Mandibular MovementsLecture notes”

Abdulsalam A. ZwiadBDS,HD., M.Sc. Int.Ce. Impl.

Associ. Prof. Faculty of Medical Sciences Queen Arwa University

Former Assist. Prof. Baghdad University

It is a complex (hinge and glide) articulation with

limited free movements).

Temporomandibular Joint (TMJ)

TMJ is Composed of

Condyle of mamdible , Articular disc and Glenoid fossae

CondyleIt is the oval- or kidney-shaped structure found on the end of the condyloid process.

Articular Disc (meniscus)

The articular disc is a pad of tough, flexible fibrocartilagesituated between the condyle and the glenoid fossa.

The disc is a shock-absorbing mechanism. When the condyle moves out onto the articular eminence, the disc travels with it.

Synovial CavitiesThe synovial cavities could be divided to the upper and lower joint compartments:

1. The upper synovial cavity is found between the top of the disc and the glenoid fossa.

2. The lower synovial cavity is found between the bottom of the disc and the condyle of the mandible.

Synovial Membrane and Associated Synovial Fluid

- The synovial membrane is the lining of a synovial cavity.

- The cells of the lining make a lubricating liquid called synovial fluid.

Auxillary Ligaments

Auxillary ligaments generally act to restrict the condyle to a normal range-of-movement and prevent dislocation.

1. Stylomandibular Ligament; originates on the styloid process of the temporal bone and inserts on the posterior border of the ramus near the angle.

2. Sphenomandibualr Ligament; originates on the spine of the sphenoid bone and inserts on the anterior-superior of the mandibular foramen (lingula). The mandibular foramen is found on the internal surface of the ramus of the mandible.

Capsuler ligamentous- It is the major ligament of the TMJ. This ligamentous originates from the entire rim of the glenoid fossa and articular eminence, attaches to the edges of the articular disc, and passes to insert around the rim of the condyle.

- The capsule holds the disc in place between the condyle and the fossa, it retains the synovial fluid in the upper and lower joint compartments, and it acts to prevent dislocation of the mandible.

MASSETER M.

Temporalis

Functions of Ligaments

• Accessory ligaments may limit border movements of the mandible.

• Fibrous capsule and TM ligament may limit of extreme lateral movements in wide opening of mandible

Basic Mandibular MovementsOpening and ClosingFrom a position of centric relation, pure hinge movements are possible in opening and closing.

In a hinge movement, the condyles rotate within the glenoidfossa.

Opening and closing movements, where the measured distance between maxillary and mandibular incisors is greater than 25mm, result in combined rotation and translation of the condyles.

Translation occurs whenever a condyle leaves the glenoid fossa.

FRONTAL or CORONAL plane

HORIZONTALplane

Vertical AxisVertical Axis

SagittalSagittalaxisaxis

Horizontalaxis

Mandibular movement about the 2 vertical and 2 sagittal condyle axes of rotation

SAGITTALplane

Each condyle moves about 3 axes (but the Horizontal axes are a shared axis)

axes of rotation5total of = therefore a

Protrusion and Retrusion

Protrusion is when the mandible moves forward and both condyles leave their respective fossae and move down their eminences.

The opposite process is called Retrusion. Protrusion and Retrusion are translatory movements.

Right and Left Lateral1. Working side: The side toward which the mandible moves.

When the mandible moves laterally, the condyle on the working side stays in its fossa, rotates and moves laterally.

2. Balancing side: The side opposite the working side. In a lateral movement, the balancing side condyle leaves the fossa and moves forward and down the eminence, and medially.

A dynamic biomechanical musculoskeletal system

The Masticatory System

Components of the Mastication

• Teeth• Periodontium• Maxilla and Mandible• TMJ• Mandibular musculature• Muscles of the lips, cheeks, and

tongue• Innervations and vasculation

Loss of Teeth Causes Occlusal Disharmony

• Early loss of deciduous teeth without space retaining appliances

• Loss of mandibular first molar•• lingual and lingual and mesialmesial tipping of mandibular 2nd and 3rd tipping of mandibular 2nd and 3rd

molarmolar•• Loss vertical dimensionLoss vertical dimension•• Changing in Changing in masticatorymasticatory habit and muscle tonicity habit and muscle tonicity

Periodontal Supporting Tissues ( periodontium)

• Cementum• Periodontal ligament• Supporting bone

Usually, periodontium is protected against injury by neuromuscular reflexes

Problems to Periodontium

• Periodontal trauma• pattern of mastication• Loss of teeth• loss of periodontal support• Faulty restoration• Abnormal occlusal force; bruxism,

clenching

Masticatory Muscles

• Masseter muscle

• Temporalis muscle

• Medial pterygoid

muscle

• Lateral pterygoid

muscle

Non Masticatory Muscle

• Digastric muscle

• Mylohyoid muscle

• Geniohyoid muscle

• Orbicularis Oris

Types of Mandibular Movement

• Rotational movement• Horizontal axis of rotation• Frontal (vertical) axis of rotation• Sagittal axis of rotation

• Translational movement

Rotational Movement

Around the horizontal axis (hinge axis)

Rotational Movement

Around the frontal (vertical) axis

Rotational Movement

Around the sagittal axis

Translational movement

Mandibular border movements could be illistratedby tracing a map or envelop in:

- Sagittal

- Horizontal and

- Frontal Planes

Sagittal Plane

Horizontal Plane

• Left lateral border• Continued left lateral border

with protrusion• Right lateral border• Continued right lateral border

with protrusion• Functional movements

Frontal Vertical

References

• Ash and Ramfjord. Occlusion 4th edition. W.B. Saunders Company, 1995

• Mohl, Zarb, Carlsson and Rugh. A textbook of Occlusion. Quintessence Publishing Co., 1998

• Sicher and DuBrul. Oral Anatomy 6th edition. The C.V. Mosby Co, 1975

• Kraus, Jordan and Abrams. Dental anatomy and Occlusion. The Williams and Wilkins Co, 1969

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