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1. INTRODUCTION
The process of chewing and deglutition taken together are often
considered to represent the totality of feeding process.
The details of the process of deglutition are still controversial. Parts of
this complicated act are so rapid that it is impossible to follow with the eye all
the movements. When observing radiologically the deglutition of radiopaque
material, and even cinematography has not cleared a number of points.
When the food is in the mouth, or part of it, has been masticated the
chain of reflexes involved in deglutition is begun by voluntary act. Although
mastication and deglutition are really one continuous action it has been
customary to regard mastication as a separate process and to divide deglutition
into 3 stages. The decision to swallow depends on several factors:
1. Degree of fineness of food.
2. Intensity of taste extracted.
3. Degree of lubrication of bolus.
PHYSIOLOGY OF DEGLUTITION
It is a reflex response triggered by Afferent impulses by
Glossopharyngeal nerve. Which is sensory to pharynx and Efferent impulses by
cranial accessory nerve. Which joins vagus to give motor supply to the
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2. constrictors. These impulses are integrated in Nucleus of Tractus
Solitarius(taste sensation) and Nucleus ambiguous.
Deglutition is initiated by a voluntary action of collecting the oral
contents on the tongue and propelling them backwards into the pharynx. This
starts a wave of involuntary contraction in the pharyngeal muscles that pushes
the material in the oesophagus. Inhibition of respiration and closure of glottis
are part of the reflex response. Deglutition is difficult if not impossible when
the mouth is open.
A normal adult swallows frequently by eating but deglutition continues
between meals. The total number of swallows /day are:
 600-200 While eating and drinking.
 350 While awake without food.
 50 While sleeping.
Deglutition is a complicated mechanism because the pharynx most of
the time sub serves several other functions besides deglutition and is converted
only for a seconds at a time for the act of propulsion of food. It is important
that respiration especially should not be compromised because of deglutition.
In General 3 stages of deglutition are:
1. Oral stage - voluntary phase, which initiates the swallowing process.
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3. 2. Pharyngeal stage – Involuntary phase, constitutes the passage of food
through the pharynx into the oesophagus.
3. Oesophageal Stage –Involuntary phase, which promotes the passage of
food from pharynx into the stomach.
1. Oral Stage:
 Forces for propelling the bolus.
 Tongue is lifted by mylohyoid muscle.
SAFEGUARDING FACTORS ie to prevent the food from going to wrong
place – Mouth is closed ( contraction of orbicularis oris).
- Elevators of mandible are raised.
- Buccinator contracts to prevent food from going to vestibule. From here
on deglutition becomes almost entirely automatic and ordinarily
cannot be stopped.
2. Pharyngeal stage: The posterior border of the soft palate is lifted, or pulled
upwards to contact the passavant’s ridge present over the superior
constrictor of pharynx to prevent food from going to the nasopharynx.
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4. - The palatopharyngeal folds on either side of the pharynx are pulled
medially to approximate each other. In this way these folds form a
sagittal slit.
Through this saggital slit food must pass into the posterior pharynx. This
slit performs a selective function, of allowing the food that has been masticated
sufficiently to pass with ease while impeding the passage of large objects.
Since this stage of swallowing lasts for less than a second any large object is
usually impeded too much to pass through the pharynx into the oesophagus.
The vocal cords of the larynx are closely approximated. Larynx is lifted
and tongue pulled backwards. This action of larynx combined which the
presence of ligaments which prevents the upward movement of the epiglottis
causes the epiglottis to swing backward over the opening of the larynx. Both
effects prevent the passage of food from going to trachea. Most essential is the
close approximation of vocal cords. Destruction of the vocal cords of the
muscles that approximate them can cause strangulation.
Further constriction of Inferior constrictor (has two parts
Thyropharyngeous and Cricopharyngeous) ie. Thyropharyngeous propels the
food into the oeosphagus with relaxation of cricopharyngeous.
3. Oesophageal phase – Involuntary phase. The oesophagus functions
primarily to conduct food from the pharynx to the stomach. The
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5. oesophagus normally exhibits 2 types of peristaltic movements: primary
peristaltic movements and* secondary peristaltic movements.
