Dental Luting Agents Flashcards
What comes under luting agents
dental cements
composite resins
self adhesive composite resins
surface modifying chemicals
What are properties of a luting agent
viscosity and film thickness ease of use radiopaque marginal seal aesthetics solubility cariostatic biocompatible mechanical properties
What is viscosity and film thickness dependent on
size of powder or filler particles in the material
Should a luting agent be viscous
no
must be low to allow seating of the restoration without interference
What happens to the viscosity once the material sets
increases
need to seat the restoration quickly and maintain pressure
What is the ideal film thickness
should be as thin as possible ideally
25 um or less
What is required for ease of use
easy to mix
working time should be long to allow for seating of the restoration
setting time should be short
What are systems that allow for something to be easy to mix
encapsulated
clicker system
What is the ideal way of setting
command set
Why is radiopacity important
some ceramic crowns are radiolucent
makes it easier to see marginal breakdown
What is the ideal way for a marginal seal to be made
ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond
What is the ideal aesthetics
tooth colored and a variation in shade and translucency
non staining as long term if there is luting agent at the surface of the restoration we don’t want it to stain
What is the ideal solubility
LOW
don’t want it to wash away under influence of saliva
What is the ideal cariostatic properties
fluoride releasing
antibacterial
to prevent secondary caries around margins and prevent leakage
What is ideal biocompatible properties
non toxic
not damaging to the pulp whether it be that on setting or an inappropriate pH
low thermal conductivity
Why is low thermal conductivity significant
many restorations that we fit are metal based and it would be good for low thermal conductivity to have similar to a lining under a metal filling to protect from hot and cold
What are important mechanical properties
high compressive strength
high tensile strength
high hardness value
young’s modulus similar to tooth
What are the types of materials
dental cements
GIC cements
composite resin luting agents
What are the dental cements
zinc phosphate
zinc polycarboxylate
What are the GIC
conventional
RMGI
What are the composite resin luting agents
total etch for use with DBA
self etch
requires etch but has own bonding agent incorporated
Describe zinc phosphate as a dental cement
acid base reaction powder and liquid excellent clinical service easy to use cheap
What is the powder composition of zinc phosphate cement
zinc oxide (main reactive ingredient) magnesium oxide other oxides (alumina and silica)
What is the function of magnesium in the ZPC
gives white colour
increases the compressive strength
What is the function of the other oxides in ZPC
improves physical properties
alters shade of set material
What is the liquid part of ZPC
aqueous solution of phosphoric acid
oxides which buffer the solution (aluminum and zinc oxides)
What is the function of aluminum oxide in the liquid portion of zinc phosphate cement
ensures even consistency of set material
What is the function of zinc oxide in the liquid component of zinc phosphate cement
slows the reaction giving better working time
What is the initial reaction of ZPC
acid base
zinc oxide + phosphoric acid –> zinc phosphate + water
What is the second reaction in ZPC
hydration reaction resulting in the formation of a crystallized phosphate matrix
results in matrix of zinc phosphate surrounded by unreacted zinc oxide particles
What does the aluminum oxide prevent in zinc phosphate setting reaction
crystallization
leads to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder
What is the resultant matrix of zinc phosphate cement like
almost insoluble, but it is porous and contains free water from the setting reaction
cement subsequently matures binding this water leading to a stronger less porous material
What are problems with zinc phosphate cement
low initial pH (approx. 2) and can take 24h to return to neutral
exothermic reaction
not adhesive to tooth or restoration
not cariostatic
final set takes 24h
brittle
opaque
What does the zinc phosphate cement do in relation to the tooth or restoration
works like grout on tiles filling any spaces
retention may be slightly micro mechanical due to surface irregularities on prep restoration
What is zinc polycarboxylate cement
similar material but phosphoric acid replaced by poly acrylic acid
What are advantages of zinc polycarbonate cement
this material had the advantage of bonding to tooth surfaces in a similar way to GIC
there is less heat reaction
the pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate dentine as easily
cheap
What are disadvantages of zinc polycarboxylate cement
difficult to mix difficult to manipulate soluble in oral environment at lower pH opaque lower modulus and compressive strength than zinc phosphate
