Intro, Terminology, Centric Relation Flashcards
Reasons to study occlusion (9)
- to prevent failure of routine restorations
- to prevent fractured teeth, restorations and crowns
- to prevent overerupting and tilting of teeth
- to prevent wearing of teeth opposite crowns
- for treatment of complex restorative cases
- for treatment of tooth wear
- to prevent periodontitis
- to prevent loss of tooth vitality
- to prevent facial pain due to parafunction
Mandibular positions (2)
ICP (intercuspal position)
RCP (retruded contact position)
Two positions associated with RCP
Centric relation
Terminal hinge axis
Mandibular movements (3)
From side to side (lateral excursions)
Forwards (protrusive excursion)
Working and non-working side
ICP definition
The position of the mandible when there is maximum intercuspation of the teeth
Centric Relation definition
Relation of mandible to maxilla when condyles are seated in midmost uppermost position in the glenoid fossa
Is centric relation a jaw relationship or a tooth relationship? (3)
Jaw relationship
- optimum position for neuromuscular system
- muscles of mastication are able to fully contract and relax
- leads to efficient, pain free muscular function
What is the range of movement within centric relation? (2)
Hinge movement
25mm
Terminal Hinge Axis definition
When the condyles hinge about horizontal axis in centric relation
Muscles in Terminal Hinge Axis
Lateral Pterygoids can relax, because there is no
stimulus for muscle hyperactivity – the condyles
are braced by bone
Is RCP related to the jaws or the teeth? (2)
Teeth
First tooth contact when condyles are fully seated in glenoid fossa
RCP vs ICP (3)
Usually these do not coincide
-we can close to RCP then slide to ICP
When they are different the muscles may be in confict, causing trigger sites of pain/ inflammation
Vh or vH
Protrusive excursion - class I vs class II vs class III vs AOB
Class I - anterior teeth
Class II - anterior teeth (shallower/ steeper)
Class III and AOB - no overbite, no anterior guidance from upper incisors so guidance from posterior teeth
What happens to the condyles in protrusive excursion?
Condyles move downwards and forwards - depends on condylar angle
Lateral excursions - working side (2)
The side the jaw is moving to
Guidance can be in canine guidance or group function
Lateral excursions - non-working side (2)
The side opposite to which the jaw is moving
Posterior teeth should ideally separate in order to avoid destructive forces on inclines of teeth
Non-working side interferences
Non-working side contacts can lead to failed restorations and
occlusal disharmony
What happens to the condyles in lateral excursions?
Working side: Bennett movement
Non-working side: Bennett angle
Bennett movement (2) (Bennett shift/ lateral shift)
Bodily shift of mandible towards working side during lateral excursion followed by rotation around vertical axis
The slacker the TMJ ligaments, the greater the movement
Average Bennett movement
0-4mm
Average 1mm
Bennett angle definition
The angle in the horizontal plane between sagittal plane and downward, inward and forward path of non-working condyle
Mean Bennett angle
Mean Bennett angle is 7.5 degrees
How do we find Centric Relation? (5 steps plus name of technique)
Dawson technique:
- Firmly stabilise head
- Position fingers on lower border of mandible
- Thumbs on symphysis - no pressure yet
- With very gentle touch, manipulate so that jaw hinges slowly open and close FREELY
- Gently but firmly guide condyles upward with little fingers
Verification of centric relation after Dawson technique
To verify, once mandible is freely hinging , apply firm
upward pressure with little fingers. Only assume CR is
obtained if there is no discomfort.
This position should be consistently repeatable.
Recording centric relation - anterior jig (2 steps and how it works)
Flat anterior stop separates posterior teeth, allowing elevator muscles to seat condyles 1. Manipulate to centric relation 2. Record using wax and silicone
When is CR useful for restorative dentist? (5)
- Routine restorations
-assess preoperatively – if RCP contact on tooth to be
restored consider changing type of restoration or contact
point - Occlusal reorganisation
-complex restorative cases – ICP should = RCP - Diagnosis of TMJ dysfunction
-construct splint in CR – neuromuscular dissociation - Occlusal analysis & equilibration
-changing ICP to = RCP – only for experts! - Complete denture construction
-complete dentures are made so RCP=ICP as this is
reproducible and comfortable for pt
