Anatomy and physiology/ cosmetic dentistry training

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Anatomy & Physiology
of the
Denture Bearing areas

Contents
Introduction
Anatomy of the denture supporting
structures of Maxilla
Anatomy of Peripheral or limiting
structures of Maxilla
Anatomy of the denture supporting
structures of Mandible
Anatomy of Peripheral or limiting
structures of Mandible
Conclusion
Bibliography

MUCOUS MEMBRANE
It is composed of mucosa and sub mucosa.
The mucosa is formed by stratified squamous
epithelium, which often is keratinised and a
subjacent narrow layer of connective tissue
known as the laminapropria.
In the edentulous person the mucosa covering
the ridge and the palate is called the masticatory
mucosa

The mucosa varies in its thickness and density ,
thinnest covering the midpalatine raphe next
thinnest being the mucosa covering the ridges
and thickest covering the blood vessels and
nerves of the lateral aspects of the palate.

Residual ridge
The bone that is left behind after all the teeth are
removed and after a disease or surgery affected.
First it was considered to be the primary stress
bearing area but it is looked upon the secondary
stress bearing area because of the fact that bone
is subjected to continuous resorption though it
decreases as the span of the edentulousness
increases.

The ridge varies greatly in size and shape and its
ultimate form is dependent on the following
factors:-
Original size, shape and calcification of the bone .
Size of the natural teeth
General health of the patient.
Forces exerted by the surrounding

Musculature.
Amount of the bone loss due to the
disease
before extraction
Duration of edentulousness and the rate
of resorption
Effect of previous prosthesis

Hard palate
The ultimate support for the maxillary
denture is the hard palate
The two palatine process of the maxilla
fuse together to form the hard palate at the
mid palatine suture.
It is covered by the mucosa of varying
thickness.

In the region of the midpalatine suture the sub
mucosa is very thin and it has to be relieved .
Quite often in the mid palatine suture, a
hyperplastic growth of bone is seen.
This intervenes with the stability of the
denture, this called as torus palatinus.
Steps should be taken to obtain considerable
relief by using the special impression
techniques, mechanical relief or by the last
resort, by its surgical excision.

Rugae
In the area of the rugae the palate is set at
an angle to the ridge and rather thinly
covered by the soft tissue.
This is considered to be the secondary
stress bearing area
Rugae are said to be associated with the
sense of taste and the function of speech
They assist the tongue to absorb via its
papillae.

They also enable the tongue to form a
perfect seal when it is pressed against the
palate in making the linguo palatal
constant stops of speech.
Rugae should not be displaced,otherwise
the rebounding may dislodge the denture.
They provide anteroposterior resistance to
movement of the denture and increased
surface area helps in retention.

Maxillary tuberosity
It is a bony prominence situated at the posterior
aspect of alveolar ridge.
A broad well rounded tuberosity of sufficient
height is favorable.
Large maxillary tuberosities bounded by deep
sulci offer very satisfactory resistance to the
lateral movement of the denture.

Tuberosities sometimes exhibit buccal undercuts ,
if it is unilateral it can be utilized for the retention.
If excess hyperplastic tissue is present it should be
surgically corrected.

Incisivepapilla
It is a thick fibrous connective tissue covering the
incisive foramen.
It is located on the line immediately behind and
between the central incissors.
Relief for the papilla should be provided to prevent
any possible interferences with the blood and nerve
supply.
Clinical significance:-
it helps to determine the midline.
it determines the position of the upper anteriors.
it helps to assess the amount of resorption
because it does not change the position.

The horizontal distance between the
perpendicular line from incisive papilla to labial
surfaces of incisors should be about 8-10mm.
It helps in selecting the size of the upper
anteriors i.e the horizontal line drawn cutting
the papilla and extending over the land surface
should coincide with the position of the upper
canine tooth.
It helps in determing the vertical dimension of
occlusion i.e distance between the incisal edge
and the papilla should be 4 mm.

Zygomatic process
It is also called as malar process.
It is located opposite the first molar region.
It is prominent in the long span edentulous
people.
In some cases it requires relief over this
area to aid in retention and prevent
soreness of the underlying tissues.

Pterygomandibular raphe
It originates from the hamular process and
in close proximity to the distal edge of the
upper denture.
If this edge is over extended it will impinge
on the fold of the soft tissue which is
elevated when the mouth is open and the
raphe becomes tensed.
This causes inflammation and often
reported as soreness of the throat or the
denture flips downwards each time when
patient opens the mouth.

