Jaw relations and registration Flashcards
RFH and OFH
Rest face height > occlusal face height
Vertical jaw relations
Rest face height = relaxed, not fixed
Occlusal face height is fixed position
Freeway space
Difference between RFH and OFH
Ideally 2-4mm
Some pxs need larger freeway space to aid adaptation
Increasing OFH reduces FWS (inversely proportional)
Horizontal jaw relations
ICP and retruded position
Retruded position
First point of ccontact at desired occlusal face height in rotational movement of lower jaw (centric relation)
RP + (RFH-3mm) = pain-free dentures
ICP
Intercuspal position
Point of maximum intercuspation
Clinical procedure
- Special equipment
- Lip support and tooth position
- Record jaw relations
- occlusal face height
- retruded jaw position - Confirm tooth characteristics: shape, size, shade
Blocks
Wax registration rims
Special equipment
Dividers Foxes plane guide Wax knife heaters Rim inclinator Hot pate Hot air burner
Three key measurements
The OFH with old dentures in
The RFH with px’s most comfortable denture in
Determine what you want OFH to be when new dentures are made
Why is OFH of old set so important?
View px from front & profile when in occlusion
Make reasonable assumption on px: if right, midly overclosed, grossly overclosed or has no FWS
OFH of old dentures much easier to measure than RFH as px has something to bite against that is relatively reproducible
Pxs struggle to adapt to large changes in OFH
Beware mobile metalis
Not always natural for lips to be touching in severe class 2 and class 3 cases
Beware mobile mentalis
Mentalis can change occlusal face height - they need to be relaxed
How can I relax my px to find RFH
Ask px to touch lips together very gently whilst staring at distant object 1, 2, 3 test Gentle imperceptible blowing Say 'mmm' Look away and wait until px is relaxed Measure with px only wearing one denture
Fox’s Bite Plane
Measures Ala-tragal line
Upper teeth should slope up parallel to plane
Mark incisal plane parallel to interpupillary line at approx. level of upper lip
Mark posterior occlusal plane parallel to alar of nose/ tragus of ear
Adjust rim using
Inclinator and hot air burner
Confirm occlusal plane is approx parallel to alar/ tragus line using Fox’s plane guide
Wax can be added to improve lip support
Insert lower block & trim until meeting evenly in retruded position at predetermined OFH
Why do we use finger rests on registration blocks?
Finger rests allow clinician to maintain secure hold of mandible and prevent registration blocks from moving during registration process
Put silicone in gaps
Centre line marking
Face in line with px
Look where midline frenum is
If dealing with Class II ensure scribed centre line goes through occclusal plane
Notching of both rims function
To allow accurate mutual location using some form of intermediate rigid fixation
Why do we use occlusal notches on both upper and lower registration blocks?
They allow silicone to seal blocks together in unique position & allow technicians to reattach blocks in correct position if they come apart
How do we notch rims
Upper and lower opposing occlusal notches should be placed bilaterally
Place small amount of registration paste on either side in region of notches
Lower jaw manipulated into retruded arc of closure - tongue retraction, & occlusion, extruding registration paste into location notches
If blocks touch perfectly at correct OVD
Use gently warmed wax
Remove part of rim
Which appears likely to interfere with occlusion
Confirm tooth characteristics
Match shade of tooth with px’s complexion but make sure px agrees with choice
Select appropriate shape and size, using px’s face shape and body size as reference points
What gives realism to teeth
Use of simulated attrition and stains
Mould selection
Are teeth small medium or large
If face round, tapered or square
Ask px
