Deglutition and Chewing cycle Dr. Pratistha, PG Resident CODS, BPKIHS, Nepal

1. DEGLUTITION AND
CHEWING CYCLE
Presented By:
Dr. Pratistha Ghimire
PG Resident, 1st Year
Dpt. Of Prosthodontics And Crown-Bridge
CODS, BPKIHS, Dharan, Nepal1

2. Contents
Chewing (Mastication)
 Introduction
 Significance
 Chewing cycle
 Control of Mastication
2

3. Introduction
 Mastication: Process of chewing food to prepare for
swallowing and digestion
 It is a complex process involving activities of masticatory
muscles along with tongue, cheeks, lips, palate, etc.
 These activities result in rhythmic mandibular movements,
food manipulation and crushing of food between the teeth
3

4. Significance Of Chewing
 Large pieces are broken down into small pieces, resulting in
a increase in surface area, where digestive enzymes work
 Softening of food and transformation into a size which can
easily be swallowed
 Grinding the food to a very fine particulate consistency
which prevents excoriation of the gastrointestinal tract
 Mixes food with saliva, initiating digestion by the activity of
salivary amylase
4

5. It involves:
 Action of teeth: incising, tearing and grinding
 Co-ordinated movements of tongue (positioning the food
between occlusal surfaces of teeth) and muscles of
mastication
 Saliva (softens & lubricates the food and forms bolus
and its enzymatic activities help in digestion)
 Structural components of Temporomandibular Joint
(TMJ)
5

6. Muscles of mastication
 Masseter
 Temporalis
 Lateral pterygoid
 Medial pterygoid
6

7. Actions of muscles during masticatory
movements
 Closing/ Elevator jaw muscles
Medial pterygoid
Masseter
Temporalis
 Opening/ depressor jaw muscles
Lateral pterygoid
Mylohyoid
Digastric
Geniohyoid
7

8. Components of TMJ
 Temporomandibular joint is formed by articulation
between condylar head of mandible and anterior part of
glenoid fossa of squamous part of temporal bone
 All the mandibular movements occurs along this joint
 Consists of:-
a. Articular surface
b. Ligaments
c. Articular disc
8

9. MOVEMENT ACTION
Protrusion of mandible Articular disc glides forward over the upper
articular surface, the head of mandible moving
with it.
Retraction of mandible Articular disc glides backward over upper
articular surface with head of mandible with it.
Slight opening of mouth or
Depression of mandible
The head of the mandible moves on the surface
of disc like a hinge.
Wide opening of mouth or
Elevation of mandible
Hinge like movement is followed by gliding of
disc and mandible movements are reversed in
closing the mouth or elevator of mandible.
9

10. Several features provide protection for
the adjacent gingiva during chewing
10

11.  Marginal ridges- deflect most of the food, potentially
driven between adjacent teeth by their opponents, onto
the occlusal surfaces
 Contact points- abut firmly to prevent food being wedged
between the teeth and above the interdental papillae
 The buccal cusps of the mandibular teeth bite between
the buccal and palatal cusps of the maxillary teeth
 Food trapped between them is forced up over the palatal
sides of the maxillary teeth and down over the buccal
sides of the mandibular teeth

12. Forces of mastication
 The maximal biting force that can be applied to the
teeth varies from individual to individual
 Males > females
 Maximal biting load in females ranges from 79 to 99 lb
(35.8-44.9 kg)
 In males, 118 to 142 lb (53.6-64.4 kg)
12

13. 13
• All the jaw muscles working together can close the
teeth with a force as great as 55 pounds on the incisors
and 200 pounds on the molars
• The bite force exerted during routine mastication of
food is of the order of 5-15kg (11-33 lb) (70-150 N)

14. Mastication with complete denture
 60 N - 80 N in denture wearers
 Patient comfort and mastication may be impaired due to
excess flow of the saliva for few days after placement of
new complete denture
14
1/4th of forces in subjects
with natural dentition

15.  Patient should begin chewing relatively soft food (requires
less mastication) and also ready for swallowing with a
simple push of tongue against the palate
 When biting with the denture, patients should be
instructed to place the food between their teeth towards
the corner of mouth - then the food should be pushed
inward and upwards as this will tend to seat the denture
 Learning with new denture requires at least 6-8 weeks
as memory patterns are established for muscle of
mastication
15
Mastication with complete denture

16. Chewing cycle
 Is highly complex process
 The jaw moves in a series of cyclic movements
 There occurs rhythmic and well-controlled separation and
closure of the maxillary and mandibular teeth
16

17.  The mean of the vertical dimension of the chewing cycle
are 16-20 mm and 3-5 mm for lateral movements
 The duration varies between 0.6s and 1s
 The average length of time for tooth contact is 194 ms
 Most of the chewing process is caused by a chewing
reflex
17
Chewing cycle

