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• The teeth and jaws of modern humans are much smaller than our ancestors

  
• Evolution of human masticatory system

  • It is functionally involved in not only with diet and food processing techniques, but also brain size, bipedalism and speech (language)
• Reduction in size of the jaws and teeth of human populations

  Linked to transition from hunter gatherer community to a fully Neolithic (agriculturist) community
• Evolution of the maxillo mandibular system


  Closely related to the development of brain, by stressing that language provides communication and coordination between the individuals and also plays an important role in "thinking" for humans think in their native language
• Dental disease and tooth loss are not restricted to modern man
• Temporormandibular Joint (TMJ)


  A type of ginglimoarthrodial articulation (gliding movement + hinge movement)
• Components of TMJ

  • Mandibular (condylar) fossa
  • Condyloid process (or condylar head)
  • Joint capsule
  • Mandibular ligaments
  • Articular disc
• Mandibular fossa

  An oval or oblong depression in the temporal bone just anterior to the auditory canals, the shape of which conforms to the posterior and superior surfaces of the condyloid process of the mandible
• Condyloid process


  The condyloid process of the mandible is convex on all bearing surfaces, perpendicular to the ascending ramus of the mandible, with articular surfaces covered with cartilage
• Joint capsules

  The TMJ is enclosed in a fibrous capsule that resists medial, lateral, and inferior forces and confines the synovial fluid, consisting of an internal synovial layer and an outer fibrous layer
• Mandibular ligaments


  • Lateral temporomandibular ligament
  • Stylomandibular ligaments
  • Sphenomandibular ligaments
• Lateral temporomandibular ligament


  Composed of an outer oblique portion that limits mandibular-condylar rotation resulting in translation, and an inner horizontal portion that resists posterior displacement protecting retrodiscal tissues
• Sphenomandibular ligaments


  Origin: angular spine of the sphenoid bone & the petrotympanic fissures, Insertion: the lingula of the mandible, Function: Suspensory (support)
• Stylomandibular ligaments


  Origin: the tip of styloid process, Insertion: the angle of mandible, Function: Restricts mandibular protrusion
• Articular disk


  Consists of dense fibrous connective tissue shaped to accommodate the shape of the condyle and concavity of the mandibular fossa, dividing the articulating surfaces into upper and lower compartments to provide smooth gliding function and distribute joint stresses
• Regions of the articular disk

  • Posterior band
  • Intermediate zone
  • Anterior band
• Anterior band of articular disk

  Attaches anteromedially with the superior head of the lateral pterygoid muscle, and laterally with the fibers of the masseter and temporalis muscles
• Posterior band of articular disk

  Divided into 3 parts: temporal part (superior) attaching to the posterior wall of the glenoid fossa, intermediate part attaching to the "retrodiscal tissue", and condylar part (inferior) attaching to the posterior aspect of the condylar head
• Muscles of mastication (innervation)

  • Superior head of lateral pterygoid (CN V)
  • Masseter (CN V)
  • Medial pterygoid (CN V)
  • Temporalis muscles (CN V)
  • Suprahyoids
  • Infrahyoids
  • Inferior head of lateral pterygoid (CN V)
• Muscles of mastication

  • Play important roles in masticatory functions, speaking, yawning, and swallowing
• Articular disk


  • Posterior band (PB) attachment is divided into 3 parts: Temporal part (superior), Intermediate part, Condylar part (Inferior)
• Muscles of Mastication

  1. Elevator muscles

  2. Depressor muscles
• Elevator muscles

  Muscles that close the mandible
• Elevator muscles

  • Superior head of lateral pterygoid
  • Medial pterygoid
  • Masseter
  • Temporalis
• Inferior head of Lateral Pterygoid

  Origin: on the outer surface of the lateral pterygoid plate, Insertion: the anterior surface of the neck of the condyle
• Superior head of Lateral Pterygoid

  Origin: on the greater sphenoid wing, Insertion: into the articular capsule, anterior aspect of the articular disk, and neck of the condyle
• Masseter


  Origin: the zygomatic arch, Insertion: the region of the second molar on the lateral surface of the mandible to the posterior lateral surface of the ramus, Function: Elevation - forceful jaw closing (elevates the jaw) and in protrusion of the mandible
• Medial Pterygoid


  Origin: the medial surface of the lateral pterygoid fossa, Insertion: the medial surface of the angle of the mandible and on the ramus up to the mandibular foramen, Function: Elevation, Protrusion, Side to side mandibular motion to help with the grinding of food
• Temporalis Muscle


  Fan-shaped with anterior fibers (vertical), mid fibers (oblique) and posterior fibers (horizontal), Origin: in the temporal fossa and lateral surface of the skull, Insertion: coronoid process and ascending ramus, Function: The posterior fibers retrud the mandible on closure, The ant. & mid fibers elevate the mandible
• Depressor muscles


  Muscles that OPEN the mandible
• Depressor muscles


  • Suprahyoid muscles
  • Infrahyoid muscles
  • Inferior head of lateral pterygoid
• Suprahyoid muscles


  Extend superiorly from the hyoid bone to the mandible
• Infrahyoid muscles


  Extend inferiorly from the hyoid bone to the clavicle (collarbone) and sternum (breastbone) and adjacent structures
• Digastric


  Origin: Anterior belly - lingual surface of the mandible at the midline, Posterior belly - Mastoid notch of temporal bone, Insertion: A tendon between the anterior and posterior digastric muscles that is attached by a looplike strip of fascia to the hyoid bone, Function: jaw opening and balancing mandibular movements
• Geniohyoid


  Origin: inferior genial tubercle, Insertion: on the anterior surface of the hyoid bone, Function: raises the tongue/hyoid bone superiorly/anteriorly during deglutition
• Mylohyoid


  Origin: Mylohyoid ridge on mandible, Insertion: body of the hyoid bone, Function: elevates floor of mouth, tongue, hyoid bone and depresses mandible
• Stylohyoid


  Origin: Styloid process of temporal bone, Insertion: body of the hyoid bone, Function: elevates and retract the hyoid bone during swallowing
• Omohyoid


  Origin: Inferior belly - superior border of scapula, Superior belly - Intermediate tendon, Insertion: Inferior belly - intermediate tendon, Superior belly - body of hyoid bone, Function: Depresses and retracts hyoid and larynx
• Sternohyoid

  Origin: Manubrium of sternum, medial end of clavicle, Insertion: Inferior border of body of hyoid bone, Function: Depresses hyoid bone
• Sternothyroid

  Origin: posterior surface of manubrium of sternum, costal cartilage of rib 1, Insertion: Oblique line of thyroid cartilage, Function: Depresses the larynx