temporary materials (2.0)

Question 1

what is PEMA

Answer 1

polyethylmethacrylate

Question 2

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

Answer 2

fabrication = indirect

duration = long term

crown / bridge = short & long

Question 3

Where can PEMA be fabricated, the duration it lasts and crown / bridge

Answer 3

fabrication = direct §/ chairside

duration = short term

crown / bridge = single crown

Question 4

Where can bis-acryl composite be fabricated, the duration it lasts and crown / bridge

Answer 4

fabrication = direct / chairside

duration = long term

crown / bridge = short span bridges

Question 5

name temporary materials

Answer 5

• PolyMethylMethAcrylate (PMMA)
○ Eg Jet

• PolyEthylMethAcrylate (PEMA)
○ EG Trim II, Snap

• Bis-acryl Composite
○ Eg Protemp4, Quicktemp

• UrethaneDiMethAcrylate (UDMA)
Eg Provipoint DC

Question 6

What is the methacrylate’s monomer structure

Answer 6

CH2 double bond to C

C single bones with CH3 and COOCH3

Question 7

what in the methacrylate monomer structure enables polymer development

Answer 7

the double bond via cross linking

Question 8

what happens when the methacrylate monomer polymerises

Answer 8

it forms a long chain molecule PMMA

Question 9

what does polymerisation produce

Answer 9

Polymerisation produces a long chain molecular structure or network - PMMA - yielding a material with greater weight, rigidity and strength

Question 10

what is PMMA

Answer 10

PolyMethylMethAcrylate

Question 11

List properties of PMMA

Answer 11

• Self-curing
• Good marginal fit
• Good transverse strength
• Polishable

But 
○ Poor abrasion resistance
○ High shrinkage
○ High thermal release
○ Free monomer may be toxic

Question 12

What can be done to make sure there is no free monomer in PMMA

Answer 12

fully cure it

Question 13

what is PMMA like structurally

Answer 13

○ 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

Question 14

what monomer has PEMA got

Answer 14

Has ethyl methacrylate monomer

Question 15

what is the structure of bis-acryl(ate) composite like

Answer 15

○ 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

Question 16

what are sources of scientific information on materials

Answer 16

○ 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

Question 17

what are the types of product literature

Answer 17

• Brochures
• Websites
• Product profile

Question 18

what are the pros and cons of brochures

Answer 18

○ 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

Question 19

what are the pros and cons of websites

Answer 19

○ Info-rich
○ Not always relevant re properties
○ Gather lots of data but can take some time to sift through

Question 20

what are pros and cons of product profiles

Answer 20

○ 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

Question 21

how is assessment of materials carried out

Answer 21

• 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?

Question 22

what needs to be considered when looking at the property of temperature for temporary materials

Answer 22

○ 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

Question 23

what needs to be considered when looking at the property of colour stability for temporary materials

Answer 23

○ 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

Question 24

why is polymerisation shrinkage important property for temporary materials

Answer 24

Important for assessing a temporary material’s accuracy of fit

Question 25

does low or high polymerisation shrinkage give a good clinical fit of temporary restorations

Answer 25

• Low polymerisation shrinkage gives good clinical fit of the temporary restoration
○ Obviously the lower the shrinkage the better

Important for permanent restoratives such as composite resins

Question 26

what are other important factors for temporary materials

Answer 26

Ease of use

Working and settling time