1. Assalamu-alaikum
DR. TAJAMMUL AHMED

2. IMPRESSIONS & TECHNIQUES IN FIXED PARTIAL DENTURE

3. Impression
GPT-8
Impression : a negative likeness or copy in reverse of the surface of an object; an imprint of the teeth and adjacent structures for use in dentistry.

4. Considerations for Precision Impression Taking
Before Impression Making (Extra-oral):
- Easy to mix
- Long working time
During Impression Making (Intra-oral):
- Hydrophilic
- Ability to flow around preparation without slumping
- Detail-capturing
- Snap set
- Good taste & odor

5. Upon Removal from Mouth: - Easy to remove
- High tear strength
- Good recovery from deformation
After Impression Making (Storage):
- Dimensional stability
- Easy to read
- Can be disinfected

6. During Pouring:
- Compatibility with gypsum
- Reproduction of details (ADA Specification 19: 20 microns)
- Ability for multiple pouring

7. CLASSIFICATION OF IMPRESSION MATERIAL
Nonelastic
Elastic
Hydrocolloids
Synthetic elastomers
Waxes, gums, resins
Polysulphides
Plaster of paris
Agar-Agar
Condensation-silicone
(Type I silicone)
Zinc oxide eugenol
Alginate
Impression compound
Polyether
Addition silicone
(Type II silicone)
Eugenol-free paste

8. ELASTOMERIC IMPRESSION MATERIALS
Depending on viscosity
Light body
Medium body / regular body
Heavy body
Putty

9. Reversible hydrocolloid (Agar-Agar) :
Introduced by Sears 1937
First elastic impression material
Longest continuous use
Available as :
Tray material
Syringe material

10. Tubes and cartridges of hydrocolloid placed in liquefying bath
Hydrocolloid conditioning with three baths : liquefying, storage and tempering
Tubes and cartridges of hydrocolloid placed in liquefying bath
Tubes and cartridges of hydrocolloid transferred from liquefying bath to storage bath
Tray filled with impression material placed in tempering bath

11. Cartridge of liquefied hydrocolloid is removed from storage bath
Cartridge of impression material is loaded into syringe
Blunt needle is attached to impression syringe

12. Irreversible hydrocolloid (Alginate) :
During World War II
Salt of alginic acid (anhydro d mannuronic acid)
Available as :
Dust free alginate
Chromatic indicator

13. ELASTOMERIC IMPRESSION MATERIALS
Accuracy / Detail capture :
ADA No. 19 fine detail of 25m
PVS impression material  best
Reversible hydrocolloid  least
Reproduction of fine detail of gypsum die materials  50 m
Lower the viscosity  Increased fine detail
Putty material  reported fine detail of 75m

14. Point of consideration  Interproximal, subgingival areas
Tear strength:
Measures the resistance to fracture of an elastomeric material subjected to tensile force acting perpendicular to a surface flaw.
Point of consideration  Interproximal, subgingival areas
 Slot and groove
Polymerized material in the gingival crevice
Torn material during removal

15. Hydrophilic group
Hydrocolloids
Polyether
Hydrophobic group
Polysuphide
C – silicone
A – silicone (PVS)
Works in wet environment (blood and saliva)
Readily wettable by the gypsum
Resistant to wetting (repelled by hemorrhage or tissue fluids)
Not readily wettable by the gypsum

16. Limited to small isolated areas
CONTAMINATION
Inhibition of polymerization of PVS impression material.
Direct inhibition
Direct contact with latex gloves
Impression are made with rubber dam in place
Mechanism of inhibition  Element sulphur react with chloroplatinic acid catalyst present in PVS impression material.
Indirect inhibition
Indirect contact of tooth and periodontal tissues during tooth preparation and gingival displacement procedure.
Limited to small isolated areas

17. Unpolymerized material remain adherent to prepared tooth surface
Contaminated surface will be slippery and sticky to touch
Clinical consideration :
Use of non latex gloves – Vinyl gloves
– Polyethene gloves
Avoid touching the tooth preparation and gingival areas
Avoid handling retraction cord with gloved hands.

