Click here to load reader

Dental impression materials

  • View
    126

  • Download
    5

Embed Size (px)

DESCRIPTION

Dental impression materials. Libyan International Medical University. Introduction, types, classification. What is a dental impression?. It’s a negative likeness of the teeth and/or other tissues of the oral cavity. - PowerPoint PPT Presentation

Text of Dental impression materials

  • Dental impression materialsLibyan International Medical University

  • ** Introduction, types, classification

  • **What is a dental impression?Its a negative likeness of the teeth and/or other tissues of the oral cavity.The impression materials must be in a plastic or fluid status which become hard or set while in contact with oral tissues.Impression tray is a device used to carry and control impression material while making an impression.

  • **Ideal requirements of impression materialsBiocompatible, non toxic and non irritant.Should have acceptable taste, colour and smell.Adequate shelf life for storage.Easy to manipulate.Suitable working and setting time.Should be elastic to allow removal from undercuts without permanent deformation.7. Adequate strength so that will not tear or break on removal from the mouth.

  • **8. Should give accurate reproduction of tissue details.9. Compatible with cast or die materials.10. Adhere to the impression tray.11. Should have good flow.12. Dimensionally stable.13. Can be disinfected without any changes of properties.14. Economic or not expensive.

  • **

  • **Classification of impression materialsNon-elastic imp. Compound, imp. Plaster, zinc oxide eugenol and imp. Wax.Must not have undercuts

  • **2. Elasticcan be used in undercutHydrocolloidsReversible (agar)sol. gel (temp)Irreversible (alginate)..sol. gelb. ElastomersPolysulfide (PS)............set by polymerizationSilicon rubber (AS and CS)Polyethers (PE)

  • **Impression techniquesFull denturesPartial denturesFixed prosthodontics

  • **

  • **What's important?PatientNeutral taste and odourShort setting timeSmall trayEasily removedNo retakesNon-toxic

  • **What's important?DentistsEasily mixedShort working timeGood quality impressionLow costEasily disinfectedSimple procedure

  • **Ease of mixingLow viscosity less viscous is easier silicones are easiest to mix followed by polyether and polysulphidesAutomatic mixing reduces mixing time and bubbles use correct mixing tip

  • **Auto-mixer

  • **Working and setting timeDentist's time requirements must be balanced with patient's comfort. A total working and setting time of 4 min is adequate for most crown and bridge procedures.Using auto-mixing device for direct injection reduce working time to one minute.A fast setting material can be removed from the mouth in about 3 min.

  • **Working and setting time

    Chart1

    4

    6

    7

    6

    4.5

    8

    Total time (min)

    Sheet1

    IdealHASASCSPEPS

    46764.58

    Sheet1

    Total time (min)

    Sheet2

    Sheet3

  • **Easy of removalFlexible. depends on the elastic modulusMinimal distortion. depends on degree of permanent deformation.Sufficient tear strength.

  • **Flexibility of Impression materialsHardModerateEasy

    Chart3

    4

    4

    4

    4

    3

    6

    Sheet1

    IdealHASASCSPEPS

    46764.58

    IdealHASASCSPEPS

    444436

    Sheet1

    Total time (min)

    Sheet2

    Sheet3

  • **Resistance to TearingHighMediumLow

    Chart5

    6

    4

    4

    4

    5

    6

    Sheet1

    IdealHASASCSPEPS

    46764.58

    IdealHASASCSPEPS

    444436

    IdealHASASCSPEPS

    644456

    Sheet1

    Total time (min)

    Sheet2

    Sheet3

  • **Accurate reproduction of surface detailsViscosity High- muco-compressive Low- muco-staticWettability..ability of liquid to cover the surface of the substrate completely Hydrophobic Hydrophilic

  • **Why do we want good wetting?Fewer voidsLess entrapment of oral fluidsBubble-free dies and modelsFewer retakes

  • **Wettability of Impression materialsFairGoodExcellent

    Chart1

    6

    6

    2

    2

    6

    4

    Sheet1

    IdealHASASCSPEPS

    46764.58

    IdealHASASCSPEPS

    444436

    IdealHASASCSPEPS

    644456

    IdealHASASCSPEPS

    662264

    Sheet1

    Total time (min)

    Sheet2

    Sheet3

  • **Wettability of Impression materialsDisplace water and other oral fluids from the surfaces in the mouth so as to prevent voids in the impression and consequent bubbles in the casts.Improve adaptation of gypsum so as to prevent voids in the casts.Disinfection procedure!

