Biomechanics of edentulous state new

BIOMECHANICS OF
EDENTULOUS STATE
PRESENTED BY :
DR. PRAJAKTA BALI GIR
MDS 1ST YEAR
1
DEPARTMENT OF PROSTHODONTICS, CROWN AND BRIDGE. DDCH, UDAIPUR

CONTENTS
• INTRODUCTION
• SUPPORT MECHANISM FOR NATURAL DENTITION
• SUPPORT MECHANISM FOR COMPLETE DENTURES
• OCCLUSION : FUNCTIONAL AND PARAFUNCTIONAL
CONSIDERATIONS
2

CONTENTS
• POSTURAL REST POSITION
• CYCLIC JAW MOVEMENT
• THE TONGUE
• SALIVARY GLANDS
3

CONTENTS
• CHANGES IN MORPHOLOGICAL FACE HEIGHT AND
TEMPOROMANDIBULAR JOINT
• ESTHETIC, BEHAVIORAL AND ADAPTIVE RESPONSES
• CONCLUSION
• REFERENCES
4

INTRODUCTION
DEPARTMENT OF PROSTHODONTICS, CROWN AND BRIDGE. DDCH, UDAIPUR 5

• BIOMECHANICS = The application of mechanical laws to
living structures, specifically the locomotor systems of the body.
(GPT-9)
• DENTAL BIOMECHANICS = The relationship between the
biologic behaviour of oral structures and the physical influence
of a dental restoration. (GPT-9)
INTRODUCTION

• The edentulous state represents a compromise in the integrity of
the masticatory system.
• It is frequently accompanied by adverse functional and esthetic
sequelae, which are varyingly perceived by the affected patient.
• Consequently, the required treatment addresses a range of
biomechanical problems that involve a wide range of individual
tolerances and perceptions.

SUPPORT MECHANISM FOR NATURAL
DENTITION.

• The natural or prosthetic dentition and its supporting mechanism
are the most visible and frequently managed parts of the
masticatory system.
• The masticatory system is made up of closely related
morphological, functional, and behavioral components.
SUPPORT MECHANISM FOR NATURAL DENTITION

• Their interactions are affected by changes in the mechanism of
support for a dentition when natural teeth are replaced by
artificial or prosthetic ones.
• The masticatory apparatus is involved in the trituration of food.
• Direct responsibility for this task falls on the teeth and their
supporting tissues.

FUNCTIONS AND PARAFUNCTIONS
Dentulous state with a periodontal ligament
mechanism of support
Edentulous state without a periodontal
ligament mechanism of support
Morphologic face height
temporo-mandibular joints
Behavioural/adaptive responses
Possible interactions among the various components of the masticatory system in the context of a change in
the mechanism of occlusal support

• Teeth function properly only if adequately supported, and this
support is provided by the periodontium, an organ composed of
soft and hard connective tissues.
• The periodontium attaches the teeth to the bone of the jaws,
providing a resilient suspensory apparatus resistant to functional
forces.
• It allows the teeth to adjust their position when under stress.

• The periodontal ligament provides the means by which force
exerted on the tooth is transmitted to the bone that supports it.
• The two principal functions of the periodontium are support and
positional adjustment of the tooth, together with the secondary
and dependent function of sensory perception.

• The patient who needs complete denture therapy is deprived of
periodontal support, and the entire mechanism of functional load
transmission to the supporting tissues is altered.
• The occlusal forces exerted on the teeth are controlled by the
neuromuscular mechanisms of the masticatory system.
• Reflex mechanisms with receptors in the muscles, tendons,
joints, and periodontal structures regulate mandibular
movements

• The greatest forces acting on the teeth are normally produced
during mastication and deglutition, and they are essentially
vertical in direction.
• Each thrust is of short duration, and for most people, chewing is
restricted to short periods during the day.
• Deglutition, on the other hand, occurs about 500 times a day, and
tooth contacts during swallowing are usually of longer duration
than those occurring during chewing

• Loads of a lower order but longer duration are produced
throughout the day by the tongue and circumoral musculature.
• These forces are predominantly in the horizontal direction.
• During rest or inactive periods, the total forces may be of similar
magnitude.
• In healthy dentitions, teeth are in occlusion only during the
functional movements of chewing and deglutition and during the
movements associated with parafunction

• It has been calculated that the total time during which the teeth
are subjected to functional forces of mastication and deglutition
during an entire day amounts to approximately 17.5 minutes .
• More than half of this time is attributable to jaw closing forces
applied during deglutition.
• Therefore the total time and the range of forces seem to be well
within the tolerance level of healthy periodontal tissues.