18. Chewing Reflex
18
Automatically raises the
jaw to close the mouth
Presence of bolus of
food in the mouth
reflex inhibition of the
muscles of mastication
Allows lower jaw
to drop
Initiates stretch reflex
of the jaw muscles
Leads to
Rebound
contraction

19. 19
Mouth is closed
Buccal receptors get
stimulated by food
Reflex inhibition of muscles of
mastication and reflex contraction
of digastric and lateral pterygoid
muscle
Opening of mouth
Allows lower jaw
to drop
Leads to Rebound
contraction

20. Chewing strokes
 Each opening and closing movement of the mandible
represents a chewing stroke
 The complete chewing stroke has a movement
pattern described as tear-shaped
20

21. Chewing strokes…
 Chewing cycle consist of 3 basic phases:
1. Closing stroke
2. Power stroke
3. Opening stroke
21

22. 1. Closing stroke
 Brings the teeth into initial contact with the food
 The work done in this phase is against the gravity
 The closing movement has been further subdivided into the
crushing phase and the grinding phase
22

23. 2. Power stroke
 The food undergoes reduction
 The movement of mandible in this phase is slower than in
the closing stroke because of the resistance caused by the
food
 Greater masseter and temporalis muscle activity
23

24. 3. Opening stroke
 When the mandible is lowered, with an initial
slower stage followed by a faster stage
24

25. 25

26. 26

27. 27

28. 28

29. 29

30. Food texture modifies-
 Masticatory forces (Yurkstas and curby, 1953; gibbs et al.,
1981; horio and kawamura, 1989; bishop et al., 1990),
 Mandibular jaw movements (Thexton et al., 1980;
proèschel and hofmann, 1988),
 The duration of mastication cycle (Pierson and le magnen,
1970; luschei and goodwin, 1974)
 The number of cycles preceding the swallow (Hiiemae et
al., 1996)
30

31. Oral physiology and mastication
Mastication is a sensory-motor activity aimed at the preparation of food for swallowing. It is a
complex process involving activities of the facial, the elevator and suprahyoidal muscles, and the
tongue. These activities result in patterns of rhythmic mandibular movements, food manipulation
and the crushing of food between the teeth. Saliva facilitates mastication, moistens the food
particles, makes a bolus, and assists swallowing. The movement of the jaw, and thus the
neuromuscular control of chewing, plays an important role in the comminution of the food.
Characteristics of the food, e.g. water and fat percentage and hardness, are known to influence the
masticatory process. Food hardness is sensed during mastication and affects masticatory force, jaw
muscle activity, and mandibular jaw movements. When we chew for instance a crispy food, the jaw
decelerates and accelerates as a result of resistance and breakage of food particles. The
characteristic breakage behavior of food is essential for the sensory sensation. This study presents a
short review of the influence of oral physiology characteristics and food characteristics on the
masticatory process.
31
Department of Oral–Maxillofacial Surgery, Prosthodontics and Special Dental Care, Oral
Physiology Group, University Medical Center, Utrecht, The Netherlands
Food hardness is sensed during mastication and affects
masticatory force, jaw muscle activity and mandibular jaw
movements. When we chew for instance a crispy food, the
jaw decelerates and accelerates as a result of resistance
and breakage of food particles. The characteristic breakage
behavior of food is essential for the sensory sensation
Van der Bilt A, Engelen L, Pereira LJ, Van der Glas HW, Abbink JH. Oral physiology and
mastication. Physiology & behavior. 2006 Aug 30;89(1):22-7.

32. The influence of product and oral
characteristics on swallowing
The urge to swallow food could be triggered by a threshold level in both food particle size and
lubrication of the food bolus. Thus, both oral physiology and product characteristics may
influence the swallowing threshold.
Hard and dry products require more chewing cycles and longer time in mouth until swallowing
for sufficient breakdown to take place and for enough saliva to be added to form a coherent
bolus safe for swallowing.
In conclusion, product characteristics and to a lesser extent oral physiology significantly
affect swallowing threshold.
32
Department of Oral–Maxillofacial Surgery, Prosthodontics and Special Dental Care, Oral
Physiology Group, University Medical Center, Utrecht, The Netherlands
Hard and dry products require more chewing cycles
and longer time in mouth until swallowing for
sufficient breakdown to take place and for enough
saliva to be added to form a coherent bolus safe for
swallowing
Engelen L, Fontijn-Tekamp A, van der Bilt A. The influence of product and oral
characteristics on swallowing. Archives of Oral Biology. 2005 Aug 1;50(8):739-46.

