GICs Flashcards
types
conventional: anhydrous vs original
resin modified: self/light cure
uses
restorative filling material core build up lining luting cement FS dressing
chemistry
acid - liquid
base - glass powder
chemistry - liquid
polyacrylic acid tartaric acid (control setting characteristics)
tartaric acid
control setting characteristics
chemistry - base - glass powder
SiO2
Al2O3
CaF2
strontium and lithium salts
strontium and lithium salts
increase radiopacity
no role in reaction
aluminium/silica ratio
alters translucency
more silica = more translucent
variations in composition
anhydrous
encapsulated
anhydrous
acid freeze dried and added to powder
liquid distilled water
easier handling
encapsulated
consistent
variations
powder particle size
molecular weight of acid
variations - powder particle size
<20um for luting cement to give low film thickness
smaller=quicker setting reaction=more opaque set cement
variations - molecular weight of acid
higher = better mechanical properties
but more viscous - difficult to mix
setting reaction
acid base
glass+acid = salt+silica gel
setting reaction stages
dissolution
gelation
hardening
dissolution
H+ ions attack surface of glass
Ca, Al, Na, F ions released
leaves silica gel around unreacted glass
gelation
form calcium polyacrylate
Ca ions crosslink with polyacid by chelation with the carboxyl groups
Ca ions bivalent - can react with 2 carboxyl groups on the same molecule
hardening
form aluminium polyacrylate
trivalent - better mechanical properties
takes long time
protection
from moisture and desiccation following gelation
- when ‘set hard’ in mouth but before maturation begun
contamination
- excessive drying
- absorb water
protection at later date if working on other areas of mouth
protection mechanisms
varnishes
resins - best
greases/gels e.g. vaseline
handling
better now due to tartaric acid - working time similar but setting time shortened
aesthetics
lack translucency (opaque)
increased silica content better
translucency improves over 24+ hours when extra X-linking
not suitable where aesthetics really important
once set less susceptible to staining and colour change than composite
mechanical properties
poor tensile strength
low compressive strength
poor wear resistance
low hardness
F release
can release F without damage to their structure
initial fluoride release but diminishes v quickly
F reservoir/sink - can take it up from the env then release when ambient conc falls
bonding
bonds to E and D
low bond strength compared to composite
cohesive strength low
good sealing ability
chelation between carboxyl groups in cement and Ca on tooth surface
H bonding/metallic ion bridging to collagen
acid base reaction between poly acrylic acid and Ca ions in HA
good bond requires:
clean surface
conditioned surface - polyacrylic acid
physical properties
higher solubility than composite - dissolution during gelation - long term erosion by acids no contraction on setting lower modulus - cervical margin - flexing is good as tooth moves when bite
thermal properties
good - expansion similar to dentine
cermets
developed to overcome GI brittleness
silver added to glass to increase toughness and wear resistance
just ended up making a silver GIC
disadvantages
brittle poor wear resistance moisture susceptible when first placed poor aesthetics poor handling characteristics susceptible to acid attack and drying out over time possible problems bonding to composite
advantages
stable chemical bond to E and D low microleakage F release good thermal properties no contraction on setting much easier to use than composite
RMGIC chemistry
powder and liquid
RMGIC chemistry - powder
F-Al-Si glass barium glass (radiopacity) vacuum dried polyacrylic acid potassium persulfate (redox catalyst) ascorbic acid pigments
RMGIC chemistry - barium glass
radiopacity
RMGIC chemistry - redox catalyst
potassium persulfate
RMGIC chemistry - liquid
HEMA - water miscible resin polyacrylic acid with pendant methacrylate groups - acid base and polymerisation reactions tartaric acid H2O photoinitiators
RMGIC chemistry - tartaric acid
speeds setting
RMGIC chemistry - H2O in liquid
allows reaction between poly acid and glass
advantages of RMGIC
bonds to E and D better physical properties lower solubility F release handling better translucency and aesthetics
dual curing
acid base reaction - starts initially on mixing free radical methacrylate reaction - light activation - complete 20s
acid base reaction continues within resin matrix for several hours
tricuring
will set even if insufficient light penetration
- but in absence of light physical properties reduced by 25%
acid base
redox (continues around 5mins)
free radical methacrylate reaction
RMGIC disadvantages
polymerisation contraction
exothermic setting reaction - both polymerisation and dark cure
swelling due to uptake of water - HEMA extremely hydrophillic
monomer leaching
reduced strength if not light cured
light curing slows down acid base reaction
benzoyl iodides and bromides can be released which are cytotoxic
moisture sensitive
