of the maxillary division of the trigeminal nerve, via the zygomatico
is also associated with phonation and ventilation.
facial and infraorbital nerves, and by the buccal branch of the mandibu
lar division of the trigeminal nerve.
CHEEKS
LIPS
The external features of the cheeks are described on page 475. Internally,
the mucosa of the cheek is tightly adherent to buccinator and is thus The external features of the lips are described on page 475. The central
stretched when the mouth is opened and wrinkled when closed. Ectopic part of the lips contains orbicularis oris. Internally, the labial mucosa
sebaceous glands may be evident as yellow patches (Fordyce spots). is smooth and shiny, and shows small elevations caused by underlying
Their numbers increase in puberty and in later life. mucous glands.
Medial pterygoid Pterygomandibular raphe
Pterygoid hamulus
Torus tubarius Tensor veli palatini Hard palate Orbicularis oris
Pharyngeal tonsil
Levator veli palatini
Buccinator
Lateral pterygoid
Mylohyoid
Apical ligament of dens
Sphenomandibular ligament
Anterior atlanto-occipital membrane Sublingual papilla
Median atlanto-axial joint
Genioglossus
Styloid process
Orbicularis oris
Ramus of mandible
Styloglossus Sublingual gland
Digastric, intermediate tendon
Stylopharyngeus
Hyoid bone, lesser cornu
Stylohyoid ligament
Mandible
Longus capitis
Mylohyoid
Stylohyoid
Stylomandibular ligament Geniohyoid
Hyoid bone, body
Hyoid bone, greater cornu
Hyoglossus
Fig. 31.1 The oral cavity. The tongue and soft palate have been removed. (With permission from Waschke J, Paulsen F (eds), Sobotta Atlas of Human
Anatomy, 15th ed, Elsevier, Urban & Fischer. Copyright 2013.) 507


Oral cavity
508
4
NOitcES
The position and activity of the lips are important in controlling LINING MUCOSA
the degree of protrusion of the incisors. With normal (competent) lips,
the tips of the maxillary incisors lie below the upper border of the The lining mucosa is red in colour, and covers the soft palate, ventral
lower lip, and this arrangement helps to maintain the ‘normal’ inclina surface of the tongue, floor of the mouth, alveolar processes excluding
tion of the incisors. When the lips are incompetent, the maxillary inci the gingivae, and the internal surfaces of the lips and cheeks. It has a
sors may not be so controlled and the lower lip may even lie behind nonkeratinized stratified squamous epithelium, which overlies a
them, thus producing an exaggerated proclination of these teeth. A loosely fibrous lamina propria, and the submucosa contains some fat
tight, or overactive, lip musculature may be associated with retroclined deposits and collections of minor mucous salivary glands. The oral
maxillary incisors. The lips are kept moist both by tongue deposition mucosa covering the alveolar bone – which supports the roots of the
of saliva and by numerous minor salivary glands within them. These teeth – and the necks (cervical region) of the teeth is divided into two
glands are liable to trauma by the teeth, particularly in the lower lip; main components. That portion lining the lower part of the alveolus is
this can produce a mucocele as a result of either extravasation of saliva loosely attached to the periosteum via a diffuse submucosa and is
into the submucosal tissues or retention of saliva within the gland or termed the alveolar mucosa. It is delineated from the masticatory gin
its duct. gival mucosa, which covers the upper part of the alveolar bone and the
necks of the teeth, by a welldefined junction, the mucogingival junc
Vascular supply and innervation tion. The alveolar mucosa appears dark red; the gingival appears pale
pink (see Fig. 31.2). These colour differences relate to differences in the


The lips are mainly supplied by the superior and inferior labial branches type of keratinization and the proximity to the surface of underlying
of the facial artery. The upper lip is innervated by superior labial small blood vessels, which may sometimes be seen coursing beneath
branches of the infraorbital nerve, and the lower lip is innervated by the alveolar mucosa.
the mental branch of the mandibular division of the trigeminal.
MASTICATORY MUCOSA AND THE GINGIVAE
ORAL VESTIBULE
Masticatory mucosa, i.e. mucosa that is subjected to masticatory stress,
The oral vestibule is a slitlike space between the lips or cheeks on one is bound firmly to underlying bone or to the necks of the teeth, and
side and the teeth on the other. When the teeth occlude, the vestibule forms a mucoperiosteum in the gingivae and palatine raphe. Gingival,
is a closed space that only communicates with the oral cavity proper in palatal and dorsal lingual mucosae are keratinized or parakeratinized
the retromolar regions behind the last molar tooth on each side. Where (Schroeder and Listgarten 1997).
the mucosa that covers the alveolus of the jaw is reflected on to the lips The gingivae may be further subdivided into the attached gingivae
and cheeks, a trough or sulcus is formed, which is called the fornix and the free gingivae. Attached gingivae are firmly bound to the perios
vestibuli. A variable number of sickleshaped folds containing loose teum of the alveolus and to the teeth, whereas free gingivae, which
connective tissue run across the fornix vestibuli. In the midline, these constitute approximately a 1 mm margin of the gingivae, lie unattached
are the upper and lower labial frena (or frenula). Other folds may around the cervical region of each tooth. The free gingival groove
traverse the fornix near the canines or premolars. The folds in the lower between the free and attached gingivae corresponds roughly to the floor
fornix are said to be more pronounced than those in the upper fornix of the gingival sulcus that separates the inner surface of the attached


(Fig. 31.2). gingivae from the enamel. The interdental papilla is that part of the
The upper labial frenulum is normally attached well below the gingivae that fills the space between adjacent teeth. The surface of the
alveolar crest. A large frenulum with an attachment near or on the crest attached gingivae is characteristically stippled, although there is consid
may be associated with a midline gap (diastema) between the maxil erable interindividual variation in the degree of stippling, and variation
lary first incisors. This can be corrected by simple surgical removal of according to age, sex and the health of the gingivae. The free gingivae
the frenulum (frenulectomy) because it contains no structures of clini are not stippled. A mucogingival line delineates the attached gingivae
cal importance. Prominent frena may compromise the stability of on the buccal surface of the upper and lower jaws (see Fig. 31.2) and
dentures. the lingual surface of the lower jaw from the alveolar mucosa. There is
no corresponding obvious division between the attached gingivae and
the remainder of the palatal mucosa because this whole surface is
ORAL MUCOSA
orthokeratinized masticatory mucosa, which is pink.
A submucosa is absent from the gingivae and the midline palatine
The oral mucosa is continuous with the skin at the labial margins (ver raphe, but is present over the rest of the hard palate. Posterolaterally, it
milion border) and with the pharyngeal mucosa at the oropharyngeal is thick where it contains mucous salivary glands and the greater pala
isthmus. It varies in structure, function and appearance in different tine nerves and vessels, and it is anchored to the periosteum of the
regions of the oral cavity and is traditionally divided into lining, mas maxillae and palatine bones by collagenous septa.
ticatory and specialized mucosae (Presland and Dale 2000).
Vascular supply and lymphatic drainage
The gingival tissues derive their blood supply from the maxillary and
lingual arteries. The buccal gingivae around the maxillary cheek teeth
are supplied by gingival and perforating branches from the posterior


superior alveolar artery and by the buccal branch of the maxillary artery.
The labial gingivae of anterior teeth are supplied by labial branches of
the infraorbital artery and by perforating branches of the anterior su
perior alveolar artery. The palatal gingivae are supplied primarily by
branches of the greater palatine artery.
The buccal gingivae associated with the mandibular cheek teeth are
supplied by the buccal branch of the maxillary artery and by perforating
branches from the inferior alveolar artery. The labial gingivae around
the anterior teeth are supplied by the mental artery and by perforating
branches of the incisive artery. The lingual gingivae are supplied by
perforating branches from the inferior alveolar artery and by its lingual
branch, and by the main lingual artery, a branch of the external carotid
artery.
No accurate description is available concerning the venous drainage
of the gingivae, although it may be assumed that buccal, lingual, greater
Fig. 31.2 An anterior view of the dentition in centric occlusion, with the palatine and nasopalatine veins are involved. These veins run into the
lips retracted. Note the pale pink, stippled gingivae and the red, shiny, pterygoid plexuses (apart from the lingual veins, which may pass
smooth alveolar mucosa. The degree of overbite is rather pronounced, directly into the internal jugular veins).
and the gingiva and its epithelial attachment have receded on to the root The lymph vessels of the labial and buccal gingivae of the maxillary
of the upper left canine. Note the frena (arrows). and mandibular teeth unite to drain into the submandibular nodes,


Floor of the mouth
509
13
rEtPaHc
though in the labial region of the mandibular incisors they may drain may aid breast feeding (National Institute for Health and Clinical Excel
into the submental lymph nodes. The lingual and palatal gingivae drain lence 2005, Webb et al 2013). The submandibular salivary ducts open
into the jugulodigastric group of nodes, either directly or indirectly into the mouth at the sublingual papilla (caruncle), which is a large,
through the submandibular nodes. centrally positioned protuberance at the base of the tongue.
The sublingual folds lie on either side of the sublingual papilla and
Innervation cover the underlying submandibular ducts and sublingual salivary
glands. The blood supply of the floor of the mouth is described with
the blood supply of the tongue. The main muscle forming the floor
The nerves supplying the gingivae in the upper jaw come from the
of the mouth is mylohyoid, with geniohyoid lying immediately
maxillary nerve via its greater palatine, nasopalatine, and anterior,
above it.
middle and posterior superior alveolar branches (see Table 31.2). Surgi
cal division of the nasopalatine nerve, e.g. during the removal of an Mylohyoid
ectopic canine tooth, causes no obvious sensory deficit in the anterior
Mylohyoid lies superior to the anterior belly of digastric and, with its
part of the palate, which suggests that the territory of the greater palatine
contralateral fellow, forms a muscular floor for the oral cavity. It is a
nerve reaches as far forwards as the gingivae lingual to the incisor teeth
flat, triangular sheet attached to the whole length of the mylohyoid line
or that the nerve has large regenerative potential. The mandibular nerve
of the mandible (Fig. 31.4A; see Figs 31.1, 31.7, 31.10). The mylohyoid
innervates the gingivae in the lower jaw by its inferior alveolar, lingual
line is of variable length, sometimes ending before the lower third
and buccal branches.
molar (wisdom) tooth. The posterior fibres of mylohyoid pass medially


and slightly downwards to the front of the body of the hyoid bone near
its lower border. The middle and anterior fibres from each side decus
SPECIALIZED ORAL MUCOSA
sate in a median fibrous raphe that stretches from the symphysis menti
to the hyoid bone. The median raphe is sometimes absent, in which
The specialized mucosa covering the anterior twothirds of the dorsum
case the two muscles form a continuous sheet, or it may be fused with
of the tongue is described on page 515.
the anterior belly of digastric. In about onethird of subjects, there is a
hiatus in the muscle through which a process of the sublingual gland
protrudes.
OROPHARYNGEAL ISTHMUS
Relations The inferior (external) surface is related to platysma, the
The oropharyngeal isthmus lies between the soft palate and the dorsum anterior belly of digastric the superficial part of the submandibular
of the tongue, and is bounded on both sides by the palatoglossal arches. gland, the facial and submental vessels, and the mylohyoid vessels and
Each palatoglossal arch runs downwards, laterally and forwards, from nerve. The superior (internal) surface is related to geniohyoid, part of
the soft palate to the side of the tongue, and consists of palatoglossus hyoglossus and styloglossus, the hypoglossal and lingual nerves, the
and its covering mucous membrane (Fig. 31.3). The approximation of submandibular ganglion, the sublingual gland, the deep part of the
the arches shuts off the mouth from the oropharynx, and is essential submandibular gland and its duct, the lingual and sublingual vessels,
for deglutition. and, posteriorly, the mucous membrane of the mouth.
Vascular supply Mylohyoid receives its arterial supply from the
FLOOR OF THE MOUTH
sublingual branch of the lingual artery, the maxillary artery, via the
mylohyoid branch of the inferior alveolar artery, and the submental
The floor of the mouth is a small, horseshoeshaped region situated branch of the facial artery.


