1. Impression materials أحمد عبد العزيز الحسين
أخصائي تركيبات سنيه في وزارة الصحة الأردنية
محاضر غير متفرغ في جامعة العلوم والتكنولوجيا الأردنية
Ahmad Abdul Aziz Alhussien
Prosthodontist at M.O.H
Part time lecturer at J.U.S.T
BSc , MSc, Jor. Board/ prosthodontics

2. The function of an impression material is to make a negative copy of the oral tissue … that is poured to produce a positive replica for these tissues

3. Requirement of an impression material
Must be a semi-liquid material that will flow and adapt itself around the structure of interest.
It must set and harden into a solid ?? that is rigid enough “not too rigid” to be removed from the mouth without becoming deformed.
Copy details accurately
Dimensional stability after removal from the mouth
Appropriate working time (from the start of mix)
Appropriate time to harden in the mouth (setting time)
Bio-compatibility/Aesthetic, odor/taste
Chemically compatible with material used to pour cast or dies

4. Impression trays
Used to carry the impression material into the oral cavity
Can be
metal or plastic
Perforated or non perforated
for edentulous or dentate
pre-manufactured (stock trays) or custom-made (made in the lab. From resin).
Trays need to be rigid enough to support impression material.
For impression material to be retained in tray, tray maybe perforated, and adhesive spray can be used to enhance retention.

5. Variety of trays

6. replica of dental arch Cast Die
replica of a single tooth (cut from a cast)

7. Classification of dental impression materials
Inelastic / Elastic
Mechanism of hardening

8. Impression material (rigid)
Inelastic materials
Setting mechanism
Impression compounds
‘Dental compounds’
Cooling to mouth temperature
Zinc-oxide eugenol (ZOE)
Chemical reaction
Impression plaster
Impression wax

9. Impression materials (aqueous)
Elastic material (hydro-colloid)
Setting mechanism
Reversible (Agar)
Cooling
Irreversible (Alginate)
Chemical reaction

10. Impression materials (rubber)
Elastic material (non-aqueous)
Setting mechanism
Polysulfides
Polymerization reaction
Condensation silicon
Polyether
Addition silicon

11. Inelastic impression materials (rigid)
Plaster of Paris (Type I gypsum)
Dental compound/impression compounds
Softened by heat and pressed against tissue before it hardens. Thermoplastic softens at 60°C, remains plastic at 45°C and becomes firm at mouth temperature. Used for primary impression
ZOE (Zinc oxide eugenol)
Other uses ???
Impression wax
Elastic impression materials (non-rigid)
Hydrocolloids
Elastomers (Rubber)

12. Hydrocolloids

13. Hydrocolloids
The colloid state represents a highly dispersed phase of fine particles within another phase, some where between solution and a suspension.
The colloid can exist as a viscous liquid known as a sol or a solid known as gel.
If the particles are suspended in water, the suspension is called a hydrocolloid (hydrosol, hydrogel
Hydrocolloids come in two forms:
Reversible agar
Irreversible alginate

14. Agar Composition of agar: Material Percentage purpose
Agar (seaweed extract)
12-15%
Colloidal particles as basis of the gel
Potassium sulfate 1%
Ensures set of gypsum materials
Borax
0.2%
Strengthens gel
Alkyl benzoate
0.1%
Antifungal agent
water
85%
Dispersing medium for the colloidal suspension

15. Properties
Flows well and adapts readily to hard and soft tissue contours
Accurate reproduction (hydrophilic nature), however, the impression need to be poured immediately.
Need to be stored in 100% humidity for short period of time if not poured immediately
Distortion is more likely to occur if impression not poured within an hour.

16. Tear strength is not high.
If compressed it might rebound if compression is not too sever otherwise deformation occurs.
Material suffers from loss or gain of water:
Syneresis: a process by which the gel contracts and some of the liquid is squeezed out, forming an exudate on the surface.
Evaporation: loss of water which causes the material to shrink, and impression is distorted.
Imbibition: uptake of water, this will swell and distort the impression.

17. Clinical application
The use of agar requires special equipment consisting of hydrocolloid conditioner (has 3 water bath chambers) and water -cooled tray connected to a rubber hose that delivers water.
Usually used in lab for cast duplication
Agar is supplied in two viscosities, thick and thin (depending on the amount of agar).

