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GLASS IONOMER CEMENT
Glass ionomer cement is a tooth coloured material, introduced by Wilson & Kent in 1972.Material was based on reaction between silicate glass powder & polyacrylic acid.They bond chemically to tooth structure & release fluoride for relatively long period.
Type I. For luting
Type II. For restoration
Type III. For liner & bases
Type IV. Fissure & sealent
Type V. As Orthodontic cement
Type VI. For core build up
Type VII. High fluoride releasing command set GIC
Type VIII GIC for ART
Type IX. Geriatric and paediatric GIC
CLASSIFICATION
Type I. For luting
Type II. For restoration
Type III. For liner & bases
Type IV. Fissure & sealent
Type V. As Orthodontic cement
Type VI. For core build up
Type VII. High fluoride releasing command set GIC
Type VIII GIC for ART
Type IX. Geriatric and paediatric GIC
COMPOSITION
SETTING REACTION
When the powder & liquid are mixed, Surface of glass particles are attacked by acid. then Ca, Al, sodium, & fluoride ions are leached into aqueous medium.
- Calcium poly salts are formed first, then followed by aluminum poly salts which cross link with poly anion chain.
- Set cement consist of unreacted powder particle surrounded by silica gel in amorphous matrix of hydrated calcium & aluminum poly salts.
- Calcium poly salts are responsible for initial set.
- Aluminum poly salts form the dominant phase.
- Water plays an important role in structure of cement.
- After hardening, fresh cement is extremely prone to the cracking & crazing, due to drying of loosely bound water .
- Hence these cements must be protected by application of varnish.
SETTING TIME
- Type I 4 - 5 minutes
- Type II 7 minutes
PROPERTIES
- Compressive strength - 150 mpa
- Tensile strength - 6.6 mpa.
- Hardness - 49 KHN.
Solubility & Disintegration:-
- Initial solubility is high due to leaching of intermediate products.
- The complete setting reaction takes place in 24 hrs, cement should be protected from saliva during this period.
Adhesion :-
- Glass ionomer cement bonds chemically to the tooth structure.
- Bonding is due to reaction occur between carboxyl group of poly acid & calcium of hydroxyl apatite.
- Bonding with enamel is higher than that of dentin ,due to greater inorganic content.
Esthetics :-
- GIC is tooth coloured material & available in different shades.
- Inferior to composites.
- They lack translucency & rough surface texture.
- Potential for discolouration & staining.
Biocompatibilty :-
- Pulpal response to glass ionomer cement is favorable.
- Pulpal response is mild due to
MANIPULATION
1.Preparation of tooth surface :-
The enamel & dentin are first cleaned with pumice slurry followed by swabbing with polyacrylic acid for 5 sec. After conditioning & rinsing ,tooth surface should isolate & dry.
2.Proportioning & mixing :-
- Powder & liquid ratio is 3:1 bywt. Powder & liquid is dispensed just prior to mixing.
- First increment is incorporated rapidly to produce a homogenous milky consistency.
- Mixing done in folding method to preserves gel structure.
- Finished mix should have a glossy surface.
3. Protection of cement during setting :-
- Glass ionomer cement is extremely sensitive to air & water during setting.
- Immediately after placement into cavity, preshaped matrix is applied to it.
4. Finishing :-
- Excess material should be trimmed from margins.
- Hand instruments are preferred to rotary tools to avoid ditching.
- Further finishing is done after 24hrs.
5. Protection of cement after setting :-
- Before dismissing the patient ,restoration is again coated with the protective agent to protect trimmed area.
- Failure to protect for first 24hrs results in weaken cement.
USES
- Anterior esthetic restoration material for class III & V restorations.
- For luting.
- For core build up.
- For eroded area .
- For atraumatic restorative treatment.
- As an orthodontic bracket adhesive.
- As restoration for deciduous teeth.
- Used in lamination/ Sandwich technique.
SANDWICH TECHNIQUE
- Devolped by Mclean,
- To combine the beneficial properties of GIC & composite.
Clinical steps
- After cavity preparation, condition the cavity to develop good adhesion with GIC.
- Place Type III GIC into prepared cavity.
- After setting, etch the enamel & GIC with orthophosphoric acid for 15 seconds.
- This will improve micromechanical bond to composite resin.
- Apply a thin layer of low viscosity enamel bonding agent & finally place the composite resin over GIC & light cure it.
ADVANTAGES
- Polymerisation shrinkage is less,due to reduced bulk of composite.
- Favorable pulpal response.
- Chemical bond to the tooth.
- Anticariogenic property.
- Better strength,finishing,esthetics of overlying composite resin.
MODIFICATIONS
1. Water settable glass ionomer cement :-
- Liquid is delivered in a freeze dried form ,which is incorporated into the powder.
- Liquid used is clean water.
2. Resin modified glass ionomer cement :-
Powder component consist of ion leachable fluroalumino silicate glass particles & initator for light curing.Liquid component consist of water & poly acrylic acid with methacrylate & hydroxyl ethyl methacrylate monomer.
3. Metal modified glass ionomer cement:-
- Glass ionomer have been modified by addition of filler particles ,to improve strength ,fracture toughness & resistance to wear.
Silver alloy admix / miracle mix:-
- This is made by mixing of spherical silver amalgam alloy powder with glass ionomer powder.
- Bonding of silver particles to glass ionomer particles by fusion through high temperature sintering.
4. Compomer :-
- Compomer is a composite resin that uses an ionomer glass which is the major component of glass ionomer as the filler.
