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Flashcards in 1 - Dental Waxes Deck (16):
1

waxes:
- 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

2

waxes:
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

3

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

4

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.

5

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)

6

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)

7

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

8

wax blending:
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
- 65-90deg

- raise MP, lower SP, lower brittleness

9

wax blending:
beeswax: what structure?
what changes when beeswax is added to paraffin wax?

- crystalline natural polyester
- less brittle, reduced flow

10

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

11

how do wax manufacturers cotrol the melting and softening temperature of waxes?

- by blending mixtures of various mineral, animal and vegetable components

12

wax as modelling material: describe the lost wax technique?

makes prostheses/appliances
wax embedded in investment material
boiled/burnt out
vacant space for the prosthesis material

13

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

14

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

15

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

16

what is a prerequisite of refractory die materials? what are they formed with?

- the materials have to be able to withstand rigours of processing, up to temperatures of firing ceramic
- from phosphate bonded investments