Oral biology

Sensory root : Afferents Somatic / Special
Motor root : Efferents Motor / Secretion

Sensation ( Somatosensory system )
• Special senses : smell, sight, taste, hearing and balance
• General senses : touch - position - pain- temperature
• There are two basic types of general sensation:
• touch/position pain/temperature
• touch/position information is carried by myelinated (fast-conducting)
nerve fibers,
• pain/temperature information is carried by unmyelinated (slow-
conducting) nerve fibers.

The primary sensory receptors for touch/position :
Meissner’s corpuscles,
Merkel's receptors,
Pacinian corpuscles,
Ruffini’s corpuscles,
hair receptors,
muscle spindle organs, Golgi tendon organs
The primitive receptors for pain/temperature: bare nerve endings.
Proprioceptors (muscle spindle organs and Golgi tendon organs) provide
information about joint position and muscle movement. Much of this
information is processed at an unconscious level (mainly by the
cerebellum and the vestibular nuclei).

Sensory fiber types
Type
Erlanger-Gasser
Classification
Diameter Myelin
Conduction
velocity
Associated sensory
receptors
Ia Aα 13-20 µm Yes 80-120 m/s
Primary receptors of muscle
spindle
Ib Aα 13-20 µm Yes 80-120 m/s Golgi tendon organ
II Aβ 6-12 µm Yes 33-75 m/s
Secondary receptors of
muscle spindle
All cutaneous
mechanoreceptors
III Aδ 1-5 µm Thin 3-30 m/s
Free nerve endings of touch
and pressure
Nociceptors of
neospinothalamic tract
Cold thermoreceptors
IV C
0.2-1.5
µm
No 0.5-2.0 m/s
Nociceptors of
paleospinothalamic tract
Warmth receptors

Sensory pathways
The two types of sensation in humans, touch/position and pain/temperature, are
processed by different pathways in the central nervous system. The distinction is hard-
wired, and it is maintained all the way to the cerebral cortex.

• 1 Olfactory (CN I)
• 2 Oculomotor (CN III)
• 3 Abducens (CN VI)
• 4 Facial (CN VII)
• 5 Hypoglossal (CN XII)
• 6 Accessory (CN XI)
• 7 Vagus (CN X)
• 8 Glossopharyngeal (CN IX)
• 9 Vestibulocochlear (CN VIII)
• 10 Trigerminal (CN V)
• 11 Trochlear (CN IV)
• 12 Optic chiasma
• 13 Optic nerve (CN II)
Cranial Nerves

Cranial nerves
Sensory –Motor –Parasympathetic
•Trigeminal nerves(V)
•Facial nerve (VII)
•Glossopharyngeal nerve (IX)
•Vagus nerve (X)
•Hypoglossal nerve(XII)

Oral Sensation
The trigeminal nerve is the largest cranial nerve

It emerges from the side of the pons.
The trigeminal nerve is a mixed nerve.
Function
•It is the great sensory nerve of the
head and face.The sensory function of
the trigeminal nerve is to provide the
tactile, proprioceptive, and
nociceptive afferent of the face and
mouth.
(The posterior scalp and the neck are
innervated by C2-C3, not by the trigeminal
nerve.)
•The motor function activates the
muscles of mastication(biting,
chewing, and swallowing).

It has three major branches:
the ophthalmic nerve(V1),
the maxillary nerve (V2),
the mandibular nerve (V3).

• The three branches converge on the trigeminal ganglion( semilunar
ganglion or gasserian ganglion) .This location can be found along the
temporal bone and contains the cell bodies of incoming sensory nerve
fibers.
• From the trigeminal ganglion, a single large sensory root enters the
brainstem at the level of the pons.
• Adjacent to the sensory root, a smaller motor root emerges from the
pons.Their cell bodies are located in the motor nucleus of the fifth nerve.

The sensory innervation can be
traced to the nuclei in the pons, the
midbrain, and the medulla
oblongata.

The ophthalmic, maxillary and mandibular branches leave the skull through
three separate foramina: the superior orbital fissure, the foramen rotundum
and the foramen ovale.
•The ophthalmic nerve :the scalp and forehead, the upper eyelid,
the conjunctiva and cornea of the eye, the nose(including the tip of the nose)
, the nasal mucosa, the frontal sinuses.
•The maxillary nerve :the lower eyelid and cheek, upper lip, the upper teeth and
gums, the nasal mucosa, the palate and roof of the pharynx, the maxillary,
ethmoid and sphenoid sinuses, and parts of the meninges.
•The mandibular nerve carries sensory information from the lower lip, the lower
teeth and gums, the chin and, parts of the external ear. the mandibular is joined
outside the cranium by the motor root.
•The mandibular nerve carries touch/position and pain/temperature sensation from
the mouth. It does not carry taste sensation,
but one of its branches, the lingual nerve carries multiple types of nerve fibers that
do not originate in the mandibular nerve.

Motor branches of the trigeminal nerve
• Motor branches of the trigeminal nerve are distributed in the mandibular nerve.
These fibers originate in the motor nucleus of the fifth nerve, which is located
near the main trigeminal nucleus in the pons.
• The motor branches of the trigeminal nerve control the movement of eight
muscles, including the four muscles of mastication.
Muscles of mastication
• masseter
• temporalis
• medial pterygoid
• lateral pterygoid
Other
• tensor veli palatini
• mylohyoid
• anterior belly of digastric
• tensor tympani
• With the exception of tensor tympani, all of these muscles are involved in biting, chewing
and swallowing. All have bilateral cortical representation.

Touch/position information from the body is carried to the thalamus by the medial
lemniscus;
touch/position information from the face is carried to the thalamus by the trigeminal
lemniscus.
Pain/temperature information from the body is carried to the thalamus by the
spinothalamic tract;
pain/temperature information from the face is carried to the thalamus by the
trigeminothalamic tract .

Pathways for touch/position sensation from the face and body merge together in the
brainstem. A single touch/position sensory map of the entire body is projected onto
the thalamus. Likewise, pathways for pain/temperature sensation from the face and
body merge together in the brainstem. A single pain/temperature sensory map of
the entire body is projected onto the thalamus.

The facial nerve is mixed nerve containing both sensory and motor components.
The nerve emanates from the brain stem at the ventral part of the pontomedullary junction.
facial nerve

All of the muscles of facial expression and some of the muscles of mastication are
innervated by the facial nerve.
The facial nerve also carries some parasympathetic fibers to the salivary glands.
It also carries the sensation of taste.

The nerve enters the internal auditory meatus where the sensory part of the nerve
forms the geniculate ganglion.

In the internal auditory meatus is where the greater petrosal nerve branches
from the facial nerve. The facial nerve continues in the facial canal where the
chorda tympani branches from it.
The main body of the facial nerve is somatomotor and supplies the muscles of
facial expression.
The somatomotor component originates from neurons in the facial motor nucleus
located in the ventral pons.

The visceral motor (parasympathetic) components of the facial nerve originate in the lacrimal or superior
salivatory nucleus.
The visceral motor part of the facial nerve is carried by the greater petrosal nerve.The greater petrosal
nerve synapses in the pterygopalatine ganglion. The ganglion then gives of nerve branches which supply
the lacrimal gland and the mucous secreting glands of the nasal and oral cavities.
The other parasympathetic part of the facial nerve travel with the chorda tympani.They travel with lingual
nerve prior to synapsing in the submandibular ganglion which is located in the lateral floor of the oral
cavity. The submandibular ganglion originates nerve fibers that innervate the submandibular and sublingual
glands.

There are two sensory (special and general) components of facial nerve both of which
originate from cell bodies in the geniculate ganglion.
The special sensory component carries information from the taste buds in the tongue
and travel in the chorda tympani.
The general sensory component conducts sensation from skin in the external auditory
meatus, a small area behind the ear, and external surface of the tympanic membrane.
The general sensory component enters the brainstem and eventually synapses in the
spinal part of trigeminal nucleus.
The special sensory or taste fibers enter the brainstem and terminate in the gustatory
nucleus which is a rostral part of the nucleus of the solitary tract.

The ninth cranial nerve exits the brain stem between the olive and inferior cerebellar
peduncle.
Glossopharyngeal nerve

Functions
There are a number of functions of the glossopharyngeal nerve:
• It receives general sensory fibers (ventral trigeminothalamic tract) from the
tonsils, the pharynx, the middle ear and the posterior 1/3 of the tongue
Spinal nucleus of the trigeminal nerve
• It receives special sensory fibers (taste)
from the posterior one-third of the tongue
Solitary nucleus
Inferior salivatory nucleus
It supplies parasympathetic fibers to
the parotid gland via the otic ganglion
Nucleus ambiguus It supplies motor
fibers to stylopharyngeus muscle, the only
motor component of this cranial nerve.

The glossopharyngeal nerve:
The IXth nerve has no real nucleus to itself. Instead it shares nuclei with VII and X. The
sensory information in IX goes to the solitary nucleus, a nucleus it shares with VII and X.
All motor information, essentially the innervation of the stylopharyngeus muscle,
comes from the nucleus ambiguus, also shared with X. Finally, like VII, there are some
parasympathetic fibers in IX that innervate the salivary glands.

The tympanic nerve is a branch that is occurs prior to exit the skull

CN XII. Hypoglossal Nerve
The hypoglossal nerve can be found below the tongue.
It is a somatomotor nerve that innervates all the intrinsic and all but one of the
extrinsic muscles of the tongue.
The neuronal cell bodies that originate the hypoglossal nerve are found in the dorsal
medulla of the brain stem in the hypoglossal nucleus.