Sharp spiny process
Frequently there are sharp spiny process
on the maxillary and palatine bones that
are deeply covered with the soft tissue.
In patients with the considerable
resorption of the ridge these spines
irritates the soft tissues left between them
and the denture base.

Labial Frenum
It is a fan shaped fibrous pack covered by mucus
membrane that extends from the inner aspect of upper
lip and attached to the labial aspect of residual ridge.
It is usually single and does not contain muscle fibres
It has to be relieved while making impression in order
to prevent dislodgement of the denture and to prevent
Ulceration and the upper lip will be pushed away from
the functional depth and there will be more visibility of
the teeth

It is relieved by making up and downward
movements of upper lip.It is seen as a V shaped
notch in the impression

Labial Vestibule
Labial Vestibule is divided in to left and right by
the labial frenum
The mucous membrane lining the labial vestibule
has a relatively thin mucosa with a epithelium that
is non keratinised
The depth of the labial sulcus depends on
-height of the alveolar ridge
-Mobility and tension of the surrounding
muscles
The labial sulcus is relieved by functional moulding of
the upper lip

Over extension of labial flange of the denture
causes ulceration or instability of the denture
The thickness of the flange provides stability
and peripheral seal

Buccal frenum
It’s a fold of mucous membrane overlying the muscles
near the premolar region
It may be single or multiple. It divides the labial and
buccal vestibules.
It requires more clearance for its action than the labial
frenum
It moves mesially,buccaly and vertically
Orbicularis oris- Mesial movement
Buccinator-Buccal movement
Levator angulioris and Canninus –Vertical movement

Buccal Vestibule
It lies opposite the tuberosity and extends from
the buccal frenum to the Hamular notch
The size of the vestibule varies with the
contraction of the Buccinator muscle,position of
the mandible,amount of the bone loss from the
maxilla
Compare to the labial flange ,buccal flange has
less interferences and so provides maximum
retention

Width of the buccal flange is determined by
making side ward movement of the mandible and
during this movement the coronoid process will
be closed to the tuberosity
Excessive thickness of buccal flange will
displace the denture when the patient opens the
mouth wide

Pterygomaxillary notch
It’s a bony depression between tuberosity
and hamulus of the medial pterygoid plate
This forms the distal limit of the upper
denture
It is covered by the mucosa of sufficient
thickness and can be compressed to
achieve peripheral seal
Over extension will lead to the pain and
dislodgment of the denture

Fovea palatine
These are the depressions or indentations
situated on the soft palate on the either
side of the midline
It helps to determine the midline and
positioning of the posterior border
These are the ductal openings in to which
ducts of other palatal mucous glands drain

Posterior palatal seal
It is defined as the soft tissues along the
junction of the hard and soft palates on
which pressure with in the physiologic
limits of the tissues can be applied by a
denture to aid in the retention of the
denture.
Its significance is
-To maintain contact with the anterior
portion of the soft palate during the
functional movements,therefore the
primary purpose of it is retention of the
denture.

The proper placement of it will reduces the
patient awareness of this area with subsequent
reduction in the Gag reflex.
It reduces the food accumulation beneath the
posterior aspect of the denture
It reduces the patient discomfort when contact
occurs between the dorsum of the tongue and
the posterior end of the denture base
As it lies in close approximation to the soft
palatal tissue, it compensates for the volumetric
shrinkage that occurs during polymerization of
Methyl Methacrylate resin

The correct placement of the seal will not
impinge up on the non displaceable tissues of
hard palate and it will not limit the muscular
movements of the soft palate
It will create a partial vacuum beneath the
maxillary denture. It is activated only when
horizontal or tipping forces are directed against
denture base

Anterior vibrating line
It is an imaginary line located at the junction of
the attached tissues overlying the hard palate
and the movable tissues of immediately
adjacent soft palate
One way to locate the line is to ask the patient
perform the Valsalva maneuver which requires
that both nostrils be held firmly while the
patient blows gently through the nose
It can also be approximated by visualisig the
area while instructing the patient to say ”AH”
with short vigorous bursts

Due to the projection of the posterior nasal
spine, this line is not a straight line between both
Hamular processes
It is always on soft palatal tissues

Posterior vibrating line
It is an imaginary line at the junction of the
aponeurosis of the Tensorveli palatina muscle
and the muscular portion of the soft palate.
It represents the demarcation between that part
of the soft palate that has limited or shallow
movement during function and the remainder of
the soft palate that is markedly displaced during
functional movements

It is visualised by instructing the patient to say
“AH” in short bursts in a normal un exaggerated
fashion.
It marks the most distal extension of the denture
base.

