilla and palatine bone are described on
The infratemporal fossa has a roof and anterior, lateral and medial pages 484 and 486, respectively the temporal bone is described on page
walls, and is open to the neck posteroinferiorly, i.e. it has no anatomical 624, and the sphenoid and mandible are described here.
floor. Approximately 80% of the roof is formed by the infratemporal
surface of the greater wing of the sphenoid. The remainder is formed Sphenoid bone
by the infratemporal surface of the temporal bone, ending at the articu-
lar eminence of the temporomandibular joint and the spine of the The sphenoid bone lies in the base of the skull between the frontal,


sphenoid on the deep medial aspect. It contains the foramina ovale and temporal and occipital bones. It has a central body, paired greater and
spinosum. The anterior wall is formed by the posterior surface of the lesser wings that spread laterally from the body, and two pterygoid
maxilla, ending inferiorly at the maxillary tuberosity. The inferior processes that descend from the junction of the body and greater wings
orbital fissure forms the upper limit of the anterior wall, meeting the (Fig. 32.3).
pterygomaxillary fissure at right angles. The medial wall is formed
Body
anteriorly by the lateral pterygoid plate of the pterygoid process of the
sphenoid, and more posteromedially by the pharynx and tensor and The body of the sphenoid is cuboidal. It contains two air sinuses, sepa-
levator veli palatini. It contains the pterygomaxillary fissure, across rated by a septum. Its cerebral (superior) surface articulates in front
which structures pass between the infratemporal and pterygopalatine with the cribriform plate of the ethmoid bone. Anteriorly lies the
fossae (Fig. 32.1). The lateral wall is formed by the medial surface of smooth jugum sphenoidale, which is related to the gyri recti and olfac-
the ramus of the mandible. tory tracts. The jugum is bounded behind by the anterior border of the
Lateral pterygoid provides a key to understanding the relationships sulcus chiasmaticus, which leads laterally to the optic canals. Posteri-
of structures within the infratemporal fossa. This muscle lies in the roof orly lies the tuberculum sellae, behind which is the deeply concave
of the fossa and runs anteroposteriorly in a more or less horizontal sella turcica. In life, the sella contains the hypophysis cerebri in the
plane from the region of the pterygoid plates to the mandibular condyle hypophysial fossa. Its anterior edge is completed laterally by two
(see Fig. 32.1). Branches of the mandibular nerve and the main origin middle clinoid processes, while posteriorly the sella turcica is bounded


of medial pterygoid are deep relations and the maxillary artery is super- by a square dorsum sellae, the superior angles of which bear variable
ficial. The buccal branch of the mandibular nerve passes between the pos terior clinoid processes. The diaphragma sella and the tentorium
two heads of lateral pterygoid. Medial pterygoid and the lingual and cerebelli are attached to the clinoid processes. On each side, below the
A Zygomatic bone Sphenoid bone B Inferior orbital fissure C
Pterygopalatine fossa Sphenopalatine foramen
Temporal fossa
Palatovaginal
canal
Foramen
Palatine bone rotundum
Pterygoid canal
Maxilla Greater
palatine canal
Infratemporal
fossa
Alveolar foramen
Maxilla Palatine bone
Sphenoid Zygomatic bone
Fig. 32.1 A, The pterygopalatine fossa after detachment of the mandible and removal of the zygomatic arch. B, Anteromedial view. C, Lateral view;
the arrows show that the floor of the temporal fossa is open medially to the infratemporal fossa and laterally to the region containing the masseter.
534 (With permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright 2010.)


