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Trang 2 Swallowing, suckling, mastication are biological functions of the masticatory systemSwallowing is innate unlearned behavior first occurring in the fetusSuckling can be observed i
§ FUNCTIONAL ACTIVITIES: SWALLOWING, SUCKLING, MASTICATION People’s Teacher Prof Hoàng Tử Hùng, DDS, PhD E: tuhung.hoang@gmail.com W: hoangtuhung.com INTRODUCTION Swallowing, suckling, mastication are biological functions of the masticatory system All functional movements are highly coordinated complex neuromuscular events Sensory input from structures of the masticatory system (teeth, periodontal ligament, lips, cheek, TMJ, jaw muscles …) Swallowing is innate unlearned behavior first occurring in the fetus Suckling can be observed in human fetus at 20 weeks in utero, although full swallowing and suckling begin only after approximately at 32 – 36 weeks Mastication is learned process that matures from suckling with growth and development of an individual hoangtuhung.com SWALLOWING (DEGLUTITION) hoangtuhung.com Swallowing is an innate unlearned behavior first occurring in the fetus and is a complex reflex that is functionally both supportive and protective Effector sites in the mouth, pharynx, and esophagus elicit the supportive reflex when exposed to air and food intake Swallowing protects the larynx from invasion by saliva, esophageal regurgitation, and nasopharyngeal and tracheal secretions Swallowing occurs ≈ 600 times a day: 150 times during eating, 50 during sleep, 400 between meals hoangtuhung.com Stabilization of mandible is an important part of swallowing In the infant, the mandible is braced by placing the tongue forward and between the gum pads or anterior teeth (tongue thrusting): [infantile or visceral swallow] In normal adult, teeth are used for stabilization of the mandible for swallowing [adult or somatic swallow] The characteristic tooth-apart infantile swallowing is quite normal in adults when swallow liquids or soft boluses Retention of the infantile swallow in adult can result in labial displacement (open-bite) of the anterior teeth by powerful tongue muscle hoangtuhung.com PHASES OF SWALLOWING Although swallowing is one continuous act, it may be divided into three phases The oral phase: The oral phase is under voluntary control Continuous with mastication, the food mass is moulded into a bolus by integrated action of the cheek and tongue muscles and particularly by the action of the tongue against the hard palate Retropulsion of the bolus into the pharynx: the creation of a pressure gradient between mouth and pharynx: 40 – 50 mmHg intra-oral pressure vs atmospheric pressure intra-pharynx hoangtuhung.com PHASES OF SWALLOWING (cont’d) Pharynx phase The pharynx phase occurs reflexly and simultaneously over a 0.1 sec period, in order to maintain the food-way and protect the airway The lips are sealed, pharynx opens, the hyoid bone is raised by mylohyoid muscles, the soft palate is elevated and the palatopharyngeal muscles constrict to close the passage of the nasal cavity and mandible is stabilized in posterior position (MIP or CR) The epiglottis blocks the laryngeal airway and interrupts the respiration while the bolus passes In this time, there is an equalizing pressure of the middle ear because of activity of pharyngeal muscle opens the pharyngeal orifices of the eustachian tube, which are normally closed hoangtuhung.com PHASES OF SWALLOWING (cont’d) Oesopharyngeal phase This phase begins with the cricopharyngeal muscle relaxes The bolus passes through the length of the esophagus into stomach Peristaltic waves carry the bolus down the oesophagus (take – 7seconds) As the bolus approaches the cardiac sphincter, the sphincter relaxes and lets it enter stomach hoangtuhung.com SUCKLING Suckling is the process by means of which the infant obtains milk from the mother’s breast It is not the same as sucking, even though some negative pressure is generated within the infant’s mouth G J Ebrahim, 1978 hoangtuhung.com Newborns and infants feed by suckling which is a complex process involving the development of negative pressure or suction in the oral cavity combined with jaw movements to express the milk from the nipple During suckling, the nipple is suckled deep into the posterior part of the mouth to