Amalgam
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what type of material is amalgam?
an alloy
how can amalgam be classified?
by its: • composition • particle shape & size
what are the different compositions of amalgam?
• traditional • copper enriched
what materials is amalgam composed of?
• Ag (silver) • Sn (tin) • Cu (copper) • Zn (zinc) • Hg (mercury)
what makes up the powder aspect of amalgam?
• silver-tin (Ag3Sn) • copper • zinc • mercury in powder
what is the liquid aspect of amalgam composed of?
Hg (mercury)
what is the function of the silver-tin compound found in amalgam?
it reacts with the Hg liquid to form amalgam
what is the function of copper in the makeup of amalgam?
increases strength and hardness of material
what are the characteristics of the gamma-1 phase of the amalgam setting reaction?
• good corrosion resistance
what are the characteristics of the gamma-2 phase of amalgam?
• weak and poor corrosion resistance
what amalgam phase has the highest tensile strength?
gamma phase
what handling factors may affect the properties of amalgam?
• proportioning and titration • condensation/how well it is packed into cavity • carving and polishing
what are the amalgam properties dependant on?
• handling factors • cavity design • affected by corrosion
what type of cavities are amalgam restorations particularly suited to? why is this?
Cavities in posterior teeth, due to higher abrasion resistance than materials such as composite.
what factors may decrease the strength of an amalgam restoration?
• undermining • low condensation pressure (when packing into cavity) • slow rate of packing • corrosion
why is creep a problem in amalgam restorations?
affects marginal integrity & can contribute to microleakage
what is creep?
when a material experiences: • low level stress levels (below elastic limit stress) which are applied repeatedly over a prolonged time period • causes material to flow resulting in permanent deformation
how might ditching occur in amalgam restorations?
• low magnitude forces are applied to amalgam repeatedly • amalgam flows and changes shape • amalgam sitting proud of tooth surface • prone to fracture, resulting in ditched margins
what is the thermal expansion of amalgam? is this good or bad?
x3 of tooth - not ideal & may lead to margin gaps
what is the thermal conductivity of amalgam? is this good or bad?
High, which is may lead to sensitivy from heat and cold. A lining could be used to help alliviate this.
what is the thermal diffusivity of amalgam? what does this mean for the material?
• high • when a transient thermal stimuli is applied amalgams temperature rises quickly • can damage the pulp
how can corrosion be reduced in amalgam materials?
• enrich with copper • polish margins • avoid galvanic cells
what is copper enriched amalgam?
amalgam with: • non gamma 2 phase • high copper (copper>6%)
what does an increased copper content provide amalgam?
• higher early strength • less creep • higher corrosion resistance • increased durability of margins