7 - Luting Cements Flashcards by Helena Condotta

2 types of restorations? describe how each is done + give 3 examples of each

direct restoration: material placed in/on a cavity which hardens into a solid (chemically or by light curing)
e. g. amalgam, composite, GI restorations
indirect restorations: a solid object made outside of the mouth which is placed in/on a prepared tooth
e. g. crowns, bridge, veneer, inlays, onlay
can be provisional/temporary or definitive

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die relief - helps to do what?

die relief helps to accommodate the thickness of luting cements

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what is a luting cement? what are its 2 main purposes?

it is a material used for the

1) retention of indirect restorations, and to
2) seal the space between restoration and the tooth

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choice of luting cement depends on?

choice of luting cement depends on the type of restoration being cemented
1. provisional/temporary?
2. material of indirect restoration:
metal? ceramic? composite?
3. type of restoration?
veneer? resin retained bridge? conventional bridge?

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2 types of luting cement?

active luting material

- passive luting material

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active luting material: what does it do? and what are its roles?

it bonds to the tooth and the restoration
helps with retention
provides a marginal seal

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passive luting material: what does it do? how does it bring retention?

it fills the gap between tooth and restoration
there is no bond between tooth and restoration, instead retention is brought about by method of tooth tooth preparation

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what are the methods of tooth preparation?

taper
preparation height
surface roughness
mechanical interlocking

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general ideal properties of a luting cement?

biocompatible
retention
mechanical properties
marginal seal
low film thickness
ease of use
pseudoplastic
radiopacity
aesthetics: ceramic restorations
inhibit plaque accumulation
antibacterial
clear up of excess
good shelf life

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ideal luting cement: importance of biocompatibility?

able to contact with tooth tissue and periodontal tissues

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ideal luting cement: importance of retention?

additional bonding for active luting cements, preparation morphology and mechanical interlocking of irregularities for passive luting cements

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ideal luting cement: examples of ideal mechanical properties?

high tensile strength, fracture toughness, fatigue strength, wear resistance

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ideal luting cement: importance of marginal seal?

low solubility. advantageous for active luting, reduced hypersensitivity

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ideal luting cement: importance of low film thickness?

allows full seating of restoration

- good marginal adaptation

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ideal luting cement: in what ways should it be easy to use?

powder:liquid ratios

- working and setting times

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ideal luting cement: describe how it should be pseudoplastic?

it should coat the fit surface of the restoration without slumping, but it should also flow readily under pressure on fitting

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ideal luting cement: how can it inhibit plaque accumulation

it should be easy to polish

it should eliminate the air inhibition layer in resin composites

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passive luting cements: 4 examples? what are they based on?

zinc phosphate
zinc polycarboxylate
glass ionomer luting materials
resin modified glass ionomer luting cements
all are water based

zinc phosphate luting cements: what is its presentation?

powder: zinc oxide, up to 10% magnesium oxide (improves compressive strength, adds colour)
liquid: aqueous phosphoric acid (45-64%)

zinc phosphate:
working time?
how to extend setting time?
what does using a chilled glass slab help with?

3-6 minutes
by slaking the fluid; small amount of powder added to fluid about 1 minute before
increases working time
increases powder incorporated
increase strength
decreases solubility

zinc phosphate: setting reaction

what kind of reaction?
describe the reaction that occurs
how does viscosity change?
how much strength in 10 mins? how long does it take to reach full strength?
how does the size change on setting?
antibacterial effect?

acid base reaction
dissolution of surface of ZnO powder. insoluble hydrated zinc phosphate matrix crystals effective bind to the unreacted ZnO particles
viscosity increases rapidly
50% strength in 10mins, 100% str in 24 hours
shrinks slightly on setting
no antibacterial effect

zinc phosphate

initially unset material has what pH
pH depends on?
what is this relevant to?
describe properties

1.6-3.6
depends on thickness of mix
relevant to vital pulp
good compressive strength,
low tensile strength (brittle)
high solubility

zinc polycarboxylate

presentation?
alternative presentation?