beneath the movable part of the tongue and above the muscular dia
phragm formed by the mylohyoid muscles. A fold of tissue, the lingual Innervation Mylohyoid is supplied by the mylohyoid branch of the
frenulum, extends on to the inferior surface of the tongue from near inferior alveolar nerve, which can sometimes also supply accessory
the base of the tongue. It occasionally extends across the floor of the innervation to the posterior mandibular teeth.
mouth to be attached on to the mandibular alveolus, a condition called
ankyloglossia (known colloquially as a ‘tongue tie’); historically, the Actions Mylohyoid elevates the floor of the mouth in the first
‘tied’ frenulum has been divided to aid speech but the evidence for this stage of deglutition. It may also elevate the hyoid bone or depress the
procedure is scanty. However, there is some evidence that frenulotomy mandible.
Fig. 31.3 The oral cavity, oropharyngeal
Palatine raphe isthmus and muscles of the palate. (With
permission from Waschke J, Paulsen F
(eds), Sobotta Atlas of Human Anatomy,
15th ed, Elsevier, Urban & Fischer.
Palatine glands Greater palatine artery Copyright 2013.)
Greater palatine nerve
Musculus uvulae Greater palatine foramen
Pterygoid hamulus
Palatopharyngeal arch
Superior constrictor
(posterior pillar of fauces)
Pterygomandibular raphe
Palatoglossal arch Buccinator
(anterior pillar of fauces)
Palatoglossus
Lingual nerve
Isthmus of fauces
(oropharyngeal isthmus); oropharynx
Palatine tonsil
Palatopharyngeus
Dorsum of tongue, anterior part
(presulcal part)


Oral cavity
510
4
NOitcES
A Sublingual gland B
Submandibular duct
Mylohyoid
Fimbriated fold
Lingual nerve
Lingual vein
Frenulum of
tongue
Submandibular
duct
Deep Opening of ducts Sublingual fold
Submandibular
gland Superficial of sublingual gland overlying
Hyoglossus sublingual gland
Genioglossus
Opening of Sublingual
submandibular duct papilla
Fig. 31.4 The floor of the mouth. A, View from above when the bulk of the tongue musculature has been removed. Note the relationships between the
lingual nerve and the submandibular duct, and between the submandibular and sublingual salivary glands. B, The ventral surface of the tongue, visible
when the tip of the tongue is turned upwards. (With permission from Drake RL, Vogl AW, Mitchell A (eds), Gray’s Anatomy for Students, 2nd ed, Elsevier,
Churchill Livingstone. Copyright 2010.)
Geniohyoid The submucosa in the posterior half of the hard palate contains
minor mucoustype salivary glands. They secrete via numerous small
Geniohyoid is a narrow muscle that lies above the medial part of mylo
ducts, which often drain into a larger duct that opens bilaterally at the
hyoid (see Figs 31.6, 31.10). It arises from the inferior mental spine
paired palatine foveae. These depressions, sometimes a few millimetres
(genial tubercle) on the back of the symphysis menti, and runs back
deep, flank the midline raphe at the posterior border of the hard palate.
wards and slightly downwards to attach to the anterior surface of the
They provide a useful landmark for the extent of an upper denture; they
body of the hyoid bone. The paired muscles are contiguous and may
cause an overextended denture to become unstable when the soft palate
occasionally fuse with each other or with genioglossus.
moves during deglutition and mastication. The upper surface of the


Vascular supply The blood supply to geniohyoid is derived from hard palate is the floor of the nasal cavity and is covered by ciliated
the lingual artery (sublingual branch). respiratory epithelium.
Innervation Geniohyoid is supplied by the first cervical spinal nerve, Vascular supply and lymphatic drainage
through the hypoglossal nerve.
of the hard palate
Actions Geniohyoid elevates the hyoid bone and draws it forwards,
and therefore acts partly as an antagonist to stylohyoid. When the hyoid The palate derives its blood supply principally from the greater palatine
bone is fixed, geniohyoid depresses the mandible. artery, a branch of the third part of the maxillary artery. The greater
palatine artery descends with its accompanying nerve in the palatine
canal, where it gives off two or three lesser palatine arteries, which are
PALATE
transmitted through the lesser palatine canals and foramina to supply
the soft palate and tonsil, and anastomose with the ascending palatine
The palate forms the roof of the mouth and is divisible into two regions, branch of the facial artery. The greater palatine artery emerges on to the
namely: the hard palate in front and soft palate behind. oral surface of the palate at the greater palatine foramen adjacent to the
second maxillary molar and runs in a curved groove near the alveolar
border of the hard palate to the incisive canal. It ascends this canal and
SOFT PALATE
anastomoses with septal branches of the nasopalatine artery to supply
the gingivae, palatine glands and mucous membrane.
The soft palate is described with the pharynx on page 575. The veins of the hard palate accompany the arteries and drain largely
to the pterygoid plexus.
HARD PALATE
Innervation of the hard palate
The hard palate is formed by the palatine processes of the maxillae and
the horizontal plates of the palatine bones (see Figs 30.8B, 30.9, The sensory nerves of the hard palate are the greater palatine and
31.16A). The hard palate is bounded in front and at the sides by the nasopalatine branches of the maxillary nerve, which all pass through


toothbearing alveolus of the upper jaw and is continuous posteriorly the pterygopalatine ganglion. The greater palatine nerve descends
with the soft palate. It is covered by a thick mucosa bound tightly to through the greater palatine canal, emerges on the hard palate from the
the underlying periosteum. In its more lateral regions, it also possesses greater palatine foramen, runs forwards in a groove on the inferior
a submucosa containing the main neurovascular bundle. The mucosa surface of the bony palate almost to the incisor teeth and supplies the
is covered by keratinized stratified squamous epithelium, which shows gums and the mucosa and glands of the hard palate (see Fig. 31.3). It
regional variations and may be ortho or parakeratinized. also communicates with the terminal filaments of the nasopalatine
The periphery of the hard palate consists of gingivae. A narrow ridge, nerve. As it leaves the greater palatine canal, it supplies palatine branches
the palatine raphe, devoid of submucosa, runs anteroposteriorly in the to both surfaces of the soft palate. The lesser (middle and posterior)
midline. An oval prominence, the incisive papilla, lies at the anterior palatine nerves, which are much smaller, descend through the greater
extremity of the raphe. It covers the incisive fossa at the oral opening palatine canal and emerge through the lesser palatine foramina in the
of the incisive canal and also marks the position of the fetal nasopala tubercle of the palatine bone to supply the uvula, tonsil and soft palate.
tine canal. Irregular transverse ridges or rugae, each containing a core The nasopalatine nerves enter the palate at the incisive foramen and are
of dense connective tissue, radiate outwards from the palatine raphe in branches of the maxillary nerve that pass through the pterygopalatine
the anterior half of the hard palate; their pattern is unique to the ganglion to supply the anterior part of the hard palate behind the
individual. incisor teeth.


tongue
511
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Fibres conveying taste impulses from the palate probably pass via Epiglottis Median glossoepiglottic fold
the palatine nerves to the pterygopalatine ganglion, and travel through
it without synapsing to join the nerve of the pterygoid canal and the Palatopharyngeal
greater petrosal nerve to the facial ganglion, where their cell bodies are Foramen arch
situated. The central processes of these neurones traverse the sensory caecum Palatine tonsil
root of the facial nerve (nervus intermedius) to pass to the gustatory
nucleus in the nucleus of the tractus solitarius. Parasympathetic post
ganglionic secretomotor fibres from the pterygopalatine ganglion run
with the nerves to supply the palatine mucous glands.
TONGUE Pharyngeal
part
Sulcus
The tongue is a highly muscular organ of deglutition, taste and speech. terminalis Palatoglossal
It is partly oral and partly pharyngeal in position, and is attached by its arch
muscles to the hyoid bone, mandible, styloid processes, soft palate and
the pharyngeal wall. It has a root, an apex, a curved dorsum and an
Foliate
inferior surface. Its mucosa is normally pink and moist, and is attached
papillae
closely to the underlying muscles. The dorsal mucosa is covered by
numerous papillae, some of which bear taste buds. Intrinsic muscle Vallate
papillae
fibres are arranged in a complex interlacing pattern of longitudinal,
Oral part
transverse, vertical and horizontal fasciculi, and this allows great mobil
ity. Fasciculi are separated by a variable amount of adipose tissue, which
increases posteriorly. The root of the tongue is attached to the hyoid
Fungiform
bone and mandible, and between them it is in contact inferiorly with
papillae
geniohyoid and mylohyoid. The dorsum (posterosuperior surface) is
generally convex in all directions at rest. It is divided by a Vshaped
Filiform
sulcus terminalis into an anterior, oral (presulcal) part that faces


papillae
upwards, and a posterior, pharyngeal (postsulcal) part that faces pos
teriorly. The anterior part forms about twothirds of the length of the Fig. 31.5 The dorsum of the tongue, adjoining palatoglossal and
tongue. The two limbs of the sulcus terminalis run anterolaterally to palatopharyngeal arches, and epiglottis. The palatine tonsils lie in the
the palatoglossal arches from a median depression, the foramen tonsillar recesses between the palatoglossal and palatopharyngeal
caecum, which marks the site of the upper end of the embryonic thyroid arches.
diverticulum (thyroglossal duct). The oral and pharyngeal parts of the
tongue differ in their mucosa, innervation and developmental origins.
the former extending outside the tongue and moving it bodily, the latter
wholly within it and altering its shape. The extrinsic musculature con
ORAL (PRESULCAL) PART
sists of four pairs of muscles, namely: genioglossus, hyoglossus, stylo
glossus (and chondroglossus) and palatoglossus.
The presulcal part of the tongue is located in the floor of the oral cavity.
It has an apex touching the incisor teeth, a margin in contact with the Genioglossus
gums and teeth, and a superior surface (dorsum) related to the hard and Genioglossus is triangular in sagittal section, lying near and parallel to
soft palates. On each side, in front of the palatoglossal arch, there are the midline. It arises from a short tendon attached to the superior genial
four or five vertical folds, the foliate papillae, which represent vestiges tubercle behind the mandibular symphysis, above the origin of genio
of larger papillae found in many other mammals. The dorsal mucosa hyoid. From this point, it fans out backwards and upwards (Fig. 31.6).
has a longitudinal median sulcus and is covered by filiform, fungiform The inferior fibres of genioglossus are attached by a thin aponeurosis