(general sensation-taste-motor-parasympathetic)
Pharyngeal nerve( Superior, middle and inferior pharyngeal constrictors)
Superior laryngeal nerve : Muscles of the larynx(speech).
(X)Vagus nerve

When you think vagus, you tend to think parasympathetic .However, the vagus has
dozens of functions. They can be grouped into about four categories, and each
category is associated with a medullary nucleus.
• Nucleus ambiguus is a motor nucleus. Cells in the nucleus ambiguus are very
difficult to see (hence the name), and innervate striated muscle throughout the
neck and thorax. This includes some muscles of the palate and pharynx, muscles
of the larynx, and the parasympathetic innervation of the heart.
• The second is the dorsal nucleus of the vagus, which is the secretomotor
parasympathetic nucleus. Secretomotor primarily means that it stimulates glands -
including mucus glands of the pharynx, lungs, and gut, as well as gastric glands in
the stomach. (Incidentally, it is fair-inks, not far-nicks).
• The third is the sensory nucleus of the vagus, the solitary nucleus. It receives taste
information, sensation from the back of the throat, and also visceral sensation.
Visceral sensation includes blood pressure receptors, blood-oxygen receptors,
sensation in the larynx and trachea, and stretch receptors in the gut.
• The general sensory components of the tenth cranial nerve conduct sensation
from the larynx, pharynx, skin the external ear and external auditory canal,
external surface of the tympanic membrane, and the meninges of the posterior
cranial fossa. The central processes from both ganglia enter the medulla and
terminate in the nucleus of the spinal trigeminal tract.

nucleus ambiguus :The pharyngeal branch travels between the internal and external
carotid arteries and enters the pharynx at the upper border of the middle constrictor
muscle. It supplies the all the muscles of the pharynx and soft palate except the
stylopharyngeas and tensor palati. These include the three constrictor muscles, levator
veli palatini, salpingopharyngeus, palatopharyngeus and palatoglossal muscles.
The superior laryngeal nerve branches distal to the pharyngeal branch and descends
lateral to the pharynx. It divides into an internal and external branch. The internal branch
is purely sensory and will be discussed later. The external branch travel to the cricothyroid
muscle which it supplies.
The visceromotor or parasympathetic component of the vagus nerve originates from the
dorsal motor nucleus of the vagus in the dorsal medulla. These cells give rise to axons
that travel in the vagus nerve. The visceromotor part of the vagus innervates ganglionic
neurons which are located in or adjacent to each target organ. The target organs in the
head-neck include glands of the pharynx and larynx (via the pharyngeal and internal
branches).
The general sensory components of the tenth cranial nerve conduct sensation from the
larynx, pharynx, skin the external ear and external auditory canal, external surface of
the tympanic membrane, and the meninges of the posterior cranial fossa. Sensation
from the larynx travels via the recurrent laryngeal and internal branches of the vagus to
reach the inferior vagal ganglion. Sensory nerve fibers from the skin and tympanic
membrane travel with auricular branch of the vagus to reach the superior vagal ganglion.
The central processes from both ganglia enter the medulla and terminate in the nucleus
of the spinal trigeminal tract.

Stimulation of a nociceptor, due to a chemical, thermal, or mechanical event that has the
potential to damage body tissue, may cause nociceptive pain.
pain
All nociceptors are free nerve endings
that are widely distributed throughout
the body. They innervate the skin, bone,
muscle, most internal organs,
blood vessels, and the heart.
They are generally absent from the brain substance itself, although they are in the
meninges.
fast-conducting myelinated A delta fibers : fast, localized, sharp pain
slow-conducting unmyelinated C fibers : slow, poorly-localized, dull pain. They are called
polymodal because of their ability to respond to a mechanical, thermal or chemical
stimulus,(dental pain).
Glutamate and substance p
(>45o C or <5o C)
H+,K+,PG,polypepyides,
Histamin,serotonin,bradykinin

Central pain control mechanisms
1-(Medulla) spinal cord : The gate control theory
2- Direct desending pathways from the brain
3-Opioids induced analegsia

• Gate control theory :activation of nerves which do not transmit pain signals, called
nonnociceptive fibers, can interfere with signals from pain fibers, thereby
inhibiting pain.
• The nonnociceptive fibers indirectly inhibit the effects of the pain fibers, 'closing a
gate' to the transmission of their stimuli. In other parts of the laminae, pain fibers
also inhibit the effects of nonnociceptive fibers, 'opening the gate‘.
• An inhibitory connection may exist with Aβ and C fibers, which may form a synapse
on the same projection neuron. The same neurons may also form synapses with an
inhibitory interneuron that also synapses on the projection neuron, reducing the
chance that the latter will fire and transmit pain stimuli to the brain .
• Thus, depending on the relative rates of firing of C and Aβ fibers, the firing of the
nonnociceptive fiber may inhibit the firing of the projection neuron and the
transmission of pain stimuli.
Ι

One area of the
brain involved in
reduction of pain
sensation is the
periaqueductal
gray matter that
surrounds the
third ventricle and
the cerebral
aqueduct of the
ventricular
system.
Stimulation of this
area produces
analgesia by
activating
descending
pathways that
directly and
indirectly inhibit
nociceptors in the
laminae of the
spinal cord.

The body possesses an additional mechanism to control pain: the release of endogenous
opioids, especially at the level of the PAG,ventral medulla and spinal dorsal horn . There
are neurons that release enkephalins, endorphins, and dynorphins at the PAG, and in this
way modulate its ability to modulate pain perception. Other neurons can release their
endogenous opioids at the source of the pain.
Synapse between nociceptive afferent & projections neurons:
1- presynaptic inhibition( inhibit ca2+ entry)
2- postsynaptic inhibition (increase K+ conductance)

• Allodynia is a pain due to a stimulus which does not normally provoke pain .The
cell types involved in nociception and mechanical sensation are the cells
responsible for allodynia. injury to the spinal cord might lead to loss and re-
organization of the nociceptrors, mechanoreceptors and interneurons, leading to
the transmission of pain information by mechanoreceptors.
• Hyperalgesia is induced by platelet-activating factor (PAF) which comes about in
an inflammation or an allergic response. This seems to occur via immune cells
interacting with the peripheral nervous system and releasing pain-producing
chemicals (cytokines and chemokines).
• Referred pain : pain perceived at a site adjacent to or at a distance from the site of
an injury's origin. One of the best examples of this is during ischemia brought on
by a myocardial infarction(heart attack) where
pain is often felt in the neck, shoulders,
and back rather than in the chest, the site
of the injury.

• Skin, joints, or muscles that have been damaged or inflamed are unusually
sensitive to further stimuli. This phenomenon is called hyperalgesia.
• Hyperalgesia seems to involve processes near peripheral receptors , as well as
mechanisms in the CNS(spinal dorsal horn).
• Damaged skin releases a variety of chemical substances from itself, blood cells,
and nerve endings : bradykinin, prostaglandins, serotonin, substance P, K+, H+
they trigger the set of local responses that we know as inflammation. As a result,
blood vessels become more leaky and cause tissue swelling (or edema) and
redness . Nearby mast cells release the chemical histamine, which directly excites
nociceptors. Finally, the spreading axon branches of the nociceptors themselves
may release substances that sensitize nociceptive terminals and make them
responsive to previously nonpainful stimuli. Such "silent" nociceptors among our
small Aδ and C fibers are normally unresponsive to stimuli-even destructive ones.
Only after sensitization do they become responsive to mechanical or chemical
stimuli and contribute greatly to hyperalgesia.
• Aspirin suppresses the synthesis of prostaglandins.

Taste:
Taste fibers, from the taste buds, are predominantly (from the front 2/3 of the tongue,
anyway) carried by the facial nerve. (Keep in mind that touch and pain sensation from
the tongue is V, and motor to the tongue is XII.) Taste from the back of the tongue and
palate is carried by the glossopharyngeal nerve. Regardless of their origin, the taste
fibers enter the solitary tract of the medulla, and synapse in the surrounding solitary
nucleus.

Taste is a form of direct chemoreception and is one of the traditional five senses.
In the West, experts traditionally identified four taste sensations: sweet, salty, sour, and
bitter.
Eastern experts traditionally identified a fifth, called umami (savory).
Taste
diagrams of the tongue showing levels of sensitivity to different tastes in different
regions. In fact, taste qualities are found in all areas of the tongue. the different sorts
of tastes our tongue can identify are between 4000-10000 chemicals.
Discrimination of different taste:proportion of different primary taste quality, smell,mouth
mechanoreceptors(capsaicin)

Taste buds are small structures on the upper surface of the tongue, soft palate, upper
esophagus and epiglottis that provide information about the taste of food being eaten.
These structures are involved in detecting the five elements of taste perception: salty,
sour, bitter, sweet, and umami (or savory). Via small openings in the tongue epithelium,
called taste pores, parts of the food dissolved in saliva come into contact with the taste
receptors. These are located on top of the taste receptor cells that constitute the taste
buds.
The taste receptor cells send information
detected by clusters of various receptors
and ion channels to the gustatory areas of
the brain via the seventh, ninth and tenth
cranial nerves.
the human tongue has 2,000–8,000 taste buds.
The receptor cells for taste "taste buds" in humans are found on the surface of the tongue,
along the soft palate, and in the epithelium of the pharynx and epiglottis. A single taste
bud contains 50–100 taste cells representing all 5 taste sensations .

Types of papillae
The majority of taste buds on the tongue sit on raised protrusions of the tongue surface
called papillae.
There are four types of papillae present in the human tongue:
Fungiform papillae - these are slightly mushroom-shaped . These are present mostly at
the apex (tip) of the tongue, as well as at the sides. Innervated by facial nerve.

• Filiform papillae - these are thin, long papillae "V"-shaped cones that don't
contain taste buds but are the most numerous. These papillae are mechanical and
not involved in gustation. Characterized increased keratinization.
Foliate papillae - these are ridges and grooves towards the posterior part of the
tongue found on lateral margins. Innervated by facial nerve (anterior papillae) and
glossopharyngeal nerve (posterior papillae).

• Circumvallate papillae - there are only about 3-14 of these papillae on most
people, and they are present at the back of the oral part of the tongue. They are
arranged in a circular-shaped row just in front of the sulcus terminalis of the
tongue. Innervated by the glossopharyngeal nerve.

• Sweet, Bitter, and Umam work with a signal through a G protein-coupled receptor.
• Salty and Sour, which work with ion channels.
More than 90%of receptor cells respond to 2 or more of the basic taste and many
respond to all. There is different sensitivity of taste cells to basic tastes.
One taste cells may have all kind of transduction pathway.

• Cellular basis of taste transduction. A, Salty taste is mediated by an epithelial Na+
channel (ENaC) that is sensitive to amiloride. Sour is mediated by H+ entering
through the same ENaC channel or by the effect of low pH inhibiting a K+ channel.
The resulting depolarization opens voltage-gated Ca2+ channels, increasing [Ca2+]i
and leading to transmitter release. B, Sugar binds to a 7-transmembrane receptor
that activates heterotrimeric G protein, stimulating AC, increasing cAMP, and
activating PKA, which then closes a K+ channel. The resulting depolarization opens
voltage-gated Ca2+ channels, increasing [Ca2+]i and leading to transmitter release.
Bitter substances can act via any of three pathways. (1) A bitter compound directly
inhibits K+ channels. The resulting depolarization opens voltage-gated Ca2+
channels, increasing [Ca2+]i and leading to transmitter release. (2) A ligand binds to
a 7-transmembrane receptor and activates a G protein called gustducin that
stimulates phosphodiesterase. The resultant decrease in [cAMP]i somehow leads
to depolarization. (3) Ligand binds to a receptor that is linked to a G protein, which
activates phospholipase C. The resultant increase in [IP3] releases Ca2+ from stores,
raises [Ca2+]i, and leads to transmitter release. D, Glutamate binds to a glutamate-
gated, nonselective cation channel and opens it. The resultant depolarization
opens voltage-gated Ca2+ channels, increases [Ca2+]i, and leads to transmitter
release.
• AC, adenylyl cyclase; AMP, adenosine monophosphate; cAMP, cyclic adenosine monophosphate; DAG,
diacylglycerol; ER, endoplasmic reticulum; IP3, inositol 1,4,5-triphosphate; PDE, phosphodiesterase; PIP2,
phosphatidyl inositol 4,5-biphosphate; PLC, phospholipase C.

Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth.
It is the first step of digestion and it increases the surface area of foods to allow more
efficient break down by enzymes.
As chewing continues, the food is made softer and warmer, and the enzymes in saliva begin
to break down carbohydrates in the food. After chewing, the food (bolus) is swallowed. It
enters the esophagus and continues on to the stomach, where the next step of digestion
occurs.

The chewing cycle
Mastication is a repetitive sequence of jaw opening and closing with a profile in the
vertical plane called the chewing cycle. Mastication consists of a number of chewing
cycles.
Opening phase: the mouth is opened and the mandible is depressed
Closing phase: the mandible is raised towards the maxilla
Occlusal or intercuspal phase: the mandible is stationary and the teeth from both upper
and lower arches approximate

Mastication motor program
• Mastication is primarily an unconscious act, but can be mediated by higher
conscious input. The motor program for mastication is a hypothesized central
nervous system function by which the complex patterns governing mastication are
created and controlled.
• The presence of food in the mouth causes a reflex inhibition of the muscles of the
lower jaw. Those muscles relax and the lower jaw drops, causing a stretch reflex
which causes muscle contraction and closure of the mouth. During mastication,
the tongue and, to a lesser extent, the lips and cheeks acts to keep food between
the grinding surfaces of the teeth.
• It is thought that feedback from proprioceptive nerves in teeth and the
temporomandibular joints govern the creation of neural pathways, which in turn
determine duration and force of individual muscle activation.
• The motor program continuously adapts to changes in food type or occlusion.

• Mastication is accomplished through the activity of the four muscles of mastication:
• The masseter
• The temporalis
• The medial pterygoid
• The lateral pterygoid
Each of these primary muscles of mastication is paired, with each side of the mandible
possessing one of the four.

The muscles of mastication are all innervated by the trigeminal nerve, they are innervated
by the mandibular branch or V3 and to lesser extend by fascial nerve.
the mandible is connected to the temporal bone of the skull via the temporomandibular
joint, an extremely complex joint which permits movement in all planes. The muscles of
mastication originate on the skull and insert into the mandible, thereby allowing for jaw
movements during contraction.
The mandible is the only bone that moves during mastication and other activities, such as
talking.
While these four muscles are the primary participants in mastication, other muscles are
usually if not always helping the process, such as those of the tongue and the cheeks.

• Mammalian mastication results from the interaction of an intrinsic rhythmical
neural pattern and sensory feedback generated by the interaction of the effecter
system (muscles, bones, joints, teeth, soft tissues) with food.
• The main variables that explain variation in the pattern of human mastication are
the subjects themselves, their age, the type of food being eaten, and time during a
sequence of movements.
• The intrinsic pattern of mastication is generated by a central pattern generator
(CPG) located in the pons and medulla. The output of the CPG is modified by
inputs that descend from higher centers of the brain and by feedback from
sensory receptors.
• Intraoral touch receptors, muscle spindles in the jaw-closing muscles, and
specialized mechanoreceptors in the periodontal ligament have especially
powerful effects on movement parameters.

• The CPG receives inputs from higher centers of the brain, especially from the
inferio-lateral region of the sensorimotor cortex and from sensory receptors.
Mechanoreceptors in the lips and oral mucosa, in muscles, and in the periodontal
ligaments around the roots of the teeth have particularly powerful effects on
movement parameters. The central pattern generator includes a core group of
neurons with intrinsic bursting properties, as well as a variety of other neurons
that receive inputs from oral and muscle spindle afferents. Reorganization of
subpopulations of neurons within the CPG underlies changes in movement
pattern.
• In addition to controlling motoneurons supplying the jaw, tongue, and facial
muscles, the CPG also modulates reflex circuits. It is proposed that these brainstem
circuits also participate in the control of human speech.

swallowing is a complex neuromuscular activity consisting essentially of three phases:
oral, pharyngeal and esophageal phase.
Each phase is controlled by a different neurological mechanism.
•The oral phase, a bolus of food is pressed backward into the pharynx by the tongue, which
is entirely voluntary, is mainly controlled by the medial temporal lobes and limbic system of
the cerebral cortex with contributions from the motor cortex and other cortical areas.

– The pharyngeal swallow is started by the oral phase and subsequently is co-
ordinated by the swallowing centre in the medulla oblongata and pons. The
reflex is initiated by touch receptors in the pharynx. which basically involve
shunting the bolus into the esophagus while at the same time closing
alternative routes of escape.
– The soft palate and uvula fold upward and cover the nasopharynx to prevent
the passage of food up and into the nasal cavity.
– The lumen of the larynx is squeezed shut and the epiglottis swings backward
to cover the larynx. The larynx is also pulled forward and down making the
opening to the esophagus larger.

• Swallowing is a complex mechanism using both
skeletal muscle (tongue) and smooth muscles of the
pharynx and esophagus. The ANS coordinates this
process in the pharyngeal and esophageal phases.
•The upper esophageal sphincter relaxes to let food pass, after which various striated
constrictor muscles of the pharynx as well as peristalsis and relaxation of the lower
esophageal sphincter sequentially push the bolus of food through the esophagus into
the stomach.
The esophageal phase occurs involuntarily in the esophagus.
The esophageal sphincter, normally closed,
opens to allow food to pass when the larynx rises during
swallowing. When food reaches the lower end of
the esophagus, the cardia sphincter opens
to allow the food to enter the stomach.

Mucosal Membrane
Its role
1- Protection
•Mecanical
•Microorganisms
2- Sensation
3- Secretion
Structure
1- Epitelium
2- Lamina Propia

The epitelium is the outer layer,composed of terminally differentiated stratified squamous
epithelium. The epitelium is avascular, nourished by diffusion from the dermis, and
composed of four types of cells, i.e. keratinocytes, melanocytes, Langerhans cells, and the
Merkel cells.Keratinocytes are the major constituent, constituting 95% of the epidermis
Lamina dura :fibroblasts,collagen,elastin,macrophage,mast cell,proteogelican
Blood supply,nerves(ANS,5,7,9,10)

Oral mucosa
The oral mucosa is the mucous membrane epithelium of the mouth. It can be
divided into three categories:
•Masticatory mucosa - keratinized stratified squamous epithelium, found on the
dorsum of the tongue, hard palate and attached gingiva.
•Lining mucosa - non-keratinized stratified squamous epithelium, found almost
everywhere else in the oral cavity.
•Specialized mucosa - specifically in the regions of the taste buds on the
dorsum of the tongue.

A stratified squamous epithelium consists of squamous (flattened) epithelial cells
arranged in layers upon a basement membrane. Only one layer is in contact with the
basement membrane; the other layers adhere to one another to maintain structural
integrity. Although this epithelium is referred to as squamous, many cells within the
layers may not be flattened; this is due to the convention of naming epithelia according
to the cell type at the surface.
This type of epithelium is well suited to areas in the body subject to constant abrasion, as
the layers can be sequentially sloughed off and replaced before the basement membrane
is exposed.
Stratified squamous epithelium is further classified by the presence or absence of keratin
at the apical surface. Non-keratinized surfaces must be kept moist by bodily secretions to
prevent them drying out and dying, whereas keratinized surfaces are kept hydrated and
protected by keratin.
Non-keratinized stratified squamous epithelium: cornea (see also corneal epithelium),
oral cavity, esophagus, rectum, vagina, and the internal portion of the lips
Keratinized stratified squamous epithelium: skin, tongue (partially keratinized), and the
external portion of the lips
Keratinization is the process of making the top layer(s) of a stratified squamous sheet
hardened and dead. It's an adaptation to wear and tear found on abraded surfaces. Not
all stratified squamous epithelial sheets are keratinized, but most are. This example is
from the footpad of a dog.

The gingiva or gums, consists of the mucosal tissue that lies over the alveolar bone.
Gingiva are part of the soft tissue lining of the mouth. They surround the teeth and provide
a seal around them. Compared with the soft tissue linings of the lips and cheeks, most of
the gingiva are tightly bound to the underlying bone and are designed to resist the friction
of food passing over them.
The alveolar process is the thickened ridge of bone that contains the tooth sockets on bones
that bear teeth. It is also referred to as the alveolar bone. In humans, the tooth-bearing bones
are the maxilla and the mandible. The mineral content of alveolar bone is mostly
hydroxyapatite, which is also found in enamel as the main inorganic substance.
On the maxilla, the alveolar process is a ridge on the inferior surface, and on the mandible it is
a ridge on the superior surface. It makes up the thickest part of the maxilla.
Gingiva

•Free gingiva
•Attached gingiva
•Interdental gingiva

Marginal gingiva
• The marginal gingiva is the terminal edge of gingiva surrounding the teeth in collar
like fashion. In about half of individuals, it is demarcated from the adjacent,
attached gingiva by a shallow linear depression, the free gingival groove. Usually
about 1 mm wide, it forms the soft tissue wall of the gingival sulcus. The marginal
gingiva is supported and stabilized by the gingival fibers.
H, principal gingival fibers
The gingival fibers are
the connective tissue fibers
that inhabit the
gingival tissue adjacent to
the teeth and help hold the
tissue firmly against the
teeth.They are primarily
composed to type I
collagen,
although type III fibers
are also involved.

Attached gingiva
• The attached gingiva is continuous with the marginal gingiva. It is firm, resilient,
and tightly bound to the underlying periosteum of alveolar bone. The facial aspect
of the attached gingiva extends to the relatively loose and movable alveolar
mucosa, from which it is demarcated by the mucogingival junction. Attached
gingiva may present with surface stippling.

Interdental gingiva
• The interdental gingiva occupies the gingival embrasure, which is the interproximal
space beneath the area of tooth contact. The interdental gingiva can be pyramidal
or have a col shape.

