occlusion

• Intercuspal contact (IC)

  Contact between the cusps, fossa and marginal ridges of opposing teeth

  
• Intercuspal Position (ICP)


  Position of the jaw when the teeth are in intercuspal contact (IC)

  
• Retruded Contact Position 


  Guided occlusal relationship occurring at the most retruded position of the condyles in the joint cavities
• Maximum Intercuspation Position


  Maximum upper and lower tooth contact that occurs with clenching (heavy bite force), when the number and area of tooth contacts are greatest

  
• Centric Occlusion (CO)


  Tooth contact position when the jaw is in centric relation (CR)

  
• Centric relation 


  Maxillomandibular relationship in which the condyles are located in an antero-superior position in contact with the central bearing surface of the articular disc, against the articular eminence

  
• Rest Position of the Mandible (RP)


  When the mandible is in rest position, the teeth are held slightly separated. The mandible is held by the sling of medial pterygoid and masseter

  
• Mandibular Movements

  1. Rotational movements

  2. Translational movements
• Rotational movements


  • Occur when the condyle rotates around an imaginary axis
  • Described around 3 imaginary axes: sagittal, horizontal, vertical
• Rotation around horizontal axis

  • In CR, the mandible can only execute hinge opening and closing
  • Pure rotational movements occur during mouth opening in the sagittal plane in the range of 20-25 mm when measured between the upper and lower incisors
  • When the mouth is open wider than this, the mandible "translates"

  
• Rotation around vertical axis

  • The vertical axis passes through the working condyle during lateral excursion of the mandible
• Rotation around sagittal axis

  • The sagittal axis is an anteroposterior axis, which passes through the working condyle during the lateral excursion of the mandible
  • The non-working condyle is seen rotating downwards and medially
• Translation

  When the condyle and disc move together along the articular eminence as in the mandibular protrusion
• Mediotrusive/non-working/balancing side

  Side of the jaw which moves towards the midline (or medially) in lateral jaw movement

  
• Laterotrusive/working side

  Side of the jaw which moves laterally away from the midline in jaw movement

  
• Bennett movement

  Bodily lateral movement or lateral shift of the mandible resulting from the movement of the condyle along the lateral inclines along the mandibular fossae in lateral jaw movements

  
• Bennett angle

  Angle formed by movement of the non-working condyle with the sagittal plane during lateral jaw movement

  
• Envelope of Motion


  Full range of jaw movement in the 3 planes by tracing the path of the lower incisor teeth as the jaw is guided through the border paths

  
• Border Movement of the Mandible or Posselt's Envelope of Motion

  1. Posterior opening border

  2. Anterior opening border

  3. Superior contact border

  4. Functional movement
• Posterior Opening Border

  • Occurs in 2 stages: Stage 1 - pure rotation (20-25 mm), Stage 2 - translation (>20-25 mm)
• Anterior Opening Border

  • Occurs when closure accompanied by contraction of inferior lateral pterygoid, not a pure hinge movement due to eccentricity
• Superior Contact Border


  • Determined by the occlusal and incisal surfaces of the teeth

  
• Functional Movement


  • Occur during functional activity such as chewing and speech, take place within the border movement so they are considered free movements, require ICP so they start below ICP
• Border Movement

  • Limited anteriorly by the anterior guidance, posteriorly by the TMJ
• Anterior guidance


  • Overbite, overjet
• Posterior limitation by TMJ

  • Inclination of the articular eminence, morphology of the medial wall of the glenoid fossa, shape of the condyle
• Mandibular Movements


  Protrusion/Retrusion, Lateral excursion, Depression/Elevation
• Muscles that depress the mandible

  • Supra- and infrahyoid muscles, inferior head of the lateral pterygoid
• Jaw-closer muscles


  • Masseter, temporalis, medial pterygoid, superior head of the lateral pterygoid

  
• Mandibular movement during normal function and during parafunction (e.g. bruxism) involve complex neuromuscular patterns originating in part in a pattern generator in the brainstem and modified by influences from higher centers i.e. the cerebral cortex and basal ganglia and from peripheral influences (e.g. the periodontium, muscles etc)
• Mandibular Opening

  • Digastric, mylohyoid and geniohyoid are active, lateral pterygoid muscles show initial and sustained activity, in forced depression the digastric muscle is activated almost as soon as the lateral pterygoid muscle is
• Mandibular Closing

  • With no tooth contact: masseter and medial pterygoid muscles, with resistance: temporalis, masseter and medial pterygoid

  
• Depression of the Mandible

  • Requires extreme anterior translation (protrusion) of each mandibular condyle relative to its mandibular fossa, the articular disc translates anteriorly along with each mandibular condyle
• Elevation of the Mandible

  • The disc is "reseated" into the joint as the mandible is elevated and retrudes (retracts) during closure of the mouth, the articular disc is essential in minimizing the contact stress between the mandibular condyle and the articular eminence of the temporal bone

  
• Mandibular Retrusion

  • Temporalis muscle (post. fibers) and suprahyoid & infrahyoid muscles, temporalis muscles (post. and middle fibers)

  
• Mandibular Protrusion

  • Lateral & medial pterygoid and masseter, with resistance: lateral and medial pterygoid and masseter + suprahyoid muscle group, with teeth in occlusion: pterygoid and masseter, combined protraction and opening: medial and lateral pterygoid, masseter and sometimes temporalis muscles (ant. fibers)

  
• Lateral Movement

  • Ipsilateral contraction of temporalis muscle (post. & middle fibers), contralateral contraction of the lateral and medial pterygoid muscles, temporalis muscle (ant. fibers)
• Chewing

  • Speed, duration and form vary with type of occlusion, kind of food and presence of dysfunction, dimensions: 16-20 mm vertical, 3-5 mm lateral, duration: 0.6-1 second, occlusal contacts in centric occlusion in at least 80%-90% of all chewing cycles, max chewing force in centric occlusion lasts for 40-170 milliseconds
• Swallowing

  • Involves most of the tongue muscles and buccal musculature, activity of suprahyoid+++, geniohyoid++, medial pterygoid+++, temporalis, masseter: active with occlusal contact
•  Digastric, mylohyoid and geniohyoid are active

  during jaw opening, either slowly or maximally

  against resistance.