and circumvallate papillae (Fig. 31.5). The mucosa on the inferior to the upper anterior surface of the hyoid body near the midline (a few
(ventral) surface is smooth, purplish and reflected on to the oral floor fasciculi passing between hyoglossus and chondroglossus to blend with
and gums; it is connected to the oral floor anteriorly by the lingual the middle constrictor of the pharynx). Intermediate fibres pass back
frenulum. The deep lingual vein, which is visible, lies lateral to the wards into the posterior part of the tongue, and superior fibres ascend
frenulum on either side. The plica fimbriata (fimbriated fold), a fringed forwards to enter the whole length of the ventral surface of the tongue
mucosal ridge directed anteromedially towards the apex of the tongue, from root to apex, intermingling with the intrinsic muscles. The muscles
lies lateral to the vein. This part of the tongue develops from the lingual of opposite sides are separated posteriorly by the lingual septum. An
swellings of the mandibular arch and from the tuberculum impar, and teriorly, they are variably blended by decussation of fasciculi across the
this embryological derivation explains its sensory innervation. midline. The attachment of the genioglossi to the genial tubercles pre
vents the tongue from sinking back and obstructing respiration; there
fore, anaesthetists pull the mandible forwards to obtain the full benefit
PHARYNGEAL (POSTSULCAL) PART
of this connection. In infants and children, ‘chin lift’ and ‘jaw thrust’
are standard resuscitative manœuvres that rely on this anatomical
The postsulcal part of the tongue constitutes its base and lies posterior arrangement to relieve obstruction of the pharynx by the tongue falling
to the palatoglossal arches. Although it forms the anterior wall of the back.
oropharynx, it is described here for convenience. Its mucosa is reflected
laterally on to the palatine tonsils and pharyngeal wall, and posteriorly Vascular supply Genioglossus is supplied by the sublingual branch


on to the epiglottis by a median and two lateral glossoepiglottic folds, of the lingual artery and the submental branch of the facial artery.
which surround two depressions or valleculae. The pharyngeal part of
the tongue is devoid of papillae and exhibits low elevations. There are Innervation Genioglossus is innervated by the hypoglossal nerve.
underlying lymphoid nodules, which are embedded in the submucosa
and collectively termed the lingual tonsil. The ducts of small sero Actions Genioglossus brings about the forward traction of the tongue
mucous glands open on the apices of these elevations. The postsulcal to protrude its apex from the mouth. Acting bilaterally, the two muscles
part of the tongue develops from the hypobranchial eminence. On depress the central part of the tongue, making it concave from side to
the rare occasions that the thyroid gland fails to migrate away from the side. Acting unilaterally, the tongue diverges to the opposite side.
tongue during development, it remains in the postsulcal part of the
Hyoglossus
tongue as a functioning lingual thyroid gland.
Hyoglossus is thin and quadrilateral, and arises from the whole length
of the greater cornu and the front of the body of the hyoid bone (see
MUSCLES OF THE TONGUE Fig. 31.6). It passes vertically up to enter the side of the tongue between
styloglossus laterally and the inferior longitudinal muscle medially.
The tongue is divided by a median fibrous septum, attached to the body Fibres arising from the body of the hyoid overlap those from the greater
of the hyoid bone. There are extrinsic and intrinsic muscles in each half, cornu.


Oral cavity
512
4
NOitcES
Tensor veli palatini Fig. 31.6 Muscles of the tongue and
pharynx. Palatoglossus is not shown here
Levator veli palatini
but is depicted in Figure 34.3A, see also
Pterygoid hamulus Fig. 34.6.
Rectus capitis
lateralis
Obliquus capitis superior
Stylohyoid ligament (cut)
Transverse
process of atlas
Pterygomandibular raphe
Obliquus capitis inferior
Vertebral artery
Anterior intertransverse
muscle
Transverse
process of axis
Stylopharyngeus
Genioglossus Stylohyoid
Geniohyoid Middle constrictor
Buccinator
Superior constrictor
Styloglossus Inferior constrictor
Hyoglossus
Thyrohyoid membrane
Cricothyroid
Relations Hyoglossus is related at its superficial surface to the digas Actions Styloglossus draws the tongue up and backwards.
tric tendon, stylohyoid, styloglossus and mylohyoid, the lingual nerve
and submandibular ganglion, the sublingual gland, the deep part of the Stylohyoid ligament
submandibular gland and duct, the hypoglossal nerve and the deep The stylohyoid ligament is a fibrous cord that extends from the tip of
lingual vein. By its deep surface it is related to the stylohyoid ligament, the styloid process to the lesser cornu of the hyoid bone (see Fig. 31.6).
genioglossus, the middle constrictor and the inferior longitudinal It gives attachment to some fibres of styloglossus and the middle con
muscle of the tongue, and the glossopharyngeal nerve. Posteroinferiorly, strictor of the pharynx, and is closely related to the lateral wall of the
it is separated from the middle constrictor by the lingual artery. This oropharynx. Below it is overlapped by hyoglossus. The ligament is
part of the muscle is in the lateral wall of the pharynx, below the pala derived embryologically from the second branchial arch. It may be


tine tonsil. Passing deep to the posterior border of hyoglossus are, in partially calcified.
descending order: the glossopharyngeal nerve, stylohyoid ligament and
Palatoglossus
lingual artery.
Palatoglossus is closely associated with the soft palate in function and
Vascular supply Hyoglossus is supplied by the sublingual branch of innervation, and is described with the other palatal muscles.
the lingual artery and the submental branch of the facial artery. Intrinsic muscles
The intrinsic muscles of the tongue are the bilateral superior and in
Innervation Hyoglossus is innervated by the hypoglossal nerve.
ferior longitudinal, the transverse and the vertical (Fig. 31.7).
Actions Hyoglossus depresses the tongue. Superior longitudinal
The superior longitudinal muscle constitutes a thin stratum of oblique
Chondroglossus
and longitudinal fibres lying beneath the mucosa of the dorsum of the
Sometimes described as a part of hyoglossus, this muscle is separated
tongue. It extends forwards from the submucous fibrous tissue near the
from it by some fibres of genioglossus, which pass to the side of the
epiglottis and from the median lingual septum to the lingual margins.
pharynx. It is about 2 cm long, and arises from the medial side and
Some fibres are inserted into the mucous membrane.
base of the lesser cornu and the adjoining part of the body of the hyoid.
It ascends to merge into the intrinsic musculature between hyoglossus inferior longitudinal
and genioglossus. A small slip occasionally springs from the cartilago The inferior longitudinal muscle is a narrow band of muscle close to
triticea and enters the tongue with the posterior fibres of hyoglossus. the inferior lingual surface between genioglossus and hyoglossus. It
extends from the root of the tongue to the apex. Some of its posterior
Vascular supply, innervation and actions These are similar to fibres are connected to the body of the hyoid bone. Anteriorly, it blends
those described for hyoglossus. with styloglossus.
Styloglossus transverse
Styloglossus is the shortest and smallest of the three muscles attached The transverse muscles pass laterally from the median fibrous septum


to the styloid process (see Fig. 31.6). It arises from the anterolateral to the submucous fibrous tissue at the lingual margin, blending with
aspect of the styloid process near its apex, and from the styloid end of palatopharyngeus.
the stylomandibular ligament (MéridaVelasco et al 2006). Passing
downwards and forwards, it divides at the side of the tongue into a vertical
longitudinal part, which enters the tongue dorsolaterally to blend with The vertical muscles extend from the dorsal to the ventral aspects of the
the inferior longitudinal muscle in front of hyoglossus, and an oblique tongue in the anterior borders.
part, overlapping hyoglossus and decussating with it.
Vascular supply of intrinsic muscles The intrinsic muscles are
Vascular supply Styloglossus is supplied by the sublingual branch supplied by the lingual artery.
of the lingual artery.
Innervation of intrinsic muscles All intrinsic lingual muscles are
Innervation Styloglossus is innervated by the hypoglossal nerve. innervated by the hypoglossal nerve.


tongue
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Vertical muscle Styloglossus Fig. 31.7 A coronal section
intersecting through the tongue, the
the superior mouth and the body of the
longitudinal mandible opposite the lower
muscle first molar tooth.
Buccinator
Hyoglossus
Submandibular duct
Genioglossus
Sublingual gland,
posterior pole
Geniohyoid
Lingual nerve
Mylohyoid
Submandibular gland,
Digastric,
superficial part
anterior belly
Platysma
dorsum of the tongue. The vessels supply its mucous membrane and
Inferior longitudinal
Soft palate the palatoglossal arch, tonsil, soft palate and epiglottis. They anasto
muscle
mose with their contralateral fellows.
Salpingopharyngeal
fold
Submandibular Sublingual artery
duct Palatopharyngeal
The sublingual artery arises at the anterior margin of hyoglossus. It
arch
passes forwards between genioglossus and mylohyoid to the sublingual
Lingual nerve Lingual artery gland, and supplies the gland, mylohyoid and the buccal and gingival
Sublingual gland mucous membranes. One branch pierces mylohyoid and joins the sub
Genioglossus (cut) mental branches of the facial artery. Another branch courses through
the mandibular gingivae to anastomose with its contralateral fellow. A
Hypoglossal nerve Hyoglossus
anterior fibres single artery arises from this anastomosis and enters a small foramen
(lingual foramen) on the mandible, situated in the midline on the
Epiglottis
Geniohyoid posterior aspect of the symphysis immediately above the genial
Hyoid bone, tubercles.
Mylohyoid (cut) body
Deep lingual artery
Fig. 31.8 The left half of the tongue, viewed from the medial side, The deep lingual artery is the terminal part of the lingual artery and is
showing the lingual artery and ramifications of the hypoglossal and lingual found on the inferior surface of the tongue near the lingual frenulum.


nerves. In addition to the lingual artery, the tonsillar and ascending palatine
branches of the facial and ascending pharyngeal arteries also supply
tissue in the root of the tongue. In the region of the valleculae, epiglottic
Actions The intrinsic muscles alter the shape of the tongue. Thus,
branches of the superior laryngeal artery anastomose with the inferior
contraction of the superior and inferior longitudinal muscles tend to
dorsal branches of the lingual artery.
shorten the tongue, but the former also turns the apex and sides
upwards to make the dorsum concave, while the latter pulls the apex
Lingual veins
down to make the dorsum convex. The transverse muscle narrows and
elongates the tongue, while the vertical muscle makes it flatter and
wider. Acting alone or in pairs and in endless combination, the intrinsic The lingual veins are formed from the union of the dorsal lingual and
muscles give the tongue precise and highly varied mobility, important deep lingual veins and the vena comitans of the hypoglossal nerve. The
not only in alimentary function but also in speech. veins draining the tongue follow two routes. Dorsal lingual veins drain
the dorsum and sides of the tongue, join the lingual veins accompany
ing the lingual artery between hyoglossus and genioglossus, and empty
VASCULAR SUPPLY AND LYMPHATIC DRAINAGE into the internal jugular vein near the greater cornu of the hyoid bone.
OF THE TONGUE The deep lingual vein begins near the tip of the tongue and runs back
just beneath the mucous membrane on the inferior surface of the
Lingual artery tongue. It joins a sublingual vein from the sublingual salivary gland
near the anterior border of hyoglossus and forms the vena comitans
nervi hypoglossi, which runs back with the hypoglossal nerve between
The tongue and the floor of the mouth are supplied chiefly by the
mylohyoid and hyoglossus to join the facial, internal jugular or lingual
lingual artery, which arises from the anterior surface of the external
vein. The lingual veins usually join the facial and retromandibular veins
carotid artery. It passes between hyoglossus and the middle constrictor


