1. Impression Materials Chapter 46 1
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2. Impression
A negative reproduction of a patient’s oral tissues including all teeth and surrounding hard and soft tissues used to create a positive model which can be used for diagnosis and fabrication of devices.
Impression materials are used to obtain an impression ( an imprint) of teeth, the surrounding oral tissues, or both.
How many students have had impressions taken?
For what reasons?
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3. Types of Impressions
Preliminary
Taken by Doctor or Expanded Function Dental Assistant (RDA)
Used for diagnostic models, fabrication of custom tray, orthodontic appliances, provisional coverage, bleaching procedures, pretreatment and post-treatment records
Final
Taken by Doctor only
Most accurate reproduction
Used to create indirect restorations, partial and full dentures, and implants
Occlusal ( Bite Registration)
reproduction of occlusal relationship between maxillary and mandibular teeth when in occlusion
Allows dentist and CDT to establish proper centric occlusion on stone and plaster models

4. Examples of impressions
Preliminary Impression
Final Impression

5. Bite Registrations Impression Paste Bite Wax Bite
Why are bite registrations important in the fabrication of indirect restorations?
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6. Impression Trays Must be sufficiently rigid to:
Carry the impression material into the oral cavity
Hold the material in close proximity to the teeth
Avoid breaking during removal
Prevent warping of the completed impression
Are impressions a positive or negative reproduction?
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7. Types of Impression Trays
Stock – trays that fit a variety of people
Types:
Rimlock – solid or perforated
Plastic solid or perforated
Triple tray – takes upper, lower and bite registration at one time
Custom- trays that are made for one particular person

8. Shapes of Stock Impression Trays
Quadrant tray
Covers one half of the arch
Section tray
Covers the anterior portion of the arch
Full-arch tray
Covers the entire arch
Perforated tray
Has holes in the tray to create a mechanical lock to hold the material in place
Smooth tray
Interior painted or sprayed with an adhesive to hold the impression material
Are impression trays metal or plastic?
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9. Fig. 46-1 Types of stock trays.
What is a triple tray?
What are the advantages of using a triple tray?
Which of these impression trays needs to have an adhesive applied?
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10. Fig. 46-3 Examples of quadrant, section, and full-arch impression trays.
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11. Example of Custom tray

12. Tray-Selection Criteria
Must feel comfortable to the patient
Should extend slightly beyond the facial surfaces of the teeth
Should extend approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch
Depth to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth
Try the tray in the patient’s mouth before mixing material.
Explain the procedure to the patient.
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13. Tray Adhesives Define: substance used to hold material into tray
Types:
Hold Spray on or liquid adhesive (blue)
For alginate and hydrocolloid impression materials
VPS adhesives (blue)
For polyvinylsiloxane and polyether impression materials.
Rubber base adhesive (brown)
Used with rubber base impression materials.
Silicone adhesive (orange-pink)
Used with silicone impression materials.
Tray adhesives should be applied after the tray has been tried in the patient’s mouth.
How long should the tray adhesive be applied to the tray before the impression material is added?
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14. How & When is adhesive applied?
After fitting and sizing tray in patient’s mouth
Rinse and dry
When using spray; apply over a protected area
When using liquid; apply with disposable brush or applicator; do not double dip
Coat internal surfaces with thin layer of adhesive
Allow adhesive to dry at least 15 minutes or it may not hold the impression material tightly into the tray

15. Categories of Impression Materials
Inelastic (Rigid)
Elastic (Flexible)
Impression compound
Zinc oxide eugenol
Impression Plaster
Mostly obsolete
Aqueous-(water-based)(Hydrocolloids)
Irreversible Hydrocolloids(Alginate)
Reversible Hydrocolloids(Agar-Agar)
Non-aqueous-(rubber-based)(elastomers)
Polysulfide
Polyether
Condensation silicone (polysiloxane)
Addition silicone (polyvinylsiloxane)

16. Hydrocolloid Impression Materials
Types:
Reversible Hydrocolloid
AKA - Agar
Irreversible Hydrocolloid
AKA – Alginate
These materials are used to obtain preliminary and final impressions
Which one is used for preliminary?
Irreversible Hydrocolloid (Alginate)
Which one is used for final?
Reversible Hydrocolloid (Agar) 16

17. Hydrocolloids Which one is which? Define sol: Define gel:
Hydro means water (dispersion medium is water)
Colloid means suspension of molecules or groups of molecules in some type of dispersing medium; it is a gelatin substance
Depending on type: physical change between sol and gel comes from irreversible chemical reaction or changes in temperature
Which one is which?
Alginate (chemical) Agar (temperature)
Define sol:
Viscous liquid ( colloidal solution) ; solid particles in a liquid
Define gel:
Rigid form of sol; setting of a sol, looks like gelatin

