DMS- impression materials

Question 1

Compare muco-static and muco-compressive materials?

Answer 1

muco-static mateiral are fluid materials that displace the soft tissue slightly e.g. low viscoity alginate

Muco-compressive material is a viscous mateiral that records the mucosa impression under load. (denture produced is more stable at function than at rest)

e.g. high viscosity alginate & elastomers

Question 2

Why do we want impression materials to be elastic?

Answer 2

So that when we are removing the impression material, it can flex over the bulbosity of the tooth without being distorted or fracturing.

An elastic material is then able to recover.

Question 3

What do we mean by the impression material being

“visoelastic”

Answer 3

It is not completely elastic, there is a slight distortion of the impression material.

Question 4

How do we minimise the permanent strain of an impression material?

Answer 4

Apply the removal force quickly (a sharp pull)

A quicker force experiences less strain and recovers with less strain.

Question 5

WHat are the ideal properties for an impression material?

Answer 5

Interaction

• Surface wetting - good contact with material and teeth?
• High flow- To record detail

Accuracy

• Elastic- (you want elastic recovery)
• Low thermal contraction (change in temperature between mouth and room)
• Setting reaction- do not want it to contract on setting.
• Surface reproduction- you want the material to be able to flow into the smaller gaps.

Deal with Undercuts

• high tear strength- to withstand stress of removal
• Low rigidity- To be less rigid (easing removal of material)

Question 6

What makes the impression material comfortable for the patient?

Answer 6

Not toxic

Not irritant

Acceptable taste and smell

Short setting time

Removable without damaging oral tissues.

Question 7

What makes the impression material convenient for the operator?

Answer 7

convenient working time

short setting time.

Question 8

What are hydrocolloids?

Answer 8

Fine particles dispersed in a liquid. e.g. alginate.

Question 9

What does alginate consist of?

Answer 9

Sodium alginate

Calcuium sulphate

Trisodium phosphate

Question 10

Describe the reaction to produce alginate?

Answer 10

Trisodium phosphate reacts with calcium causing the delay.

When this runs out,

Sodium alginate reacts with calcium.

(Producing alginate)

Question 11

How do we manipulate alginate?

Answer 11

• Use correct powder/ liquid ratio
• Use water at 18-24*
• Use an adhesive and a perforated tray (has holes in it)
• Remove impression with a sharp pull
• Increase temperature to speed up setting
• Wait 2 minutes after setting for cross linking to be completed.

Question 12

Discuss the less ideal properties of alginate?

Answer 12

Alginate can release (syneresis) or take up water imbition over time- this causes distortion.

Alginate has a poor tear strength.

Question 13

Give examples of elastomeric impression materials?

Answer 13

Polyether and addition silicones.