CSA clinical aspects of amalgam

Question 1

What is amalgam?

Answer 1

alloy of silver, mercury and tin

Question 2

What is the chemistry of amalgam?

Answer 2

silver, tin powder and liquid mercury

Question 3

what happens if too much mercury ?

Answer 3

wont be strong enough

Question 4

What happens if too much powder?

Answer 4

too dry to mould and shape

Question 5

what does capsule % of mercury contain?

Answer 5

slightly > 50% mercury in it - creates slightly wetter material easier to (mouldable/shape able)

Question 6

What happens during packing

Answer 6

• 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

Question 7

What are good properties of amalgam?

Answer 7

• Good compressive strength
• Good wear resistance
• Kind to opposing teeth
• Easy to use
• Chemically set
• Cheap
• Radiopaque

Question 8

what are bad things about amalgam?

Answer 8

• Non-adhesive
• Weak in sections
• Thermal conductor
• Unaesthetic
• Corrosion
• Creep
• Lichenoid type reaction

Question 9

What is creep?

Answer 9

high in occlusion, squashed and change shape,

Question 10

What can creep lead to?

Answer 10

plaque retentive factors

Question 11

Why do we need undercut for amalgam ?

Answer 11

filling kept in mechanically

Question 12

What is undercut?

Answer 12

Base of cavity wider than top of cavity

requires removal of healthy tooth tissue

Question 13

What can happen if matrix band not properly placed?

Answer 13

amalgam leach under band, becomes a PRF

Question 14

What are indications for amalgam?

Answer 14

• 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

Question 15

What is retentionin cavity design?

Answer 15

micromechanical feature caused by undercuts

Question 16

What is resistance n cavity design?

Answer 16

feature that prevents the filling from moving laterally

Question 17

What is Infected dentine in cavity design?

Answer 17

scoops out easily & easy to remove

Question 18

What is affected dentine in cavity design?

Answer 18

Hard to remove & dark brown/orange/stained could be normal colour

Question 19

How to get rid of last bits of hard stained affected dentine?

Answer 19

excavator , slow speed

Question 20

What does lock and key mechanism ensure?

Answer 20

no filling falling out

Question 21

What should margins be like interproximally?

Answer 21

cavity must be flat

Question 22

what should the cavo surface angle be ?

Answer 22

90 degrees

Question 23

What should amalgam margin angle be?

Answer 23

> 70 degrees

Question 24

what if amalgam margin angle is too acute?

Answer 24

surface would be very thin and thin amalgam is weak

Question 25

What do we do if patient has lost half of their tooth?

Answer 25

drill into dentine pits & grooves with a small bur

Question 26

What bonding is used for amalgam?

Answer 26

active substances (MDP or 4-META) form hybrid layer with dentine and chemical bond to amalgam

Question 27

What is an alternative bonding agent ?

Answer 27

wet uncured RMGIC placed in the base of a cavity can have amalgam packed directly on top

Question 28

How do we polish amalgams?

Answer 28

mirror finishing

Question 29

is amalgam safe?

Answer 29

• Mercury vapour is highly toxic
• vapour ingested whenever amalgams are mixed, placed or removed
• vapour is released from amalgam filling during chewing/tooth brushing

Question 30

What is an enviro. problem of mercury ?

Answer 30

can be converted by bacteria into methyl mercury (MeHg) in fresh/salt water
• Methyl mercury is highly poisonous

Question 31

Is composite safe?

Answer 31

• Bis-GMA & TEG-ma are in composite and are highly corrosive