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  1. 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 1
  2. 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. 2
  3. 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. 3
  4. 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 4
  5. 5. oesophagus normally exhibits 2 types of peristaltic movements: primary peristaltic movements and* secondary peristaltic movements. 5
  6. 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. 6
  7. 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 7
  8. 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. 8
  9. 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. 9
  10. 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. 10
  11. 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 11
  12. 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, 2. Lavelle Christopher L.B.: Applied oral physiology. 2nd addition, 1988 Wright publications, London 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. 12
  13. 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. 13