18. Key Ingredients of Alginate
Soluble Potassium alginate (chief ingredient)
Comes from seaweed; also used in foods such as ice cream as a thickening agent
Calcium sulfate(reactor)
Helps the potassium alginate readily dissolve into the water to form a viscous sol
Trisodium phosphate (retarder)
Reacts with the reactor to slow up the gelation so there is time to load and place the tray in the mouth before gelation or setting occurs
Diatomaceous earth
A filler that adds bulk to the material
Zinc oxide
Adds bulk to the material
Potassium titanium fluoride
Added so as not to interfere with the setting and surface strength of gypsum
No taste.
Flavors are available. (Cherry is the most common.)
Odor-free. 18

19. Physical Phases of Alginate
First phase
In the sol (as in solution) phase, the material is in a liquid or semiliquid form.
Second phase
In the gel phase, the material is semisolid, similar to a gelatin dessert.
On completion of both phases, alginate is susceptible to tearing and stretching.
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20. Packaging and Storing of Alginate*
Alginate material is supplied as a powder
How is it packaged?
Containers / Canisters (bulk)
Premeasured packages (unidose)
*The shelf life of alginate is approximately 1 year.
Alginate should be stored at room temperature. 20

21. Fig. 46-5 Packaging of alginate.
Alginate impression materials come in a reusable tub with a measuring scoop. This is the most common form of alginate.
Premeasured foil packets are available at a slightly higher cost.
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22. Cause of Distortion and Dimensional Change
Define Imbibition?
Soaking up of liquid
Alginate impression stored in water or a very wet paper towel will absorb the additional water and expand.
Define Syneresis?
Loss of liquid
If an alginate impression remains in the open air, its moisture will evaporate, causing the impression to shrink and distort.
How long after the impression is obtained should we proceed to pouring?
Storing the impression in a plastic bag can help prevent distortion.
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23. Alginate Settings Normal-set alginate Fast-set alginate Working time
Working time of 2 minutes and a setting time of up to 4½ minutes after mixing
Fast-set alginate
Working time of 1¼ minutes and a setting time of 1 to 2 minutes
Working time
The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth
Setting time
The time required for the chemical action to be completed.
Which setting time would be preferred for a patient who has a sensitive gag reflex?
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24. Hydrocolloids: Handling Alginate: Fluff powder and measure accurately
Measure water – temp!
Mix in a flexible,
rubber bowl
Stir to wet powder
Stir mixture against side of bowl to eliminate air bubbles
Mix until creamy & homogeneous; 60 sec.
Water temperature is a factor in setting time!!
Cooler water will INCREASE the working time (Slows down the setting time)
Warmer water will DECREASE the working time (Faster setting time)
Can purchase regular or FAST set alginate.

25. Hydrocolloids: Handling Alginate:
Load alginate into tray from posterior
Press material into tray to eliminate voids
Smooth & indent alginate with wet finger
Use extra alginate to wipe onto occlusal surfaces of teeth
Load the mandibular tray from a posterior and lingual direction. Press alginate into tray to make sure no air is trapped.

26. Altering the Setting Time of Alginate
Cooler water can increase the setting time if additional time is needed for the procedure.
Warmer water can reduce or shorten the setting time of the procedure.
Which water temperature would be preferred for a patient who has a sensitive gag reflex? Why?
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27. Water-to-Powder Ratio
The mixture is equal in ratio: 1 water to 1 powder
General Rules:
Adult mandibular impression
Two scoops of powder and two measures of water
Adult maxillary impression
Three scoops of powder and three measures of water
These ratios are only guidelines for measurement.
Check the manufacturer’s directions before measuring.
Adjustments may have to be adjusted, because not all patients are the same.
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28. Fig. 46-6 A plastic scoop and plastic cylinder are supplied with alginate.
Do not pack powder into scoops.
Use a spatula to level the top of the scoop.
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29. Taking an Alginate Impression
Which arch should be taken first?
Mandibular less gagging
Where does the assistant stand to take the impressions?
Mandibular, in front on the side
Maxillary, in back of patient on the side
Explain the procedure to the patient:
The material will feel cold, there is no unpleasant taste, and the material will set quickly.
Breathe deeply through your nose to help relax and feel more comfortable.
Use hand signals to communicate any discomfort.
Never leave the patient alone during this procedure.
Would we ask the patient whether he or she has a sensitive gag reflex? Why or why not? 29

