DLA 1201, exam 6

1. Final Impression
Materials
CHAPTER 15

2. Impression Material
Used primarily to reproduce the form of the teeth
in a negative reproduction
This includes existing restorations, hard and soft
tissues, and preparations
Also used to fabricate prostheses and other oral
devices
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3. Impression Material
Making impressions of oral structures is an almost
everyday occurrence in a busy dental practice.
Selection of the impression material will be influenced
by what the impression will be used for.
Typically, a material must be in a moldable or plastic
state that can adapt to the teeth and tissues.

4. Types of Impressions
Dental impressions can be categorized into
three basic types based on how they will be
used:
1. Preliminary impressions
2. Final impressions
3. Bite registration (occlusal) impressions
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5. Types of impressions
 Preliminary impressions are made as precursor to other
treatment.
 Final impressions are more accurate in their replication of the
oral structures. They are used to make final restorations, such
as crowns, bridges, partials, and complete dentures.
 Bite registration is a replication of the patient’s bite and is
used to establish the proper relation between a restoration
or prosthesis and the opposing teeth.

6. Types of Impression Materials
Two major groups:
Elastic materials
Inelastic materials
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7. Types of Impression Materials
Elastic impression materials include the hydrocolloids
(agar and alginate), polysulfides, silicone rubber
materials, polyethers, and a hybrid of polyether and
polyvinyl siloxane.
Inelastic materials are the older impression materials
and include dental compound, impression plaster, zinc
oxide eugenol, and impression wax.

8. Key Properties
 The key properties of impression materials are their accuracy, tear
resistance, and dimensional stability.
 When the impression is made, the impression material must closely
adapt and flow over the surface of the tooth preparation and tissues
to record the minute details in order to be accurate.
 After the impression material sets, it must have good tear resistance
to prevent tearing during removal from the mouth.
 After the impression is removed, the set material must remain
dimensionally stable.

9. Elastomers
Four types of elastomers:
Polysulfides
Polyethers
Condensation silicones
Addition silicones (polyvinyl siloxane)
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10. Elastomers
The two most widely used elastomers are
polyvinyl siloxane (PVS) and polyether.
More recently, a hybrid material, vinyl
polyether, has been introduced that
combines the best properties of polyethers
and polyvinyl siloxane.

11. Elastomers
They are not water based, so they are not as sensitive
as the hydrocolloids to water loss or imbibition (water
uptake)
Shelf life is ~12-18 months
Storage in refrigerator to lengthen shelf life

12. Adhesives
 Elastomers do not adhere well to metal or custom acrylic impression
trays.
 An adhesive is placed in the tray to prevent the material from
separating from the tray and causing distortion.
 Each type of elastomer has its won adhesive with which it is compatible.
 Therefore, adhesives should not be interchanged among different types of
materials.
 Tray adhesive should be placed in a thin layer and allowed to dry
 If it is not applied in advance to allow drying, use an AW syringe to dry faster.

13. Elastomers
Elastomers are highly accurate elastic impression
materials that have qualities similar to rubber and are
often called rubber materials.
Because of their rubbery nature, elastomers have a
certain amount of elastic recovery or rebound from
deformation.
Rebound reduces distortion in the cast that is poured
from the impression
PVS has the best elastic recovery of the elastomers

14. Wettability
 Elastomers generally are not wet well by water, and are therefore
referred to as hydrophobic, because the water forms a high contact
angle with them.
 In other words, water beads on their surface much like raindrops on a newly
waxed car.
 Of the elastomers, the polyethers are the most hydrophilic, or wettable.
 Wettability can be seen clinically when impression materials are able to
capture the detail of the tooth preparation when the surface is moist
(but not submerged in water or saliva).
 It also means that gypsum materials will flow better into the fine details of the
prep when the impression is poured.

15. Elastomers- Polysulfides
 Polysulfides are the oldest of the elastomers; they are more dimensionally stable
and have greater tear strength than alginate or agar hydrocolloids.
 More dimensionally stable and have greater tear strength than alginate or agar
hydrocolloids.
 More accurate than alginate, but not as accurate as other elastomers.
 Have been used successfully for crown and bridge impressions and for partial and
complete denture impressions.
 Cannot be used in an automix, must be hand mixed
 Messy, and have an unpleasant sulfur odor.
 Still used by some practitioners for complete dentures, but not really used much
since PVS and polyethers.