Why are dental cements rarely used now
modern materials utilize chemical bonding to tooth surface and can also bond to indirect restoration too
What is main difference between GI and GIC
GIC has a particle size of glass which is less than 20um to allow for suitable film thickness
if they were bigger they would interfere with the ability of the restoration to seat hence why you can’t use the GI filling material as a luting agent
What is the reaction of GIC
acid base
between glass and acid
What is the glass in GI made up of
silicone oxide
aluminum oxide
calcium fluoride
What is the poly acid mixture of GIC
mixture of acrylic, malice and itaconic acid and their copolymers
How does GIC bond to the tooth surface
ion exchange with calcium in enamel and dentine
hydrogen bonding with the collagen in the dentine
What does the GIC bond result in
fairly strong durable and possibly diamond bond to tooth
no chemical bond to restoration surface
surface of the restoration should be sandblasted to allow mechanical adhesion
What makes GIC clinically easy to use
it is easy to use and a durable cement
low shrinkage low term stability relative insoluble once fully set aesthetically better than zincphosphate self adhesive to tooth substance fluoride release cheap
What is the chemistry of RMGI
same as filling material
glass particle smaller to allow acceptable film thickness
What does RMGI contain that the conventional GI doesn’t
hydrophilic monomer
Why must the RMGI monomer be hydrophilic
as GIC is water based material
What is the hydrophilic monomer in RMGI
HEMA
What is the reaction of RMGI
same acid base reaction
light activation causes polymerization of the HEMA and any copolymers in the material leading to a rapid initial set
acid base reaction then continues for some time
some materials have a secondary cure via a REDOX reaction which allows for dark curing where material is not exposed to light will cure
What are the improved problems due to incorporation of resin in GI
shorter setting time longer working time higher compressive strength and tensile strengths higher bond strength to tooth decreased solubility
What are potential problems with RMGI
HEMA is cytotoxic
HEMA swells and expands in a wet environment
no bond to indirect restoration
What is the consequence of HEMA swelling in wet environment
cannot be used to cement conventional porcelain crowns as they may crack
shouldn’t be used to cement posts as they may split the root
What are temporary cements
made to cement temporary restorations in place while permanent is fabricated
What are features 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 trail lute of permanent restorations to allow assessments by patient or clinical
How are temp cements supplied
two paste systems - base and catalyst or accelerator
What does the base of temp cements contain
ZNO, starch and mineral oil
What does the accelerator of temp cements contain
resins, eugenol or ortho-EBA and carnauba wax
What is the role of wax in temp cements
weakens the structures of set cement and makes it easier to remove
How can temp cements be modified
make it weaker by incorporating petroleum jelly into mixture
What are the two types of temp cements
eugenol containing and without eugenol containing
Where should eugenol temp cements not be used
to cement the provisional restoration where the permanent restoration will be cemented with a resin cement
What may residual eugenol interfere with
the setting of this type of resin luting agent
What are the 3 phases of GI setting reaction
dissolution
gelation
hardening
What is the dissolution phase
- Acid goes into solution and reacts with outer layer of glass
- Layer becomes depleted in aluminium, calcium and fluorine ions so that only a silica gel remains
- Hydrogen ions that are released from the carboxyl group of the acid diffuse to the glass and makeup for the loss of other ions
LEAVES AN UNREACTED GLASS CORE WITH SILICA GEL ON THE OUTSIDE
What is the gelation phase
Initial set is due to calcium ion crosslinking with the carboxyl group of the polyacid (chelation) but the cross linking is not ideal as the calcium can chelate with the two carboxyl groups on the same molecule
Initial set is caused by formation CALCIUM POLYACRYLATE
What is the hardening phase
w Aluminium is what provides the final strength to cement
w Aluminium is trivalent so ensures a high degree of cross linking on the polymer molecule
Once cement has fully reacted the final structure consists of glass particles, each which is surrounded by a silica gel in a matrix of cross linked polyacrylic acid
What is the bond to indirect composite restorations
the bond strength is lower to inlay fitting surfaces than to new composite
the bond is micromechanical
bond is also chemical
we use a dual curing cement
What is the micro mechanical bond to in indirect composite restorations
rough internal surface of the inlay
What is the chemical bond to in indirect composite restorations
