elastomeric impression materials

Question 1

what are meow types of elastomers

Answer 1

• polyether

- addition silicones

Question 2

what are addition silicones also called

Answer 2

• poly vinyl siloxanes

Question 3

what do you need to judge impression materials by

Answer 3

• material characteristics

- clinical performance = patient acceptance and ease of use

Question 4

how to assess materials

Answer 4

• look at source
• look at product
• look at the evidence= look at actual data not just claims
• reliability = need to be able to trust material
• ask questions = were the people asked paid or independent, how many people were asked, why were people not satisfied with it?

Question 5

what properties of the material do you want to know about

Answer 5

• flow/viscosity
• surface detail = reproduction
• wettability = ability to make good contact with tooth
• elastic recovery = %
• stiffness = flexibility (want flexibility for impression materials and rigid for composite)
• tear strength = only applies to impression materials
• mixing time
• working time

Question 6

what is ISO

Answer 6

• international standard organisation

Question 7

what is the dental standard for ISO

Answer 7

• designed to assess relevant properties of a product to see whether it meets acceptable requirements for safe and effective use

Question 8

what do ISO do

Answer 8

• produces a whole series of requirements and rests that materials being used on humans should satisfy before they are classified as safe and reliable

Question 9

what is the ISO standard for impression materials

Answer 9

• is that grooves/indentations of either 20µm or 50µm (depending on viscosity) are replicated

Question 10

what is wettability

Answer 10

• if wettability is good then impression material will not be affected by things on the tooth such as saliva

Question 11

what properties are important for impression materials

Answer 11

• quality of surface interaction between material and tooth tissue = viscosity and surface wetting and contact angle
• accuracy = surface reproduction, viscoelasticity/elastic recovery
• handling with removal and undercuts = tear strength, rigidity
• dimensional stability

Question 12

what is important with viscosity

Answer 12

• material must be able to flow readily
• viscosity determines a materials potential for making close contact with hard and soft tissue surfaces= how well it records surface detail
• range of viscosity= low, medium and high

Question 13

what is wanted with wettability

Answer 13

• must make intimate contact with teeth/mucosa
• interface between impression material
• if don’t have good contact then will get a bubbly/rough surface and will be a poor model to work with
• impression material globules sit and spread out on the surface and if there is not a lot of gaps between globules then that is good, but if there is then that is poor wettability

Question 14

what are the standard notch dimensions

Answer 14

• 20µm
• 50µm
• 75µm

Question 15

how is the surface detail reproduction determines

Answer 15

• apply impression material and see what size of notches it fills

Question 16

what is the surface reproduction limit if material flows into notch size 50µm and 75µm but not 20µm

Answer 16

• this means that the material meets the ISO standard if 50µm limit

Question 17

what is the ideal behaviour of elasticity

Answer 17

• reach maximum strain
• stays at maximum strain until removed
• then returns to normal

Question 18

what is the impression material elastic recovery

Answer 18

• gradually strains
• reaches load
• releases load
• gradually relaxes back but not to normal = there is a permanent strain/deformation

Question 19

what is the ideal elasticity score

Answer 19

• 100% elastic recovery

Question 20

what is viscoelastic behaviour of impression material

Answer 20

• no materials are truly elastic, all are viscoelastic
• when impression material, having been stretched/compressed on removal from mouth, fails to return to its original dimensions
• there is a permanent deformation

Question 21

how can the permanent deformation be reduced

Answer 21

• if load time is less then there is less overall permanent strain
• lower deformation if remove impression faster and with a sharp pull

Question 22

what is the ideal viscoelasticity

Answer 22

• low = small deformation

Question 23

what is the tear strength

Answer 23

• the stress a material will withstand before fracturing

Question 24

where is the impression material most likely to tear and fracture

Answer 24

• undercut regions = want a high tear strength in these areas

Question 25

what is rigidity

Answer 25

• stress/strain

- rigid = large stress needed to cause material to change shape

Question 26

what rigidity do you want the impression material to be

Answer 26

• flexible

- has low rigidity to ease it removal from undercut/interdental regions

Question 27

how does the setting time and working time of polyether compare to addition silicones

Answer 27

• polyether working time = 2 mins, setting time = 5 mins
• addition silicone working time = 4 mins, setting time = 6mins
• depends on how fast you work as to which to use

Question 28

what must you know of the material before you use it

Answer 28

• its limitations

Question 29

what must you consider when deciding whether or not to use a material

Answer 29

• know key properties
• review product specification data
• know typical values expected for specific properties
• identify properties not mentioned = need to know why its not there
• reject claims not supported with scientific and/or clinical data