CSA clinical aspects of amalgam Flashcards
What is amalgam?
alloy of silver, mercury and tin
What is the chemistry of amalgam?
silver, tin powder and liquid mercury
what happens if too much mercury ?
wont be strong enough
What happens if too much powder?
too dry to mould and shape
what does capsule % of mercury contain?
slightly > 50% mercury in it - creates slightly wetter material easier to (mouldable/shape able)
What happens during packing
- excess mercury drawn to top (surface becomes wetter)
- scraped away during carving
- allows for just under 50% of mercury to be present in the set material
What are good properties of amalgam?
- Good compressive strength
- Good wear resistance
- Kind to opposing teeth
- Easy to use
- Chemically set
- Cheap
- Radiopaque
what are bad things about amalgam?
- Non-adhesive
- Weak in sections
- Thermal conductor
- Unaesthetic
- Corrosion
- Creep
- Lichenoid type reaction
What is creep?
high in occlusion, squashed and change shape,
What can creep lead to?
plaque retentive factors
Why do we need undercut for amalgam ?
filling kept in mechanically
What is undercut?
Base of cavity wider than top of cavity
requires removal of healthy tooth tissue
What can happen if matrix band not properly placed?
amalgam leach under band, becomes a PRF
What are indications for amalgam?
- Larger cavities affecting posterior teeth
- heavy occlusal forces encountered
- aesthetics is not important
- high caries rate
- Posterior restorations that extend subgingivally
- Building up broken down teeth prior to crowning
What is retentionin cavity design?
micromechanical feature caused by undercuts
What is resistance n cavity design?
feature that prevents the filling from moving laterally
What is Infected dentine in cavity design?
scoops out easily & easy to remove
What is affected dentine in cavity design?
Hard to remove & dark brown/orange/stained could be normal colour
How to get rid of last bits of hard stained affected dentine?
excavator , slow speed
What does lock and key mechanism ensure?
no filling falling out
What should margins be like interproximally?
cavity must be flat
what should the cavo surface angle be ?
90 degrees
What should amalgam margin angle be?
> 70 degrees
what if amalgam margin angle is too acute?
surface would be very thin and thin amalgam is weak
What do we do if patient has lost half of their tooth?
drill into dentine pits & grooves with a small bur
What bonding is used for amalgam?
active substances (MDP or 4-META) form hybrid layer with dentine and chemical bond to amalgam
What is an alternative bonding agent ?
wet uncured RMGIC placed in the base of a cavity can have amalgam packed directly on top
How do we polish amalgams?
mirror finishing
is amalgam safe?
- Mercury vapour is highly toxic
- vapour ingested whenever amalgams are mixed, placed or removed
- vapour is released from amalgam filling during chewing/tooth brushing
What is an enviro. problem of mercury ?
can be converted by bacteria into methyl mercury (MeHg) in fresh/salt water
• Methyl mercury is highly poisonous
Is composite safe?
• Bis-GMA & TEG-ma are in composite and are highly corrosive
