Glass Ionomer Cement (GIC) - Science of Dental materials
Glass Ionomer Cements By: Abbas Naseem firstname.lastname@example.org Oct 17, 2010
INTRODUCTIONGlass ionomer cement is a tooth coloured material, introduced by Wilson &Kent in 1972.Material was based on reaction between silicate glass powder & polyacrylicacid.They bond chemically to tooth structure & release fluoride for relatively longperiod. GLASS IONOMER CEMENTS (a.k.a. glass polyalkenoate) Silicate Cement Polycarboxylate fluoride release Cement tooth color adhesion to tooth translucency structure Glass Ionomer Cement
CLASSIFICATIONType I. For lutingType II. For restoration Type II.1 Restorative esthetic Type II.2 Restorative reinforcedType III. For liner & basesType IV. Fissure & sealentType V. As Orthodontic cementType VI. For core build up
Physical Properties1. Low solubility2. Coefficient of thermal expansion similar to dentin3. Fluoride release and fluoride recharge4. High compressive strengths5. Bonds to tooth structure6. Low flexural strength7. Low shear strength8. Dimensional change (slight expansion) (shrinks on setting, expands with water sorption)9. Brittle10.Lacks translucency11.Rough surface texture
•Indications for use of Type II glass ionomer cements 1) non-stress bearing areas 2) class III and V restorations in adults 3) class I and II restorations in primary dentition 4) temporary or “caries control” restorations 5) crown margin repairs 6) cement base under amalgam, resin, ceramics, direct and indirect gold 7) core buildups when at least 3 walls of tooth are remaining (after crown preparation)•Contraindications 1) high stress applications I. class IV and class II restorations II. cusp replacement III. core build-ups with less than 3 sound walls remaining
SETTING REACTIONWhen the powder & liquid are mixed, Surface of glass particles are attacked by acid.Then Ca, Al, sodium, & fluoride ions are leached into aqueous medium.
Setting Reaction a) Acid-Base Reaction (metal + acid = salt) b) Water is critical for the reaction to occur c) If the material does not have this reaction, it is not a true glass ionomer. In other words, if you do not have to mix anything, the material is not a glass ionomer. Reaction Steps 1. Acid soluble glass is attacked by the polyacids releasing Ca++, Al+++, Na+, and F -. 2. Initially calcium, and later, aluminum replaces the hydrogens on the carboxyl groups of the polyacids to make calcium and aluminum polysalts 3. The salts hydrate to form a gel matrix while the unreacted portion of the glass particles are surrounded by silica gel that arises from the loss of the surface cations. 4. The set cement consists of unreacted glass surrounded by silica gel bound together by a matrix of hydrated calcium and aluminum polysalts. 5. Notice that fluoride is not an integral part of the matrix formation, therefore it is available for release without compromising the structural integrety of the restoration.
Reactions notes:1. Water is what hydrates the salts and allows them to crosslink. Too much water dilutes the metal ions resulting in an opaque restoration that lacks strength and hardness. If water is lost during setting, the maturation of the cement will be disrupted resulting in cracking and crazing of the material. Initially, water is loosely bound and the material will dessicate quite readily.2. At the initial set, calcium polysalts dominate the matrix and the cement is rather opaque. As post-set maturation progresses, aluminum polysalts become the dominate component and opacity decreases.
ROLE OF WATERReaction medium into which the cement forming cations are leached and transportedto react with poly acid to form a matrixHydrates siliceous hydrogel and metal polyacrylate salts formed.Water can be of two forms:1. Loosely bound water – Readily removed by Dessication2. Tightly bound water- cannot be removed and is associated with the hydration shellof the cation- polyacryate bond, particularly that of aluminium and some silica gelwater.With aging, tightly bound water increases, increasing the strength, modulus ofelasticity and decreasing the plasticity.Cement is stable in an atmosphere of 80% relative humidityHigh humidity absorbs water hygroscopic expansionDry conditions loses water shrinking and crazingLoss of water also retards cement formation.
Factors affecting the rate or setting1. Glass composition:Higher Alumina – Silica ratio, faster set and shorter working time.2. Particle Size: finer the powder, faster the set.3. Addition of Tartaric Acid:-Sharpens set without shortening the working time.4. Relative proportions of the constituents: Greater the proportion of glass and lower the proportion of water, the faster the set.5. Temperature
CEMENT STRUCTURE• Cored filler is bound together by a hydrogel of calcium and aluminium polyacrylates that contains fluorine as fluoroaluminium polyacrylate.• Filler particles contain a glassy core pitted by a siliceous hydrogel.