Calculation of Total Time during 24 Hours When Direct
Functional Occlusal Force Is Applied to the Periodontal Tissues
CHEWING
Actual chewing time 450 sec per meal
Four meals per day 1800 sec
One chewing stroke 1800 strokes per sec
Duration of each stroke 0.3 sec
Total chewing forces 540 sec (9 min) per
day

SWALLOWING
MEALS
Duration of one deglutition 1 sec
During chewing, three
deglutition per min, one third
with occlusal force
30 sec (0.5 min)

SWALLOWING
BETWEEN MEALS
Daytime: 25/hr (16 hr) 400 sec (6.6 min)
Night time: 10/hr (8 hr) 80 sec 80 sec (1.3 min)
Total 1050 sec = 17.5 min

SUPPORT MECHANISM FOR
COMPLETE DENTURES

• The basic challenge in the treatment of edentulous patients lies in
the nature of the difference between the ways natural teeth and
their artificial replacements are supported.
SUPPORT MECHANISM FOR COMPLETE
DENTURES

• Masticatory loads are much smaller than those that can be
produced by conscious effort and are in the region of 44 lb (20
kg) for the natural teeth. ( PICTON 1969 )
• Maximum forces of 13 to 16 lb (6 to 8 kg) during chewing have
been recorded with complete dentures, but the average loads are
probably much less than these.
MUCOSAL SUPPORT AND MASTICATORY LOADS

Maximal bite forces
appear to be five to
six times less for
complete denture
wearers than for
persons with natural
teeth.
DEPARTMENT OF PROSTHODONTICS,
CROWN AND BRIDGE. DDCH, UDAIPUR
25

• The residual ridge consists of denture-bearing mucosa, the
submucosa and periosteum, and the underlying residual alveolar
bone.
• Residual bone is that bone of the alveolar process that remains
after teeth are lost.
RESIDUAL RIDGE

• When the alveolar process is made edentulous by loss of teeth,
the alveoli that contained the roots of the teeth fill in with new
bone.
• This alveolar process becomes the residual ridge, which is the
foundation for dentures.
RESIDUAL RIDGE

• IT IS KNOWN THAT :
1. Function can modify the internal structure of human bone
2. Pressure can cause its resorption
3. Tension may bring about bone deposition
RESIDUAL RIDGE

• Alveolar bone supporting natural teeth receives tensile loads
through a large area of periodontal ligament, whereas the
edentulous residual ridge receives vertical, diagonal, and
horizontal loads applied by a denture with a surface area much
smaller than the total area of the periodontal ligaments of all the
natural teeth that had been present
RESIDUAL RIDGE

• One of the few firm facts relating to edentulous patients is that
wearing dentures is almost invariably accompanied by an
undesirable and irreversible bone loss.
• The magnitude of this loss is extremely variable.
RESIDUAL RIDGE

DEPARTMENT OF
PROSTHODONTICS, CROWN
AND BRIDGE. DDCH, UDAIPUR 31

DEPARTMENT OF
PROSTHODONTICS,
CROWN AND BRIDGE.
DDCH, UDAIPUR
32

• TWO CONCEPTS HAVE BEEN ADVANCED CONCERNING
THE INEVITABLE LOSS OF RESIDUAL BONE:
1. A direct consequence of loss of the periodontal structures,
variable progressive bone reduction occurs.
2. Residual bone loss is not a necessary consequence of tooth
removal but depends on a series of poorly understood factors.

• The tissue support for complete dentures is conspicuously
limited in both its adaptive ability and inherent capability of
simulating the role of the periodontium.
• This compromised support is further complicated because
complete dentures move in relation to the underlying bone
during function.

• This movement is related to the resiliency of the supporting
mucosa and the inherent instability of the dentures during
functional and parafunctional movement.
• Brill in 1967 described the factors related to complete denture
retention :
1. Maximal extension of denture base.
2. Maximal area of contact between the denture base and the mucous
membrane.
3. Intimate contact of the denture base and the basal seat.

• Muscular factors can be used to increase retention (and stability)
of dentures.
• In fact, the buccinator, the orbicularis oris, and the intrinsic and
extrinsic muscles of the tongue are key muscles that the dentist
harnesses to achieve this objective by means of impression
techniques.

• Furthermore, the design of the labial, buccal, and lingual
polished surfaces of the denture and the form of the dental arch
are considered in balancing the forces generated by the tongue
and perioral musculature.
• As the form and size of the denture-supporting tissues (the basal
seat) change, harnessing muscular forces in complete denture
design becomes particularly important for denture retention.

