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ELASTOMERIC IMPRESSION MATERIALS

K.PRIYADHARSHINI

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CONTENTS

  • INTRODUCTION
  • CHARACTERISTICS

VISCOELASTIC PROPERTIES

DIMENSTIONAL STABILITY

ELASTIC RECOVERY

STRESS IN COMPRESSION

FLOW

HARDNESS

TEAR STRENGTH

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CREEP COMPLIANCE

WETTABILITY AND HYDROPHILIZATION

BIOCOMPATIBLITY

  • EFFECT OF MISHANDLING
  • CONCLUSION

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REQUIREMENTS OF IMPRESSION MATERIAL

  • Adapt to oral tissue
  • contained in Tray
  • In mouth they should transform into solid in reasonable amount of time
  • should not distort or tear on removal
  • maintain its dimensional stability after removal
  • Biocompatible
  • Cost-effective

Philips science of dental materials -12th edition

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INTRODUCTION

ELASTOMERIC IMPRESSION MATERIAL

a group of flexible chemical polymers that are either chemically or physically cross-linked generally they can be easily stretched and rapidly recover their original dimensions when applied stresses are released [GPT-9]

  • They were quick to gain acceptance because it offers solution for two main problems

-Poor tear resistance

-Poor dimensional stability

Mc cabe and walls applied dental materials-9th edition

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VISCO

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deform permanently proportional to loading time

ELASTIC

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elastic deformation, reversed completely

VISCOELASTIC PROPERTY

Philips science of dental materials -12th edition

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  • Removal should not be Teasing or rocking method. After breaking the air seal, the removal should be sudden and parallel to long axis of the tooth.
  • Delayed pouring after removal.

MAXWELL-VOIGT VISCOELASTIC MODEL

100

90

80

93

88

100-90 –S1 CONTRACTS

90-80-D1 & D2 PISTON MOVES ON TIME

80-88-S1 ELASTIC RECOVERY

88-93 RECOVERY IN S2 & PISTON MOVES IN D2 ON TIME

Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

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BIOCOMPATIBLITY

Polysulfide results show lowest cell death count

Polyether shows highest cytotoxic score

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Impression material lodged in gingival sulcus leads to severe gingival inflammation

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Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

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TEAR STRENGTH

  • Tear strength test measures the resistance to fracture of an elastomeric material subjected to a tensile force acting perpendicular to a surface flaw[interproximal and subgingival areas]
  • The material can tear and embedded within the sulcus

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Consistency TEAR STRENGTH

Thinner- TEAR STRENGHT FLEXIBLITY

POLYSULFIDE

POLYETHER

ADDITION AND CONDENSATION SILICONE

Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

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VISCOSITY

MATERIAL

CONSISTENCY

VISCOSITY 45 SEC AFTER MIXING[cp]

POLYSULFIDES

LOW

MEDIUM

HIGH

60,000

110,000

450,000

CONDENSATION SILICONE

LOW

VERY HIGH

70,000

ADDITION SILICONE

LOW

MEDIUM

HIGH

VERY HIGH

150,000

POLYETHER

LOW

MEDIUM

HIGH

130,000

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POLYSULFIDE LIGHT

POLYSULFIDE REGULAR

POLYSULFIDE HEAVY

CONDENSATION SILICONE

ADDITION SILICONE

POLYETHER

Viscosity increases on time more rapidly in polyether and addition silicone

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So attention must paid on proper mixing time and time of insertion

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Viscosity decreases on increase in shear rate. Shearing force affects the viscosity of polyether and addition silicone[shear thinning effect or pseudoplasticity]

Craig’s restorative dental materials-13th edition

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WORKING TIME AND SETTING TIME

MATERIAL

CONSISTENCY

WORKING TIME

SETTING TIME

POLYSULFIDES

LOW

MEDIUM

HIGH

4-7

3-6

3-6

7-10

6-8

6-8

CONDENSATION SILICONE

LOW

VERY HIGH

2.5-4

2-2.5

6-8

3-6

ADDITION SILICONE

LOW

MEDIUM

HIGH

VERY HIGH

2-4

2-4

2.5-4

1-4

4-6.5

4-6.5

4-6.5

3-5

POLYETHER

LOW

MEDIUM

HIGH

3

2.5-3

2.5

6

6

5.5

Polysulphide >silicone>polyether

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End of working time- blunt needle of certain diameter and weight fails to penetrate to a specific depth