The rational for the placement of seal in the
impression tray is as follows
1).To establish positive contact posteriorly to
prevent the final impression material from sliding
down the pharynx
2).To serve as a guide for positioning the
impression tray
3).To create slight displacement of the soft palate
4).To determine if adequate retention and seal of
the potential denture border is present

Technique to determine posterior palatel seal
are
1).Conventional approach
2).Fluid wax technique
3).Arbitaryscraping of the master cast

Crest of the residual ridge
The ridge is covered by fibrous connective
tissue.
The under lying bone is cancellous bone
which cannot take up the masticatory
loads.
the fibrous connective tissue closely
attached to the bone is favourable for
resisting applied forces, such as those
from a denture.
The mean denture bearing area is
13.95sq.cm www.indiandentalacademy.com

The buccal shelf or buccal flange
The area between the mandibular buccal
frenum and the anterior edge of the
masseter muscle is known as buccal shelf.
It is bound medially--crest of the residual
ridge.
Laterally--external oblique ridge.
Distally --retromolar pad.
The total width of the bony foundation in
this region becomes greater as alveolar
resorption continues.

The mucous membrane covering this area is
loosely attached and less keratinised and has
thicker submucosal layer.Hence it may not be
histologically suitable to provide primary support
for the denture.
How ever the bone of the buccal shelf and the
fact that it lies at right angles to the vertical
occlusal forces makes it suitable primary stress
bearing area for the denture.
The inferior part of the buccinator muscle is
attached to the buccal shelf and its fibers are
found in the submucosa immediately overlying
the bone

Mylohyoid ridge
Soft tissue usually hides the sharpness of the
mylohyoid ridge.
The shape and inclination of the ridge vary
greatly among the edentulous people.
Anteriorly the mylohyoid muscle is attached and
lies close to the inferior border of the mandible.
posteriorly following resorption, it often lies
flush with the superior surface of the ridge.

The mucous membrane over a sharp or
irregular mylohyoid ridge will be easily
traumatized by the denture base.
The area under the ridge is an undercut.

Mental foramen
Severe resorption of bone results in
mental foramen lying close to or at the
crest of the ridge results in compression
of the mental nerves and blood vessels,if
relief is not provided in the denture base.
Pressure on the mental nerve can cause
numbness of the lower lip.

Genial Tubercles
They usually lie well away from the crest of
the ridge
However with the resorption the genial
tubercles become increasingly prominent

Torus mandibularis
This is a bony prominence usually found
bilaterally and lingually near the first and
second premolars mid way between the
soft tissues of the floor of the mouth and
the crest of the alveolar ridge
In the edentulous mouth where
considerable resorption takes place, the
superior border of the torus may be flush
with crest of the ridge

It is covered by extremely thin layer of mucous
membrane which often needs to be corrected
surgically as it cannot be relieved with in the
denture with out breaking the border seal

External oblique line
It is a ridge of the dense bone extending
from just above the mental foramen in a
superior and distal direction to become
continuous with the anterior border of the
ramus
It is an anatomical guide for the lateral
termination of the buccal flange of the
denture

Buccal & Labial borders
The labial frenum contains a band of
fibrous connective tissue that helps attach
the orbicularis oris
Therefore the frenum is quite sensitive and
active and must be carefully fitted to
maintain a seal without causing soreness

Buccal Frenum
It connects as a continuous band through the
modiolus at the corner of the mouth to the
buccal frenum in the maxilla
This fibrous and muscular tissues pull actively
across the denture borders, polished surfaces
and teeth
Therefore denture should extend less in this
region and the impression must be functionally
trimmed to have the maximum seal and yet not
displace the denture when the lip is moved

Labial Vestibule
It runs from the buccal to the labial frenum
The mentalis muscle is particularly active
muscle in this region
It contains a band of fibrous connective
tissue that helps attach the orbicularis oris
muscle

Buccal vestibule
It extends posterior from the buccal frenum to the outside
back corner of the retro molar pad
The extent of the vestibule is influenced by buccinator
muscle anteriorly to the pterygomandibular raphe
posteriorly its lower fibres attached to the buccal shelf and
external oblique ridge