• The dentures may have an adverse psychological effect on some
patients, and the nervous influences that result may affect
salivary secretions that affect retention.
• Eventually, most patients seem to acquire an ability to retain their
dentures by means of their oral muscle control.
PSYCHOLOGICAL EFFECT ON RETENTION

• This muscular stabilization of dentures is probably also
accompanied by a reduction in the actual physical forces used in
retaining their dentures.
• Clearly, the physical forces of retention can be improved and
reestablished, up to a point, by careful and frequent attention to
the denture status.
• Periodic inspection, including relining procedures, will help
prolong the usefulness of the prosthesis.

OCCLUSION : FUNCTIONALAND
PARAFUNCTIONAL CONSIDERATIONS

• The masticatory system appears to operate best in an
environment of continuing functional equilibrium.
• This equilibrium depends on the interactions of the many
components represented here.
DEVELOPING DENTITION 1. Extensive sensory input
2. Development of motor skills and
neuromuscular learning
3. Dental, alveolar, craniofacial
adaptability

HEALTHY ADULT DENTITION 1. Dental adaptation (wearing,
drifting, extrusion)
2. Bone adaptation is reparative
3. Learned protective reflexes and
functional adaptation
DETERIORATING ADULT
DENTITION
1. Partial edentulism
2. Periodontal disease
3. Diminished dental reflex
adaptation
4. Risk of maladaptive prosthesis-
wearing experience

THE EDENTOLUS STATE 1. Residual ridge reduction
2. Compromised reflex adaptability
3. Possible increase in parafunctional
movements
4. Increased risk of maladaptive
denture-wearing experience
Development and adaptation of the occlusion
• The substitution of a complete
denture for the teeth/periodontium
mechanism alters this equilibrium.
• An analysis of this alteration is the
basis for understanding the
significance of the edentulous state.

• THE PRIMARY COMPONENTS OF HUMAN DENTAL
OCCLUSION ARE :
(1)The dentition,
(2) the neuromuscular system, and
(3) the craniofacial structures.
OCCLUSION

• The development and maturation of these components are
interrelated so that growth, adaptation, and change actively
participate in the development of an adult occlusion.
• In a healthy adult dentition, dental adaptive mechanisms are
restricted to wear, extrusion, and drifting of teeth.
• Bony adaptations are essentially of a reparative nature and are
slow in their operation.

• Protective reflexes are learned so one can avoid pain and
inefficiency of the masticatory system.
• If and when an adult dentition begins to deteriorate, the dentist
resorts to fixed or removable prosthodontic therapy in attempts
to maintain a functional occlusal equilibrium.
• This period is characterized by greatly diminished dental and
reflex adaptation and by bone resorption.

• In the edentulous state, there are few natural adaptive
mechanisms left.
• The prosthesis rests on tissues that will change progressively and
irreversibly, and the artificial occlusion serves in an environment
characterized by constant change that is mainly regressive.
• Complete dentures are designed so that their occlusal surfaces
permit multidirectional contact movements of the mandible.

• Orofacial and tongue muscles play an important role in retaining
and stabilizing complete dentures.
• This is accomplished by arrangement of the artificial teeth to
occupy a “neutral zone” in the edentulous mouth so the teeth will
occupy a space determined by the functional balance of the
orofacial and tongue musculature.

• Mastication consists of a rhythmic separation and apposition of
the jaws and involves biophysical and biochemical processes,
including the use of the lips, teeth, cheeks, tongue, palate, and all
the oral structures to prepare food for swallowing.
FUNCTION: MASTICATION AND SWALLOWING

• During masticatory movements, the tongue and cheek muscles
play an essential role in keeping the food bolus between the
occlusal surfaces of the teeth.
• The control of mastication within the narrow limits of tolerance
of the mouth requires considerable sensory information because
deviations from the normal path of mandibular movement can
injure the tongue, buccal mucosa, and even the teeth and their
supporting tissues

• Loss of teeth can lead to a diminished masticatory efficiency.
• The results of studies of mandibular movement patterns of
complete denture patients indicate that these movements are
similar in denture-wearing patients and persons with natural
teeth.
• Therefore treatment of partially edentulous and edentulous
patients might improve their chewing efficiency and masticatory
muscle activity , which would be accompanied by decreased

• duration of the occlusion phase and contribute to a lessening of
elevator muscle activity.
• Chewing occurs chiefly in the premolar and molar regions, and
both right and left sides are used to about the same extent.
• The position of the food bolus during mastication is dependent
on the consistency of the food, and the tougher the consistency
the greater is the person’s preference for using the premolar
region.