remaining C=C bonds on the fitting surface of the inlay
What is used to bond the composite inlay
tooth –> DBA –> composite luting resin –> resin inlay
Why should porcelain be bonded to tooth
to prevent fracture
untreated porcelain to is smooth and non retentive
How is porcelain treated for boding to tooth
hydrofluoric acid
What does hydrofluoric acid do to the porcelain
produced a rough retentive surface but it is still not hydrophobic and compatible with composite resin luting agents
What is required to bond the hydrophilic porcelain to the composite resin luting agent
a surface wetting agent - silane coupling agent
What is the silane coupling agent applied to
etched porcelain surface in a monolayer
How does the silane bonding agent work
Has a hydrophilic end (hydroxyls on it) that can bond to the oxide groups on the porcelain surface
Has a hydrophobic (C=C) double bond which reacts with the composite resin luting agent
What are the components of bonding porcelain to tooth
tooth > DBA > comp luting agent > silane > porcelain
Why is a dual curing cement needed for indirect composite
as light penetration through the inlay will be poor
What kind of luting agent do we use for bonding to porcelain
light cured if restoration is thin
if thick use a dual cured composite
How do we bond tooth to metal
does not bond to metal directly
metal surface needs roughened
can be done by etching but more usually done by sandblasting
What did etching the metal do
was called electrolytic etching
removes diff phases of alloy at diff rates giving a retentive surface
What were the issues with etching metal
technique sensitive
cannot etch precious metals
What does sandblasting the e-mail do
roughens surface but does not give the undercut surface of etching
chemical bond required to strengthen bond
How do we bond the composite luting agent to the non precious metal
materials with carboxylic and phosphoric acid derived resin monomers
MDP and 4-META
How do the metal bonding agents work
have a acidic end of the molecule that reacts with the metal oxide and renders the surface hydrophobic
What type of cure does the luting agent need to be when bonding to metal
dual
light will not penetrate
What is the issues with the materials used to bond the non precious metal
technique sensitive
will not work unless moisture control is adequate
we don’t use it for everything
will not bond to precious metal
What is the components of bonding non precious metal to tooth
tooth > DBA > composite luting resin > metal bond agent > non precious metal
How do we bond to precious metal
change precious alloy composite to allow oxide formation
tin plate
sulphur based chemistry of bonding agent
all complicated and technique sensitive
How do we change the precious alloy composition to allow oxide formation
increase copper content and heat 400 degrees in the air
What are self adhesive composite resins
metal and coupling agent is incorporated into the composite resin
this simplifies the bonding process
What are the adv and disadv of self adhesive composite resin (panavea)
anaerobic self cured material consistent results over many years good film thickness opaque moisture sensitive expensive
So what is required in bonding non precious material to tooth using panavia
tooth > DBA > panacea ex > non precious metal
What is self etching composite resin cements
combo of comp resin cement and self etching DBA
What are the issues with self etching composite resin cements
Dentine bonding requires good moisture control
there is doubt about the bond strength to enamel due to inadequate etching
pH of carboxylic monomer doesn’t stay low for long to give good etch
How does the self etching composite resin luting agents work
acidic groups bind with calcium in hydroxyapatite forming a stabilizing attachment between tooth and resin
ions form dissolution of filler neutralize the remaining acid groups forming a chelate reinforced methacrylate network
limited removal of smear layer or significant infiltration into tooth surface
good bond strength to dentine
What are the mechanical properties for self etching composite resin luting agent
compressive strength
tensile strength
hardness
wear resistant
all slightly lower than conventional resin luting agents but better than ‘cements’
How does self etching composite resin luting agent compare in bonding to enamel
lower than dentine
should be etched with acid prior to application
How does self etching composite resin luting agent compare in bonding to dentine
better than enamel
should not be etched with acid prior to application
How does self etching composite resin luting agent bonding to ceramic
brand specific
How does self etching composite resin luting agent compare in bonding to metal
better to non precious
not good enough to cement ortho brackets
When can you not use a self etching composite resin luting agent
if you can’t use a DBA or conventional resin cement can’t use this as still have issue of moisture control
