word document

1. Major functions of masticatory
system
Prepared by: Delkhaz F. Taher PhD student
Supervised by: dr.bahar jaafer

2. CONTENT
1-Introduction.
1-Mastication.
2-Swallowing.
3-speech.
4-conclusion.
5-Reference.

3. Introduction:
The neuroanatomy and physiology discussed above comprise a mechanism by which important
functional movements of the mandible can be executed. The masticatory system has three major
functions: (1) mastication, (2) swallowing, and (3) speech.
All functional movements are highly coordinated complex neuromuscular events. Sensory input
from the structures of the masticatory system (i.e., teeth, periodontal ligaments, lips, tongue,
cheeks, palate) is received and integrated in the CPG with existing reflex actions and learned muscle
engrams to achieve a desired function.
Since occlusion of the teeth plays a principal role in the masticatory system’s function, a sound
understanding of the dynamics of these major functional activities is essential.

4. Three main functions
1-Mastication
2-Swallowing(deglutition)
3-Speech

5. 1-Mastication
Mastication is defined as the act of chewing food.22 It represents the initial stage
of digestion, when the food is broken down into small particles for ease of
swallowing.
It is most often an enjoyable activity utilizing the senses of taste, touch, and
smell. When a person is hungry, mastication is a pleasurable and satisfying act.
When the stomach is full, feedback inhibits these positive feelings.

6. Structures involve in the mastication
process
1-musceles of mastication’s.
2-Teeth and periodontal supportive
Structures.
3-lips.
4-cheaks.
5-tongue.
6-palate.
7-salivary glands.

7. CON….
It is a functional activity that generally automatic and particularly in voluntary yet
when decided it can readily brought under voluntary control.

8. The Chewing Stroke
1-Rhythmic and well-controlled separation and closure of the mandible
2-Under the control of the CPG (brainstem).
3- Each opening and closing movement of the mandible represent a chewing stroke.
4- Complete chewing stroke represent has a movement pattern as tear- shaped.

9. The chewing stroke

10. Phases of chewing stroke
1-Opening phase.
2-Closing phase. Which further sub-divided into:
A- crushing phase.
B- grinding phase.

11. 1-Opening phase:
It drops down word from inter cuspal to a
point where incisal edge of the teeth are
about 16 mm to 18 mm apart then laterally
5mm-6mm from the midline when closing
phase begin.

12. 2-closing phase
A-Crushing phase: As the teeth approach each other, the
lateral displacement is lessened so that, when the teeth are
only 3 mm apart, the jaw occupies a position only 3 to 4 mm
lateral to the starting position of the chewing stroke.
- At this point the teeth are so positioned that the buccal cusps
of the mandibular teeth are almost directly under the buccal
cusps of the maxillary teeth on the side to which the mandible
has been shifted.
-As the mandible continues to close, the bolus of food is
trapped between the teeth.

13. The amount of lateral movement of the mandible relates to the stage of mastication.
when food is initially introduced into the mouth, the amount of lateral movement is great;
it then diminishes as the food is broken down.
The amount of lateral movement also varies according to the consistency of the food The
harder the food, the more lateral the closure stroke becomes.
The hardness of the food also has an effect on the number of chewing strokes necessary
before a swallow is initiated. As one might expect, the harder the food, the more chewing
strokes needed.

14. B-Grinding phase
B-Grinding phase, the mandible is guided by
the occlusal surfaces of the teeth back to the
inter-cuspal position, which causes the cuspal
inclines of the teeth to pass across each other,
permitting shearing and grinding of the bolus
of food.

15. In the early stages, incising of food is often necessary. During incising, the
mandible moves forward a significant distance, depending on the alignment and
position of the opposing incisors.
After the food has been incised and brought into the mouth, less forward
movement is necessary. In the later stages of mastication, crushing of the bolus is
concentrated on the posterior teeth and very little anterior movement occurs; yet
even during the later stages of mastication, the opening phase is anterior to the
closing stage.

