Biomaterials Exam - Composite, Glass Ionomers, Sealants, and Adhesives Flashcards
What makes up a composite?
hybrid material of an organic phase (resin) and an inorganic (filler) phase
What is the role of resin in a composite?
helps processing and handling
What is the role of filler in a composite?
helps modulus and wear resistance
What are the characteristics of organic polymers?
tougher, but not as strong or wear resistant
What are the characteristics of inorganic materials?
strong and wear resistant, but brittle
What type of reaction occurs in order to cure composite?
cross-linking reaction
What triggers the cross-linking of polymers when composite is cured?
visible light
What are 2 ways to change the density of cross-linking?
- number of cross-linking groups
- degree of cross-linking or degree of curing
What are the 4 components of composite resin?
- resin system
- filler
- bonding agent
- visible light initiator
What are the 3 types of fillers?
- micron (fine)
- nano (microfine)
- nano (microfine) in polymer matrix
What are the benefits of having a smaller filler size?
- teeth are nanocomposites
- smaller fillers should have better wear properties
- allows for better polishing and finish
- expectation of better mechanical properties
What is the difference between a nano (microfine) filler and a nano (microfine) filler in a polymer matrix? In other words, which has a tendency to aggregate? Which has poorer filler to matrix bonding?
- nano (microfine) filler has a tendency to aggregate
- nano (microfine) filler in a polymer matrix has poorer filler to matrix bonding because there is no coupling agent
What is a coupling agent?
a chemical substance that can react with the resin and the filler and enhance filler-to-matrix bonding
When a composite polymerizes, does it swell or shrink? Why?
shrink because there is a density change when it goes from monomer to polymer
What are the clinical consequences of polymerization shrinkage?
- causes stress on the tooth structure
- can cause microleaks and lead to secondary caries
What are the components of glass-ionomer cement?
- acidic polymer in aqueous solution
- basic glass
- water
- modifiers (+) tartaric acid (*don’t need to know?)
What type of reaction cures glass-ionomer cement?
acid/base reaction
What type of bond is formed between polyacids and basic glass in the setting of glass-ionomer cement?
salt bridges
Explain the steps of the setting process of glass-ionomer cement.
- glass-ionomer mix is applied
- acid matrix dissolves periphery glass
- glass releases ions: Ca, Al, and F
- divalent Ca ions quickly chelate with acid polymer chains
- in the next 24-72 hours, Al replaces Ca which increases the strength and F is released
- acid side groups can also chelate with glass and hydroxyapatite
Why does the glass-ionomer cement become stronger when Al replaces Ca in the salt bridges?
because Ca has a +2 charge so it can bind 2 of the acid or base together, but Al has a charge of +3 so it can bind 3
Is a coupling agent required in the setting reaction of glass-ionomer cement?
No, but it is required in the composite setting reaction
What is released during the setting of glass-ionomer cement?
fluoride and sodium which continue to be released over time
True or false: Glass-ionomer cement is a water-based restorative material.
true
What are some similarities or differences between adhesives and composites?
Similarities:
- light cured
- made of dimethacrylates (?)
Differences:
- composite is hydrophobic while adhesives are hydrophobic and hydrophilic
- adhesives may be unfilled (or lightly filled)
What is the difference between a macrotag and microtag of an adhesive?
- macrotag - interprism (between prisms) resin penetration
- microtag - intraprism (within prism) resin penetration
Which side of the adhesive (hydrophilic or hydrophobic) binds to the enamel of the tooth? Which side binds to the composite?
- hydrophilic binds to the tooth
- hydrophobic binds to the composite
What are some similarities and differences between sealants and composites?
Similarities:
- has a BisGMA/TEGDMA system
Differences:
- no filler in sealants
What is the oxygen inhibition layer? With what type of material is this more of a problem?
When a material is being cured with radical polymerization, free radicals are generated in order to form cross-links. But oxygen can terminate the free radicals so the top layer that is exposed to the atmosphere may not be cured. This is a problem with thin layers like sealants.
