Mastication. Chewing Cycles Oral Reflexes Dr: Mu’taz alshawabekah

2. • Mastication.
• Chewing Cycles
• Oral Reflexes
• Dr: Mu’taz alshawabekah

3. Definition
• Mastication:
is process whereby ingested food is cut or
crushed into small pieces mixed with saliva
and formed into bolus in preparation for
swallowing.

4. Function of Mastication
• Function of Mastication:
1. Enables the food bolus to be easily swallowed
2. Enhances the digestibility of food by:
a. Decreasing the size of particles to increase the surface area for
enzyme activity
b. Reflexively stimulating the secretion of digestive Juices (saliva and
Gastric Juice)
3.Mixes the food with saliva, initiating digestion by the activity of
salivary amylase
4.Prevent irritation of the GI system be large food masses
5.Enusres healthy Growth and development of the oral tissues.
6. Increase in Digestive efficiency, the Primary purpose of mastication

5. How does it occur?
• Mastication occurs by the convergent movements of
max. & man. Teeth.
• Most foods are first crushed by vertical movements of
the mandible before being sheared by lateral to
medial movements of the mandible to make a bolus.
• The initial crushing of the food does not require full
occlusion of the teeth. Indeed, it is often only after the
food has been well softened that the maxillary and
mandibular teeth eventually contact.
• Once the cusp can interdigitate, the ridges on the
slopes of the cusp shear the food as the mandibular
teeth move across the maxillary teeth.

6. Cont’d
• PIC FIG 6.1 pg 91
Several features provide protection for the adjacent
gingiva during chewing.
1)The marginal ridges bounding the interproximal edges
of the occlusal surfaces of the tooth are the important
protective features. These ridges deflect most of the
food, potentially driven between adjacent teeth by
their opponents, onto the occlusal surfaces.
2)The Contact points beneath the marginal ridges should
abut firmly to prevent food being wedged between the
teeth and above the interdental papillae.

8. Cont’d
• The buccal cusps of the mandibular teeth bite
between the buccal and palatal cusps of the
maxillary teeth, with the result that 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.
Fig 6.1 page 91 B

10. Cont’d
• Mastication is not simply a result of
rhythmically closing teeth of a particular form
on a piece of food. Also it includes the
placement of food between the occluding
surfaces of the teeth by the tongue and the
selection by the tongue of those pieces of
food in the mouth.

11. Structural features associated with mastication:
• TMJ articulation
• Serous salivary gland
• Prismatic Enamel
• 2nd Palate
• Significant muscle development associated with
lips ,cheeks, tongue and muscles of mastication
• Diphyodonty
• Gomphosis type of tooth attachment

12. Bite Force
• Mastication is dependent upon a complex chain of events,
that produce rhythmic opening and closing movements of
the jaws and correlated tongue movements.
• The forces that are exerted on the teeth and jaws are very
large and physiologically significant.
• The bite Force exerted on the food during mastication is of
the order of 5-15kg. It varies according to the texture of the
food
• The bite pressure is measured with a gnathodynamometer,
maximum pressures of the order of 50 kg can be recorded
• 64 N in denture Wearer.

13. Fig 6.2 pg 91
• Rhythmic jaw movements are generated by a
centre within the brainstem. This is referred to
as an Oral Rhythm/Pattern generator and is
activated both by drive from the higher
centers and peripheral sensory input. And the
pattern of activity is distributed to the motor
neuron pools which receive excitatory or
inhibitory sensory inputs from a variety of
peripheral structures

15. • Sensory input generated by closing on hard
food generation of rhythmic jaw
activity closing on a softened bolus
Tongue movement and food transport
swallow terminate the rhythmic jaw
activity.

16. Sensory Receptors in masticatroy
Muscles
• Control of Muscle Movement
• Unevenly distributed in the muscle of mastication.
Muscle Spindles:
• Many in elevators and tongue muscles
• Few in the depressor muscles
Golgi tendon organs:
• Not known if they exist in Elevators
• Protect against overdevelopment of muscle tension
• Performed by PDL receptors= it limits the force applied
in the mastication.

17. Control of mastication
 Amount of chewing before swallowing is :
Characteristic of the individual.
Influenced by nature of food.
 Number of strokes before swallowing:
In men>women
women> children
Not markedly influenced by state of Dentition

18. Chewing/Chewing Cycle
• Is highly complex process.
• 2 methods of chewing have been distinguished depending
upon the texture of the food:
1) puncture/crushing :hard food is first crushed and pierced
between the teeth without direct tooth-to-tooth contact.
This results in wear of the teeth, especially at the tips of
the cusps.
2) Shearing stroke. This method involves tooth contacts that
take place only after the food has been reduced. This type
of movement produces attrition facet with characteristic
directional scratch lines on the faces of the cusps
• .