18. TRAY SELECTION AND PREPARATION OF THE TRAY
Tray should be rigid.
Dimensionally stable.
Resist the deformation (loading heavy body material).
Provides the space for optimal thickness.
Plastic vs metal stock trays

19. Tray should be 2-3mm thick to ensure sufficient rigidity.
Incorporation of stops
Guide the clinician for positive seating
Three widely spaced stops
Non functional cusp of unprepared teeth, edentulous areas or the palate.

20. Tin foil or aluminium foil should be used over the wax spacer to prevent decrease in adhesive bond

21. Adhesion of the impression material to the tray
For accurate impression  proper adherence to the tray
Tray adhesive composition
– poly dimethyl siloxane and ethyl silicate.

22. Adequate mixing and loading :
Earlier materials  base and catalyst tubes
Present materials  cartridges with mixing tips
 Gun like dispenser
Automixing system :
Lesser inherent voids
Extend the essential working time
Reduced waste
Uniformity in proportioning

23. ELECTRIC MACHINE DEVICE (Dynamic Mechanical Mixer)
Provides uniform mix with touch of a button
Far fewer voids in the set elastomers

24. IMPRESSION TECHNIQUES

25. AGAR IMPRESSION TECHNIQUE
Armamentarium :
Tray and syringe material
Water cooled trays
Conditioning unit
Procedure :
Tray material
Syringe material
Loaded tray in tempering bath

26. Dentate arch is flooded with water
Water cooling tubes connected to seated tray
Completed impression
Disadvantages –
Dimensionally unstable / distortion during gelation
Initial expenditure for instruments
Multiple pouring is not possible

27. ALGINATE IMPRESSION TECHNIQUE
Clinical interest :
For the study cast / diagnostic cast – diagnostic wax up
– mock preparations
For interim restoration (temporization)
Clinical considerations
Tray selection
Perforated metal / rigid plastic trays
Tray adhesive
Perforations – insufficient
To prevent detachment of impression, Extend 2-3 mm outer surface

28. Loading the tray Making the impression Sectional placement
Wet gloved finger
Making the impression

29. HYDROCOLLOID LAMINATE TECHNIQUE ALGINATE – AGAR METHOD
Prepared tooth surfaces
Injection of reversible hydrocolloid
Stock tray with chilled alginate
Combined alginate –agar impression
Master cast

30. Critical to success  bond between agar and alginate
Advantages :
Satisfactory surface reproduction
Good wettability (smooth, dense model)
Simple conditioning (no tempering bath / water cooled trays)
More economical
Disadvantages :
The bond between agar and alginate is not sound
Higher viscosity alginate displaces agar hydrocolloid

31. PUTTY WASH IMPRESSION TECHNIQUES (Stock tray impression technique)
One stage or one step putty wash impression
(Simultaneous technique / squash technique)
In this technique putty and wash are recorded simultaneously
Disadvantage :
Difficult to control thickness of wash material
Higher viscosity material displaces the wash material
- Critical areas captured in putty rather than light body
Setting distortion of the putty add to over all distortion of impression

32. TWO STAGE OR TWO STEP PUTTY WASH TECHNIQUE
Two step unspaced impression technique
Preoperative putty impression is recorded
Preset putty impression is relined with thin layer of wash
Two step spaced impression technique
Preoperative putty impression is made
Space for the light body wash material is provided to reline the putty

33. DUAL PHASE IMPRESSION TECHNIQUE
(Multiple mix technique, laminate single impression technique, custom tray impression technique)
Two consistencies
Light body syringe material
(wash type)
Heavy body – tray material
Tray material will force the light body material into the gingival sulci and preparation detail
Custom tray with 2–3mm space

34. ADVANTAGES
Uniform thickness of impression material (2-3 mm)
Viscosities of 2 materials reduces drags and improves the blending of 2 phases.
Good marginal definition.
Less impression material is required.
DISADVANTAGES
Construction of custom tray (time / cost)
Differential shrinkage

35. Monophase impression technique (Single viscosity technique)
Medium viscosity – polyether or addition silicone
Used as both tray material and syringe material
Custom tray with 3 mm spacer
Depends on pseudoplastic property
DISADVANTAGES
Reduced ability to flow into intra coronal features and gingival crevice
Greater amount of polymerization shrinkage compared to heavy body
Surface reproduction may not be as good as light body material

