Glass Ionomer Cement Flashcards
What are the uses of GIC/RMGIC?
Restorative - filling material, endodontic access cavity temporary filling Core build up - prior to crown placement Lining - underneath restorations Luting - cementing indirect restorations Fissure sealant Orthodontic cement
What are the two components of conventional GIC?
Acid - liquid
Base - glass powder
What are the three stages in the setting reaction of conventional GIC?
Dissolution - bath bomb
Gelation - calcium ion cross linking
Hardening - aluminium polyacrylate formation
What is dissolution?
Acid into solution
H+ ions attack the glass surface
Ca, Al, Na & F ions are released
Leaves silica gel around unreacted glass
What is gelation?
Calcium ion crosslinking with the polyacid by chelation with the carboxyl groups. Caused by formation of calcium polyacrylate.
Equates to the initial set of the material.
Takes several minutes depending on the particular material.
Following this, the material appears hard in the mouth.
What is hardening?
Does not start for at least 30 mins and can take a week+ to complete.
Trivalent aluminium ions ensure a higher degree of crosslinking and increase strength. Triggered by aluminium polyacrylate formation?
Improves mechanical properties of material.
What problems are caused if contamination occurs during placement of conventional GIC?
Aluminium ions diffuse out Excessive drying - water will be lost Saliva contamination - absorption of water Weak material Poor aesthetics
How can conventional GIC be protected?
Varnishes (copal ether, acetate)
Resins (DE bonding agents)
Greases or gels (vaseline)
Why was tartaric acid added to the composition of GIC?
To improve ease of use as older formulations had v long working and setting times.
What is the bond strength of GIC?
5MPa
Bonds without need for an intermediate material
How does GIC bond to the tooth’s surface?
Chelation between carboxyl groups in the cement and Ca on the tooth surface.
Hydrogen bonding or metallic ion bridging to collagen.
What is key for good bond formation?
Clean surface Conditioned surface (e.g. polyacrylic acid)
What are the aesthetics of GIC like?
Colour okay but lacking in translucency
New materials with higher silica content are better
Translucency improves over 24hrs due to extra cross linking
What are the thermal properties of GIC?
Expansion similar to dentine
No contraction on setting
What are the mechanical properties of GIC?
Poor tensile strength Lower compressive strength than composite Poor wear resistance Lower hardness than composite Higher solubility than composite
What are the benefits of fluoride release from GIC?
Doesn’t damage the GIC structure
Beneficial against secondary caries
Inhibits bacterial growth
Ability to recharge it’s fluoride supply
What are advantages of GIC?
Stable chemical bond to enamel and dentine
Low microleakage
Fluoride release
Good thermal properties - no contraction on setting
What are the disadvantages of GIC?
Brittle Poor wear resistance Moisture susceptible when first placed Poor aesthetics Poor handling characteristics Susceptible to acid attack & drying out over time Possible problems bonding to composite
What are cermets?
Material composed of ceramic and metallic materials.
Silver was added to the glass to increase toughness and wear resistance of GIC. Only ended up making silver GIC.
What is RMGIC?
GIC with added 75% HEMA bis-GMA
Combine the acid-base reaction of traditional GIC with a self-cure amine-peroxide polymerization reaction.
Developed to overcome the disadvantages of traditional GIC - command set, improved physical properties, better aesthetics.
What are the components of RMGIC?
Powder: Fluoro-alumino-silicate glass Barium glass Vacuum dried poyacrylic acid Potassium persulphate Ascorbic acid Pigments Liquid: HEMA Polyacrylic acid with pendant methacrylate groups Tartaric acid Water Photo-initiators
What is the purpose of barium glass in RMGIC?
Provides radiopacity
What is the purpose of potassium persulphate in RMGIC?
Redox catalyst to provide resin cure in the dark
What is the purpose of pigments in RMGIC?
Varies shade
What is the purpose of tartaric acid in RMGIC?
speeds up the setting reaction
What is the purpose of water in RMGIC?
allows the reaction between polyacid and glass
What is the setting reaction for RMGIC (dicuring)?
Much more complex than conventional.
Initially on mixing the acid-base reaction begins in the same way as conventional GIC.
On light activation a free radical methacrylate reaction occurs resulting in a resin matrix being formed.
Light activation is complete v quickly (20s).
Acid-base reaction continues within the resin matrix for several hours.
What is the setting reaction of GIC?
Alumino-silicate glass powder + polyalkenoic acid -> calcium + aluminium polyalkenoates
base + polyacid -> polysalt + water
What is the setting reaction for RMGIC (tricuring)?
Initially the same as conventional GIC
REDOX reaction begins
On light activation, free radical methacrylate reaction occurs resulting in a resin matrix being formed
Light activation complete 20s
REDOX reaction continues for around 5mins after initial mixing
Acid-base reaction continues within the resin matrix for several hours
Final hardening of the acid/base phase with aluminium polyacrylate can take days
What are the negative properties of RMGIC?
Polymerisation contraction
Exothermic setting reaction
Swelling due to uptake of water
Monomer leaching (if HEMA is not fully polymerised)
Light curing slows down the acid-base setting reaction
Benzoyl iodides and bromides can be released which are cytotoxic
What are the beneficial properties of RMGIC?
Good bond to enamel and dentine Better physical properties Lower solubility Fluoride release Better translucency and aesthetics Better handling
What are the two components of GIC?
acid - liquid
base - glass powder
What caries risk should patient be to justify use of GIC?
High caries risk
Frequent attenders
Medium risk - compomer
Low risk - composite resin
