week three - class II, amalgam, matrix systems

Question 1

describe the clinical considerations of class II

Answer 1

1. dx proximal caries through BWs or clinical exam
2. proximal lesions that appear 2/3 through enamel to DEJ have already penetrated DEJ
   - rmbr if caries have only slightly penetrated DEJ - can still be remin w frequent cleaning and F- use
3. proximal resto should only be undertaken if there is spread of caries at DEJ or definitive cavitation

Question 2

describe the characteristis of class II amalgam preps

Answer 2

1. bucco-lingual proximal margins extended to break contact w adjacent tooth [0.5mm cow-horn explorer’s tip should pass through]
2. axial wall 0.5 - 0.8mm from DEJ + maintain convex curvature bucco-lingually
3. flat gingival/pulpal floor
4. occlusal convergance of walls
5. dovetail design of occ step

Question 3

describe amalgam/mech properties, the advantages/disadvantages and composition

Answer 3

• typical life span ~ 15 yrs - may last up to 40yrs

mechanical properties
- HIGH compressive strength [esp high copper]
- LOW tensile strength
- creep/tarnish/corrosion
- thermal expansion - dimensional changes - microleakage, fracture, pulpal damage in deep cavs

advantages
- longevity
- cheap + easy to use
- wear resistance + compressive strength

disadvantages
- not in line w MID
- safety concerns
- lacks aesthetics

composition
- modern alloys = high in copper [13-30%] - ^ strength, corrosion resistance, durability + tarnish resistance
- 40-70% silver [^ strength,durability,expansion][dec. flow,setting time]
- 12-30% tin [^flow,workability,setting time][dec. expansion]
- 43-50% mixed w mercury
- sometimes Zn added - inhibits corrosion [workability, cleanliness]

Question 4

describe the clinical effects of microleakage

Answer 4

adv
- corrosion products –> weaken surface but fill gaps in between amalgam/tooth = reduced microleakage

dis
- discolouration
- reduced strenth = ^ risk of fracture
- marginal degradation = ditching
- ^ internal porosities

Question 5

explain the characteristics of amalgam trituration and placement/considerations

Answer 5

trituration = mixing of alloy + mercury

over trituration
- HOT/shiny/soft alloy, hard to remove from capsule
- decreases working time
- increases contraction

under trituration
- dry alloy - will crumble if dropped from 30am
- ^ chance of creep

well mixed alloy
- will stay tgt if dropped, be slightly flattened and have wet surface gloss

placement
- should be placed and completed within 3 mins of mixing
- place into deepest place in cav first
- pack laterally as vertically overlapping strokes
- burnish surface of resto for 15 sec to bring mercury to surface
- dont prod deep fissues and grooves - makes material more likely to fracture

Question 6

distinguish tarnish and corrosion in amalgam

Answer 6

tarnish
- surface chemical reactions which cause discolouration/dulling
- does not compromise structural integrity

corrosion
- chemical reaction which affects both surface and internal structure weakening the resto - causing fractures/ break downs
- can also lead to microleakage, marginal breakdown, rough surfaces

Question 7

outline four reasons to recontour, finish and polish restorations

Answer 7

1. longevity
   - good marginal finishes, appropriate contou and high polish = less likely to fail
2. reduce plaque accumulation
   - smoother resto = less plaque accumulation = avoids recurrent caries
3. aesthetics
   - polishes restos reflect light = makes CR look more tooth like // minimises dark appearance of amalgam
4. pt comfort
   - high/rough resto can be uncomfortable and disrupt occlusion

Question 8

List THREE contraindications to polishing a restoration

Answer 8

1. freshly placed amalgam/GIC
   - requires 24hr to fully set
   - premature polishing may weaken resto
2. fractured/deteriorating restos
   - may exacerbate damage or lead to resto failure
   - resto should be repaired or replaced instead
3. marginal leakage/recurrent caries
   - polishing can seal in decay or exacerabate resto’s seal

Question 9

outline some instruments/materials suitable for polishing

Answer 9

amalgam
- plain steel burs [flame, round, pear]
- metal finishing strips
- finishing stones to remove high spots

• finishing stones
• finishing discs [GIC, CR]
• celluloid finishing strips [GIC, CR]
• diamond burs [CR]

US scaler
- removal of THIN overhangs
- less effective for bulky overhangs