16. Silicone Rubber Impression Materials
 Two types of silicone impression materials have been
developed and are named according to the type of the
polymerization reaction they undergo during setting.
 Condensation silicones were introduced in the 1960’s and
were useful for crown and bridge procedures.
 Addition silicone in the form of polyvinyl siloxane was
introduced in the late 1970’s and because of its superior
properties, it soon replaced condensation silicone.

17. Addition Silicone
 Properties provide greater dimensional stability and
accuracy.
 They are clean and easy to use, with no foul odor or taste.
 As a result of these improvements, they have become the
most popular materials for crown and bridge procedures.
 Most expensive of the impression materials.

18. Polyvinyl siloxane (PVS)
AKA vinyl Polysiloxane
Addition silicone
Smallest dimensional change on setting
High elastic recovery after removal
Resist tearing (high tear strength
Cannot be poured until at least 2 hours after
set due to hydrogen being released
Will cause porous surface

20. PVS
 Can be poured in stone several times
 Dimensionally stable for at least a week without distortion.
 Exhibits little flow (deformation when subjected to load after
setting)
This accounts for their accuracy even after repouring.

21. Polyvinyl siloxane
 Polyvinyl siloxane (PVS) materials are hydrophobic by nature and must
be used in a dry field.
 Little moisture on prepped tooth will result in the loss of surface detail
 PVS is manufactured in light, extra light, regular (monophase), and
heavy viscosities.
 Materials come in an assortment of fast to regular set materials.
 https://www.youtube.com/watch?feature=player_detailpage&v=MgdH
WSUb2UA

22. “hydrophilic” nature of some
 Some materials are called “hydrophilic” but in actuality they are hydrophobic
materials that a wetting agent, a soap like surfactant has been added, so that it can
tolerate the presence of a small amount of moisture.
 In a newly placed impression, it takes several seconds for the surfactant to move to
the surface.
 Initially, the material Is not hydrophilic when it first contacts the teeth and tissues,
but becomes more moisture tolerant as the surfactant rises to the surface.
 This delay in the emergence of the surfactant means that the preparation needs to be dry when
the wash material is placed.
 However, the set impression will be more receptive to pouring with die stone.

23. PVS
 The accuracy of an impression material is measured by how well it
captures the surface detail of a structure.
 To capture the detail, it must wet (have low contact angle) and flow over the
surface well.
 Low-viscosity materials (wash/syringe) wet and flow better than high-viscosity
(tray/heavy body), therefore capture more detail.
 Two-chamber cartridge is the most popular dispensing system
 A mixing tip fits over the end, and a hand-operated gun-type dispenser pushes
out the base and catalyst through the mixing tip at the same time.

24. Clinical Tip
Before placing the mixing tip onto the syringe,
extrude a little to ensure no blockages from set
material.
Also extrude the first inch of the mixed material,
to ensure homogeneous mixing throughout.

25. Polyvinyl siloxane (PVS)
 Examix- yellow- heavy body
 Automix- pink- light body
 Final impression material for crown and bridges
 Has smallest dimensional change
 High elastic recovery with removal form from undercuts
 Mixing time is 30-45 seconds for syringe
 Mixing time is 45-60 seconds for tray
 4-6 minutes vinyl polysiloxane

26. PVS Putty/Wash Techniques
 Some like to use putty for the tray material, and a light body
wash material to syringe around the prepared tooth.
 They feel that with subgingival margins on the preparations,
the stiff putty causes a hydraulic pressure that forces the wash
material into the gingival sulcus to better capture the margins
in the impression.
 There are two techniques.
One-step technique
Two-step technique

27. One-step
 Putty is mixed and loaded into the tray by the assistant,
while the operator injects the syringe material around the
prepared tooth.
An indentation should be made in the putty in the area of the prep
to allow wash material to cover the prep without being displaced
by the putty
 The tray is seated while the putty and syringe material are
still unset, allowing them to bond together.

