Elastic impression materials/ esthetic dentistry programs

ELASTIC
IMPRESSION
MATERIALS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com

Contents
• Introduction
• Definition
• History
• Classifications
• Ideal requirements
• Impression materials and techniques
• Latest advances
• Conclusions
• References

INTRODUCTION
The ideal impression material for accurately
reproducing tooth form and relationship would be some
substance which would be sufficient elastic to be
withdrawn from the undercut area and would return to
its original form without any distortion.

DEFINITIONwww.indiandentalacademy.com

“ A negative imprint of an oral structure used to
produce a positive replica of the structure to be used as a
permanent record or in the production of a dental restoration or
prosthesis. .”

HISTORY:
• 1925 Poller introduced Agar for impressions.
• 1936 Alginate impression material introduced.

By the manner in which they harden or set
Chemical / irreversible Temp / reversible
• Plaster of Paris
• ZOE
• Alginate
• Elastomers
Thermoplastic
• Impression
compound
• Wax
•Agar

According to the ability of the set material to be
withdraw over undercuts :Elastic
impression materials
Non-elastic or Rigid
impression materials
 Agar
 Alginate
 Impression compound
 ZOE
Hydrocolloid Rubbers
 Polysulfide.
 Silicones.
 Polyether.

MucocompressiveMucostatic
According to the viscosity or tissue displacement:
- Impression plaster - Impression
- Agar Compound
- Alginate - Putty elastomers

Based on interaction with saliva / water:
1. Hydrophilic
2. Hydrophobic
Based on use :
1. Primary impression materials
2. Secondary impression materials
3. Duplicating materials

Ideal Requirements of DentalIdeal Requirements of Dental
Impression MaterialsImpression Materials

1. Compatibility with patient
2. Ease of manipulation
3. Fluid enough to record fine details of the oral tissues
4. Viscous enough to be contained in the tray
5. Adequate strength
6. Dimensionally stable
7. Good elastic properties
8. Compatible with die and cast
9. Shelf life
10. Disinfection
11. Cost effective

Hydrocolloids:
• Kola - ‘glue’ and ‘oid’- like, a ‘glue-like’ character.
• Colloids are classified as the fourth state of matter , they
lie between suspension and solutions.
•The size of the particles larger than solutions & range from
1 to 200nm

sol –gel transformation:
• Colloids with a liquid as the dispersion medium can exist
in two different forms known as Sol & Gel.
• in gel state , the dispersed phase agglomerates forming
fibrils or chains called Micelles.
• Gelation is the conversion of a sol to gel, & the
temperature at which this occurs is called Gelation
Temperature.

• The colloidal materials that are dissolved in water are termed
hydrocolloids
• If the change of sol to gel is thermal and reversible –
reversible hydrocolloid (agar)
• If the change of sol to gel is chemical and irreversible -
irreversible hydrocolloid (alginate)

• An important characteristic of gels is the processes of
syneresis and imbibition.
These both alter the original dimensions of the gel

AGAR :
An aqueous impression material used for
recording maximum detail, such as that required to
produce dies for fixed restorations

Reversible Hydrocolloid – AGAR
 Introduced by “Alphous poller of Vienna” in 1925
 Adopted commercially as “Dentacol” in 1928
 It was the first successful elastic impression material

•agar is an organic hydrophilic colloid extracted from
certain “seaweed”
• it is a sulphuric ester of a linear polymer of galactose
• though highly accurate, it has been largely replaced by
Alginates and elastomers due to its cumbersome
manipulation

The Material is supplied as:
 Gel in collapsible tubes (for impressions)
 A number of cylinders in a glass jar (syringe material)
 In bulk containers (for duplication)

ComponentComponent FunctionFunction CompositionComposition
(%)(%)
AgarAgar Brush Heap structureBrush Heap structure 13 – 1713 – 17
BorateBorate StrengthStrength 0.2 – 0.50.2 – 0.5
Pot. SulfatePot. Sulfate Gypsum hardenerGypsum hardener 1.0 – 2.01.0 – 2.0
Wax, Silica,Wax, Silica,
diatamaceous earthdiatamaceous earth
FillerFiller 0.5 – 1.00.5 – 1.0
Thymol ,Thymol ,
GlycerinGlycerin
Bactericide ,Bactericide ,
plasticiserplasticiser
0.3 – 0.50.3 – 0.5
WaterWater Reaction mediumReaction medium Balance 84%Balance 84%
AlkylbenzoatesAlkylbenzoates PerservativePerservative 0.10.1
Composition:

Gelation process
• Gelation – ( 37 – 50 degrees )
brush heap structure
dispersion medium
• Liquefaction –(70-100 degrees )
• Hysterisis

Conditioner Consists of:Conditioner Consists of:
a. Boiling or liquefaction section: 10 mins in boiling water (1000
C).
b. Storage section: 65-680
C is ideal it can be stored till needed
c. Tempering section: 460
C for about 2mins

WATER COOLED RIM LOCK TRAYS

FINAL IMPRESSION WITH AGAR

Properties of agar
• Accuracy
• Viscosity of sol
• Viscoelastic property
• Distortion during gelation
• Reproducibility

Advantages:
1. Hydrophilic Impression material
2. Good elastic properties, Good recovery from distortion
3. Long working time and low material cost
4. No mixing technique
5. High accuracy and fine detail recording
Disadvantages:
1. Only one model can be used
2. Extensive and expensive equipment required
3. Impossible to sterilize for reuse
4. Low dimensional stability & tear resistance

Uses of Agar:
1. Widely used at present for cast duplication
2. For full mouth impression without deep undercuts
3. Was used for crown & bridge before the advent of elastomers

1. Laminate technique or agar-alginate combination
technique.
2.Wet field technique
•

Irreversible HydrocolloidIrreversible Hydrocolloid
AlginateAlginate

1. Alginate is found in a wide variety of
brown seaweeds and is present as a
structural polysaccharide.
2. Alginate is made up of a linear block
copolymer of α-L-guluronic acid and β-D-
mannuronic acid.
3. The type of structure is influenced by the
seaweed source as well as the growing
conditions of the weed.
4. Alginate can also be produced from a
bacterial source (Azobacter Vinelandii).

• ‘Alginate was developed as a substitute for agar when it
became scarce due to II world war.
• Currently, alginate is more popular than agar because,
 It is easy to manipulate
 It is comfortable for the Patient
 It is relatively inexpensive and does not require
elaborate equipment

Component Function Wt%
Potassium alginate Soluble alginate 15
Calcium sulfate Reactor 16
Zinc oxide Filler particles 4
Potassium Titanium fluoride Accelerator 3
Diatomaceous earth Filler Particles 60
Sodium phosphate Retarder 2
COMPOSITION OF ALGINATE

SETTING REACTION:
Alginic acid is a linear polymer of Anhydro- B-D mannuronic
acid of high molecular weight
Two main reactions occurs during setting:
i) 2 Na3 PO4 + 3 Ca SO4 Ca3 (PO4)2 + 3 Na2 SO4
(Sodium phosphate) (Calcium sulphate)
(Retarder) (Reactor)
ii) Sodium Alginate + Ca SO4 + H2O Ca Alginate + Na2 SO4
(Powder) (Reactor) (Gel)

Control of gelation time:
Optimum gelation time is 3-4 min
1. By manufacturers : by adding retarders
2. By Dentist - Cold water : Longer is the geln
. time
- Warm water : Shorter is the geln
. Time
 1 min of reduction in gelation time for 10 degree raise of
temperature
3. Water : powder ratio

manipulation of alginate
• Preparing the mix:
Measured water : powder
Mixing
Contamination during mixing.
Water : powder ratio alterations.

• making the impression
Loading the tray
Seating the tray
Removal of impression

properties
• Gel strength
• Viscoelasticity
• Accuracy
• Shelf life

• Disinfection
• Dimensional stability
Imbibition
Evaparation
Synerisis
• Compatibility with gypsum
• Duplication

Modified Alginates:
1. Sol - containing water
2. 2 paste system – alginate sol and calcium reactor
3. Chromatic alginates
4. Dustless Alginate

AUTOMIX DISPENSING: (Alginate from
Kerr international)
• No hand mixing. Eliminates mess
and cleanup. Saves time and
material.
• Delivery options. Cartridge auto
mix dispensing.
• Impressions remain stable. You
can pour immediately or when it’s
convenient. Impressions retain
dimensional stability for months.