A, crown of the tooth covered by enamel. B,
root of the tooth covered by cementum. C,
alveolar bone.
D, subepithelial connective tissue. E, oral
epithelium. F, free gingival margin. H, principal
gingival fibers. I, alveolar crest fibers of the
PDL. J, horizontal fibers of the PDL. K, oblique
fibers of the PDL.
The periodontal ligament : PDL is a group of
specialized connective tissue fibers that
essentially attach a tooth to the alveolar bone
within which it sits. These fibers help the tooth
withstand the naturally substantial
compressive forces which occur during
chewing and remain embedded in the bone.
Another function of the PDL is to serve as a
source of proprioception, or sensory
innervation, so that the brain can detect the
forces being placed on the teeth and react
accordingly. To achieve this end, there are
pressure sensitive receptors within the PDL
which allow the brain to discern the amount of
force being placed on a tooth during chewing,
for example. This is important because the
exposed surface of the tooth, called enamel,
has no such sensory receptors itself.

The salivary glands
The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva.
Salivary glands produce the saliva used to moisten your mouth, initiate digestion, and help
protect your teeth(enamel) from decay.
Most animals have three major pairs of salivary glands that differ in the type of secretion
they produce:
parotid glands produce a serous, watery secretion
submaxillary (mandibular) glands produce a mixed serous and mucous secretion
sublingual glands secrete a saliva that is predominantly mucous in character

The glands are enclosed in a capsule of connective tissue and internally divided into
lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out
into the lobules.
In the duct system, the lumens formed by intercalated ducts, which in turn join to form
striated ducts. These drain into ducts situated between the lobes of the gland (called
interlobar ducts or secretory ducts).
The basic secretory units of salivary glands are clusters of cells called an acini. These
cells secrete a fluid that contains water, electrolytes, mucus and enzymes
(amylase that breaks down starch into glucose)all of which flow out of the acinus
into collecting ducts.

Saliva consists of mucus and serous fluid; the serous fluid contains the enzyme amylase
important for the digestion of carbohydrates. Minor salivary glands of von Ebner present
on the tongue secrete the amylase. The parotid gland produces purely serous saliva.
The other major salivary glands produce mixed (serous and mucus) saliva.
All of the human salivary glands terminate in the mouth, where the saliva proceeds to
aid in digestion. The saliva that salivary glands release is quickly inactivated in the
stomach by the acid that is present there.

• Mucus is a "slimy" material that coats many epithelial surfaces and is secreted into
fluids such as saliva. It is composed chiefly of mucins and inorganic salts
suspended in water.
• Mucus adheres to many epithelial surfaces, where it serves as a diffusion barrier
against contact with noxious substances (e.g. gastric acid, smoke) and as a
lubricant to minimize shear stresses; such mucus coatings are particularly
prominent on the epithelia of the respiratory, gastrointestinal and genital tracts.
Mucus is also an abundant and important component of saliva, giving it virtually
unparalleled lubricating properties.

Functions of Saliva
•Lubrication and binding: the mucus in saliva is extremely effective in binding masticated
food into a slippery bolus that slides easily through the esophagus without inflicting
damage to the mucosa. Saliva also coats the oral cavity and esophagus, and food basically
never directly touches the epithelial cells of those tissues.
•Solubilizes dry food: in order to be tasted, the molecules in food must be solubilized.
•Oral hygiene: The oral cavity is almost constantly flushed with saliva, which floats away
food debris and keeps the mouth relatively clean. Flow of saliva diminishes considerably
during sleep, allow populations of bacteria to build up in the mouth -- the result is
dragon breath in the morning. Saliva also contains lysozyme, an enzyme that lyses many
bacteria and prevents overgrowth of oral microbial populations.
•Initiates starch digestion: in most species, the serous acinar cells secrete an alpha-
amylase which can begin to digest dietary starch into maltose.
•Provides alkaline buffering and fluid: Bicarbonate secretion along with phosphate,
provides a critical buffer that neutralizes acid in oral cavity.

Multifunctionality
Salivary
Families
Anti-
Bacterial
Buffering
Digestion
Lubricat-
ion &Visco-
elasticityTissue
Coating
Anti-
Fungal
Anti-
Viral
Carbonic anhydrases,
Histatins
Amylases,
Lipase
Mucins, StatherinsAmylases,
Cystatins, Mucins,
Proline-rich proteins, Statherins
Histatins
Cystatins,
Mucins
Amylases, Cystatins,
Histatins, Mucins,
Peroxidases

Parotid Glands
• The parotid glands are a pair of glands located in the subcutaneous tissues of the
face overlying the mandibular ramus and anterior and inferior to the external ear.
The secretion produced by the parotid glands is serous in nature, and enters the
oral cavity through the Stensen's duct after passing through the intercalated ducts
which are prominent in the gland. Despite being the largest pair of glands, only
approximately 25% of saliva is produced by the glands.Saliva contains a mixture of
enzymes like salivary amylase (ptyalin), maltase(trace amounts), lysozyme (which
disinfect and kills bacteria and germs which enter the mouth), salts and water.
Saliva helps converting starch into maltose which is then converted patially to
glucose by the maltase.

Submandibular Glands
The submandibular glands are a pair of glands located beneath lower jaws, superior to
the digastric muscles. The secretion produced is a mixture of both serous and mucous
and enters the oral cavity via Wharton's ducts. Approximately 70% of saliva in the oral
cavity is produced by the submandibular glands, even though they are much smaller
than the parotid glands.

Sublingual Gland
The sublingual glands are a pair of glands located beneath the tongue to the
submandibular glands. The secretion produced is mainly mucous in nature, however it is
categorized as a mixed gland. Unlike the other two major glands, the ductal system of
the sublingual glands do not have striated ducts, and exit from 8-20 excretory
ducts.Approximately 5% of saliva entering the oral cavity come from these glands
through sublingual duct(Bartholin) .

Minor Salivary Glands
There are over 600 minor salivary glands located throughout the oral cavity within the
lamina propria of the oral mucosa. They are 1-2mm in diameter and unlike the other
glands, they are not encapsulated by connective tissue only surrounded by it. The gland
is usually a number of acini connected in a tiny lobule. A minor salivary gland may have
a common excretory duct with another gland, or may have its own excretory duct. Their
secretion is mainly mucous in nature (except for Von Ebner's glands) and have many
functions such as coating the oral cavity with saliva.

Von Ebner's Glands
These glands are located around circumvallate and foliate papillae in the tongue, and
they secrete lingual lipase, beginning the process of lipid hydrolysis in the mouth.
These glands empty their serous secretion into the base of the moats located around
the foliate and circumvallate papillae. This secretion presumably flushes material from
the moat to enable the taste buds to respond rapidly to changing stimuli.

the acini and the striated ducti, participate in salivary secretion.
Transport of water and electrolytes, and synthesis of enzymes, proteins, mucin and
other organic components, occur in the acini, which secrete a fluid isotonic with plasma.
This fluid is then modified in the ductus system, by both reabsorption and secretion of
electrolytes.
Salivary glands are effector organs in which a large amount of fluid and electrolytes is
transferred from the interior of the body to the outside. The amount of fluid translocated
each day through salivary glands approaches 750 ml, which represents approximately 20%
of total plasma volume.

• Within the ducts, the composition of the secretion is altered. Much of the sodium
is actively reabsorbed, potassium is secreted, and large quantities of bicarbonate
ion are secreted. Small collecting ducts within salivary glands lead into larger
ducts, eventually forming a single large duct that empties into the oral cavity.

Saliva is characteristically a colorless dilute fluid, Its pH is usually around 6.64
Although a variety of components is always present in saliva, the total concentration of
inorganic and organic constituents is generally low when compared to serum.
Of the inorganic constituents, sodium and potassium (and perhaps calcium) are the
cations of major osmotic importance in saliva; the major osmotically active anions are
chloride and bicarbonate. Other organic components existing in saliva include: maltase,
serum albumin, urea, uric acid, creatinine, mucine, vitamin C, several amino acids,
lysozime, lactate, and some hormones such as testosterone and cortisol. Some gases
(CO2, O2, and N2) are also present in saliva. Saliva contains immunoglobins such as Ig A
and Ig G.

Innervation
Salivary glands are innervated by the parasympathetic and sympathetic arms of the
autonomic nervous system.
Secretion of saliva is under control of the autonomic nervous system, which controls both
the volume and type of saliva secreted.
Parasympathetic innervation to the
glands is carried via cranial nerves.
The parotid gland receives its
parasympathetic input from the
glossopharyngeal nerve (CN IX) via
otic ganglion.
The submandibular and sublingual glands receive
their parasympathetic input from the facial nerve
(CN VII) via the submandibular ganglion.

Direct sympathetic innervation of the salivary glands takes place via preganglionic
nerves in the thoracic segments T1-T3 which synapse in the superior cervical ganglion
with postganglionic neurons that release norepinephrine, which is then received by β-
adrenergic receptors on the acinar and ductal cells of the salivary glands, increase of
saliva secretion. Note that in this regard both parasympathetic and sympathetic stimuli
result in an increase in salivary gland secretions.The sympathetic nervous system also
affects salivary gland secretions indirectly by innervating the blood vessels that supply
the glands.

Parasympathetic stimulation results in a copious flow of saliva low in organic and
inorganic compounds concentrations.
Sympathetic stimulation produces a saliva low in volume. In addition, saliva evoked by
action of adrenergic mediators is generally higher in organic content and its
concentration of certain inorganic salts is also higher than saliva evoked by cholinergic
stimulation. The higher organic content of saliva evoked by adrenergic stimulation
trough the activity of adenyl-cyclase, includes elevated levels of total protein, especially
the digestive enzyme alpha-amilase. The levels of inorganic compounds, i.e., Ca++, K+
and HCO3-, are usually higher with sympathetic stimulation.
The secretory cells are not the only glandular elements that respond to stimulation of the
sympathetic innervation. Myoepithelial cells and blood vessels of the glands also respond
to such innervation, and these responses can in turn modify the quantity and composition
of the elaborated saliva. It has been shown, for example, that sympathetic stimulation to
salivary glands can produce a markedly increased degree of vasoconstriction.

Bone
Oral rigid tissues:
• Bone
•Cement
•Enamel
•Dentin
Bones are rigid organs that form part of the
endoskeleton of vertebrates.
-Mechanical
Protection — Bones can serve to protect internal organs,
such as the skull protecting the brain or the ribs protecting
the heart and lungs.
Shape — Bones provide a frame to keep the body supported.
Movement — Bones, skeletal muscles, tendons, ligaments and joints function together to
generate and transfer forces so that individual body parts or the whole body can be
manipulated in three-dimensional space.
Sound transduction — Bones are important in the mechanical aspect of overshadowed
hearing.
-Synthetic
Blood production — The marrow, located within the medullary cavity of long bones and
interstices of cancellous bone, produces blood cells in a process called haematopoiesis.