• The latter observation is apparent even in patients who have
worn bilateral, soft-tissue–supported, mandibular partial dentures
opposing complete upper dentures.
• There is an obvious advantage that the patient accrues with the
replacement of missing premolar and molar segments, and these
patients do not chew predominantly in the segments where
natural teeth are present .

• The pronounced differences between persons with natural teeth
and patients with complete dentures are conspicuous in this
functional context:
1) The mucosal mechanism of support as opposed to support by the
periodontium;
2) The movements of the dentures during mastication;
3) The progressive changes in maxillomandibular relations and the
eventual migration of dentures; and
4) The different physical stimuli to the sensor motor systems.

• The denture-bearing tissues are constantly exposed to the
frictional contact of the overlying denture bases.
• Dentures move during mastication because of the dislodging
forces of the surrounding musculature.
• These movements manifest themselves as displacing, lifting,
sliding, tilting, or rotating of the dentures.

• Furthermore, opposing tooth contacts occur with both natural
and artificial teeth during function and parafunction when the
patient is both awake and asleep.
• Apparently, tissue displacement beneath the denture base results
in tilting of the dentures and tooth contacts on the nonchewing
side.

• In addition, occlusal pressure on the dentures displaces soft
tissues of the basal seat and allows the dentures to move closer to
the supporting bone.
• This change of position under pressure induces a change in the
relationship of the teeth to each other.

• Nonfunctional or parafunctional habits involving repeated or
sustained occlusion of the teeth can be harmful to the teeth or
other components of the masticatory system.
• Teeth clenching is common and is a frequent cause of the
complaint of soreness of the denture-bearing mucosa .
PARAFUNCTION

• In the denture wearer, parafunctional habits can cause additional
loading on the denture-bearing tissues .
• Direction, Duration, and Magnitude of the Forces Generated
during Function and Parafunction :
FORCE GENERATED
DIRECTION DURATION AND
MAGNITUDE
MASTICATION Mainly vertical Intermittent and light Diurnal
only
PARAFUNCTION Frequently horizontal as well
as vertical Prolonged
possibly excessive Both
diurnal and nocturnal

• The neurophysiological basis underlying bruxism can be
explained by an increase in the tonic activity in the jaw muscles.
• It is a very complex area of research and has been shown to
result from psychosocial factors (such as stress or anxiety) or to
be a reaction to strong emotions (e.g., anger, frustration).
• It may be associated with specific medical conditions (oral
tardive dyskinesia, Parkinson’s disease),

• or with sleep parasomnia (e.g., bruxism [tooth grinding], rapid
eye movement [REM] behavior disorders, oromandibular
myoclonus) or sleep disorders (apnea).
• It may also be found concomitantly with certain intraoral
conditions such as pain, oral lesions, xerostomia, and discomfort
with prostheses or occlusion.
• The initial discomfort associated with wearing new dentures is
known to evoke unusual patterns of ,

behavior in the surrounding musculature.
• Frequently, the complaint of a sore tongue is related to a habit of
thrusting the tongue against the denture.
• The patient usually is unaware of the causal relationship between
the painful tongue and its contact with the teeth.
• Similarly, patients tend to occlude the teeth of new dentures
frequently at first—perhaps to strengthen confidence in retention

until the surrounding muscles become accustomed or to provide
some accommodation in the chewing pattern—and experimental
closure of the teeth is part of the process of adaptation.
• A strong response of the lower lip and mentalis muscle has been
observed electromyographically in long-term complete denture
wearers with impaired retention and stability of the lower
denture.

• It is feasible and probable that the tentative occlusal contacts
resulting may trigger the development of habitual nonfunctional
occlusion.
• The mechanism whereby pressure causes soreness of the mucous
membrane is probably related to an interruption or a diminution
of the blood flow in the small blood vessels in the tissues

• Yemm in 1972 suggested that stress can induce, increase in
activity of the masseter and temporomandibular muscles in
denture wearers, which in turn can cause tooth contact and
eventually soreness of underlying mucosal tissues.

• DISTRIBUTION OF STRESS TO DENTURE SUPPORTING
TISSUES :

FUNCTION AND
PARAFUNCTION
GENERATE
PRESSURE
TISSUE DAMAGED
BY OCCLUDING
LOCAL
CIRCULATION
FORCE
1. ADEQUATE PREPARATION OF
SUPPORTING HARD AND SOFT
TISSUES.
2. COMPLETE DENTURE BASE
EXTENSION WITHIN MORPHOLIC
AND FUNCTIONAL LIMITS.
3. USE OF RESILIENT DENTURE BASE
LINING MATERIALS.
4. REDUCTION OF AREA OF
OCCLUSAL TABLE.
5. DEVELOPING OPTIMAL DENTURE
OCCLUSION.
6. PT. INSTRUCTED TO HANDLE
PARAFUNCTIONAL HABITS THRU
EDUCATION AND
UNDERSTANDING.
TIME
CONTROLLED
PARTIALLY BY
NOCTURNAL
TISSUE REST.