33. Occlusal relationship of the tooth during
chewing
33

34. Occlusal relationship of the tooth
during chewing…
 From an open position the mandible is moved upwards
and outwards, bringing the buccal cusps of the maxillary
and mandibular teeth on the working ( left) side in
contact. Buccal phase (fig a)
 • In power stroke the mandibular teeth then slide
upwards and medially against the maxillary teeth to
momentarily attain intercuspal position. Intercuspal
phase (Fig b)
 • The mandibular teeth continue downwards and inwards
against the maxillary teeth. Lingual phase (Fig c)

35. Masticatory Sequence
 Consists of numerous chewing cycles
 Extend from ingestion to swallowing
 Divided into 3 consecutive periods:
35

36. 36
Lips • Guide And Control Intake
• Seals off the oral cavity
Role of the soft tissues in mastication
• Maneuvering the food within the oral cavity for
sufficient chewing
• Initiates the breaking up process by pressing it
against the hard palate
• Pushes the food onto occlusal surfaces of teeth,
where it can be crushed during chewing stroke
Tongue

37. 37
• During opening phase, repositions the partially
crushed food onto teeth for further breakdown
• Divides food into portions that require more chewing
and portions that are ready to be swallowed
• After eating, it sweeps the teeth to remove any food
residue that has been trapped in oral cavity
Tongue
Role of the soft tissues in mastication….

38. Role of the soft tissues in mastication….
38
Buccinator m.
• Repositioning the food from the buccal side
• The food is thus continuously replaced on the
occlusal surfaces of the teeth until the
particles are small enough to be swallowed
efficiently

39. Control of Mastication
Cerebral Hemispheres Theory:
Mastication is a conscious act, a patterned set of instructions
originating in the higher centers of the CNS
(particular the motor cortex) and descending to directly drive
the motor neurons within the brainstem (trigeminal, facial,
hypoglossal motor neurons)
39

40. Reflex Chain Theory: C.S. Sherrington in 1917
Mastication involved a series of interacting chains of
reflexes, accordingly sensory input from the region of the
mouth (e.g. pressure on the teeth) triggered the motor
neurons in the brainstem to elicit a jaw opening movement
In turn, this movement produced another sensory input
(E.g. from stretch receptors in the jaw muscles), which
resulted in a jaw closing reflex, such a theory could explain
the rhythmic jaw movements seen in decerebrate animals
40

41. Biting on a piece of food initiated the jaw opening
reflex, which resulted in opening of the stretched
closing muscles and initiated jaw closing response
The alteration of these processes then maintained the
rhythmic pattern, and produced the movements of
mastication
41

42. Rhythm (pattern) generation theory
 Most accepted theory
 Is based upon the proposition that there are central
pattern generators (CPGs) within the brainstem, which,
on being stimulated from either higher centers or
sensory input in the region of the mouth, are driven on
rhythmic activity
42

43. 43

44. Deglutition (Swallowing)
 Introduction
 Phases of deglutition
 Neural control
 Role of muscles in deglutition
 Comparison between infantile and adult swallow
 Applied aspects
44

45.  Swallowing is a series of coordinated muscular
contractions that move a bolus of food from the oral cavity
through the esophagus to the stomach
45
Introduction
 Over a period of 24 hours, swallowing occurs as many as 1000
times
 Swallowing frequency:
 Highest during eating
 Least during sleep
 Occurs at a rate of about once per minute at other times
The total time during which the teeth are
subjected to functional forces of mastication and
deglutition during an entire day= 17.5 minutes

46. 46
 Involves coordinated activity of muscles of oral cavity,
pharynx, larynx and esophagus
Swallowing is a complicated mechanism, principally
because the pharynx subserves respiration and
swallowing

47. 47
Deglutition – phases
1. ORAL (Voluntary)
2. PHARYNGEAL
(Involuntary)
3. ESOPHAGEAL
(Involuntary)
47

48. 48
I. Oral Phase
 This phase is divided into:
A. Oral preparatory phase
B. Oral phase proper
48

49. 49
A. Oral Preparatory Phase
 Involves breaking down of food
in oral cavity
BOLUS FORMATION
 During this phase, food is
chewed and mixed with saliva
making it into bolus which can
easily be swallowed
49

50.  Extrinsic muscles changes its position within oral cavity
there by helping in chewing (Elevates the tongue)
 Tongue plays a vital role in bolus formation by action of
its intrinsic muscles which alters its shape (forms a
central trough)
 Lips close and help in creating an effective seal
preventing the bolus from dribbling out of oral cavity
 Buccinator muscle helps in pushing the bolus out of
vestibule into oral cavity
50

51. B. Oral Phase Proper
 During this phase, bolus is passed into the pharynx by
upward and backward movement of tongue against palate
 This stimulates the touch receptors that initiate
swallowing reflex
 Transmit of bolus from mouth to oropharynx takes place
in a short time (0.5 sec)
51

52. 52

53. 53
 The bolus passes through the pharynx into esophagus
 This stimulates epithelial swallowing receptor areas all
around the opening of the pharynx, especially on the
tonsillar pillars
 Impulses from these areas pass to the brain stem to
initiate a series of automatic pharyngeal muscle
contractions
II. Pharyngeal Phase