the junction of the hard and soft palate Suckling can be divided into two phases: Lowering of the jaw with a forward and downward displacement of the body of the tongue*, and Elevation of the jaw with an upward and backward displacement of the tongue *Infant sucking rate ranges 40 – 90 suck/minute The negative pressure ranges 20 – 200 mmHg hoangtuhung.com Physiology of suckling A The lips of the baby close around the nipple at the junction of the nipple and the areola C The tongue pulls back bringing the nipple against the hard palate and the areola into the mouth B The tongue protrudes to grasp the nipple D Negative pressure is created by the action of the cheeks, the gums compress the areola and, with an active 'let-down' reflex, milk flows from the breast to the area of negative pressure in the baby’s mouth hoangtuhung.com (R M Applebaum, 1970) In some circumstances, milk is expressed directly into the pharynx coincident with the first phase → The posterior part of the tongue is engaged in swallowing while the remainder part is involved in suckling The fetus is capable of sucking and swallowing aminiotic fluid in utero, thus, the motor program for these activities is developed long before birth hoangtuhung.com MASTICATION hoangtuhung.com Mastication: - a learned process that matures from suckling - a semi-automatic, cyclical activity in which a pattern generator in the brainstem alternately activate the jaw-opening and the jaw-closing muscles - a complex 3-D movement under central nervous system control and modulation of peripheral sensory inputs STAGES OF MASTICATION Mastication is often described in three stage: • Incision with the anterior teeth • Crushing, and with premolars and molars • Milling or shearing - No clear-cut between stage and - Chewing can be sufficient on a shortened dental arch with opposing pairs of occluding premolars hoangtuhung.com THE CHEWING CYCLE Chewing is the first step in the digestion of food/ a complex process that involves number of muscles/ integrated with swallowing Chewing pattern is relatively consistent for individual Chewing cycles occur well within the envelope of mandibular motion and as view from the frontal plane is “tear drop” shaped It can be devide into: - Opening phase - Closing phase: - Crushing,and - Grinding Duration of each chewing cycle is about 700 ms hoangtuhung.com THE CHEWING CYCLE (cont’d) During a single chewing stroke, the mandible traces in frontal plane: 1- Opening phase from MIP to the non-working side with a small gliding on non-working contacts, mandible drops downward ≈ 20 mm Working side Nonworking side Opening phase: Fleeting contacts occur on inner aspect incline of supporting cusp (nonworking side) for ≈ 1.5 mm 2- Closing phase: mandible moves laterally ≈ mm from midline and then upward hoangtuhung.com THE CHEWING CYCLE (cont’d) 3- The crushing phase (of the closure stroke) begins when the food is trapped between the teeth, the buccal cusps of lower teeth are almost directly under the buccal cusps of upper teeth on the working side, distance between occlusal surfaces ≈ mm - As the mandible continues to close, the grinding phase (of the closure stroke) begins, the food is crushed down into small particles Opening phase: Fleeting contacts occur on inner aspect incline of supporting cusp (nonworking side) for ≈ 1.5 mm Closure in MIP: Closing force: 70 – 400 kg applied for 40 – 200 ms hoangtuhung.com Closing phase: fleeting contacts occur on inner aspect incline of guiding cusp (working side) for – 1.5 mm Masticatory Habits The mean percentage of gliding contacts is found in - 57% during opening phase and - 60% during closing phase Closure occurs at MI for a brief period [40 to 200 ms] Multi directional, alternating, bilateral mastication is ideal for stimulation of entire supporting tissues, for stability of occlusion and for cleansing of teeth Although mastication may be accomplished satisfactorily with unilateral, and/or even no lateral movement, these are not good habits for masticatory function The pattern of chewing cycle and the sequence and distribution of activities of the jaw muscles during mastication normally depend #on the type of food being chewed and #on the individual’s habit In human, chewing cycles take place in a closed cavity, the lips are sealed hoangtuhung.com