Setting time- Blunt instrument fails to permanently indent the impression

VISCOSITY

HUMIDITY

TEMPERATURE

WORKING AND SETTING TIME

Craig’s restorative dental materials-13th edition

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Polyether has the clearly defined working time with sharp transition[SNAP SET]

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The working time which begins at the start of mixing and ends just before the elastic properties have developed.

The setting time is time elapsing from beginning of mixing until curing process has advanced sufficiently and can be removed with minimal distortion

Polymerisation continue after setting

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Inadequately set—less elastic recovery—more permanent deformation

tray seated after working time passed-spring back

Philips science of dental materials -12th edition ,Craig’s restorative dental materials-13th edition ,Mc cabe and walls applied dental materials-9th edition

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DIMENSIONAL STABILITY

  • POLYMERIZATION SHRINKAGE(cross-linking and rearrangement of bonds within and between polymer chains)

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  • LOSS OF BY-PRODUCTS(polysulfide-water, condensation silicone-ethanol)

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  • THERMAL CONTRACTION FROM ORAL TO ROOM TEMPERATURE

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  • IMBIBITION ON EXPOSURE TO WATER OR DISINFECTANT OR HIGH HUMIDITY ENVIRONMENT

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  • INCOMPLETE RECOVERY

Preparing a tray –acrylic tray to increase DIMENSIONAL STABILITY[polymerization shrinkage,loss of by products],DEFORMATION [tray seating and removal],use adhesive

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Philips science of dental materials -12th edition ,Craig’s restorative dental materials-13th edition ,Mc cabe and walls applied dental materials-9th edition

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  • About half of the shrinkage occurs in first hour of condensation silicone and polysulfide ; so for maximal accuracy slurry mix of stone is poured immediately within 30 mins
  • Polyether and addition silicone does not show significant change in accuracy poured within 1 hr and after 1 week
  • Polyether has property of absorbing water or fluid and leaching out water soluble plasticizer
  • Distortion or creep will occur if material does not recover elastically when removed from undercuts

Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

Mc cabe and walls applied dental materials-9th edition

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ELASTIC RECOVERY�

Permanent deformation following strain in compression

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Elastic property curing time in mouth

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No advantage of bench curing of polysulfide impression material if the polymer chain stretched beyond their elastic limit

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POLYSULPHIDE

POLYETHER

CONDENSATION SILICONE

ADDITION SILICONE

Non uniform mix of base and catalyst-curing will not be uniform-distortion[improper elastic recovery]

Philips science of dental materials -12th edition

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EXCELLENT ELASTIC PROPERTY

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Distortion on removal from undercuts shows Low permanent deformation after strain in compression

Excellent elastic property present a problem in that the heavy body material begins to acquire elasticity on working .so the material elastically rebound on removal that results in small die

Philips science of dental materials -12th edition

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STRAIN IN COMPRESSION

  • Strain in compression under a stress of 0.1MPA which measures the flexibility of the material
  • Generally low consistency material are more flexible

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POLYSULFIDE

CONDENSATION SILICONE

ADDITION SILICONE

POLYETHER

Custom tray is not advisable for severe undercut [less material for stress on compression so difficulty in removal will occur]

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HARDNESS

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  • HARDNESS TIME

CONSISTENCY

ADDITION SILICONE PUTTY

POLYETHER

CONDENSATION SILICONE

Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

Mc cabe and walls applied dental materials-9th edition

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CREEP COMPLIANCE

POLYSULFIDE

CONDENSATION SILICONE

ADDITION SILICONE

POLYETHER

  • Mechanical properties of elastomers are time dependent
  • Higher the rate of deformation –higher the tear strength
  • Longer the impressions are deformed –higher the permanent deformation
  • Initial creep complaints indicates the flexibility and parallelism or flatness indicates the low permanent deformation on removal
  • Addition silicone has the lowest viscoelastic quality and require less time to recover viscoelastic deformation

Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

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WETTABILITY

Wettability may be assessed by measuring the advancing contact angle of water on the surface of the set impression

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When gypsum products are poured into addition silicone ,high contact angles are formed making bubble-free models difficult

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Philips science of dental materials -12th edition

Craig’s restorative dental materials-13th edition

Mc cabe and walls applied dental materials-9th edition

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POLYVINYL SILOXANE -56

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POLYETHER-59

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CAD/CAM SCANNABLE POLYVINYL SILOXANE -102

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VINYLSILOXANETHER -56.5

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Anna Theocharidou et al, Evaluation of elastomeric impression material’s hydrophilicity: An invitro study, Acta stomatal Croat,2021;55(3):256-262

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HYDROPHILIZATION

HYDROPHILIZED ADDITION SILICONE

Surfactants have be added to reduce the contact angle and improve wettability

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Surfactant-Nonionic surfactants

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Hydrophilic part-Oligoether or Polyether

Hydrophobic part-silicone compatible

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Alters the surface tension of surrounding liquid

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POLYETHER

Their molecular structure contains polar oxygen atoms, which have an affinity for water

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Because of this affinity ,it flows onto hydrated intraoral surface and cast with gypsum more easily

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DRAGGED AND PULLED EFFECT

REMOVE IMPRESSION IN PARALLEL TO LONG AXIS OF THE PREPARED TOOTH

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AIR BUBBLE

THE MIXING TIP SHOULD BE INSERTED INTO THE IMPRESSION MATERIAL

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  • USING PROPER RETRACTION METHOD

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  • PREVENTING FLUID ACCUMULATION AROUND THE MARGINS

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INADEQUATE MARGINAL DETAIL

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AIR ENTRAPMENT AND FLUID ACCUMULATION

  • THOROUGH FLUSHING AND DRYING OF THE PREPARATION

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  • PLACING THE CURVED INTRAORAL TIP INTO DEEPEST PART OF THE CAVITY

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USING UNDERSIZED TRAY

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POOR TRAY PLACEMENT

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SEPERATION OF IMPRESSION MATERIAL FROM THE TRAY

  • USING TRAY WITH SLOTS AND HOLES TO LOCK THE IMPRESSION MATERIAL

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  • USING ADHESIVE FROM SAME MANUFACTURER AS IMPRESSION MATERIAL

  • ADHESIVE SHOULD BE COMPLETELY DRIED

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INADEQUATE OCCLUSAL INTERCUSPATION

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MOVEMENT WHILE THE MATERIAL IS SETTING

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CONCLUSION

  • The understanding of basic knowledge of the impression material and their behaviour during handling are important for their use in oral environment and clinical success

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REFERENCE

  • Philips science of dental materials -12th edition
  • Craig’s restorative dental materials-13th edition
  • Mc cabe and walls applied dental materials-9th edition
  • Sivaranjani Gali et al, A technique of designing a 3- dimensionally printed elastomeric impression mixing tip for reuse : A step toward eco-friendly dentistry , J Prosthet Dent , 2020.

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  • Karsten Mann et al ,Experimental study on the use of spacer foils in two-step putty and wash impression procedures using silicone impression materials , J Prosthet Dent , 2014.
  • Ana Teresa Maluly-Proni et al, Evaluation of material waste , dimensional stability and detail reproduction of polyvinyl siloxane impression materials mixed with different mixing tips, J Prosthet Dent ,2020.
  • Pragya Pandey et al ,Mechanical properties of a new vinyl polyether silicone in comparison to vinyl polysiloxane and polyether elastomeric impression material . Contemp Clin Dent 2019;10:203-7.
  • Anna Theocharidou et al, Evaluation of elastomeric impression material’s hydrophilicity: An invitro study, Acta stomatal Croat,2021;55(3):256-262

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THANK YOU