GIC Flashcards
What is the main reaction involved in GIC
Acid base reaction between polyalkenoic acid and calcium fluoro silicate glass
Glass base (powder) + poly acid (liquid) —> poly salt gel + silica gel (particle coating)
What compounds does the glass base powder in gic contain (3)
Silica oxide
Aluminium oxide
Calcium fluoride
(Some strontium fluoride instead because imparts radioopacity)
** fluoride releasing!
SAC
Why is calcium fluoro aluminosilicate glass able to react with polyalkenoic acid (a weak acid)
Calcium fluoro aluminosilicate glass has increased ratio of alumina to silica which increases reactivity of the glass
Function of itaconic acid in gic
Itaconic acid is liquid component
Reduce viscosity of liquid
Inhibit gelation caused by intermolecular hydrogen bonding
Ie make more liquidy
Function of tartaric acid in gic
Improve handling characteristics
Increase working time, decrease setting time
Name the 2 phases in setting reaction in gic
Dissolution and gelation
What happens in dissolution phase in gic setting
Surface of glass is attacked by poly acid, corroding surface and increasing environmental availability of ions
Limited dissolution of glass with release of calcium, aluminium, fluoride
Calcium is released more readily than aluminium, which has a slower rate of diffusion
Calcium and aluminium form complexes with fluoride. AlF more stable and is formed preferentially
What happens in gelation phase of setting reaction in gic
Crosslinking of coo- with more mobile, more readily available calcium to form clcium polysalt. Ph increases as polyacid is converted to polysalt
At maturation phase, over the next 24 hours, aluminium salts are formed leading to more rigid cross linking. Initial sharp increase in physical properties
How does glass composition affect setting time of gic
Higher alumina:silicate ratio increases setting rate as more al3+ released over time. Setting time decreases
How does powder liquid ratio affect setting rate of gic
Increased powder:liquid ratio increases the setting rate
Also:
Increased number of unreacted particles which agglomerate and form impurities, decreasing mechanical properties
How does particle size affect gic setting rate
Smaller particle size, more surface area for acid to attack, increase setting rate
How long is the total setting time and working time for gic setting
Total setting time 7 min
Working time 2 min
What does the matrix in gic contain
Hydrated fluoridated calcium and aluminium polysalt
What are some effects of increased liquid to powder ratio in gic
Increase pulp irritation
- more liquid, more unreacted acid, lower pH
Lower setting rate, longer working time, longer setting time
Lower mechanical properties because powder more dilute given fixed cavity volume
Lower resistance
Why is GIC hydrolytically unstable during initial stages of setting reaction
Gic is a water based hydrophilic cement
Hence sensitive to water uptake and loss (for at least 1 hour after uptake). This dilutes ions and there is movement of ions along with water in and out, Al3+ move out ie essential ions eluted
Importance of water in gic setting
Water is reaction medium that cement forming cations are leached
Water hydrates cross linked matrix, increasing material strength
Desiccation can retard reaction
Dessication can cause shrinkage and crazing (minute cracks)
Effect of water loss/uptake in early stages of setting reaction of gic
Decrease physical properties
Compromise colour and translucency
What is gic compressive strength
High compressive strength, 200MPa
What are the two key properties of gic
Self adhesion, fluoride releasing
What is the flexural strength of gic
Low flexural strength 5-40MPa (composite has 3x greater flexural strength 120MPa)
How does strength of gic change over time
Cement gets stronger over time
How does moisture in mouth affect gic strength
Desiccation eg in dry mouth will weaken gic
Water serves to hydrate cross linked matrix!
