retaining large amalgam restorations Flashcards

1
Q

how is amalgam retained

A

convergenet cavity walls (mechanical locking)

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2
Q

what does loss of retention lead to

A

poor margins

Plaque accumulation

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3
Q

features that improve retention

A

grooves
channels, slots
bonding
pins

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4
Q

slots

A

inverted cone bur

generates a dove tail for locking

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5
Q

amalgampins

A

0.8mm diameter
2mm deep
slight angle

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6
Q

risk of amalgapin

A

damage the pulp

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7
Q

shelves

A

need to be 2mm deep

cut around the tooth

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8
Q

when can undercut fail

A

when the restoration moves bucally

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9
Q

success of a restoration retentive

A

place features where they will resist loads
destribute forces around the tooth
consider direction of forces

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10
Q

adhesive amalgam process

A

develops adhesions through molecular entanglement

micromechanical locking between resin and amalgam

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11
Q

clinical trial results for bonded amalgam

A

lower sensitivity of the tooth
retention rates exceed that of pins
less iatrogenic damage
better restoration survival

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12
Q

problems with bonding amagalm

A

loss of bond layer
oxygen inhibition, need to prevent oxygen getting in
weakening of amalgam
adhesion to matrix band

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13
Q

pins

A

restoration can lock onto the screw ontop
must have 0.5mm sound dentine to surround
one pin per missing wall/cusp

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14
Q

avoid placement of pins at

A

bifurcation
curved roots
thin dentine
pulp

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15
Q

how to place pin

A
maximise all other retention
find flat anatomically safe location
-	mark a centre with ½ round bur
-	select drill angle
-	drill hole
-	clean debris
-	place pin
-	adjust pin if required
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16
Q

why are pins not advised to use

A

placement at high speed results in poor thread
cause dentine fractures
surlus lining reduced retentive action
not used for composutes