Polymer-Based Cements Flashcards
What do all polymer based cements not have?
water unless contamination occurred
Composition of zinc polycarboxylate cement:
- liquid: copolymer of poly acrylic acid and itaconic acid
- powder: zinc oxide and magnesium oxide
What type of reaction occurs with polycarboxylate cements?
chelation
- carboxylate groups chelate to calcium
- this one does bond to tooth structure (unlike zinc oxide that just chelates internally)
Which material is very acidic but doesn’t penetrate into tubules much due to size of molecule?
- zinc polycarboxylate
Poly carboxylate is a ______ to glass ionomer.
forerunner
Composition of glass ionomer:
- powder: aluminosilicate glass and fluoride flux
- liquid:polyacrylic acid, itaconic acid, tartaric acid (setting modifier)
How you can use glass ionomer
- linear/base
- durable filler
- cementing
Properties of glass ionomer:
- strong (2x more than zinc phosphate)
- anticariogenic
- low solubility once set
- adhesion (to tooth structure)
- biocompatible (doesn’t go into dentin tubules)
- technique sensitive
- can be light cured
difference between adhesive and self adhesive resin cements:
- adhesive resin cement: adhere to tooth structure but require separate etch and bonding agent
- self-adhesive resin cement: adhere to tooth and other structures without separate etch and bond agent
What is a primer for?
it is a chemical agent used to increase the affinity of an adhesive to metallic or ceramic materials (inside the crown/restoration)
Two basic categories:
- resin based cements
- resin based glass ionomers
ideal properties for cement:
- high bond strength to tooth structure and other materials
- high tensile/compressive strengths
- low solubility
- colo stability
- low water absorption
- low film thickness
- radiopacity
- tolerance to moisture during cementation
disadvantages of resin based cements:
- technique sensitive in that bond strength is affected by: pre tx procedures, depth of cure, degree of polymerization, opacity/shade of restoration and cement
- difficult to clean up
- change shade during curing
- may darken during lifetime
Resin cements are classified via:
- polymerization mechanism (light/chemical/dual)
- adhesive scheme (adhesive vs self adhesive)
Why should you selectively etch even when you’re using self adhesive resin cement?
because it is less strong in that it relies solely on the acidity of the cement and does not acid etch enamel very well
Advantage of light cured resin cement:
- increased working time
- decreased finishing time so should remove excess cement before final curing
- color stability
When is dual cure resin cements indicated?
when ceramic is too thick or too opaque (white) or metallic crown
What are the self and light cure imitators used in dual cure resin cements?
- self cure initiator: benzoyl peroxide
- light cure initator: camphorquinone
What is tack cure?
- after seating restoration, cure marginal excess for ~2 seconds
- then, remove cured excess easily with scaler
- this makes cleanup after full set much faster
Downside of chemical/self cure resin cements:
- not as color stable as light cured
- limited shade selection
Which resin cement has a universal bonding agent?
adhesive resin cements
(self-etch, total etch, selective etch)
What does the universal bonding agent do in adhesive resin cements?
bonds cement to the tooth
What does the optional phosphoric acid (30-40%) do?
- etches enamel/dentin
- removes smear layer and opens tubules
- can be total or selective etch
How is adhesive resin cement cured?
light or dual cured
Which cement has the highest bond strength, especially to enamel?
adhesive resin cements (because it has a bonding agent)
What is the one-component, “universal” adhesive?
self-adhesive resin cement
Difference in bonding structures between adhesive and self adhesive resin cements?
- adhesive: bonds cement to tooth
- self-adhesive: bonds to enamel, dentin, metal and ceramic
Properties of self-adhesive resin cements:
- acidic monomer
- better bond to dentin than enamel… this is why you want to separate acid etch enamel only if possible (but can adversely affect dentin bond)
Self adhesive resin cement that is used in clinic:
RelyX Unicem 2 (3M ESPE)
What is the molecule in self adhesive resin cements that allows bonding to different structures?
10-MDP
Bond strength of cements:
- self adhesive alone isn’t as strong as adhesive resin cements
- etching of enamel by phosphoric acid when using self adhesive strengthen bond strength to enamel but lowered bond of dentin
- resin modified glass ionomer typically 1/2-1/3 bond strength of resin cements
In dual cure,
light cure accessible margins!!!
How does the pH change in self adhesive resin cements?
acidic to neutral in 24 hours
- pH= 2 after mixing
- ability to self etch, hydrophilic for interaction with moist collagen fibers
- pH= 7 after 24 hours
- hydrophobic, resistant to water uptake, helping prevent staining and cracking, and adding to long term stability
If you had a metallic restoration, which cement would you choose?
- almost any cement not requiring light activation
- dual cured possible
If you had an all ceramic restoration, which cement would you choose?
- one of the resin cements
- RMGI second choice
If you had a porcelain veneers, which cement would you choose?
- light cured preferable to avoid possible color change
Advantages of RMGI:
- exhibit fluoride release comparable to true glass ionomer cements
- moisture tolerance during cementation
- adhere to tooth structure
- less soluble than glass ionomers
Disadvantages of RMGI:
- potential expansion after setting due to water absorption (can cause crack propagation in all ceramic restoration)
- preparation needs to be more retentive in design