17. Although masticationcan occur bilaterally,about 78% of observed subjects have a
preferred side where the majority of chewing occurs Side with the greatestnumber
of tooth contacts during lateral glide.
-People who seem to have no side preference simply alternate their chewing
from one side to the other.
-Hardness of food also has an effecton the number of chewing strokes.

18. ToothContacts During Chewing
Early studies suggested that the teeth does not contact during mastication was
speculated the food in between the teeth. (acute response of the neuromuscular
system, prohibits such contact).
-Other studies revealed that tooth contact does occur during mastication. When
food is initially introduced into the mouth, few contacts occur. As the bolus is
broken down the frequency of tooth contact increases.
-Average contact time during mastication 194ms

19. Two types of contacts have been identified:
gliding, which occurs as the cuspal inclines pass by each other during the opening and
grinding phases of mastication, and single, which occurs in the maximum inter-cuspal
position.
It appears that all individuals have some degree of gliding contact.
The mean percentage of gliding contact that occurs during chewing has been found to be
60% during the grinding phase and 56% during the opening phase.
The average length of time41 for tooth contact during mastication is 194 ms.

20. Condition of the occlusal surface on the chewing stroke
tall cusps and deep fossae promote a
predominantly vertical chewing stroke
Flattened or worn teeth encourage a broader
chewing stroke

21. When the chewing strokes of a normal person are compared
to those of one who has TMJ pain, marked differences can be
Seen:
-Normal individuals masticate with chewing strokes that
are well rounded, more repeated, and with definite borders.
-When the chewing strokes of a person with TMJ pain are
observed, a less repeated pattern is often noted. The strokes
are much shorter and slower and have an irregular pathway.
These slower, irregular but repeatable pathways appear to
relate to the altered functional movement of the condyle
around which the pain is centered.

22. Forces of mastication
The maximal biting force that can be applied to the teeth varies from individual
to individual. It is generally found that males can bite with more force than can
females.
In one study43 it was reported that a female’s maximal biting load ranges from 79
to 99 lb (35.8-44.9 kg), whereas a male’s biting load varies from 118 to 142 lb (53.6-
64.4 kg). The greatest maximal biting force reported is 975 lb (443 kg).44

23. It has also been noted that the maximal amount of force applied to a molar is
usually several times that which can be applied to an incisor. In another study45 the
range of maximal force applied to the first molar was 91 to 198 lb (41.3-89.8 kg),
whereas the maximal force applied to the central incisors was 29 to 51 lb (13.2-23.1
kg).

24. The amount of force
The amount of force placed on the teeth during mastication varies greatly from
individual to individual. A study by Gibbs and colleagues51 reports that the
grinding phase of the closure stroke averaged 58.7 lb on the posterior teeth. This
represented 36.2% of the subject’s maximal bite force.

25. Different food consistencies
An earlier study that examined different food consistencies52 suggested much
less force. Anderson reported that chewing carrots produced approximately 30 lb
(14 kg) of force on the teeth, whereas chewing meat produced only 16 lb (7 kg).

26. Natural teeth versus complete dentures
The biting force of subjects with complete dentures is only 1/4 that of subjects
with natural teeth.
-during chewing, the greatest amount of force is placed on the first molar region.
With tougher foods, chewing occurs predominantly on the first molar and second
premolar areas.

27. aid of adjacent soft tissue:
Role Of Soft Tissues In Mastication
Mastication could not be performed without the
1- Role of lips:
A- Guide and control intake.
B-Sealing off the oral cavity
C-Lip are specially necessary when liquid is
introduced.

28. CON….
2-Tongue:
A- Maneuvering of food.
B- initiates the breaking up process by
pressing it against the hard palate.
C- Push food onto the occlusal surfaces of
teeth.
D- After eating, tongue sweeps the teeth to
remove any food residue that has been
trapped in the oral cavity.