36. Copper band or tube method
The copper band is used to salvage an impression of multiple preparation where there is only vague margins on one or two preparation that are not adequately replicated in the impression.
Copper band with orentation holes
Copper band contoured
Evaluating the fit of the copper band
Copper band with the final impression

37. Close bite double arch method
Close bite double arch method . synonyms: dual quad tray, double arch ,triple arch, accu-bite, closed mouth impression.
Advantages
The physical deformation of the mandible is minimal
The shifting of teeth occurring during maximum intercuspation is captured.
Less impression material is needed.
Less gagging may occur.
Disadvantages
The tray is not rigid .
Limited to one casting per quadrant .
The distribution of impression material is not uniform

38. Close bite double arch method
Close bite double arch method . synonyms: dual quad tray, double arch ,triple arch, accu-bite, closed mouth impression.
Technique
Evaluate the fit of the tray in the patients mouth & observe the complete bilateral closure and the patients comfort.
The high viscosity material is used in the tray & then the low viscosity material is syringed over the high viscosity in the tray & positioned on the arch.
Instruct the patient to close the mouth and observe for the interdigitation on the opposite arch. Wait for the material to set .
Instruct the patient to open the mouth & remove it by applying equal pressure bilaterally. Evaluate the impression.

39. Closed mouth impression
Close bite double arch method . synonyms: dual quad tray, double arch ,triple arch, accu-bite, closed mouth impression.
Closed mouth impression

40. FLAWS RELATED TO IMPRESSION TECHNIQUE
Visible flaws :
Finish line not visible  Inadequate gingival displacement
Gingival inflammation and bleeding
Crevicular fluid and heamorrhage
Poor moisture control
Dry field

41. Air bubbles / voids in critical areas
Mixing
Syringing
Keep syringe tip in expressed material
Start syringing from distal interproximal area (distoligual)
Fill the base of grooves, boxes first
Tray loading and tray seating

42. Drags
Reason :
Poor flow of putty
Premature syringe of impression material
Poor bond between the tray and syringe material
Unset / unpolymerized impression material  contamination
INVISIBLE FLAWS
Tray and impression recoil
Permanent deformation
Detachment of impression from the trays

43. DISINFECTIONS OF IMPRESSIONS
To prevent exposure and cross infection
Disinfection before poring the cast.
Disinfection methods :
Spray-on disinfectants
Immersion of impression in chemical disinfectant (Submerged / soaking)
Types of chemical disinfectant used :
Chlorine compounds
Synthetic phenolic compounds
Glutaraldehyde
Idophores
Combination of phenols and alcohols
Hydrophilic impression material  hydrocolloids, polyether should be sprayed rather than immersion.
Idophore sprays, sodium hypochlorite sprays (1:10 ratio).
Agar (reversible hydrocolloid)  10 min immersion in 2% alakaline glutaraldehyde  more than 20 min affects the dimensional stability and surface detail.
Alginate (irreversible hydrocolloid)  Westerholm et al (1992) full strength (5.25%) sodium hypochlorite spray.
Polysulphide and condensation silicone immersion in sodium hypochlorite, glutaraldehyde 10-30min.

44. ADA recommends the use of 1: 2.13 dilution of iodophor
If an impression has not been disinfected, or if the laboratory has no assurance that an appropriate disinfection protocol was followed, it is necessary to disinfect the stone cast.
ADA recommends the use of
1: 2.13 dilution of iodophor
1: dilution of sodium hypochlorite
Stone cast be disinfected by
Spraying until wet
Immersing for the time recommended for tuberculocidal disinfection.
Use of disinfecting solutions, spray disinfectants (containing iodophor or hypochlorite)
Disinfectant containing dental stone
When a patient with known cases of infections are being treated, overnight gas sterilization is an option
Cast to be disinfected should be fully set (i.e. stored for atleast 24 hours).
A disinfectant stone is marketed now and has been shown to have bactericidal properties. However, this product has not yet EPA registered as a disinfectant.

45. CaviCide
A broad-spectrum tuberculocidal disinfectant decontaminant cleaner that effectively kills TB (in 5 minutes) and HBV (in 3 minutes).
CaviWipes
Durable, non-woven, nonabrasive towels pre-saturated with CaviCide.

46. Conclusion

47. Thankyou