temporary materials (2.0)
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what is PEMA
polyethylmethacrylate
Where can PMMA be fabricated, the duration it lasts and crown / bridge sorry i dont know what the table at the start of this lecture means when it says crown / bridge but i’ve thrown in what it is for each on anyway hahahaha
fabrication = indirect duration = long term crown / bridge = short & long
Where can PEMA be fabricated, the duration it lasts and crown / bridge
fabrication = direct §/ chairside duration = short term crown / bridge = single crown
Where can bis-acryl composite be fabricated, the duration it lasts and crown / bridge
fabrication = direct / chairside duration = long term crown / bridge = short span bridges
name temporary materials
• PolyMethylMethAcrylate (PMMA) ○ Eg Jet • PolyEthylMethAcrylate (PEMA) ○ EG Trim II, Snap • Bis-acryl Composite ○ Eg Protemp4, Quicktemp • UrethaneDiMethAcrylate (UDMA) Eg Provipoint DC
What is the methacrylate’s monomer structure
CH2 double bond to C C single bones with CH3 and COOCH3
what in the methacrylate monomer structure enables polymer development
the double bond via cross linking
what happens when the methacrylate monomer polymerises
it forms a long chain molecule PMMA
what does polymerisation produce
Polymerisation produces a long chain molecular structure or network - PMMA - yielding a material with greater weight, rigidity and strength
what is PMMA
PolyMethylMethAcrylate
List properties of PMMA
• Self-curing • Good marginal fit • Good transverse strength • Polishable But ○ Poor abrasion resistance ○ High shrinkage ○ High thermal release ○ Free monomer may be toxic
What can be done to make sure there is no free monomer in PMMA
fully cure it
what is PMMA like structurally
○ mono-functional monomer (ie one C=C double bond) § That is it has one C-C double bond and forms a long chain polymer ○ linear chain-like polymer
what monomer has PEMA got
Has ethyl methacrylate monomer
what is the structure of bis-acryl(ate) composite like
○ bis-GMA monomer ○ bifunctional (ie 2 of C = C double bonds) § 3D polymer network ○ Has 2 C-C double bonds and this allows it to generate a 3D polymer network
what are sources of scientific information on materials
○ Journals § Peer-reviewed § Trustworthy ○ Product literature § Detailed § Objective? § Common way for a GDP to assess products - though DATA is not always complete or accurate § Some firms give lots of details but others not so much § There is always the issue of whether this is biased - conscious or not ○ There’s also information from research studies, where perhaps a series of materials are compared ~ this type of independent data is very useful as it is objective
what are the types of product literature
• Brochures • Websites • Product profile
what are the pros and cons of brochures
○ Superficial ○ "positive" presentation ○ Sales orientation ○ They are here to sell the product ○ Glossy photos, bold assertions, cherry-picked quotes from prominent dentists ○ This information is not reliable
what are the pros and cons of websites
○ Info-rich ○ Not always relevant re properties ○ Gather lots of data but can take some time to sift through
what are pros and cons of product profiles
○ Scientific info… but not definitive ○ Not often supplied for products ○ Some manufacturers offer this detailed product profile ○ Usually lots of interesting data ○ Sometimes a bit complicated, as they describe lots of methodologies and technologies they used ○ Does provide relevant data
how is assessment of materials carried out
• Quality of data ~ crucial ○ In house [may be somewhat biased] ○ Independent § Single study □ Ideally □ Not many reported § Review (may be out of date) □ Where a series of commercially available materials are compared □ This scenario is ideal in many respects, but by its nature is done only for mature materials that have been commercially available for some time • Competitive performance Are rival products compared?
what needs to be considered when looking at the property of temperature for temporary materials
○ Exothermic reaction § This is generated by the polymerisation reaction § There is thermal release ○ Material encapsulates tooth prep ○ Safety… § Too much heat will potentially harm the dental pulp - this is a safety issue as pulp damage is to be avoided so as a dentist you need to be sure that the material when used clinically is harmless ○ Dentist’s concerns
what needs to be considered when looking at the property of colour stability for temporary materials
○ Aesthetics § An unsightly looking temporary crown will make many people self conscious ○ Anterior teeth ○ Patient’s concern § Normally concerned that any material, even temporary ones, look good § Obviously the reason for the provisional is to protect eg crown prep and the end goal is for an aesthetic replacement of the natural tissue
why is polymerisation shrinkage important property for temporary materials
Important for assessing a temporary material’s accuracy of fit