1. Impression materials
by
Bibinbhaskaran

2. Impressionmaterials
Definition :-(GPT):
A negative likeness or copy in reverse of the surface or object.
2)An imprint of the teeth and adjacent structures for use in dentistry
3. Impression material:-
Any substance or combination of substances used for making an impression or negative reproduction.
Impression technique:-
A method and manner used in making a negative likeness.
4. classification
5. 6. Classification
Based on rigidity : Rigid
egPlaster,Zincoxideeugenol
impression compound
Elastic
egAlginate,polyether,silicone
Based on setting of the material:1.)Chemical reaction(irreversible)
eg plaster of paris,zincoxideeugenol
alginate,additon and condensation silicones
2 )Physical change of state(reversible)
eg agar
7. Based on viscosity : Mucostatic
eg impression plaster,agar,
light body elastomer
Mucocompressive
eg Impression compound,alginates
Pseudoplastic
eg addition silicones
8. Based on interaction with saliva
and water : Hydrophobic
eg polysulfide ,condensation
silicones
Hydrophilic
egputty,impression plaster
Based on use:
Primary
impression material
eg impression compound,alginate
Secondary
Impression material
egZoe,medium bodied elastomers
Duplicating
material
eg agar
9. Based on
Chemical composition : impression plaster
impression compound
metal oxide(zinc oxide eugenol)
pastes
agar hydrocolloid
alginate hydrocolloid
polysulfides
condensation silicones
addition silicones
polythers
light curing polyether
(urethanedimethacrylate)
10. Desirable qualities
Pleasant odor taste and color
Absence of toxic irritants
Adequate shelf life
Economical
Easy to use
Setting that meet clinical requirements
Satisfactory consistency
11. Readily wet oral tissues
Elastic
Adequate strenght
Dimensional stability
Compatiblity with cast and die materials
Accuracy
Disinfection
12. Impression plaster
13. Impression plaster
The impressions are very accurate
Being hydrophilic it has got intimate contact with oral tissues by absorbing surface moisture
14. Impression compound
15. Impression compound
Fusion temperature of impression compound is 43.5 degree celesius
16. Zinc oxide eugenol impression material
17. Zincoxideeugenol impression material
Non eugenol pastes-
One of the chief disadvantages of Zoe pastes is the possible burning sensation caused by eugenol.orthoethoxybenzoic acid (EBA) is a valuable substitute for eugenol in this regard.
18. Alginate
19. Alginate
Gelation reaction-
2Na3P04 + 3CaSo4----- Ca3(Po4)2+3 Na2SO4
20. Recent advances in alginates
Dust free alginates-
De-dusting agent (glycerin or glycol)
Siliconized alginates-
silicon polymers are added to strengthen the material
Alginates containing disinfectants-
eg quaternary ammonium salts or chlorohexamine are added to alginate powder.
Hard and soft set alginates-
by adjusting the amount of fillers
21. Reversible hydrocolloid-AGAR
22. Agar
Gelation-
Gelation is accomplished by circulating cold water ofapproximately 18-23 degree for not less than 5 min.
23. Elastomeric impression materials
Classification :-
Based onviscosity-
Class 1 heavy body heavy viscosity
Class 2 regular body or medium body
Class 3 light body or low viscosity
Based on chemistry-
Polysulfides
Condensation silicones
Additional slilicones
Polythers
Visible light curable polyether
24. POLYSULFIDES
25. polysulfides
Polysulfide is one of the least stiff or highly flexible of elastomeric material
For accurate polysulfide impressions-
The cast should be poured immediately after taking impression
Minimise the amount of material used to take impression by using custom made acrylic trays
26. Condensation silicones(Double mix type)
27. Condensation silicones
It is also called room temperature vulcanising silicones(RTV)
Uses
It is widely used in recording dentulous impressions in preparation of crowns,bridges,inlays,onlays and to some extent for partial dentures
It is also used to record edentulous impressions in preparation of complete denture
28. Putty type
Advantages
No custom tray required
No special equipment required
Moderate strength in deep sulcus
Pleasant odor
Adequate shelf life
Disadvantages
Should be poured shortly after removal
Hydrophobic
Difficult to electroplate
Easily distorted
29. Addition silicones(Double mix type)
30. Addition silicones
Addition polysilicones are the most stable of all the existing materials
It has an excellent recovery of 99.93%
It exhibits pseudoplasticproperties.it can be used both as syringe and tray materials
31. Putty type
Advantages
No custom tray
No special equipment
Good shelf life
Can be poured more than once
Disadvantages
Extremely hydrophilic
More difficult to pour
Most expensive
32. Polyether materials
33. Polythers
Uses-
For recording impression in preparation of crowns and bridges
Cavity preparation for inlays and onlays
For construction of partial and complete dentures
34. Visible light cured polyether
35. Light cured polyether
It has excellent elasticity
It has infinite working time and short setting time
The impression can be stored upto two weeks
36. Disinfection
Most manufacturers recommend a specific
disinfectant,such as iodophor,bleach,orglutaldehyde,for disinfection.
Certain disinfectants may result in gypsum casts that have a lower surface hardness or diminished surface detail.
The current protocol for disinfecting hydrocolloid impressions recommended by the centre for disease control is to use house hold bleach(1 to 10 dilutions),iodophor or synthetic phenols as disinfectants
An alternate disinfection method is by immersion,but this should not exceed 10 min.
37. Duplicating materials
Duplicating is required for two reasons:-
1, The cast on which the wax pattern of the metal frame work is to be formed must be made from refractory investment because it must withstand the casting temperatures required for gold or base metal alloys
2, The original cast is needed for checking the accuracy of the metal frame work and for processing the denture base portion of the partial denture
The most common duplicating materials are agar hydrocolloid compounds, The primary advantage of agar is their set is reversible.the disadvantage is it is subject to dimensional change.The best storage condition is 100% humidity.
38. Tissue conditioners
Tissue conditoners are soft elastomers used to treat an irritated mucosa supporting a denture.it is used to provide time for healing of soft tissues
Tissue conditioners are composed of powder containing poly(ethyl methacrylate)and a liquid containing an aromatic ester ethyl alcohol.
The properties that make tissue conditioners effective are-
1,viscous behavior which allows adaptation to irritated denture bearing mucosa
2,viscoelastic behavior which cushions the cyclic forces of mastication and bruxism
39. References
Zardiackas.L.D , Dental materials,Dentla clinics of morthamerica,July 2007,vol 51,pg 629-643 .
OBrien.W.J, Dental materials and their selection, 3rd edition, Quintessence publications.
Craig.R.G, Dental Materials, 12th edition, Elsevier publications.
Anusavice, Phillips Science of Dental Materials, 11th edition, Saunders publications. Impression materials.