POSTURAL REST POSITION

• Postural rest position is not a border position of the mandible.
• With the mandible in this position and with the head upright, an
interocclusal distance or freeway space of 2 .5 -3 .0 mm usually
exists between the opposing teeth in the premolar area.
POSTURAL REST POSITION

• Yemm and Berry believe that mandibular posture at rest is a
position of passive equilibrium , governed by gravity and the
elastic qualities of the tissues and muscles that attach to the
mandible.
• Mc Namara, on the other hand, has stated that “ the postural
position of the mandible in man is maintained by tonic activity in
the elevator musculature opposing gravitational forces” .

• Postural rest position of the mandible is influenced by the
myotatic (stretch) reflex, which is activated by stretch of the
muscle spindles in the elevator muscles.
• When gravitational forces act to depress the mandible, this reflex
causes the appropriate number of motor units in the closing
muscles to be activated, resulting in the mandible being elevated
to its original position.

• This unconscious activity maintains the posture of the jaw.
• Emotional stress or psychic tension increases muscle tone.
• An increase in the tone of the mandibular elevators will decrease
rest vertical dimension and consequently reduce interocclusal
distance.
• Thus, the psychological status of the patient is an important
consideration in all stages of complete denture construction

in which the postural rest position is used as a reference position of
the mandible.
• Mandibular position during minimal muscle activity (EMG rest)
is at a more open jaw position, about 8 - 10 mm , than the
clinically determined postural rest position.
• It is evident that postural rest position should not be regarded as
a static immutable position of the mandible.

• There is a collective tendency for rest vertical dimension to
decrease following loss of the natural dentition and for postural
rest position variability to increase in edentulous patients without
denture.
• It is believed by some that the tongue-palate relationship acts as a
sensory mechanism to help determine postural rest position.

• Among the long-term factors that should be considered in
dealing with postural rest position are age, health status, history
of bruxism , sequence and duration of tooth loss, alveolar ridge
height, and past experiences with oral prostheses.
• In addition to emotional and psychological status, respiratory and
postural changes have immediate effects on postural rest
position.

• Since postural rest position is largely maintained by a balance
between muscular tone, particularly of the elevator muscles, and
the effect of gravitational forces, any changes in these factors
will immediately influence this position of the mandible.
• For example, when the head is flexed in a relaxed patient,
interocclusal distance is decreased as the mandible moves
slightly upward and forward in relation to the maxilla.

• Likewise, with head extension, the mandible moves down and
back and interocclusal distance increases.
• For the purposes of standardization and accuracy, therefore,
postural rest position usually implies that the patient is sitting or
standing in an upright position and looking straight ahead.

CYCLIC JAW MOVEMENT

• Cyclic jaw movement involves the sequential rhythmic
depression and elevation of the mandible as occurs during
mastication.
• Although the human fetus and new born can suck and swallow,
most jaw movements are relatively random .
CYCLIC JAW MOVEMENT

• Each person has an individualized pattern of cyclic movement,
what many clinicians call the “ occlusal gait.”
• Although many factors may influence this gait, few are so
immediate and dramatic as the loss of teeth, the insertion of
dentures, or the combination of both.
• The dentulous person usually demonstrates smooth jaw motion
during mastication .

• It is shaped somewhat like a teardrop when viewed in the frontal
plane.
• On the other hand, the edentulous patient will often have a
distortion of this movement with the process becoming more
random and indiscriminate.
• During the closing part of the cycle, the dentulous subject will
decelerate the movement just before tooth contact to dampen the
effect of closure on the dentition.

• The edentulous patient seems to elevate the jaw at a constant
velocity with no deceleration near the end of closure.
• Recent evidence indicates that cyclic jaw movement is controlled
and coordinated by a central pattern generator or “ chewing
center” in the brain stem .
• A central pattern generator, once initiated, coordinates the muscle
contraction sequences that produce the rhythmic alternation of
opening and closing movements that constitutes mastication .

• This rhythmic act, however, can be modified by the shape, size,
and consistency of the bolus as well as by other variables.
• Since neurosensory input, such as from periodontal and other
intraoral receptors, can influence the central pattern generator
and the chewing cycle, it is reasonable to consider that a state of
edentulism will provide somewhat different neurosensory
information to the neurological control mechanism of
mastication.

