Occlusion - Intro, terminology and centric relation Flashcards
Why study occlusion?
Failure of restorations Fractured teeth and restorations Overeruption and tilting of 16, 17 Undercontoured amalgams Fractured crowns - if heavy ICP have metal backings on crowns rather than porcelain Worn teeth opposing porcelain crown Treatment of complex restorative cases Treatment of tooth wear Effects - localised perio, loss of tooth vitality, facial pain due to parafunction
Mandibular movements?
Lateral excursions
Protrusive excursion
Working and non-working side
Name the mandibular positions and define them
Intercuspal position - Position of mandible when there is maximum intercuspation of the teeth
Retruded contact position - 1st tooth contact when the condyles are fully seated in the glenoid fossa
Centric relation - Relation of the mandible to the maxilla when the condyles are seated in the uppermost position in the glenoid fossa. Allows a range of movement - 25mm when the condyles are fully seated in the glenoid fossa. Optimum position for neuromuscular system - position of muscles of mastication are able to fully contract and relax = Hinge movement
What is the Terminal hinge axis?
Condyles hinge about a horizontal axis when it’s in CR. 25mm. = Where you can draw a horizontal line through the condyles. Lateral pterygoids are relaxed in this position
What can cause pain/inflammation?
When RCP and ICP do NOT coincide
How does protrusive excursion vary in class I, II and III? Variation in anterior open bites?
When anteriors are in contact in ICP - the contacts in protrusive excursion are determined by their occlusal relationship class I - anterior teeth class II - anterior teeth (shallower/steeper) class III and AOB - No OB, no anterior guidance from upper incisors = guidance from posterior teeth = if crown on posterior tooth remember this tooth will likely be involved in protrusive excursions = make sure it's in harmony with ICP, lateral and protrusive excursions
What happens to the condyles in protrusive excursion?
Condyles move forwards and downwards
Lateral excursions - working side and non-working side?
Working side - the side the jaw is moving to
On the working side guidance can be canine guided, group function (more than 1 guiding tooth)
Non-working side - the side opposite to which the jaw is moving
What should posterior teeth on non-working side contacts do? What can non-working side contacts lead to?
Posterior teeth should separate to avoid destructive forces on the inclines of the teeth
Can lead to failed restorations and occlusal disharmony
What happens to the condyles in lateral excursions? (Bennett movement)
(Bennett stuff not that important)
Bodily shift of the mandible towards working side during lateral excursions followed by rotation around the vertical axis = condyle moves laterally
The slacker the TMJ ligaments = greater the movement (0-4mm, average 1mm)
What is the bennett angle?
Angle in the horizontal plane between the sagittal plane and the downward, inward and forward path of the non-working condyle
(NWS condyle moves down, forwards and inwards)
What is the mean bennett angle?
7.5 degrees
Muscle activity in CR?
No tooth interferences = condyle-disc assembly can slide all the way up to the eminentia until stopped by bone
Lateral pterygoids can relax as there is no stimulus for muscle hyperactivity - the condyles are braced by bone
How to find CR?
Stabilise head
Position fingers on lower border of mandible
Thumbs on symphysis (chin)
Gentle touch, manipulate jaw hinges slowly open and closed
Gente guide condyles upwards with little fingers
How to record CR?
Anterior Jig - Flat anterior stop separates posterior teeth, allowing elevator muscles to seat condyles
Record using wax or silicone
