PRD 131: zirconium, amalgam Flashcards
what are the biologic considerations for treatment planning single crown restoration
- remaining tooth structure
- vitality of pulp
- periodontium and surrounding structures
- occlusion & function
- prognosis
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
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
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.
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
what are the properties of glass ceramics
- low thermal conductivity
- low tensile strength, poor mechanability
- high transperancy, high brittleness,
- poor impact strength
how do esthetics and strength change with glass
more glass - more aesthetic
more glass - less strong !
what is feldspathic
glass ceramic type
what are examples of glass ceramics with fillers?
-leucite reinforced lithium disilicate
wha tare examples of glass free ceramics and what are these called
POLYCHRYSTALLLINE:
- alumina
- zirconia
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)
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
what to consider regarding monolithic zirconia
- wear
- surface roughness
- fracture strength
- oprtical properties
- marginal fit
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
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
what are other names for monolithic zirconia
-monolithic zirconia crown, full zirconia crown, full crown zirconia, monolithic zirconia restoration, full veneer zirconia
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