• For example, anesthesia experiments have demonstrated that
coordinated chewing can occur after sensory deprivation.
• However, absence of sensory information appears to affect the
preciseness of occlusal contacts during jaw function.
• This factor is an important consideration in treating edentulous
patients, since the occlusal scheme to be developed on complete
dentures should attempt to account for any loss of ability to close
to a precise position .

THE 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.
THE TONGUE

• In some patients the origins of these muscles may be of great
significance.
• For example, the genioglossus (the largest of the group) arises
from the genial tubercles on the inner aspect of the mandible in
the midline.
• In those patients in whom the tubercles become extremely
prominent due to excessive resorption of the alveolar process,

• Attention must be paid to the contouring of the lingual flange of
a lower denture in order that the denture is not displaced every
time the genioglossus muscle contracts.
• There is a tendency for the tastebuds to diminish in number in
old age.
• “ Bald ” tongue, one in which the filiform papillae are atrophic,
is not an uncommon finding in elderly people.

• Atrophy of the lingual papillae may occur in patients with iron-
deficiency or vitamin B12 deficiency anemia or those with
nutritional disorders, but, in many cases, no satisfactory
explanation can be given for the presence of a smooth tongue .
• In many elderly people there is a nodular enlargement of the
superficial veins on the ventral surface of the tongue.

• The presence of such lingual varicosities (“ caviar tongue” ) is
not thought to be of any special significance and should not be
regarded as evidence of disease of the blood vessels or of the
cardiovascular system.

SALIVARY GLANDS

• Saliva has many functions.
• In addition to its protective functions, and its role in taste and
digestion, it is important in the lubrication of the oral mucosa and
lips—a most necessary factor for adequate speech articulation
and satisfactory denture wearing.
SALIVARY GLANDS

• From the prosthodontist’s point of view, the salivary glands are
of great importance both anatomically and physiologically.
• The orifice of Stensen’s duct, the duct of the parotid gland,
normally opens on a small mucosal fold that is located in the
cheek at the level of the crown of the maxillary first molar tooth.
• Occasionally, the relation of the duct orifice to a complete
denture is well demonstrated,

• However, it is rare for a maxillary denture to produce obstruction
of Stensen’s duct.

• The submandibular gland is located in the submandibular fossa
of the lingual aspect of the mandible, and a part of the gland is
wrapped around the posterior part of the “ diaphragma oris,” the
mylohyoid muscle.
• It is from this portion of the submandibular gland that Wharton’s
duct curves forward to open at the apex of a small mucosal
papilla in the anterior floor of the mouth just lateral to the
midline.

• Extension of the lingual flange of a denture in this region can
lead to obstruction of the submandibular gland and, in such
cases, patients may complain of developing swellings under the
jaws when eating .

99

• The sublingual glands are of varying size and, on occasion, may
present as large swellings that may interfere with satisfactory
lower denture wearing .
• There are usually 8 -12 separate ducts for each sublingual gland ,
and it is rare for a denture to produce any significant obstruction
of this duct system .

• The amount of saliva secreted per day varies from individual to
individual.
• The quantity will depend on many factors, such as hydration ,
eating habits, whether the patient habitually breathes through the
mouth , and so on .
• Recent studies have shown that in healthy older patients, salivary
flow does not diminish with age.

• Indeed , some older patients complain of excessive salivary flow
(sialorrhea ).
• However, because of the high incidence of older patients taking
medications such as diuretics, tranquilizers, antihistamines, and
others that have an effect on salivary flow, dry mouth
(xerostomia) Is not uncommon in the aged .

• Difficulty in denture wearing is often the first sign of Sjogren’s
disease.
• Although the condition is rare , the dentist should always
consider it to be a possibility in an elderly patient with
xerostomia .

CHANGES IN MORPHOLOGICAL FACE
HEIGHT AND TEMPOROMANDIBULAR
JOINT

• Posselt in 1952 showed that the border movements of the
mandible were reproducible and that all other movements took
place within the confines of his classic “ envelope of motion.”
• However this reproducibility has been established in healthy
young patients only.
FACE HEIGHT

• The terminal stage of skeletal growth is usually accepted as
being at 20 to 25 years of age.
• It is also recognized that growth and remodeling of the bony
skeleton continue well into adult life and that such growth
accounts for dimensional changes in the adult facial skeleton.
• It has been reported that morphological face height increases
with age in persons possessing an intact or relatively intact
dentition

• Nevertheless, a premature reduction in morphological face height
occurs with attrition or abrasion of teeth.
• This reduction is even more conspicuous in edentulous and
complete denture wearing patients .
• Maxillomandibular morphological changes take place slowly
over a period of years and depend on the balance of osteoblastic
and osteoclastic activity.