-Metabolic
Mineral storage — Bones act as reserves of minerals important for the body, most
notably calcium and phosphorus.
Growth factor storage — Mineralized bone matrix stores important growth factors such
as insulin-like growth factors, transforming growth factor, bone morphogenetic proteins
and others.
Fat Storage — The yellow bone marrow acts as a storage reserve of fatty acids
Acid-base balance — Bone buffers the blood against excessive pH changes by absorbing
or releasing alkaline salts.
Detoxification — Bone tissues can also store heavy metals and other foreign elements,
removing them from the blood and reducing their effects on other tissues. These can
later be gradually released for excretion.
Endocrine organ - Bone controls phosphate metabolism by releasing fibroblast growth
factor - 23 (FGF-23), which acts on kidney to reduce phosphate reabsorption

•Maxilla
•Mandible
•Alveolar bone

The majority of bone is made of the bone tissue.Bone tissue is a mineralized connective
tissue. It has inorganic and organic parts.
Inorganic
The inorganic is mainly crystalline mineral salts and calcium, which is present in the form of
hydroxyapatite.
Organic
The organic part of matrix is mainly composed of Type I collagen. This is synthesised
intracellularly as tropocollagen and then exported, forming fibrils.

Inorganic :60%-65%
The inorganic is mainly crystalline mineral salts and calcium, which is present in the form
of hydroxyapatite. The matrix is initially laid down as unmineralised osteoid
(manufactured by osteoblasts). Mineralisation involves osteoblasts secreting vesicles
containing alkaline phosphatase. This cleaves the phosphate groups and acts as the foci
for calcium and phosphate deposition. The vesicles then rupture and act as a centre for
crystals to grow on.
Organic : 30%-35%
The organic part of matrix is mainly composed of Type I collagen. This is synthesised
intracellularly as tropocollagen and then exported, forming fibrils. The organic part is also
composed of various growth factors, the functions of which are not fully known. Factors
present include glycosaminoglycans, osteocalcin, osteonectin, bone sialo protein,
osteopontin and Cell Attachment Factor. One of the main things that distinguishes the
matrix of a bone from that of another cell is that the matrix in bone is hard.

Cellular structure
There are several types of cells constituting the bone:
Osteoblasts are mononucleate bone-forming cells that descend from osteoprogenitor
cells located in the periosteum and the bone marrow. They are located on the surface of
osteoid seams and make a protein mixture known as osteoid(It is composed of fibers and
ground substance. The predominant fiber-type is Type I collagen. The ground substance is
mostly made up of chondroitin sulfate and osteocalcin) which mineralizes to become
bone. Osteoid is primarily composed of Type I collagen. Osteoblasts also manufacture
hormones, such as prostaglandins, to act on the bone itself. They robustly produce
alkaline phosphatase, an enzyme that has a role in the mineralisation of bone, as well as
many matrix proteins. Osteoblasts are the immature bone cells.
Bone lining cells are essentially inactive osteoblasts. They cover all of the available bone
surface and function as a barrier for certain ions.

Endosteum lines the inner surface of all bones. The interface between the cancellous bone
and the marrow is called the endosteum, and it is largely at this site that bone is removed
in response to a need for increased calcium elsewhere in the body.
Periosteum is a membrane that lines the outer surface of all bones, except at the joints of
long bones. As opposed to osseous tissue, periosteum has nociceptors nerve endings,
making it very sensitive to manipulation. It also provides nourishment by providing the
blood supply. Periosteum is attached to bone by strong collagenous fibers called Sharpey's
fibres, which extend to the outer circumferential and interstitial lamellae. It also provides an
attachment for muscles and tendons.

Osteocyte a star-shaped cell, is the most abundant cell
found in compact bone. Cells contain a nucleus and a thin
ring of cytoplasm. Originate from osteoblasts that have
migrated into and become trapped and surrounded by bone
matrix that they themselves produce. Osteocytes have many
processes that reach out to meet osteoblasts and other
osteocytes probably for the purposes of communication.
Their functions include to varying degrees: formation of bone, matrix maintenance and
calcium homeostasis. They have also been shown to act as mechano-sensory receptors—
regulating the bone's response to stress and mechanical load. They are mature bone cells.
Osteoclasts are the cells responsible for bone resorption. Osteoclasts are large,
multinucleated cells located on bone surfaces in what are called Howship's lacunae or
resorption pits. Because the osteoclasts are derived from a monocyte stem-cell lineage,
they are equipped with phagocytic like mechanisms similar to circulating macrophages.
Osteoclasts mature and/or migrate to discrete bone surfaces. Upon arrival, active enzymes,
such as tartrate resistant acid phosphatase, are secreted against the mineral substrate.
These bone cells can only resorb mineralized bone matrix.
Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which build
bone, and osteoclasts, which resorb bone.

Bone resorption is the process by which osteoclasts break down bone and release the
minerals, resulting in a transfer of calcium from bone fluid to the blood.
The osteoclasts are multi-nucleated cells that contain numerous mitochondria and
lysosomes. These are the cells responsible for the resorption of bone. Attachment of the
osteoclast to the osteon begins the process. The osteoclast then induces an infolding of
its cell membrane and secretes collagenase and other enzymes important in the
resorption process. High levels of calcium, magnesium, phosphate and products of
collagen will be released into the extracellular fluid as the osteoclasts tunnel into the
mineralized bone.
Bone resorption can be the result of disuse and the lack of stimulus for bone
maintenance. Astronauts, for instance will undergo a certain amount of bone resorption
due to the lack of gravity, providing the proper stimulus for bone maintenance.
During childhood, bone formation exceeds resorption, but as the aging process occurs,
resorption exceeds formation.

Regulation
Bone resorption is stimulated or inhibited by signals from other parts of the body,
depending on the demand for calcium:
PTH,vit D Osteocyte Osteoclast
Calcium-sensing membrane receptors in the parathyroid gland monitor calcium levels in
the extracellular fluid. Low levels of calcium stimulates the release of parathyroid
hormone (PTH). In addition to its effects on kidney and intestine, PTH also increases the
number and activity of osteoclasts to release calcium from bone, and thus stimulates
bone resorption.
High levels of calcium in the blood, on the other hand, leads to decreased PTH release
from the parathyroid gland, decreasing the number and activity of osteoclasts, resulting
in less bone resorption.
secretion of osteoid is stimulated by the secretion of growth hormone by the pituitary,
thyroid hormone and the sex hormones (estrogens and androgens).
Osteoclast inhibition
The rate at which osteoclasts resorb bone is inhibited by calcitonin and
osteoprotegerin. Calcitonin is produced by parafollicular cells in the thyroid gland, and
can bind to receptors on osteoclasts to directly inhibit osteoclast activity.
Osteoprotegerin is secreted by osteoblasts and inhibiting osteoclast stimulation

Compact bone or (Cortical bone)
The hard outer layer of bones is composed of compact bone tissue, so-called due to its
minimal gaps and spaces. This tissue gives bones their smooth, white, and solid
appearance, and accounts for 80% of the total bone mass of an adult skeleton.
Trabecular bone(cancellous or spongy bone)
Filling the interior of the organ is the trabecular bone tissue which is composed of a
network of rod- and plate-like elements that make the overall organ lighter and allowing
room for blood vessels and marrow. Trabecular bone accounts for the remaining 20% of
total bone mass but has nearly ten times the surface area of compact bone.

The primary anatomical and functional unit of mammalian compact bone consists of a
repeating structure called Haversian system, or osteon. Each osteon has concentric
layers of mineralized matrix, called concentric lamellae, which are deposited around a
central canal, also known as the Haversian canal, containing blood vessels and nerves
that service the bone.

Two types of bone can be identified microscopically
according to the pattern of collagen forming the
osteoid :
1) woven bone characterised by haphazard organisation of collagen fibers and is
mechanically weak (tooth sockets )
2) lamellar bone which has a regular parallel alignment of collagen into sheets (lamellae)
and is mechanically strong.
Woven bone is produced when osteoblasts produce osteoid rapidly which occurs initially
in all fetal bones (but is later replaced by more resilient lamellar bone). In adults woven
bone is created after fractures. Woven bone is weaker, with a smaller number of
randomly oriented collagen fibers, but forms quickly; it is for this appearance of the
fibrous matrix that the bone is termed woven. It is soon replaced by lamellar bone,
which is highly organized in concentric sheets with a much lower proportion of
osteocytes to surrounding tissue. Lamellar bone is stronger and filled with many collagen
fibers parallel to other fibers in the same layer (these parallel columns are called
osteons).
Woven or lamellar

Bundle bone is a histologic term for the portion of the bone of the alveolar process
that surrounds teeth and into which the collagen fibers of the periodontal ligament
are embedded.It can also be referred to as alveolar bone proper.
Bundle bone is functionally dependent in that it resorbs following tooth extraction or
loss. lamina dura, a radiographic term denoting the plate of compact bone (alveolar
bone) that lies adjacent to the periodontal ligament.
From arrow to PDL = alveolar bone proper
A. Haversian bone
B. Bundle bone
D. Periodontal ligament
E. Radicular dentin with contour lines of Owen
F. Radicular pulp

Primary (baby) teeth start to form between the sixth and eighth weeks,
and permanent teeth begin to form in the twentieth week.
If teeth do not start to develop at or near these times, they will not
develop at all.
Tooth development
Histologic slide showing a tooth bud
A: enamel organ : enamel , thooth crown ,initiate dentin formation
B: dental papilla : dentin , pulp
C: dental follicle :supporting structure like PDL(fibroblasts),cement
( cementoblasts ),
alveolar bone( osteoblasts )

Dentin
Along with enamel, cementum , and pulp is one of the four major components of teeth.
It is covered by enamel on the crown and cementum on the root and surrounds the
entire pulp. It serves to protect the sensitive pulp of the tooth and create a base under
the enamel.
The dentine contains more minerals than the bone.
By weight, 70% of dentin consists of the mineral hydroxylapatite,
20% is organic material(collagen I, phosphoproteins , glycoproteins ,proteoglycans),
and 10% is water.

Yellow in appearance, it greatly affects the color of a tooth due to the translucency of
enamel.
Dentin, which is less mineralized and less brittle than enamel, is necessary for the
support of enamel. Because it is softer than enamel, it decays more rapidly and is
subject to severe cavities if not properly treated, but due to its elastic properties it is a
good support for enamel. Its flexibility prevents the brittle enamel fracturing. Thereby
providing teeth with the ability to flex and absorb tremendous functional loads without
fracturing.
The formation of dentin, dentinogenesis, begins prior to the formation of enamel and is
initiated by the odontoblasts of the pulp. Unlike enamel, dentin continues to form
throughout life and can be initiated in response to stimuli, such as tooth decay or
attrition.