54. 54
 Trigger points are present on the mucosa of the posterior
pharyngeal wall
 Stimulation of trigger points present in the oropharynx
starts off the pharyngeal reflexive stage of swallowing
 The initiation of swallowing involves contact of the food
with the faucial arches or with the mucosa overlying the
posterior pharynx in the region, innervated by
glossopharyngeal nerve
Functions of trigger points in oro - pharynx

55. 55

56. Protective reflex during pharyngeal phase
56

57. Protective reflex during pharyngeal phase
 Elevation of soft palate
 Adduction of vocal cords
 Temporary apnea
 Retroversion of epiglottis
 Elevation of larynx against epiglottis
 Entire process occurs: 0.6-1 sec
57
Doty RW. Neural organization of deglutition.Handbook of Physiology. The Alimentary Canal.1968Am Physiol SocWashington,
DC, sect. VI, vol. IV, p. 1861–1902.

58.  Elevation of soft palate
1) CN X stimulates and contracts uvula---elevation of soft
palate -- prevents the entry of bolus into nasopharynx
(prevents nasal regurgitation)
2) CN X also stimulates levator veli palatine m. that elevates
the soft palate and hence prevent entry of bolus into
nasopharynx
3) CN V stimulates tensor veli palatine m.---that tenses the
soft palate----accentuates the axn of levator veli palatine m.-
---elevation of soft palate
58

59. Vocal cords of larynx are strongly
approximated and larynx is pulled
upward and anteriorly by neck
muscles
These actions, combined with the
presence of ligaments that
prevent upward movement of the
epiglottis cause the epiglottis to
swing backward over the
opening of the larynx
Prevents passage of food into
trachea 59
 Adduction of vocal cords

60. 60
 Temporary apnea
• Interruption of respiration occurs for only a fraction of a
usual respiratory cycle
• The swallowing center specifically inhibits the
respiratory center of the medulla during this time
• Halts the respiration at any point in its cycle to allow
swallowing to proceed
• Also known as Deglutition apnea

61. 61
 The epiglottis move from vertical – horizontal position
 The upper third of epiglottis moves below the
horizontal to cover the narrowed laryngeal inlet
 This in turn, prevents the bolus from going into the
larynx
 Retroversion of epiglottis

62. 62
 Upward movement of the larynx also elevates and
enlarges the opening to the esophagus
 Supra hyoid muscles contract and pull up hyoid
bone---Moves larynx upwards and anteriorly
 At the same time, the upper 3-4 cm of the
esophageal muscular wall i.e. upper esophageal
sphincter (Crico-pharyngeus) relaxes
 Elevation of larynx against epiglottis

63. To summarize the mechanics of the pharyngeal stage of
swallowing:
 The trachea/ larynx is closed
 The esophagus is opened
 A fast peristaltic wave initiated by the nervous system of
the pharynx forces the bolus of food into the upper
esophagus
 The entire process occurring in less than 2 seconds
63

64. 64

65. Nervous Initiation of Pharyngeal Stage
of Swallowing
 Food comes in contact with certain trigger areas in the
mucosa of posterior pharyngeal wall (Greatest sensitivity in
tonsillar pillars)
 Impulses are transmitted through sensory portion of
trigeminal and glossopharyngeal nerves
 Medulla oblongata (either into/closely associated with
tractus solitarius)
 The successive stages of swallowing are then automatically
initiated in orderly sequence by neuronal areas of reticular
substance of medulla and lower portion of pons 65
Deglutition/ swallowing center

66.  Motor impulses from swallowing center to the pharynx and
upper esophagus are transmitted successively by :
 5th, 9th, 10th and 12th cranial nerves and
 even by few superior cervical nerves
66

67. 67
 Involuntary passage of bolus of food from esophagus to
stomach
 The esophagus normally exhibits two types of
peristaltic movements:
 Primary peristalsis and Secondary peristalsis
III. Esophageal Stage

68. Primary peristalsis
Simply continuation of the peristaltic wave that begins in the
pharynx and spreads into the esophagus during the pharyngeal
stage
This wave passes all the way from pharynx to stomach in
about 8 - 10 sec
68
Secondary peristalsis
Results from distention of the esophagus due to the presence
of the bolus
Any food that has not passed into the stomach by the primary
peristalsis will continue until all the food has emptied into the
stomach

69. Factors responsible for passage of food
through esophagus
 Force generated due to contraction of constrictors of
pharynx
 Gravity
Food swallowed by a person in upright position is usually
transmitted to the lower end of esophagus even more
rapidly than the peristaltic wave itself: 5- 8 secs
 Peristaltic wave (Primary, Secondary)
69

70. Function of lower esophageal sphincter
(Gastroesophageal sphincter)
 At the lower end of the esophagus, the esophageal
circular muscle functions as a broad lower esophageal
sphincter
 Normally remains tonically constricted
 When a peristaltic swallowing wave passes down the
esophagus, there is receptive relaxation of the lower
esophageal sphincter which allows easy propulsion of
swallowed food into the stomach
70