28. Two-step
 Putty is used to create a custom tray within a stock tray.
 In the first step, the putty is mixed and placed in the stock tray.
 It is seated over the teeth with a plastic sheet placed between the putty and the teeth to create
room for light body material.
 Some prefer to cut away some of the putty after it has set to create space for the light body material,
rather than using the plastic sheet.
 In the second step, light body is syringed around the prepped teeth, and some is injected into the
space in the putty created by the teeth.
 The tray with the putty is seated over the teeth.
 The putty should NOT show through the wash material.
 Show-through areas are pressure spots where the preparation hit the putty.
 The putty will compress while the tray is in the mouth, and then rebound after the tray is removed.
 This will cause distortion in the impression.

29. Polyvinyl siloxane
 Paint tray with adhesive
 Lubricate the plunger of syringe
 Dispense equal lengths of catalyst and base
 Place syringe material on one pad, and the tray material on the other
 Use stiff bladed spatula to pick up catalyst and incorporate into base
 Load syringe by wiping barrel across the material on the mixing pad, wipe excess
 Pass loaded syringe to operator
 While operator injects, mix the tray material and load tray
 Receive the syringe from operator and pass loaded tray
 Set timer
 https://www.youtube.com/watch?feature=player_detailpage&v=0RjUBTF8RJ0

30. Clinical Tip
PVS putty should NOT be mixed while latex gloves are
worn.
Sulfur products from the gloves can interfere with the
material.
Washed hands, covered with vinyl gloves should be
worn.

31. Polyether
Polyethers
Hydrophilic nature: Good wetting properties for making
detailed impressions in presence of small amount of
moisture
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Pentamix; 3M ESPE.

32. Polyether
 Polyethers are very accurate materials with good flow and tear
strength and are excellent for use in crown and bridge procedures.
 They are more hydrophilic than PVS.
 They do not release hydrogen gas, so they can be poured immediately.
 They have excellent mechanical properties with good elastic recovery,
and they do not shrink.
 Originally a very stiff material but newer formulas have made the
material more flexible.

33. Polyether
 With all elastomers, undercuts around bridge pontics, open
embrasures around periodontally involved teeth, and fixed
implant fixtures should be blocked out with utility wax,.
 This will prevent the impression material from flowing under
them and locking the impression tray in the mouth.
 It is a very unpleasant experience for both the patient and
the assistant to have locked-in impression trays cut with burs
to remove them from the mouth.

34. Before taking a polyether impression…

35. Polyether
Polyethers are supplied as light, medium and heavy
body viscosities.
Regular set materials have a working time of 2 to 3
minutes and setting time of 5 to 6 minutes.
Fast set materials have a working time of 1 minute and
a setting time of 4 minutes.
https://www.youtube.com/watch?feature=player_detail
page&v=RpKXYWTEXKg

36. Polyether
 Mixing time- 30-45 seconds
 Setting time- 5-7 minutes
 Paint tray with adhesive
 Lubricate plunger of syringe
 Equal lengths of catalyst and base
 Mix syringe material on one pad, and tray material on another (need two pads
and two spatulas)
 Load syringe and pass to operator
 Mix tray material and load tray
 Receive syringe and transfer tray
 Set timer

38. Polyether
Impressions from this material can be
poured up repeatedly for up to a week and
can be shipped to a dental laboratory and
remain dimensionally stable for up to 14
days if properly stored.

39. Pentamix
https://www.youtube.com/watch?feature=player
_detailpage&v=z20Yk1O68bk
https://www.youtube.com/watch?feature=player
_detailpage&v=bxowdm6Nn4Q

40. Impression
Material
Cost Surface
Detail
Dimensio
nal
Stability
Tear
Strength
Ease of
Use
Pour
Within
Ability to
Re-pour
Alginate Low Lowest Low Low High 1 hour No
Addition
Silicone
(PVS)
High High Highest Medium High 1 week Yes
Polyether High High High Low to
medium
High 1 week yes

41. Suggested Homework
 Review information on chapter 15 at
https://evolve.elsevier.com/cs/product/9781455773886?role=student