clinical amalgam Flashcards
what is amalgam?
an alloy of mercury with another metal(s)
what are the direct restorative materials?
amalgam
composite resin
glass ionomer/RMGI
what are the indirect restorative materials?
gold
other metals
ceramic
composite resin
what are the possible indications for amalgam?
direct rest. mod/large size cavity in posteriors
core build up when definitive rest. will be indirect cast restoration eg crown/bridge retainer
when should amalgam not be used?
aesthetic important
history of sensitivity to mercury/other components
if retentive cavity cant be cut
excessive healthy tooth would have to be removed
what are the advantages of amalgam?
durable good long term performance long lasting if good conditions long term resistance to surface corrosion short placement time corrosion products may seal tooth rest. interface radiopaque colour contrast economical
what are the disadvantages of amalgam?
poor aesthetics not easy bond high thermal diffusivity cavity prep may require destruction of sound tooth tissue marginal breakdown corrosion at interface may cause ditching local sensitivity reactions lichenoid lesions -hypersensitivity galvanic response can occur tooth discolouration amalgam tattoo mercury toxicity
why is amalgam a ‘go to’?
quick and easy self-hardening at mouth temp load-bearing bulk strength, wear resistance 1 visit economical
what is retention form?
features that prevent the loss of the restoration in any direction
does an occlusal restoration need a significant undercut?
no a parallel or minimal undercut is all that is necessary
what is resistance form?
features that prevent loss of material due to distortion or fracture by masticatory forces
describe appropriate cavity floor in reference to resistance form
should be aprrox parallel to occlusal surface w/ sufficient depth to give adequate mechanical strength (1.5-2mm)
describe the gingival floor of an interproximal box
approx 90 degrees to axial wall
if greater sloping incline make filling liable to sliding out
what is a self-retentive box preperation?
minimal prep box
what is a proximo-occlusal prep?
take out fissure as well as interproximal caries for better retention
-more healthy tissue removed
what are the advantages of self-retentive box?
less tooth tissue removed
reduced amount of amalgam placed
sound tissue retained between proximal box and any occlusal cavity
what are the disadvantages of self-retentive box?
can be more technically demanding that proximo-occlusal
further tx of any pit and fissure caries may be required
what are the advantages of proximo-occlusal prep?
very retentive
treats pi & fissure caries
less/no opportunity for future caries in pit and fissures
what are the disadvantages of proximo-occlusal prep?
destruction of tooth tissue for retention
increased risk of weakening the tooth
describe mechanical additional retention
include grooves or dimples w/i cavity design
pin placement-titanium/stainless steel
used to increase retention in large non-retentive cavities or cores beneath crowns
self tapping screws
in dentine in greatest bulk of tooth
pack amalgam around pin
what are initial problems with pins?
stress in tooth around pin
cracking of dentine
sensitivity of tooth due to temperature transference
what are long term problems with pins
filling can leak but not fall out
-secondary caries can progress further into tooth
describe adhesive technology (additional retention)
sealing and bonding restorations
bonding
RMGIC
how is an amalgam cavity prep finished?
ensure all caries is removed
smooth and round internal line angles
check and finish cavo-surface angles
smooth cavity margins
what are the consequences of moisture contamination
reduces strength increases creep increases corrosion increases porosity not as critical as in bonded composite rest
how is dentine sealed?
cavity varnished
RMGIC
what is microleakage?
passage of fluid and bacteria in micro gaps between rest and tooth
- pulpal irritation and infection
- discolouration
- secondary caries
how does microleakage occur?
over time mechanical loading and thermal stress
what is the function of a matrix?
recreate walls of cavity
allows creation of proximal form
allows adequate condensation
confines amalgam to cavity
what does mixing time (trituration) affect?
handling characteristics
working time
amalgam microstructure
rest. longevity
what is condensation?
expels excess mercury bringing it to the surface where it will be carved off
adapts material to cavity walls
reduces layering
eliminates voids
how is optimal condensation achieved?
require correct size of instruments
easier to control initial increment with large plugger
-smear into cavity
-smaller plugger
-overlapping axial strokes
lateral as well as axial condensation
spherical alloys require less force for condensation
what are the consequences of inadequate condensation?
lack of adaptation to cavity
poor bonding between layers
inadequate mercury expression and consequently removal during carving
inferior mechanical properties
should the cavity be overfilled?
yes
what is recreated during carving?
marginal ridge inter-proximal contact areas fissure pattern cusps and cuspal inclines re-establishes occlusal contacts
describe finishing
only if required to adjust anatomical contour after amalgam has set
amalgam finishing burs with water spray
aspiration
unnecessary - can create heat
what is corrosion?
detrimental change in the character of amalgam due to reactions in the mouth
associates with gamma 2 phase
-can cause marginal breakdown with creep and ditching
-expansion may assist in development in marginal seal
what is creep?
slow internal stressing and deformation of amalgam under stress
-copper decreases
-more creep-weaker amalgam
correct cavo-surface angle is essential
how are amalgam restorations removed
dental dam high volume aspiration minimal cutting selective cutting hand instruments -break up with handpiece then remove, least drill possible
when is the greatest amount of mercury released?
during the insertion and removal of restorations
what is the usual mecury hygiene?
dental dam high volume aspiration amalgam traps-seperators spillage kit correct disposal of waste amalgam correct disposal of unused amalgam
what are the signs of mercury toxicity?
neuro-toxicity kidney dysfunction reduced immunocompetence effects on the oral and intestinal bacterial flora effects on general health foetal and birth defects
who can amalgam not be used on without appropriate reson?
children under 15
pregnant women
breastfeeding women
what are blacks cavity classifiacations?
I- pit and fissure caries II approximal caries posterior III - approximal caries anterior IV - approximal caries involving incisal angle V - caries affecting cervical surfaces VI caries affecting cusp tips