71. Receptive relaxation of stomach:
When the esophageal peristaltic wave approaches towards
the stomach, a wave of relaxation precedes the peristalsis,
causing the relaxation of entire stomach to receive the food
71

72. 72

73. Neural control of swallowing
73

74. Neuronal control - Cortex
 Oral phase of swallowing
 Pharyngeal and esophageal
phases of swallowing
74

75. Neuronal control – Brain Stem
7075

76. 76

77.  The nuclei receiving afferent input from the trigger
zones : nucleus tractus solitarius and spinal trigeminal
nucleus
 Efferent pathways from the medulla and pons to the
muscles involved in swallowing involve several cranial
motor nuclei. Most important are:
 Nucleus ambigus
 Hypoglossal nucleus
 Motor nuclei of the trigeminal and facial nerves and
 Motor neurons within the cervical spinal cord
77

78. Functional
Group
Muscle Innervation
Site of motor
neurons
Function in deglutition
Masticatory Temporalis
Mandibular
branch (CN V)
CN V nucleus
(pons)
Raise mandible; chewing,
closing oral cavity
Masseter
Mandibular
branch CN V nucleus
(pons)
Raise mandible; chewing,
closing oral cavity
Medial
pterygoid
Mandibular
branch (CN V)
CN V nucleus
(pons)
Raise mandible; chewing,
closing oral cavity
Lateral
pterygoid
Mandibular
branch (CN V)
CN V nucleus
(pons)
Lower/protrude mandible;
chewing
Facial
Orbicularis
oris
Facial nerve (CN
VII)
Facial nucleus
(pons)
Seal lips/mouth
Buccinator
Facial nerve (CN
VII)
Facial nucleus
(pons)
Push food toward teeth
during mastication, help close
mouth
Role of muscles in deglutition
78

79. Functional
Group
Muscle Innervation
Site of
motor
neurons
Function in deglutition
Intrinsic:
tongue
Superior
longitudinal
Hypoglossal
nerve (CN XII)
Hypoglossal
nucleus
(medulla)
Shorten/tip deflect; bolus
preparation, formation,
positioning, transport
Inferior
longitudinal
Hypoglossal
nerve (CN XII)
Hypoglossal
nucleus
(medulla)
Shorten/tip deflect; bolus
preparation, formation,
positioning, transport
Transverse
Hypoglossal
nerve (CN XII)
Hypoglossal
nucleus
(medulla)
Narrow/lengthen tongue; bolus
preparation, formation,
positioning, transport
Verticalis
Hypoglossal
nerve
(CN XII)
Hypoglossal
nucleus
(medulla)
Broaden/flatten tongue, bolus
preparation, formation,
positioning, transport
79

80. Extrinsic:
tongue
Hyoglossus
Hypoglossal
nerve (CN XII)
Lower/retract tongue; bolus preparation,
formation, positioning, transport
Genioglossus
Hypoglossal
nerve (CN XII)
Protrude/retract tongue; bolus preparation,
formation, positioning, transport
Styloglossus
Hypoglossal
nerve (CN XII)
Raise/retract tongue; bolus preparation,
formation, positioning, transport; seal oral
cavity
80

81. Functional
Group
Muscles Innervation
Site of motor
neurons
Function in deglutition
Suprahyoid Mylohyoid
Mylohyoid n.
(CN V3)
Trigeminal
nucleus (V),
pons
Raise/stabilize hyoid; stabilize
tongue, mouth floor
Geniohyoid
Hypoglossal n.
(CN XII)
C1
Raise/protract/stabilize hyoid
bone
Stylohyoid
Mandibular
branch, facial
nerve (CN VII)
Facial nucleus
(VII), pons
Raise/retract/stabilize hyoid;
elongate mouth floor
Anterior belly
of digastric
Mylohyoid
nerve (CN V3)
Trigeminal
nucleus (V),
pons
Raise/stabilize hyoid; lower
mandible
Posterior
belly of
digastric
Auricular
branch, facial
n. (CN VII)
Facial nucleus
(VII), pons
Raise/retract/stabilize hyoid;
lower mandible
81

82. Infrahyoid Omohyoid Ansa cervicalis C1-C2 Lower/stabilize hyoid
Sternohyoid Ansa cervicalis C1-C2 Lower/stabilize hyoid
Thyrohyoid
Ansa
cervicalis/hypo
glossal n.
C1-C2
Lower/stabilize hyoid; raise larynx to
hyoid
Sternothyroid Ansa cervicalis C1-C2 Lower/stabilize larynx
82

