Luting Agents Flashcards
luting agents aka (4)
- dental cements
- composite resins
- self adhesive composite resins
- surface modifying chemicals
properties of luting agents (9)
Viscosity and film thickness
Ease of Use
Radiopaque
Marginal seal
Aesthetics
Solubility
Cariostatic
Biocompatible
Mechanical properties
viscosity and film thickness importance for luting agents
Must be low to allow seating of the restoration without interference.
Viscosity increases as material sets, so must seat restoration quickly and maintain pressure.
Film thickness should be as thin as possible ideally 25um or less.
viscosity and film thickness of luting agents dependent on
Dependant on the size of powder or filler particles in the material.
ideal viscosity and film thickness luting agents
thin as possible ideally 25um or less.
ease of use of luting agents importance
Easy to mix
- Many products encapsulated
- Clicker system
Working time should be long to allow for seating of the restoration
Setting time should be short
radiopaque of luting agents importance
some ceramic crown are radiolucent
makes it easier to see marginal breakdown
marginal seal of luting agents importance because
Ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond.
- Some of the newer materials approach this, but not quite
aesthetics of luting agents importance
tooth coloured - variation in shade and translucency
non-staining
solubility of luting agents should be
low
cariostatic nature of luting agents should be
F releasing
antibacterial
imp in preventing secondary caries around crown margins
biocompatibility of luting agents
non toxic
not damaging to pulp
- inappropriate pH
- heat on setting low
low thermal conductivity
mechanical properties of luting agents
High compressive strength
- Dentine around 275 MPa
High tensile strength
- Dentine around 50MPa
High Hardness Value
- Dentine around 70K
- Enamel around 400K
Young’s Modulus similar to tooth
- Dentine around 15 GPa
No luting agent gets close to tooth values for more than one or two physical properties
types of luting agent material (3)
Dental Cement
- Zinc Phosphate
- Zinc polycarboxylate
Glass ionomer Cement
- Conventional
- Resin modified
Composite resin luting agents
- Total etch for use with DBA
- Self etch
- Requires etch but has own bonding agent incorporated
dental cement - zinc phosphate
In use for 100+ years
Acid base reaction
Powder and liquid
Excellent clinical service
Easy to use
Cheap
zinc phosphate cement - constitutes
Powder - Zinc Oxide >90% (Main reactive ingredient) - Magnesium Dioxide <10% (Gives white colour Increases compressive strength) - Other Oxides (Alumina and Silica) Improve physical properties Alter shade of set material
Liquid
- Aqueous solution of phosphoric acid (approx. 50%)
- Oxides which buffer the solution
Aluminium oxide
- Ensures even consistency of set material
Zinc Oxide
- Slows the reaction giving better working time
liquid component of zinc phosphate cement
- Aqueous solution of phosphoric acid (approx. 50%)
- Oxides which buffer the solution
Aluminium oxide
- Ensures even consistency of set material
Zinc Oxide
- Slows the reaction giving better working time
powder component of zinc phosphate cement
- Zinc Oxide >90% (Main reactive ingredient) - Magnesium Dioxide <10% (Gives white colour Increases compressive strength) - Other Oxides (Alumina and Silica) Improve physical properties Alter shade of set material
reaction for zinc phosphate cement
The initial reaction is acid base
ZnO + 2 H3PO4 -> Zn(H2PO4)2 + H2O
This is followed by a hydration reaction resulting in the formation of a crystalised phosphate matrix
ZnO + Zn(H2PO4)2 + 2H2O -> Zn3(H2PO4)2.4H2O
(Hopiete)
The aluminium oxide prevents crystalisation leading to an amorphous glassy matrix of the acid salt surrounding unreacted ZnO powder.
This matrix is almost insoluble, but it is porous and contains free water from the setting reaction.
- The cement subsequently matures binding this water leading to a stonger, less porous material
problems with zinc phosphate cement (7)
Low initial pH approx. 2
- Can cause pulpal irritation as pH can take 24hrs to return to neutral
Exothermic setting reaction
Not adhesive to tooth or restoration
- It works like grout on tiles just filling in any spaces.