1. powder: zinc oxide + up to 10% magnesium oxide
  1. aqueous copolymer of polyacrylic acid (30-40%), high viscosity
acid freeze dried and added to powder
liquid: distilled water

zinc polycarboxylate - setting reaction

acid dissolves what?
zinc ions form cross links between what?
unreacted powder bound where?

zinc oxide
zinc ions form cross links with carboxyl groups on polyacrylic acid polymer chains
unreacted powder bound in matrix of zinc polyacrylate

``` zinc polycarboxylate: working time? - how can it be extended? what causes it to have a short working time? what can altering the ratio have an impact on? appears viscous but is actually _____? ```

- 30-40s - extended by adding tartaric acid and mixing on a cold glass slab - high powder:liquid ratio. altering the ratio would have an impact on the physical properties - appears viscous but is actually pseudoplastic

``` zinc polycarboxylate: initial pH? how does this relate to pulp? how does the pH change? antibacterial effect? adhesive to? ```

- initial low pH (3-4) - less injurious to pulp - pH increases rapidly - it has antibacterial properties - adhesive to enamel, dentine, and some metals (via oxide layer)

zinc polycarboxylate: - describe its compressive str and tensile strength - how much strength is reached in 1 hour? - soluble in? - clean up?

- low compressive strength, high tensile strength - 80% str - soluble in acid - messy to clean up

glass ionomer: how is it different from the restorative glass ionomer? presentation? alternative presentation?

- same chemistry, but luting GI has smaller glass particle size - presentation: 1. powder: fluoro-alumino-silicate glass 2. liquid: aqueous poly alkenoic acid - alternatively: 1. acid freeze-dried, added to powder 2. liquid: distilled water

glass ionomer setting reaction? + what element is responsible for strong cross linking?

- chemical set 1. dissolution: calcium ions released first, then aluminium 2. gelation 3. hardening: aluminium trivalent, slower to be released from glass, ensures strong cross linking of polymer chains

``` glass ionomer: setting reaction - - dissolution and initial set: how long? - seated by how long? - hardening can take up to how long? - need protection to prevent what? ```

- 3-6minutes - 2-2.5mins - up to 7 days - need to prevent dissolution or contamination

glass ionomer - properties? what may cause pulpal inflammation? how does it compare to zinc oxide cements?

- anti-caries effect via fluoride release - initial acidity may cause pulpal inflammation - 1. better compressive str 2. low tensile str and fracture toughness 3. less soluble

resin modified glass ionomer: | constituents?

1. components of GI + monomer (HEMA, Bis-GMA) | * no photo initiator, chemical cure only (acid base reaction of GI)

resin modified glass ionomer: advantages over GI?

- low solubility - improved biocompatability - improved fluoride release - improved physical properties - improved adhesion to tooth tissue

RMGI cements - disadvantages?

- can undergo hygroscopic expansion - avoid under conventional all-ceramic crowns - suitable under zirconia core / CAD-CAM crowns

resin based luting cements: what are the constituents that are in restorative composite resins as well? why does it have lower viscosity? how are most of them cured?

- silenated filler - resin e.g. bis GMA - low filler content -> low viscosity - mostly dual cured (chemical and light)

resin based luting cements: | conventional resin luting cements - for use with?

- all ceramic restorations | - indirect composite or quartz fibre posts e.g. veneers, dentine bonded crowns

chemically adhesive resin luting cements: for?

- for adhesively bonding to metals | resin retained bridges, metal veneers, poorly retained indirect restorations

resin luting cements: bonding to ceramic - how does it bond to tooth? - when bond has to fit surface of cermic: etched with? what is applied before cementing? what kind of bond is each one?

- conventional way: acid etch, rinse, dry, DBA - etched with hydrofluoric acid - micromechanical bond - silane coupling agent applied and air dried - chemical bond

``` hydrofluoric acid: why lab use only? why must it be neutralized? why will it not etch periphery of veneers well? - can cause damage to? ```

- because it is very toxic - to prevent it from leaching out and causing tissue damage - because it tends to slump - to periphery of ceramic

veneers: how does try in paste change its appearance?

- it causes more light to be transmitted, less light reflected

veneers: what is applied on top of enamel to be treated?

1. etch and DBA 2. resin luting cement - hydrofluoric acid etch fit surface + silane coupling agent

bonding to metal | - how to bring micromechanical retention?

- roughen the fit surface with 50micrometer alumina grit

``` bonding to metal - chemically adhesive resin luting cement: what kind of chemical? name 2 monomers both have high affinity for? ```

- modified bis-GMA resin 1. carboxylic monomer (4 META), e.g. C&B Superbond 2. phosphate monomer (MDP), e.g. Panavia 21, F - both have high affinity for metal oxide on base metal alloy

bonding to metal - precious alloys: - chemically adhesive resin luting cement? - how to modify fit surface?

- low affinity - tin plate: irregular surface, attracted to tin oxide on alloy surface - silica coating to metal: then use silane coupling agent - metal primers: bifunctional monomers - one end methacryl group, other mercapto or thiol group