Dental Impression Material.ppt, for denture adhesive and other denture material for the crown, bridge and removable prosthetic appliances in edentolous patient...

Lab material

1. Dental Impression
Material
Dr Lorna C Carneiro
DDS, Dipl Odont, MSc Odont, PhD Odont
Lecturer, Department of Restorative Dentistry
School of Dentistry, MUCHS.

2. Impression:
Is a record in negative form of the shape of the
oral tissues
Impression of the mouth are taken to obtain an
accurate model whereupon an appliance is
constructed. The accuracy of the impression
influences the fit of the completed appliance
While being used impression materials must
be in a plastic or fluid state – following which it
hardens

3. Characteristics of an impression
material
Easily manipulated at a tolerable temperature
Not irritable
Set quickly in the mouth
Must be elastic or non elastic
Dimensionally stable
Must give a good reproduction of the denture
bearing area

4. Classification:
Non elastic
Elastic
Others

5. I.Non elastic impression
materials
Compo (kerr)
Zinc oxide paste (SS white)
Plaster of paris (Calspar, Gypsogum)
Impression waxes (Correcta)
Gutta percha

6. 1.Impression composition
(compound)
Type I - low fusion
•Impression compo
•Peripheral adaptation compo – greenstick
Type II – high fusion
•Base material for special trays and record
blocks eg
1.Resin – shellac
2.waxes – bees or paraffin

7. Characteristics
Fairly thermoplastic – soften by heating (water
bath 60
o
C) and hardens by cooling (mouth
37
o
C). Frequently used – unhygienic, looses
characteristics, and some leech in water bath.
Muco compressive – bad flow with over
extended periphery
Inflexible – deforms in undercuts
Separating media - not required during casting
of models except for compo during model
removal

8. Uses
Primary impression
Obturator impression
Facial paralysis impressions

9. Dental Compound
different colors reflect slightly different thermodynamic
behavior
material is thermodynamic meaning corrections and
additions are easily made
the viscosity of the material is controlled with temperature
the compound can be employed as the final impression
trays
compound can be employed to support edentulous areas
or saddle areas, and facilitate either preliminary or final
impressions for partial dentures or better study models
Lastly, compound is cheap

10. 2.Zinc Oxide (eugenol paste)
•Type I – hard – by SS White
•Type II – soft – Kelleys
Ingredients:
Red paste - activator (eugenol)
- Filler (Kaolin/talc)
- Plasticiser (olive oil)
White paste - activator (zinc Oxide)
- resin (hydrogenated resin/wax)
-plasticiser – olive oil
- accelerator (metal salts eg zinc acetate or magnesium
acetate )
Reaction: mix equal lengths of paste – absorption of eugenol by zinc
oxide forms zinc eugenol

11. Characteristics
Hardens chemically within 3-4min
Irritation of skin by eugenol
Non elastic – fractures with undercuts
Dimensionally stable
No separating media required
Heat eases removal of impression from model
Bad flowing characteristics

12. Uses
Final impressions for tight fitting trays
Can be added onto dry surfaces
Can enhance vomiting reflex – diversion
Burning sensation

13. 3.Plaster of Paris
Type I – impression plaster of paris
Type II – model plaster of paris
Ingredients:
1. calcium sulphate
2. supplements - accelerator – 4% potassium sulphate
- retarder – 0.4% Borax, Alizarin
3. anti expansion medium – 0.04% potassium sulphate,
Alizarin R
4. other- colouring - alizarin S
- Hardener – gum Tragacanth
Reaction: powder/water (100gm/50mls)
calcium sulphate hemihydrate + water and calcim sulphate dehydrate + heat

14. Characteristics and uses
Mucostatic impression material
Dynamically stable
Spaced special tray
Requires separating media during casting of
models eg cold mould seal, water glass, soap
solution
Inflexible brittle material – easily fractured – joined
with sticky wax
Uses
Final impressions of flabby alveolar ridges

15. 4. Waxes
Ingredients:
bees, plant waxes and resin
Flows at mouth temperature – low melting point
used in the altered cast technique with partial
denture impressions

16. 5.Gutta percha
Base – rubber + plasticisers
Characteristics – softens at 60
o
C
Used in operative obturator patients or
patients with cranio-mandibular disorders
requiring reduction of freeway space.