- Retention may be slightly micromechanical due to surface irregularities on prep and restoration
Not cariostatic
Final set takes 24hrs
Brittle
Opaque
zinc polycarboxylate cement
Similar material to zinc phosphate but phosphoric acid replaced by polyacrylic acid.
zinc polycarboxylate cement advantages (4)
This material had the advantage of bonding to tooth surfaces in a similar way to glass ionomer cements.
There is less heat of 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.
zinc polycarboxylate cement disadvantages (5)
Difficult to mix
Difficult to manipulate
Soluble in oral environment at lower pH
Opaque
Lower modulus and compressive strength than Zinc Phosphate
dental cements are
mainly historic
seldom used nowadays
All of the more modern materials utilise chemical bonding to the tooth surface.
Many of these materials can also bond to the indirect restoration as well.
glass ionomer cement
Chemistry of the luting cement is exactly the same as the filling material
The main difference is particle size of the glass which is less than 20um to allow for suitable film thickness – can’t be used as a filling material
glass ionomer cement reaction
Acid base reaction between Glass and Acid
- Glass is SiO2, Al2O3 and CaF2.
- Poly acid mixture of Acrylic, Maleic and Itaconic acid and their copolymers.
The reaction goes through the same dissolution, gelation and hardening stages.
glass ionomer cement bonding
Cement bonds to tooth surface through
- Ion exchange with calcium in enamel and dentine
- Hydrogen bonding with the collagen in the dentine
This results in a fairly strong, durable and possibly dynamic bond to the tooth.
There is no chemical bond to the restoration surface.
- The surface of the restoration should be sandblasted to allow mechanical adhesion
benefits of GIC as luting agent
Clinically easy to use and durable cement
Low shrinkage
Long term stability.
Relatively insoluble once fully set.
Aesthetically better than ZnPhos. – can come in different colours
Self adhesive to tooth substance.
Fluoride release.
Cheap.
Resin modified glass ionomer cement
Chemistry is the same as RMGI filling material
Glass particle size is smaller to allow acceptable film thickness
In addition to conventional GIC powder and liquid the liquid contains a hydrophilic monomer
The monomer must be hydrophilic as GIC is a water based material.
HEMA (Hydroxyethyl methacrylate)
RMGI reaction
The same acid base reaction occurs.
Light activation causes polymerisation of the HEMA and any copolymers in the material leading to a rapid initial set.
The acid base reaction then continues for some time.
Some materials have a secondary cure via a REDOX reaction
- This allows ‘Dark Curing’ where material not exposed to light will cure.
incorporation of resin to GIC improves (5)
Shorter setting time
Longer working time
Higher compressive and tensile strengths
Higher bond strength to tooth
Decreased solubility
3 issues with RMGI
HEMA is cytotoxic
- Very important that no monomer remains as it can damage the pulp.
HEMA swells, it expands in a wet environment
- It cannot be used to cement conventional porcelain crowns as they may crack
- It shouldn’t be used to cement posts as it may split the root
No bond to indirect restoration
composite luting agents
simplest of these materials are variants on composite filling materials with suitable viscosity and filler particle size
composite luting agents needs to be used in conjunction with
a suitable DBA
composite luting agents properties
light or dual cured
- need light cured as properties reduced by 25% if not
better physical properties, lower solubility and better aesthetics
but
technique sensitive
bonding of composite luting cements to indirect composite
Composite bonds to composite
Bond strength is lower to inlay fitting surface than to new composite
Bond is micromechanical to rough internal surface of inlay
Bond is also chemical to remaining C=C bonds on the fitting surface of the inlay
Use a dual curing cement as light penetration through the inlay will be poor
bonding of composite luting cements to porcelain
Porcelain is brittle and requires to be bonded to tooth to prevent fracture
Untreated porcelain is smooth and non retentive.
It can be treated with HF to etch the surface (v toxic).
This produces a rough retentive surface but it is still not hydrophobic and compatible with composite resin luting agents.
A surface wetting agent is required.
silane coupling agent
Gamma-methacryoxypropyltrimothoxysilane
Applied to the etched porcelain surface, ideally as a monolayer
Very strong bond between oxide groups on the porcelain surface and the silane.
The other end of the silane molecule has C=C bond which reacts with the composite resin luting agent.
This works in the same manner as a dentine bonding agent does with tooth.
This is the same mechanism as bonding filler material to resin matrix in composite resin filling materials.
type of bond to porcelain from composite bonding luting agents
Strong durable bond
Only use a light cured composite luting agent if the porcelain restoration is thin.
