Luting Agents Flashcards
What properties of a luting agent should be considered?
• Viscosity and film thickness • Ease of Use • Radiopaque • Marginal seal • Aesthetics • Solubility • Cariostatic • Biocompatible • Mechanical properties
What is the viscosity and film thickness dependent on?
the size of powder or filler particles in the material
What do you want the viscosity to ideally be like in a luting agent?
- Viscosity must be low to allow seating of the restoration on the prep you have made and not change this prep (not interfere with prep)
What happens to the viscosity of the materials as they set? Why is this relevant for luting agents and the procedure?
Viscosity increases as material sets -must seat restoration quickly and maintain pressure
What should the film thickness of a luting agent ideally be?
As thin as possible but at least 25um or less
In terms of ease of use, you want the luting agent to what?
• Be easy to mix (many products are encapsulated and have a clicker system) • Have a long working time to allow for the seating of the restoration • Have a short setting time (command set is always the best)
Why do you want a radiopaque luting agent?
Some ceramic crowns are radiolucent so you want a luting agent that is radiopaque. This makes it easier to see if there is any secondary caries or marginal breakdown.
What would the ideal marginal seal of a luting agent be like?
Ideally the luting agent should bond chemically to the tooth and the indirect restoration with a permanent and impenetrable bond. Some newer materials are getting close to this but none have yet reached this.
In terms of aesthetics, how do you want the material to look?
You want the material to be tooth coloured and come in various shades and translucencies while also being non-staining.
What do you want the solubility of a luting agent to be like?
You want LOW solubility so it does not wash away under the influence of saliva.
Why do you want a luting agent to be cariostatic?
to help prevent secondary caries around crown margins etc
In terms of biocompatibility, how do you want a luting agent material to act?
Be non-toxic Not damaging to the pulp -Appropriate pH -Don’t release heat on setting Have low thermal conductivity (Many restorations/crowns are metal based so you want the material to have a low thermal conductivity to help protect the pulp)
What do you want the mechanical properties of a luting agent to be like?
Similar to that of tooth structure
What are the different luting agent material types you can get?
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
What are the main components of zinc phosphate? (the powder and liquid)
powder: -zinc oxide -magnesium dioxide -other oxides Liquid -phosphoric acid -oxides -zinc oxide
Describe the types of reactions that happen to form zinc phosphate cement.
An acid base reaction followed by a hydration reaction
What are the 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 (Retention may be slightly micromechanical due to surface irregularities on prep and restoration)
- Not cariostatic
- Final set takes 24hrs
- Brittle
What is the difference between zinc phosphate cement and zinc polycarboxylate cement?
Phosphoric acid replaced by polyacrylic acid
What are the advantages of Zinc Polycarboxylate?
• It can bond to tooth structure in a similar way to GIC’s (Only to a small extent though) • Less of a heat reaction than zinc phosphate • pH is low to begin with but returns to neutral more quickly and longer chain acids do not penetrate the dentine as easily • Cheap v
What are the disadvantages of Zinc polycarbonate?
• Difficult to mix • Difficult to manipulate (is jelly like) • Lower modulus and compressive strength than Zinc Phosphate • Opaque • More soluble in the mouth/oral environment Note: Zinc phosphate/polycarboxylate cements are mainly historic. More modern materials utilise bonding to the tooth structure and may can also bone to the indirect restoration as well.
What is the main difference between GIC that is used as a filling material and GIC that is used as a luting agent?
The particle size of the glass is smaller in luting agent to allow for suitable film thickness (less than 20um)
What kind of reaction occurs to form GIC?
acid base reaction between glass and acid The reaction goes through the same dissolution, gelation and hardening stages
How does GIC cement bond to the tooth surface?
Ion exchange with the calcium in enamel and dentine Hydrogen bonding with the collagen in the dentine
There is no chemical bond between GIC and the restoration surface. What needs to be done to overcome this?
The surface of the restoration should be sandblasted to allow mechanical adhesion.