Infratemporal and pterygopalatine fossae and temporomandibular joint
534.e1
23
RETPAHC
There is a lack of consensus in the surgical literature with regard to
both the boundaries and contents of the infratemporal fossa. Thus, the
fossa is sometimes defined as the anatomical space beneath the floor
of the middle fossa, incorporating the remainder of the subcranial
temporal bone as part of the roof, with the exception of the glenoid
fossa of the temporomandibular joint. In this description, the fossa is
limited posteriorly by the prevertebral fascia and includes the internal
carotid artery, the internal jugular vein, the lower cranial nerves, the
cervical sympathetic trunk, and the styloid process with its attached
muscles and ligaments. Alternatively, the ‘extended’ infratemporal fossa
is said to consist of the parapharyngeal and masticator spaces
(Fig. 32.2) (Falcon et al 2010, Hosseini et al 2012, Bejjani et al 1998,
Joo et al 2013).
Foramen ovale Lateral and medial
pterygoid plates
TMJ (Mandibular fossa)
Fig. 32.2 The ‘extended’ infratemporal fossa. The boundaries of the
infratemporal fossa are delineated by the dotted line. Note that the lateral
pterygoid plate and pharyngotympanic tube constitute the medial wall of
the fossa, and that the temporomandibular joint (TMJ) forms part of its
lateral wall. The carotid and jugular foramina lie in the posterior part of
this extended infratemporal fossa. (Adapted with permission from
Berkovitz BKB, Moxham BJ, Telling D 1994 Color Atlas of the Skull,
London, Mosby and Hosseini SMS, Razfar A, Carrau RL, et al. Endonasal
transpterygoid approach to the infratemporal fossa: correlation of
endoscopic and multiplanar CT anatomy. Head and Neck.
2012;34:313−320.)


Infratemporal fossa
535
23
RETPAHC
Sphenoidal sinus
A
Lesser wing Body Superior orbital fissure
Greater wing
Infratemporal crest
Sphenoidal concha
Foramen rotundum
Spine
Pterygoid canal
Lateral pterygoid plate
Pterygoid process
Medial pterygoid plate Pterygoid hamulus
Carotid sulcus Dorsum sellae Posterior clinoid process
B Foramen rotundum Anterior clinoid process
Lesser wing
Groove for middle
meningeal artery
Superior orbital fissure Lingula
Groove for auditory tube
Spine
Body
Scaphoid fossa
Pterygoid canal Rostrum
Lateral pterygoid plate
Vaginal process
Medial pterygoid plate Pterygoid fossa
Pterygoid hamulus
Jugum sphenoidale Tuberculum sellae
C Anterior clinoid process
Lesser wing
Optic canal
Foramen rotundum
Superior orbital fissure
Greater wing Middle clinoid process
Sella turcica
Maxillary nerve
Internal carotid artery Foramen ovale
Foramen spinosum
Greater petrosal nerve
Carotid sulcus
Cartilage in the foramen lacerum
Occipital bone
Posterior clinoid process
Fig. 32.3 The sphenoid bone. A, Anterior view. B, Posterior view. C, Superior view. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of
Human Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.)
dorsum sellae, a small petrosal process articulates with the apex of The lateral surfaces of the body are united with the greater wings
the petrous part of the temporal bone. The body of the sphenoid and the medial pterygoid plates. A broad carotid sulcus accommodates
slopes directly into the basilar part of the occipital bone posterior both the internal carotid artery and the cranial nerves associated with
to the dorsum sellae; together these bones form the clivus. In the the cavernous sinus above the root of each wing. The sulcus is deepest


growing child, this is the site of the spheno-occipital synchondrosis; posteriorly. It is overhung medially by the petrosal part of the temporal
premature closure of this joint gives rise to the skull appearances seen bone and has a sharp lateral margin, the lingula, which continues back
in achondroplasia. over the posterior opening of the pterygoid canal.


