Linings/Bases Flashcards
Phosphoric acid cements commonly in what form?
powder to liquid
powder phosphoric acids?
zinc oxide with other metallic oxides
liquid phosphoric acid is?
aqueous solution of phosphoric acid (50-60%)
buffers of AlPO4 and Zn3(PO4)2
where does the setting reaction occur for phosphoric acid cements?
what kind of reaction
at the powder surface
rapid and exothermic
how to mix the powder and liquid of phosphoric acid cement?
add powder incremently into the liquid = delays set and increases working time
use cool glass slab
always replacing the cap lid prevents what?
crystallisation
how long does PA cements take to harden?
4-7 minutes
irritability properties of PA cements?
low pH
low MW
= high irritancy
properties of PA cements?
insulator
can withstand condensing
radiopaque
PA cements not good for?
compatibility
obtundant
not adhesive/no coronal seal
variants of PA cement components?
silicophosphate cement = powder and liquid
aqueous phosphoric acid and buffers
zinc oxide and aluminasilicate glass
properties of silicophosphate cements?
increased strength
fluoride
less soluble
copper cement variant of PA cement?
aqueous phosphoric acid and buffers
powder is zinc oxide, black copper cement
black in colour
bacteriocidal
how to zinc oxide eugenol cements come?
powder and liquid or 2 pastes
liquid part of zinc eugenol cement?
eugenol with olive oil to control viscosity
powder part of zinc eugenol cement?
zinc oxide with hydorgenated resin/polystyrene for reinforcement
accelerator in zinc oxide?
zinc acetate creates iconic medium to faster set
how do ZnO eugenols set?
set by chelation
continuous in cavity as moisture present
zno eugenol beneficial in what way?
bacteriocidal because of?
insulator?
has a beneficial irritancy
zinc
yes
zno eugenol :
can withstand if?
radiopaque because?
obtundant?
resin reinforced
zinc
yes
disadvantages of zno eugenol?
not adhesive = no coronal seal
not compatible with resin composites
deriviatve of zno eugenol?
ortho ethoxy benzoic acid
powder - zno 60%, quartz 35%
liquid - ortho ethoxy benzoic acid eugenol
stronger than zinc oxide eugenol
calcium hydroxide is?
a suspension of calcium hydroxide in water - dries easily
fractured friable film
instead of water use?
1) methylo cellulose in water
2) synthetic polymer in volatile solvent
both still weak
modern caoh activated how?
chemically
VLC activated
paste 1?
paste 2?
1 - glycol salicylate e.g butylere glycol disalicylate
2 - zinc oxide with calcium hydrozie
on reacting of pastes what is formed?
reacting chelate compounds maily form zinc
how is caoh light activated?
vlc activated polymerisation of a mma
or monomer mixed with HEMA = absorbs water to liberate hydroxyl from caoh
calcium hydroxide moisture increases?
rate of set
the vlc reaction with calcium hydroxide is ?
exothermic
high ph of caoh gives?
beneficial irritancy
high ph of caoh renders it what?
bacteriocidal
other properties of caoh?
insulator
radiopaque
good restorative
