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Impression Materials in Denstistry

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Research work made for the curricular unit of Prosthodontics, 5th class, of the Ege Üniversitesi Dis Hekimligi Fakültesi (Dentistry Faculty of Ege University), Turkey. 2012

Text of Impression Materials in Denstistry

  • There are many impression materials used in prosthetic dentistry and there are many different techniques employed to

    obtain a true replica of the teeth and mucosa

    Impression materials are used to record the shape of the teeth and alveolar ridges

    There are a wide variety of impression materials available each with their own properties, advantages and disadvantages

    2

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 1. Non toxic and non irritant

    2. Acceptability to the patient:

    3. Accuracy:

    4. Use of material:

    5. Compatible with

    model materials

    6. Economics of material

    3

    (a)Setting time,

    (b)Taste,

    (c)Consistency

    (a) Surface reproducibility

    (b) Dimensional stability

    (a) Ease of mixing

    (b) Working time

    (c) Setting time

    (d) Handling of the material (a) Cheap

    (b) Long shelf life

    (c) Accuracy (save redoing impression)

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • Mucodisplacive : compound, high viscosity alginates, high viscosity elastomers - these record an impression of the mucosa

    under load.

    This results in a wider distribution of load during function, making

    it more stable it also compensates for the differing

    compressibility of the denture bearing area reducing the risk of a

    fracture due to flexion.

    4

    The retention of the dentures may be

    compromised as the soft tissues wish to

    return to their original position at rest.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • Mucostatic : plaster, zinc oxide eugenol, low viscosity alginates since they are more fluid displace the tissues less.

    These essentially record an impression of the undisplaced

    mucosa. This results in better retention of the denture because

    of closer adaptation to the mucosa at rest.

    5

    Instability of the denture may occur during

    function as the tissues distort

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 6

    Non-elastic impression materials

    Impression compound Impression Plaster Zinc Oxide Eugenol Impression Waxes

    Elastic impression materials

    Hydrocolloids Agars Alginates

    Elastomers Polysulphides Silicones Polyethers

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 7

    These materials are rigid and therefore exhibit little or no elasticity.

    Any significant deformation produces a permanent deformation.

    Used where there are no undercuts and are mainly used for edentulous

    patient cases.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 8

    Characteristics

    Thermoplastic Poor surface detail High coefficient of thermal expansion

    (contraction of up to

    0.3%)

    Distorts wen removed over undercut areas

    Mucocodisplacive Poor dimensional stability

    Can be modified by re-heating

    Non toxic and non irritant Good shelf life

    Advantages

    Non irritant and non toxic

    Reusable (but with re-use the constituents are

    leached out)

    Can be reheated and readapted

    Can support other materials for wash

    impressions

    Mucocompressive

    Disadvantages

    Poor dimensional stability

    Poor surface detail

    Expansion coefficient

    Will distort if removed from undercuts

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 9

    Characteristics

    Excellent at recording fine detail

    Dimensionally stable if anti expansion solution

    used

    Fractures if undercuts present

    Mucostatic Needs to be treated with a separating medium

    before being cast in

    stone or plaster

    Exothermic reaction Non toxic but may be unpleasant due to

    dryness and heat

    evolved during setting

    Advantages

    Good surface detail Excellent dimensional stability

    Rate of the setting reaction can be

    controlled by the

    clinician

    Disadvantages

    Cannot be used for mucocdisplacive

    impressions

    Cannot be added to Properties affected by operator handling

    technique

    Taste and roughness may cause the patient to

    vomit

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 10

    Characteristics

    Used for recording edentulous ridges in a

    close fitting special tray

    or the patients existing

    dentures

    Non toxic Adherence to tissues Mucostatic or mucocodisplacive

    Good surface detail in thin section

    Good dimensional stability

    Can be added to with fresh zinc oxide eugenol

    Stable on storage and good shelf life

    Advantages

    Dimensional stability Good surface detail Can be added to Mucostatic or mucocodisplacive

    Disadvantages

    Cannot be used in very deep undercuts

    Only sets quickly in thin section

    Eugenol allergy in some patients

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 11

    Not commonly used thermoplastic materials, which flow at mouth temperature and are soft a room temperature.

    Normally used to correct small imperfection (e.g. airblows) in other impressions, especial zinc oxide impressions.

    Combination of a low melting paraffin wax and beeswax in a ratio of approximately 3:1 to ensure the wax flows at room

    temperature.

    A cast should be poured up immediately after taking the impression to avoid distortion which readily occurs in wax.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 12

    Can be stretched and bent to a fairly large degree without suffering any

    deformation.

    Used for recording the patient's mouth where undercuts are present.

    Usually used for partial dentures, overdentures, implants and crown and

    bridge work.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 13

    Relatively fluid materials when the solute particles present are

    dispersed throughout the liquid.