GLASS IONOMERS HYBRID = SC [Powder] and PCC [Liquid] = A.S.P.A. H2O Si+4 PAASiO2, in Al+3 SiO2,Al2O3, H2O Na+ Al2O3,Na, Ca, Ca+2 Na, Ca,F F- F PAA Residual Glass Particle SiO2, POLYACRYLATE HYDROGEL Al2O3, (initially Ca polyacrylate gel Na, Ca, and later Al polyacrylate gel) F Si+4, Al+3, Ca+2, Na+, F- Ions
SETTING STEPSCalcium poly salts are formed first, then followed by aluminum poly salts which crosslink with poly anion chain.Set cement consist of unreacted powder particle surrounded by silica gel in amorphousmatrix 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
STAGES IN SETTING REACTION (Based on the work of Crisp and Wilson 1972-1974)1. Decomposition: of glass and release of cement forming metal ions (A13+ and Ca2+)2. Migration: of these metal ions into the aqueous phase of the cement.3. Gelation: of the polyacid by metal ions leading to set.4. Post set hardening: when metal ions become increasingly bound to the polyacid chain. (continues for 24 hrs)5. Further Slow Maturation: takes place even after 24 hrs. Translucency develops further as does resistance of desiccation and acid attack.
PROPERTIESAdhesion :-☻ 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. 1. Primarily chemical (calcium – carboxyl groups) 2. Micromechanical 3. Bond to enamel better than bond to dentin 4. Barriers to adhesion i. smear layer not removed ii. contamination (blood, saliva, too much water) iii. setting reaction too far advanced before application (cement must have a glossy surface when applying to tooth.)Esthetics :-GIC is tooth coloured material & available in differentshades.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 - High buffering capacity of hydroxy apatite. - Large molecular weight of the polyacrylic acid ,which prevents entry into dentinal tubules. a) Pulp reaction – ZOE < Glass Ionomer < Zinc Phosphate b) Powder:liquid ratio influences acidity c) Manufacturer recommends using a Ca(OH)2 liner when within 0.5 mm’s of the dental pulpSolubility & Disintegration:-Initial solubility is high due to leaching of intermediate products.The complete setting reaction takes place in 24 hrs, cement should be protectedfrom saliva during this period.
Anticariogenic properties :-•Fluoride is released from glass ionomer at the time of mixing & lies with in matrix.Fluoride can be released out without affecting the physical properties of cement.Initial release is high. But declines after 3months.After this, fluoride release continuous for along period.Fluoride can also be taken up into thecement during topical fluoride treatmentand released again ,thus GIC act as fluoridereservoir.
Fluoride Release1. derived from flux used during glass fusion2. fluoride release is not part of the structural matrix of the material3. fluoride released in form of NaF4. initial high fluoride release (1 – 2 day burst) followed by low sustained release, constant release occurs at about 3 weeks5. fluoride release requires water movement6. more fluoride is released from Type II glass ionomers than from liners or luting cements7. applying varnish or resin to the surface of the restoration decreases fluoride release until abrasion removes the coating.8. restorations with larger surface area release more fluoride9. materials must be recharged in order to provide fluoride levels necessary to remineralize tooth structure.10. most recharged fluoride released again in 24 hours11. application of acidic fluorides should be avoided with glass ionomer restorations as the acid will cause surface deterioration of the restoration.12. higher fluoride releasing materials are more effective at reducing recurrent caries than are low fluoride releasing materials.
MANIPULATION1. Preparation of tooth surface2. Proportioning & mixing3. Protection of cement during setting4. Finishing5. Protection of cement after setting
MANIPULATION1.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 3.6:1 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.
Advantages of glass ionomer Disadvantages of glass ionomer1. bonds to enamel and dentin 1. opacity higher than resin2. significant fluoride release, can be 2. less polishability than resin recharged 3. poor wear resistance 4. brittle, poor tensile strength3. coefficient of thermal expansion similar to 5. poor longevity in xerostomic tooth structure patients4. tooth colored5. low thermal conductivity ♦ Low fracture resistance.6. 10 year clinical studies (conventional GI) ♦ Low wear resistance. ♦ Water sensitive during setting♣ Inherent adhesion to the tooth surface. phase .♣ Good marginal seal. ♦ Less esthetic compared to composite.♣ Anticariogenic property.♣ Biocompatibilty♣ Minimal cavity preparation required.
Uses :-1. Anterior esthetic restoration material for class III & V restorations.2. For luting.3. For core build up.4. For eroded area .5. For atraumatic restorative treatment.6. As an orthodontic bracket adhesive.7. As restoration for deciduous teeth.8. 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 goodadhesion with GIC.Place Type III GIC into prepared cavity.After setting, etch the enamel & GICwith orthophosphoric acid for 15seconds.This will improve micromechanicalbond to composite resin.Apply a thin layer of low viscosityenamel bonding agent & finally place thecomposite resin over GIC & light cure it.
