Clinical applications of amalgam Flashcards
When should amalgam NOT be used
If aesthetics are paramount to patient
The patient has a history of sensitivity to mercury or other amalgam components
Where the loss of tooth substance is such that a retentive cavity cannot be produced
Where excessive removal of sound tooth substance would be required to produce a retentive cavity.
What are the advantages of amalgam
Durable
Good long term clinical performance
Long lasting if placed under ideal conditions median survival 12 – 15 years
Long-term resistance to surface corrosion
Shorter placement time than composite
Corrosion products may seal the tooth restoration interface
Radiopaque
Colour Contrast
Economical
Disadvantages of amalgam
Poor aesthetic qualities
Does not bond easily to tooth substance
Thermal diffusivity high (1.7cm2 /sec vs 0.0026cm2 /sec for dentine)
Cavity preparation may require destruction of sound tooth tissue
Marginal breakdown
What is an amalgam tattoo
When fine amalgam particles migrate into the soft tissues (appears as an abnormal grey coloured lesion)
What is retention form
Features that prevent the loss of the restoration in any direction
In an occlusal direction significant undercut is not required, parallel or minimal undercut is all that is necessary.
What is resistance form
Features that prevent loss of the material due to distortion or fracture by masticatory forces
Ideally the cavity floor should be approximately parallel to the occlusal surface with sufficient depth of the cavity to give the restoration adequate mechanical strength (approx 1.5 – 2mm)
What cavity designs are used to treat interproximal caries
Self-retentive box preparation (minimal preparation box)
Proximo-occlusal preparation
What are the advantages and disadvantages of self-retentive box prep
ADV
Less tooth tissue removed than with a proximo-occlusal preparation
Reduced amount of amalgam placed
Sound tooth tissue retained between proximal box and any occlusal cavity
DISADV
Can be more technically demanding than proximo-occlusal preparation
Further treatment of any pit and fissure caries may be required
What are the adv and disadv of a proximo-occlusal prep
Advantages
(Should be) Very retentive
Also treats any caries in pits and fissures
Less or no opportunity for future caries in pits and fissures
Disadvantages
Destruction of tooth tissue for retention
Increased risk of weakening of the tooth
What are pins used for and where are they placed
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Added for increased retention of the amalgam
self-tapping screws
Pinned into dentine in the greatets bulk of the tooth
Never placed in enamel or at the ADJ as they might fracture the tooth
Avoid pulp and PDL
What are the problems with pins
Place stress on the tooth around the pin
Can crack dentine
Cause tooth sensitivity
Secondary caries can spread further due to presence of the pin
Is there benefits to bonding amalgam
‘There is no evidence to claim or refute a difference in survival between bonded and non-bonded amalgam restorations’ - cochrane
What happens with moisture contamination
Reduces Strength
Increases creep
Increases corrosion
Increases porosity
Critical but not as critical as in bonded composite restorations
What are the benefits of matrices
- Recreate wall(s) of the cavity
- Allows creation of proximal form
- Allows adequate condensation
- Confines amalgam to the cavity
What are the desired properties of matrices
- Should be < 0.05mm thick
- Smooth and strong
- Allow close adaptation especially at the cervical margin
- Allow good contact with adjacent tooth
What do wedges do
Temporary tooth separation
Prevents excess amalgam gingivally
Aids proximal wall contour
Prevents movement of matrix band
What is the adequate bulk of material needed for a retentive amalgam restoration
1.5 - 2mm
What does mixing time affect
- Handling characteristics
- Working time
- Amalgam microstructure
- Restoration longevity
Why is condensation important
- Expels excess mercury bringing it to the surface where it will be carved off
- Adapts material to cavity walls
- Reduces layering (homogenous)
- Eliminates voids
What alloys require less condensing force
Spherical alloys
What does inadequate condensation lead to
- Lack of adaptation to cavity
- Poor bonding between layers
- Inadequate mercury expression and consequently removal during carving
- Inferior mechanical properties
What is microleakage
Passage of fluid and bacteria in micro gaps (10 microns) between restoration and tooth
What does microleakage cause
- Pulpal irritation and infection
- Discolouration
- Secondary Caries
What alteration to current amalgam composition reduces likelihood of corrosion
Non-gamma 2 phase which is associated with corrosion risk
What is creep
Slow internal stressing and deformation of amalgam under stress
What does increased copper reduce
Creep as the Ag - Sn - Cu phase is stronger
When is the most mercury released with amalgam fillings
The greatest amount of mercury is released during the insertion and removal of amalgam restorations
How does the body absorb mercury
Vapour into lungs
Contact with skin
Gingiva and mucosa
Gastro-intestinal tract
Dentine and Pulp as metal ions?
How is mercury hygeine managed to protect against absorption
Dental dam
High Volume aspiration
Amalgam traps – separators
Spillage Kit
Correct disposal of waste amalgam
Correct disposal of unused amalgam
What can mercury toxicity cause
Neuro-toxicity
Kidney dysfunction
Reduced immunocompetence
Effects on the oral and intestinal bacterial flora
Effects on general health
Foetal and birth effects
What are the Blacks cavity classifications
- Class I: Pit and fissure caries
- Class II: Approximal caries (posterior teeth)
- Class III: Approximal caries (anterior teeth)
- Class IV: Approximal caries involving incisal angle
- Class V: Caries affecting cervical surfaces
- Class VI: Caries affecting cusp tips
What is the Class 1 cavity
Pit and fissue caries
What is a class 6 cavity
Caries affecting the cusp tips
What is the class 4 cavity
Approximal caries involving incisal angle
What is a class 2 cavity
Approximal caries (posterior)
What is a class 5 cavity
Caries affecting cervical surfaces
What is a class 3 cavity
Approximal caries (anterior)
What people should amalgam not be used on
Children under 13
Preganant women
Breastfeeding women
