Abrasives and Polishing Flashcards
Why is it important that all intra-oral surfaces are smooth?
food debris and dental plaque accumulation is reduced
corrosion of metals is prevented
no damage done to oral soft tissues
more comfortable for patient
What factors effects the abrasiveness?
hardness of abrasive
shape of abrasive particles
size of the abrasive particles
mechanical properties of abrasive
speed and movement of abrasive over surface
direct of movement
amount of load applied to substrate
properties of substrate
What is the sequence of using abrasives?
start with the most coarse and them go down onto the small/fine
What is the effect of heat generation during finishing?
surface substrate may melt
What can happen with thermoplastic polymers?
changes to properties of surface produced as it flows to fill in any scratches
excessive heat can cause stress relief and warping
What cab occur due to heat with resin-based materials?
smearing can occur as polymer approaches its glass transition temperature
What are common abrasives used in dentistry?
alumina and silica
What is the most popular method of finishing restorations?
finishing discs
What handpiece is used for the finishing discs?
slow speed
What do the finishing discs clip onto?
mandrel
Where would you use the finishing strips?
interproximally
Is there griot in the centre of the finishing strips?
no grit in the middle to facilitate insertion into area to be smoothed
What is the active ingredient of the rubber wheels?
silicon carbide or alumina bonded with rubber
What colour of rubber wheels tends to be coarser?
darker colour
What are rubber wheels used for?
polishing
What are the abrasives bonded with to produce various types of finishing instruments?
a binder
What are types of polishing instruments?
sintering
vitreous bonding
resinous bonding
rubber binding
What is sintering?
abrasive is heated so that it softens and particles bind together
strongest type
What is vitreous bonding?
using either glass or ceramic
glass acts as a binder holding abrasive particles together
What is resinous bonding?
binder is usually a phenolic resin
softer than abrasive and wears quickly
What is rubber bonding?
achieved using a silicone rubber
wear very quickly is used on a hard surface
What do resinous and rubber bonding require?
rely on cold or hot pressing to mould instrument
What are the features of hot pressing?
produces a more durable material which frequently has low porosity
What occurs if the polishing instrument wears too slowly?
will become clogged with swarf and debris which they have removed
What is the risk of swarf and debris build up?
heat generation leading to damage to substrate
What are polishing stones made from?
alumina that has been sintered
What handpiece do you use polishing stones in?
slow speed
What are the colours of polishing stones in order of most to least abrasive?
pink
blue
green
white
What colour of polishing stones do you use intra-orally?
green
white
Do you use a polishing stone with or without water?
can be both but probs use with to reduce friction and heat generation
What are brushes simiar to?
extra hard toothbrush
What speed do you use brushes at?
600-1000rpm
What is the recent movement of brushes?
impregnated bristles with an abrasive rather than using a separate slurry
What are the polishing materials?
lustre paste
What is lustre paste used on?
resin composite
What are polishing materials - lustre paste composed of?
diamond or aluminium oxide in glycerin
What colours are lustre paste available in?
pink and white
white is less abrasive
What is a pumice slurry?
crushed porous volcanic stone that is a highly siliceous volcanic glass
What is used to remove stains?
prophylaxis paste
What composes prophylaxis paste?
abrasive usually pumice or chalk (calcium carbonate) within a solution of oils
- oils act as binder
What is electrolytic polishing?
used when only a minimum amount of material is to be polished
