Amalgam Flashcards
Lathe cut vs spherical amalgam alloy particles
Lathe cut require higher condensation pressure, generate proximal contacts more easily
Spherical require less mercury for amalgamation, hence
- Superior tensile strength
- Higher early compressive strength
- More rapid hardening
- better surface finish
What is the self sealing property of amalgam
Self limiting process where by percolation of oral fluids between amalgam restoration and the tooth result in corrosion. Corrosion products accumulate in the space and reduce microleakage.
What are the demands of an amalgam restoration/cavity prep given that it has relatively low tensile and shear strength
Restoration is prone to fracture during flexure, and must be supported by tooth structure. 90º marginal configuration
Also requires sufficient bulk of 1.5-2mm in occlusally loaded area
Advantages of amalgam
- High compressive strength
- Self sealing
- Excellent wear resistance
- Little creep and flow (for high copper amalgams) hence no marginal ditching
- Less technique, moisture sensitive
- Lower cost
Disadvantages of amalgam
- Non insulating
- Less conservative prep
- Wet corrosion (chemical/electrochemical), cause tarnishing, pitting, discolouration
- Galvanism
- Bulk fracture
- Amalgam tattoo
- Excess mercury seep into dentinal tubules
What happens if I use amalgam containing zinc and have issues with moisture control
Delayed expansion due to production of hydrogen gas which exerts pressure
Contraindications to use of amalgam
Allergy to alloy components
Aesthetic (relative contra)
CR offer more conservation of tooth structure and equal clinical performance
Oblique ridge should be conserved when doing tooth prep unless
Undermined by caries
Cross by deep fissure
>0.5mm between MO and DO
Amalgam should be burnished immediately to
Finalise condensation and remove excess mercury rich amalgam
Finishing of amalgam
Should not be done within 24 hours of placement (crystallisation incomplete)
Use green carborundum, white alumina stone to smoother. Small round finishing bur to define features
Things you may notice when evaluating amalgam restoration
Discolouration of tooth
Proximal overhang
Marginal ditching (due to enamel wear, fracture of restoration edge)
Voids
Fracture lines
Improper anatomic contours
Improper proximal contacts
Improper occlusal contacts
Recurrent caries
Disadvantages of complex amalgam restoration vs indirect restoration
Difficult to create proper contours and occlusal contacts
Resistance form difficult to develop
Does not protect tooth from fracture as effectively
