Luting Agents Flashcards
What properties are advantageous for luting agents?
Low viscosity and film thickness
Easy to mix
Long working time
Short setting time
Radipaque
Bond chemically to tooth
Tooth coloured
Low solubility
Cariostatic
Non-toxic
High compressive strength, tensile strength, hardness.
YM similar to tooth
Why do you want a luting agent with a low viscosity?
Must be low to allow seating of the restoration without interference.
Why do you want a luting agent that is radiopaque?
Some ceramic crowns are radiolucent, so it is important that the cement is radiopaque to see marginal breakdown.
Why do you want a luting agent that has a low solubility?
So that the cement does not wash away with fluid in the mouth, otherwise, the restoration will fall out.
Why is Zinc Phosphate not a good luting agent?
It does not bond directly to teeth, takes 24 hours for final set, brittle.
What type of reaction is involved in zinc phosphate cement?
Acid-base reaction between zinc oxide and phosphoric acid.
Name a use for zinc phosphate cement.
Cement in a temporary only where there are not lots of retentive surfaces.
It doesn’t bond to tooth, so will come out easily when you remove the temporary and not damage the tooth.
What type of reaction occurs in glass ionomer cement?
Acid-base reaction between glass- SiO2, Al2O3 and CaF2, poly acid- poly acrylic acid.
What are the three stages of the reaction?
Dissolution
Gelation
Hardening
What occurs during the dissolution phase?
Dissolving of the glass in the acid.
Causes release of polyions.
What occurs during the gelation reaction?
Initial set- calcium ions cross link with he poly acid by chelation with the carboxyl groups.
- makes calcium polyacrylate.
Takes several minutes.
What occurs during the hardening reaction?
Trivalent aluminium ions crosslink with the calcium polyacrylate to make aluminium polyacrylate.
Starts after 30 minutes and can take a week or longer to complete.
How does GI cement bond to the tooth surface?
Ion exchange with calcium in female and dentine
Hydrogen bonding with the collagen in dentine.
What must be done to the surface of the restoration before bonding with GI cement?
Surface of restoration should be sandblasted to allow mechanical adhesion.
What is the difference between GI as a filling material and GI as a cement?
GI cement has smaller particle size to allow for suitable film thickness.
Advantages of GI cement
Insoluble once set
Self adhesive to tooth substance
Fluoride release
Cheap
Long term stability
What is the extra component in RMGI cement that is not in GI cement?
HEMA- hydrophilic monomer.
What type of reaction occurs in RMGI cement?
Acid-base reaction
Light activation causes polymerisation of the HEMA.
Also redox reaction which cures the resin where light has not reached.
Advantages of RMGI
Shorter setting time
Longer working time
Higher compressive and tensile strengths
Higher bond strength to tooth
Decreased solubility
Why can RMGI not be used to cement in porcelain crowns or posts?
HEMA swells in a wet environment.
Porcelain crowns may crack under this pressure.
Why do you need a DBA. when using a composite cement?
Need to turn the tooth from hydrophilic to hydrophobic, so that the composite cement will bond.
What is a disadvantage of composite cements?
Very technique sensitive
- needs to be very dry, light penetration is poor for light cured.
What bond is present between the composite cement and the surface of the inlay?
Micromechanical through the roughened surface of the inlay and also chemical through the C=C bonds on the fitting surface of the inlay.
Why is it better to use a dual-cured composite cement than light cured?
Light penetration through the inlay is poor.