Advantages:
1. Easy to mix and manipulate.
2. Minimum requirement of equipment.
3. Accuracy (if properly handled)
4. Low cost
5. Comfortable to the patient
6. Hygienic (as fresh material is used for each impression)
Disadvantages:
1. Distortion occurs easily
2. Poor dimensional stability (poured within 15 min.)
3. Poor tear strength

Applications :
1. Complete denture prosthesis & orthodontics
2. Mouth protectors
3. Study models and working casts
4. Duplicating models

Common causes of failures
1. Grainy material
2. Tearing
3. External bubbles
4. Irregularly shaped voids
5. Rough stone surface
6. distortion

COMPARISON BETWEEN HYDROCOLLOIDS
Properties Agar Alginate
Flexibility 15 % 14 %
Elasticity &
elastic recovery
98.8 % 97.3 %
Reprodn
. of
details
25 um < agar
Tear strength 715 gm/cm2
350-700 gm/cm2
Comp. strength 8000 gm/cm2
500-8000 gm/cm2
Diml
. Stability Better Poor
Reuse Possible Not possible
Manipulation Conditioner & rim
lock trays
Normal trays

Review of literature :
Effect of long term storage on properties of an alginate
impression material
J prosthet dent 1997 ; 77 ; 601-606.
The purpose of this study
was to document changes in the properties of an alginate
on exposure to various environmental conditions for more
than 78 months and concluded that some changes in
properties of an alginate impression material may be
expected after 3years, the alginate impression material
tested remained with in ADA specification limits and
efficacious for most clinical cases well past manufacturers
designated shelf life

Impact of water quality on setting of irreversible
hydrocolloid impression materials .
J prosthet dent 2006;96;443-448.
Purpose.The purpose of this study was to compare the
setting behavior of irreversible hydrocolloid impression
materials when mixed with tap and distilled water, and to
determine the impact of typical cations present in tap
water and their concentrations on the setting process
Conclusion. Setting of irreversible hydrocolloid impression
materals can be significantly accelerated when tap water
with high water hardness is used for mixing or when
mixing water containing higher concentrations of cations
,such as Na+,Ca2+,and Al3+.
• www.indiandentalacademy.com

The effect of a retarder on compressive strength and working and
setting times or irreversible hydrocolloid impression material.
J of prosthet dent 2003;90:276-81
Purpose. This study tested the compressive strength (elastic recovery)
and working time and setting times for an ireversible hydrocolloid
impression material after retarder was added.
Conclusion:
Predictable longer working and setting times were demonstrated for
irreversible hydrocolloid specimens
The specimens with 8 drops of retarder solution exhibited variable
setting times and would not be suitable for clinical use.The
compressive strength was compromised because of the addition of
sodium phosphate. however recovery from deformation remained
satisfactory as retarder solution was added

CONCLUSION
• Hydrocolloids are widely used for recording impressions
of edentulous and partial dentate arches
• In orthodontics,they are extensively used for recording
impressions for study models.
• They are rarely used for crown and bridge framework,
because of their poor tear resistance and poor dimensional
stability,which is a serious disadvantage when considering
this application

References:
1. Anusavice - Phillips Sciences of Dental materials, 10th
Edition
2. Dental materials- Properties and manipulation – Craig, Obrein,
Powers, 5th
Edition.
3. E.C. Combe-Notes on Dental Materials, 6th
Edition.
4. John N.Andreson – Applied dental materials, 5th
Edition.
5. John F. McCabe- applied dental materials, 7th
edition
Restorative dental materials – Robert, G. Craig and John H.
powers. 11th edition.

 The effect of Storage Period of Alginate Impressions following Spray
with Disinfectant Solutions on the Dimensional Accuracy and
Deformation of Stone Models. J prosthet dent 1996 ; 74 ; 168-172.
 Effect of long term storage on properties of an alginate impression
material . J prosthet dent 1997 ; 77 ; 601-606.
 Impact of water quality on setting of irreversible hydrocolloid
impression materials. J prosthet dent 2006; 96; 443-448
 The effect of a retarder on compressive strength and working and
setting times or irreversible hydrocolloid impression material.
J of prosthet dent 2003;90:276-81

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Elastic impression materials/ esthetic dentistry programs

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