Anatomy and histology of the denture bearing area - Dentistry ...

Anatomy and histology
of the denture bearing area
Dr. Aylin BAYSAN
The University of Birmingham
School of Dentistry
Anatomy of the edentulous area
Other structures should also be identified to
establish their precise relation to denture
base. These are as follows:
• Ligaments
• Frenulum
• Glandular tissues
Lower jaw
• Labial frenulum
It is a fold of fibrous tissue in the midline between
lip and alveolus.
• Mentalis muscle
This muscle arises from the symphysis menti and
is inserted downward into skin of the chin.
It elevates the lower lip and may lift up the lower
denture.
Anatomy of the edentulous area
In the mouth, complete or partial dentures are
surrounded by muscles.
Muscles tend to distabilise the denture if they
are encroached upon during contraction.
Upper and Lower jaw
• Orbicularis oris
Orbicularis oris forms a muscular circle within
the lips. It is inserted near the midline into labial
aspect of the maxilla and mandible.
• Modiolus
This muscular knot is at the angles of the mouth
where the dilator muscles:
- Levator anguli oris
- Zygomaticus major and minor
- Depressor anguli oris
Modiolus is lateral to the lower premolars so it
will displace a lower denture if those teeth are set
too far BUCCALLY.
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Muscles of facial expression which form modiolus
• Buccinator muscle
It arises from both jaws opposite the molar
alveolar area and posteriorly from the
pterygomandibular raphé.
As the buccinator fibres run almost parallel to the
denture border, they can slightly be displaced for
additional retention.
In this respect, it is the UNIQUE and ONLY
muscle that can be used this way.
Denture bearing area
• Mental nerve
This nerve emerges from the mental foramen near
the apices of the lower premolars.
In patients with extreme alveolar resorption, the
nerve may lie on or near the crest of the alveolar
ridge.
Pain or paraesthesia may be experienced if the
nerve is trapped by a denture base, usually by the
fitting surface.
• Massater muscle
This muscle is the MOST powerful of the
muscles which close the MANDIBLE.
The lower denture periphery related to it
should be shaped according to its
structure so that displacement of the
denture can be avoided when the muscle
contracts.
• Anterior fibres of temporalis
These fibres are sometimes attached low
down on the anterior border of the ramus
as far as the attachment of the buccinator
in the retromolar fossa.
The contraction of these fibres may
sometimes displace a lower denture.
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• Retromolar pad
Retromolar pad lies distal to the lower third molar
and is composed of fibrous tissue and mucous
glands.
• Superior constrictor muscle
This muscle originates from the pterygomandibular
raphé with a small extension continuing on the
lingual surface of the mandible to the posterior end
of the mylohyoid line.
• Genioglossus muscle and genial tubercle
The genioglossus arises from the superior genial
tubercles on the lingual surface of the mandible.
When the tongue is protruded, this muscle may lift
the lower denture.
When the edentulous mandible is severely
resorbed, the superior genial tubercle may project
above the level of the alveolar ridge and the
mucosa may become traumatised by a lower
denture.
Muscles limiting the extension of
a lower denture
• Lingually
The posterior extension is limited by fibers
from the superior constrictor muscle.
Fibres from the palatoglossus also form a
posterior limit.
The depth of the lingual flange is governed
by the mylohyoid.
• Mylohyoid muscle
It is a thin sheet of muscle and forms the floor of
the mouth. Its linear origin from the mylohyoid line
of the mandible continues posteriorly to the level of
the third molar.
• Sublingual salivary gland
This gland rests on the mylohyoid muscle medial to
the mandible. It is usually adjacent to the lower
canine region.
Its indentation is often seen on lower impressions
Muscles limiting the extension of
a lower denture
• Anterior labial flange
Orbicularis oris as far as the first premolar
region.
• Buccally
Buccinator muscle
• Retromolar pad
Buccinator and its insertion into the
pterygomandibular raphé.
Upper jaw
• Coronoid process
Coronoid process lies lateral to the maxillary
tuberosity.
It may sometimes impinge on the buccal flange of
a denture and cause pain or instability.
• Hamular notch
This notch is the junction of the maxillary
tuberosity and hamular process.
The periphery of a correctly extended denture
should extend through these notches via the area
of the fovea palatinae.
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• Fovea palatinae
These are a pair of mucous gland duct orifices
near the midline at the junction of the hard and
soft palate.
These landmarks provide a guide to the position
of the posterior palatal border of a denture.
• Incisive papilla
Incisive papilla is a mass of fibrous tissue about 1
cm behind the upper incisors.
Its position in the edentulous mouth indicates
where the incisors and canines should be set.
Facial curtain
The orbicularis oris and buccinator muscles
are draped around the mouth to form a
curtain, which is supported by teeth and
alveoli.
In edentulous patients, this curtain collapses
to give the characteristic toothless look.
Maxilla and mandible
There is difference in resorption pattern for
maxilla and mandible.
This leads to the appearance of prognatism
and gross positional discrepancies between
opposing residual ridges.
Muscles limiting the extension of
a upper denture
• Anterior labial flange
Anterior labial flange is limited by the
orbicularis oris as far as the first premolar
region.
• Buccally
From the second premolar region
posteriorly, the buccal flange is limited by
the buccinator.
Collapse of elevator and depressor muscles
and modiolus following loss of teeth
Edentulous face
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Muscles attachment changes with
progressive bone loss
The varying thickness of the mucosa
covering the oral cavity
Tongue
The tongue is highly mobile muscular organ
that needs careful attention during the
construction of complete dentures.
In coordination with lips, cheek, palate and
pharynx, the tongue functions in speech,
mastication and swallowing.
Oral mucous membrane
• Oral cavity
Stratified squamous type and shows differences in
degree of development, which correlates with the
functions of a particular area.
Apart from systemic that affect the integrity of the
oral mucous membrane, it should be noted that there
are age changes that are frequently seen in the
elderly edentulous patient including tendency to
dryness and general atrophy of the mucous
membrane.
Oral mucosa
Tongue
The tongue is in intimate contact with a
complete lower denture and its position in
relation to an edentulous ridge varies widely.
This relationship must be considered very
carefully in each particular patient.
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Salivary glands
Saliva is derived from the major and minor
salivary glands. The major salivary glands
consist of three pairs of glands:
• Parotid Gland
• Submandibular Gland
• Sublingual Gland
The outline of the lingual flange of the lower
denture in relation to submandibular gland
• Submandibular Gland
Extension of the lingual flange of a denture in
this region can lead to obstruction of the
submandibular gland.
Patients may complain of developing
swellings under the jaws when eating.
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