Amalgam Flashcards by Amalia Gazala

What is amalgam?

an alloy formed by the reaction of mercury (liquid) with silver, tin, copper and other metals (powder)

How well did you know this?

Not at all

Perfectly

How many amalgam restorations are placed annually in England and Wales?

22 million restorations

How well did you know this?

Not at all

Perfectly

How many amalgam restorations are placed annually in the USA?

160 million restorations

How well did you know this?

Not at all

Perfectly

When did the history of amalgam begin?

659 AD China - silver dough (45 parts Ag, 900 parts Sn, 100 parts Hg - same 3 elements still in amalgam but in different proportions)

How well did you know this?

Not at all

Perfectly

What was the first amalgam war?

1840 American Society of Dental Surgeons ban use of amalgam

How well did you know this?

Not at all

Perfectly

What was G.V. Black’s role in the history of amalgam?

carried out a systematic study of composition and properties of modern amalgam in 1895 and found it was strong with low dimensional changes

How well did you know this?

Not at all

Perfectly

What changes occurred to amalgam from 1960s onwards?

new alloys, handmixing replaced by automatic mixers, encapsulated materials (safety)

How well did you know this?

Not at all

Perfectly

When was the second amalgam war?

1970s-1990s

How well did you know this?

Not at all

Perfectly

What drove the second amalgam war?

mercury fear with respect to health and environment

How well did you know this?

Not at all

Perfectly

Describe the % composition of amalgam

70% Ag, 25% Sn (tin), 3% Cu, 1% Zn, 1% Hg (mercury)

How well did you know this?

Not at all

Perfectly

What percentage weight of amalgam is composed of powder?

50% weight

How well did you know this?

Not at all

Perfectly

What form is silver and tin in the powder?

intermetallic compound Ag3Sn

How well did you know this?

Not at all

Perfectly

What is the intermetallic compound Ag3Sn known as?

gamma (y) phase

How well did you know this?

Not at all

Perfectly

What is the function of the Ag3Sn / gamma phase in powder of amalgam?

gamma phase (Ag3Sn) reacts with Hg liquid to form amalgam

How well did you know this?

Not at all

Perfectly

What is the function of copper in the powder component of amalgam?

increases strength and hardness

How well did you know this?

Not at all

Perfectly

What is the function of zinc in the powder component of amalgam?

scavenger during production (reacts with and removes particular molecules). Preferentially oxidises and slag formed / removed

How well did you know this?

Not at all

Perfectly

What element are some types of amalgams made without?

zinc - some amalgams are zinc free

How well did you know this?

Not at all

Perfectly

What percentage weight of amalgam is composed of liquid?

50% by weight

How well did you know this?

Not at all

Perfectly

What element(s) makes up the liquid component of amalgam?

How well did you know this?

Not at all

Perfectly

What is the function of Hg in the powder component of amalgam?

means it is a pre-amalgamated alloy so will react faster

How well did you know this?

Not at all

Perfectly

How is the mercury (Hg) in the liquid component of amalgam purified?

triple distilled - very pure

How well did you know this?

Not at all

Perfectly

What is the function of mercury in the liquid component of amalgam?

Hg reacts with other metals

How well did you know this?

Not at all

Perfectly

What are the different particle types in amalgam?

lathe cut and spherical/spheroidal particles

How well did you know this?

Not at all

Perfectly

What are lathe cut particles?

random shavings of coarse, medium, fine particles

How well did you know this?

Not at all

Perfectly

How are lathe cut particles formed?

lathe cut particles are formed by filling ingots

What size are the spherical, spheroidal particles?

range of particle sizes

How are spherical / spheroidal particles formed?

formed by spraying molten metal into inert atmosphere

Outline the simplified setting reaction of traditional amalgam in formula

Ag3Sn + Hg -> Ag3Sn + Ag2Hg3 + Sn7Hg9

Why is Ag3Sn both a reactant and product in the setting formula of amalgam?

Ag3Sn is the powder / gamma phase reactant but also appears in the product due to unreacted particles

What is gamma phase 1 (y1)?

Ag2Hg3 (silver mercury) - forms part of amalgam matrix

What is gamma phase 2 (y2)?

