Clinical Techniques of RPDs (2)

Question 1

Name 2 materials used for master impressions

Answer 1

1. Polyvinylsiloxane type II medium viscosity

2. Alginate (if appropriate)

Question 2

Describe the 5 steps used to modify a master impression tray

Answer 2

1. Check fit of tray in mouth
2. Reduce overextension
3. Correct underextension
4. Apply red impression compound to saddle areas and postdam
5. Perform border moulding

Question 3

What are the benefits of border moulding?

Answer 3

Allows for mucocompressive impression of displaceable saddle mucosa and reduces movement differential between tooth and mucosal supported areas when under occlusal load

Question 4

How is border moulding used if there is little mucosal support?

Answer 4

Greenstick compound used in saddle areas and postdam

Question 5

Name 4 common faults in impressions

Answer 5

1. Tray not in correct position
2. Impression material set before seat or removed too early
3. Tray extension errors
4. Voids / Defect

Question 6

Name 6 causes of voids / defects

Answer 6

1. Air
2. Debris
3. Saliva
4. Blood
5. Drags
6. Insufficient material

Question 7

What is the master cast poured in?

Answer 7

Improved Dental Stone (densite)

Question 8

Name 4 reasons alginate is not first choice for making casts

Answer 8

1. Not accurate enough
2. Dimensionally unstable
3. Tears easily
4. Poorer quality of surface stone detail in poured cast

Question 9

Name 4 reasons alginate may be used for master impressions

Answer 9

1. Gross undercuts (tilted teeth)
2. Large interdental spaces between contiguous teeth
3. Periodontally involved teeth (gross recession / mobility)
4. Patients with poor tolerance / compliance impressions

Question 10

What is the aim of the sub-lingual bar impression technique?

Answer 10

Record functional width and depth of anterior lingual sulcus

Question 11

Describe how the sub-lingual bar technique is carried out

Answer 11

• Tray is modified with soft green impression compound and being trimmed back
• This ensures only soft compound contacts tissues not the tray
• Impression poured in stone and sublingual bar can be designed on cast

Question 12

Name 2 aims of the altered cast technique

Answer 12

1. Obtain compressive impression of mucosa to mimic functional load
2. Load applied to abutment tooth is reduced as greater proportion is borne by edentulous area

Question 13

What is the result of the altered cast technique being carried out accurately?

Answer 13

Greater stability and reduced technique

Question 14

Describe how the altered cast technique is carried out

Answer 14

• Following master impression, cast produced for lower RPD with extension trays
• Master cast has space laid down over DES for tray to be produced
• Impression taken inside DES with zinc oxide eugenol base
• Original master cast modified, new casting seated against model and new stone poured
• Occlusal registration will be made from new stone

Question 15

Name 3 things to check for during a casting trial

Answer 15

1. Check prescription is followed correctly (components in correct position)
2. Check fit in patient’s mouth
3. Check occlusion

Question 16

Name 5 operator errors if the framework fits casts but not in the mouth

Answer 16

1. Impression moved during set
2. Debris / saliva on teeth
3. Air trapped
4. Detached from tray
5. Posterior drag

Question 17

Name 5 technician errors if the framework fits casts but not in the mouth

Answer 17

1. Improperly poured cast
2. Broken teeth from cast
3. Model wear forcing tight casting on and off
4. Movement of natural teeth (long delay between imp and fit)
5. Tooth restorations since impression

Question 18

How is ICP checked for a patient being restored to ICP?

Answer 18

Shimstock foil 8mm

Question 19

Name 4 important things to check for in trial dentures

Answer 19

1. Aesthetics
2. Tooth position
3. Occlusion
4. Polished surfaces

Question 20

Name 4 modifications which may be made to trial dentures before final dentures created

Answer 20

1. Mould
2. Shade
3. Flange design
4. Flange edge

Question 21

Name 5 things to check when inserting a trial denture and ensuring fit

Answer 21

1. Fit
2. Occlusion
3. Activated clasps
4. Check patient can insert and remove denture
5. Instruction in after care

Question 22

Name 3 things to check for during an initial review 1 or 2 weeks after a patient receives a denture

Answer 22

1. Fit surface faults
2. Occlusal surface faults
3. Oral and denture hygeine