Clinical applications of amalgam

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.

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

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​

When fine amalgam particles migrate into the soft tissues (appears as an abnormal grey coloured lesion)

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.

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)

Self-retentive box preparation (minimal preparation box) Proximo-occlusal preparation

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

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

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

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

‘There is no evidence to claim or refute a difference in survival between bonded and non-bonded amalgam restorations’​ - cochrane

Reduces Strength​ Increases creep​ Increases corrosion​ Increases porosity​ Critical but not as critical as in bonded composite restorations

• Recreate wall(s) of the cavity​ • Allows creation of proximal form​ • Allows adequate condensation​ • Confines amalgam to the cavity

• Should be < 0.05mm thick​ • Smooth and strong​ • Allow close adaptation especially at the cervical margin​ • Allow good contact with adjacent tooth

Temporary tooth separation​ Prevents excess amalgam gingivally​ Aids proximal wall contour​ Prevents movement of matrix band​

1.5 - 2mm

• Handling characteristics​ • Working time​ • Amalgam microstructure​ • Restoration longevity

• Expels excess mercury bringing it to the surface where it will be carved off • Adapts material to cavity walls • Reduces layering (homogenous) • Eliminates voids

Spherical alloys

• Lack of adaptation to cavity​ • Poor bonding between layers​ • Inadequate mercury expression and consequently removal during carving​ • Inferior mechanical properties

Passage of fluid and bacteria in micro gaps (10 microns) between restoration and tooth

• Pulpal irritation and infection​ • Discolouration​ • Secondary Caries

Non-gamma 2 phase which is associated with corrosion risk