    Alternatively, the particles can

    become attached to each other,

    forming a loose network which

    restricts movement of the solute

    molecules. The colloid becomes

    viscous and jelly like, and is called

    a gel.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 14

    Some colloids have the ability to change reversibly from the sol state to the gel state. A sol can be converted into a

    gel in one of two ways:

    1. Reduction in temperature, reversible because

    sol is formed again on heating (eg agar).

    2. Chemical reaction which is irreversible (eg

    alginates). A gel can lose (syneresis which results

    in shrinkage) or take up (imbibition which results

    in expansion) water or other fluids.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 15

    Hydrocolloids are placed in the mouth in the sol state when it can record sufficient detail, then removed when it

    has reached the gel state.

    Hydrocolloid materials especially the alginates, may display a lack of incompatibility with some makes of dental

    stones. The resultant model may show reduced surface

    hardness and possibly surface irregularities and

    roughness.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 16

    Characteristics

    Good surface detail can be used for crowns

    and bridges

    Can be used on undercuts, but liable to

    tear on deep undercuts

    Evaporation or imbibition Non toxic and non irritant Slow setting time Poor tear resistance Adequate shelf life Can be sterilised by an aqueous solution of

    hypochlorite.

    Advantages

    Good surface detail Reusable and easily sterilised

    Disadvantages

    Need special equipment (water bath) and special

    technique

    Dimensional instability

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 17

    Characteristics

    Good surface detail used for study models

    and for removable partial

    dentures

    Reaction is faster at higher temperatures

    Elastic enough to be drawn over the

    undercuts, but tears over

    the deep undercuts

    Not dimensionally stable on storing due to

    evaporation

    Non toxic and non irritant Setting time can depend on technique

    Advantages

    Non toxic and non irritant Good surface detail Ease of use and mix Cheap and good shelf life

    Setting time can be controlled with

    temperature of water

    used

    Disadvantages

    Poor dimensional stability

    Incompatibility with some dental stones

    Setting time very dependent on operator

    handling

    Messy to work with

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 18

    On mixing the powder with water a sol is formed, a chemical reaction takes place and a gel is formed. The powder contains

    1. Alginate salt (e.g. sodium alginate)

    2. Calcium salt (e.g. calcium sulphate)

    3. Trisodium phosphate

    SODIUM

    ALGINATE

    SODIUM

    SULPHATE

    + +

    CALCIUM

    SULPHATE

    CALCIUM

    ALGINATE

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 19

    Clinical considerations: Powder and water should be measured to manufactures

    instructions.

    Water at room temperature should be used, this gives a reasonable working time of a couple of minutes. Faster or slower

    setting times can be achieved by using warm or cold water

    respectively.

    The material nearer the tissues sets first Retention is needed to the impression tray and is provided by

    perforations in the tray and/or adhesives.

    Once removed, it should be covered in a damp gauze/napkin to prevent syneresis (not placed in water which would cause

    imbibition-expansion).

    The impression should be soaked in hypochlorite for 60 seconds and then cast as soon as possible.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 20

    Used where a high degree of accuracy is needed, especially in crown and bridge work.

    Two main advantages over the Hydrocolloids - good tear resistance and dimensional stability.

    Hydrophobic rubber based materials.

    Come in different viscosity's ranging from low to high viscosity.

    The light bodied material maybe used as a wash impression over a medium or heavy-bodied material.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 21

    ONE STAGE IMPRESSION

    Light bodied impression material is placed in a syringe, and placed over the areas

    where high detail is required (e.g. over a crown preparation). Some is then

    squirted over the heavy-bodied impression material which has been loaded into an

    impression tray. The impression is then taken as normal.

    This technique saves time, but it can be very labour intensive because the two need to mixed at the same time.

    TWO STAGE IMPRESSION

    An impression is taken with the heavy-bodied material. This is then removed from

    the mouth and inspected. The light bodied material is then prepared and again

    placed in a syringe. This is then squirted over heavy-bodied material and then

    impression relocated in its original impression.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 22

    Characteristics

    Used for complete denture, crown and

    bridge work mainly, but

    also used for partial

    dentures, overdentures

    and implants

    Dimensional stability Excellent surface detail Varying viscosity Very small setting contraction

    Contraction on cooling from mouth to room

    temperature

    Very good tear resistance

    Viscoelastic

    Advantages

    Dimensional stability Accuracy Comes in a number of different viscosity's

    Long working time (although this may be a

    disadvantage in some

    clinical situations)

    Long shelf life

    Disadvantages

    Lead oxide in base paste may have toxic effects

    Staining of clothes due to the Lead oxide

    Messy to work with - unpleasant rubbery

    smell

    Can only be used in a special traY

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 23

    Characteristics

    Used for crown, bridge and bite registration

    Hydrophillic Good shelf life of up to 2 years

    Good elastic recovery Non toxic Low setting contraction Low tear strength Excellent surface detail Good dimensional stability

    Advantages

    Accuracy Good on undercuts Ease of use

    Disadvantages

    May cause allergic reaction due to the

    sulphonic acid ester

    Poor tear strength Rapid setting time (short working time)

