Oral Mucosa

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Oral Mucosa
Dr Jamal Naim PhD in Orthodontics
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Definition
Mucous membrane is used to describe the moist
lining of the gastrointestinal tract, nasal
passages and other cavities of the body that
communicate with he exterior. In the oral cavity
this lining is called oral mucous membrane or
oral mucosa. The oral mucosa is located between
skin and gastrointestinal mucosa and shows some
of the properties of each.
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Definition

• Like skin the oral mucosa consists of two tissue
  components
• A covering epithelium and
• underlying connective tissue
• Both of those tissues together perform a common
  function and so we consider them as an organ.

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Functions of the oral mucosa

• The main functions of the oral mucosa are
• Protection
• Sensation
• Secretion
• Thermal regulation

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Protection

• OM separates and protects deeper tissues and
  organs from the environment of the oral cavity
• Protection from mechanical stress such as
  compression, stretching, shearing and abrasions.
• Protection from chemical substances and toxins.
• Protection from the pathologic effect of the
  microorganisms in the oral cavity.

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Sensation

• The sensory function of the OM is important
  because it provide considerable information about
  events in the oral cavity
• Receptors respond to temperature, touch and pain
• Taste buds on the tongue
• Receptors respond to water taste and give signal
  about the satisfaction of thrist.

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Secretion
Salivary secretion by the salivary glands, major
and minor, is important for moistening the
OM. The minor salivary glands, which are
distributed among the oral cavity, are
responsible for about 80 of the salivary
secretion of mucous saliva. The mucous saliva
(mucin) is an important factor for the
lubrication and moistening of the OM.
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Thermal regulation
Only in some animals the OM plays an important
role in the regulation of the body
temperature. In humans there isn't any influence
of the OM by the regulation of the body
temperature.
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Anatomical considerations
The oral cavity consists of the oral vestibule
and the oral cavity proper. Laying between them
is the alveolar process bearing the teeth. Hard
and soft palate form the roof of the oral cavity
proper. The floor of the mouth and the tongue
form the inferior border of the oral cavity
proper.
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Anatomical considerations

• There are three main types of the oral mucosa,
  identified according their primary function
• Masticatory mucosa
• Lining mucosa
• Specialized mucosa
• The larger part of the OM is lining mucosa (60),
  followed by the masticatory (25) and specialized
  mucosa (15)

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Components of The OM

• The two main tissue components of the OM are
• The oral epithelium, it is a stratified squamous
  epithelium
• The lamina propria, it is the underlying
  connective tissue.
• The interface between oral epithelium and lamina
  propria (basement membrane) is usually irregular
  and the so called connective tissue papillae
  interdigitate with the epithelial ridges.

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Basement membrane
Connective tissue papillae
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Components of The OM
The tissue component under the oral mucosa is the
submucosa and it is less easy to recognize the
junction between them than between oral
epithelium and lamina propria. In some regions
such as cheek and lips a layer of loose fatty or
glandular connective tissue containing the major
blood vessels separates the OM from underlying
bone or muscles.
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Components of The OM
The components of the submucosa determine the
flexibility of the attachment of the oral mucosa
to the underlying structures. For example we
speak about mucoperiosteum in regions such as
hard palate because the OM is attached directly
to the palatal bone. Mucoperiosteum provides a
firm inelastic attachment of the OM to bone.
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Oral mucoperiosteum it lacks on submucosa (e. g.
region of the intermaxilary suture
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Components of The OM
In the OM there are minor salivary glands,
sebaceous cells and nodules of lymphoid
tissues. The largest accumulation of lymphoid
tissue are found in the posterior part of oral
cavity, where they form the lingual, palatine and
pharyngeal tonsils. Those accumulations are known
as the waldeyer's ring
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Oral Epithelium

• It is derived from the embryonic ectoderm and
  forms the primary barrier between oral
  environment and underlying tissues.
• It consists of stratified squamous cells arranged
  in many layers (strata)
• It maintains its continuity by a continuous cell
  renewal
• Cell proliferation
• Cell maturation

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Oral Epithelium

• The cells of oral epithelium that take part in
  the renewal are
• Progenitor cells the function is to divide and
  provide new cells
• Maturing cells they undergo a process of
  maturation to form the protective cell layer.

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Epithelial proliferation
The progenitor cells are located in the basement
membrane in thin epithelia (floor of the mouth)
and in the lower two to three cell layers in
thicker epithelia (cheek) Progenitor cells divide
into new progenitor cells or into maturing cells.
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Epithelial proliferation
The turnover time is the period of time is needed
by a cell to divide and pass through the entire
epithelium. The turnover time is 52 to 75 days in
skin, 41 to 57 days in the gingiva and 25 days in
the cheek.
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Epithelial maturation

• Cells that are driven from progenitor cells and
  ready for maturation passes the entire epithelium
  to form the protective layer.
• In general maturation in the oral cavity follows
  two main patterns
• Keratinization
• Nonkeratinization

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Epithelial maturation
Keratinization or cornification is the formation
of a surface of keratin. Such process is seen in
the oral mucosa of the palate, gingiva and in
some regions of the tongue dorsum. A keratinized
epithelium shows in histological sections a
number of layers (strata)
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Epithelial maturation

• The basal cell layer - stratum basale - contains
  cuboidal or columnar cells and is adjacent to the
  basement membrane.
• The cells of the st. basale shows the highest
  mitotic activity.

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Epithelial maturation

• The prickle cell layer - stratum spinosum - lies
  above the first one and contains several rows of
  elliptical or spherical cells.
• The cells have cytoplasmatic processes that have
  contact with other processes of other cells.

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Epithelial maturation
The mechanical adhesions between the cells are
called desmosomes. Both, st. basale and st.
spinosum, together constitute half to two third
of the thickness of the oral epithelium.
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Epithelial maturation

• The granular layer - stratum granulosum - is the
  next layer and consists of larger flattened cells
  containing small granules.

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Epithelial maturation

• The keratinized layer - stratum corneum is the
  surface layer and consists of flattened
  (squamous) cells.

squamous cells.
St. corneum
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Epithelial maturation
Nonkeratinization occurs in regions with less
mechanical influences to the OM, such as cheek,
lips, underside of the tongue and the soft
palate. Nonkeratinized epithelium is usually
thicker than keratinized epithelium. No sudden
changes in the cells above the st. spinosum occur
in nonkeratinized epithelium, and the outer half
of the tissue is divided into two zones
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Epithelial maturation

• Intermediate layer - stratum intermedium -
• Superficial layer stratum superficiale

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Epithelial maturation in Non-keratinized oral
mucosa
Epithelial maturation in keratinized oral mucosa
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Epithelial maturation
In so called parakeratinized mucosa, such as
parts of the hard palate and the gingiva, in the
surface layer the nuclei are shrunken and
retained in many or all squames. Also
keratohyaline granules are present in this
layer. Such phenomenon is a normal event in the
oral epithelium, but not true for the epidermis,
where parakeratinization is associated with
diseases such as psoriasis.
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Ultrastructure in the OE
In the next session
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Epithelial maturation