InfRATEmPoRAl And PTERygoPAlATInE fossAE And TEmPoRomAndIbulAR joInT
536
4
noITCEs
A median triangular, bilaminar sphenoidal crest on the anterior bone preferentially pass through this articulation with the greater wing
surface of the body of the sphenoid makes a small contribution to the because it is a line of weakness in the lateral orbit.
nasal septum. The anterior border of the crest joins the perpendicular
Lesser wings
plate of the ethmoid bone, and a sphenoidal sinus opens on each side
of it. In the articulated state, the sphenoidal sinuses are closed anter- The lesser wings of the sphenoid are triangular pointed plates that
oinferiorly by the sphenoidal conchae, which are largely destroyed protrude laterally from the anterosuperior regions of the body. The
when disarticulating a skull. Each half of the anterior surface of the superior surface of each wing is smooth and related to the frontal lobe
body of the sphenoid possesses a superolateral depressed area joined of the cerebral hemisphere. The inferior surface is a posterior part of
to the ethmoidal labyrinth that completes the posterior ethmoidal the orbital roof and upper boundary of the superior orbital fissure, and
sinuses; a lateral margin that articulates with the orbital plate of the overhangs the middle cranial fossa. The posterior border projects into
ethmoid above and the orbital process of the palatine bone below; and the lateral fissure of the cerebral hemisphere. The medial end of the
an inferomedial, smooth, triangular area, which forms the posterior lesser wing forms the anterior clinoid process. The anterior and middle
nasal roof, and near whose superior angle lies the orifice of a sphenoi- clinoid processes are sometimes united to form a caroticoclinoid
dal sinus. foramen. The lesser wing is connected to the body by a thin, flat anterior
The inferior surface of the body of the sphenoid bears a median root and a thick, triangular posterior root (the optic strut), between
triangular sphenoidal rostrum, embraced above by the diverging lower which lies the optic canal. The optic strut extends from the base of the


margins of the sphenoidal crest. The narrow anterior end of the rostrum anterior clinoid process to the body and separates the optic canal from
fits into a fissure between the anterior parts of the alae of the vomer, the superior orbital fissure. The optic canal is bounded by the body of
and the posterior ends of the sphenoidal conchae flank the rostrum, the sphenoid medially, the lesser wing superiorly, and the optic strut
articulating with its alae. A thin vaginal process projects medially from inferiorly and laterally.
the base of the medial pterygoid plate on each side of the posterior part
Superior orbital fissure
of the rostrum, behind the apex of the sphenoidal concha.
The superior orbital fissure connects the cranial cavity with the orbit. It
Greater wings is bounded medially by the body of the sphenoid, above by the lesser
The greater wings of the sphenoid curve broadly superolaterally from wing of the sphenoid, below by the medial margin of the orbital surface
the body. Posteriorly, each is triangular, fitting the angle between the of the greater wing, and laterally, between the greater and lesser wings,
petrous and squamous parts of the temporal bone at a sphenosqua- by the frontal bone. The contents of the superior orbital fissure are
mosal suture. The cerebral surface contributes to the anterior part of the described on p. 667 (see Fig. 41.4).
middle cranial fossa. Deeply concave, its undulating surface is adapted
Pterygoid processes
to the anterior gyri of the temporal lobe of the cerebral hemisphere.
The foramen rotundum lies anteromedially and transmits the maxillary The pterygoid processes descend perpendicularly from the junctions of
nerve. Posterolateral to the foramen rotundum is the foramen ovale, the greater wings and body. Each consists of a medial and lateral plate,
which transmits the mandibular nerve, accessory meningeal artery and whose upper parts are fused anteriorly. The plates are separated below
sometimes the lesser petrosal nerve, although the latter nerve may have by the angular pterygoid fissure, whose margins articulate with the


