Alginate Impression Materials Flashcards Preview

BDS2 Dental Material Science > Alginate Impression Materials > Flashcards

Flashcards in Alginate Impression Materials Deck (39)
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1
Q

what is the main function of impression materials?

A

to produce an accurate replica of the surface and shape of hard and soft oral tissues

2
Q

what type of reproduction of the tissues does an impression give?

A

a NEGATIVE reproduction (indentations not protrusions)

3
Q

what material is used to produce a positive replica of the teeth after the impression stage?

A

dental stone (stone casts)

4
Q

why is a stone cast produced?

A

to evaluate dentition for;

  • orthodontic uses
  • occlusion problems
  • fabrication of restorations
  • fabrication of prostheses
5
Q

what are the clinical classifications of impression materials?

A
  • mucostatic

- mucocompressive

6
Q

what are the property classifications fo impression materials?

A
  • elastic

- non-elastic

7
Q

give examples of mucostatic materials & what they are used for:

A
  • zinc oxide eugenol & low viscosity alginates
  • fluid materials that displace the soft tissues slightly
  • give an impression of the undisplaced mucosa
8
Q

give examples of mucocompressive materials and their uses?

A
  • impression compounds & high viscosity alginates/elastomers
  • viscous materials that record an impression of the mucosa
  • give impression of displaced soft tissue
9
Q

what is good about elastic impression materials?

A

when removing the material form the mouth, they stretch around the bulbous part of the tooth and then recovery back to the original shape of the tooth quickly (almost 100%)

10
Q

in what way can the dentist prevent a high amount of permanent strain on the impression material?

A

remove the impression tray with a sharp and quick pull

11
Q

what type of impression material is alginate?

A

an irreversible hydrocolloid made from agar

12
Q

what are some examples of elastomer impression materials?

A
  • polysulphides
  • polyethers
  • silicones
13
Q

what would happen if a non-elastic material was used to take an impression?

A

on removal of the plate from the mouth, the material will become deformed or fractured

14
Q

how are impression materials prepared?

A
  • mixing of the material
  • chemical reaction
  • heat
15
Q

what setting reactions can impression materials undergo & what is this dependent on?

A
  • chemical
  • polymerisation
  • cooling

DEPENDENT ON THE MATERIAL USED

16
Q

what are the ideal accuracy properties required for an impression material?

A
  • appropriate flow
  • setting changes
  • removal
  • storage
  • decontamination
  • compatible with cast material
17
Q

when removing the material from the mouth, what is important?

A

that the material;

  • has NO effect on oral tissues
  • has NO dimensional change (eg thermal contraction)
  • has COMPLETE ELASTIC RECOVERY
18
Q

what is meant by viscosity?

A

determines the ability to flow over surface & so good level of detail is recorded

19
Q

in terms of viscosity, what is ideal for a material?

A

low viscosity

20
Q

what should the thermal expansion coefficient be of an impression material?

A

ideally low (to cope with mouth to room temperature transition)

21
Q

why is tear strength important when considering impression materials?

A

determines a materials ability to withstand tearing during removal (especially from undercuts)

22
Q

what are ideal properties for an impression material in terms of patient comfort?

A
  • non-toxic/non-irritant
  • acceptable taste and smell
  • short setting time
  • removable without damage to oral tissues
23
Q

what are the ideal properties for an impression material in terms of operator convenience?

A
  • quick, simple technique
  • convenient working/setting times
  • must be able to be decontaminated
    (cost = inexpensive… not as important)
24
Q

what is a hydro colloid?

A
  • a colloid is a TWO phase system of fine particles of one phase dispersed in another phase
  • therefore hydrocolloid is fine particles dispersed in water!
25
Q

what states can hydrocolloid materials come in?

A
  • SOL = viscous liquid state

- GEL = jelly like consistency

26
Q

what is alginates composition?

A
  • salt of alginic acid (12%)
  • calcium sulphate (12%)
  • trisodium phosphate (2%)
  • filler (70%)
    (small traces of modifiers/flavourings)
27
Q

what is the function of the trisodium phosphate found in alginate material?

A

delays bell formation (this corresponds to material working time)

28
Q

what does the filler in alginate material provide?

A
  • cohesion

- strength

29
Q

what is the alginate setting reaction?

A

2Na(n)Alg + CaSO(4) ——> Na(2)SO(4) + Ca(n)Alg

30
Q

what type of bonding occurs in alginate & what does this allow for?

A

CROSSLINKING

- allows viscosity and strength of the material to develop

31
Q

what type of tray should be used when performing an impression with alginate material?

A

a perforated tray & adhesive

32
Q

what temperature should the water be when using alginate to perform an impression?

A

18-24°C

33
Q

how can distortion and tearing be avoided when using alginate to perform an impression?

A

using a large bulk of material (typically 5mm)

34
Q

why is alginate a good impression material to use in terms of patient comfort?

A
  • non-toxic/non-irritant
  • acceptable taste & smell
  • setting time OK
35
Q

what is important to note when storing alginate?

A
  • avoiding moisture is CRUCIAL (alginate can experience syneresis and imbibition)
  • preparing the cast ASAP to avoid dimensional change is important
36
Q

what is meant by syneresis?

A

release of water

37
Q

what is meant by imbibition?

A

uptake of water

38
Q

why is alginate an appropriate impression material to use in terms of accuracy?

A
  • acceptable flow
  • acceptable setting changes
  • nearly elastic (not 100% though)
39
Q

when should alginate not be used on a patient?

A

when the patient has deep undercuts as alginate has a poor tear strength