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6. MECHANISM OF DEGLUTITION
Primary peristalsis is simply the continuation of the peristaltic wave that
beings in the pharynx and spreads into the oesophagus during the 2nd
stage of
deglutition. This wave passes all the way from pharynx to the stomach in about
8-10secs. Food swallowed by a person who is in upright position is usually
transmitted to the lower end of oesophagus even more rapidly than the
peristaltic wave itself in about 5-8seconds. Because of the additional effect of
gravity pulling the food downwards. If the primary peristaltic wave fails to
move all the food that has entered the oesophagus into the stomach then the
secondary peristalsis wave starts. These secondary waves are initiated partly by
Intrinsic neural circuits in the oesophageal myenteric nervous system and partly
by reflexes that are transmitted through Vagal afferent fibers.
The musculature of the pharynx and the upper third of the oesopahgus is
striated muscle. Therefore the peristaltic waves in these regions are controlled
only by skeletal nerve impulse in the Glossopharyngeal and Vagus nerves. In
the lower two-thirds of the oesophagus, the musculature is smooth but this
portion of oesophagus is also strongly controlled by the vagus nerve acting
through their connections with the myenteric nervous system.
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7. THEORIES AND HYPOTHESIS
1. In 1880, the theory was proposed that fluids and semi fluids are
propelled directly into the stomach by the contraction of the tongue and
the mylohyoid muscles effecting a syringe like action to pressure the
liquid downwards. The muscles of the pharynx proper came into play
only for propulsion of solid food substances.
2. Another concept of the mechanism of deglutition was advanced as the
results of the use of fluoroscopy. A radioluscent area in the
laryngopharyngeal cavity was observed just prior to the propulsion of
the bolus in to the pharynx. The radiolucent area disappeared
immediately to provide space for the bolus. This concept gave rise to the
theory of an instant negative pressure within the laryngopharyngeal
cavity that pulled the bolus in by suction.
3. The concept that the process of deglutition is performed successively by
contraction of the oral, pharyngeal, and oesophageal muscles has been
confirmed by the roentogenographic studies by Bosma. Who announced
a new theory based on his roentgenographic studies which he called
“motion in anticipation of the approaching bolus”. He was impressed by
a particular position or posture assumed by the upper part of the pharynx
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8. and the consecutive elveation of the larynx and laryngopharyngeal area
an instant prior to penetration by the bolus.
All theorists agree that the pharynx is endowed with extreme rapidity
and therefore all the structures involved in deglutition must be flexible and
elastic. Correspondingly, these structures, while favoring the mobility of the
pharynx, make it more vulnerable to impairment by various pathologic
conditions such as peritonsilar, parapharyngeal and postparapharyngeal
abscesses as well as by abscesses in the Thyroglossal duct of the tongue.
CLINICAL SIGNIFICANCE:
1. Used in making Lower impressions: The complicated neuromuscular
events of the swallowing involve several muscles whose actions should
be especially considered when making impressions for mandibular
dentures. Anatomically and functionally the mylohyoid muscles forms
the floor of the mouth. The Anterior fibers of the muscle are thin and
weak and have a low attachment below the residual ridge, on the inner
surface of the mandible. However the posterior fibers are thick and
strong and may be attached as high as crest of the ridge. These fibers
from a sling – tongue- hyoid –larynx column –act as curtain.
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9. The retromylohyoid space: the posterior border of mylohyoid runs
inward, downward and forward. Behind this border is the retromylohyoid
space.
Superior Constrictor Pharynx
– Glossopharyngeal.
– Palatopharyngeal.
– Buccopharyngeal.
During deglutition, the hyoglossus muscle affects the retromylohyoid
space. The Hyoglossus muscle with styloglossus muscle raises and ‘balls’ the
tongue. At this stage the hyoglossus muscle compresses the retromylohyoid
space.
