Waxes Flashcards
What does thermoplastic mean?
- solid at room temperature
- at higher temperatures melt with no decomposition
What are waxes formed around?
cristalline structure
What is the ‘softening temperature’ of waxes?
the temperature before they melt when they become pliable
What happens when waxes are at softening temperature?
undergo solid-solid transition
- results in profound change in physical properties, becoming pliable and mouldable
- offers scope for manipulation
What are the components of waxes?
- animal
- vegetable - from tress and plants
- mineral - hydrocarbons
What is an example of an animal component of wax?
beeswax - partially crystalline natural polyester
What is an example of a vegetable component of wax?
carnauba wax, candelilla wax
What is an example of a mineral component of wax?
paraffin wax (straight chain), microcrystalline (branched chain)
What are the dental applications of waxes?
- modelling
- indirect - modelling wax
- direct - inlay wax
- carding
- boxing in
- joining components to facilitate union
By international convention, how thick is a base plate sheet of wax?
1.5mm thick
What type of wax is used to set denture teeth in?
modelling wax
What colour is inlay wax?
blue
What is inlay wax used for?
to wax up a crown etc
What can be used to repair dentures?
sticky wax
What is carding wax used for?
for putting denture teeth on e.g. when you have a stip of denture teeth on the ‘senator’ strip that is carding wax they are placed on
Other than the waxes, what are the other variety of components incorporated in?
- waxes
- resins
- oils
- fats
- pigments
What dictates the properties of wax products?
the blending off the different components
Between what temperatures do paraffin waxes soften?
~37-55 degrees C
Between what temperatures so paraffin waxes melt?
~48-70 degrees C
What can be added to paraffin wax to adjust the properties?
microcrystalline (MP 65-90 degrees C)
beeswax
carnauba/candelilla
What effect does adding microcrystalline to paraffin wax have?
increases melting point, decreases softening point
What effect does adding beeswax to paraffin wax have?
decreases brittleness, decreases flow
What effect does adding carnauba wax to paraffin wax have?
enbrittles the wax
What are the steps of wax being used a a modelling material (lost wax technique)?
- used to form dental restoration or prosthesis
- embedded in investment material
- boiled/burnt out
- vacant space for definitive restoration/prosthesis material
Why is modelling wax used when making acrylic dentures?
- withstands intraoral temperature
- amenable to chairside/laboratory adjustment
- tough enough for undercut withdrawal
- no tearing/chipping/flaking
- no residue in investment mould upon boiling out
What wax is used when making crowns/inlays/bridges?
inlay wax (blue)
What is a unique feature of inlay wax?
locks into undercut and will fracture if you try to remove it
- will tell you whether your cavity has undercuts
What are the features of inlay wax?
- fractures if locks into undercut
- good colour contrast
- no tearing/chipping/flaking
- no residue in investment mould upon burning off
What is an example of a wax specialist component?
wax patterns preformed for components of partial denture and bridgework