(anterior division) to form the common facial vein, which drains into
of the pharynx to reach the floor of the mouth, accompanied by the
the internal jugular vein.
lingual veins and the glossopharyngeal nerve. At the anterior border of
hyoglossus, the lingual artery bends sharply upwards (Fig. 31.8). It is
Lymphatic drainage
covered by the mucosa of the tongue and lies between genioglossus
medially and the inferior longitudinal muscle laterally. Near the tip of
the tongue, it anastomoses with its contralateral fellow; this contribu The mucosa of the pharyngeal part of the dorsal surface of the tongue
tion is important in maintaining the blood supply to the tongue in any contains many lymphoid follicles aggregated into domeshaped groups:
surgical resection of the tongue. The branches of the lingual artery form the lingual tonsils. Each group is arranged around a central deep crypt,
a rich anastomotic network, which supplies the musculature of the or invagination, which opens on to the surface epithelium. The ducts
tongue, and a very dense submucosal plexus. Named branches of the of mucous glands open into the bases of the crypts. Small isolated fol
lingual artery in the floor of the mouth are the dorsal lingual, sublingual licles also occur beneath the lingual mucosa. The lymphatic drainage
and deep lingual arteries. of the tongue can be divided into three main regions: marginal, central
and dorsal. The anterior region of the tongue drains into marginal and
Dorsal lingual arteries central vessels, and the posterior part of the tongue behind the circum
The dorsal lingual arteries are usually two or three small vessels. They vallate papillae drains into the dorsal lymph vessels. The more central
arise medial to hyoglossus and ascend to the posterior part of the regions may drain bilaterally, and this must be borne in mind when


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NOitcES
The sensory innervation of the tongue reflects its embryological
development: the anterior twothirds (presulcal part) is derived from
first arch mesenchyme and the posterior third (postsulcal part) from
third arch mesenchyme. The nerve of general sensation to the anterior
twothirds is the lingual nerve. Taste sensation travels in the chorda
Jugulodigastric tympani branch of the facial nerve. The nerve supplying both general
node and taste sensation to the posterior third is the glossopharyngeal nerve.
An additional area in the region of the valleculae is supplied by the
Submental nodes internal laryngeal branch of the vagus nerve.
Upper deep
Submandibular cervical nodes Lingual nerve
nodes
Infrahyoid node
The lingual nerve is sensory to the mucosa of the floor of the mouth,
mandibular lingual gingivae and mucosa of the presulcal part of the
Jugulo-omohyoid tongue (excluding the circumvallate papillae). It also carries postgan
Prelaryngeal node node glionic parasympathetic fibres from the submandibular ganglion to the
sublingual and anterior lingual glands.
Pretracheal node The lingual nerve arises from the posterior trunk of the mandibular
Lower deep
cervical nodes nerve in the infratemporal fossa (see Fig. 32.23), where it is joined by
Anterior cervical the chorda tympani branch of the facial nerve and often by a branch
node (in of the inferior alveolar nerve. It then passes below the mandibular
suprasternal
attachment of the superior pharyngeal constrictor and pterygoman
space)
dibular raphe, closely applied to the periosteum of the medial surface
of the mandible. Here it lies opposite the distal (posterior) root of the
third molar tooth, where it is covered only by the gingival mucoperios
Fig. 31.9 The lymphatic drainage of the tongue. Removal of teum. In about 1 in 7 cases, the lingual nerve may be located above the
sternocleidomastoid has exposed the whole chain of deep cervical lymph lingual bony plate and is susceptible to damage during surgery in the


nodes. region. It next passes medial to the mandibular attachment of mylo
hyoid, which carries it progressively away from the mandible, and sepa
rates it from the alveolar bone covering the mesial root of the third
planning to remove malignant tumours of the tongue that are approach molar tooth. The lingual nerve then passes downwards and forwards
ing the midline. If the tumour has a propensity for lymphatic spread, on the deep surface of mylohyoid (i.e. the surface nearer the mucosa
both cervical chains may be involved. covering the floor of the mouth), crossing the lingual sulcus beneath
the mucosa. In this position, it lies on the deep portion of the sub
Marginal vessels mandibular gland, which bulges over the top of the posterior border of
Marginal vessels from the apex of the tongue and the lingual frenulum mylohyoid. It passes below the submandibular duct, which crosses it
area descend under the mucosa to widely distributed nodes. Some from medial to lateral, and curves upwards, forwards and medially to
vessels pierce mylohyoid as it contacts the mandibular periosteum to enter the tongue by medial and lateral branches (see Fig. 31.8; Fig.
enter either the submental or anterior or middle submandibular nodes, 31.10). Within the tongue, the medial branch sends small branches to
or else to pass anterior to the hyoid bone to the juguloomohyoid node. the medial part of the ventrolateral tongue, and the lateral branch runs
Vessels arising in the plexus on one side may cross under the frenulum along the lateral border of the tongue and sends larger branches to
to end in contralateral nodes. Efferent vessels of median submental innervate the mucosa of the anterior tip of the tongue. The lingual nerve
nodes pass bilaterally. Some vessels pass inferior to the sublingual gland is connected to the submandibular ganglion (see Fig. 32.23) by two or
and accompany the companion vein of the hypoglossal nerve to end in three branches. It forms connecting loops with twigs of the hypoglossal


jugulodigastric nodes. One vessel often descends further to reach the nerve at the anterior margin of hyoglossus (Fitzgerald and Law 1958)
juguloomohyoid node, and passes either superficial or deep to the and within the tongue (Zur et al 2004).
intermediate tendon of digastric. The lingual nerve is at risk during surgical removal of (impacted)
Vessels from the lateral margin of the tongue cross the sublingual lower third molars: patients occasionally develop lingual sensory dis
gland, pierce mylohyoid and end in the submandibular nodes. Others turbance postoperatively but this is rarely persistent (Renton 2011). The
end in the jugulodigastric or juguloomohyoid nodes. Vessels from the nerve is also at risk during operations to remove the submandibular
posterior part of the lingual margin traverse the pharyngeal wall to the salivary gland because the duct must be dissected from the lingual
jugulodigastric lymph nodes (Fig. 31.9). nerve, and because its connection to the submandibular ganglion pulls
it into the operating field.
Central vessels
The regions of the lingual surface draining into the marginal or central Glossopharyngeal nerve
vessels are not distinct. Central lymphatic vessels ascend between the
fibres of the two genioglossi; most pass between the muscles and
The glossopharyngeal nerve is distributed to the posterior third of the
diverge to the right or left to follow the lingual veins to the deep cervical
tongue and the circumvallate papillae. It communicates with the lingual
nodes, especially the jugulodigastric and juguloomohyoid nodes.
nerve. The course of the glossopharyngeal nerve in the neck is described
Some pierce mylohyoid to enter the submandibular nodes.
on page 465.
Dorsal vessels
Hypoglossal nerve
Vessels draining the postsulcal region and the circumvallate papillae run
posteroinferiorly. Those near the median plane may pass bilaterally.


They turn laterally, joining the marginal vessels, and all pierce the pha The course of the hypoglossal nerve in the neck is described on page
ryngeal wall, passing around the external carotid arteries to reach the 468. After crossing the loop of the lingual artery a little above the tip
jugulodigastric and juguloomohyoid lymph nodes. One vessel may of the greater cornu of the hyoid, it inclines upwards and forwards on
descend posterior to the hyoid bone, perforating the thyrohyoid mem hyoglossus, passing deep to stylohyoid, the tendon of digastric and the
brane to end in the juguloomohyoid node. posterior border of mylohyoid. Between mylohyoid and hyoglossus, the
hypoglossal nerve lies below the deep part of the submandibular gland,
the submandibular duct and the lingual nerve, with which it commu
INNERVATION OF THE TONGUE nicates. It then passes on to the lateral aspect of genioglossus, continu
ing forwards in its substance as far as the tip of the tongue (see Fig.
The muscles of the tongue, with the exception of palatoglossus, are 31.8). It distributes fibres to styloglossus, hyoglossus and genioglossus
supplied by the hypoglossal nerve. Palatoglossus is supplied via the and to the intrinsic muscles of the tongue. Cadaveric tongues stained
pharyngeal plexus. The pathways for proprioception associated with using Sihler’s stain (a whole mount nerve staining technique that
the tongue musculature are unknown, but presumably may involve renders a large specimen transparent while counterstaining all nerves)
the lingual, glossopharyngeal or hypoglossal nerves, and the cervical or acetylcholinesterase or silver stains show the basic mammalian
spinal nerves that communicate with the hypoglossal nerve. intralingual pattern of hypoglossal nerve distribution but with notable


tongue
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Fig. 31.10 The lingual nerve,
submandibular duct, and
submandibular and sublingual
salivary glands in the floor of
the mouth. Lingual aspect,
left side. (With permission
from Waschke J, Paulsen F
(eds), Sobotta Atlas of Human
Anatomy, 15th ed, Elsevier,
Urban & Fischer. Copyright
Sublingual papilla
2013.)
Genioglossus
Medial pterygoid
Geniohyoid
Lingual nerve
Digastric, anterior belly
Submandibular gland
Submandibular duct
Sublingual gland
Mylohyoid
differences, even from nonhuman primates. Thus, many muscle fibres,
particularly in the transverse group of intrinsic muscles, contain mul
tiple en grappe motor endplates (suggesting that they are some variant
of slow tonic muscle fibres). Presumably, these specializations facilitate
the fine motor control of tongue shape that is required in speech and
swallowing (Mu and Sanders 2010) (Fig. 31.11). If the nerve suffers
either iatrogenic or pathological damage, the tongue, on protrusion,
will deviate towards the affected side and there may also be wasting of
the muscles on the affected side.
Special sensory innervation of the tongue
The sense of taste is dependent on scattered groups of sensory cells, the
taste buds, which occur in the oral cavity and pharynx, and are particu
larly plentiful on the lingual papillae of the dorsal lingual mucosa.
Dorsal lingual mucosa
Fig. 31.12 The dorsal surface of the anterior tongue showing non-
The dorsal mucosa is somewhat thicker than the ventral and lateral keratinized fungiform papillae (left) and two keratinized filiform papillae
mucosae, is directly adherent to underlying muscular tissue with no (centre and right) with non-keratinized regions between. (With permission
discernible submucosa, and is covered by numerous papillae. The from Young B, Heath JW 2000 Wheater’s Functional Histology.
dorsal epithelium consists of a superficial stratified squamous epithe Edinburgh: Churchill Livingstone.)


