Libyan International medical University Prosthodontics Mandibular movements



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Libyan International medical University - Prosthodontics

Mandibular movements

Face bows and Articulators
Overview

Mandibular Movements

  1. Anatomic Considerations

Tempero-mandibular Joints

Muscles


Ligaments

  1. Basic Mandibular Movements

Opening and Closing

Protrusive (forward)

Retrusive (backward)

Lateral


  1. Significance of studying Mandibular Movements

Facebows

Articulators
MANDIBULAR MOVEMENTS

Anatomic Considerations

Temporo-mandibular Joint (Also called the Cranio-mandibular joint)

The mandible articulates with the skull at the tempero-mandibular joint.

The condyle of the mandible fits into the mandibular fossa on the underside of the temporal bone – so it is called Tempero-mandibular Joint



  1. It is the articulation between the mandible and the cranium .

  2. It is a bilateral articulation.


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Parts of the TMJ

  • Articullar Tubercle and Fossa

  • Intra-articular Disc

  • Articular Eminence

  • Fibres Of Lateral Pterygoid

  • Upper Joint Compartment

  • Lower Joint Compartment

The TMJ is a Synovial joint but different from others because here the articular surfaces of the bony components are covered with dense fibrous connective tissue instead of hyaline cartilage seen usually.



Also the TMJ alone has a fibrous intra-articular disc, to which muscle fibres are attached.

This disc divides the joint into two compartments upper and lower giving the mandible a wide range of movements

The possible movements of the lower compartment is a simple hinge movement ,

while that in the upper is a sliding movement.



The mandible moves in all three planes during movement

Muscles

Muscles that move the mandible are under voluntary control, these muscles can be directed to move the mandible in various directions

There are powerful muscles, which elevate and rotate the mandible so that the opposing teeth may occlude for mastication.


The muscles of mastication include the

  1. Temporalis,

  2. Masseter and

  3. Internal (medial) and,

  4. External pterygoids (lateral)

The first three of these are elevators.

The fourth (Lateral Pterygoid) is a guiding muscle, partly helping to depress the mandible.






Action of muscles during masticatory movements.

Elevator jaw muscles - Closing

  • Medial Pterygoid

  • Superficial Masseter

  • Temporalis

  • Superior Division Of Lateral Pterygoid

Depressor jaw muscles - Opening

    • Mylohyoid

    • Digastric

    • Inferior Division Of Lateral Pterygoid



Remember the muscles of mastication develop their greatest power within a short range of vertical dimension – upto 400 pounds - Artificial teeth – maximum upto 30 pounds





Mandibular Ligaments

The different mandibular Ligaments are



  1. Temporo-mandibular ligament

  2. Sphenomandibular Ligament

  3. Stylomandibular Ligament



Basic Mandibular Movements are

  1. Opening

  2. Closing

  3. Protrusive or forward

  4. Retrusive or Backward

  5. Right lateral

  6. Left lateral

Types of Condylar Movements During opening or closing of the mandible



Rotational movement

Translational movement



  • Rotational Movement-

Around the horizontal axis (hinge axis)

Opening of the jaw

Closing the jaw



  • Translational movement

Wide Opening Protrusive



Retrusion

Right Lateral

Left Lateral


Border Movements of the Mandible

Border movements of the Mandible in Sagittal plane






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Border Movement of the Mandible Horizontal Plane

  1. Left lateral border.

  2. Continued left lateral border with protrusion.

  1. Right lateral border.

  2. Continued right lateral border with protrusion.


Border Movement of the Mandible Frontal plane




Lateral Movement (Bennett Angle [1])




5a




Lateral Movement

(Bennett Shift [2])


FACE BOW

It is a calliper -like instrument used to record the relationship of the maxiIIary arch

to the hinge axis and then transfer this relationship to an articulator.It orients the dental cast in the same relationship to the opening axis of the articulator

Uses of Face bow

  • Establish the relationship between the maxillary arch and the Hinge axis

  • Transfers this this relationship to the articulator

  • Provides an accurate mounting of the maxillary cast to the articulator


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Types of Face Bows

Ear-piece Face Bow

Fascia Type Face Bow
Facebow earpiece type


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Facebow fascia type

ARTICULATORS
Articulator

An articulator is are mechanical instrument that represents the temporomandibular joints and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements.
Function of Articulators

  1. Prosthetic work is carried out in the absence of the patient.

  2. It simulates but cannot duplicate all the possible mandibular movements.

  3. Mounting dental casts for diagnosis and treatment planning.

  4. Maintain jaw relation record during teeth arrangement.



Advantages :

  1. Visualization of patient's occlusion from the lingual side .

  2. Patient cooperation is not a factor , once the inter occlussal records are obtained from the patient .

  3. Chair time and patient appointment time is saved .

  4. Saliva , tongue and cheeks are not interfering factors during using the articulators.


Requirements

  1. Able to open and close in hinge motion.

  2. Casts must be easily removed and attached

  3. Articulator must have an incissal guide pin with a positive stop to maintain vertical dimensions.

  4. Rigid , accurate and of non corrosive materials.

  5. Guidance mechanism should be able to move freely and be accurately secured .

  6. Minimal weight , not bulky and stable on the bench .


Special Requirements

  1. The articulator should accept face bow transfer.

  2. The condylar guidance should allow right lateral, left lateral and protrusive movements.

  3. The incisal guidance should be adjustable.


BASIC PARTS OF ARTICULATOR

  • Upper member

  • Lower member

  • Mounting plates

  • Condylar analogues

  • Condylar guidance

  • Incisal guide pin

  • Incisal guide table


Types of Articulators

  1. Based on the anatomic similarity to humans

    1. ARCON and NON ARCON

    2. Based on their functionality (adjustability)

  1. Simple hinge articulators.

  2. Fixed or mean value condylar path articulators.

  3. Adjustable condylar path articulators:


Types of Articulators
Based on the anatomic similarity to humans

ARCON and NON ARCON
What is ARCON and NON-ARCON?
ARCON-ARticulator like CONdyle

Here the articulator is like the mandible, because it has the condylar head attached to the Lower member and the condylar path is attached to the upper member

Non ARCON-ARticulator NOT like CONdyle

Here the articulator is different from the mandible in that the condylar head is in the Upper member and the condylar path is attached to the lower member.

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Natural


Condylar Path


Condyle


ARCON Non ARCON


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Condylar Path


Condylar Element

Condylar Path

Condylar Element


Types of Articulators

    1. Based on their functionality (adjustability)

  1. Simple hinge articulators.

  2. Fixed or mean value condylar path articulators.

  3. Adjustable condylar path articulators:

      1. Semi-adjustable condylar path articulators

( NON-ARCON or ARCON )

      1. Fully-adjustable condylar path articulators


Simple Hinge Articulators.

Records are fixed to the Articulator.

Simple Hinge Movements given by the Articulator.


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Fixed or Mean Value Condylar Path Articulators .


1



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Adjustable Condylar Path Articulators :

a.Semi - adjustable condylar path articulators

( may be NON-ARCON or ARCON )

b. Fully - adjustable condylar path articulators .
Semi adjustable articulators


Here many features may be recorded from the patients mouth and transferred to the articulator. This type of an articulator is a basic requirement for Balanced Occlusion






This type of an articulator accepts transfer of almost all the features needed to do complex restorations which may be recorded from the patients mouth. Commonly these articulators allow adjustment of the intercondylar distance according to the individual patient.
Fully Adjustable Articulators




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