PRD 131: zirconium, amalgam Flashcards by Hayley Epstein

what are the biologic considerations for treatment planning single crown restoration

remaining tooth structure
vitality of pulp
periodontium and surrounding structures
occlusion & function
prognosis

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what are properties of restorative materials to consider

thermal conductivity

strength
expansion or shrunk
resistance to wear: attrition, abrasion, chemical erosion
good bonding to tooth
radiopacity or radiolucent
esthetics

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how does lost wax technique work

restoration is waxedm a mold is formed from the wax.
-then casting is when restorative material (gold) is liquified using high heat and poured into a mold. mold contains a hollow cavity of the desired shape. after pouring material allowed to solidify. the solidified part is termed casting, which is taken out of the mold to complete the process .

-cd

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what is milling fabrication type

chairside or lab processed - dental mills are designed to fabricate restorations from materials such as ceramics- including zirconia and porcelain . milling can be in lab or in office.

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what are the 3 ceramic classifications and wha they mean

glass : highly esthetic
particle-filled glass: filter added to glass matrix , thisimproved mechanical properties
polycrystalline: contains NO glass

-evolved from glass to polycrystalline in history

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what are the properties of glass ceramics

low thermal conductivity
low tensile strength, poor mechanability
high transperancy, high brittleness,
poor impact strength

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how do esthetics and strength change with glass

more glass - more aesthetic

more glass - less strong !

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what is feldspathic

glass ceramic type

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what are examples of glass ceramics with fillers?

-leucite reinforced lithium disilicate

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wha tare examples of glass free ceramics and what are these called

POLYCHRYSTALLLINE:

alumina
zirconia

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when would you use lithium disilicate vs zirconia and hwy

zirconia is stronger, would use on posterior teeth. lithium disilicate is more aesthetic so would use for when esthetics are a concern-anterior/premolar area. (160 mpa vs 900 mpa)

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what is the usual material of choice for single unit crowns?

zirconia
could be monolithic and solid or biolithic and layered
-used to be ugly but now they made them better with color/translucency

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what to consider regarding monolithic zirconia

wear
surface roughness
fracture strength
oprtical properties
marginal fit

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what are the pros/cons of monolithic zirconia

good chemical properties and dimensional stability
high mehcanical strength and toughness- high flexural strength
enhanced translucency (starting to look better) but not as good as lithium disilicate
can be abrasive - need proper finish and polish

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what are the 7 principals of tooth prep for all restorations

conservation of tooth
retention form
resistance form
structural durability
marginal integrity
preservation of periodontium
aesthetics

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what are other names for monolithic zirconia

-monolithic zirconia crown, full zirconia crown, full crown zirconia, monolithic zirconia restoration, full veneer zirconia

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when would you use a zirconia crown?

ideal if patient wants a conservative prep but doesn’t want gold /metal crown.
if patient doesnt have adequate preparation space for a PFM and require conservatio nof tooth, dont want metal basically.

what are the criteria for a zirconia crown: occlusal reduction, axial reduction, margin, margin location, and taper (ideal)

occlusal reduction: 1.5
axial reduction: 1 mm
margin: .8mm heavy chamfer
margin location: .5mm above gum
taper: 6 degrees

what is the composition of amalgam %s

silver: 40-70% by weight
tin: 12-30% by weight
- copper: 12-30% by weight

zinc is also in there to reduce oxidation
palladium reduces tarnish, builds early strength
indium strengthens

mix with metal of 41-50% by weight of mercury

what is lathe cut alloys properties? whats it used for

alloy (powder)
– lathe cut was formerly used- irregular pieces, stiff material, resists condensation (packing of material), good contacts-> resists deformation

what is spherical alloy?

used to use this powder (alloy)- heat up hot, solidified from there

droplets
fast setting
good adaptation
slippery, not as good contact w other tooth

what is admixed powder?

combination of lathe cut and spherical! now its used- only thing on market now:
-good all around properties

what is mixed to make low copper alloys? when are they used

previously used!! combining agsn (silver and tin) with mercury

what are the intermetallic compounds formed/ chem reaction of mixing low copper alloy

Ag2Hg3 and Sn8Hg are formed ..