Sn7Hg9 (tin mercury) - forms part of amalgam matrix

What is the traditional amalgam matrix composed of?

y phase (unreacted Ag3Sn), y1 phase (Ag2Hg3) , y2 phase (Sn7Hg9)

Describe the set structure of amalgam

matrix of y1 phase (Ag2Hg3), containing y particles (Ag3Sn), and y2 particles (Sn7Hg9)

What are the properties of y phase (Ag3Sn / silver tin)?

good strength and corrosion resistance

What are the properties of y1 phase (Ag2Hg3 / silver mercury)?

good corrosion resistance

What are the properties of y2 phase (Sn7Hg9 / tin mercury)?

weak and poor corrosion resistance

How do voids impact the properties of amalgam?

voids decrease strength and increase corrosion

What is the tensile strength of gamma phase (Ag3Sn)?

170 MPa (megapascals)

What is the tensile strength of gamma 1 phase (Ag2Hg3)?

30 MPa

What is the tensile strength of gamma 2 phase (Sn7Hg9)?

20 MPa

What is the resultant tensile strength of traditional amalgam?

60 MPa

Describe the setting dimensional changes that traditional amalgam undergoes?

- initial contraction (solution of alloys and particles in Hg) - followed by large expansion (y1 / Ag2Hg3 crystallisation)

Describe the setting dimensional changes that modern amalgam undergoes

small contraction that is maintained (solid solution of Hg in Ag3Sn)

Why is the setting dimensional change of amalgam not seen clinically?

expansion / contraction is <0.2% so there is little clinical sign of it

Why are do zinc-free amalgams exist?

to eliminate expansion of amalgam as a result of zinc interacting with saliva / blood

What happens if zinc interacts with saliva / blood?

Zn + H2O -> ZnO + H2 therefore H2 bubbles form within amalgam causing pressure build up and expansion

What are the possible consequences of amalgam expansion (due to Zn reacting with H2O)?

downward pressure can cause pulpal pain, upward pressure can result in the restoration sitting proud of the surface

What factors can have an effect on amalgam properties?

handling factors (proportioning, trituration, condensation, carving, polishing), cavity design, corrosion

What are the advantages of amalgam with spherical particles?

less Hg required, higher tensile strength, higher early compressive strength, less sensitivity to condensation, easier to carve

What properties of dental materials should be considered?

strength, rigidity, abrasion resistance, creep, setting shrinkage, thermal expansion, thermal conductivity, corrosion, bonding / microleakage, handling / viscosity, biocompatibility, aesthetics, radiopaque, anticariogenic, smooth surface

What is the compressive strength for traditional amalgam?

early (1hr) compressive strength is poor, late (>24hrs) is ok

What is the abrasion resistance for amalgam?

high therefore suitable for posteriors. But abrasion resistance too high for deciduous teeth

What factors can decrease the strength of amalgam?

undermixing, too high Hg content after condensation, too low condensation pressure, slow rate of packing (increments do not bond), corrosion

What is the creep in traditional amalgams?

creep is high in traditional amalgams

What factors can affect marginal integrity?

creep, cavity design, corrosion

What is creep?

process by which a material flows (changes shape) and becomes permanently deformed due to low-level stresses (below elastic limit) applied repeatedly for a prolonged time

What materials can undergo creep?

amalgam, alloys, waxes, plastics

Outline the process of creep in amalgam

- amalgam fits cavity - low magnitude force applied repeatedly - amalgam changes shape and sits proud of the tooth surface - vulnerable to fracture at margins - ditched margins - secondary caries

What is / was a biocompatibility concern related to amalgam?

concern about mercury toxicity - but evidence shows release of Hg from amalgams are very small and do not have an effect

What is the thermal expansion of amalgam?

3 times the thermal expansion of tooth (enamel / dentine)

What is the thermal conductivity of amalgam?

high

What is a clinical action done due to the high thermal conductivity of amalgam?

use a liner in deep cavities (acts as an insulator to protect pulp from heat)

What is thermal diffusivity?

a measure of how quickly heat spreads through a material

What is the thermal diffusivity of amalgam?

high, so when a transient thermal stimuli is applied (e.g. drinking tea) amalgam's temp rises quickly

How is amalgam's bond to tooth / compatibility with bonding systems?

- does not bond to tooth - requires mechanical retention - some suggest new bonding systems based on 4-META which is not yet widely accepted

What is the handling / viscosity properties of amalgam?

- okay mixing / working / setting times which varies between types of amalgam - viscosity is user friendly as amalgam can be packed / condensed into cavity

What is an alternative term for packing (into cavity)?

condensing

Which component of amalgam is the easiest to corrode?

y2 phase (Sn7Hg9) - weakens amalgam especially at margins

Why is y2 phase (Sn7Hg9) the most likely amalgam component to corrode?

y2 phase is the most electronegative

How can the corrosion of amalgam be reduced?

using copper enriched AM, polishing margins, avoiding galvanic cells (?)