    Stiff set material (sometimes hard to

    remove from mouth)

    Bad taste

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 24

    Two kinds, depending on the chemical reaction: Addition Silicones

    Excellent dimensional stability Cannot be manipulated with latex gloves The cast can be done up to a week after the impression

    Condensation Silicones Releases ethanol molecules upon setting Contraction after ethanol's evaporation Inlays, partial fixed prosthesis

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 25

    Characteristics

    Used for complete dentures, crown and

    bridge work mainly, but

    also for partial dentures,

    implants and

    overdenture

    Hydrophobic Ethenol release Moderate shelf life Moderate tear strength Good surface detail Shrinking of impression over time

    Non toxic and non irritant Very elastic (near ideal)

    Advantages

    Accurate Ease of use Can be used on severe undercuts

    Disadvantages

    Ethenol release Liquid component of paste/liquid system may

    cause irritation

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 26

    Characteristics

    Used for crown and bridge, denture, bite

    registration

    Good shelf life Dimensionally stable Moderate tear strength Excellent surface detail No gas evolution Non toxic and non irritant

    Advantages

    Accurate Ease of use Fast setting Wide range of viscosities

    Disadvantages

    Hard to mix Sometimes difficult to remove the impression

    from the mouth

    Cannot be manipulated with latex gloves (may

    prevent setting)

    Hidrogen release

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 27

    Impression Material Usage by General Dentists

    Crown & Bridge addition silicone 81% alginate 38% polyether 28%

    Inlays and Onlays addition silicone 71% polyether 22% alginate 20%

    DPR 2001

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 28

    Impression Material Usage by General Dentists

    Complete dentures alginate 58% addition silicone 55% polyether 27%

    Partial dentures alginate 78% addition silicone 43% polyether 15%

    DPR 2002

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 29

    Handling Properties

    Agar Alginate Polysulfide Condensation

    Silicone

    Addition

    Silicone Polyether

    Preparation Boil, temper,

    store Powder, water 2 pastes

    2 pastes or

    paste/liquid 2 pastes 2 pastes

    Ease of use Technique

    sensitive Good Fair Fair Excellent Good

    Patient

    Reaction Thermal Shock Pleasant, clean

    Unpleasant,

    stains Pleasant, clean Pleasant

    Unpleasant

    clean

    Ease of

    Removal Very easy Very easy Easy Moderate Moderate

    Moderate to

    difficult

    Disinfection Poor Poor Fair Fair Excellent Fair

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 30

    Handling Properties

    Agar Alginate Polysulfide Condensation

    Silicone

    Addition

    Silicone Polyether

    Working

    Time (min) 7 15 2.5 5 7 3 2 4.5 2.5

    Setting

    Time

    (min)

    5 3.5 8 12 6 8 3 7 4.5

    Stability 1 hour Immediate pour 1 hour Immediate pour 1 week 1 week kept dry

    Wettability

    and

    castability

    Excellent Excellent Fair Fair Fair to good Good

    Cost Low Very low Low Moderate High to very

    high Very high

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 31

    Comparison of proprieties

    Working time longest to shortest agar > polysulfide > silicones > alginate = polyether

    Setting time shortest to longest alginate < polyether < agar < silicones < polysulfide

    Stiffness most to least polyether > addition silicone > condensation silicone > polysulfide = hydrocolloids

    Tear strength greatest to least polysulfide > addition silicone > polyether > condensation silicone >> hydrocolloids

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 32

    Comparison of proprieties

    Cost lowest to highest alginate < agar = polysulfide polyether > polysulfide > condensation silicone > hydrocolloid

    Wettability best to worst hydrocolloids > polyether > hydrophilic addition silicone > polysulfide > hydrophobic

    addition silicone = condensation silicone

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • 33

    Materials for Study Models

    Alginate most widely used inexpensive displaces moisture lower detail reproduction dimensionally unstable

    Materials for Prosthodontics

    Addition silicones most popular accurate dimensionally stable user friendly expensive

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References

  • Phillips Science of Dental Materials, edited by K Anusavice, 11th ed., 2008, Saunders Publishing.

    Dental Materials and their Selection, edited by WJ OBrien, 4th ed., 2008, Quintessence Publishing.

    Dental Products Report, 2001, 2002, 2005. CW Caswell, AS von Gonten, and TR Meng, Volumetric proportioning techniques for

    irreversible hydrocolloids: a comparative study, J Am Dent Assoc 1986 112:859-861.

    MN Mandikos, Polyvinyl Siloxane Impression Materials: An Update on Clinical Use, Australian Dental Journal, Dec 1998, 43(5): 428-434.

    RG Craig, Review of Impression Materials, Advance in Dental Research, Aug 1988, 2,51-64.

    Introduction

    Properties

    Mucostatic vs

    Mucodisplasive

    Classification

    Non-elastic

    Elastic

    Summary

    References