3. Repairs and Additions

Question 1

How do you repair a fractured PMMA (acrylic) base with pecies that fit precisely together

Answer 1

• Gather the pieces
• Lute them together with sticky wax
• Block out undercuts
• Pour a matrix in plaster (or putty)
• Cut away a gap between the two pieces
• Add self-cure PMMA in excess
• Pressure pot at 10 lbs/sq in for 20 mins
• Trim and polish

Question 2

How do you repair a denture with a fractured PMMA base without the pieces or with pieces that don’t fit together

Answer 2

• Pick up impression
• Self-cure PMMA repair on master cast
• Construct new piece

Question 3

How do you fix a denture after a patient has brokwn a tooth off but kept the toothpiece

Answer 3

• Make a matrix (so tooth remains in same position)
• Grind acrylic away
• Add self-curing acrylic
• Finish and polish

Question 4

How to adda tooth to a partial due to an extraction

Answer 4

-Pick up impression
-Opposing cast
-May need to add a clasp as well if the tooth was an abutment
-Sandblast the metal
-Metal and PMMA bond is made with 4-META
-

Question 5

Which repair is easier when there is framework or acrylic (closer/further) from the repair site

Answer 5

closer

Question 6

How does 4-META promote a bond between metal and PMMA

Answer 6

• Lowers surface tension
• Promotes bond/adhesiosn
• Prevents thin areas of PMMA from separating from metal

Question 7

Fractured clasp may be the result of

Answer 7

• Repeated excess flexure
• Defect in metal
• Nick or bend mark
• Incorrect removal
• Patient drops RPD
• WW breaks due to overheating during soldering to frame

Question 8

Clasps (near/far) from acrylic can’t be repaired easily

Answer 8

-far

Question 9

What type of clasp is used to replace a fractured circumferential clasp

Answer 9

WW

Question 10

How do you repair a fractured clasp

Answer 10

• Pick up impression
• Survey tooth
• Specify wire gauge (18 or 19)
• Adapt wire to tooth and bring to lingual
• Make a recess in the acrylic denture base and adapt the lingal aspect of the wire to that
• Can’t solder (retained by PMMA)
• Self cure PMMA added and finished

Question 11

Fractured rests most commonly occur where and the most common reson for a fractured rest is

Answer 11

• Most occur at the marginal ridge

- Reason is insufficient rest prep (too shallow)

Question 12

What are the steps to replace a rest

Answer 12

• Deepen the rest
• Pick up impression
• Add rest to RPD via soldering

Question 13

Fractured major/minor connector fracture are the result of

Answer 13

• Defect in framework casting

- Major accident by patient

Question 14

Repairing major/minor connectors is (easy/difficult) and why

Answer 14

difficult (consider remaking RPD)

• Alignment of pieces not possible due to RPD framework distortion
• Can’t stabilize fragments during pick up impression

Question 15

List the different types of soldering and welding

Answer 15

Soldering

• Electric
• Torch

Welding
-Laser

Question 16

Describe the differences between torch soldering, electric soldering, and laser welding

Answer 16

Torch
-Requires removal of all acrylic

Electric

• May require removal of acrylic
• Smaller area heated than torch
• Less prep (no refractory cast)
• Can’t solder adjacent to PMMA due to heat

Laser

• No removal of acrylic needed
• Small beam (0.2-2 mm diameter)
• Melts metal in very small area (up to 4 mm deep)
• Minimal distortion

Question 17

Diameter of laser welding

Answer 17

0.2-2 mm

Question 18

Depth of laser welding

Answer 18

4mm

Question 19

Which soldering requires removal of all acrylic

Answer 19

torch

Question 20

does electric welding require removal of acrylic? laser?

Answer 20

yes- some…. no