lium, which varies from nonkeratinized stratified squamous epithe
lium posteriorly, to fully keratinized epithelium overlying the filiform
papillae more anteriorly. These features probably reflect the fact that the functions appear to be to increase the friction between the tongue and
apex of the tongue is subject to greater dehydration than the posterior food, and to facilitate the movement of particles by the tongue within
and ventral parts and is subject to more abrasion during mastication. the oral cavity.
The underlying lamina propria is a dense fibrous connective tissue, with
numerous elastic fibres, and is continuous with similar tissue extending Fungiform papillae
between the lingual muscle fasciculi. It contains numerous vessels and Fungiform papillae occur mainly on the lingual margin but also irregu
nerves from which the papillae are supplied, and also large lymph larly on the dorsal surface, where they may occasionally be numerous
plexuses and lingual glands. (see Fig. 31.12). They differ from filiform papillae because they are
larger, rounded and deep red in colour, this last reflecting their thin,
lingual papillae nonkeratinized epithelium and highly vascular connective tissue core.
Lingual papillae are projections of the mucosa covering the dorsal Each usually bears one or more taste buds on its apical surface.
surface of the tongue (see Fig. 31.5). They are limited to the presulcal
part of the tongue, produce its characteristic roughness and increase the Foliate papillae
area of contact between the tongue and the contents of the mouth. Foliate papillae lie bilaterally in two zones at the sides of the tongue
There are four principal types, named filiform, fungiform, foliate and near the sulcus terminalis, each formed by a series of red, leaflike
circumvallate papillae, and all except the filiform papillae bear taste mucosal ridges, covered by a nonkeratinized epithelium. They bear
buds. Papillae are more visible in the living when the tongue is dry. numerous taste buds.
Filiform papillae Circumvallate papillae
Filiform papillae are minute, conical or cylindrical projections that Circumvallate papillae are large cylindrical structures, varying in number


cover most of the presulcal dorsal area, and are arranged in diagonal from 8 to 12, which form a Vshaped row immediately in front of the
rows that extend anterolaterally, parallel with the sulcus terminalis, sulcus terminalis on the dorsal surface of the tongue. Each papilla,
except at the lingual apex, where they are transverse. They have irregular 1–2 mm in diameter, is surrounded by a slight circular mucosal eleva
cores of connective tissue and their epithelium, which is keratinized, tion (vallum or wall), which is separated from the papilla by a circular
may split into whitish fine secondary processes (Fig. 31.12). Their sulcus (Figs 31.13–31.14). The papilla is narrower at its base than its


Oral cavity
515.e1
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Fig. 31.11 A,B, Entire nerve maps of an adult
A B
human tongue, Sihler’s stain. Several muscles,
including genioglossus and the posterior
transverse (T) and vertical (V) intrinsic muscles,
were removed in order to track individual nerves.
TT The hypoglossal nerve (XII) and its lateral (l-XII)
VV and medial (m-XII) branches lie between the
TT lingual (LN) and glossopharyngeal (IX) nerves in
TT VV
VV the posterior part of the tongue. The lateral branch
TT is derived from the main trunk of the hypoglossal
VV nerve as either a short single branch (left side in
VP A) or multiple branches (right side in A and both
sides in B). Other abbreviations: VP, vallate
LN
papillae. (With permission from Mu L, Sanders I
2010 Human tongue neuroanatomy: nerve supply
m-XII
and motor endplates. Clin Anat 23:777–91.)
L-XII
XII
IX


Oral cavity
516
4
NOitcES
apex and the entire structure is generally covered with nonkeratinized
stratified squamous epithelium. Numerous taste buds are scattered in
both walls of the sulcus, and small serous glands (of von Ebner) open
into the sulcal base.
Taste buds
Taste buds are microscopic barrelshaped epithelial structures that
contain chemosensory cells in synaptic contact with the terminals of
gustatory nerves. They are numerous on all types of lingual papillae
(except filiform papillae), particularly on their lateral aspects. Taste
buds are not restricted to the papillae; they are scattered over almost
the entire dorsal and lateral surfaces of the tongue and, rarely, on the
epiglottis and lingual aspect of the soft palate. Each taste bud is linked
by synapses at its base to one of three cranial nerves that carry taste, i.e.
the facial, glossopharyngeal or vagus. They share some physiological
features with neurones, e.g. action potential generation and synaptic
transmission, and are therefore often referred to as paraneurones.
There is considerable individual variation in the distribution of taste
buds in humans. They are most abundant on the posterior parts of the
Fig. 31.13 A section through a circumvallate papilla. Serous glands (of
tongue, especially around the walls of the circumvallate papillae and
von Ebner) empty via ducts into the base of the trench. Numerous taste
buds (pale structures on the inner wall of the cleft, left side) are contained their surrounding sulci, where there is an average of 250 taste buds for
within the stratified epithelium of the papillary wall. (With permission from each of the 8–12 papillae. Over 1000 taste buds are distributed over the
Young B, Heath JW 2000 Wheater’s Functional Histology. Edinburgh: sides of the tongue, particularly over the more posterior folds of the
Churchill Livingstone.) foliate papillae, whereas they are rare, and sometimes even absent, on
fungiform papillae (53 per papilla). Taste buds have been described on
the fetal epiglottis and soft palate but most disappear from these sites
during postnatal development.
Microstructure of taste buds


Each taste bud is a barrelshaped cluster of 50–150 fusiform cells, which
lies within an oval cavity in the epithelium and converges apically on
a gustatory pore, a 2 µm wide opening on the mucosal surface. The
whole structure is about 70 µm in height by 40 µm across and is sepa
rated by a basal lamina from the underlying lamina propria. A small
fasciculus of afferent nerve fibres penetrates the basal lamina and spirals
around the sensory cells. Chemical substances dissolved in the
oral saliva diffuse through the gustatory pores of the taste buds to
reach the taste receptor cell membranes, where they cause membrane
depolarization.
innervation of taste buds
Individual nerve fibres branch to give a complex distribution of taste
bud innervation. Each fibre may have many terminals, which may
A spread to innervate widely separated taste buds or may innervate more
than one sensory cell in each bud. Conversely, individual buds may
receive the terminals of several different nerve fibres. These convergent
and divergent patterns of innervation may be of considerable functional
importance.
The gustatory nerve for the anterior part of the tongue, excluding the
circumvallate papillae, is the chorda tympani, which travels via the
lingual nerve. In most individuals, taste fibres run in the chorda tympani
to cell bodies in the facial ganglion, but occasionally they diverge to
the otic ganglion, which they reach via the greater petrosal nerve. Taste
buds in the inferior surface of the soft palate are supplied mainly by
B P B the facial nerve, through the greater petrosal nerve, pterygopalatine
ganglion and lesser palatine nerve; they may also be supplied by the
glossopharyngeal nerve. Taste buds in the circumvallate papillae, post
sulcal part of the tongue and in the palatoglossal arches and the
oropharynx are innervated by the glossopharyngeal nerve, and those in
the extreme pharyngeal part of the tongue and epiglottis receive fibres
from the internal laryngeal branch of the vagus.
Each taste bud receives two distinct classes of fibre: one branches in
the periphery of the bud to form a perigemmal plexus, whereas the


other forms an intragemmal plexus within the bud itself, which inner
vates the bases of the receptor cells. The perigemmal fibres contain
various neuropeptides including calcitonin generelated peptide
(CGRP) and substance P, and appear to represent free sensory endings.
Intragemmal fibres branch within the taste bud and each forms a series
of synapses.
B
Central connections
On entering the brainstem, gustatory afferents constitute the tractus
Fig. 31.14 A circumvallate papilla. A, A scanning electron micrograph
solitarius and terminate in the rostral third of the nucleus solitarius of
showing a circumvallate papilla surrounded by a trench. B, A section of a
the medulla oblongata.
circumvallate papilla showing pale barrel-shaped taste buds (B) in its
walls. Other abbreviations: P, apical pore. (A, courtesy of S Franey and
taste discrimination
with permission from Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral
Anatomy, Embryology and Histology, 4th ed. Edinburgh: Mosby; B, with Historically, gustatory receptors have been reported to detect four
permission from Dr JB Kerr, Monash University, from Kerr JB 1999 Atlas main qualities of taste sensation; these socalled basic tastes are salt
of Functional Histology. London: Mosby.) (typically NaCl), sour (typically acids), sweet (typically sugars) and


teeth
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bitter (typically quinine). More recently, a fifth basic taste has been permanent molar erupts around 6 years, and thence the deciduous teeth
identified, namely umami (Japanese for delicious taste), which is a are exfoliated one by one, to be replaced by their permanent successors.
glutamatelike receptor stimulated by monosodium glutamate (Smith A complete permanent dentition is present when the third molars erupt
and Margolskee 2006). at around the age of 18–21 years. In the complete deciduous dentition,
Although it is commonly stated that particular areas of the tongue there are 20 teeth, 5 in each jaw quadrant. In the complete permanent
are specialized to detect these different tastes, evidence indicates that dentition, there are 32 teeth, 8 in each jaw quadrant (Berkovitz et al
all areas of the tongue are responsive to all taste stimuli. Each afferent 2009).
nerve fibre is connected to widely separated taste buds and may respond There are three basic tooth forms in both dentitions: incisiform,
to several different chemical stimuli. Some respond to all four classic caniniform and molariform. Incisiform teeth (incisors) are cutting teeth
categories, others to fewer or only one. Within a particular class of and have thin, bladelike crowns. Caniniform teeth (canines) are pier
tastes, receptors are also differentially sensitive to a wide range of cing or tearing teeth and have a single, stout, pointed, coneshaped
similar chemicals. Moreover, taste buds alone are able to detect only a crown. Molariform teeth (molars and premolars) are grinding teeth and
rather restricted range of chemical substances in aqueous solution. It is possess a number of cusps on an otherwise flattened biting surface.
difficult to separate the perceptions of taste and smell because the oral Premolars are bicuspid teeth that are restricted to the permanent denti
and nasal cavities are continuous. Indeed, much of what is perceived as tion and replace the deciduous molars.
taste is the result of airborne odorants from the oral cavity that pass The toothbearing region of the jaws can be divided into four quad


through the nasopharynx to the olfactory area above it (Linden 1998). rants: the right and left maxillary and mandibular quadrants. A tooth
Perceived sensations of taste are the results of the processing (pre may thus be identified according to the quadrant in which it is located
sumably central) of a complex pattern of responses from particular (e.g. a right maxillary tooth or a left mandibular tooth). In both the
areas of the tongue. deciduous and permanent dentitions, the incisors may be distinguished
In newborn infants, oral sucrose has been shown to reduce proced according to their relationship to the midline. Thus, the incisor nearest
ural pain from single events; the mechanism of this nociceptive effect the midline is the central (first) incisor and the incisor that is more
is not yet fully understood (Stevens et al 2013). laterally positioned is termed the lateral (second) incisor. The perma
nent premolars and the permanent and deciduous molars can also be
Autonomic innervation of the tongue distinguished according to their mesiodistal relationships. The molar
most mesially positioned is designated the first molar, and the one
behind it is the second molar. In the permanent dentition, the tooth
The parasympathetic innervation of the various lingual mucous glands
most distally positioned is the third molar. The mesial premolar is the
is via the chorda tympani branch of the facial nerve, which synapses in
first premolar, and the premolar behind it is the second premolar.
the submandibular ganglion; postganglionic branches are distributed
to the lingual mucosa either via the lingual nerve or via plexuses around The terminology used to indicate tooth surfaces is shown in Figure
the lingual arteries.
31.16B. The aspect of teeth adjacent to the lips or cheeks is termed labial
or buccal, that adjacent to the tongue being lingual (or palatal in the
The postganglionic sympathetic supply to lingual glands and vessels
maxilla). Labial and lingual surfaces of an incisor meet medially at a
arises from the carotid plexus (fibres derived from neurones in the
mesial surface and distally at a distal surface, terms that are also used