What are the advantages of GIC as a luting agent?
• Clinically easy to use and durable cement • Low shrinkage • Long term stability. • Relatively insoluble once fully set (but this can take up to weeks to happen) • Aesthetically better than ZnPhos. • Self-adhesive to tooth substance. • Fluoride release. • Cheap
What is the main difference between GIC luting agent and RMGI luting agent?
The powder component of the RMGI contain a hydrophilic monomer (HEMA)
Why must the monomer in the cement be hydrophilic?
Because GIC is water based
Describe the reaction process of GIC cement
• The same acid base reaction occurs as with conventional GIC’s • 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.)
Why do we need some RMGI materials that have a secondary cure by a REDOX reaction?
Because if you are setting a restoration that is made from something like metal, light won’t penetrate well through it so it needs to be able to set in the dark
What are the advantages of incorporating resin into GIC’s?
• Shorter setting time • Longer working time • Higher compressive and tensile strengths • Higher bond strength to tooth • Decreased solubility (because of the resin) • Cheap
What are the disadvantages/problems with RMGI?
• HEMA is cytotoxic o Very important that no monomer remains as it can damage the pulp. • HEMA swells, it expands in a wet environment (because it is hydrophilic) o It cannot be used to cement conventional porcelain crowns as they may crack due to the swelling and pressure created by this o It shouldn’t be used to cement posts as it may split the root • No bond to indirect restoration
What are temporary cements?
cements that are used to cement temporary restorations in place while the permanent restoration is fabricated (can also be used as a trial luting agent for a permanent restoration to allow assessment by the patient or clinician)
Describe the basic properties of temporary cements.
-soft to allow easy removal (some dont set at all) -doesnt bond so the tooth prep needs to be retentive
Describe the composition of temporary cements (what is found in them)
They are supplied as a two-paste system which is a base and a catalyst/accelerator: -Base contains ZnO, starch and mineral oil -Acceleration contains resin, eugenol or ortho-EBA and carnauba wax
What is the purpose of the wax in these cements?
Weakens the structure of the cement to make it easier to remove NOTE: the material can be modified to make it weaker still by incorporating petroleum jelly into the mixture
What are the 2 main types of temporary cements?
those containing eugenol and those that do not contain eugenol
When should temporary cements containing eugenol not be used? Why?
If the permanent restoration will be cemented with a resin cement -Because any residual eugenol may interfere with the setting of resin luting agents
What must composite luting agents be used in conjunction with?
a suitable dentine bonding agent
How can composite luting agents be cured?
Either light cured or dual cured
How to composite luting agent properties compare to dental cements and GIC/RMGI?
have better physical properties, lower solubility and better aesthetics BUT are technique sensitive
How does composite bond to indirect composite/what has to be done?
- composite will bond to composite
- the bond us microchemical to the rough internal surface of the inlay
- it is also a chemical bond to the remaining C=C bonds on the fitting surface of the inlay note: a dual curing cement should be used as light penetration through inlay will be poor
Note: in the pic can see DBA is required. This is becasue the tooth is hydrophilic and comp is hydrophobis. The DBA makes the tooth hydorophobic
What is porcelain treated with before being seated on a prep and why?
Hydrofluoric acid to etch the surfcea nd make it rough and retentive
What is needed to bond porcelain to a tooth?
tooth - DBA (to make tooth hydrophobic) - composite resin - silane coupling agent - porcelain
NOTE- the silane coupling agent (wetting agent) makes the porcelain hydrophoic so it can chemically bond with the composite resin
Describe the silane coupling agent and how it works.
oxide groups bond to etched porcelain surface
The C+C react with the composite luting agent
What is used to bond a precioius metal to a tooth?
Composite luting agents with a metal bonding agent incorporated (panavia most common one)
For bonding a non-precious metal to a tooth, what is required?
- DBA
- composite luting resin
- metal bondign agent
What luting agent do you use where?