MODIFICATIONSModifications in the powder:• Dried Poly Acrylic Acid (Anhydrous GIC)• Silver-Tin Alloy (Miracle Mix)• Silver-Palladium/ Titanium (Cermet cement)• BisGMA, TEGDMA, HEMA (Light cure/Dual cure GIC)Modifications in the liquid:• Only water and tartaric acid (Anhydrous GIC)• HEMA (Light cure components)
MODIFICATIONS1.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.
• Resin Modified Glass Ionomer – Also known as: • Visible Light Cure Glass Ionomers (VLC) • Hybrid Glass Ionomers – Composition • Liquid – Polyacrylic acid copolymer – Tartaric acid – Methacrylate groups (HEMA) – Photoinitiator • Powder – Same powder as chemical cure glass ionomer – Photosensitizer • Setting Reaction – Polymerization of resin + normal glass ionomer acid-base reaction – If not supplied in two components, not a glass ionomer
•Requirements to be a Resin Modified Glass Ionomer Cement i. Acid-base reaction critical to setting ii. Have a pH change & formation of carboxylate salt iii. Material must contain fluoroaluminosilicate glass, a polymeric carboxylic acid and water•Comparison to Conventional Glass Ionomer I. Generally improved physical properties II. Improved shades and translucency III. Water sensitivity reduced IV. Can be finished almost immediately V. Slightly less fluoride release VI. Fluoride can still be recharged VII. Slight increase in thermal expansion VIII. Can be dual or tri-cure•Precautions I. Must be light cured to achieve good bond II. Fill in increments of 2 mm’s or less III. Bond to dentin highly dependent on surface conditioning
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.Cerment:-• Bonding of silver particles to glass ionomer particles by fusion through high temperature sintering.a) Strength Silver alloy admix (silver amalgam alloy particles mixed with glass particles)b) Cermet (glass sintered with silver)a) Physical Properties compared to conventional glass ionomer cement a) Strength>> Same b) Fracture Toughness>> Same c) Wear Resistance>> Increased slightly d) Fluoride release >> reduced with Cermet, same or slightly increased with admix
4.Compomer :- ( POLYACID MODIFIED COMPOSITE RESINS )1. Compomer is a composite resin that uses an ionomer glass which is the major component of glass ionomer as the filler.2. Small quantity of dehydrated polyalkenoic acid incorporated with filler particles,3. Setting reaction is light activated.4. Adhesive system used with compomer is based on acid etch found with all composite resin. Combination of composites (comp) and glass ionomers (omers). Compomer is a one-paste material consisting of fillers and a matrix that is similar to that of composite resin. contains fluoroaluminosilicate glass powder as filler to release fluoride. Contains dimethacrylate monomer and carboxylic groups along with ion leachable glass. There is no water in the composition Glass particles are partially silanated to ensure some bonding with the matrix. contains strontium or some other metal to make the material radiopaque
Giomers•A recent addition to the continuum of hybrid materials is a class of anhydrous resin-based restoratives that utilizes prereacted glass ionomer technology (PRG).•E.g. Beautiful (Shofu); Reactmer paste (Shofu).•Known as “giomers” in Japanese market, these materials incorporate fillers that areproduced from the complete or partial reaction of ion-leachable glasses withpolyalkenoic acid.•giomers may contiain either fully prereacted (F-PRG) or surface prereacted (S-PRG)fillers as part of the total filler composition.•Unlike compomers, immediate fluoride release may occur from the PRG fillerswithout the need for in-situ acid-base reaction via water sorption.
Conventional Resin- Compomers Fluoride Composite Glass Modified Releasing Resin Ionomer Glass Ionomer Resin Typical Ketac-fil Fuji II LC, Dyract AP, GeriStore, Herculite XRV, Products Fuji II, Fuji Photac-fil Elan, F2000, Variglass, Prisma TPH, IX, *Ketac- Quik, Vitremer Compoglass Resinomer, Heliomolar, silver, F Hytac Tetric Ceram, Miracle Mix Solitaire, SureFil Fluoride High High Medium Low Lowest Release (*Ketac-silver medium) Fluoride High High Some Very Low None Recharge Thermal Lowest Medium Highest ExpansionTranslucency Lowest Highest Tensile Lowest Highest Strength & Fracture Toughness
THANK YOU Abbas Naseem(BDS) Dated: Oct 17, 2010 email@example.com