OP Mastication

Chewing

Other term for Mastication

Mastication

Process by which the food is being crushed and grounded by the teeth.

Mastication

A complex function that uses not only the muscles, teeth, periodontal supportive structures but also the lips, cheeks, tongue palate and salivary glands.

Mastication

First step of breaking down of the food stuff

Mastication

It consists of a number of chewing strokes

Premastication

Being performed by the parents for the infants who are incapable to do such how to masticate the food

Masticatory Movements

Requirements for the food to be properly masticated

• Mandibular elevation

• Mandibular depression

• Tooth alignment and accurate regulation of masticatory forces

• Requires the coordinated activity of several groups of muscles attached to the mandible.

Masticatory Movements

• Responsible for adduction and abduction during mastication

• Have shorter contraction times than most other body muscles.

• Incorporate muscles spindles to monitor their activity (especially. elevator muscles

• No Golgi tendon organs

• Controlled by brain stem centers

Masticatory mucles

• Good dentitions

• Partial or fully edentulous individuals

Two subjects of Masticatory mandibular movement

• All teeth must be present

• Have greater masticatory efficiency

Good dentitions

• Swallow large food particles/boluses

• Difficulty in crushing the food well

Partial or fully edentulous individuals

Ulrich and Bennett

They describe the range of mandibular masticatory movements

Ulrich and Bennett

They showed that there is no fixed axis of mandibular rotation

• Food bolus consistency

• Individual masticatory habits

• Status of dentition

Such mandibular movement patterns that are not fixed may be affected by a number of factors:

Lateral Pterygoid

Protuster muscle

• Temporalis

• Masseter

• Median pterygoid

• Lateral pterygoid

Elevator muscles

• Digastric

• Mylohyoid

• Geniohyoid

• Genioglossus

Depressor-retractor muscles

Normal movements

How the jaw moves by forming chewing strokes

• Opening

• Closing

• Occlusal plane

Chewing strokes are:

Transitional/hinge movements

Upper compartment

Meniscus

Controls the movement of the mandible

Articular disc

It acts as shock absorber

Articular Disc

Meniscus is also known as

• Upper compartment

• Lower compartment

Division of Meniscus

Gliding movement

Lower compartment

• Preparatory Phase

• Food contact phase

• Occlusal phase

Phases of chewing cycle

Lateral

Movement of the condyle of working side during opening stage (preparatory phase)

Medially downward and forward

Movement of the opposing condyle of non-working side during opening stage (preparatory phase)

Lateral deviation

This begins when the jaw opens and pulls the mandibular downward from the resting position.

Working side

Food on the functional occlusion

• Digastric muscles

• External/lateral pterygoid

Muscles that depresses/Jaw opening muscles

Working site

Means ready to contact tooth either left or right

Early closing phase

Condyle on the working side resume its position within the fossa

Late closing phase

The opposing condyle moves back to its fossa

Working side

What side of temporalis muscle is to first activate during closing stage?

Temporalis muscle

First muscle of the working side to activate during closing stage

• Masseter

• Pterygoids

What muscles are active in incisive movement during closing stage?

Lateral Pterygoid

What muscle is active at mandibular protrusion and opening during closing stage?

• Digastric

• Geniohyoid

• Mylohyoid

Suprahyoid muscles that are active at jaw opening during closing stage

• Infrahyoid

• Stylohyoid

Suprahyoid muscles that acts as prerequisite stabilization during closing stage

Neutral Masticatory Receptors

Various receptors which act on the muscles that are related to mastication and helps them to perform their functions

a-efferent motor neurons

Supply the extrafusal muscle fibers

y-efferent neurons

Supply the intramural muscle fibers of the muscle spindle

• Isotonic contraction

• Isometric contraction

Types of contraction of masticatory muscles

Isotonic contraction

Shortening of muscle protrudes jaw movement against constant load

Isotonic Contraction

Muscle shorts and movement occurs

Isometric Contraction

Produce contractile tension with no change length

Isometric Contraction

Muscle does not shorten but tension increases

• White fibers/Fast twitch

• Red fibers/Slow twitch

Rate of contraction of masticatory muscles

White fibers/Fast twitch

Fibers that exhibits rapid twitch contraction but quickly fatigues

Red fibers/Slow twitch

Fibers that are fatigued resistant and adjusted to maintain the mandible posture.

Muscle Tension

Condition in which muscles of the body remain semi-contracted for an extended period.

Contraction of individual muscle fiber

Main function of a muscle unit

1. Increase individual motor unit discharge

2. Increase in the number of motor units discharging (recruitment)

3. Increased motor unit discharge synchrony

Increase in muscle tension involves the following:

Muscle spindles

Compromises of stretch-sensitive, slowly-adapting specialized muscle fibers that are contained within a capsule lying parallel to the extrafusal muscle fibers.

Muscle spindles

Monitors stretch or change in muscle length

Muscle tendon junction

Where are Golgi tendon organs primarily located?

1 beta myelinated afferent fibers

GTOs are innervated by what fibers?

8-12 micrometer

Size of 1 beta myelinated afferent fibers

Golgi Tendon Organs

Masticatory muscles do not have this receptors

Golgi Tendon Organs

Monitors tension or force

Mucous membrane receptors

These are cells in the mesencephalic nucleus mainly sensory and spinal trigeminal nuclei that respond to pressure in the palate and tongue

Palate

Pressure receptor such in region distal to the central incisors

Tongue

Touch receptors

Joint Receptors

Free nerve fibers that compromise the predominant receptor in the TMJ capsule

• Ruffini

• Pacinian

• Golgi receptors

Joint receptors consist some of the following:

Up to 2 micrometer

What is the diameter of the majority of myelinated nerve fibers innervating TMJ?

Up to 12 micrometers

What is the diameter of some myelinated nerve fibers that presumably innervate more complex TMJ receptors?