superior cervical ganglion) and enters the tongue through plexuses
to describe the equivalent surfaces of premolar and molar (postcanine)
around the lingual arteries. Isolated nerve cells, perhaps postganglionic
teeth. On account of the curvature of the dental arch, mesial surfaces
parasympathetic neurones, have been reported in the postsulcal region;
of postcanine teeth are directed anteriorly and distal surfaces are
presumably, they innervate glandular tissue and vascular smooth
directed posteriorly. Thus, the point of contact between the central inci
muscle.
sors is the datum point for mesial and distal. The biting or occlusal
surfaces of postcanine teeth are tuberculated by cusps that are separated
TEETH by fissures forming a pattern characteristic of each tooth. The biting
surface of an incisor is the incisal edge.
INTRODUCTION AND TERMINOLOGY
Humans have two generations of teeth: the deciduous (primary) denti TOOTH MORPHOLOGY
tion (Fig. 31.15) and the permanent (secondary) dentition. The first
deciduous teeth erupt into the mouth at about 6 months after birth and There are two incisors, a central and a lateral, in each half jaw or quad
all of the deciduous teeth have erupted by 3 years of age. The first rant (see Fig. 31.16; Fig. 31.17). In labial view, the crowns are trapezoid,
Central incisor
Lateral incisor
Canine
First premolar
Second premolar
First molar
Second molar
Third molar
A B
Fig. 31.16 The permanent teeth: occlusal aspect. A, The upper dental arch. B, The lower dental arch. The terminology employed for the identification of
teeth according to their location is shown in the lower jaw; the same terminology is used to describe the teeth in the upper jaw.
enildiM
Incisors
Labial
Canine
molars
Pre
Buccal
ars Lingual
ol
M
Mesial
Distal


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Natal and/or neonatal teeth (teeth present at birth and teeth erupted
within the first month of life, respectively) are rare, with an incidence
of 1 in 3000 births. More than 90% of natal and neonatal teeth are
prematurely erupted deciduous mandibular incisors, while less than
10% are supernumerary. Several syndromes have been associated with
natal teeth, namely: Ellis–van Creveld, Hallermann–Streiff, Jadassohn–
Lewandowski and Pierre Robin syndromes. Histological features are
failure of root formation, a large vascular pulp, irregular dentine form
ation and a failure of cementum formation (Mhaske et al 2013).
Fig. 31.15 The primary dentition. An anterior view of the complete
deciduous (primary) dentition at age 3 years. (Courtesy of Miss Victoria
Clark.)


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Molars Premolars Canine Incisors
Molars Canine Incisors
Fig. 31.17 The permanent upper and lower teeth of the right side: labial
and buccal surfaces.
Fig. 31.18 The deciduous upper and lower teeth of the right side: labial
and buccal surfaces.
and the maxillary incisors (particularly the central) are larger than the
mandibular. On eruption, the biting or incisal edges initially have three
tubercles or mamelons, which are rapidly removed by wear. In mesial
or distal view, their labial profiles are convex while their lingual surfaces
are concavoconvex (the convexity near the cervical margin is caused by
a low ridge or cingulum, which is prominent only on upper incisors).
The roots of incisors are single and rounded in maxillary teeth, but
flattened mesiodistally in mandibular teeth. The upper lateral incisor
may be congenitally absent or may have a reduced form (pegshaped
lateral incisor).
Behind each lateral incisor is a canine tooth with a single cusp
(hence the American term cuspid) instead of an incisal edge. The maxil
lary canine is stouter and more pointed than the mandibular canine,
whose cusp tip is inclined lingually. The canine root, which is the
longest of any tooth, produces a bulge (canine eminence) on the alveo
lar bone externally, particularly in the upper jaw. Although canines
usually have single roots, those of the lower jaw may sometimes be
bifid. A
Distal to the canines are two premolars, each with a buccal and
lingual cusp (hence the term bicuspid). The occlusal surfaces of the
maxillary premolars are oval (the long axis is buccopalatal) and a
mesiodistal fissure separates the two cusps. In buccal view, premolars
resemble the canines but are smaller. The maxillary first premolar has
two roots (one buccal, one palatal) but may have one root, or very rarely
three roots (two buccal and one palatal); this makes the tooth more


likely to fracture on removal. The maxillary second premolar usually
has one root. The occlusal surfaces of the mandibular premolars are
more circular or squarer than those of the upper premolars. The buccal
cusp of the mandibular first premolar towers above a diminutive lingual
cusp to which it is connected by a ridge separating the mesial and distal
occlusal pits. In the mandibular second premolar, a mesiodistal fissure
usually separates a buccal from two smaller lingual cusps. Each lower
premolar has one root, but very rarely the root of the first is bifid. Rarely,
B
lower second premolars fail to develop.
Posterior to the premolars are three molars whose size decreases
distally. Each has a large rhomboid (upper jaw) or rectangular (lower Fig. 31.19 A, The upper deciduous dentition. Note the channels (arrows)
jaw) occlusal surface with four or five cusps. The maxillary first molar leading to the developing permanent teeth. B, The lower deciduous
dentition. (With permission from Berkovitz BKB, Moxham BJ 1994 Color
has a cusp at each corner of its occlusal surface, and the mesiopalatal
Atlas of the Skull. London: Mosby.)
cusp is connected to the distobuccal by an oblique ridge. A smaller
cusplet or tubercle (cusplet of Carabelli) usually appears on the mesio
palatal cusp (most commonly in Caucasian groups). The tooth has
three widely separated roots: two buccal, of which the mesiobuccal is of the first molar) and its two roots are closer together. The mandibular
larger and broader and the distobuccal is rounder and smaller, and one third molar is smaller still and, like the upper third molar, is variable
large palatal. Their proximity to the maxillary air sinus is thought to be in form. Its crown may resemble that of the lower first or second molar
the reason first molar roots are wide apart and second and third molar and its roots are frequently fused. One or more third molars (upper or
roots are converged. The smaller maxillary second molar has a reduced lower) often fail to develop.


or occasionally absent distopalatal cusp. Its three roots show varying
Deciduous teeth
degrees of fusion. The maxillary third molar, the smallest, is very vari
able in form. It usually has three cusps (the distopalatal being absent)
and commonly the three roots are fused. The incisors, canine and premolars of the permanent dentition replace
The mandibular first molar has three buccal and two lingual cusps two deciduous incisors, a deciduous canine and two deciduous molars
on its rectangular occlusal surface, the smallest cusp being distal. The in each jaw quadrant (Figs 31.18–31.19). The deciduous incisors and
cusps of this tooth are all separated by fissures. It has two widely sepa canine are shaped like their successors but are smaller and whiter and
rated roots: one mesial and one distal. The smaller mandibular second become extremely worn in older children. The deciduous second molars
molar is like the first, but has only four cusps (it lacks the distal cusp resemble the first permanent molars rather than their successors, the


teeth
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Birth 9 months 18 months 3 years
6 years 8 years 9 years
10 years 12 years 21 years
Fig. 31.20 The development of the deciduous (blue) and permanent (yellow) teeth. (Modified with permission from Schour I, Massler M 1941 The
development of the human dentition. J Am Dent Assoc 28:1153–1160.)
premolars. The upper first deciduous molar has a triangular occlusal Table 31.1 Chronology of the human dentition
surface (its rounded ‘apex’ is palatal), and a fissure separates a double
Dentition Tooth First evidence Crown Eruption Root
buccal cusp from the palatal cusp. The lower first deciduous molar is
of calcification completed (months) completed
long and narrow; its two buccal cusps are separated from its two lingual (weeks in utero (months) (years)
cusps by a zigzagging mesiodistal fissure. Both deciduous molars have for deciduous
large buccal protuberances on their mesial aspect. Upper deciduous teeth)
molars have three roots (fusion of the palatal and distobuccal root is Deciduous i1 14 11 10 (8–12) 11
2 2
commonplace), and lower deciduous molars have two roots. These upper i2 16 21 11 (9–13) 2
2
roots diverge more than those of permanent teeth because each devel C 17 9 19 (16–22) 31 4
oping premolar tooth crown is accommodated directly under the crown m1 151 2 6 16 (13–19) 21 2
m2 19 11 29 (25–33) 3
of its deciduous predecessor. The roots of deciduous teeth are progres
i1 14 21 8 (6–10) 11
sively resorbed by osteoclastlike cells (odontoclasts) prior to being i2 16 3 2 13 (10–16) 112
2
shed. Deciduous C 17 9 20 (17–23) 31
4


lower m1 151 51 16 (14–18) 21
2 2 4
Eruption of teeth m2 18 10 27 (23–31) 3
l1 3–4 months 4–5 years 7–8 years 10
l2 10–12 months 4–5 years 8–9 years 11
Information on the sequence of development and eruption of teeth into
Permanent C 4–5 months 6–7 years 11–12 years 13–15
the oral cavity (Fig. 31.20) is important in clinical practice and also in upper P1 11–13 years 5–6 years 10–11 years 12–13
2 4
forensic medicine and archaeology. Dental development is one of the P2 2–21 years 6–7 years 10–12 years 12–14
4
best indicators of chronological age when no record of birth exists M1 At birth 21 2–3 years 6–7 years 9–10
M2 21–3 years 7–8 years 12–13 years 14–16
(Garn et al 1965). The tabulated data provided in Table 31.1 are largely 2
M3 7–9 years 12–16 years 17–21 years 18–25
based on Europeanderived populations and there is evidence of ethnic l1 3–4 months 4–5 years 6–7 years 9
variation. When a permanent tooth erupts, about twothirds of the root l2 3–4 months 4–5 years 7–8 years 10
is formed and it takes about another 3 years for the root to be com Permanent C 4–5 months 6–7 years 9–10 years 12–14
pleted. For deciduous teeth, root completion is more rapid. The devel lower P1 13 –2 years 5–6 years 10–12 years 12–13
4
opmental stages of initial calcification and crown completion are less P2 21 4–21 2 years 6–7 years 1–12 years 13–14
M1 At birth 21–3 years 6–7 years 9–10


affected by environmental influences than is eruption, the timing of 2
M2 21–3 years 7–8 years 11–13 years 14–15
which may be modified by several factors such as early tooth loss and M3 8–12 0 years 12–16 years 17–21 years 18–25
severe malnutrition.
Figure 31.21 shows the panoramic appearance of the dentition seen
(Modified with permission from Ash MM 1993 Dental Anatomy, Physiology and Occlusion. Philadelphia:
with orthopantomograms at the time of birth and at 21 2, 61 2, 10 and WB Saunders.)
16 years of age.
Dental alignment and occlusion
centric occlusion. In this position, the lower teeth are normally opposed
symmetrically and lingually with respect to the upper. Some important
It is possible to bring the jaws together so that the teeth meet or occlude features of centric occlusion in a normal (idealized) dentition may be
in many positions. When opposing occlusal surfaces meet with maximal noted. Each lower postcanine tooth is slightly in front of its upper
‘intercuspation’ (i.e. maximum contact), the teeth are said to be in equivalent and the lower canine occludes in front of the upper. Buccal