83. Functional
Group
Muscle Innervation
Site of
motor
neurons
Function in
deglutition
Palatal
Tensor veli
palatini
CN V3
Trigeminal
nucleus (V),
pons
Tense soft palate
Levator veli
palatini
CN XI via pharyngeal
branch of CN X
(pharyngeal plexus)
Nucleus
ambiguus (X),
medulla
Raise soft palate; widen
entrance to oropharynx;
seal nasopharynx
Palatoglossus
CN XI via pharyngeal
branch of CN X
(pharyngeal plexus)
Nucleus
ambiguus (X),
medulla
Raise posterior tongue;
lower soft palate; seal
back of oral cavity from
oropharynx
Uvular
CN XI via pharyngeal
branch of CN X
(pharyngeal plexus)
Nucleus
ambiguus (X),
medulla
Raise uvula; brace soft
palate
83

84. Functional
group
Muscle Innervation
Site of motor
neurons
Function in deglutition
Pharyngeal Stylo-pharyngeus CN IX
Nucleus
ambiguus (X),
medulla
Raise/shorten pharynx; raise
larynx
Palato-
pharyngeus
CN XI via
pharyngeal
branch, CN X
Nucleus
ambiguus (X),
medulla
raise/shorten pharynx; raise
larynx; seal oral cavity
Salpingo-
pharyngeus
CN XI via
pharyngeal
branch, CN X
Nucleus
ambiguus (X),
medulla
Raise/shorten pharynx; raise
larynx
Superior
pharyngeal
constrictor
CN XI via
pharyngeal
branch, CN X
Nucleus
ambiguus (X),
medulla
Narrow pharyngeal lumen;
seal nasopharynx; bolus
transport
Middle
pharyngeal
constrictor
Pharyngeal
branch, CN X
Nucleus
ambiguus (X),
medulla
Narrow pharyngeal lumen;
bolus transport
Inferior
pharyngeal
constrictor
CN XI via
pharyngeal
branch, CN X
Nucleus
ambiguus (X),
medulla
Narrow pharyngeal lumen;
bolus transport; distal most
component of upper
esophageal sphincter
84

85. Laryngeal Thyroarytenoid
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Adduct vocal folds
Transverse
arytenoid
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Adduct vocal folds
Oblique
arytenoid
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Adduct vocal folds
Lateral
cricoarytenoid
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Adduct vocal folds
Posterior
cricoarytenoid
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Open vocal folds (end of
swallow)
Aryepiglottic
(not universally
present)
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Approximate arytenoids
cartilages to epiglottis
Thyroepiglottic
Recurrent
laryngeal (X)
Nucleus ambiguus
(X), medulla
Lower epiglottis
85

86. Brain Stem Control of Swallowing: Neuronal
Network and Cellular Mechanisms
 Swallowing movements are produced by a central pattern generator located
in the medulla oblongata.
 Swallowing network includes two main groups of neurons.
 One group is located within the dorsal medulla and contains the generator
neurons involved in triggering, shaping and timing the sequential or rhythmic
swallowing pattern.
 The second group is located in the ventrolateral medulla and contains
switching neurons, which distribute the swallowing drive to the various pools
of motoneurons involved in swallowing.
86
Jean A. Brain stem control of swallowing: neuronal network and cellular mechanisms.
Physiological reviews. 2001 Apr 1;81(2):929-69.
 Swallowing movements are produced by a central pattern generator
located in the medulla oblongata
 Two main groups of neurons:
One group is located within the dorsal medulla
Second group is located in the ventrolateral medulla

87. Infant vs Adult mouth
87

88. Adult mouth and pharynxInfantile mouth and pharynx
88

89. Parameter Infant Adult
Relative size of the
oral cavity
Small size, retruded
position of the mandible
Larger
Tongue position Entirely within the oral
cavity
Oral and pharyngeal
Epiglottis position C2 level C3 level
Hyoid and larynx Higher level Lower level
Buccal fat pad Highly developed Less developed
Auditory tube Floor of the nose -
junction of the hard and
soft palate
Superior and posterior in
the nasopharynx

90. Infantile swallow
 Infants swallow food by suckling
 This is an autonomic reflex
90

91. Characteristics
 Lips are sealed and appear stiff
 Tongue is abnormally large and is caught between maxillary
and mandibular gum pads
 There is no harmonious relationship between the maxilla
and the mandible
 There is no harmonious relationship between cranial and
facial structures
91

92. Mature swallow
 Mature swallow develops around 4-5 years
 Maturation of swallow pattern occurs with the addition
of semisolid and solid food to the diet
92

93. Characteristics
 Cessation of lip activity, i.e. lips relaxed
 Placement of tongue tip against the palate and behind upper
incisors
 Posterior teeth into occlusion during swallow
 Downward and forward mandibular growth increases; intraoral
volume and vertical growth of the alveolar process changes
tongue posture
 Mandible stabilized by contraction of muscles of mastication
93

94. SUMMARY
94

95. Applied aspects
 Abolition of deglutition reflex: Causes regurgitation of
food into nose/ aspiration into larynx and trachea
 Dysphagia : Difficulty in swallowing
 Cardiac achalasia: Neuromuscular disorder of the lower
2/3rd of esophagus, characterized by absence of
esophageal peristalsis and failure of LES to relax during
swallowing
95

