Dental Materials - Glass Ionomer Cements Flashcards
What are the types of glass ionomer cements?
Conventional
Resin modified;
Light cure
Self cure
What acids are used in GIC’s?
Tartaric
Polyacrylic
What components of the GIC base controls translucency?
The ratio of aluminium to silica.
More silica = more translucent.
In terms of particle size, what size speeds up the setting reaction?
Smaller particles
In terms of particle size, what size makes the GIC more opaque?
Smaller particles
What properties are improved when a higher molecular weight of acid is used in a GIC?
Improved mechanical properties.
What kind of reaction is the conventional GIC setting reaction?
Acid base reaction
What are the 3 setting phases of CONVENTIONAL GIC.
Dissolution
Gelation
Hardening
Describe what occurs in the dissolution phase of conventional GIC setting reaction.
Acid turns to a solution
H ions attack the glass particles
Al, Ca, Na, F ions are released.
Silica gel surrounds the unreacted glass.
Describe what occurs in the Gelation phase of conventional GIC setting reaction.
Ca ions in enamel crosslink with the polyacid by chelation with the carboxyl groups in the cement.
Ca ions are bivalent - joins molecules.
Takes several minutes
What is the disadvantage of crosslinking?
Ca can chelate with 2 carboxyl groups on the same molecule therefore doesn’t join molecules.
Describe what occurs in the hardening phase of conventional GIC setting reaction.
Starts 30 minutes after the reaction - can take > 1 week to fully harden.
Trivalent Al ions ensure crosslinking and increase the strength. (significantly increases the mechanical properties.
During the hardening stage what must be avoided?
Moisture and dessication - (removal of moisture)
What is the bonding mechanism of GIC?
Chelation between Ca in enamel and the carboxyl groups in the cement.
What must you NOT do to the tooth before adding GIC?
Etch the tooth - will remove some of the Ca required for chelation with the carboxyl groups.
What are the advantages of GIC? (6)
Fluoride release - without damaging the structure.
Stable bond to enamel and dentine via chelation with Ca in enamel and carboxyl groups in the cement.
Low microleakage - no contraction when setting.
Resistance to staining
Thermal expansion similar to dentine.
Low modulus = ability to bed (ideal for cervical restorations)
What are the disadvantages of GIC? (8)
Poor tensile strength
Poor wear resistance
Higher solubility
Susceptible to erosion by acid attack.
Poor aesthetics
Lower compressive strength
Brittle
Poor handling
What is the function of tartaric acid?
Speeds up reaction
What are the advantages of RMGI? (6)
Stable bond to enamel and dentine.
Better handling - than conventional as there is longer working times and reduced setting times.
Better aesthetics/ translucency - than conventional
lower solubility
Fluoride release without any damage to the structure
Better physical properties.
What are the disadvantages of RMGI?
Polymerisation contraction stresses.
Exothermic reaction
Swelling from water uptake
Monomer leaching - HEMA is toxic to the pulp therefore must be completely polymerised .
Redox reaction can release substances which as cytotoxic - damage the pulp.