An odontoblast (differentiate from cells of the dental papilla) is part of the outer surface of
the dental pulp.
The odontoblasts secrete dentin throughout life (secondary dentin, once root formation is
complete). Odontoblasts also secrete tertiary dentin when irritated.
Odontoblasts are large columnar cells arranged in an epithelioid sheet along the junction
between dentin and pulp, all the way down to the root apex. It is rich in endoplasmic
reticulum and golgi apparatus, especially during primary dentin formation, to give it a high
secretory capacity ,firstly collagenous matrix to form predentine, then mineral to form the
complete dentine.
On initial dentine formation it moves pulpally, away from the primitive amelodentinal
junction (then Inner Enamel Epithelium/dental papillary junction) leaving behind a tubular
structure known as the odontoblast process. This process lies in a tubule, known simply as
a dentinal tubule.
Enamel spindle
A: enamel organ
B: dental papilla
C: dental follicle

The functions of the odontoblast process are as follows:
1. Causes the secretion of hydroxyapatite crystals and mineralization of the matrix
2. General maintenance of the dentinal tubule and dentinal fluid (ion/protein content etc.)
3. To secrete sclerotic dentin upon carious attack to block off dentinal tubules, slowing the
progress of the attack (air space above blockage is known as a dead tract)
4. To channel signals of attack to the odontoblast cell body, initiating reactionary dentin
secretion
5. To aid in the secretion of tubular dentin (dentin surrounding tubule)

dentin areas characterized by degenerated odontoblastic processes; may result from
injury caused by caries, attrition, erosion, or cavity preparation.
Sclerotic dentin is generally caused by some insult to the dentinal tubules and is a hyper-
mineralized layer of dentin intended to block dentinal fluid flow, decreasing the
stimulation of the pulp. Sclerotic dentin is a protective biologic response.
sclerotic dentine a dense clear dentine formed when the dentinal tubules are filled with
mineralized material.

Dentinogenesis is the formation of dentin. The formation of dentin must always occur
before the formation of enamel.
The different stages of dentin formation result in different types of dentin: mantle dentin,
primary dentin, secondary dentin, and tertiary dentin.
The unmineralized zone between the odontoblasts and mineralized dentin is called
predentin.
Dentin is formed by two simultaneous processes, the formation of collagenous matrix
(predentin) and the formation of mineral crystals on this matrix . Dentin formation starts
with the synthesis of the extracellular matrix which is mainly formed by the fibrous web of
type I collagen. In addition, type V collagen, proteoglycans and other non-collagenous
proteins (serum proteins, phosphoproteins) are also secreted.Non-collagenous proteins
could be involved in the nucleation of calcium- and phosphate crystals (hydroxyapatite)

They begin secreting an organic matrix around the area directly adjacent to the inner
enamel epithelium, closest to the area of the future cusp of a tooth. The organic matrix
contains collagen fibers with large diameters (0.1-0.2 μm in diameter). The odontoblasts
begin to move toward the center of the tooth, forming an extension called the
odontoblast process. Thus, dentin formation proceeds toward the inside of the tooth.
This area of mineralization is known as mantle dentin and is a layer usually about 5-30
μm thick. The outer portion of dentin bordering the enamel or cementum of the tooth.
Mantle dentin is slightly less mineralized than other layers of the primary dentin.
A. Striae of Retzius
B. Reparative dentin (irregular secondary
dentin)
C. Cementum
D. Mantle dentin
E. Circumpulpal dentin

The primary dentin is formed rapidly during tooth formation. It outlines the pulp
chamber and constitutes the main part of the dentin mass. The outer layer of primary
dentin, which is synthesised at the onset of dentinogenesis, is called mantle dentin. The
formation of primary dentin continues until the tooth becomes functional or until the root
apex is closed .
The larger odontoblasts cause collagen to be secreted in smaller amounts, which results
in more tightly arranged, heterogeneous nucleation is used for mineralization. Other
materials (such as lipids, phosphoproteins, and phospholipids) are also secreted.
Thereafter dentin formation proceeds as secondary dentinogenesis, which continues at a
slower rate than the primary dentinogenesis during the life-time of the individual. The
secondary dentin is considered to be more irregular in structure and sometimes less
mineralized than the primary dentin.
A. Striae of Retzius
B. Reparative dentin (irregular secondary
dentin)
C. Cementum
D. Mantle dentin
E. Circumpulpal dentin

Odontoblasts also secrete tertiary dentin(reactionary dentin) when irritated. Tertiary
dentin secreted by odontoblasts is often due to chemical attack, either by chemicals
diffusing through the dentin and insulting the odontoblasts, or by diffusion of toxic
bacterial metabolites down the dentinal tubules in the instance of a carious attack.
This is an attempt to slow down the progress of the caries so that it does not reach the
pulp. Reactionary dentine is secreted at varying speeds, dependant on the speed of
progression of caries above. Histologically, it is easily distinguishable by its disordered tube
structure, its local secretion (causing it to protrude into the pulpal cavity) and its slightly
lower degree of mineralisation than normal.
In the case of an infection breaching the dentin to or very near the pulp, or in the instance
of odontoblast death due to other attack (e.g. chemical or physical), Pulpal Stem Cells can
differentiate into odontoblast-like cells which then secrete the other kind of tertiary
dentin, reparative dentin, underneath the site of attack. This is not only to slow the
progress of the attack, but also to prevent the diffusion of bacteria and their metabolites
into the pulp, reducing the probability of partial pulp necrosis.

Dentin consists of microscopic channels, called dentinal tubules, which radiate outward
through the dentin from the pulp to the exterior cementum or enamel border , so span
the entire thickness of dentin. These tubules follow an S-shaped path. The diameter and
density of the tubules are greatest near the pulp. there are branching canalicular systems
that connect to each other.
These tubules contain fluid(a mixture of albumin, transferrin and proteoglycans) and
cellular structures(odontoblast process). As a result, dentin has a degree of permeability
which can increase the sensation of pain and the rate of tooth decay.
However, dentin also contains mineral rich fluids called dentinal fluids, which may be
responsible for the mineralization of the dentin as it is secreted by the odontoblasts.
Dentinal fluids contain proteins, sodium, and calcium, and are concentrated in the
dentinal tubules.

A, Stria of Retzius; B, Dentino-enamel junction

The dentine may be divided into(ITD) intertubular dentine and (PTD)peritubular dentine.
The former is the main product of the odontoblasts constituting the largest volume of the
dentine. The intertubular dentine consists of a fibrous network of collagen with
deposited mineral crystals.
The peritubular dentine forms a highly mineralized sheath around the dentinal tubule
(0.5-1 micrometers thick in humans). The peritubular dentine gradually (partly or
completely) fills up the dentinal tubules at some distance away from the pulp chamber.

Figure left. SEM of fractured dentin showing the open dentinal tubule (T), peritubular dentin
(P), and intertubular dentin (I).
Figure right. SEM showing on the top left the intact smear layer and a longitudinal section of
an odontoblastic process (OP) demonstrating the peritubular dentin (P) and the intertubular
dentin (I).

The term granular layer may refer to:
the granular layer of Tomes, seen in dentin of the teeth.A granular layer is seen adjacent
to cementum.It is believed to be caused by coalescing & looping of terminal portion of
dentinal tubules.
Left to right:Tubules, granular layer of Tomes, hyaline layer, acellular cement

Incremental lines in the dentine of representatives from various dinosaur clades. The
incremental lines of von Ebner run from left to right in each plate and are the smallest
visible laminations. The teeth were thin sectioned longitudinally and viewed with
polarized microscopy. (A) Tyrannosaurus (Tyrannosauridae); (B) Triceratops
(Ceratopsidae); (C) Edmontosaurus (Hadrosauridae); (D) Edmontonia (Nodosauridae).
Incremental lines

Cementum
Cementumis a specialized calcified substance covering the root of a tooth.
Cementum is excreted by cells called cementoblasts within the root of the tooth and is
thickest at the root apex.
Its coloration is yellowish and it is softer than enamel and dentin due to being less
mineralized.
There is no blood vessels
And nerve fibers in cementum.
There is incrimental lines as
Dentin.

Cementum's main role is to anchor the tooth by attaching it via the periodontal ligaments
and blockade of dentinal tubules.
It meets the enamel lower on the tooth at the cemento-enamel junction.
The chemical makeup of cementum is similar to that of bone, but it lacks vascularization.
Volumetrically, it is approximately 65% inorganic material (mainly hydroxyapatite),
23% organic material (mainly collagen type1) and 12% water.
Cementum is slowly formed throughout life and this allows for continual reattachment of
the periodontal ligament fibres.

Intermediate cementum
Epithelial root sheet is the source of
Thin,amorphous,structurless and highly mineralized secretion on the surface of the root
dentin.
Lack of collagen and similar to enamel.
More evident in the apical region of the root.
Cementum:
•Intermediate cementum
•Cellular and acellular cementum
The cervical loop area: (1) dental follicle cells,
(2) dental mesenchyme, (3) Odontoblasts, (4)
Dentin, (5) stellate reticulum, (6) outer enamel
epithelium, (7)inner enamel epithelium, (8)
ameloblasts, (9) enamel.

Cellular and acellular cementum
Cells from dental follicle becomes cementoblasts and secrete cementum which covers
roots.
Cementogenesis is slower than dentogenesis.
Cementoid(collagen,proteoglycans and glycoproteins)
and mineralisation.
Acellular cementum (cervical half of the root dentin)
Cellular cementum (apical half)
A: enamel organ
B: dental papilla
C: dental follicle

The Hertwig's epithelial root sheath (frequently abbreviated as "HERS") is a proliferation
of epithelial cells located at the cervical loop of the enamel organ in a developing tooth.
Hertwig's epithelial root sheath initiates the formation of dentin in the root of a tooth by
causing the differentiation of odontoblasts from the dental papilla. The root sheath
eventually disintegrates, but residual pieces that do not completely disappear are seen as
epithelial cell rests of Malassez (ERM).

After dentin formation begins, the cells of the inner enamel epithelium secrete an
organic matrix against the dentin. This matrix immediately mineralizes and becomes the
tooth's enamel.
Outside the dentin are Ameloblasts, which are cells that continue the process of enamel
formation; therefore, enamel formation moves outwards, adding new material to the
outer surface of the developing tooth.
A: enamel organ
B: dental papilla
C: dental follicle
Tooth enamel

Tooth enamel is the hardest and most highly mineralized substance of the body.
96% of enamel consists of mineral, with 4% water and organic material.
The normal color of enamel varies from light yellow to grayish white. Since enamel is
semitranslucent, the color of dentin and any restorative dental material underneath the
enamel strongly affects the appearance of a tooth.
Enamel varies in thickness over the surface of the tooth and is often thickest at the cusp,
up to 2.5 mm, and thinnest at its border, which is seen clinically as the cementoenamel
junction (CEJ).
Enamel's primary mineral is hydroxylapatite, which is a crystalline calcium phosphate.
Unlike dentin and bone, enamel does not contain collagen. Instead, it has two unique
classes of proteins called amelogenins and enamelins.