96. Structural abnormalities
 CLP : Hampers the control for feeding, decreases oral
suction and causes nasal regurgitation
 Strictures : Are common in the body of the esophagus
which can obstruct the passage of bolus leading to GERD
96

97. Structural abnormalities
97
Cervical osteophytes Zenker diverticulum
Cervical osteophytes : Bony outgrowths from cervical vertebrae narrows the food pathway
and direct the bolus towards the airway
Zenker diverticulum : It is a diverticulum of the hypopharynx, that acts as a weak spot in
the muscular wall. The bolus can enter into it and be regurgitated to the pharynx, resulting in
coughing or aspiration

98. Functional abnormalities
 Drooling: Reduced closing pressure of lips
 Premature leakage of bolus into pharynx: Weak
contraction of tongue and soft palate
 Tongue dysfunction: Impaired mastication, bolus formation
and bolus transport
 Loss of teeth
 Xerostomia
 Impaired opening of UES: Weakness of anterior suprahyoid
muscles
98

99. 99
The paper reviews human mastication, focusing on its age-related changes. The
first part describes mastication adaptation in young healthy individuals.
Adaptation to obtain a food bolus ready to be swallowed relies on variations in
number of cycles, muscle strength and volume of emitted saliva. As a result, the
food bolus displays granulometric and rheological properties, the values of
which are maintained within the adaptive range of deglutition. The second part
concerns healthy aging. Some mastication parameters are slightly modified by
age, but aging itself does not impair mastication, as the adaptation possibilities
remain operant. The third part reports on very aged subjects, who display
frequent systemic or local diseases. Local and/or general diseases such as tooth
loss, salivary defect, or motor impairment are then indistinguishably
superimposed on the effects of very old age. The resulting impaired function
increases the risk of aspiration and choking. Lastly, the consequences for eating
behavior and nutrition are evoked.
Age – related changes in mastication
Peyron MA, Woda A, Bourdiol P, Hennequin M. Age‐related changes in mastication.
Journal of oral rehabilitation. 2017 Apr;44(4):299-312.
In the orofacial region, the cross-sectional areas of the masseter and
medial pterygoid muscles diminish in the elderly, along with bite force
and tongue activity. These changes are accompanied by a reduction in
salivation flow rate, and a decrease in the number of orosensory
receptors leading to a rise in sensory thresholds, perhaps affecting
reflex responsiveness and perception of food texture
In sum, it appears that only minor adaptations are needed to
compensate for the physiological changes induced by aging in subjects
in good health. The main adaptation of the masticatory process to
healthy aging is an increased number of masticatory cycles

100. 100
Three factors have a major impact on masticatory function in elderly persons:
Dental state, Salivation, Motor impairment
 Masticatory efficiency was decreased by 50–85% in full denture wearers compared with
subjects with intact dentition
 Denture wearers make a much coarser bolus than dentate subjects
 An increase in the number of chewing cycles, duration of mastication sequence and EMG
activity per sequence is found in studies with denture wearers chewing various foods
No. of posterior
teeth was a key
factor in predicting
chewing efficiency
Xerostomia and other dysfunctions
related to saliva supply may influence
the masticatory process negatively by
making it impossible to gather food into
a bolus before swallowing
It is assumed that older adults compensate for their loss of muscular force and/or teeth by
chewing for a longer sequence, as this increases their salivary output
Dysfunction of tongue motor skills
and lack of tonicity of muscles
involved in masticatory
movements also reduce
masticatory efficiency
Parkinson, stroke, Alzheimer and other neurodegenerative diseases are good examples. Edentate
subjects with insufficiently trained masticatory muscles are another common example

101. Age – related changes in swallowing
101
The pharyngeal stage of deglutition is apparently delayed and shortened, with a short
opening duration of the pharyngo-esophageal sphincter, a slowing down of the
pharyngeal peristalsis movements (amplitude and speed), hypotony of the vocal cords,
and a weakened cough reflex
Aging brings a deterioration of tactile sensations, and significant decrease in
perceptions of bolus viscosity, because of either an age-related loss in the density of
sensory receptors involved in viscosity perception, or a higher sensory threshold of
these receptors. Bolus viscosity may influence the timing of deglutition
The esophageal stage of the swallowing function is apparently not modified by aging.
Few modifications are noticeable at the upper esophageal sphincter, which takes
longer to relax after swallowing, and undergoes a modification of its contraction
pressure
Peyron MA, Woda A, Bourdiol P, Hennequin M. Age‐related changes in mastication.
Journal of oral rehabilitation. 2017 Apr;44(4):299-312.

