Intro, Terminology, Centric Relation

Question 1

Reasons to study occlusion (9)

Answer 1

• 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

Question 2

Mandibular positions (2)

Answer 2

ICP (intercuspal position)

RCP (retruded contact position)

Question 3

Two positions associated with RCP

Answer 3

Centric relation

Terminal hinge axis

Question 4

Mandibular movements (3)

Answer 4

From side to side (lateral excursions)
Forwards (protrusive excursion)
Working and non-working side

Question 5

ICP definition

Answer 5

The position of the mandible when there is maximum intercuspation of the teeth

Question 6

Centric Relation definition

Answer 6

Relation of mandible to maxilla when condyles are seated in midmost uppermost position in the glenoid fossa

Question 7

Is centric relation a jaw relationship or a tooth relationship? (3)

Answer 7

Jaw relationship

• optimum position for neuromuscular system
• muscles of mastication are able to fully contract and relax
• leads to efficient, pain free muscular function

Question 8

What is the range of movement within centric relation? (2)

Answer 8

Hinge movement

25mm

Question 9

Terminal Hinge Axis definition

Answer 9

When the condyles hinge about horizontal axis in centric relation

Question 10

Muscles in Terminal Hinge Axis

Answer 10

Lateral Pterygoids can relax, because there is no
stimulus for muscle hyperactivity – the condyles
are braced by bone

Question 11

Is RCP related to the jaws or the teeth? (2)

Answer 11

Teeth

First tooth contact when condyles are fully seated in glenoid fossa

Question 12

RCP vs ICP (3)

Answer 12

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

Question 13

Protrusive excursion - class I vs class II vs class III vs AOB

Answer 13

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

Question 14

What happens to the condyles in protrusive excursion?

Answer 14

Condyles move downwards and forwards - depends on condylar angle

Question 15

Lateral excursions - working side (2)

Answer 15

The side the jaw is moving to

Guidance can be in canine guidance or group function

Question 16

Lateral excursions - non-working side (2)

Answer 16

The side opposite to which the jaw is moving

Posterior teeth should ideally separate in order to avoid destructive forces on inclines of teeth

Question 17

Non-working side interferences

Answer 17

Non-working side contacts can lead to failed restorations and
occlusal disharmony

Question 18

What happens to the condyles in lateral excursions?

Answer 18

Working side: Bennett movement

Non-working side: Bennett angle

Question 19

Bennett movement  (2)
(Bennett shift/ lateral shift)

Answer 19

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

Question 20

Average Bennett movement

Answer 20

0-4mm

Average 1mm

Question 21

Bennett angle definition

Answer 21

The angle in the horizontal plane between sagittal plane and downward, inward and forward path of non-working condyle

Question 22

Mean Bennett angle

Answer 22

Mean Bennett angle is 7.5 degrees

Question 23

How do we find Centric Relation? (5 steps plus name of technique)

Answer 23

Dawson technique:

1. Firmly stabilise head
2. Position fingers on lower border of mandible
3. Thumbs on symphysis - no pressure yet
4. With very gentle touch, manipulate so that jaw hinges slowly open and close FREELY
5. Gently but firmly guide condyles upward with little fingers

Question 24

Verification of centric relation after Dawson technique

Answer 24

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.

Question 25

Recording centric relation - anterior jig (2 steps and how it works)

Answer 25

Flat anterior stop separates
posterior teeth, allowing elevator muscles
to seat condyles
1. Manipulate to centric relation
2. Record using wax and silicone

Question 26

When is CR useful for restorative dentist? (5)

Answer 26

1. Routine restorations
   -assess preoperatively – if RCP contact on tooth to be
   restored consider changing type of restoration or contact
   point
2. Occlusal reorganisation
   -complex restorative cases – ICP should = RCP
3. Diagnosis of TMJ dysfunction
   -construct splint in CR – neuromuscular dissociation
4. Occlusal analysis & equilibration
   -changing ICP to = RCP – only for experts!
5. Complete denture construction
   -complete dentures are made so RCP=ICP as this is
   reproducible and comfortable for pt