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BDS3 Dental Materials Science > Luting Agents > Flashcards

Luting Agents Flashcards

1
Q

properties a luting agent should have

A

viscosity & film thickness
ease of use
radiopaque
marginal seal
aesthetics
solubility
cariostatic
biocompatible
mechanical properties

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2
Q

viscosity & film thickness

A

dependent in size of powder / filler particles in material
must be low to allow seating of restoration without interference
viscosity increases as material sets so must seat restoration quickly & maintain pressure
film thickness should be thin as possible ideally 25um or less

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3
Q

ease of use

A

easy to mix
working time should be long to allow for seating of restoration
setting time should be short

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4
Q

radiopaque

A

some ceramic crowns are radiolucent
makes it easier to see marginal breakdown

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5
Q

marginal seal

A

ideally luting agent should bone chemically to tooth & indirect restoration with permanent & impenetrable bond

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6
Q

aesthetics

A

variation in shade & translucency
non staining

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7
Q

solubility

A

this should be low

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8
Q

cariostatic

A

fluoride releasing & antibacterial
important in preventing 2ndary caries in crown margins

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9
Q

biocompatibility

A

non toxic
non damaging to pulp via inappropriate pH or heat on setting
low TEC

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10
Q

ideal mechanical properties

A

high compressive strength - dentine = 275 MPa
high tensile strength - dentine = 50MPa
high hardness - dentine = 70k, enamel = 400k
YM similar to tooth - dentine = 15GPa
no luting agent gets close to tooth values for more than 1/2 physical properties

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11
Q

types of materials that are luting agents

A
  1. dental cement - zinc phosphate / zinc polycarboxylate
  2. GIC - conventional / resin modified
  3. composite resin luting agents - total etch for use with DBA, self etch
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12
Q

zinc phosphate cement

A

acid base reaction
powder & liquid
excellent clinical service
easy to use
cheap

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13
Q

powder constituents of zinc phosphate cement

A

zinc oxide >90%
magnesium dioxide <10% - gives white colour & increases compressive strength
aluminium & silica oxide - improves physical properties & alter shade of set material

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14
Q

liquid constituents of zinc phosphate cement

A

aqueous solution of phosphoric acid ~50%
oxides which buffer solution:
-aluminium oxide; ensures even consistency of set material
- zinc oxide; slows reaction giving better working time

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15
Q

reactions of zinc phosphate cement

A

initial is acid base reaction followed by hydration reaction resulting in formation of crystallised phosphate matrix

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16
Q

problems with zinc phosphate cement

A
  • low initial pH; can cause pulpal irritation as can take 24hrs to return to neutral
  • exothermic setting reaction
  • not adhesive to tooth or restoration
  • not cariostatic
  • final set takes 24hrs
  • brittle
  • opaque
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17
Q

how does zinc polycarboxylate cement differ to zinc phosphate

A
  • phosphoric aid replaced by polyacrylic acid
  • bond to tooth surface similar to GICs
  • less of a heat reaction
  • pH low to begin with but return to neutral more quickly & longer chain acids don’t penetrate dentine as easy
  • cheap
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18
Q

problems with zinc polycarboxylate acid

A

difficult to mix & manipulate
soluble in oral environment at low pH
opaque
lower modulus & compressive strength than zinc phosphate

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19
Q

difference between GIC & filling material

A

chemistry is the same
but in GIC particle size of glass is less than 20um to allow for suitable film thickness

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20
Q

reaction & constituents of GIC

A

acid base reaction between glass & acid
glass - SiO2, Al2O3, CaF2
poly acid mixture - acrylic, maleic, itraconic acid and their copolymers
reaction goes through same dissolution, gelation & hardening stages

21
Q

GIC bonding

A

cement bonds to tooth surface via:
- ion exchange with Ca in enamel & dentine
- hydrogen bonding with collagen in dentine
results in fairly strong, durable & possibly dynamic bond to tooth
no chemical bond to restoration surface
surface of restoration should be sandblasted to allow mechanical adhesion

22
Q

why use GIC

A

easy to use & durable
low shrinkage as no polymer in conventional GIC
relatively insoluble once fully set
aesthetically better than zinc phosphates
self adhesive to tooth surface
fluoride release
cheap

23
Q

RMGIC

A

chemistry same as RMGI filling material
glass particle size smaller to allow acceptable film thickness
in addition to GIC powder & liquid, the liquid contains a hydrophilic monomer - HEMA; hydroxyethyl methacrylate