its own canaliculus innominatus medial to the foramen spinosum. A pyramidal process of the palatine bone, and diverge behind. Medial
small emissary sphenoidal foramen (foramen of Vesalius), which trans- pterygoid lies in the cuneiform pterygoid fossa between the plates.
mits a small vein from the cavernous sinus, sometimes lies medial to Above is the small, oval, shallow scaphoid fossa, which is formed by
the foramen ovale (on one or both sides). The foramen spinosum, division of the upper posterior border of the medial plate. Part of tensor
which transmits the middle meningeal artery and meningeal branch of veli palatini is attached to the fossa. The anterior surface of the root of
the mandibular nerve, lies behind the foramen ovale. the pterygoid process is broad and triangular, and forms the posterior
The lateral surface is vertically convex and divided by a transverse wall of the pterygopalatine fossa; it is pierced by the anterior opening
infratemporal crest into temporal (upper) and infratemporal (lower) of the pterygoid canal.
surfaces. Temporalis is attached to the temporal surface. The infratem-
poral surface is directed downwards and, with the infratemporal crest, lateral pterygoid plate
is the site of attachment of the upper fibres of lateral pterygoid. It con- The lateral pterygoid plate is broad, thin and everted. The lateral surface
tains the foramen ovale and foramen spinosum. The small downward- forms part of the medial wall of the infratemporal fossa; the lower part
projecting spine of the sphenoid lies posterior to the foramen spinosum; of lateral pterygoid is attached to it. The medial surface is the lateral
the sphenomandibular ligament is attached to its tip. The medial side wall of the pterygoid fossa; most of the deep head of medial pterygoid
of the spine bears a faint anteroinferior groove for the chorda tympani is attached to it. The upper part of its anterior border is a posterior


nerve and appears in the lateral wall of the sulcus for the pharyngotym- boundary of the pterygomaxillary fissure, and the lower part articulates
panic (auditory) tube. Medial to the anterior end of the infratemporal with the palatine bone. The posterior border is free.
crest, a ridge passes downwards to the front of the lateral pterygoid
plate, thereby forming a posterior boundary of the pterygomaxillary medial pterygoid plate
fissure. The medial pterygoid plate is narrower and longer than the lateral. Its
The quadrilateral orbital surface of the greater wing faces antero- lower end is continued into an unciform projection, the pterygoid
medially and forms the posterior part of the lateral wall of the orbit. It hamulus, which curves laterally. The pterygomandibular raphe is
has a serrated upper edge, which articulates with the orbital plate of the attached to the hamulus, and the tendon of tensor veli palatini winds
frontal bone, and a serrated lateral margin, which articulates with the around the hamulus. The lateral surface forms the medial wall of the
zygomatic bone. Its smooth inferior border is the posterolateral edge pterygoid fossa and the medial surface provides a lateral boundary of
of the inferior orbital fissure, and its sharp medial margin forms the the posterior nasal aperture. The medial plate is prolonged above on
inferolateral edge of the superior orbital fissure, on which a small the inferior aspect of the body of the sphenoid as a thin vaginal process
tubercle gives partial attachment to the common anular ocular tendon. that articulates anteriorly with the sphenoidal process of the palatine
Below the medial end of the superior orbital fissure, a grooved area bone and medially with the ala of the vomer. The plate articulates with
forms the posterior wall of the pterygopalatine fossa; the latter is pierced the posterior border of the perpendicular plate of the palatine bone in
by the foramen rotundum. the lower part of its anterior margin. Inferiorly, it bears a furrow, which
The irregular margin of the greater wing, from the body of the sphen- is converted anteriorly into the palatovaginal canal by the sphenoidal


oid to the spine, is an anterior limit of the medial half of the foramen process of the palatine bone. The palatovaginal canal transmits pharyn-
lacerum. It also displays the posterior aperture of the pterygoid canal. geal branches of the maxillary artery and pterygopalatine ganglion. The
Its lateral half articulates with the petrous part of the temporal bone at pharyngobasilar fascia is attached to the whole of the posterior margin
a sphenopetrosal synchondrosis. Inferior to this, the sulcus tubae con- of the medial plate, and the superior pharyngeal constrictor is attached
tains the cartilaginous pharyngotympanic (auditory) tube. Anterior to to its lower end. The small pterygoid tubercle is found at the upper end
the spine of the sphenoid the concave squamosal margin is serrated – of the plate, just below the posterior opening of the pterygoid canal.
bevelled internally below, externally above – for articulation with the The processus tubarius, which supports the cartilaginous pharyngeal
squamous part of the temporal bone. The tip of the greater wing, bevel- end of the pharyngotympanic tube, projects back near the midpoint of
led internally, articulates with the sphenoidal angle of the parietal bone the margin of the medial pterygoid plate.
at the pterion. Medial to this, a triangular rough area articulates with Though adjacent, the medial and lateral pterygoid plates have dis-
the frontal bone; its medial angle is continuous with the inferior tinct roles. The lateral plate is the province of the infratemporal fossa
boundary of the superior orbital fissure, and its anterior angle joins the and masticator space, forming part of the medial boundary of the
zygomatic bone by a serrated articulation. Fractures of the zygomatic infratemporal fossa and providing origin to the lateral and medial


