What are the three common types of temporary materials?
- PMMA
- PEMA
- Bis-acryl composite
What component do all temporary materials have in common?
resin
What is the brand name for temporary PMMA?
Jet
What are brand names for temporary PEMA?
Trim II
Snap
What are brand names for temporary bis-acryl composite?
Protemp4
Quicktemp
What is the brand name for temporary UDMA
Provipont DC
What are the beneficial properties of PMMA (e.g. Jet)
- powder/liquid formulation
- self-curing
- good marginal fat
- good transverse strength
- polishable
What are the negative properties of PMMA (e.g jet)
- poor abrasion resistance
- high shrinkage
- high thermal release
- free monomer may be toxic
Describe the molecular structure of PMMA
- methacrylate monomer
- monofunctional monomer (one C=C bond)
- linear chain-like polymer formed
Describe the molecular structure of bis-acryl composite
- bis-GMA monomer
- bifunctional (2 C=C bonds)
- 3D polymer network formed
What are the key properties of a temporary material to assess?
- temperature reached during setting
- compressive strength
- colour stability
- abrasion resistance
- polymerisation shrinkage
Why must be temperature during setting be considered for temporary materials?
- setting is an exothermic reaction
- temperature reached is a safety consideration
- too great an increase in temperature can harm the pulp
Why is colour stability considered for temporary materials
- aesthetics, especially anteriorly
- patient will be concerned about this
Briefly outline the Zach & Cohen (1965) study
- animal study
- soldering iron used to apply heat to a tooth
- did not consider length of application
- found an 11 degree increase resulted in irreparable pulp necrosis
Briefly outline the Tjan (1989) study
- in vitro study
- measured temperature rise in the pulp chamber during the fabrication of provisional resin crowns
- suggested amount of heat transferred may be sufficient to cause thermal damage to the dental pulp
Briefly outline the Baldissara (1997) study
- pair of teeth used
- one exposed to thermal stimulus and monitored then extracted to examine histological changes
- other extracted and exposed to the same thermal stimulus
- peak temperature higher than than involved in temporary material setting
- increase of 11 degrees does not damage the pulp
What does colour stability refer to?
- the resistance of a material to staining
- even temporary materials must be in the mouth for months in some cases
What is used to measure colour change and what is it measured in?
a colorimeter is used to measure the discolouration and it is measured as Delta E
Why is polymerisation shrinkage to be considered for temporary materials?
- assessing the accuracy of fit
- low polymerisation shrinkage provides a good clinical fit
- mean marginal discrepancy can be used to measure shrinkage
Why is compressive strength important to consider for temporary materials?
materials must be able to withstand biting forces (<700N)
Why is abrasion resistance important to consider for temporary materials?
although the materials do not need to be as strong as those used for permanent restorations they still must resist abrasion
What factors must be considered when selecting a temporary material?
- ease of use
- working time
- setting time
What crowns/bridges can PMMA be used for?
- short bridges
- long bridges
What crowns/bridges can PEMA be used for?
- single crowns