102. 102
Grigoriadis J, Trulsson M, Svensson KG. Motor behavior during the first chewing cycle in subjects with
fixed tooth‐or implant‐supported prostheses. Clinical oral implants research. 2016 Apr;27(4):473-80.
Motor behavior during the first chewing cycle in subjects
with fixed tooth- or implant-supported prosthesis
With fixed tooth-supported prostheses, connection of several teeth in rigid
constructions reduce the movement of individual teeth and, consequently, the
stimulation of PMRs when forces are applied to these teeth. Edentulous individuals
with fixed implant supported prostheses in both jaws lack PMRs and thus also the
sensory information they supply
(Weinberg 1957a,b; Picton 1990; Nyman & Lang 1994; Svensson et al. 2013)
Inappropriate regulation of mandibular movement can result in suboptimal occlusal
contact and difficulty in splitting food when chewing. Subjects with implant-supported
prostheses find it difficult to fragment gelatinous food
(Grigoriadis et al. 2011)
Dental status (e.g., the number of teeth remaining, the presence of removable
prostheses), along with several other factors (e.g., temporomandibular disorders, age,
size of the food, etc.) may influence the adaptation of mastication to the hardness of
food
(Peyron et al. 2002; Woda et al. 2006)

103. 103
Only the first chewing cycle, from the start of jaw opening until the nut was initially
fractured, was analyzed. Several noteworthy differences indicating impaired motor
control were exhibited by individuals with fixed tooth- or implant-supported
prostheses
The occurrence of slips differed significantly between the groups (P = 0.031). 30% of
subjects with natural teeth exhibited slips in at least one of their five trials than
those with tooth- 82%, P = 0.038 or implant-supported 70%, P = 0.006) prostheses
The time that elapsed from the start of jaw opening until fracture of the hazelnut
differed between the groups (P = 0.049), with subjects with natural teeth requiring
0.44 s, those with tooth-supported prostheses 0.57 s and with implant-supported
prostheses 0.58 s
(due to the impairment or the absence of
sensory input from the PMRs)

104. 104
In 66% of the subjects with natural dentition, the largest part of the lateral
displacement of the mandible occurred during jaw closure, whereas this
occurred during jaw opening in most of the subjects in the TSP (67%) and ISP
(78%) groups
Visual analysis of the range of motion of the mandible during the first chewing
cycle revealed a narrower pattern of movement for the TSP and ISP groups
The trajectory of the mandibular movement was obviously smoother for the
subjects with natural dentition, while more sluttering and probing behavior
(regardless of the presence or absence of slips) for those with prostheses

105. 105
In such cases, other types of mechanoreceptors in the oro-facial tissues, with
different sensitivities (e.g., possibly those located in muscle, joint, mucosal,
cutaneous and/or periosteal tissues) must provide information about the magnitude
and direction of forces employed during biting and chewing
(Dellow & Lund 1971; Lund 1991; Trulsson & Johansson 2002; Luraschi et al. 2012)
Reduced occlusal area of their posterior teeth. Narrower posterior teeth (in the
buccolingual direction) are often included in implant-supported prosthesis to reduce
the area that transmits the bite force and thereby the load on the implants; and the
pontics of tooth-supported prosthesis are sometimes narrow for a similar reason, that
is, to reduce the load on abutment teeth (Douglas 2003; Klineberg et al. 2007)

106. Conclusion
 Deglutition and chewing cycle are important
physiological processes which are important for proper
development and growth of an individual
 There occurs various changes in these processes with age
 So, clinicians should have thorough knowledge about
these processes
106

107. References
1. Textbook of Medical Physiology, Guyton and Hall 12th edition
2. Essentials of Oral Physiology, Robert M Bradley 1st edition
3. Textbook of Dental and Oral Anatomy, Physiology and Occlusion- Satish Chandra, Shaleen Chandra, Sourabh
Chandra
4. Management of TMJ disorders and Occlussion- Jeffrey P. Okesson- 7th edition
5. Van der Bilt A, Engelen L, Pereira LJ, Van der Glas HW, Abbink JH. Oral physiology and mastication.
Physiology & behavior. 2006 Aug 30;89(1):22-7.
6. Engelen L, Fontijn-Tekamp A, van der Bilt A. The influence of product and oral characteristics on swallowing.
Archives of Oral Biology. 2005 Aug 1;50(8):739-46.
7. Miller AJ. Neurophysiological basis of swallowing. Dysphagia. 1986 Jun 1;1(2):91.
8. Doty RWNeural organization of deglutition.Handbook of Physiology. The Alimentary Canal.1968Am Physiol
SocWashington, DC, sect. VI, vol. IV, p. 1861–1902.
9. Jean A. Brain stem control of swallowing: neuronal network and cellular mechanisms. Physiological reviews.
2001 Apr 1;81(2):929-69.
10. Peyron MA, Woda A, Bourdiol P, Hennequin M. Age‐related changes in mastication. Journal of oral
rehabilitation. 2017 Apr;44(4):299-312.
11. Grigoriadis J, Trulsson M, Svensson KG. Motor behavior during the first chewing cycle in subjects with fixed
tooth‐or implant‐supported prostheses. Clinical oral implants research. 2016 Apr;27(4):473-80.
107