30. Acceptable Alginate Impressions
The impression tray is centered.
The "peripheral roll," including all of the vestibular areas, is completed.
The tray is not "overseated."
The impression is free of tears or voids.
Sharp anatomic detail of all teeth and soft tissues is captured.
The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression.
The hard palate and tuberosities are recorded in the maxillary impression.
If these criteria are not met, you must retake the impression.
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31. Fig. 46-7 How an impression must appear.
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32. Supplies needed for taking alginate impressions
Alginate powder / room temperature water
Rubber bowl/wide blade spatula
Water measuring device/ powder scoop
Impression tray/ tray adhesive if needed
Utility wax
Emesis basin
Baby oil / tissues (optional)
Disinfecting spray

33. Irreversible Hydrocolloid:
Advantages:
Easy & economical
Many applications
Patient comfort
Excellent wetting by gypsum
Disposable tray
Disadvantages:
Not enough detail for final impression
Must be poured immediately

34. Reversible Hydrocolloid
Agar or Agar-agar (from seaweed)
Premixed and comes as a semisolid material
Needs special equipment

35. Reversible Hydrocolloid
Conditioning Bath -Three compartments
A conditioning water bath liquefies the semisolid material at 212° F (100˚ C)
Boil for 10 minutes minimum (more if previously heated(3 min minimum))
Tray and syringe materials are changed from gel to sol
A storage water bath, holds materials at 150˚ F (66˚ C)
readies the material for the impression in its tubes.
Syringe material never leaves this compartment until impression (stored tip side down)
A tempering water bath keeps material at 110° F (45˚ C)
Tray material is held here for 5 minutes
Cools material so it doesn’t burn the patient
Can be placed while in tubes or tray
Longer steps are required to obtain this type of impression. 35

36. Reversible Hydrocolloid:
Agar – a gelatinous material + water
Thermoplastic – NO chemical reaction
“Reversible” –
Goes from gel, to sol, and back to gel,
by raising and lowering temperature
Dispensed in tubes & syringes
Very accurate final impression material
The tubes of the material are used to dispense material into the impression tray. The syringe carpules are used to dispense the material in areas of the most detail – for example, the prep site. The syringe material will be extruded all around the prep; the tray will be filled from the tube; then the tray will be placed over the arch or quadrant. The syringe material will be imbedded into the tray material when it is set.

37. Reversible Hydrocolloids:
Handling Reversible Hydrocolloid:
Load syringe; extrude onto prep site
Seat tray in mouth
Attach cooling hoses to tray
Hold firmly in patient’s mouth until cooled and transformed to gel state
Remove from patient’s mouth and pour immediately

38. Elastomers 38

39. Elastomeric Impression Materials
Elastomeric impression materials are used when an extremely accurate impression is essential. The term elastomeric means “having elastic or rubberlike qualities.”
Commonly used in dental offices.
Easier to use than reversible hydrocolloids.
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40. Elastomers: Two-paste systems: Set by chemical reaction
Two tubes – pastes mixed by hand
Two putties – mixed/kneaded by hand
Cartridge & Extruder Gun – automix tips used
Cartridge & Motor-driven Mixer – automix tips used
Set by chemical reaction
Warmth and moisture may slow setting
Must use a tray adhesive (if tray not perforated)
Latex may inhibit set of polyvinylsiloxanes
Tray adhesives vary per each elastomer – if a tray has good retention holes or perforations, then an adhesive may not be necessary.
Latex gloves and rubber dams should not contact impression material – it will inhibit the set. Use of vinyl gloves are recommended when kneading putty or handling materials.

41. Elastomers: Elastomers are used in a two-step process:
Preliminary Impression - the material used to form the base or the “tray” material used in an impression; usually more viscous or heavy-body
Secondary or “Wash” Impression – the material applied through a syringe around the prep site for detail; usually less viscous;
light or medium -body.

42. Elastomers: POLYSULFIDE: Oldest elastomeric used in dentistry
Two pastes – mix base with catalyst
Liquid polymer with “sulfhydryl” group – contains sulfur
“rubber-base” impression material
Used best with custom trays
Other materials have replaced this one

43. Elastomers: Handling Polysulfides: Equal lengths of pastes on pad
Pastes are “swirled” together, then stropped
Material placed in custom tray
Take impression – hold in place for up to 15 min.
Remove from pt’s mouth slow & steady force
Rinse & disinfect
Pour-up impression within several hours

44. Polysulfides: Advantages: Economical Good tear resistance
Good compatibility with gypsum
Disadvantages:
Bad odor
Stains clothing
Long setting time
Fair stability
Less accurate

45. Elastomers: Condensation Silicones:
Similar to silicone rubber products (but non-toxic)
Setting by-product of alcohol
“Hydrophobic” – results in voids in stone
Shrinkage occurs as it sets
Must be poured immediately
Accurate, but slow setting time
Replaced by improved products
The better materials are hydrophilic – water loving and have better wettability for the gypsum. This material resulted in bubbles and voids in the stone, since it is hydrophobic – not attracted to water

46. Elastomers: POLYETHERS: Developed in 1960’s
No reaction by-product produced
Shorter working and setting time
Only come in a single viscosity
Stiff material – can use a triple tray
Very popular – “Impregum”
No need to pour-up immediately
The polymerization of the polyether does not yield a by-product as it sets.