Infratemporal fossa
537
23
RETPAHC
pterygoids. The medial plate is functionally related to the pharynx, Although the sphenoidal sinus can be identified in the fourth month
providing attachment for the pharyngobasilar fascia, superior constric- of fetal life as an evagination of the posterior part of the nasal capsule,
tor and pterygomandibular raphe. by birth it represents an outgrowth of the spheno-ethmoidal recess.
Pneumatization of the body of the sphenoid commences at around 7
Midface fractures Midface fractures at Le Fort I, II and III levels months of age and a distinct cell is visible by the age of 2 years. Pneu-
invariably involve the pterygoid plates; displacement of the outlines of matization spreads first into the presphenoid and later invades the
these bones radiographically confirms the diagnosis. postsphenoid part. The sinus reaches full size in adolescence, but often
enlarges further by absorption of its walls as age advances.
Sphenoidal conchae
Certain parts of the sphenoid are connected by ligaments that may
The sphenoidal conchae are two thin, curved small plates, attached occasionally ossify, e.g. the pterygospinous ligament between the
anteroinferiorly to the body of the sphenoid bone. The superior concave sphenoidal spine and the upper part of the lateral pterygoid plate; the
surface of each forms the anterior wall and part of the floor of a interclinoid ligament joining the anterior to the posterior clinoid
sphenoidal sinus. In situ, each has vertical quadrilateral anterior and process; and the caroticoclinoid ligament that connects the anterior to
horizontal triangular posterior parts. The anterior part consists of a the middle clinoid process.
superolateral depressed area, which completes the posterior ethmoidal Premature synostosis of the junction between pre- and postsphenoi-
sinuses and joins below with the orbital process of a palatine bone, and dal parts, or of the spheno-occipital suture, produces a characteristic
a smooth and triangular inferomedial area, which forms part of the appearance, obvious in profile, of an abnormal depression of the nasal
nasal roof and is perforated above by the round opening connecting bridge.


the sphenoidal sinus and spheno-ethmoidal recess.
Anterior parts of the two bones meet in the midline, and protrude
Stylohamular plane
as the sphenoidal crest. The horizontal part appears in the nasal roof
and completes the sphenopalatine foramen. Its medial edge articulates
Available with the Gray’s Anatomy e-book
with the rostrum of the sphenoid and the ala of the vomer. Its apex,
directed posteriorly, is superomedial to the vaginal process of the
medial pterygoid plate and joins the posterior part of the ala. A small Mandible
conchal part sometimes appears in the medial wall of the orbit, lying
between the orbital plate of the ethmoid in front, the orbital process The mandible is the largest, strongest and lowest bone in the face. It
of the palatine bone below and the frontal bone above. has a horizontally curved body that is convex forwards, and two broad
Ossification rami that ascend posteriorly (Fig. 32.5). The body of the mandible
supports the mandibular teeth within the alveolar process. The rami
Until the seventh or eighth month in utero, the sphenoid body has a
bear the coronoid and condylar processes. Each condyle articulates with
presphenoidal part, anterior to the tuberculum sellae, with which the
the adjacent temporal bone at the temporomandibular joint.
lesser wings are continuous, and a postsphenoidal part, consisting of
the sella turcica and dorsum sellae, and integral with the greater wings Body
and pterygoid processes. Much of the bone is preformed in cartilage.
The body is somewhat U-shaped. It has external and internal surfaces
There are six ossification centres for the presphenoidal parts and eight
separated by upper and lower borders. Anteriorly, the upper external
for the postsphenoidal parts.
surface shows an inconstant faint median ridge indicating the site of
Presphenoidal part the fused symphysis menti. Inferiorly, this ridge divides to enclose a
At about the ninth week of fetal life, a centre appears in each wing, triangular mental protuberance; its base is centrally depressed but raised


