Denture Repairs and Additions

Question 1

What are the common types of dental fracture?

Answer 1

Midline- bruxists form microcracks

Tooth detaches from denture base- adhesive failure

Loss of flange

Acrylic saddle detaches from Co/Cr baseplate
-> adhesive/bonding failure

Fracture/bent

Question 2

What are the causes of dental fracture?

Answer 2

Impact

Acrylic in thin section

Work hardening of metal (clasps)

Parafunctional habits

Occlusion – deep overbite

Soft linings- reduces overall fracture resistance

Denture processing problem- porosity (improver mixing)

Bonding between tooth & base acrylic or acrylic & Co/Cr

Question 3

What must be determined when a denture fractures?

Answer 3

Whether it is a design or fabrication issue

Whether a new denture is requires

Question 4

How are midline cracks in dentures repaired

Answer 4

If fractured pieces can be located together, disinfect & send to lab (no impression needed), cast poured, fractured area removed, new acrylic processed

Question 5

What is done if part of acrylic flange is lost?

Answer 5

Take impression with fractured denture in mouth

Disinfect

Cast poured with denture in place

New acrylic poured to replace defect

Question 6

How is loss of acrylic tooth on a denture managed?

Answer 6

If patient has tooth- rebond

If not- take impression with denture in situ and send to lab

Question 7

What features may be added to a Co/Cr denture when it is getting repaired? How is this done?

Answer 7

May need to add retentive tags
-> solder on tags and/or use 4-META

Silicoat Co/Cr to retain acrylic on Co/Cr

Question 8

What materials can be used in temporary denture repair? (chair side)

Answer 8

Self-cure acrylic- difficult to use and time consuming

Cyanoacrylate glue- consider new denture at this stage

Question 9

What kind of strengthens can be added to dentures? What is the issue with them?

Answer 9

Wire mesh
Glass-fibre mesh
Stainless steel wire

-> often have opposite effect and weaken denture as it is not one piece

Question 10

What is the stance on self denture repair?

Answer 10

Discourage this and advise them to return to dental professional for repairs

-> if patient gets this wrong it can render denture useless

REMEMBER- some dentures are unrepairable

Question 11

On what type of dentures can additions be done?

Answer 11

Partial Only

-> usually involves adding teeth or clasps

Question 12

What are the types of additions?

Answer 12

Immediate addition

Post-immediate addition

Retentive additions- addition of wrought stainless steel clasp (impression with denture in situ required)

Question 13

What is an immediate addition?

Answer 13

When a tooth is lost after denture construction & tooth added on the day of tooth extraction

Question 14

What is a post immediate addition?

Answer 14

When a tooth is lost after denture construction & at a later date a tooth added

Question 15

What are the issues with additions?

Answer 15

If chair side and done in self cure it is often temporary

Often the denture will need to be in situ, imp taken and will need to be sent away

Question 16

What type of co/cr denture would be impossible to add lower incisor to?

Answer 16

Lingual bar

Question 17

Why are additions and repairs not possible in Flexible (nylon) dentures?

Answer 17

Due to weak bonding between teeth and nylon

generally longevity is short-term

Question 18

What are the components of the powder used to make Acrylic (PMMA)?

Answer 18

Polymer – PMMA beads

Initiator – Benzoyl Peroxide (0.5 %)

Pigments – salts of Cd/Fe or organic dyes

Question 19

What re the components of the liquid used to make PMMA?

Answer 19

Monomer – MMA (methacrylate)

Cross linking agent – Ethyleneglycoldimethacrylate (10%)

Inhibitor – Hydroquinone

Activator – ONLY Self cure – N,N’-dimethyl-p-toluidine (1%)
-> allows chair side setting

Question 20

What are the benefits of using correct powder to liquid ratio when mixing powder and liquid when making acrylic?

Answer 20

Monomer shrinks by 21% on setting
-> using a P:L ratio of 2.5 to 1 reduces shrinkage to 5-6%

Question 21

What are the stages in setting of acrylic in terms of texture?

Answer 21

Sandy-> stringy-> doughy-> rubbery-> hard

Remove at rubbery stage to stop it front getting stuck in patient’s mouth (have acrylic on table to monitor set)

Question 22

What type of reaction occurs during setting of PMMA?

Answer 22

Free radical additions polymerisation
-> Exothermic- spray water on to cool

Question 23

What is the stages in the curing cycle of heat cure PMMA?

Answer 23

7 hours at 70 degrees (65 required to decompose benzoyl peroxide initiator), 3 hours at 100 degrees

-> do not exceed 100.3 degrees- boiling point of monomer

Question 24

What equipment is used on curing of heat cure PMMA?

Answer 24

Water bath

Electric oven

Question 25

What are the advantages of using acrylic dentures?

Answer 25

• Cheap
• Easy to add to or reline or repair
• Technically easier to make
• Aesthetic

Question 26

What are the disadvantages of acrylic dentures?

Answer 26

• Low impact resistance
• Poor resistance to fracture fatigue – needs to be thick
• Poor impact strength – needs to be thick
• Water absorption & Candida growth
• Allergy to residual monomer
• Denture whitening (alterations in microstructure)
• Risks to technician’s