Post on 27-May-2015
description
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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