Denture Repairs and Additions Flashcards
What are the common types of dental fracture?
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
What are the causes of dental fracture?
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
What must be determined when a denture fractures?
Whether it is a design or fabrication issue
Whether a new denture is requires
How are midline cracks in dentures repaired
If fractured pieces can be located together, disinfect & send to lab (no impression needed), cast poured, fractured area removed, new acrylic processed
What is done if part of acrylic flange is lost?
Take impression with fractured denture in mouth
Disinfect
Cast poured with denture in place
New acrylic poured to replace defect
How is loss of acrylic tooth on a denture managed?
If patient has tooth- rebond
If not- take impression with denture in situ and send to lab
What features may be added to a Co/Cr denture when it is getting repaired? How is this done?
May need to add retentive tags
-> solder on tags and/or use 4-META
Silicoat Co/Cr to retain acrylic on Co/Cr
What materials can be used in temporary denture repair? (chair side)
Self-cure acrylic- difficult to use and time consuming
Cyanoacrylate glue- consider new denture at this stage
What kind of strengthens can be added to dentures? What is the issue with them?
Wire mesh
Glass-fibre mesh
Stainless steel wire
-> often have opposite effect and weaken denture as it is not one piece
What is the stance on self denture repair?
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
On what type of dentures can additions be done?
Partial Only
-> usually involves adding teeth or clasps
What are the types of additions?
Immediate addition
Post-immediate addition
Retentive additions- addition of wrought stainless steel clasp (impression with denture in situ required)
What is an immediate addition?
When a tooth is lost after denture construction & tooth added on the day of tooth extraction
What is a post immediate addition?
When a tooth is lost after denture construction & at a later date a tooth added
What are the issues with additions?
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
What type of co/cr denture would be impossible to add lower incisor to?
Lingual bar
Why are additions and repairs not possible in Flexible (nylon) dentures?
Due to weak bonding between teeth and nylon
generally longevity is short-term
What are the components of the powder used to make Acrylic (PMMA)?
Polymer – PMMA beads
Initiator – Benzoyl Peroxide (0.5 %)
Pigments – salts of Cd/Fe or organic dyes
What re the components of the liquid used to make PMMA?
Monomer – MMA (methacrylate)
Cross linking agent – Ethyleneglycoldimethacrylate (10%)
Inhibitor – Hydroquinone
Activator – ONLY Self cure – N,N’-dimethyl-p-toluidine (1%)
-> allows chair side setting
What are the benefits of using correct powder to liquid ratio when mixing powder and liquid when making acrylic?
Monomer shrinks by 21% on setting
-> using a P:L ratio of 2.5 to 1 reduces shrinkage to 5-6%
What are the stages in setting of acrylic in terms of texture?
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)
What type of reaction occurs during setting of PMMA?
Free radical additions polymerisation
-> Exothermic- spray water on to cool
What is the stages in the curing cycle of heat cure PMMA?
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
What equipment is used on curing of heat cure PMMA?
Water bath
Electric oven
What are the advantages of using acrylic dentures?
- Cheap
- Easy to add to or reline or repair
- Technically easier to make
- Aesthetic
What are the disadvantages of acrylic dentures?
- 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