lateral to the optic canal, and a little later two bilateral centres appear on each side as a mental tubercle. The mental protuberance and mental
in the presphenoidal body. Each sphenoidal concha has a centre, tubercles constitute the chin. The mental foramen, from which the
appearing superoposteriorly in the nasal capsule in the fifth month in mental neurovascular bundle emerges, lies below either the interval
utero. As this enlarges, it partly surrounds a posterosuperior expansion between the premolar teeth, or the second premolar tooth, midway
of the nasal cavity, which becomes the sphenoidal sinus. The pos- between the upper and lower borders of the body. The posterior border
terior conchal wall is absorbed and the sinus invades the presphenoi- of the foramen is smooth and accommodates the nerve as it emerges
dal component. In the fourth year, the concha fuses with the posterolaterally. A faint external oblique line ascends backwards from
ethmoidal labyrinth and, before puberty, it fuses with the sphenoid each mental tubercle, and sweeps below the mental foramen; it becomes
and palatine bones. Its anterior deficiency persists as an opening for more marked as it continues into the anterior border of the ramus.
the sphenoidal sinus. The lower border of the body, the base, extends posterolaterally from
the mandibular symphysis into the lower border of the ramus behind
Postsphenoidal part the third molar tooth. Near the midline on each side, there is a rough
The first centres appear in the greater wings at about the eighth week digastric fossa, which gives attachment to the anterior belly of digastric.
of fetal life, one in the basal cartilage of each wing below the foramen Behind the fossa, the base is thick and rounded: it has a slight antero-
rotundum. These centres only contribute to the root of the greater wing posterior convexity that changes to a gentle concavity as the ramus is
(near the foramen rotundum and pterygoid canal). The remainder of approached, and so the base has an overall sinuous profile.
the greater wing and the lateral pterygoid plate are ossified in mesen- The upper border, the alveolar part, contains 16 alveoli for the roots


chyme. At about the fourth month of fetal life, two centres appear, of the lower teeth. It consists of buccal and lingual plates of bone joined
flanking the sella turcica, and soon fuse. The medial pterygoid plates by interdental and inter-radicular septa. Near the second and third
are also ossified in ‘membrane’, a centre in each probably appearing in molar teeth, the external oblique line is superimposed on the buccal
about the ninth or tenth week. The hamulus is chondrified during the plate. As in the maxilla, the form and depth of the tooth sockets is
third fetal month and at once begins to ossify. Medial and lateral ptery- related to the morphology of the roots of the mandibular teeth. The
goid plates join at about the sixth fetal month. During the fourth sockets of the incisor, canine and premolar teeth usually contain a
month, a centre appears for each lingula, soon joining the body. single root, while those for the three molar teeth each contain two or
The optic canal in the neonate is relatively large and has a keyhole or three roots. The third molar is variable in its position and root presen-
‘figure of eight’ shape rather than the circular profile seen in the adult tation. It may be impacted vertically, horizontally, mesially or distally,
(Lang 2001). and its roots may be bulbous, hooked, divergent or convergent, and
occasionally embrace the mandibular (inferior dental) canal. The inter-
Postnatal details nal surface of the mandible is divided by an oblique mylo hyoid line
Presphenoidal and postsphenoidal parts fuse at about the eighth month that gives attachment to mylohyoid (and, above its posterior end, to
in utero but an unciform cartilage persists after birth in lower parts of the superior pharyngeal constrictor, some retromolar fascicles of buc-
the junction. At birth, the bone is tripartite and consists of a central part cinator, and the pterygomandibular raphe behind the third molar). The
(body and lesser wings) and two lateral parts (each consisting of a mylohyoid line extends from a point approximately 1 cm from the