Hg dissolves Ag and Sn from the alloy (dissolution and precipitation)

what is the initial powder that gets mixed with mercury for low copper alloy called ? what % of set amalgam does it make up ? and what is an important feature?

Gamma = Ag3Sn - forms 30% of set amalgam - strongest phase and corrodes the least! (also initial powder in admixed high copper alloys)

WHAT IS gamma 1?

intermetallic compound formed in low copper alloy reaction. - precipitates on unreacted alloy - second strongest phase - 10 micron grains binding gamma - 60% of the volume (also formed in admixed high copper)

what is gamma 2?

intermetallic compound formed in low copper alloy, - weakest and softest phase - corrodes fast, voids form - corrosion yields Hg which reacts with more gamma - 10% of volume - volume decreases with time due to corrosion - becomes HgCl2

what are the reactants and products of admixed high copper alloy mixture amalgam

Ag-Cu alloy (spherical) and Ag-sn alloys are reacted with mercury -both Ag and Sn enter Hg from Ag3sn particles when all mixed. reaction results in agcu, ag3sn, ag2hg, cu6sn5 (NO GAMMA 2!)

how does Cu6sn5 get formed when admixed high copper alloys mix

Sn diffuses to surface of Ag-Cu particles and reacts with Cu to form Cu6Sn5 around unconsumed Ag-Cu particles (surface)

why is admixed high copper better than low copper?

because no gamma 2 is formed in that reaction (instead of tin and mercury, we get copper and tin combining) -this is good bc gamma 2 corrodes and is soft etc

what type of amalgam do we use at pacific

admixed- palladium enriched, high copper

what would happen if you over triturated the amalgam

- rapid hardening and shortened working time! - also setting contraction less than 1%, but thats not clinically relevant - also has higher compressive strength

what happens if youo under triturate the amalgam

it will be crumbly, grainy - excessive free Hg will be present - decreased compressive strength - increased setting expansion - increased corrosion

what does condensation of amalgam do

packing aka - drives out trapped air - presses out excess mercury - creates tooth form

how long after amalgam rest is it fragile

10 hours!! | durable after 1 day

what are pos/negs of amalgam restorations

positive: - super durable after day 1 - resistent to recurrent caries/corrosion neg: - doesnt bond to tooth; no macromechanical retention - requires bulk - chips at margin (flash and deformation)

what was used in the 1960s for amalgam

- convnetional low copper lathe cut alloys! smaller particles. and - first generation high copper alloys : dispersalloy, admixture of spherical ag-cu eutectic particles (n) with conventional lathe cut. (eliminates gamma 2 phase)

whta are the local/environmental controversies around amalgam

- local; dental providers and amalgam bearers (patients) | - environmenta; mercury entering environment from dental sources

what is the risk with health efffects of mercury on amalgam bearers

- initial placemet: vapor, swallowed | - chronic: vapor, tattoos!

what are the health risks for mercury on dental providers

vapor from stored hg, mercury hygiene taking care, aerosols (during removal)

what are the mercury facts we need to know regarding accumulation, excretion, half life, neural defects in dental providers, margin of safety

- mercury accumulates in specific tissues like kidneys - mercury excretion is NOT indicative of mercury load (urinary or blood) - half life in neural tissues is many years - subclinical neural defects in dental providers - margin of safety is debatable - there have been no clinically measurable/relevant effects of mercury levels in amalgam bearers - its very beneficial and superior to affordable alternatives in many situations

how does mercury get harmful in the environment from dental amalgam

dental amalgam -> waste water, urine and feces also to waste water , cremation and waste incineration -> atmospheric deposition and storm water runiff (from cremation and waste incineration) -> methyl mercury formaton (from wastewater anda atmospheric deposition and storm water runoff) --> methyl mercury bioaccumulation in food web leads to human and wildlife exposures