47. Elastomers: Handling Polyether:
Mix equal lengths of paste; or extrude through the automix cartridge tip
Load syringe and apply to tooth thru tip
Load tray and invert over area for impression
Allow to set; 4 – 5 minutes
Remove from mouth
Rinse & disinfect

48. Polyether: Impregum

49. Polyether: Advantages: Short setting time Single viscosity
Good stability
Good tear strength
Clean & easy to use
Disadvantages:
Bad taste
Most difficult to remove from mouth

50. Elastomers: ADDITION SILICONES:
“Polyvinylsiloxanes” – silicone polymer
Two pastes or two putties
Hydrophobic by nature – manufacturers adding components to increase wettability
Very accurate & fast setting
Avoid contact with latex (gloves, rubber dams)
Low setting shrinkage & very stable

51. Elastomers: Handling Addition Silicone:
Mix equal lengths of pastes, or automix
Apply light-body material to tooth thru syringe
Load tray with heavy-body
Set tray over prep site
Set in 4 – 5 minutes
Rinse & disinfect

52. Addition Silicone: Polyvinylsiloxane
Advantages:
Very stable
Short setting time
Good tear resistance
Great accuracy
No bad taste
Disadvantages:
May have poor wettability
Two pastes to mix
Can be poured up days after the Impression is taken.

53. Characteristics of Elastomeric Impression Materials
Name the two components of an elastomer?
Base and catalyst
Base
Packaged as a:
Paste in a tube
Cartridge
Putty in a jar
Catalyst/Accelerator
Liquid in a bottle with a dropper top
Very accurate impressions are obtained with the use of this material.
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54. Forms of Elastomeric Materials
What is another term used to describe different forms?
viscosities
Different viscosities available
Light-bodied
Also referred to as syringe type or wash type
Used because it can flow into and around the details of the prepared tooth
Placed on and immediately around the prepared teeth with the use of a special syringe or extruder guns tips
Regular ,heavy and very heavy-bodied
Also referred to as “tray-type” materials, they are much thicker. As the name implies, they are used to fill the tray. Their stiffness helps force the light-bodied material into close contact with the prepared teeth and surrounding tissues to ensure a more accurate impression of the details of a preparation.
The syringe may be disposable or sterilizable and reusable.
Extruder tips are disposed of after each use. 54

55. Impression Compound
Has been used in the past to make impressions of edentulous arches, but is used more commonly in other applications.
Common uses:
Serves as impression tray to carry some other impression material. Placed inside of stock tray to make it a custom tray then second material is placed inside to capture more detail.
Used to make impression of single tooth preparation inside of copper band that does not have significant undercut areas.
Used to record muscle attachments prior to taking final denture impressions.

56. Properties and Ingredients of Impression Compound
Impression compound is a thermoplastic material
Composition
Natural resins, waxes, fillers and pigments
Supplied
Wafers, plates, sticks and cones
Colors
Brown, Green, Gray and Ivory

57. Equipment needed to use impression compound
Water bath
Bunsen burner w/matches or lighter
Copper bands/ Crown and Bridge scissors
Tempering water bath

58. Impression plaster Used in the past to take edentulous impressions
Obsolete
See gypsum notes for further information

59. Occlusal Registration
Occlusal registration is an accurate registration of the normal centric relationship of the maxillary and mandibular arches. Also commonly referred to as the bite registration.
What is centric occlusion?
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60. Types of Occlusal Registration
Wax bite
The wax bite is useful when the diagnostic casts are trimmed.
The most common technique involves the use of a softened baseplate wax.
Polyvinylsiloxane bite-registration paste:
Supplied both as a paste system and also as cartridges
Fast-setting
No resistance to biting forces
No odor or taste for the patient
Gains dimensional stability over time
Convenient to use
Equipment needed: laboratory knife and heat source.
What type of heat source is used?
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61. Fig. 46-17 Wax bite registration.
How long should the wax bite registration stay in the patient’s mouth?
Does this impression need to be disinfected?
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62. Bite registration using PVS