18. Preparing the material for impression:
Gel heated to °C, becomes liquid (sol)
Tray and agar syringe are liquefied in 8-12 minutes in boiling water in 1st chamber
2nd chamber is used to store the agar at 60-66°C.
3rd camber kept at 45-47°C to temper agar before use to prevent burns.
Agar exhibits hysteresis, melting at 85 °C and solidifying from °C

19. Alginate Common uses: Inexpensive Easy to manipulate
Requires no special equipment
Reasonably accurate
Common uses:
Diagnostic cast (study model)
Preliminary impression for complete denture
Partial denture framework
Custom trays for fluoride or bleaching

20. Composition/setting rxn/ working time
Material
Percentage
purpose
Na, K alginate
15-20%
Basis of the gel
Ca sulfate dihydrate
14-20%
Creates irreversible gel with alginate
Potassium sulfate
10%
ensures set of gypsum
Trisodium sulfate 2%
Retarder to control setting
Diatomaceous earth
55-60%
Filler to increase thickness and strength

21. Setting rxn/working time
Setting rxn occurs when the powder is mixed with water:
Ca sulfate dihydrate + NaAlginate Ca alginate
Working time: total time from start of mixing to the final time at which an impression tray can be fully seated without distortion
Regular set: 2-3 minutes
Fast-set: minutes
Setting time: elapsed time from the start of mixing until impression material becomes firm enough to resist permanent deformation.
Regular set: 2-5 minutes, Fast set: 1-2 minutes

22. Setting rxn/working time
Controlling water temperature shortens or lengthens setting time
Changing P:L has adverse effect on materials property and strength
Allow extra 1-2 minutes, tear strength increases, and rebound from undercuts w/out deformation improves

23. Important considerations to ensure accurate impression
2-4 mm bulk material in tray
Snap action removal from mouth
Allow extra 1-2 minutes after setting to improve tear strength
Stored in a moist environment to avoid loss of water and deformation
Disinfect in less than 10 minutes to avoid dimensional instability

24. Impression making Fluff powder, wait 30 seconds for the dust to settle
Measure powder and water according to manufacturer instruction
Use spatula to stir water into powder to mix
Stir vigorously to create homogenous mix (45 seconds for regular, 30 seconds for fast setting alginate)

25. Tray should cover all anatomical features
Utility wax can be added on tray borders to extend its coverage
Adhesive spray is used to prevent separation of alginate from tray.
Tray is loaded from posterior towards anterior
Moisten and smooth alginate
Posterior part of tray is seated first then anterior.
*tips to control gag reflex*

26. Alginate impression

27. Elastomers

28. Elastomers
Often called rubber materials since they have properties similar to rubber.
Clinical uses:
Bridges
Implants
Partial dentures complete dentures
Indirect esthetic restorations

29. Polymerization reaction
Involves formation of long-chain polymers and cross-linking of chains
General properties:
Not as sensitive to water as hydrocolloids
Have a certain amount of rebound, the highest is for addition silicon and polyethers, medium for condensation silicon and poorest for Polysulfides
Not wet well by water (hydrophobic) possible solution: surfactants

30. Polysulphides Dispensing & Composition
Supplied in two tubes as base and catalyst, equal lengths are mixed. Light, regular, heavy viscosities
Chemical composition of base:
80% low-molecular-weight organic polymer containing mercaptan reactive groups (-SH), and 20% reinforcing agents: titanium dioxide, silica, zinc sulfide
Chemical composition of catalyst:
Lead dioxide or copper hydroxide

31. Setting reaction Mercaptan + lead dioxide polysulfide+H2O
The reaction is sensitive to temperature and moisture so increase in any will accelerate the setting.
Also sensitive to correct mixing ratio

32. Uses Crown and bridge impressions
Partial and complete denture impressions
Clinical considerations when used
Used with custom trays
Allow 2mm thickness
Use tray adhesive
Dry field

33. Properties of clinical interest
Setting time: 8-14 minutes
Higher tear strength than hydrocolloids
Accuracy improves if impression is poured within 30 minutes
very unpleasant taste and odor
Messy (orange solvent to remove stains)
Can be irritant to oral mucosa
For all these reasons, Polysulfides have been largely replaced by other rubber materials

34. Silicon rubber
Addition (A) silicon
Condensation (C) silicon

35. Condensation silicon Developed as alternative to Polysulfides
Has more desirable qualities in comparison:
Easy mix
Better taste and odorless
Shorter setting time (5-7 minutes)

36. Dispensing & Composition
Two pastes, base and catalyst.
Comes as light, medium, or heavy viscosity
Base: dimethylsiloxane + filler (silica)
Catalyst: suspension of stannous octoate + alkyl silicate

37. Setting rxn
Condensation reaction that produces ethyl alcohol as by product. The alcohol evaporates which causes dimensional instability.
The material continues to contract with time, so needs to be poured within minutes.