17. II.Elastic Impression Materials
Hydrocolloid
1.reversible hydrocolloid
2.irreversible hydrocolloid - alginate
Elastomere
1.polysulphide rubber
2.silicon rubber
3. poly ether

18. Alginate
Available in different colors - Blue, green etc.
Active ingredients:
1.ammonium/sodium/potassium
alginate
2.retarder – tri sodium phosphate
3.filler – diatomacious earth
4. other – coloring, chemical indicator,
disinfectant

19. Characteristics and uses:
1. Reproduces undercuts
2. Does not adhere to tray
3. Dimensionally stable – if over 4mm thick
4. Separating agent not required
5. Cannot be added to
Used for primary and secondary impressions

20. Polysulphide rubber
Has two separate tubes:
white paste - polysulphide rubber and fillers of
zinc oxide, calcium sulphide and titanium
oxide
brown paste – lead dioxide and castor oil
Reaction is polymerisation/vulcanizing –which
takes about 6min.

21. Silicon rubber
Paste – active ingredient - silicon chain
filler – silica
coloring – titanium oxide
cross linking agent – poly ethyl
silicate
Drops – activator – organic salts of heavy metals
eg dibutyl – tin – dilaurate
Reaction - polymerization

22. Poly-ether
Base – unsaturated polyether
plasticiser – oil
filler material
Catalyst – acid ester
plasticiser – oil
filler
Dilutent – sometimes present
Reaction - polymerization

23. Characteristics of elastomere
Elasticity – good reproduction of undercuts
Dimensionally stable –
polyether<silicon<polysulphide
Adhesive required on tray
Separating media not required
Due to stiffness of material – more difficult to
remove from the mouth
Uses – for final impressions

24. Other
Viscoelastic material – eg viscogel
powder – poly ethyl methacrylate
liquid – ethyl alcohol and aromatic ester
Reaction – physical
powder + liquid =acrylic/alcohol
solution – hardening occurs over 24-36hrs
due to evaporation of alcohol

25. Characteristics and uses
- Constant flow under pressure during dissolved
stage
- After hardening – elastic
- Progressive decrease in elasticity after
hardening with lapse of time
Uses –
-functional impression material
-lining in denture base – with medications
-tissue conditioner – to improve quality of
traumatized denture bearing tissues

26. Disinfection of impressions
Using a chlorine sol, iodine sol, phenols, aldehyde
sols –
Used to prevent transmission of organisms to
technical staff or other patients via laboratory
For alginates – spray with disinfectant
polysulphides/silicones – immersion
polyethers – spray or immersion

27. Choice of Impression Material
Will depend on the need to result in efficient, predictable
impressions, yielding well-fitting prostheses.
In addition, one must consider the economics of material
management
and not have boxes of unused or seldom-used materials
expiring on our shelves. The materials we choose must be
predictable and provide efficiency.
Materials that don’t work result in remakes of our prosthetics
and increase our costs in both material used and that finite
commodity, time.
When possible, it is better to have materials with multiple uses,
thus lowering our holding and ordering costs. But in any event,
the material must be workable in a dentist’s hands.

28. Type of stock tray and type of impression material
can result in overextensions and an improper fit of the
prosthesis
Also there is the raw cost of purchasing supplies, and
then there is the cost of retaking impressions
There is also the impact on our reputations
Repeated impressions can initially impart a feeling in
the patient that the dentist is paying attention to detail
After several impressions, the patient may start to
question your ability.
In short, the impression process must be an efficient,
predictable part of your practice not to be overlooked