Resin composite! Flashcards
what were the earliest tooth coloured restorative materials? and when were they used?
silicate cements - 1950-1960s
what is the reaction to give silicate cements?
aluminosilicate glass + phosphoric acid = salt and water
give 4 properties of silicate cements
- releases fluoride
- moisture sensitive
- erosion prone (due to acid)
- brittle
what causes the silicate cement to be brittle?
the glass
where would you use silicate cements?
only on anterior teeth
what was used between 1960-1980s?
acrylic resin
what type of product is acrylic resin made from?
the same product used to fabricate dentures
what is vital in avoiding inferior properties for acrylic resin restorations?
a correct powder:liquid mixing ratio
how is acrylic resin set and what is the disadvantage to this
chemically set which decreases working timeq
what is contained within the powder for acrylic resin? 3 things
- pmma beads
- chemical indicator
- pigment
what is contained within the liquid for acrylic resin? 2 things
- mma monomer
- chemical activator
what type of chemical activator is contained in the liquid for acrylic resin?
tertiary amine
what is the function of the tertiary amine?
starts off the setting reaction
what is the setting reaction for acrylic resin?
free-radical addition polymerisation of methyl methacrylate
what are the 4 stages in free radical addition polymerisation of methyl methacrylate?
- activation
- initiation
- propagation
- termination
what happens in the initiation phase? in free radical addition polymerisation of methymethacrylate
the tertiary amine is in liquid and it cleaves the molecule at o-o
at which stage does the joining up occur? in free radical addition polymerisation of methymethacrylate
the propagation stage
what occurs at the initiation stage? in free radical addition polymerisation of methymethacrylate
the double bond breaks up
what happens at activation phase? in free radical addition polymerisation of methymethacrylate
o - o bond is cleaved due to the tertiary amine in the liquid of the acrylic resin
what does the material do on polymerisation?
shrinks (6% by volume)
what occurs at termination? in free radical addition polymerisation of methymethacrylate
- when a chain attaches to free radicals or further growing chain
When does the process stop all together? in free radical addition polymerisation of methymethacrylate
when there is a lack of properties
what type of reaction is free radical polymerisation of methylmetacrylate? (endothermic or exothermic)
exothermic - releases heat
what happens if the tertiary amine is not all used up??
poor colour stability occurs (clear to brown)
what are 5 benefits to acrylics compared to silicates?
- less brittle
- less prone to erosion
- less acidic
- less soluble
- exhibits lower thermal diffusivity
if there is amine still present in the acrylic then what may happen to the tooth shade and how is this avoided?
it may loose its shade and you can avoid by getting a perfect powder to liquid ratio
what type of lining can acrylic resin react with?
zinc oxide eugenol
what makes acrylic resin irritant to the pulp? 2 reasons
residual mma monomer in the liquid and exothermic (only irritant in deep cavity
who investigated acrylic in 1951? what did they conclude?
knock and glenn discovered
