Luting Agents Flashcards
properties a luting agent should have
viscosity & film thickness
ease of use
radiopaque
marginal seal
aesthetics
solubility
cariostatic
biocompatible
mechanical properties
viscosity & film thickness
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
ease of use
easy to mix
working time should be long to allow for seating of restoration
setting time should be short
radiopaque
some ceramic crowns are radiolucent
makes it easier to see marginal breakdown
marginal seal
ideally luting agent should bone chemically to tooth & indirect restoration with permanent & impenetrable bond
aesthetics
variation in shade & translucency
non staining
solubility
this should be low
cariostatic
fluoride releasing & antibacterial
important in preventing 2ndary caries in crown margins
biocompatibility
non toxic
non damaging to pulp via inappropriate pH or heat on setting
low TEC
ideal mechanical properties
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
types of materials that are luting agents
- dental cement - zinc phosphate / zinc polycarboxylate
- GIC - conventional / resin modified
- composite resin luting agents - total etch for use with DBA, self etch
zinc phosphate cement
acid base reaction
powder & liquid
excellent clinical service
easy to use
cheap
powder constituents of zinc phosphate cement
zinc oxide >90%
magnesium dioxide <10% - gives white colour & increases compressive strength
aluminium & silica oxide - improves physical properties & alter shade of set material
liquid constituents of zinc phosphate cement
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
reactions of zinc phosphate cement
initial is acid base reaction followed by hydration reaction resulting in formation of crystallised phosphate matrix
problems with zinc phosphate cement
- 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
how does zinc polycarboxylate cement differ to zinc phosphate
- 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
problems with zinc polycarboxylate acid
difficult to mix & manipulate
soluble in oral environment at low pH
opaque
lower modulus & compressive strength than zinc phosphate
difference between GIC & filling material
chemistry is the same
but in GIC particle size of glass is less than 20um to allow for suitable film thickness
reaction & constituents of GIC
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
GIC bonding
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
why use GIC
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
RMGIC
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
why does RMGIC need a hydrophilic monomer
as GIC is a water based material
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
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
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
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
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
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
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
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
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
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
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
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
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
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
self etch CRLA properties
mechanical - compressive / tensile strength / hardness
wear resistance
lower than conventional resin luting agents but better than cements
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
when you can use GIC
MCC, metal post, zirconia crown, gold restoration
when you can use RMGIC
MCC, zirconia crown, gold restoration
when you can use light cure comp + DBA
veneer
when you can use dual cure comp + DBA
fibres post, zirconia crown, composite inlay, porcelain inlay
when you can use anaerobic cure composite
adhesive bridge, zirconia crown
when you can use self adhesive composite
fibres post, zirconia crown, composite inlay, porcelain inlay
2 types of temporary cements
- with eugenol
- without eugenol
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
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