Ameloblasts are present only during tooth development, that deposit tooth enamel.
Ameloblasts secrete the enamelin and amelogenin which will later mineralize to form
enamel on teeth.
The secretory end of the ameloblast ends in a six-sided pyramid-like projection known as
the Tomes' process. A narrow extension of the ameloblast from which the enamel matrix is
secreted.
The ameloblasts will only become fully functional after the first layer of dentine has been
formed, as such dentine is a precursor to enamel.

Amelogenesis, or enamel formation, beginning at the future location of cusps, around the
third or fourth month of pregnancy.
The creation of enamel is complex, but can generally be divided into two stages.
The first stage, called the secretory stage, involves proteins and an organic matrix forming
a partially mineralized enamel.
The second stage, called the maturation stage, completes enamel mineralization.
At some point before the tooth erupts into the mouth, but after the maturation stage,
the ameloblasts are broken down. Consequently, enamel, unlike many other tissues of the
body, has no way to regenerate itself

The basic unit of enamel is called an enamel rod, formerly called an enamel prism, is a
tightly packed mass of hydroxyapatite crystals in an organized pattern.
In cross section, it is best compared to a keyhole, with the top, or head, oriented toward
the crown of the tooth, and the bottom, or tail, oriented toward the root of the tooth.
Enamel rods are found in rows along the tooth. Within each row, the long axis of the
enamel rod generally is perpendicular to the underlying dentin. The arrangement of
crystals within each enamel rod is highly complex.
The area around the enamel rod is known as interrod enamel. Interrod enamel has the
same composition as the enamel rods. Nonetheless, a histologic distinction is made
between the two because crystal orientation is different in each. The crystals lie nearly
perpendicular to the enamel rod.
The border where the crystals of enamel rods and crystals of interrod enamel meet is
called the rod sheath.

The rod sheath is found where enamel rods meet interrod enamel. The crystals of both
types of enamel meet at sharp angles and form the appearance of a space called the rod
sheath. As a result of this space, the rod sheath consists of more protein (as opposed to
minerals) than other areas of enamel. For this reason, the rod sheath is characterized as
being hypomineralized in comparison to the rest of the highly mineralized enamel.
The rod sheath is Inorganic matrix tying the enamel rods together.
Unerupted lower left canine germ of the
Irhoud 3 juvenile. (A) Stereo microscope
overview with position of area enlarged in B
(white box) and virtual plane of section in C
(dotted line). (B) Perikymata (white arrows),
surface manifestations of long-period Retzius
lines, were counted from the cusp tip to the
cervix on the original tooth.

Striae of Retzius are stripes that appear on enamel when viewed microscopically in cross
section, these stripes demonstrate the growth of enamel, similar to the annual rings on a
tree.
Perikymata are shallow furrows where the striae of Retzius end.
Darker than the other stripes, the neonatal line is a stripe that separates enamel formed
before and after birth.
Gnarled enamel is found at the cusps of teeth. Its twisted appearance results from the
orientation of enamel rods and the rows in which they lie.

Enamel lamellae are a type of hypomineralized structure in teeth that extend either from
the dentinoenamel junction (DEJ) to the surface of the enamel, or visa versa.
They are prominent linear enamel defects.
These structures contain proteins, proteoglycans, and lipids.
A. Enamel lamella
B. Enamel tufts
C. Enamel spindle

Enamel - transverse ground section
In a transverse section of tooth, the stria of Retzius appear as concentric bands
parallel to the dentino-enamel junction (DEJ).
In addition to the "hypo-mineralized" dark stria of Retzius,
there also exist hypo-mineralized areas perpendicular to the DEJ.
These are enamel lamellae (that traverse the entire thickness of enamel)
and enamel tufts (that traverse the inner third of enamel adjacent to the DEJ.
Legend: A, Stria of Retzius; B, Enamel tuft; C, Enamel lamella; D, Dentino-enamel junction

Enamel tufts are frequently confused with enamel lamellae, which are also enamel defects,
but which differ in two ways: lamella are linear, and not branched, and they exist primarily
extending from the enamel surface, through the enamel and towards the dentinoenamel
junction, whereas enamel tufts project in the opposite direction.
Enamel tufts should also not be confused with the similar enamel spindles. Enamel spindles
are also linear defects, similar to lamellae, but they too can be found only at the
dentinoenamel junction, similar to enamel tufts. This is because they are formed by
entrapment of odontoblast processes between ameloblasts prior to and during
amelogenesis.
Some sources consider them to be of no clinical significance. However, they have been
noted to be an important potential source of enamel fractures that arise after extended
use or overloading. It appears that, although enamel easily starts to form the fracture
defects of enamel tufts, they then enable enamel to resist the further progress of these
fractures, ultimately preventing mechanical failure. This fracture resistance is why tooth
enamel is three times stronger than its constituent hydroxyapatite crystallites that make up
its enamel rods.

Dental Pulp
The dental pulp is richly vascularized and innervated part in the center of a tooth made
up of living soft tissue and cells.
Each person can have a total of up to 52 pulp organs, 32 in the permanent and 20 in the
primary teeth.
Crowns of the teeth contain coronal pulp.
The coronal pulp has six surfaces: the occlusal,
the mesial, the distal, the buccal, the lingual and
the floor. Because of continuous deposition of dentin,
the pulp becomes smaller with age.
Radicular pulp is that pulp extending from
the cervical region of the crown to the root apex.
The radicular portion is continuous with the periapical
tissues through the apical foramen .
Apical foramen is the opening of the radicular pulp
into the periapical connective tissue. The average
size is 0.3 to 0.4 mm in diameter. There can be two
or more foramina separated by a portion of dentin and cementum or by cementum only.
Accessory canals are pathways from the radicular pulp, extending laterally through the dentin
to the periodontal tissue seen especially in the apical third of the root.

Dental pulp is an unmineralized oral tissue composed of soft connective tissue, vascular,
lymphatic and nervous elements .
Pulp has a soft, gelatinous consistency, indicates that by either weight or volume, the majority
of pulp (75-80%) is water.
Aside from the presence of pulp stones, found pathologically within the pulp cavity of aging
teeth, there is no inorganic component in normal pulp.
The pulp cavities of molar teeth are approximately four
times larger than those of incisors.
The pulp cavity extends down through
the root of the tooth as the root canal which opens
into the periodontium via the apical foramen.
The blood vessels, nerves etc. of dental pulp enter
and leave the tooth through this foramen.
This sets up a form of communication between the pulp
and surrounding tissue - clinically important in the
spread of inflammation from the pulp out into the
surrounding periodontium.

Cells: fibroblasts and undifferentiated mesenchymal and odontoblasts cells as well as other
cell types (macrophages, lymphocytes, etc.) required for the maintenance and defense of the
tissue . undifferentiated mesenchymal cells (perivascular cells) facilitates the recruitment of
newly differentiating cells to replace others when they are lost - specifically odontoblasts.
Fibrous matrix: collagen fibers, type I and II, are present in an unbundled and randomly
dispersed fashion, higher in density around blood vessels and nerves. Type I collagen is
thought to be produced by the odontoblasts as dentin, secreted by these cells, is composed of
type I collagen. Type II is probably produced by the pulp fibroblasts as this type increases in
frequency with the age of the tooth. Older pulp contains more collagen of both the bundled
and diffuse types.
Ground substance: the environment that surrounds both cells and fibers of the pulp is rich in
proteoglycans, glycoproteins and large amounts of water.
Pulpal component

The central region of the coronal and radicular
pulp contains large nerve trunks and blood
vessels.
This area is lined peripherally by a specialized
odontogenic area which has three layers
1. Odontoblastic layer; outermost layer which
contains odontoblasts and lies next to the
predentin and mature dentin.
2. Cell free zone (zone of Weil) which is rich in
both capillaries and nerve networks. The nerve
plexus of Rashkow is located in here
3. Cell rich zone; innermost pulp layer which
contains fibroblasts and undifferentiated
mesenchymal cells
Cells found in the dental pulp include
fibroblasts (the principal cell), odontoblasts,
defence cells like histiocytes, macrophages
(macrophage), granulocytes, mast cells and
plasma cells.

1 - odontoblast zone
2 - cell-free zone
3 - cell-rich zone
4 - pulp core
A - Dentin
B - nerve
C - blood vessel

Age-Related and Pathologic Changes in the Pulp
Specific changes occur in dental pulp with age. Cell death results
in a decreased number of cells. The surviving fibroblasts respond
by producing more fibrous matrix (increased type I over type II
collagen) but less ground substance that contains less water. So
with age the pulp becomes:
a) less cellular
b) more fibrous
c) overall reduction in volume due to the continued deposition of
dentin (secondary/reactive)

One or more small arterioles enter the pulp via the apical foramen and ascend through the
radicular pulp of the root canal.
Once they reach the pulp chamber in the crown they branch out peripherally to form a
dense capillary network immediately under - and sometimes extending up into - the
odontoblast layer.
Small venules drain the capillary bed and eventually leave as veins via the apical foramen.
Blood flow is more rapid in the pulp than in most areas of the body and the blood
pressure is quite high.
In recent years a number of studies have demonstrated
the presence of thin-walled, irregularly shaped lymphatic vessels.
They are larger than capillaries and have an incomplete
basal lamina facilitating the resorption of tissue fluid
and large macromolecules of the pulp matrix.
The continued formation of cementum at the apical foramen can lead to occlusion of the
opening. The walls of pulpal veins are first affected by the cemental constriction. Vascular
congestion may occur. This ultimately leads to necrosis of the pulp.
Vascular Supply to the Pulp

Innervation of the Pulp
1. Autonomic Nerve Fibers. sympathetic and colinergic autonomics fibers are found in the
pulp. sympathetic fibers extend from the neurons whose
cell bodies are found in the superior cervical ganglion
at the base of the skull.
They are unmyelinated fibers and travel with
the blood vessels. They innervate the
smooth muscle cells of the arterioles and
therefore function in regulation of blood flow
in the capillary network.
2. Afferent (Sensory) Fibers. These arise from the maxillary and mandibular branches of the 5th
cranial nerve (trigeminal). They are predominantly myelinated fibers and may terminate in the
central pulp. From this region some will send out small individual fibers that form the
subodontoblastic plexus (of Raschkow) just under the odontoblast layer. From the plexus the
fibers extend in an unmyelinated form toward the odontoblasts. The fibers terminate as "free
nerve endings" near the odontoblasts, extend up between them or may even extend further up
for short distances into the dentinal tubule.
They function in transmitting pain stimuli from heat, cold or pressure. The subodontoblastic
plexus is primarily located in the roof and lateral walls of the coronal pulp. It is less developed in
the root canals.