What to use to form barrier over gic to protect from water loss/uptake
Layer of low viscosity resin ie adhesive or varnish
Temporary layer that can peel off after one day
Increased powder to liquid ratio affects gic how
Increased mechanical properties
Why is gic biocompatible
Polyacrylic acid (liquid component) is a weak acid. Also it has large molecular weight, limited diffusibility of acid
How does linear co efficient of thermal expansion of gic compare to tooth
Similar to tooth
Unlike amalgam which expands more than tooth due to heat leading to microcracks leading to stress fracture
Can gic keep on releasing fluoride for many years
Yes, the set cement can reabsorb fluoride from the oral environment if appropriate concentration gradient present
Where is fluoride in gic located
In the matrix, not all will get released
Is gic aesthetic
Not very aesthetic, poor optical properties. More opaque than composite though translucency improves with maturity
How may water affect aesthetic of gic
Early contamination of gic with water can cause it to become more opaque
Cement can be damaged by dehydration at subsequent visits. Dehydration lead to microcrack formation —> poor visual property and more opaque
Contraindications for gic
Stress bearing areas
Aesthetic areas
Which requires stricter moisture control: GIC or CR
GIC
How quickly does GIC bond strength form
80% of bond strength developed in 15min
What is the mechanism of adhesion for gic
Self-adhesion, acid base reaction. A true ionic exchange that requires presence of water
Adheres to dentine collagen through hydrogen bonding or metallic ion bridging between carboxyl groups
What should you do before placing gic gto improve adhesion
Remove surface contaminants including the smear layer using pumice-water slurry or surface conditions. These help to increase surface energy, allowing cement to come into close contact with demineralisaing tooth surface
What are some disadvantages of gic compared to composite
Weaker mechanical properties
More opaque, less aesthetic
Advantages of using resin modified gic over gic
Increase mechanical properties
Faster setting reaction
Overcome problems of moisture sensitivity and low early mechanical strength (presence of resin matrix converse immediate resistance to water gain or loss)
More translucent
Improved adhesion to tooth structure due to superior wetting ability of HEMA
Disadvantages of using resin modified gic versus conventional gic
Lower fluoride release and lower self adhesion
Higher setting shrinkage
How to achieve resin modified gic
Replace water components with water/hydroxyl methacrylate mixture
Replace polyacrylic acid with modified paa
What is type 1 gic
Luting cements, fast set with early resistance to water uptake used for cementation of crowns, bridges, etc
Radio opaque
What is type 2.1 gic
Restorative aesthetic cements
Restore primary and permanent teeth (class 1, 2, 3, 5, nccl), repair defective restoration margins
Temporary restorations
What is type 2.2 gic
Restorative reinforced cements
Restoration of posterior primary teeth and permanent teeth (class 2 tunnel restoration)
Restore root surfaces in overdenture
Seal bifurcation area in periodontically involved teeth
AESTHETIC CONSIDERATIONS NOT IMPORTANT, RAPID SET AND GOOD PHYSICAL PROPERTIES
How does compomer bind to tooth
Mechanical bonding, bonding agents required
Of gic, resin modified gic, composite, compomer, which has the best handling properties
Compomer
Of gic, resin modified gic, composite, compomer, which has the highest CLT
Composite
Does resin modified gic or conventional gic have higher polymerisation shrinkage
Resin modified GIC
Of gic, resin modified gic, composite, compomer, which has the CLT closest to that of tooth structure
GIC
What is type 3 gic
Lining/base cements or pit and fissure sealants
Liners are less than 0.5mm in length to place over exposed dentine
Base is a relatively thick layer to replace some dentin, protect pulp via thermal insulation and absorb occlusal forces
What is a possible cause of loss of translucency in gic
Moisture contamination/dehydration during setting
What are some possible reasons for loss of retention in gic filling
Failure to clean and condition tooth
Manipulation of cement after initial set
Carving and polishing too soon
Early removal of celluloid strip (transparent matrix)
What are some possible reasons for cracks and crazing in gic filling
Dehydration
Finishing/polishing too soon
What are some possible reasons for chipped margins in gic filling
Lack of bulk in restoration
FInishing/polishing too soon
What are some possible causes of gingival irritation in gic placement
Failure to finish/polish restoration
Failure to remove excess
Poor finishing/polishing techniques
Setting of gic vs resin modified gic
Gic: acid base reaction between polyalkenoic acid and calcium fluoro alumino silicate glass
Resin modified gic: fundamental acid base reaction supplemented by 2nd polymerisation reaction
