JAW RELATIONSHIPS & REGISTRATION

define resting face height

resting face height: the distance between two fixed points when the mandible is in the habitual postural position when the patient is relaxed and the condyles are in the neutral position in the glenoid fossa

define occlusal face height

occlusal face height: the distance between two fixed points when the upper and lower dentures are contacting in their maximum intercuspation

what is the ideal difference between resting face height and occlusal face height

3mm (should be replicated in complete dentures)

what is this difference in face height known as

the freeway space: the difference between resting face height and occlusal face height

what two values are inversely proportional

occlusal face height and freeway space

what are resting face height and occlusal face height collectively known as

vertical jaw relations

define intercuspal position

intercuspal position: the relationship between the mandible and maxilla when the teeth are in maximum intercuspation

define centric relation

centric relation: the jaw position when the condyle is in the most anterior and superior position in the glenoid fossa

what are intercuspal position and centric relation collectively known as 

horizontal jaw relations

what is the aim of complete denture registration (?)

• to ensure that RCP = ICP

• to record the relationship between the maxilla and mandible when a person bites together

what is the clinical procedure after receiving the wax blocks

1. equipment to alter the wax blocks

2. lip support and tooth position

3. record jaw relations

4. confirm tooth characteristics (shape, size, shade)

what should be done before the wax blocks are put in the patient’s mouth

they should be sterilised

what equipment is needed to adjust the wax blocks

• wax knife heater

• calipers: measuring RFH and OFH

• Fox’s Plane Guide: allows you to get wax block parallel to the inter-pupillary line and ala-tragal plane)

• occlusal rim inclinator: used to ensure wax rim is parallel with the ala-tragal plane

• hot plate

• safe air burner: used to gently warm wax up

what measurement is used to indicate sufficient/ insufficient lip support

• the nasolabial angle should be approx. 90°

• if the nasolabial angle is greater than 90°, the upper lip is not supported enough

what key jaw relation measurements are required 

• the OFH with old dentures in

• the RFH with the patient’s most comfortable denture in 

» determine what you want the OFH to be when the new dentures are made 

key points to remember when taking RFH and OFH measurements

• examine the patient when they are in occlusion 

• OFH of the old dentures is much easier to measure than RFH because the patient has something to bite against

• patients struggle to adapt to large changes in OFH so do not significantly change this measurement

• it is not always natural for the lips to be touching in severe class II and III cases

methods to use to relax patients to find the resting face height

• ask patients to whisper 1, 2, 3

• gentle imperceptible blowing

• make the ‘m’ sound

how should the upper wax blocks be marked

• scribe lines parallel to the inter-pupillary and ala-tragal planes with wax knife

diagram of using a Fox’s Plane Guide

if lip support is poor, what can be done to improve this

• wax can be added

• ensure both parts of the wax are warmed when adding wax

when should the lower block should be put in

• after the upper block is perfect

how should the lower block be trimmed

• determine retruded contact position with both blocks in

• trim until the blocks meet evenly in centric relation at predetermined OFH

• scribe a line on lower block that is parallel to the upper

why are finger rests put on wax registration blocks

• allow the clinician to maintain a secure hold and prevent the wax block from moving during the registration process

what reference points should be marked on the wax blocks

• the centre line (use midline frenum)

• the canine line 

what is the final step in adjusting the wax blocks 

• notching both of the rims to allow the technicians to reattach the blocks in the correct position if they come apart 

how are notches made on the wax blocks 

• occlusal notches are made on the upper and lower registration blocks

• they should be placed bilaterally and should directly oppose each other

• index fingers should fit in the notches 

what is bite registration paste used for 

• silicone bite registration paste is applied to the finger rest notch region using a gun cartridge to seal the blocks together in a unique position

• this means the technician can reattach the blocks if they come apart

when can bite registration paste be filled intraorally

• silicone can be used to fill in notches intraorally in patients who are good at replicating their centric relation

• (gently warm the wax to stick together, then fill in the notches)

what is a useful way to get a patient into centric relation

• close mouth halfway 

• curl tip of tongue to the back of the palate

• slowly complete the bite 

what should you always check for after registration

• heel clash

• after registration, put the blocks back on the cast to ensure the back of the casts do not clash

• if they do, the cast will have to be trimmed

how should new denture teeth be selected

• use the old set of dentures as a guide

• if no old set, see if the patient has an old picture of them smiling

• if neither is possible, use the patient’s size and face shape as a guide

what are the different shapes in tooth mould selection

• K: tapered (unisex)

• O: oval (generally more feminine)

• S: square (generally more masculine)

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• teeth come in small, medium and large

how can teeth be customised

• wear and tear can be added

• stained fillings can also be added 

what is a diastema

diastema: a gap between two teeth (most commonly between upper central incisors)

example of instructions to the lab