Occlusion for partial dentures

Question 1

what is occlusion?

Answer 1

the static relationship between the incising or masticating surfaces of the maxillary and mandibular teeth or tooth analogues

Question 2

how should partial dentures affect the occlusion?

Answer 2

• partial dentures should work in harmony with the patient’s existing occlusion
• the existing occlusion should not be changed unless you have already planned to change it
• conform to the occlusion, don’t change it

Question 3

why do you need to record the occlusion?

Answer 3

• need to know the patient’s existing occlusion so you can conform to it
• facilitates denture design
• helps technician mount casts and set up teeth
• ensure the denture is stable and is not dislodged in function
• important if planning to change the occlusion
• need to know the position of the teeth in relation to each other
• ensure loading forces are applied correctly to teeth and underlying mucosa/bone

Question 4

when do you record the occlusion?

Answer 4

1. primary registration
2. secondary registration
3. framework registration

Question 5

when do you need to record occlusion in the primary registration stage?

Answer 5

• when casts cannot be hand articulated and you need to determine occlusion to design the denture and position rest seats without occlusal interference
• after primary impression, before master impression and cast

Question 6

when do you need to record occlusion in the secondary registration stage?

Answer 6

• when casts cannot be hand articulated
• if you plan to change the occlusion
• if replacing anterior teeth adn providing metal backings, a tooth trial is needed before the framework is constructed
• after master impression and master cast made

Question 7

when do you need to record occlusion in the framework trial stage?

Answer 7

if conforming to occlusion, to ensure the framework does not interfere with occlusion

occlusal rim added to framework to record jaw relationship

Question 8

what are we aiming to establish when recording the occlusion?

Answer 8

• intercuspal relationship (ICR) to allow casts to be articulated and set up the teeth
• occlusal vertical dimension (OVD) - index teeth, re-organising occlusion
• buccal/labial contours of wax record blocks - lip support, incisal plane, occlusal plane
• tooth shade and mould

Question 9

what are index teeth?

Answer 9

teeth that contact the intercuspal position (ICP) and allow easy recording of the OVD
* these teeth contacts should remain the same when the partial denture is in situ - conform to occlusion

Question 10

what is the procedure when conforming to the occlusion?

Answer 10

1. disinfect the record blocks in perform
2. adjust the upper then lower record block
3. record the occlusion
4. check registration fits the casts
5. disinfect record blocks
6. select shade and mould
7. send instructions to lab

Question 11

what is the equipment for trimming the wax blocks?

Answer 11

• hot plate
• no flame
• wax knife
• bunsen burner and palate knife

Question 12

how do you record the occlusion?

Answer 12

1. wax block should have already been adjusted to conform to occlusion
2. ensure the heels are not touching - if they touch it changes the occlusion
3. join the blocks together using pink wax or registration paste

Question 13

what is the procedure when not conforming to the occlusion?

Answer 13

1. disinfect the record blocks in perform
2. adjust the upper then lower record block
3. record the occlusion
4. check registration fits the casts
5. disinfect record blocks
6. select shade and mould
7. send instructions to lab

same as if conforming to occlusion

Question 14

what should you do if the patient does not have enough index teeth to find the occlusion?

Answer 14

• you need to decide the occlusion and OVD
• there may be stable tooth contacts when the mandible is in a retruded position
• if there is no stable tooth contacts when the mandible is protruded, you will have to determine the OVD and occlusion using record blocks

Question 15

how do you change the OVD? when is this done?

Answer 15

• use record blocks to establish the OVD you want
• frequently done with patients with tooth wear using the Dahl principle - provides space for restorations and overeruption
• used if patients are over closed and have TMJ problems or persistent angular cheilitis - reduced creasing and pooling of saliva at commisures

should always be planned and not by accident

Question 16

what is posselt’s envelope?

Answer 16

the position of teeth at different opening positions - the extremes of mandibular movement (border movements in the saggital plane)
* intercuspal position (ICP)
* retruded contact position (RCP)
* rotation of condyle (R)
* translation of condyle (T)
* protrusion (Pr)
* edge to edge incisal contact (E)

Question 17

what position can be used when intercuspal position (ICP) us not possible due to no idex teeth?

Answer 17

centric relation / occlusion
* the comfortable bite
* the habitual bite
* the bite of convenience
* need to compare it to the retruded contact position

Question 18

what is the retruded contact position?

Answer 18

• the first tooth contact when the condyle of the mandible is in a** retruded axis position**
• just behind the intercuspal position (ICP)
• mostly reproducible

Question 19

what are the ways of recording the resting vertical dimension (RVD) and the occlusal vertical dimension (OVD)?

Answer 19

• two dot method
• Willis bit gauge

Question 20

how do you record the resting vertical dimension (RVD) with the two dot method?

Answer 20

• choose point on nose and chin with minimal movement
• jaw relaxed, lips just touching, space between posterior teeth
• use dividers to measure distance between dots
• distance between divider arms = RVD

Question 21

how do you record the resting vertical dimension (RVD) with the Willis bite gauge?

Answer 21

• jaw relaxed, lips just touching, space between posterior teeth
• fixed arm in the nasio labial position
• sliding arm under the chin
• distance between sliding and fixed arms = RVD

Question 22

how do you record the occlusal vertical dimension (OVD) with the two dot method?

Answer 22

• choose point on nose and chin with minimal movement
• teeth in intercuspal position (ICP)
• use dividers to measure distance between dots
• distance between divider arms = RVD

Question 23

how do you record the occlusal vertical dimension (OVD) with the Willis bite gauge?

Answer 23

• teeth in intercuspal position
• fixed arm in the nasio labial position
• sliding arm under the chin
• distance between sliding and fixed arms = RVD

Question 24

what is free way space?

Answer 24

the space between the occluding surfaces of the maxillary and mandibular teeth when the mandible is in psychological resting position
* free way space = RVD - OVD = 2-4mm

Question 25

how do you adjust the wax block when intercuspal position is not possible?

Answer 25

* adjust the upper occlusal rim * the occlusal and incisal plane is appropriately oreintated in relation to the remaining upper natural teeth or the facial reference points * if there is an anterior saddle, ensure the rim indicates the appropriate incisal level and degree of lip support * adjust the lower occlusal rim * no teeth will be touching as you are determining the OVD * then record the occlusion

Question 26

when writing the lab prescription, what do you want the lab to do with the work and what do you want back after the primary occlusion?

Answer 26

* want the lab to **articulate** the casts to **occlusion recorded** * want to get back **special trays** with correct spacing for type of material used

Question 27

when writing the lab prescription, what do you want the lab to do with the work and what do you want back after the secondary occlusion?

Answer 27

* want the lab to **articulate** the casts to **occlusion recorded** * want to get back the **try-in tray with wax**

Question 28

when wanting to change the OVD, what can you use instead?

Answer 28

* centric relation * retruded contact position (RCP)

Question 29

what is the difference between intercuspal position (ICP) and retruded contact position (RCP)?

Answer 29

***intercuspal position (ICP)*** * **sufficient** number of index teeth * **stable** occlusion * **variable** through life * usually more **anterior** than RPC * **simpler to record** the occlusion ***retruded contact position (RCP)*** * **insufficient** number of index teeth * **unstable** occlusion * **reproducible** position * usually more **posterior** than ICP * **more challenging to record** the occlusion