Textbook Dental Materials Flashcards
Amalgam forms?
Lathe cut
Spherical
Admired
What is the silver/tin phase?
Powdered alloy mixing with mercury
What is the gamma 2 phase?
Causes increased corrosion and creep
What is the reason that more copper is added to amalgam?
To turn gamma 2 phase to gamma 1 phase causing less corrosion and creep
How is amalgam retained in a cavity?
Retention by grooves pits undercuts dovetail lock
Cavities must be over 1.5mm deep
Why are amalgam cavities overfilled and condensed?
Condensed to bring mercury to surface, overfilling allows mercury rich surface to be carved away
Disadvantages of amalgam?
Excess tissue removed for retention
Microleakage common
Potential mercury toxicity
How is composite set?
Monomers undergo a polymerisation reaction.
Monomers join together to form large chain molecules which is initiated by free radicals
How are light cure composites set?
Composed of resin, filler and camphorquinone
Camphorquinone bonds broken down by light at 470nm and free radicals are produced which initiate polymerisation
How does shrinkage occur and how much?
Polymerisation encourages monomers to join together and resin shrinks
21%
What monomers are used in the resin matrix and what are their jobs?
BISGMA - reduces shrinkage
TEGMA - controls viscosity
What does addition of a filler do to composites?
Makes resin stronger
Reduces shrinkage
Reduced how flowable the material is
What are the types of composites and their properties?
Macrofilled - quartz filler. Strong but poor aesthetics
Microfilled - silica filler. Problems with shrinkage (less filler)
Hybrid - quartz and silica
Nano composites - improved aesthetics
What is the silane coupling agent?
ensures that the resin and filler work together
What is the composition of flowable composite?
50-70% filler
Less viscous more flowable
Problems with shrinkage
What are the basic components of glass ionomer materials?
Polyalkenoic acid (e.g polyacrylic acids) and ion leachable glass (e.g aluminasilicate with calcium)
What is a cermet?
Metals added to powder
Gives unaesthetic grey material
Used as core build up in badly broken down teeth
What is a compomer?
Polyacid modified resin composite
Describe the action and composition of the etching stage of etch prime bond?
37% phosphoric acid
Etch removes the smear layer and opens dentinal tubules by dissolving the mineral portion up to 5um leaving collagen fragments exposed
Describe the composition and action of the priming stage of etch prime bond?
HEMA dissolved in a solvent
HEMA has a hydrophilic terminal which adheres to dentine and a hydrophobic terminal that can polymerise with resin composite
Describe the composition and action of the bond stage of etch prime bond?
Resin adhesive
Attaches to hydrophobic terminal of HEMA primer and locks onto exposed collagen when light cured
Why is RMGIC left uncured in a bonded amalgam?
To allow chemical cure whilst adherent to tooth tissue and amalgam