  • **Dimensional accuracy and stabilityChoice and use of traySetting shrinkagePermanent setStorage stability

  • **Choice and use of traysAvoid flexible traysUse perforated traysMake sure the trays is cleanApply only a thin layer of adhesiveWait appropriate time before taking impressionDo not mix adhesives and impression materials

  • **Dimensional change of impressionsLowMediumHigh

    Chart2

    1

    1.2

    1.2

    2

    1.6

    3.2

    Sheet1

    IdealHASASCSPEPS

    46764.58

    IdealHASASCSPEPS

    444436

    IdealHASASCSPEPS

    644456

    IdealHASASCSPEPS

    662264

    IdealHASASCSPEPS

    11.21.221.63.2

    Sheet1

    Total time (min)

    Sheet2

    Sheet3

  • **Oversized impression space results in an oversized die

  • **a. Elastic material, b. plastic material, c. viscoelastic material

  • **a. Impression in place before removal, b. during removal- the impression is subjected to both compressive and tensile stresses.

  • **View of a material being used to record an impression of a crown with subgingival shoulders. The thin areas of impression material, which are most prone to fracture are arrowed.

  • **Imp wax

  • **Impression plasterRarely used these days as they are brittle and fractures very easily.Mucostatic impression of edentulous ridgesHigh W/P ratioCan be combined with impression compound

  • **Impression plasterEasy to mixWorking time 2-3 minSetting time 2-3 minLow viscosity-mucostaticGood dimensional stability and accuracyCheapadvantages

  • **Low strengthRough surface finishPoor abrasion resistanceRigid once setDry sensation in the mouthWe need separatorDisadvantages

  • **Impression compoundSheet primary impression of edentulous mouth. close fitting special tray used with zinc oxide eugenol wash.Stick single crown impression (copper ring technique). Border molding.

  • **

  • **Composition Thermoplastic materials, natural or synthetic resin and waxes.47% characterizes the softening temp.Fillers..e.g. Talc or shalk 50%..gives body increasing viscosity of the softened materials, reduce thermal contraction.Lubricant or acids 3% e.g. stearic acid to improve flow properties (plasticizer).

  • **PropertiesSoftening temperature 55-60C. flow by Temp.High viscosity-mucocompressive37C solid.High coefficient of thermal expansion.Do not over heat because it loose oils and altered characteristicsRigid. with rigid trayPoor thermal conductivity.take time during heating or cooling.Poured as soon as possible

  • **Since pressure is applied during the formation of the impression, the residual stress occurs in the material storage in warm environments or extended storage results in warpage.

    Contraction of imp. Compound from oral temp. to room temp. is 0.3%

  • **Zinc oxide eugenolMucostatic impression of edentulous ridge.Initial ST 3-6 min.Final ST 10 min.Two pastes, different colors, equal length, different size opening.Not elastic.Temp. and moisture ST.accelerate reactiondrop of water accelerate setting. Stick to dry surfaces.Eugenol irritant, cause burning sensation of lips.Pour any time.

  • **No separator needs.Protect unsupported edges.Put Vaseline on patient lips.If patient irritant to eugenol use rubbers imp. or eugenol free (phenols) zinc oxide impression.MucostaticHydrophilic.accurate reproduction of surface detailsDimensionally stable. 0.1%Compatible with dental stone.separated by softening the set paste in water at 60C.

  • **Eugenol react with zinc-oxide to form salt of zinc eugenolate and unreacted zinc oxide.Normally used with close-fitting special tray.The thickness of paste used is normally around 1 mm.This thin section the dimensional changes.Low viscosity of the mixed paste gives accurate recorded details.Defect sometimes arise on the surface of the impression but can be corrected by imp. Wax.

  • **The major restriction is their lack of elasticity.The set material easily distort or fracture when removed from undercut.Available in two types identified as hard set and soft set.The mixed materials has adequate adhesion to acrylic or tray material, therefore adhesives do not need.

  • **HydrocolloidsHydro=water kola=glue Oid=like

    A solution is a homogenous mixture consisting of single phase.A suspension is a mixture of two phasesA colloid is a heterogeneous mixture of two phases, where the two phases are not easily differentiated.Agar and alginate impression materials.

  • **Reversible hydrocolloids ..agarGel Sol Gel

    Irreversible hydrocolloids..alginate Sol Gel

    heatingcooling Chemical reaction

  • **AgarSea weedUses..crown/bridge imp, cast duplicate-lab.Composition; Agar 15%, Borax .2%, sodium sulphate 1%, anti fungal and water 85%Good storageStrengthens gelAffect gypsum setting against? Why!!!Accurate details

  • **Largely replaced by alginate and rubber impression materials.The preference of alginate as result of minimum equipment required and rubber imp due to greater dimensional stability, high quality gypsum model and option of obtain metal or epoxy die.It supp

Search related