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MODULE 6 > DM - cement: crowns, posts and bridges > Flashcards

DM - cement: crowns, posts and bridges Flashcards

1
Q

When cementing a post and core what surfaces does the luting cement lie on?

A

all surfaces of post
all contacting surfaces of core

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2
Q

what marker can be placed to accommodate luting cement thickness?

A

die relief

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3
Q

what is the function of luting cement?

A

added retention
seals the space between restoration and tooth

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4
Q

what are the 2 types of luting cements?

A

active
passive

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5
Q

what is an active luting cement?

A

bonds to tooth and restoration chemically
has a role in retention - mechanical interlocking
creates a marginal seal

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6
Q

what is a passive luting cement?

A

fills gap between tooth and restoration
no bond between tooth and restoration
retention due to tooth prep

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7
Q

in what ways can tooth prep create renetion?

A

taper
prep height
surface roughness and mechanical interlocking

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8
Q

list the general ideal properties of a luting cement

A

biocompatible
retentive
mechanical
marginal seal
low film thickness
ease of use
pseudoplastic
radioopaque
aesthetic
antibacterial

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9
Q

why must a luting cement be biocompatible?

A

it contacts tooth tissue and periodontal tissues

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10
Q

what mechanical properties should a luting cement have?

A

high tensile strength
fracture toughness
fatigue strength
wear resistance

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11
Q

what properties must a luting cement have to create a marginal seal?

A

low solubility

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12
Q

what does low film thickness allow for in a luting cement?

A

full seating of restoration
good marginal adaptation

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13
Q

why should a luting cement be pseudoplastic?

A

coats fit surface of restoration without slumping but flows readily on fitting under pressure

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14
Q

list types of passive luting cements?

A

zinc phosphate
zinc polycarboxylate
GI
RMGI

all are water based as aqueous acid

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15
Q

what luting cement is the oldest and routinely used by 30% UK dentists?

A

zinc phosphate

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16
Q

what are the components of zinc phosphate luting cement?

A

powder: zinc oxide, 10% magnesium oxide
liquid: aqueous phosphoric acid

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17
Q

what is the working time of zinc phosphate?

A

3-6mins

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18
Q

how is zinc phosphate mixed?

A

gradual incorporation of powder over large area on mixing slab
fluid is slaked - small amount powder added to fluid 1 min before to extend setting time

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19
Q

what can be used when mixing zinc phosphate to increase its working time?

A

chilled slab

also increases its strength

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20
Q

describe the setting reaction of zinc phosphate luting cement

A

acid base reaction
exothermic
viscosity increases rapidly
shrinks slightly on setting

21
Q

is zinc phosphate antibacterial?

A

no

22
Q

what does the pH of zinc phosphate depend on?

A

thickness of mix

23
Q

describe the mechanical properties of zinc phosphate luting cement

A

good compressive strength
low tensile strength (brittle)
high solubility

24
Q

what are the components of zinc polycarboxylate?

A

powder: zinc oxide, 10% magnesium oxide
liquid: aqueous copolymer of polyacrylic acid (30-40%)

alternatively - acid freeze dries and added to powder, distilled water added

25
Q

describe the setting reaction of zinc polycarboxylate luting cement

A

acid dissolves in zinc oxide

26
Q

what is the working time of zinc polycarboxylate luting cement?

A

30-40 seconds
can be extended by adding tartaric acid, mixed on a cold glass slab

27
Q

what pH is zinc polycarboxylate?

A

3-4
less injurious on pulp

28
Q

is zinc polycarboxylate antibacterial?

A

yes

29
Q

what is zinc polycarboxylate adhesive to?

A

enamel and dentine
some metals (base metal alloys via oxide layer)

30
Q

describe the mechanical properties of zinc polycarboxylate luting cement

A

lower compressive strength
higher tensile strength
reaches 80% full strength in 1 hour
soluble in acid

31
Q

describe the presentation of GI luting cement

A

powder: fluoro-alumino-silicate glass
liquid: aqueous poly alkenoic acid

alternatively - acid freeze dried and added to powder, distilled water added

32
Q

describe the setting reaction of GI luting cement?

A

chemical set
dissolution of calcium ions, then aluminium
gelation
hardening

33
Q

setting time of GI luting cement?

A

initial set 3-6 mins
hardening can take 7 days

34
Q

why may GI initially cause pulpal inflammation?

A

acidity

35
Q

compared to ZnO cements, describe the mechanical properties of GI

A

better compressive strength
low tensile strength and fracture toughness
less soluble

36
Q

what are the constituents of RMGI cement?

A

GI plus monomer e.g., HEMA, Bis-GMA

37
Q

What are the advantages of RMGI compared to GI?

A

low solubility
improved biocompatibility
improved fluoride release
improved physical properties (tensile strength)
improved adhesion to tooth tissue

38
Q

what are the disadvantaged of RMGI?

A

can undergo hygroscopic expansion - may lead to crack propagation
avoid under conventional all ceramic crowns

39
Q

what is the name of RMGI luting cement?

A

FUGI PLUS

40
Q

what indirect restorations are suitable for the use of RMGI luting cement?

A

zirconia core/ CAD CAM crowns

41
Q

what are the constituents of resin based luting cements?

A

silanated filler
resin - Bis GMA

42
Q

how are resin-modified luting cements cured?

A

chemical and light

43
Q

what indirect restorations are suitable for conventional resin based luting cements?

A

all ceramic restorations
indirect composite or quartz fibre posts - veneers, dentine bonded crowns

44
Q

what indirect restorations are suitable for chemically adhesive resin based luting cements?

A

resin retained bridges
metal veneers
poorly retained indirect restorations

45
Q

how are resin based luting cements bonded to ceramic?

A

bond to tooth in conventional way - acid etch, rinse, dry, dentine bonding agent
bond to fit surface of ceramic - etch with hydrofluoric acid, just before cementing silane coupling agent air dry

46
Q

why can hydrofluoric acid only be used by the lab?

A

very toxic
must be neutralised
tends to slump

47
Q

how do you bond to a base metal alloy?

A

roughen fit surface with 50um aluminia grit
chemically adhesive resin luting cement - modified bis GMA resin

48
Q

how do you bond to precious metal alloys?

A

chemically adhesive resin luting cement
modify fit surface

MODULE 6 (69 decks)

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