Glass Polyalkenoate/Glass ionomer cement Flashcards
What is another name for glass polyalkenoate cement?
glass ionomer cements
What are the 2 basic ocmponents of GPC?
glass
acid (usually polyacrylic acid)
What type of reaction occurs in GPC?
acid-base reaction
Is fluoride released from GPC?
yes, throughout its life
What is the liquid component, acid or base?
acid, usually polyacrylic
Can glass ionomer cements be light cured?
no, only chemically
When can the GIC be light cured?
if resin is in there, but at that point it is not a cement, it is likely a resin modified glass ionomer
What is the glass component of the GIC?
fluoro-alumino-silicate
Where is the source of fluoride in GIC?
from the glass component,… fluoro-alumino-silicate
What is the effect of adding in elements strontium and lithium into glass?
impoact radiopacity
What is the effect of altering the aluminium/silica ratio?
make it more translucent
What is the effect f altering ion release of the glass?
determines the solubility, setting characteristics and fluoride release
What are the main components of glass?
What has the highest percentage composition of glass?
silica (silicon oxide)
it does vary though
How is the glass made?
glass mixture heated to between 1150 and 1450
molten mass poured onto metal plate and then cooled into water (shock cooling)
broken up to form a glass frit
wet or dry milled to produce small particles of glass
What is the max size of particle which can be used for restoration?
20um
What is shock cooling?
molten mass is poured onto a metal plate and then into water
What is the process called to reducing glass reactivity?
passivation treatment
What does passivation treatment involve?
washed with acetic acid for up to 24 hours and then dried
What acid is used in passivation treatment?
acetic acid
How does passivation treatment reduce the reactivity of glass?
leads to ion depletion of the glass surface - fewer ions immediately available to form the salt matrix at start of mix
When is passivation treatment maximised?
it has greater significance when the particle size of cement is reduced (smaller particle size the more rapid the set; volume: surafce area)
Polacrylic acid is the main acid in GIC, what are the others in the series?
polymaleic acid
number of copolymers of polyacrylic acid
What group is common to all of the acids?
carboxylate
Why is the carboxylate common to all of the acids?
as water ionises to carboxyl and hydrogen ions to facilitate chemical reaction
facilitate the chemical reaction
What can be added to the GIC acid component to sharpen the set?
polyphosphonic acid to provide a short sharp set
What does an cement with a higher molecular weight determine?
it will have better mechanical properties
What is the disadvantage of the high molecular weight of cement?
higher viscosity and harder to work with
How do some manufacturers package the GIC?
vacuum dry the acid solution and then mix the anhydrous powder so formed with the glass
activation of the cement is achieved by adding water
just adjust the water to powder ratio
What can molecular weight of the cement also influence?
the working and setting time
higher molecular weight, shorter the working time
What acid has been used to facilitate encapsulation of the cement?
maleic acid, makes it les viscous
What acid is added to the cement to accelerate setting reaction?
tartaric acid - it maintains the working time
What is the structure of the GIC?
Cored structure
What is the unreacted powder material (glass) encased in? (after setting)
salt matrix
What do the surface soluble components of glass react with?
acid from the matrix
What is the setting reaction of GIC?
(DONT NEED TO MEMORISE)
What gel forms around the glass particles?
silica gel
What come out of the silica gel around the glass core?
calcium, aluminium and fluoride ions
What do the calcium, aluminium and fluoride ions form? (form the silica gel)
calcium and aluminium polysalts
When does the condensation reaction occur more rapidly?
with the calcium ions
What gel the calcium ions form? (condensation)
calcium polyacrylate gel formed- within a minute
Why does the aluminium take longer to form polyacrylate gel compared to calcium ions? (condensation)
aluminium ion is triple charges and less mobile
What occurs after the polyacrylate gel has formed by condensation?
cement goes through a period of maturation
What occurs during the maturation period of setting?
further cross-linking of the matrix and more cations become bound onto the polyanion chain
What properties increase during the maturation phase of the setting reaction?
increase in mechanical properties
How long can the maturation phase take?
months
What is the compressive and flexural strength like of GIC?
relatively low but increase very time as the martial matures (maturation stage)
Do you place a protective layer over GIC and why?
yes, varnish can be put over
longer the restoration is protected from moisture, better resistance it is to erosion (not good with oral fluids)