A. Pulp
B. Dentin
C. Predentin
D. Odontoblasts
E. Subodontoblastic cell-free zone of Weil
F. Cell-rich zone
G. [Parietal plexus]

The most widely accepted hypothesis about how the stimuli influence nerve fibers is
the hydrodynamic theory, which states that pain from exposed dentin following
stimulation results from rapid fluid movement inside the dentinal tubules.

Small calcified bodies are present in up to 50% of the pulp of newly erupted teeth and in over
90% of older teeth. These calcified bodies are generally found loose within the pulp but may
eventually grow large enough to encroach on adjacent dentin and become attached. These
bodies are classified by either their development or histology:
1. Development
Epithelio-Mesenchymal Interactions. Small groups of epithelial cells become isolated from
the epithelial root sheath during development and end up in the dental papilla. Here they
interact with mesenchymal cells resulting in their differentiation into odontoblasts. They form
small dentinal structures within the pulp.
Calcific Degenerations. Spontaneous calcification of pulp components (collagen fibers, ground
substance, cell debris, etc.) may expand or induce pulpal cells into osteoblasts. These cells
then produce concentric layers of calcifying matrix on the surface of the mass - but no cells
become entrapped.
Diffuse Calcification. A variation of the above whereby seriously degenerated pulp undergoes
calcification in a number of locations. These bodies resemble calcific degenerations except for
their smaller size and increased number.
Calcified Bodies in the Pulp (Pulp Stones)

2. Histology
Calcified bodies in the pulp may be composed of dentin, irregularly calcified tissue, or
both. A calcified body containing tubular dentin is referred to as a "true" pulp stone or
denticle . True pulp stones exhibit radiating striations reminiscent of dentinal tubules.
Usually those bodies formed by an epithelio- mesenchymal interaction, are true pulp
stones.
Irregularly calcified tissue generally does not bear much resemblance to any known
tissue and as such is referred to as a "false" pulp stone or denticle . False pulp stones
generally exhibit either a hyaline-like homogeneous morphology or appear to be
composed of concentric lamellae.
shows both types of stones: A and B are false pulp
stones, C is a true pulp stone. A is an "attached"
stone (which may become embedded as secondary
dentin deposition continues. B and C are "free"
stones found within the pulp cavity

Functions of Dental Pulp
The primary function of dental pulp is providing vitality to the tooth. Loss of the pulp
following a root canal does not mean the tooth will be lost. The tooth then functions
without pain but, it has lost the protective mechanism that pulp provides.
Dental pulp also has several other functions:
Nutritive: the pulp keeps the organic components of the surrounding mineralized tissue
supplied with moisture and nutrients;
formative: the odontoblasts of the outer layer of the pulp organ form the dentin that
surrounds and protects.
Sensory: extremes in temperature, pressure, or trauma to the dentin or pulp are
perceived as pain;
protective: pulp responds to stimuli like heat, cold, pressure, operative cutting procedures
of the dentin, caries, etc.. A direct response to cutting procedures, caries, extreme
pressure, etc., involves the formation of reactive (secondary) dentin by the odontoblast
layer of the pulp. Formation of sclerotic dentin, in the process of obliterating the dentinal
tubules, is also protective to the pulp, helping to maintain the vitality of the tooth.

Periodontium
Periodontium refers to the specialized tissues that both surround and support the teeth,
maintaining them in the maxillary and mandibular bones. It consists of the Cementum,
Periodontal ligaments, Gingiva and Alveolar bone.
The tissues of the periodontium combine to form an
active, dynamic group of tissues. The alveolar bone
(C) ,The cementum (B) is attached to the adjacent
cortical surface of the alveolar bone by the alveolar
crest (I), horizontal (J) and oblique (K) fibers of the
periodontal ligament
Cementum is the only one that is a part of a tooth.
The gingiva , or gums, consists of the mucosal tissue that lies over the alveolar bone.
the gingiva is the surrounding tissue visible in the mouth.
Alveolar bone surrounds the roots of teeth to provide support and creates what is
commonly called a socket Dental alveolus.Dental alveolus are sockets in the jaws in
which the roots of teeth are held in the alveolar process of maxilla
with the periodontal ligament.
Periodontal ligaments connect the alveolar bone to the cementum.
The dentoalveolar fiber bundles occupy approximately two thirds of
the Periodontium volume.

Cells of the Periodontium
The cellular constituents of the Periodontium include:
osteoblasts, osteoclasts, Epithelial Rests of Malassez(The epithelial rests appear as small clusters of
epithelial cells which are located in the periodontal ligament adjacent to the surface of cementum. They are cellular
residues of the embryonic structure known as Hertwig's epithelial root sheath.)
Fibroblasts, undifferentiated mesenchymal cells, cementoblasts and cementoclasts,
neurovascular elements
The osteoblasts and osteoclasts are functionally associated with the alveolar bone,
and the cementoblasts and cementoclasts are functionally associated with the
cementum.
The extracellular constituents of the PDL consist of collagen fibers, oxytalan fibers, ground
substance, nerves, and vessels.

The periodontal ligament, commonly abbreviated as the PDL is a group of specialized
connective tissue fibers that essentially attach a tooth to the alveolar bone within which it
sits. These fibers help the tooth withstand the naturally substantial compressive forces
which occur during chewing and remain embedded in the bone.
Another function of the PDL is to serve as a source of proprioception, or sensory
innervation, so that the brain can detect the forces being placed on the teeth and react
accordingly. To achieve this end, there are pressure sensitive receptors within the PDL
which allow the brain to discern the amount of force being placed on a tooth during
chewing.
formation of the periodontal ligament begins with ligament fibroblasts from the dental
follicle. These fibroblasts secrete collagen, which interacts with fibers on the surfaces of
adjacent bone and cementum. This interaction leads to an attachment that develops as
the tooth erupts into the mouth.
A: enamel organ
B: dental papilla
C: dental follicle
Formation of the deciduous tooth
germs occurs on the labial aspect
of the dental lamina (DL).
An epithelial bridge (lateral lamina, LL)
is seen to connect DL with the bell-shaped
tooth germ. EK: enamel knot.
The free tip of DL proliferates into
the ectomesenchyme as the
successional lamina (SL)
providing the anlage for a permanent
tooth.
Dental papilla (DP), dental follicle (DF).

Shortly after the beginning of root formation and the formation of the outer dentinal
layer of root, the PDL is formed.
The cells of the dental follicle divide and differentiate into cementoblasts, fibroblasts
and osteoblasts.
The fibroblasts (synthesis of collagen & lysis of collagen) synthesize fibers and ground
substance that become the PDL.
These fibers then embed themselves into the newly formed cementum laid down by
cementoblasts at one end, and into the bone laid down by osteoblasts at their other end.
When a tooth erupts into the oral cavity, these fibers become oriented in a particularly
specific array.
The fiber bundles of the periodontal ligament gradually thicken after the teeth have been
in function for a while.
The periodontal ligament is one of the four supporting tissues of a tooth.
Their dimensions decrease with age.
The PDL fibers are composed primarily of type I collagen, although type III fibers are also
involved. Compared to most other ligaments of the body, these are highly vascularized.
The PDL fibers are categorized according to their orientation and location along the
tooth.

Occlusion or the arrangement of teeth and how teeth in opposite arches come in contact
with one another, continually affects the formation of periodontal ligament. This
perpetual creation of periodontal ligament leads to the formation of groups of fibers in
different orientations, such as horizontal and oblique fibers.
In humans, the width of the PDL ranges from 0.15 to 0.38 mm. Occlusal loading in function
affects the width of the PDL. If occlusal forces are within physiologic limits, increased
function leads to an increase in width through a thickening of the fiber bundles and an
increase in diameter and number of Sharpey's fibers. Forces that exceed this limit cause
lesions. When function is diminished or absent, the width of the PDL decreases. The fibers
are reduced in number and density.
The portion of the principal fiber that is embedded into either cementum or bone is called
a Sharpey's fiber.
Principal fiber groups of the periodontal ligament. (A)
Transseptal, (B) Alveolar crest, (C) Horizontal, (D) Oblique,
(E) Apical, and (F) Interradicular
The fiber bundles of human PDL are arranged into networks
having a complex three-dimensional overlapping
arrangement. The fiber bundles follow a wavy course from the
root to the bone with frequent crimping, branching, and
anastomosing. The blood vessels take a primarily longitudinal
course between the fiber bundles.

PDL fibers
Trans-septal fibers
They extend from the cemento-enamel junction of one tooth to the cemento-enamel
junction of the adjacent tooth. They serve to adhere the adjacent teeth together.
Alveolar crest fibers
Alveolar crest fibers attach to the cementum just apical to the cementoenamel junction,
run downward, and insert into the alveolar bone.
Horizontal fibers
Horizontal fibers attach to the cementum apical to the alveolar crest fibers and run
perpendicularly from the root of the tooth to the alveolar bone.

Oblique fibers
Oblique fibers are the most numerous fibers in the periodontal ligament. They attach
apical to the horizontal fibers and run diagonally toward the crown of the tooth inserting
to the alveolar bone there. Because they are the most numerous, these fibers are believed
to be primarily responsible in absorbing the chewing forces on the tooth. They are hence
the main support of the tooth.
Apical fibers
Apical fibers are at the apex of a root. They attach from the cementum and insert to the
surrounding bone at the base of the socket. They are also the first to offer resistance to
movement of the tooth in an occlusal direction (e.g. when the tooth is being extracted)
Interradicular fibers
Interradicular fibers are only found between the roots of multi-rooted teeth, such as a
molars. They also attach from the cementum and insert to the nearby alveolar bone.

In the human PDL oxytalan fibers, which resemble immature elastin fibers, are seen
among the collagen fibers. Oxytalan fibers form a network that attaches blood vessels to
the cementum . Periodontal vessels are linked vertically by fibers or multiple groups of
fibers forming tracts. Unique oxytalan-vascular structures consist not only of fibers
associated with the walls of individual arteries, veins, and Iymph vessels but a meshwork
that surrounds the total vessel complex.
Some researchers hypothesize that these fibers provide support for the blood vessels
when the PDL is under function.
Others feel that these fibers may influence blood flow and thereby effect tooth support.
Oxytalan fibers. (A) Cementum, (B) Principal
oxytalan fiber, (C) Oxytalan tract, and (D)
Periodontal vessel

Gingiva
The connection between the gingiva and the tooth is called the dentogingival junction.
This junction has three epithelial types: gingival, sulcular, and junctional epithelium.
These three types form from a mass of epithelial cells known as the epithelial cuff
between the tooth and the mouth.

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