19. • The mean of the vertical dimension of the chewing
cycle are between 16 and 20 mm and between 3 and 5
for lateral movements
• The duration of the cycle varies between 0.6 and
1second depending on the type of food
• The speed of masticatory movement varies within each
cycle according to types of food and among individuals
• Speed , duration and form of the chewing cycle vary
with the type of occlusion , kind of food and presence
of dysfunction

20. • Chewing cycle involves 3 basic phases of the mandible in relation to
the maxilla:
1) From a position in which the jaw is open , the closing stroke
results in the teeth being brought into initial contact with the
food; the work done in this phase is really against gravity.
2) This is followed by Power Stroke. When 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,
even thought there may be vastly greater masseter and
temporalis muscle activity during this time.
3) Finally there is the opening stroke, when the mandible is lowered,
with an initial slower stage followed by a faster stage.

21. Fig 6.3
• Occlusal relationship of the cheek tooth during chewing on the left
side:
• 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.fig A BUCCAL
PHASE
• In power stroke the mandibular teeth then slide upwards and
medially against the maxillary teeth to momentarily attain
intercuspal position.fig b INTERCUSPAL PHASE
• The mandibular teeth continue downwards and inwards against the
maxillary teeth fig c LINGUAL PHASE
• Note: while the teeth on the working side are moving through the
buccal phase those on the balancing (right) side are in the lingual
Phase but in the reverse direction.

23. The envelope of Motion fig 6.5
• The pathway followed by the mandible during chewing
is termed “ the envelope of Motion”
• It demonstrates the symmetrical mandibular
movements produced during opening and closing of
the jaw.
• The envelope of motion is the volume of space within
which all movements of a specified point on the
mandible occur.
• The envelope is limited by the anatomical
considerations such as ligaments and tooth contacts
• Most natural movements occur within the “envelope” .

25. • The first phase of mandibular movements is
Hinge-like movement during which the
condyles remain retruded within the
mandibular fossae
• When the teeth become separated by
approximately 25 mm, the second phase of
opening occurs and involves anterior
movement or protrusion of the condyles
down the articular eminences.

26. • Fig 6.5
• Point A is the fulcrum associated with simple hinge
movements.
• The path described between points A and B represents
the shift of the centre of rotation of the mandible , this
shift occurs because of the transition from a pure hinge
movement at the condyle to protrusion and rotation
during opening ( with reverse during closing).
• Point B has been described as representing the point of
rotation around the attachment of Sphenomandibular
ligament at the lingula.

28. Profile/envelope of motion
showing the average incisal
movements in
the frontal plane
during a masticatory
cycle

29. • Transverse movements of the lower jaw (i.e lateral excursions or
side-to-side movements)
• These movements involve bilaterally asymmetric movements of the
mandible. They are produced by protrusion of the mandibular
condyle down the articular eminence of the temporal bone on one
side with reactive movements of the other condyle ( rotation
around a laterally shifting axis)
• We can also see changes in the horizontal band of the
temporomandibular ligament passing from the articular eminence
to the lateral surface of the condyle during lateral movements
• Tension generated in the horizontal band produces a slight lateral
shift in the condyle ( Bennett shift)

31. The Control of Mastication
• In the past, there has been much controversy
concerning the origin and control of the rhythmic
activity of the jaws during mastication.
• The Cerebral Hemispheres Theory:
• Mastication was 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 motorneurons
within the brainstem ( trigeminal, facial ,
hypoglossal motorneurons)

32. Cont’d
• The reflex Chain Theory
• 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
motorneurons 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
decerbrate animals.
• Objections to this theory: mastication involves prolonged
bursts of muscle activity and not the brief and abrupt
behaviour usually associated with reflex activation of
muscle.

33. Cont’d
• 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.

34. Cont’d
• The activity of this generators depends upon
excitation descending in the pathways from
cerebral cortex and upon excitation deriving
from peripheral stimulation
• The rhythmic activity can be generated by
conscious drive and/or by the presence of the
food in the mouth.

35. Cont’d
• During mastication the cycles of jaw
movement differ depending upon the
consistency of the food initially ingested and
upon the stage of breakdown of that food
• This indicates that the cyclic activity generated
by the CPG is subjected to modification by
sensory from the mouth.

36. • Oral reflexes :
• The Jaw Jerk.
• Jaw Opening Jerk.

37. • Jaw jerk:
• Is produced when the jaw closing muscles are stretched by
tapping the chin downwards so that the jaw open suddenly.
• It is monosynaptic Reflex
• Is due to stimulation stretch-sensitive receptors (muscle
spindle ) in the masseter and temporalis muscles.
• The stretch produces a burst of impulses in the sensory
nerves that is conveyed back to the motor neurons of those
muscles
• The muscles are consequently activated briefly to produce
a short-lived contraction

38. • Jaw opening reflex
• Polysynaptic
• Produced by applying mechanical or electrical stimuli
to oral mucosa, PDL or teeth
• The stimuli do not have to be painful to elicit the reflex
but stronger stimuli do produce correspondingly more
vigorous responses
• Characterized by a brief period of inhibition of activity
in the motor neurons of the jaw closing muscles,
however in other mammals there is in addition a
simultaneous activation of the jaw opening muscles
(digastrics and infrahyoid muscles )