Impressions (for indirect restorations) Flashcards by Soph 1

How to get a good impression?

Impression tray choice
Good soft tissue management
Appropriate technique
Appropriate choice and use of material

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Which tray should I use?

Size of tray - trim the tray in the mouth, adequate seating? Room for rotation?
Rigid tray - supports material, maintains pressure on teeth and soft tissues, prevents distortion, retention with perforated holes

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Define accuracy

Ability to replicate hard and soft tissues

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Define resolution/precision

Ability to reproduce fine surface detail

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Define dimensional stability

Maintenance of the material in terms of size and shape over a prolonged period of time

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Define hydrophobic materials

Don’t like water, may lead to bubbles, voids, inaccuracies if inadequate moisture control

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Types of hydrocoloids?

Reversible (agar)

Irreversible (alginates)

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Types of synthetic elastomers?

Polysulphides
Polyethers
Silicones - addition silicones, condensation silicones

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Ideal properties of impression materials?

High accuracy
Elastic
Good dimensional stability
Good tear strength
Easy to use
Acceptable taste and smell
Cheap
Tolerant to disinfection
Good working and setting times

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Why is alginate not used for indirect restorations?

Insufficient reproduction of surface details
Poor dimensional stability
Not suitable for definitive indirect restorations
Used for the opposing arch

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Uses of addition silicones/polyvinyl siloxanes (PVS)? How does it work?

Impression material for fabrication of indirect restorations
Addition reaction between silane and vinyl groups when catalyst and base pastes are mixed
No byproducts produced - very good dimensional stability
Hydrophobic - increased risk of air entrapment

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Advantages of addition silicones?

Excellent dimensional stability
Excellent surface detail reproduction
Wide range of material choice and techniques
Biocompatable
Simple mixing and reasonable working time

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Disadvantages of addition silicones?

Expensive
Hydrophobic - but getting better
Setting time affected by temp
Can be difficult to remove from casts
Some latex gloves could inhibit setting

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Formulations of addition silicones?

Putty
Heavy bodied silicone
Medium bodied silicone
Light bodied silicone
Super light bodied silicone

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Positives of heavy bodied/putty addition silicone?

High filler
High viscosity
High dimensional stability

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Positives of light/medium bodied addition silicone?

High detail reproduction
High thermal contraction
High setting contraction

Polyether features?

Good for fixed prosthodontics
Good accuracy and hydrophilicity allows it to compete with addition silicones
Rigidity - difficult to remove from the mouth and may remove periodontically involved teeth
Rigidity is favoured - popular material, commonly used for impressions of implant copings

Advantages of polyethers?

Excellent dimensional stability
V good surface detail reproduction
Only one viscosity but undergoes shear thinning allowing it to flow
Hydrophilic

Disadvantages of polyethers?

Very stiff/rigid difficult to remove from mouth and cast
Swells with water if kept for long time in damp environment
Bitter taste

How to disinfect impressions?

Trim off excess
Contaminated in water and blood
Risk of infecting surgery and lab staff is cross infection procedure not followed
Rinse under tap to remove debris
Put in disinfectant bath - soak for 10 mins - longer can affect the accuracy of the impression

Soft tissue management?

Retraction cord
Retraction pastes
Haemostatic agents
Electrocautery
Soft tissue laser
Rotatory curettage

How to retract the gingivae?

Downward and outward movement of the free gingival margin
Allows us to syringe impression material beyond preparation margin
Does not control inflam or allow us to take an impression when the gingivae are inflammed - manage this beforehand

What is a retraction cord?

Cord that’s packed into the gingival sulcus to retract the gingivae to improve visibility, access and moisture control
Single cord technique most common (removed before impression)
Cord often soaked in haemostatic agent to prevent bleeding

What are retraction pastes?

Viscous agent syringed into gingival sulcus to provide retraction and haemostasis
Useful in simple cases with equi-gingival finish lines
More expensive

Electrosurgery and soft tissue lasers features?

``` Widen or re-contour gingival profile Widen gingival sulcus Remove overgrown tissue Used in combination with cord or paste usually Haemostasis ```

Techniques for addition silicones?

Twin mix or one stage (most common) = at least 2 viscosities used, seated in mouth together Two stage - First impression taken in putty, removed just prior to full setting - Then reline with lower viscosity (light body alone or in combo with medium body)

Protocol for the one stage addition silicone impression?

Adequate tray, adhesive applied Select material: combo of putty or heavy body with light body Soft tissue management - retraction cord, retraction paste, electrocautery Place putty/heavy body into tray Remove retraction cord (damp) if used Dry teeth Syringe light body around preparation - starting within gingival sulcus and ending at coronal part of prep - use controlled pressure to force material against tooth Place some light body into putty/heavy body on tray Seat impression Cafeful removal in 1 direction - do not rotate Inspect, rinse and disinfect Send to lab

Two stage addition silicone impression protocol?

Adequate tray, adhesive applied Select material - combo of putty/heavy body with light body Spaced placed (thin sheet of plastic) Take impression Essentially creates a special tray Follow previous steps: remove retraction cord, dry teeth, syringe light body around prep, reseat impression

Negatives of the two stage addition silicone impression technique?

If you dont sit the original impression in the same way - get a step or inaccurate

Should you use the single stage or two stage addition silicone impression technique?

Case dependent Single stage easier, quicker Putty - high viscosity so a lot of pressure is needed to seat the tray which can distort or push away the lower viscosity material If you don't have a rigid tray and you can see the lower viscosity material is being pushed from the prep margin - you could chose the 2 stage technique - however ensure you fully seat the original impression

What to look for when assessing your impression?

``` Well defined margins Good surface detail No drags or voids No tray exposure All prep in appropriate material (light body) Impression adhering to tray ```

Why may you not be able to see your finish line?

Problem with prep, may need refining or smoothing to improve the surface feature Or it may be problem with impression - excessive bleeding or gingivocrevicular fluid affecting the set of the material? Are the gingivae healthy enough? Is my gingival retraction technique suitable?

Why may your impression have bubbles/voids/drags?

Alginate mixing Drying the tooth is important to allow adequate wetting and to avoid bubbles/voids Keep tip of syringe within the material and starting from the finish line and ending occlusally should minimise the problem Whole impression tray needs to be filled with material so the impression is supported in all directions Chose the correct tray size