29. 2-Swallowing
-Series of coordinated muscular contractions.
-Food from oral cavity through the esophagus to the stomach
-Consists of voluntary, involuntary, and reflex muscular activity

30. Decision to swallow depends on the followings findings:
1-degree of fineness of food.
2-intensity of taste extracted.
3-degree of lubrication of bolus

31. Swallowing STAGES
It consist of three stages:
1-First stage:
-the bolus is placed on the dorsum of the tongue and pressed lightly
against the hard palate.
-the tip of the tongue rest on the hard palate just behind the incisors.
-the lips are sealed and teeth are brought together.
The presence of the bolus on the mucosa of the soft palate initiate a
reflex wave of contractions of the tongue and press the bolus backward
to the pharynx.

32. First stage

33. CON…
2-Second stage:
The peristatic wave caused by contraction of the pharyngeal
constrictor muscles carries it down to the esophagus.
The soft tissue rise to touch the posterior pharyngeal wall.
The epiglottis block the pharyngeal airway to the trachea and keep
the food in the esophagus.
The pharyngeal muscular activity open the pharyngeal orifices of the
Eustachian tube which are normally closed.
It is estimated that theses two stages of swallowing stages extend 1
second.

34. Second stage

35. CON…
3-Third Stage:
Passing the bolus through the length of the esophgus and into the stomach.
-peristatic wave take 6to7 seconds to carry the bolus through the esophagus.
-the upper section of esophagus muscles are mainly voluntary and can be used to
return food back to the mouth if necessary for more complete mastication.
-the lower section the muscles are entirely involuntary.

36. Third Stage

37. Frequency of swallowing
Studies65 have demonstrated that the swallowing cycle occurs
590 times during a 24-hour period: 146 cycles during eating, 394
cycles between meals while awake, and 50 cycles during sleep.
Lower levels of salivary flow during sleep result in less need to
swallow.

38. 3-speech
Speech is the third major function of the masticatory system.
It occurs when a volume of air is forced from the lungs by the
diaphragm through the larynx and oral cavity.
- Controlled contraction and relaxation of the vocal cords or
bands of the larynx create sound with the desired pitch.24
-Because speech is created by the release of air from the lungs,
it occurs during the expiration stage of respiration.
-Inspiration of air is relatively quick and taken at the end of a
sentence or pause. Expiration is prolonged, allowing a series of
syllables, words, or phrases to be uttered.

39. Articulation of sound
By varying the relationships of the lips and tongue to the
palate and teeth, one can produce a variety of sounds.24
Important sounds formed by the lips are the letters “M,” “B,”
and “P.” In making these sounds, the lips come together and
touch

40. M sound B and p sound

41. The teeth are important in saying
the “S” sound. The incisal edges of
the maxillary and mandibular
incisors closely approximate but do
not touch. The air is passed
between the teeth, and the “S”
sound is created.

42. The tongue and the palate are
especially important in forming the “D”
sound. The tip of the tongue reaches up
to touch the palate directly behind the
incisors.

43. Many sounds can also be formed
by using a combination of these
anatomic structures. For example,
the tongue touches the maxillary
incisors to form the “Th” sound.

44. The lower lip touches the
incisal edges of the
maxillary teeth to form the
“F” and “V” sounds.

45. For sounds like “K” or “G,” the
posterior portion of the tongue rises to
touch the soft palate

46. If a malspositioned tooth contacts an opposing tooth during speech, sensory
input from the tooth and periodontal ligament quickly relays the information to the
CNS.
The CNS perceives this as potentially damaging and immediately alters the
speech pattern by way of the efferent nerve pathways. A new speech pattern that
avoids the tooth contact is developed.
This new pattern may result in a slight lateral deviation of the mandible to produce
the desired sound without tooth contact.

47. In a chewing cycle the approach to tooth contact is relatively reproducible, it is
learned and programmed, but it can be altered by loss of teeth or changed by
restorations. Since tooth guidance has an enormous influence on muscle activity
during chewing and swallowing, it is advisable to make restorations compatible
with the functional movement patterns of the patient rather than expect the
patterns of the mastication to adapt to the new made restorations.