38. Addition silicon (PVS)
Desirable clinical qualities:
Dimensional stability
Accuracy
Clean
Easy to mix
No foul odor or taste
the most expensive

39. Dispensing & composition
Light, regular and heavy viscosities and also putty
Dispensed as cartridge with 2 chambers (pastes), or two putty- system
Base: low-molecular-weight silicon with vinyl groups (paste system), or low-molecular-weight silicon with silane hydrogens (putty) + silica filler
Catalyst: chloroplatinic acid

40. Setting rxn
Polymerization rxn of chain lengthening and cross-linking with reactive vinyl groups, producing a stable silicon rubber.
No ethyl-alcohol by product
Some addition silicons produce hydrogen as by product, manufacturers incorporated palladium powder that absorbs hydrogen
setting time: 3-7 minutes

41. Impression making techniques
Putty/wash technique
One step
Two step

42. Polyethers
Also used for crown and bridge work since they are very accurate and also more hydrophilic than other silicons

43. Dispensing & composition
Dispensing same as other rubber materials (2 tubes)
In addition it’s supplied in pouches of base and catalyst placed in mechanical mixer.
Composition:
Base: low- molecular-weight polyether with cation reactive group
Catalyst: aromatic sulfonic acid
*clinical tip: mix well to avoid irritation from unmixed catalyst.

44. Properties Stiff, difficult to remove from undercuts
Short working and setting times
Setting time 3-5 minutes
Sensitive to moisture and temperature
More hydrophilic (must not be stored in water or disinfectant)
accurate

45. Inelastic impression materials

46. Impression compound:
Impression compound: softens with heat, hardens in the mouth.
2 main forms:
Cakes (sheets) /low fusing
Sticks /high fusing
Clinical uses:
Sheets:
Primary impression in metal trays
To make custom trays
Sticks are used for border molding

47. Composition & properties
Thermoplastic resin and waxes
Fillers to reduce flow
Plasticizers
Organic acids or oils
Pigments
Properties
Softened at 60°C, remains plastic at 45°C, firm at 37°C
Heated in water not by flame
Should be poured ASAP to avoid distortion
Flame used to heat sticks

48. Impression plaster Impression plaster: seldom used
Composed of plaster gypsum (Ca hemihydrae)
Used for primary impression (high P:L)
Scored with a knife in the mouth then removed and reassembled in the lab (distortion?)
Wash impression
Easy to use
Inexpensive
Disadvantages?

49. ZNO eugenol
Secondary impression for complete dentures, or wash impression (mucostatic impression)
2 tube paste system, different colors
Zinc oxide (80%) and fillers, eugenol (15%) with oils, resin, fillers. In addition to chemical accelerator (zinc acetate)
Dispensed in 2 equal lengths and mixed to homogenous color forming zinc eugenolate
Initial set:3-6 minutes, final set:10 minutes
To accelerate the setting, a drop of water or zinc acetate is added.

50. Properties Brittle, so not suitable for areas with undercut
Flows readily
Accurate
Eugenol can be irritant (burning sensation)
Once set, dimensionally stable

51. Impression wax Clinical uses:
Preliminary impression for edentulous patients
Bite registration
Baseplate wax used to be used for provisional crown and bridge work
Melted to correct voids in gypsum casts

52. Disinfection of impressions
The disinfectant should be compatible with the impression materials.
After taking the impression, it should be rinsed with water, excess water shaken off, and disinfectant sprayed or impression immersed in disinfectant
Protective gloves should be worn
Rinse after disinfection is complete

53. Disinfecting casts
Maybe necessary if impression was not properly disinfected, or if immersion of impression adversely affects the impression
Casts should be set and stored for 24 hours before disinfection.
Solution used: Na hypochlorite, iodophors.

54. Sterilizing trays Trays should be properly sterilized before use
Disposable trays are recommended if appropriate
Sterilization can be achieved by heated steam, dry heat, chemical vapors

55. THANK YOU