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A B
C D
Fig. 31.21 Orthopantomograms of the dentition at birth (A), 21 years (B),
2
61 years (C), 10 years (D) and 16 years (E). (B–E, With permission from
2
Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral Anatomy, Embryology
E and Histology, 4th ed. Edinburgh: Mosby; D–E, Courtesy of Dr Eric
Whaites.)
cusps of the lower postcanine teeth lie between the buccal and palatal Variations in tooth number, size and form
cusps of the upper teeth. Thus, the lower postcanine teeth are slightly
lingual and mesial to their upper equivalents. Lower incisors bite
The incidence of variation in number and form, which is often related
against the palatal surfaces of upper incisors, the latter normally obscur
to ethnicity, is rare in deciduous teeth but not uncommon in the per
ing about onethird of the crowns of the lower. This vertical overlap of
manent dentition. One or more teeth may fail to develop, a condition
incisors in centric occlusion is the overbite. The extent to which upper
known as hypodontia. Conversely, additional or supernumerary teeth
incisors are anterior to lowers is termed the overjet. In the most habitual
may form, producing hyperdontia (Fig. 31.22). The third permanent
jaw position, the resting posture, the teeth are slightly apart, the gap
molar is the most frequently missing tooth. In declining order of inci
between them being the freeway space or interocclusal clearance.
dence, other missing teeth are the maxillary lateral incisors, maxillary
During mastication, especially with lateral jaw movements, the food is
or mandibular second premolars, mandibular central incisors and max
comminuted, which facilitates the early stages of digestion.
illary first premolars.
The ideal occlusion is a rather subjective concept. If there is an ideal
occlusion, it can only presently be defined in broad functional terms.
Therefore, the occlusion can be considered ‘ideal’ when the teeth are GENERAL ARRANGEMENT OF DENTAL TISSUES


aligned such that the masticatory loads are within physiological range
and act through the long axes of as many teeth in the arch as possible; A tooth consists of a crown covered by very hard translucent enamel
mastication involves alternating bilateral jaw movements (and not and a root covered by yellowish bonelike cementum (Fig. 31.26A).
habitual, unilateral biting preferences as a result of adaptation to occlu These meet at the neck or cervical margin. A longitudinal ground
sal interference); lateral jaw movements occur without undue mechani section (Fig. 31.26B) reveals that the body of a tooth is mostly dentine
cal interference; in the rest position of the jaw, the gap between teeth with an enamel covering over 2 mm thick, while the cementum is much
(the freeway space) is correct for the individual concerned; and the thinner. The dentine surrounds a central pulp cavity, expanded at its
tooth alignment is aesthetically pleasing to its possessor. coronal end into a pulp chamber and narrowed in the root as a pulp
Variations from the ideal occlusion may be termed malocclusions canal, opening at or near its tip by an apical foramen, occasionally
(although these could be regarded as normal, since they are more com multiple. The pulp is a soft connective tissue, continuous with the peri
monly found in the population: the majority of the population in the odontal ligament via the apical foramen. It contains vessels for the
USA has some degree of occlusal ‘disharmony’). However, the majority support of the dentine and sensory nerves.
of malocclusions should be regarded as anatomical variations rather The root is surrounded by alveolar bone, its cementum separated
than abnormalities, as they are rarely involved in masticatory dysfunc from the osseous socket (alveolus) by the connective tissue of the peri
tion or pain, although they may be aesthetically displeasing. odontal ligament, approximately 0.2 mm thick (Fig. 31.27). Coarse


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Hyperdontia affects the maxillary arch much more commonly than
the mandibular dentition. The extra teeth are usually situated on the
palatal aspect of the permanent incisors or distal to the molars. More
rarely, additional premolars develop. Supernumerary teeth in the
incisor region can often impede the eruption of the permanent teeth
(Figs 31.23–31.24) and indeed this is often the first indication of their
presence. A supernumerary tooth situated between the central incisors
is known as a mesiodens. Teeth may be unusually large (macrodontia)
or small (microdontia), e.g. the crowns of maxillary central incisors may
be abnormally wide mesiodistally; in contrast, a common variant of the
maxillary lateral incisor has a small, pegshaped crown. Epidemiologi
cal studies reveal that hyperdontia tends to be associated with macro
dontia, and hypodontia with microdontia (Fig. 31.25), the most
severely affected individuals representing the extremes of a continuum
of variation. Together with family studies, this indicates that the
causation is multifactorial, combining polygenic and environmental
influences.
Some differences in the form of teeth display geographical variation
Fig. 31.24 A child with retained maxillary central deciduous incisors
and are of anthropological and forensic interest. Mongoloid dentitions
caused by the presence of supernumerary teeth. (Courtesy of Miss
tend to have shovelshaped maxillary incisors with enlarged palatal
Victoria Clark.)
marginal ridges. The additional cusp of Carabelli is commonly found
on the mesiopalatal aspect of maxillary first permanent or second decid
uous molars in Caucasian but rarely in Mongoloid dentitions. In
African races, the mandibular second permanent molar often has five
rather than four cusps.
Fig. 31.23 An orthopantomogram showing supernumerary teeth in the
upper incisor region preventing the exfoliation of the upper primary Fig. 31.25 A child with mixed dentition showing hypodontia and
central incisors and impeding the eruption of the upper permanent central microdontia (small conical-shaped teeth). (Courtesy of Miss Victoria


incisors. (Courtesy of Miss Victoria Clark.) Clark.)


teeth
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bundles of collagen fibres, embedded at one end in cementum, cross 95–96% by weight crystalline apatites (88% by volume) and less than
the periodontal ligament to enter the osseous alveolar wall, these insert 1% organic matrix. The organic matrix comprises mainly unique
ing bundles of collagen being termed Sharpey’s fibres. Near the cervical enamel proteins, amelogenins and nonamelogenins such as enamelins
margin, the tooth, periodontal ligament and adjacent bone are covered and tuftelins. Although comprising a very small percentage of the
by the gingiva. On its internal surface, the gingiva is attached to the weight and volume of enamel, the organic matrix permeates the whole
tooth surface by the junctional epithelium, a zone of profound clinical of enamel. As its formative cells are lost from the surface during tooth
importance because just above it is a slight recess, the gingival sulcus. eruption, enamel is incapable of further growth. Repair is limited to the
As the sulcus is not necessarily selfcleansing, dental plaque may accu remineralization of minute carious lesions.
mulate in it and this predisposes to periodontal disease. Enamel reaches a maximum thickness of 2.5 mm over cusps and
thins at the cervical margins. It is composed of closely packed enamel
Enamel prisms or rods. In longitudinal section, enamel prisms extend from
close to the enamel–dentine junction to within 20 µm of the surface,
where they are generally replaced by prismless (nonprismatic,
Enamel is an extremely hard and rigid material that covers the crowns
of teeth. It is a heavily mineralized epithelial cell secretion, containing
A
C
Fig. 31.22 A plaster cast of the maxilla of a 25-year-old male showing 1
supplemental premolar and 12 peg-shaped supernumerary teeth on the
palatal side of the permanent teeth. (With permission from Berkovitz BKB, Fig. 31.27 A demineralized section of a tooth with its root attached to the
Holland GR, Moxham BJ 2009 Oral Anatomy, Histology and Embryology, surrounding bone by the periodontal ligament. Abbreviations: A, alveolar


4th ed. Edinburgh: Mosby. Courtesy of Royal College of Surgeons of bone; C, root of tooth lined by cementum. The arrow indicates the
England.) periodontal space. (Courtesy of Dr D Lunt.)
Buccal cusp Fig. 31.26 The principal parts of a tooth. A, An
extracted upper right canine tooth viewed from
Cusp Enamel
its mesial aspect. The root is covered by
Dentine
cementum (partially removed), and the curved
Lingual cervical margin is convex towards the cusp
Enamel
cusp of the tooth. B, A ground section of a young
striae
(permanent) lower first premolar tooth sectioned
CROWN
in the buccolingual longitudinal plane,
Crown
photographed with transmitted light. The enamel
striae are incremental lines of enamel growth
Cervical (compare with Fig. 31.30). Within the dentine, the
margin lines of the dentinal tubules are visible, forming
S-shaped curves in the apical region but
straighter in the root.
Position of
cervical
line
Root
Pulp ROOT
chamber
Cementum
Cementum
APEX
Apex
Apical
A B foramen
(immature)


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NOitcES
E
O
A B
SP
SR
C D E
Fig. 31.28 Enamel. A, A scanning electron micrograph of acid-etched outer enamel (O) showing enamel prisms, approximately 5 µm wide. A layer of
prismless enamel (E) is evident on the surface. B, A ground cross-section showing the cross-sectional keyhole (fish scale) appearance of enamel prisms
(pattern 3). C, A ground longitudinal section viewed with phase contrast showing prisms (vertical lines) and cross-striations (horizontal lines). D, A
low-power scanning electron micrograph illustrating the relationship of enamel prism direction (long arrow), striae of Retzius (SR) and surface perikymata
(SP). E, A ground longitudinal section showing enamel striae (arrows). Viewed between crossed polarizing filters. (A, Courtesy of Professor D Whittaker;
B–C, With permission from Berkovitz BKB, Holland GR, Moxham BJ 2009 Oral Anatomy, Embryology and Histology, 4th ed. Edinburgh: Mosby; D, With
permission from Kelley J, Smith TM 2003 Age at first molar emergence in early Miocene Afropithecus turkanensis and life-history evolution in the
Hominoidea. Journal of Human Evolution 44:307–329; E, Courtesy of Dr AD Beynon.)
aprismatic) enamel (Fig. 31.28A). In crosssection, the prisms are of 70% dry weight (largely crystalline hydroxyapatite with some calcium
mainly horseshoeshaped and are arranged in rows that are staggered, carbonate) and 20% organic matrix (type I collagen, glycosamino
such that the tails of the prisms in one row lie between the heads of glycans and phosphoproteins). Its conspicuous feature is the regular
the prism in the row above (prism pattern 3) (Fig. 31.28B) and the tails pattern of microscopic dentinal tubules, 3 µm in diameter, which
are directed rootwards. The appearance of prism boundaries results extend from the pulpal surface to the enamel–dentine junction. The
from sudden changes in crystallite orientation. Prisms have a diameter tubules show lateral and terminal branching near the enamel–dentine


of approximately 5 µm, and are packed with flattened hexagonal junction (Fig. 31.29A) and may project a short distance into the enamel
hydroxyapatite crystals, far larger than those found in collagenbased (enamel spindles). Each tubule encloses a single cytoplasmic process of
mineralized tissues. an odontoblast whose cell body lies in a pseudostratified layer that lines
Two types of incremental lines are visible in enamel: shortterm and the pulpal surface. Processes are believed to extend the full thickness of
longterm. At intervals that average 4 µm – with a range of 2–3 µm at dentine in newly erupted teeth, but in older teeth they may be partly
the enamel–dentine junction and 4–6 µm in outer enamel – along its withdrawn and occupy only the pulpal third, while the outer regions
length, each prism is crossed by a line, probably reflecting diurnal swell contain probably only extracellular fluid. The diameter of the dentine
ing and shrinking in diameter during its growth. This shortterm daily tubule is narrowed by deposition of peritubular dentine. This is differ
growth line is known as a crossstriation (Fig. 31.28C). The longerterm ent from normal dentine (intertubular dentine) because it is more
incremental lines pass from the enamel–dentine junction obliquely to highly mineralized and lacks a collagenous matrix. Peritubular dentine
the surface, where they end in shallow furrows, perikymata, visible on can therefore be identified by microradiography (Fig. 31.29B). In time,
newly erupted teeth (Fig. 31.28D). Each line, known as an enamel stria it may completely fill the tubule, a process that gives rise to translucent
(of Retzius) (Fig. 31.28E), usually represents a period of between 7 and dentine and that commences in the apical region of the root.
9 days of enamel growth with a modal value of 9 days. This is known The outermost zone (10–20 µm) of dentine differs in the crown and