How is the aesthetic of amalgam?

poor

Is amalgam anticariogenic?

Is amalgam radiopaque?

yes

Does amalgam have a smooth surface?

yes, if polished well

What are copper enriched amalgams?

non-y2 (Sn7Hg9), high copper amalgams

What percentage of copper enriched amalgams is copper?

>6% copper

What are the different types of copper enriched amalgams?

dispersion modified (original type) and single composition types

Why were single composition types of copper enriched amalgam introduced?

to increase uptake by profession

What is dispersion modified copper enriched amalgam?

contain Ag-Cu spheres and conventional lathe cut alloy

What was the rationale behind adding Ag-Cu spherical particles to make dispersion modified copper enriched amalgams?

originally though Ag-Cu spherical particles would act as a strengthening agent, but instead increased copper content gave beneficial modifications to setting reaction

Outline the dispersion modified setting reaction

1. as conventional: y (Ag3Sn) + Hg -> y (Ag3Sn) + y1 (Ag2Hg3) + y2 (Sn7Hg9) 2. y2 (Sn7Hg9) + Ag-Cu -> Cu6Sn5 + y1 (Ag2Hg3)

What is significant about the setting reaction of dispersion modified copper enriched amalgam?

all y2 (Sn7Hg9) is consumed

How long does the second part of the dispersion modified setting reaction take (reaction with Ag-Cu which consumes all y2)?

takes several days

Describe the resulting structure of dispersion modified copper enriched amalgam

y1 (Ag2Hg3) matrix encasing y (Ag3Sn) particles and Ag-Cu spheres surrounded by a Cu6Sn5 halo

What is single composition copper-enriched amalgam made up of?

Ag-Sn-Cu powder, 12-30% copper, spherical and lathe cut particles

What is the percentage of copper in single composition copper enriched amalgam?

12-30%

What element is absent from all copper enriched amalgams?

What is the setting reaction of single composition copper enriched amalgam?

Ag-Sn-Cu + Hg -> Ag-Sn-Cu + y1 (Ag2Hg3) + Cu6Sn5

What are the benefits of using copper enriched amalgams?

higher early strength, less creep, higher corrosion resistance, increased durability of margins

Order the types of amalgam in increasing compressive strength

lathe < spherical < Cu dispersion modified < Cu single composition (485 MPa)

Order the types of amalgam in decreasing % creep

traditional lathe (6.3% dimensional change) > traditional spherical (1.1) > Cu dispersion (0.46) > Cu single (0.07)

What type of amalgam is used in GDSH?

PERMITE (type of copper enriched amalgam - superior than traditional amalgam)

What type of amalgam is Permite?

non-gamma 2, spherical and lathe cut

What is the compressive strength of Permite?

500MPa (highest)

How does the compressive strength of amalgam compare to enamel, dentine and hybrid composite?

Amalgam 500MPa Enamel 250MPa Dentine 280MPa Hybrid composite 300MPa

How does the tensile strength of amalgam compare to enamel, dentine and hybrid composite?

Amalgam 60MPa Enamel 35MPa Dentine 40-260MPa Hybrid composite 50MPa

How does the elastic modulus (rigidity) of amalgam compare to enamel, dentine and hybrid composite?

Amalgam 30GPa Enamel 50GPa Dentine 12GPa Hybrid composite 14GPa

How does the hardness of amalgam compare to enamel, dentine and hybrid composite?

Amalgam 100 VHN Enamel 350 VHN Dentine 60 VHN Hybrid composite 90 KHN

What is an alternative method of assessing amount of creep?

microleakage (ml/min) - testing how much fluid enters at margins

Which type of amalgam has the lowest level of microleakage?

Permite (0.04 ml/min)

Compare the thermal expansion coefficients (ppm/degreesC) of enamel, dentine, amalgam, composite, GIC, Ceramic and Gold alloy

Enamel 11 ppm/C Dentine 8 Amalgam 22-28 (approx x3 of tooth) Composite 25-68 GIC 10-11 Ceramic 8-14 Gold alloy 12-15

Which restorative material has a thermal expansion coefficient closest to enamel / dentine?

GIC (10-11 ppm/C)

How does the failure rate of amalgam compare to posterior composites?

amalgam has a lower failure rate (5.8%) compared to all composites (13.7%)

Summarise the advantages of amalgam

- strong - hard - durable - radiopaque - user friendly

Summaries the disadvantages of amalgam

- corrosion - leakage as it does not bond - poor aesthetics - mercury (perceived toxicity, environmental impact) - (high thermal conductivity)

Amalgam Flashcards

(105 cards)