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D R M U M TA Z U L I S L A M

B.Sc . BDS. C. Implant . C. Ortho .

Waxes (Thermoplstics) in Dentistry

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Waxes

Waxes are thermoplastic materials Soft on heating hard on coolingSolid at room temperature Melt without decomposition Form mobile liquidsPoor mechanical propertiesUsed to form patterns (wax pattern)

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Patterns

Direct wax patternIndirect wax patternlost-wax technique

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Direct

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Indirect

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Types used in dentistry

Fixing denture teeth for displaying (carding wax)Boxing in dentures before making the model (boxing-in

wax)Temporary joining two broken pieces (sticky wax)For taking impression (impression waxes)To control hemeostasis (bone wax)In endodontics (gutta percha)In orthodontics (orthowax)

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Waxes

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Processing wax

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Full range of processing waxes

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Modeling wax

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Modeling wax

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Wax rims

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Wax bite blocks

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Wax bite

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Wax bite

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Base Plate Wax

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Sticky wax

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Bone wax

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Ortho wax

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Ortho wax

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Requirements of a pattern

Copy exact size Shape & Contour Dimensionally stable after formation of patternEasily be removed after mould formationFor indirect use its melting point should be above room

temperatureFor direct use it should set at mouth temperatureMolding temperature

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Sources

MineralAnimal Vegetable

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Mineral

Parrafin wax (straight chain) brittle Microcrystalline wax( branched) elasticPetrolium byproducts Hydrocarbons

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Softening and Melting Temperature

Softens at 37 to 55 : C Parrafin wax melts at 44 to 70 : CMicrocrystalline waxes melt at 65 to 90 : C

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Animal

Bees wax Honey combs Partially crystalline natural polyestersIt can flow under stress just below the melting pointVery flow able

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Vegetable

Derived from trees and plantsCarnauba wax (Brazil wax or Palm wax)Candelilla wax

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Properties

Thermal Mechanical

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Thermal

Melting pointSolid-solid transition temperature (lower than melting

point) brittle state changes into a mouldable and softer material

Softening temperature just above the mouth temperaturePoor thermal conductor (must be kept above SST for

thorough softnening)High coefficient of thermal expansion

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Mechanical

Flow more during moulding and no flow at mouth or room temperature prevents distortion

Brittleness inherent property can be controlled desired in inlay wax

Toughness more desirable in wax denture baseInternal stress Dimentional changes

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Methods of Softening

water bath Infra-red lamp 250 wattsBunsen burnerIt should not touch the flame Glossy (shiny) appearance indicates melting outer surfaceIn water uniform but leaching of constiuents occours Water incorporation also alters its composition and

properties

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Ideal method for softening

Wax annealer Thermostatically controlled oven which keeps the wax at

a constant temperaturejust above the softening pointReady for useThe annealer is most useful for inlay waxes

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Applications

Processing waxesDenture modeling waxWax rimMounting artificial teeth on that rimThree types Type 1 soft Type 2 hard Type 3 extra hard

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Application (contd,)

Type 1 material Hard at room temperature but soft at mouth temperatureBuilding contours and veneers in the laboratoryThe type 2 material For pattern production in temperate climateType 3 materialFor use in warmer climatesModelling waxes consist mainly of mixtures of paraffin

wax and beeswax and have melting points in the range 49–58ºC

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Dimentional Stability

High values of coefficient of thermal expansionManner in which the materials are used (softening with

heat and cooling) suggests that a significant dimensional change can occur

An upper limit of 0.8% expansion on heating from 25ºC to 40ºC is allowed in the ISO specification

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Pre-formed Polymeric Components

An alternative to waxes for modelling the metal components of partial dentures

Available in sheets

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Temporary Denture Bases

Constructed from wax and used during denture construction are prone to distortions unless great care is taken

For this reason alternative materials/techniques are sometimes used

Shellac a wax-like resin which is more stable at mouth temperature has been used for construction of the temporary denture base

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Shellac

Natural beetle exudate which has a considerably higher softening temperature than ordinary modelling wax

Care must be taken to ensure thorough softening prior to moulding otherwise considerable stresses are introduced which eventually lead to distortion

The wax rim is then built on top of this more stable base

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Shellac

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Inlay waxes

Inlays or cast posts etc produced by patternsDirect Indirect Two types of inlay casting waxesType 1 soft indirectType 2 hard direct (may be used indirectly)Presentation is in the form of cones, sticks and cakes

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Requirements

Should soften just above mouth temperature Magnitude of thermal contraction and internal stresses

should be minimumSoftening temperature must be tolerated without pain by

the patientThermal contraction occurring on removal of the direct

pattern material from the mouth is 0.1–0.5% Investing the pattern as soon as possible is required

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Requirements

Hard at mouth temperature On removal from the cavity fractures not to flow This enables the undercuts to be located and removedGood colour contrast with enamelEasy to carve without flaking

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Pattern of Post

The post channel is usually prepared using a proprietary system and a pre-formed pattern for the post is installed into the canal

The core is then built up in wax by melting the wax on an instrument and carrying the molten wax into the tooth

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Indirect Patterns

Soft typeSome what same like directSoftens at lower temperature than direct No flow at room temperatureThermal contraction is much lower as lower softening

temperature A distinct advantage of the indirect technique

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Thank you