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