• The articular surfaces of the temporomandibular joints (TMJs)
are also involved, and at these sites, growth and remodeling are
mediated through the proliferative activity of the articular
cartilages.
• In the facial skeleton, any dimensional changes in morphological
face height or the jawbones because of the loss of teeth are
inevitably transmitted to the TMJs.

• It is not surprising, then, that these articular surfaces undergo a
slow but continuous remodeling throughout life.
• Such remodeling is probably the means whereby the congruity of
the opposing articular surfaces is maintained, even in the
presence of dimensional or functional changes in other parts of
the facial skeleton.

• The reduction of the residual ridges under complete dentures and
the accompanying reduction in vertical dimension of occlusion
tend to cause reduction in total face height and a resultant
mandibular prognathism.
• In fact, in complete denture wearers, the mean reduction in
height of the mandibular process measured in the anterior region
may be approximately four times greater than the mean reduction
occurring in the maxillary process

• Furthermore, longitudinal studies support the hypothesis that the
vertical dimension of rest position of the jaws (which is allegedly
not teeth related) does not remain stable and can change over
time.
• This clinical fact contradicts the previously popular and
convenient concept of a stable vertical dimension of rest position
throughout the patient’s lifetime

• Centric relation is defined as the most posterior position of the
mandible relative to the maxillae at the established vertical
dimension.
• It is regarded as a very useful reference or starting point for
establishing jaw relationships in any prosthodontics treatment,
particularly in complete denture fabrication
CENTRIC RELATION

• The use of centric relation has its physiological justification as
well.
• In the vast majority of patients, unconscious swallowing is
carried out with the mandible at or near the centric relation
position.
• The erupting teeth are guided into occlusion by the surrounding
musculature (the muscle matrix),

• whereas the position of the mandible is determined by its
location in space during the act of unconscious swallowing.
• The contacts of inclined planes of the teeth aid in the alignment
of the erupting dentition.
• Tooth contacts and mandibular bracing against the maxillae
occur during swallowing by complete denture patients.

• During swallowing, the mandible is close to, in centric relation,
or the position of maximum mandibular retrusion relative to the
maxillae at the established vertical dimension of occlusion.
• It is conceded, nevertheless, that most functional natural tooth
contacts occur in a mandibular position anterior to centric
relation, a position referred to as centric occlusion .

• However, in complete denture prosthodontics, the position of
planned maximum intercuspation of teeth is established to
coincide with the patient’s centric relation.
• The coincidence of centric relation and centric occlusion is
consequently referred to as centric relation occlusion (CRO).
• The centric occlusion position occupied by the mandible in the
dentate patient cannot be registered with sufficient accuracy
when the patient becomes edentulous.

• Consequently, clinical experience suggests that the recording of
centric relation is the starting point in the design of an artificial
occlusion.
• Nevertheless, one must realize that an integral part of the
definition of centric relation—at the established vertical
dimension—has potential for change.

• This change is brought about by alterations in denture-supporting
tissues and facial height, as well as by morphological changes in
the TMJs.

• It has also been reported that impaired dental efficiency resulting
from partial tooth loss and absence of or incorrect prosthodontic
treatment can influence the outcome of temporomandibular
disorders (TMDs).
• This is thought to be particularly the case when arthritic or
degenerative changes have occurred.
TEMPOROMANDIBULAR JOINT CHANGES.

• The hypothesis has been advanced that degenerative joint disease
is a process rather than a disease entity.
• The process involves joint changes that cause an imbalance in
adaptation and a degeneration that results from alterations in
functional demands on or the functional capacity of the joints.
• However, because the onset of degenerative conditions is
frequently encountered in the adult years,

and because the greater number of denture wearers are older
patients who are edentulous, the treatment of such conditions is
very much the concern of the dentist.
• Clinical experience and long term studies indicate that a
combination of adjunctive prosthodontic protocols, and
appropriate pharmacological and supportive therapy, are usually
adequate to provide these patients with comfort

• One of the difficulties in managing degenerative joint
involvement is achieving joint rest.
• Because of the necessity for mastication and for the avoidance of
parafunctional habits, voluntary or even enforced rest may be
difficult to achieve.

