DM2 Flashcards
How can materials be dispensed? (5)
- ◦ Powder/liquid
- ◦ Paste/paste
- ◦ Paste/liquid
- ◦ Capsules and cartridges
- ◦ Single paste (light activated)
How can materials be mixed?
- ◦ Hand mixing (cheapest option)
- ◦ Mechanical mixing
- ◦ No mixing (light activation)
What 2 properties must you consider when deciding the rate of setting?
2) What factor is it dependent on?
WT (working time) and ST (setting time
2)temperature
What does rheology mean?
change in viscocity
What does a low viscocity mean? give examples and compare to a substance with a high viscocity
how easily does it flow e.g. water has a low viscocity, marmite has a high viscosity)
What thermal effects do you have to account for?
2) Why is it important?
1) exothermic reactions
2) temperatures rises of more than 5 degrees will kill the pulp if restoration is deep in dentine
What dimensional changes do you need to consider of properties when setting?
how much they expand or contract
1) When does the working time start?
2) When does the working time end?
3) normally measured at room temperature
1) from start of mix
2) till materials can no longer be effectively used (therefore must be inpace – e.g. filling must be in cavity by this stage
– e.g. impression material should be seated in mouth at this stage
3) room temperature (therefore in different countries materials will behave differently
1) When does setting time start?
2) when does it end?
1) From start of mix
2) Till material achieves minimum properties for function
Has the reaction gone to completion when material achieves minimum properties for function?
2) Do yo u want a short or long setting time?
– The reaction has not gone to 100% completetion just enough that it is functional and you can remove inlay or patient can close mouth
2) the less time the better
What temperature is setting time measured at?
2) e.g.
Measured at appropriate temperature
– e.g. at mouth temperature for materials which set in mouth
If a materials viscocity is newtonian, what does that mean?
+e.g.
As shear rate is increased viscosity is constant
e.g. water, the viscotiy doesn’t change no matter how much you shake it (shaking applies shear pressure)
If a materials viscocity is pseudoplasticity, what does that mean?
+e.g.
As shear rate increases viscocity decrease (flows more easily)
e.g. ketchup (as you shake the bottle more and more the visococity descreases) ,
If a materials viscocity is thixotropy , what does that mean?
+e.g.
certain amount of force must be applied before they flow e.g. nail polish
If a materials viscocity is dilatant, what does that mean?
e.g
As shear rate increases , viscocity increase (doesn’t flow as easily)
e.g. colloid?
Why is viscocity important? (What does it have an impact?)
Ease of manipulating
Ease of mixing
Ease of transfer (e.g. to impression tray)
How do we want a materials viscosity to change after mixing?
2) What can we add to get this type of curve?
low flat viscosity for some time then sharp increase
2) retarder
What does knowing the temperature change during setting help you determine?
the rate of set
what about the material does the rate of setting influence? e.g.
can influence structure and properties e.g.High temperature can cause porosity (which results in air holes within the set material which leads to It being weak)
1) What do reactions involve in a material that expands during setting?
+2 e.g.
reactions involving crystal growth
e.g. gypsum, amalgam
1) What do reactions involve in a material that contracts during setting?
+e.g.
reactions involing polymerisation
e.g casting alloys
