Flashcards in 1 - Dental Waxes Deck (16):
- what does it mean to be thermoplastic
- what kind of structure?
- it means that it is solid at room temperature, and melts without decomposition at higher temperatures
- crystalline structure
what happens at softening temperature?
- what kind of transition?
- results in?
- what does this change allow?
- solid - solid transition
- results in profound change in physical properties
- offers scope for manipulation
waxes - composition:
what are the 3 general components? what is each made of specifically?
- animal: beeswax
- vegetable: from trees and plants, carnauba wax & candellila wax
- mineral: hydrocarbons
dental applications for wax: describe the direct and indirect techniques, and give an example of each
indirect: methods which involve the production of a model followed by the laying down of a wax pattern. one example would be the lost-wax technique, wax pattern defines the size and shape of the resulting appliance
direct: dental restorations e.g. inlays produced by directly adapting and shaping inlay wax in the prepared cavity in the mouth.
other uses of wax in dentistry? x3 what is the name of the wax used in each method?
- attaching denture teeth to display sheets (carding wax)
- boxing in impressions prior to making a gypsum model (boxing-in wax)
- temporarily joining two components of an appliance, e.g. during soldering (sticky wax)
what are the variety of components wax can be made of? blending is carried out to produce what?
- waxes, resins, oils, fats, pigments
- blending produces a material with the required properties for a specific application (dictates application)
wax blending: what origin?
paraffin wax: what kind of structure?
microcrystalline wax: what structure?
- mineral origin. from petroleum residues following distillation
- simple straight chain hydrocarbon
- branched chain hydrocarbon
softening and melting temprature of paraffin wax?
MP of microcrystalline wax?
what happens when microcrystalline wax is added to paraffin wax? x3
- 37-55deg, 48-70deg
- raise MP, lower SP, lower brittleness
beeswax: what structure?
what changes when beeswax is added to paraffin wax?
- crystalline natural polyester
- less brittle, reduced flow
wax blending: which 2 waxes are derived from trees and plants? what property change results when they are blended with paraffin wax?
- carnuba wax, candelilla wax
- control softening temperature and further modify properties
how do wax manufacturers cotrol the melting and softening temperature of waxes?
- by blending mixtures of various mineral, animal and vegetable components
wax as modelling material: describe the lost wax technique?
wax embedded in investment material
vacant space for the prosthesis material
acrylic dentures: why is modelling wax used?
- withstands intraoral temperature (try in stage)
- amenable to chairside/lab adjustment (tough enough for undercut withdrawal, no chipping/flaking/tearing)
- no residue in investment during boiling out
crowns/inlays/bridges: use what kind of wax? why? x4
use inlay wax
- fractures if locks into undercut
- good color contrast
- no tearing/chipping/flaking
- no residue in investment mould upon burning off
what do refractory die materials make? what is the use of the object?
- dies, on which ceramic restorations (e.g. porcelain crowns) are constructed.
- the purpose of dies are to support those materials throughout processing, prevent them from deforming/disintegrating