24
Q

why does RMGIC need a hydrophilic monomer

A

as GIC is a water based material

25
reaction of RMGIC
same acid base reaction light activation causes polymerisation of HEMA & any copolymers in material leading to a rapid initial set acid base reaction continues for some time some materials have 2ndary cure via redox this allows dark curing where material not exposed to light will cure
26
why use RMGIC
incorporation of resin improves some material properties: shorter setting time longer working time higher compressive & tensile strength higher bond strength to tooth decreased solubility
27
problems with RMGIC
HEMA = cytotoxic so important that no monomer remains as it can damage pulp HEMA expands in wet environment so cannot be used to cement conventional porcelain crowns as it may split root no bond to indirect resotration
28
composite luting agents
variants on composite filling materials with suitable viscosity & filler particle size must be used in conjunction with suitable DBA can be light / dual cured have better physical properties, lower solubility, better aesthetics BUT technique sensitive although dual cure, physical properties reduced by 25% if not light cured
29
bonding to indirect composite
composite bonds to composite bond strength lower to inlay fitting surface than to new composite bond is micromechanical to rough internal surface of inlay bond is chemical to remaining C=C on fitting surface of inlay use a dual curing cement as light penetration through inlay will be poor tooth -> DBA -> CLR -> resin inlay
30
bonding to porcelain
porcelain brittle and requires bonding to tooth to prevent # treated with hydrofluoric acid to etch surface to produce rough retentive surface but still not hydrophobic & compatible with CRLA surface wetting agent required
31
what wetting agent used when bonding to porcelain and why
silane coupling agent (gamma - methacryoxypropyltrimothoxysilane) applied to etched porcelain surface hydrophilic end bonds to oxide groups on porcelain surface hydrophobic end bonds to CRLA works in same manner as DBA does with tooth tooth -> DBA -> CLRA -> Silane -> porcelain
32
light curing bond to porcelain
strong durable bond only use light cured CRLA if porcelain is thin must increase curing time if restoration thick use dual cure remove as much luting resin as possible before curing
33
bonding to metal
like porcelain, composite materials do not directly bond to metal so surface needs roughened done by etching but more commonly by sandblasting sandblasting roughens surface but does not give undercut surface of etching chemical bonding required to strengthen bond
34
bonding to non precious metal
materials with carboxylic & phosphoric acid derived resin monomers MDP & 4-META these molecules have an acidic end and a C=C end acidic end of molecule reacts with metal oxide & renders surface hydrophobic; same as DBA and silane tooth -> DBA -> CRLA -> metal bond agent -> non precious metal
35
light curing to metal
must be dual curing material as light will not penetrate metal these materials will not bond to precious metal system can be used for most crowns, bridges & posts technique sensitive & will not work unless moisture control is adequate
36
bonding to precious metal
have to change composition by increasing Cu content and heating 400 degrees in air to allow oxide formation complicated & technique sensitive
37
self adhesive composite resin
metal coupling agent incorporated into composite resin - simplifies bonding process MDP is used in panavia anaerobic self cured material low film thickness = no movement opaque moisture sensitive expensive tooth -> DBA -> panavia -> non precious metal
38
self etching CRLA
attaches like self etch primer - - acidic groups in resin bind with Ca in hydroxyapatite in tooth - ions from dissolution of filler neutralise remaining acidic groups forming chelate reinforced methacrylate network - limited removal of smear layer / significant infiltration into tooth surface - good bond strength to dentine
39
self etch CRLA properties
mechanical - compressive / tensile strength / hardness wear resistance lower than conventional resin luting agents but better than cements
40
self etch CRLA bonding
to enamel - lower than to dentine, should be etched with acid prior to application to dentine - better than to enamel, no acid etch to ceramics - brand specific, relyX bonds quite well to sandblasted zirconia to metal - better to non-precious, not good enough to cement ortho brackets tooth -> self etch CRLA -> indirect restoration
41
when you can use GIC
MCC, metal post, zirconia crown, gold restoration
42
when you can use RMGIC
MCC, zirconia crown, gold restoration
43
when you can use light cure comp + DBA
veneer
44
when you can use dual cure comp + DBA
fibres post, zirconia crown, composite inlay, porcelain inlay
45
when you can use anaerobic cure composite
adhesive bridge, zirconia crown
46
when you can use self adhesive composite
fibres post, zirconia crown, composite inlay, porcelain inlay
47
2 types of temporary cements
1. with eugenol 2. without eugenol
48
when should eugenol containing temporary cements not be used
should not be used in provisional where permanent will be cemented with a resin cement as residual eugenol may interfere with setting of luting agent complete removal required
49
properties of temporary cements
soft for easy removal - some do not set at all prep must be physically retentive or they will not work can be used for trial lute of perm restoration

BDS3 Dental Materials Science (9 decks)

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