- Small quantity of dehydrated polyalkenoic acid incorporated with filler particles,
- Setting reaction is light activated.
- Adhesive system used with compomer is based on acid etch found with all composite resin.
CALCIUM HYDROXIDE
INTRODUCTION
- Herman in 1920 introduced Ca(OH)2
- Ca(OH)2 is a white odorless powder
- It is strongly alkaline with a PH of 12.5
- It is classified as an astringent in Pharmacology.
COMPOSITION
SETTING REACTION
- Alkyl salicylate is chelating agent. On mixing this with paste containing zinc oxide and calcium hydroxide, amorphous calcium disalicylate is formed.
- The sulphonamide compound used in the paste is used as a carrier.
- Some cements contain paraffin oils instead of sulphonamides.
- These elements are more hydrophobic and release their calcium hydroxide more slowly.
- The Calcium hydroxide is present in stoichiometric excess.
Manipulation - Equal amount of base and catalyst dispensed on an oil impervious paper-pad.
- Mix to homogenous color.
- Apply on dentine as a lining.
Mixing time: 5-10 seconds
Working time: 30 seconds
Setting time: 1 minute
PROPERTIES
- Basic cement; pH : 11 – 12; used to neutralize acidic cements,
- Ideal to inhibit microbes esp. those found in carious dentine.
- Poor mechanical strength
- Compressive Strength : 8.3 to 10.3 MPa
- Tensile strength: 10 MPa
- Modulus of elasticity: low -0.37 Gpa/m2
- pH: high alkaline: 9.2 to 11.7
- Setting time: 2.5 – 5.5 minutes(powder form)
- Solubility and disintegration: solubility is high 0.4 to 7.8%
- High solubility in water.
MECHANISM OF ACTION
- High alkaline PH(11-13) Causes neutralization of acids produced by microorganisms.
- Antibacterial effect due to high PH.
- Seals the dentinal tubules offering dentin protection.
- Induces reparative dentin below existing dentin.
- Biocompatibility & calcific barrier enabling to maintain pulp vitality.
- Ca(OH)2 maintains a local state of alkaline by that is necessary for bone/dentin formation .
- Stimulates formation of reparative dentine and so is applied in instances of pulpal exposure (direct pulp- capping), or near pulpal exposure (indirect pulp- capping).
- Due to its high pH, it causes irritation to the pulp.
- Necrosis of cells adjacent to the cement, and transformation of mesenchymal cell into odontoblasts which start laying down reparative dentine.
MODE OF SUPPLY
- powder form – powder can be mixed with distilled water, saline solution to form a thick paste and applied as such.
- two paste system, one base paste another catalyst paste
- single paste (visible light).
USES
AS A LINER
The calcium hydroxide pastes are now in general use as lining materials. Their perceived advantages, in addition to their therapeutic effects are as follows:
- They have a rapid initial set in the cavity under the accelerating effect of moisture.
- They do not interfere with the setting reaction of the Bis-GMA resins.
- It is generally considered that the initial set of the material in thin sections is sufficiently hard to resist the applied condensation pressures that are required even for the lathe cut amalgam alloys.
AS A BASE AND SUBBASE
It should be placed deep in deep portions of the cavity preparation subsequently covered by a definitive supporting base.
- It helps in repair of pulpal tissue
- It provides chemical insulation
- It replaces the lost portion of the dentin.
- Calcium hydroxide bases are of relatively of low strength when compared to the other bases. These bases are used only for their therapeutic benefits, chemical insulation or for retaining the sub bases.
AS AN INTRACANAL MEDICAMENT
- plays a major role as an inter-visit dressing in the disinfection of the root canal system.
- Calcium hydroxide is normally used as slurry of Calcium hydroxide in a water base.
- At body temperature less than 0.2% of Calcium hydroxide is dissolved into ca++ and OH- ions.
- Calcium hydroxide needs water to dissolve. Therefore it is most advantageous to use water as a vehicle for the Calcium hydroxide paste
MCQs
1. Glass ionomer cements are composed of______________?
A. Zinc oxide powder and phosphoric acid
B. Aluminosillicate powder and polyacrylate
C. Alumino silicate powder and phosphoric acid
D. Zinc oxide powder and polyacrylate liquid
Answer: B
Composition of GIC
- Powder
- Acid soluble calcium fluroalumino silicate glass.
- Silica - 41.9%
- Alumina - 28.6%
- Aluminum fluoride - 1.6%
- Calcium fluoride - 15.7%
- Sodium fluoride - 9.3%
- Aluminum phosphate - 3.8%
- Fluoride portion act as ceramic flux. Strontium,
- Barium or zinc oxide provide radio opacity.
- Liquid :-
- Polyacrylic acid in the form co-polymer with itaconic acid & malice acid
- Tartaric acid: improves handling characteristic & increase working time.
- Medium of reaction & hydrates the reaction products
2.Which of the following is best for ‘cermet’ cement:
- Cermet cement is glass ionomer cement with porcelain ceramic fillers.
- Cermet cement is glass ionomer cement with silver amalgam alloy particles in it.
- Cermet cement is a mixture of glass ionomer and resin cements.
- Cermet cement is light curable glass ionomer cement.
Answer. b
Dental cermets, or silver cermets, are a type of restorative material dentists use to fill tooth cavities. Silver cermets were created to improve the wear resistance and hardness of another type of filling material, glass ionomer cements, through the addition of silver.
