Mandibular Movements PDF

BDS, MSc, PhD Lecturer of Prosthodontics, College of dentistry , AASTM  Factors that regulate the mandibular movements 1-Tempromandibular joint. 2-Muscles. 3-Ligaments 4- Dentition and supportive structures  1-TEMPROMANDIBULAR JOINT The articulation between the temporal bone (cranium) and...

BDS, MSc, PhD Lecturer of Prosthodontics, College of dentistry , AASTM  Factors that regulate the mandibular movements 1-Tempromandibular joint. 2-Muscles. 3-Ligaments 4- Dentition and supportive structures  1-TEMPROMANDIBULAR JOINT The articulation between the temporal bone (cranium) and the mandible It is one of the most complex joints in the body  Temporomandibular joint (TMJ) It is a synovial joint but differs from most synovial joints in that the articular surfaces of the bony components are covered with denes fibrous connective tissue, instead of hyaline cartilage  Fibrous articular disc The TMJ has a fibrous articular disk to which muscle fibers are attached Divides the joint into 2 Compartments upper and lower giving the mandible wide range of movements Superior Joint Cavity Articular Eminence Disk Retrodiscal Tissue Condyle Inferior Joint Cavity Lateral Pterygoid Muscle  TWO BASIC TYPES OF MOVEMENT Rotational Movement Translational Movement Hinge Sliding The TMJ provides for hinging (rotational) movement , that take place in the lower compartment. However, at the same time it also provides gliding (translational) movements, which take place in the upper compartment.  2- Muscles Move mandible under voluntary control Powerful muscles (active)  Digastrics Depressor Mylohyoid Muscles Stylohyoid Positioner Geniohyoid (guiding) Muscle Lateral pterygoid Masseter Elevator Temporalis muscles Medial pterygoid  Origin: zygomatic arch Insertion: lateral aspect of the lower border of the ramus (region of the second molar) Function: 1. Superficial portion; elevation and protrusion 2. Deep portion; elevation Origin: temporal fossa Insertion: coronoid process & anterior border of ramus Function: Elevation & Retrusion  Origin: medial surface of lateral pterygoid plate, palatine bone & maxillary tuberosity Insertion: medial surface of angle of mandible & inferior surface of ramus  Function: Elevation - Protrusion  Origin: infratempoaral surface of greater wing of sphenoid Insertion: neck of condyle & articular disc Function: keeping the disk properly aligned with the condyle during function Origin: Lateral surface of lateral pterygoid plate Insertion: Neck of condyle Function: 1. Simultaneous bilateral contraction, the condyles are pulled down the articular eminences and the mandible is protruded. 2. Unilateral contraction causes a lateral movement of the mandible to the opposite side. 3. When this muscle functions with the mandibular depressors, the mandible is lowered and the condyles glide forward and downward on the articular eminences. Depress the Mandible Hyoid Muscles  Origin: Mastoid notch (medial to mastoid process) Insertion: Intermediate tendon attached to hyoid bone  Origin: lingual surface of the mandible, just above the lower border Insertion: Intermediate tendon attached to hyoid bone  Function When the Digastrics contract and the hyoid bone is fixed by the suprahyoid and infrahyoid muscles, the mandible is depressed  3-LIGAMENTS Ligaments of the joint are composed of collagenous connective tissues that have particular lengths. They do not stretch. Ligaments do not enter actively into joint function but instead act as passive restraining devices to limit and restrict border movements.  3-LIGAMENTS Passive devices Action : to limit and restrict mandibular movements Centric relation (The Initiating position) Each tooth is highly specialized Types of Motion: Rotation – Translation according to its function. The exact Direction (Planes) of motion Degree of movement interarch and intraarch relationships of Clinical significance of movement the teeth are extremely important and greatly influence the health and function of the masticatory system  The maxillomandibular relationship in which Centric the relation (Thecondyles are in the most Initiating position) Types of Motion: Rotation – Translation retruded, Direction unstrained (Planes) of motion position within Degree of movement the glenoid fossa. Clinical significance of movement  It is the starting position Centric relation (The Initiating position) Types(The of Motion:most superior Rotation – Translation condylar Direction (Planes) of motion Degreeposition of movementfrom which a hinge Clinical significance of movement axis movement can occur) Centric relation (The Initiating position) The Types complete of Motion: Rotationstatic intercuspation – Translation of Direction (Planes) of motion theof opposing Degree movement independent of teeth, condylar position Clinical significance of movement. The occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with maximum intercuspation.