The lower denture is supported only in part by oral mucosa which is
firmly attached to base. Parts of lower denture rest on oral mucosa. The
posterior part of the lingual flange covers the posterior part of the mylohyiod
muscle and extends into retromolar space. The posterior part of the buccal
flange is determined by Buccal shelf.
The denture base covering the Retromolar pad overlies Muscle,
Glandular tissue and a Tendinous muscle attachment. The Buccopharyngeal
origin of the superior constrictor muscle attaches to Pterygomandibular Raphe.
The Buccopharyngeal muscle Fibers are thin and few. Deglutition disturbs the
resting surface anatomy of Retromylohyoid curtain.
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10. The denture borders most affected by deglutition will confirm to this
function and a correct tongue position is encouraged. The result is a functional
impression made without excessive pressure.
FINAL IMPRESSION
With the upper rim in place, a zinc oxide eugenol impression paste is
mixed and placed on tissue surface of lower tray. Tray is positioned in the
mouth and the patient is instructed to deglutate. The upper and lower rim will
come together in centric relation. The dentist should not keep his fingers in the
mouth. So that this relation is obtained in the Non-strained, physiologic
functional position.
ESTABLISHING NETURAL ZONE:
A soft material that can be molded is used to establish neutral zone.
Compound softened at 135°F is adapted to top of the lower tray and shaped
similar to a wax occlusion rim. The tray and modelling compound are placed in
the mouth. The action of muscles and tongue molds the compound. The
compound is allowed to harden.
CENTRIC AND VERTICAL RELATIONS
The compound is covered with a thin film of petroleum jelly and placed
in the mouth.
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11. The compound is softened in a 135°F water bath. The patient is
conditioned by sipping water. During swallowing the mandible is guided to
centric relation and correct vertical relation of occlusion.
The modelling compound on upper acrylic resin base is chilled and the
Base is removed from the mouth.
SUMMARY
To summarize deglutition can be divided into three stages:
1. An oral stage.
2. A pharyngeal stage.
3. An oesophageal stage.
The process of deglutition in prosthodontics can be utilized in the
following ways:
1. Making of lower primary impressions.
2. Making of upper and lower sec. impressions.
3. Establishing of neutral zone.
4. Recording vertical and centric relation.
CONCLUSION
The inter–relationship and intimate interdependence between
mastication, deglutition, respiration and phonation are from Neurophysiologic
point of view overwhelmingly complex and extremely fascinating. The smooth
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12. performance of these vertical function requires a complex integration of the
cranial somatic innervation in coordination with the A.N.S. Deglutition allows
a functional impression to be made without excessive pressure. The borders
will conform to the physiological limits and hence will allow for perfect
harmony between the dentures and the oral tissues.
BIBLOGRAPHY
1. Jenkins G.N. : The text book of physiology and biochemistry of
mouth.4th
edition, 1977, pg.no.532-541.
2. Lavelle Christopher L.B.: Applied oral physiology. 2nd
addition, 1988
Wright publications, London pg.no. 31-41.
3. Guyton and Hall: Textbook of medical physiology. 9th
edition, 1996,
Prism books pvt. Ltd., India pg .no 804 –806.
4. Landa J.S.: Relation of deglutition to the masticatory mechanism. J
Prosthet. Dent.1961; 11 : 820-826.
5. Sharry J.J : Complete denture prosthodontics 1968.
6. Schiesser F.J. : Polished surfaces in complete dentures. J. Prosthet.
Dent.1964, 14:854-865.
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13. 7. Marmer D. Herbertson J.E.: Use of swallowing in making complete
denture lower impressions. J. Prosthet. Dent. 1968; 19; 208-218.
8. Thexton A.J. : Mastication and swallowing : An overview. Br. Dent. J.
1992; 173 : 197-206.
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14. DEGLUTITION
 INTRODUCTION
 PHYSIOLOGY DEGLUTITION.
 MECHNISM OF DEGLUTITION
 THEORIES and HYPOTHESIS
 CLINICAL SIGNIFICNCE IN PROSTHODONTICS
 SUMMARY and CONCLUSION
 BIBLIOGRAPHY
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