- You must increase your curing time.
- If the restoration is thick use a dual cured composite.
- Remove as much of the luting resin as possible before curing.
bonding to metal by composite bonding luting agents
Like porcelain composite materials do not bond directly to metal
Metal surface needs to be roughened.
- done by etching
- More usually done by sandblasting
Etching metal
- Electrolytic etching removes the different phases of the alloy at different rates
- gives a very retentive surface
BUT - Technique sensitive - Beryllium containing alloys work best - Cannot etch precious metals at all Seldom Used Nowadays
sandblasting metal
roughens surface but does not give the undercut surface of etching needed for composite luting agents
chemical bonding is required to stregthen the bond
bonding to non-precious metal surface with composite luting agents
system
Materials with carboxylic and phosphoric acid derived resin monomers.
MDP and 4-META
These molecules have an acidic end and a C=C end
The acidic end of the molecule reacts with the metal oxide and renders the surface hydrophobic.
This is the same as DBA and Silane
bonding to metal with composite luting agents
system
Must use a dual curing material as light will not penetrate metal.
This system can be used to cement most crowns, bridges and posts.
These materials will not bond to precious metal.
Technique sensitive and will not work unless moisture control is adequate.
bonding to precious metal with composite luting agents
system
Change precious alloy composition to allow oxide formation
- Increase copper content and heat 400oC in air
Tin Plate
Sulphur based chemistry of bonding agent
All complicated and technique sensitive.
self adhesive composite resin
The metal coupling agent is incorporated into the composite resin.
This simplifies the bonding process
MDP is used in Panavia
This is an anaerobic self cured material
self adhesive composite resin properties
Consistent results over many years
Good film thickness
Opaque
Moisture sensitive
Expensive
self etching composite resin cements (e.g. Rely X Unicem)
This is a combination of a Composite resin cement and a
Self etching dentine bonding agent.
Sound like a great idea as it should stick to everything and it is easy to use.
However as with all dentine bonding it requires good moisture control. There is also doubt about the bond strength to enamel due to inadequate etching. The pH of the carboxylic monomer doesn’t stay low for long enough to give a good etch.
self-etching composite resin luting agents
bonding
Attaches like a self etching primer(sort of)
Acidic groups bind with calcium in hydroxyapatite forming a stabilising attachment between the tooth and the resin
Ions from dissolution of filler neutralise the remaining acidic groups forming a chelate reinforced methacrylate network
Limited removal of smear layer or significant infiltration into the tooth surface. (only a couple of microns)
Good bond strength to dentine
properties of self etching composite resin luting agents
mechanical properties
- compressive strength
- tensile strength
- hardness
wear resistance
all slightly lower than convention resin luting agents but better than cements
bonding to enamel of self etching composite resin luting agents
lower than to dentine
should be etched with acid prior to application
bonding to dentine of self etching composite resin luting agents
better than to enamel
should not be etched with acid prior to application
bonding to ceramics of self etching composite resin luting agents
brand specific
RelyX unicem seem to bond quite well to sandblasted Zironica
bonding to metal of self etching composite resin luting agents
better to non-precious
not good enough to cement ortho brackets
use of of self etching composite resin luting agents
Probably the way forward
- Very few clinical studies. Nothing long term enough
If you can’t use a DBA and conventional resin cement, you can’t use these.
They do not get round the problems of moisture control.
temporary cements
Made to cement temporary restorations in place while permanent restoration is fabricated.
- 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 permanent restoration to allow assessment by patient or clinician.
how to dispense temporary cements
Supplied as two paste systems base and catalyst or accelerator
- Base contains ZnO, Starch and mineral oil
- Accelerator contains resins, eugenol or ortho-EBA and carnauba wax
- The wax weakens the structure of the set cement and makes it easier to remove
- Material can be modified to make it weaker still by incorporating petroleum jelly into the mixture
2 main types of temporary cements
Two main types those with and those without eugenol
Eugenol containing materials should not be used to cement the provisional restoration where the permanent restoration will be cemented with a resin cement.
- Any residual eugenol may interfere with the setting of this type of luting agent.
what is essential to do when removing temporary cement
Irrespective of the type used complete removal of the temporary cement is essential.
(eugenol or non eugenol)