ESTHETIC, BEHAVIORALAND
ADAPTIVE RESPONSES

• Patients seek dental treatment for both functional and esthetic or
cosmetic reasons, and dentists have been successful in restoring
or improving many a patient’s appearance .
ESTHETIC CHANGES

Morphological Changes Associated with the Edentulous State
1. Deepening of nasolabial groove
2. Loss of labiodental angle
3. Narrowing of lips
4. Decrease in horizontal labial angle
5. Increase in columella-philtral angle
6. Prognathic appearance

• In clinical practice, we frequently encounter situations in which
factors such as a patient’s weight loss, age, and heavy tooth
attrition manifest orofacial changes suggestive of compromised,
or absent, dental support for the overlying tissues.
• Some patients fail to appreciate the fact that aspects of their
facial appearance for which they are seeking a solution are
merely magnified perceptions or are unrelated to their edentulous
predicament.

• These patients can cause the dentist considerable frustration.
• Experience suggests that early communication about a patient’s
cosmetic expectations should be established to avoid later
misunderstanding.
• Patients should be asked to provide photographs of their pre-
edentulous appearance, and relevant details from these
photographs should be carefully analyzed and discussed with the
patient.

• The process whereby an edentulous patient can accept and use
complete dentures is complex.
• It requires adaptation of learning, muscular skill, and motivation
and is related to the patient’s expectations.
BEHAVIORALAND ADAPTIVE RESPONSES

• The presence of inanimate foreign objects (dentures) in an
edentulous mouth is bound to elicit different stimuli to the
sensorimotor system, which in turn influences the cyclic
masticatory stroke pattern.
• Both exteroceptors and proprioceptors are probably affected by
the size, shape, position, pressure from, and mobility of the
prostheses.

• Learning means the acquisition of a new activity or change of an
existing one.
• Muscular skill refers to the capacity to coordinate muscular
activity to execute movement.
• The acceptance of complete dentures is accompanied by a
process of habituation, which is defined as a “gradual diminution
of responses to continued or repeated stimuli.”

• The patient who has worn a complete upper denture opposing a
few natural anterior mandibular teeth usually will find a
complete lower denture difficult to adapt to.
• Such a patient has to contend with altered size and orientation of
the tongue.
• The tongue frequently responds to the loss of posterior teeth and
alveolar bone by changing size to bring its lateral borders into
contact with the buccal mucosa.

• The insertion of a new denture introduces a new environment for
the tongue, and the intrinsic tongue musculature reorganizes the
shape of the tongue to conform to the altered space available.
• A degree of retraining tongue activity also takes place.
• Furthermore, the posterior residual ridges are exposed to new
sensations from the overlying prosthesis.

• Pressures transferred through the denture base replace tactile
stimuli from the tongue and frictional contact with food.
• In addition, control of the upper denture frequently must be
unlearned because the posterior part of the tongue is no longer
required to counter the dislodging effect on the denture produced
by the remaining mandibular dentition.
• Edentulous patients expect, and are expected, to adapt to the
dentures more or less instantaneously

• That adaptation must take place in the context of the patient’s
oral, systemic, emotional, and psychological states.
• The facility for learning and coordination appears to diminish
with age.
• Advancing age tends to be accompanied by progressive atrophy
of elements in the cerebral cortex, and a consequent loss in the
facility of coordination occurs.

• Emotional factors are known to play a significant role in the
etiology of dental problems.
• The way the patient handles other illnesses and dental situations
will aid in the prediction of future problems.
• It has been observed that the secure patient will adjust readily,
cope with discomfort, and be cooperative.

CONCLUSION

• The role of prosthodontists is to gain an understanding of the
changes in the form and function of the mouth and jaws, brought
about by the total loss of teeth and the possible social and
behavioral consequences of tooth loss.

• They should be able to critically evaluate the inﬂuence of
complete dentures on the remaining soft tissues and the
underlying bony structures so that it helps in understanding the
scope and limitations of complete dentures together with the
biocompatibility and physical properties of the materials used in
their construction.

REFERENCES
•SHELDON WRINKLER,ESSENTIALS OF COMPLETE DENTURE PROSTHODONTICS, 2ND
EDITION 1988
•ZARB, G. A., BOLENDER, C. L., CARLSSON, G. E., & BOUCHER, C. O. BOUCHER'S
PROSTHODONTIC TREATMENT FOR EDENTULOUS PATIENTS, 9TH ED, 1997
•ZARB, G. A., BOLENDER, C. L., CARLSSON, G. E., & BOUCHER, C. O. BOUCHER'S
PROSTHODONTIC TREATMENT FOR EDENTULOUS PATIENTS. 12TH ED..

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