as an individual’s periodicity and it is constant in all teeth from the the root. In the crown, it is referred to as mantle dentine and differs in
same individual. Periodicities of 6, 10, 11 and perhaps even 12 days the orientation of its collagen fibres. In the root, the peripheral zone
have been reported, but collectively they account for less than 10% of presents a granular layer – with less overall mineral – beyond which is
the observed periodicities in large samples of teeth (Reid and Dean a hyaline layer that lacks a tubular structure and may function to
2006). produce a good bond between the cementum and dentine.
A prominent striation, the neonatal line, is formed in teeth whose Dentine is formed slowly throughout life, and so there is always an
mineralization spans birth. Neonatal lines are present in the enamel unmineralized zone of predentine at the surface of the mineralized
and dentine of teeth mineralizing at the time of birth (all the deciduous dentine, adjacent to the odontoblast layer at the periphery of the pulp.
teeth and the first permanent molars) and are therefore of forensic Biochemical changes within the mineralizing matrix mean that preden
importance, indicating that an infant has survived for a few days after tine stains differently to the matrix of the mineralized dentine. The
birth. They reflect a disturbance in mineralization during the first few predentine–dentine border is generally scalloped, because dentine min
days after birth. Other accentuated lines can be observed throughout eralizes both linearly and as microscopic spherical aggregates of crystals
enamel growth; these are generally reflections in disturbances in amelo (calcospherites). Dentine, like enamel, is deposited incrementally, and
blast secretion caused by illness or nutritional deficiencies. In serious exhibits both short and longterm incremental lines (Dean 2000).
cases, these disturbances will manifest as hypoplasia (enamel thinning Longterm lines are known as Andresen lines and in the midaxial
on the tooth surface). region are approximately 20 µm apart; they represent increments of
about 6–12 days (Fig. 31.29C). Daily incremental lines (von Ebner
Dentine
lines) in the midaxial plane are typically 4 µm apart; they are consider


ably closer together (1–2 µm apart) at the enamel–dentine junction
Dentine is a yellowish avascular tissue that forms the bulk of a tooth. and in root dentine. Where mineralization spans birth (i.e. all decidu
It is a tough and compliant composite material, with a mineral content ous teeth and usually the first permanent molars), a neonatal line is


teeth
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A B C
Fig. 31.29 Dentine. A, A ground longitudinal section showing branching of dentine tubules near the enamel–dentine junction (arrow). B, A
microradiograph of transversely sectioned dentinal tubules surrounded by a more radiopaque and therefore more mineralized zone of peritubular dentine.
C, A ground longitudinal section viewed in polarized light showing alternate light and dark bands representing long-period incremental lines (Andresen
lines). The bands are orientated approximately at right angles to the direction of the dentinal tubules (arrows). (With permission from Berkovitz BKB,
Holland GR, Moxham BJ 2009 Oral Anatomy, Embryology and Histology, 4th ed. Edinburgh: Mosby; B, Courtesy of Dr G Mckay.)
ganglion, which enter with the arterioles, and by myelinated (Aδ) and
Enamel worn away unmyelinated (C) sensory nerve fibres from the trigeminal ganglion,
which traverse the pulp longitudinally and ramify as a plexus (Rasch
Enamel striae
kow’s plexus) beneath the odontoblast layer (Figs 31.31–31.32). Here,
any myelinated nerve fibres lose their myelin sheaths and continue into
the odontoblast layer, and some enter the dentinal tubules, especially
Dead tracts in dentine the region beneath the cusps. Stimulation of dentine, whether by
thermal, mechanical or osmotic means, evokes a pain response. Pulp
nerves release numerous neuropeptides such as CGRP, substance P and
Circumpulpal dentine neuropeptide Y that maintain homeostasis within the pulp.
Cementum
Irregular (tertiary)
dentine Cementum is a bonelike tissue that covers the dental roots, and is 50%
by weight mineralized (mainly hydroxyapatite crystals). However,
unlike bone, cementum is avascular and lacks nerves. The cementum
Pulp cavity generally overlaps the enamel slightly, although it may meet it end on.
Occasionally, the two tissues may fail to meet, in which case dentine is


Fig. 31.30 A longitudinal ground section of an incisor tooth. exposed in the mouth. If the exposed dentinal tubules remain patent,
then the teeth may be sensitive to stimuli such as cold water. In older
teeth, the root may become exposed in the mouth as a consequence of
formed in dentine similar to that which is seen in enamel, and it signals occlusal drift and gingival recession, and cementum is often abraded
the abrupt change in both environment and nutrition that occurs at away by incorrect tooth brushing and dentine is exposed.
birth. As with enamel, disturbances in growth of dentine will exhibit as Like bone, cementum is perforated by Sharpey’s fibres, which repre
accentuated lines, commonly called contour lines of Owen. sent the attachment bundles of collagen fibres in the periodontal liga
Primary dentine formation proceeds at a steady but declining rate ment (extrinsic fibres). New layers of cementum, which are deposited
as first the crown and then the root is completed. A slow and intermit incrementally throughout life to compensate for tooth movements,
tent deposition of dentine (regular secondary dentine) continues incorporate new Sharpey’s fibres. Incremental lines are irregularly
throughout life and further reduces the size of the pulp chamber; it is spaced. The first (primary) cementum to be formed is thin (up to
distinguished from primary dentine by the reduction and less regular 200 µm) and acellular, and contains only extrinsic fibres. Cementum
arrangement of dentinal tubules within it. The presence of the odonto formed later (secondary cementum) towards the root apex is produced
blast process means that dentine is a vital tissue. It responds to adverse more rapidly and contains cells, the cementocytes, lying in lacunae
external stimuli – such as rapidly advancing caries, excessive wear or joined by canaliculi. The latter are mainly directed towards their source
tooth breakage – by forming poorly mineralized dead tracts, in which of nutrients from the periodontal ligament. This cementum contains
the odontoblasts of the affected region die and the tubules remain mainly intrinsic collagen fibres of cementoblastic origin, which lie par
empty (tertiary dentine). A dead tract may be sealed from the pulp by allel to the surface. Varying arrangements of layering between cellular


a thin zone of sclerosed dentine and the deposition of irregular (ter and acellular cement occur. With increasing age, cellular cement may
tiary) dentine by newly differentiated pulp cells (Fig. 31.30). reach a thickness of a millimetre or more around the apices and at the
branching of the roots, where it compensates for the loss of enamel by
Dental pulp attrition. Cementum is not remodelled but small areas of resorption
with evidence of repair may be seen.
Dental pulp provides the nutritive support for the synthetic activity of
Periodontal ligament
the odontoblast layer. It is a wellvascularized, soft, loose connective
tissue, enclosed by dentine and continuous with the periodontal liga
ment via apical and accessory foramina. Several thinwalled arterioles The principal functions of the periodontal ligament are to support the
enter by the apical foramen and run longitudinally within the pulp to teeth, generate the force of tooth eruption and provide sensory informa
an extensive subodontoblastic plexus. Blood flow rate per unit volume tion about tooth position and forces to facilitate reflex jaw activity
of tissue is greater in the pulp than in other oral tissues, and tissue fluid during chewing movements. The periodontal ligament is a soft, dense,
pressures within the pulp appear to be unusually high. fibrous connective tissue 0.2 mm wide, which contains cells associated
As well as typical connective tissue cells, pulp uniquely contains the with the development and maintenance of alveolar bone (osteoblasts
cell bodies of odontoblasts whose long processes occupy the dentinal and osteoclasts) and of cementum (cementoblasts and odontoclasts).
tubules. Pulp also has dendritic antigenpresenting cells. Approximately It also contains a network of epithelial cells (epithelial cell rests of
60% of pulpal collagen is type I, and the bulk of the remainder is type Malassez, ERM cells), which are embryological remnants of an epithe
III. As dentine deposition increases with age, the pulp recedes until the lial root sheath. Although their function remains speculative, ERM cells
whole of the crown may be removed without accessing the pulp. have been implicated in root development and protection against root
Dental pulp is extensively innervated by unmyelinated postgangli resorption, and in reparative/regenerative functions of the pulp and


onic vasoconstrictor sympathetic nerve fibres from the superior cervical periodontal tissues such as apexogenesis and periodontal healing


Oral cavity
524
4
NOitcES
Fissure
Cusp
Enamel prism
Enamel spindle
Contact area
Enamel stria
Interdental papilla
Amelodentinal
junction
Pulp horn
Incremental line
(Andresen line) Dentogingival fibres
Circular fibres
Pulp chamber of periodontal
Trans-septal fibres ligament
Alveolar crest fibres
Dentinal tubules
Odontoblast
Subodontoblastic
nerve plexus
Volkmann's canal
Predentine
Acellular cement
Pulpal blood vessels and Granular layer
sympathetic plexus
Oblique fibres of the
periodontium
Interdental septum
Root canal
Lateral canal
Pulpal sensory nerve
Inter-radicular septum
Cellular cement
Apical foramen
Apical fibres
Alveolar nerve
and vessels
Fig. 31.31 A longitudinal section of a tooth and its surrounding tissues.
Fig. 31.32 A (Keinan and Cohen 2013). Proliferation of ERM cells may play a role
longitudinal in the evolution of odontogenic cysts and tumours.
demineralized section The majority of collagen fibres of the periodontal ligament are
of a tooth stained with arranged as variously orientated dense fibre bundles that connect alveo
a silver impregnation lar bone and cementum, and which may help to resist movement in
technique. Note the specific directions (Fig. 31.33; see Fig. 31.31). About 80% of the colla
small bundle of nerves gen in the periodontal ligament is type I, most of the remainder being
** within the pulp (*); one
type III. The rate of turnover of collagen is probably the highest of any
of the fine axons from
site in the body, for reasons that are as yet unclear. A very small volume
the bundle (A) passes
of fibres are oxytalan (preelastin) fibres. Fibroblast density in human
between the
periodontal ligament tissue decreases with age (Krieger et al 2013).
odontoblasts (B) lining
The periodontal ligament is innervated by autonomic and sensory
the surface of the
fibres, the former carrying vasomotor information and the latter carry
predentine (C).


ing nociceptive and proprioceptive information. Three types of nerve
endings have been identified: free nerve endings (originating from
myelinated and unmyelinated nerve fibres), Ruffinilike endings (mostly
A
found at the apical part of the periodontal ligament) and lamellated
corpuscles (for further reading, see Huang et al (2011)). The periodontal
ligament has a rich blood supply; the vessels tend to lie towards the
bone side of the periodontal ligament and the capillaries are fenestrated
B
(see below for further details).
C
Alveolar bone
That part of the maxilla or mandible that supports and protects the
teeth is known as alveolar bone. An arbitrary boundary at the level of
the root apices of the teeth separates the alveolar processes from the