The flange which starts immediately posterior to the
frenum swings wide in o the cheek and it is nearly right
angle o the biting force.
The impression is always widest in this region
The disto buccal border at the end of the vestibule
must converge rapidly to avoid displacement by the
contracting masseter muscle whose anterior fibers run
outside and behind the buccinator muscle in this
region

Retro Molar pad
It is triangular soft pad of tissues at the
digital end of he lower ridge
Its mucosa is composed of a thin non
keratinized epithelium and in addition its
sub mucosa contains glandular tissue and
fibers of the buccinator and superior
constrictor muscles,the
pterygomandibular raphe and the terminal
part of the tendon of the temporalis
muscle

The action of these muscles limits the extent of
the denture and prevents placement of extra
pressure on the distal part of the retro molar
pad during the impression procedures

Mylohyoid muscle
The floor of the month is formed by this
muscle which arises from the whole length
of the Mylohyoid ridge
This ridge is sharp and distinct in the
molar region and becomes almost
indiscernible anteriorly
Medially the fibres join those from the
mylohoid muscle of the opposite side and
posteriorly they continue to the hyoid base

The muscle lies deep to the sub lingual
gland and other structures in the anterior
region and so does not affect the denture
border except indirectly
The posterior part of h muscle in the molar
region affects the lingual impression border
in swallowing and in moving the tongue
Extension of the lingual flange under this
ridge cannot be tolerated in function
because it will interfere with the action of he
mylohyoid muscle when it contract will
displace the denture causing soreness

An extension of the lingual flange well beyond
the palpable position of the ridge,but not in to
the undercut has other advantages.
The lack of the direct pressure on the sharp
edge of the ridge will eliminate the possible
source of discomfort.

Retromylohyoid fossa
It is the area posterior to the mylohyoid
muscle
As the lingual flange moves in to this
fossa.It ceases to be influenced by the
action of the mylohyoid muscle and so can
move back towards the body of the
mandible producing the typical “S” curve
of the lingual flange

It is bounded by the retromylohyoid
curtain
The postero lateral portion of the curtain
overlies the superior constrictor
muscle,and postero medial portion covers
the palatoglossal muscle plus the lateral
surface of the tongue
The inferior wall overlies the sub
mandibular gland,which fills the gap
between the superior constrictor muscle
and the most distal attachment of the
mylohyoid muscle.

The denture border should extend posteriorly to
contact the curtain when the tip of the tongue is
placed against the front part of the upper ridge.
Protrusion of the tongue causes the curtain to
move forward.

Sublingual gland region
In the premolar region the sub lingual
gland rest above the mylohyoid
muscle
When the floor of the mouth is raised
the gland comes quite close to the
crest of the ridge and reduces the
vertical space available for the
extension of the flange in the anterior
part of the mouth

This can be avoided by shaping this part of the
flange of the tray to slope inward, toward the
tongue and making the final impression with low
viscosity impression material

Alveololingual sulcus
It is the space between the ridge and tongue
extending from the lingual frenum to the retro
mylohyoid curtain
The anterior region:
This extends from the lingual frenum back to
where the mylohyoid ridge curves down below
the level of the sulcus

Premylohyoid fossa is palpated and a
corresponding eminence seen on the
impressions
The lingual border in this region should
extend down to make contact with the
mucus membrane, floor of the mouth
when the tip of the tongue touches the
upper incisors
The flange will be shorter than the
posterior flange

Middle region:
This region extends from pre mylohyoid
fossa to the distal end of the mylohyoid
ridge,curving medially from the body of the
mandible
Posterior region:
Flange passes in to the retrohyoid fossa and
so mylohyoid muscle does not influence
the denture border in this region

Conclusion
The denture bearing areas not only support
the dentures but have a direct bearing on
the impression making procedures, the
position of teeth and the contours of the
finished denture base.
Thus thorough knowledge of the anatomy
and physiology of the supporting structures
is essential for the success of the
prosthesis

Bibliography
Boucher’s Prosthodontic Treatment for
Edentulous patients – 10th
Edition
Boucher’s Prosthodontic Treatment for
Edentulous patients – 11th
Edition
Textbook of Complete dentures – Charles
M.Heartwell
Essentials of Complete denture
prosthodontics – Sheldon Winkler

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