Glass ionomer cement

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Glass ionomer cement

  1. 1. All about Glass Ionomer Cements by dr.anoop.v.nair
  2. 2. • Introduction • Definitions & terminologies • Scientific & clinical development • Classification • Composition • Setting reaction • Water balance • Adhesion • Properties • Clinical implications • Instructions to dental assistants • Review of literature • References • Summary & conclusion
  3. 3. DEFINITIONS & TERMINOLOGIES
  4. 4. • The word “ionomer” was coined by Dupont company • Describe its range of polymers containing a small proportion of ionized or ionizable groups generally of the order of 5% to 10%. • Does not properly apply to components of GI dental cement • Therefore the term Glass polyalkenoate cement was devised. • Systematic name in Chemical Abstracts ; Official ISO terminology • Does not apply to recently developed poly(vinyl phosphonic acid) cements ---- Glass Polyphosphonates. • Therefore the term “Glass - ionomer cement” is a generic one for all glass polyacid cements.
  5. 5. • Glass : Acid-decomposable glass • Acidic polymer :Typically poly(acrylic acid) • Successful acids are – water soluble & polyelectrolytes.  Acid-base reaction :The cement forming reaction is defined as the conversion of initially viscous paste to a hard solid, & in a true glass-ionomer cement this reaction takes place within a clinically acceptable time i.e, a few minutes. Definition of glass ionomer cement A cement that consists of a basic glass & an acidic polymer which sets by an acid-base reaction between these components. (Mclean & Wilson 1994)
  6. 6. The essential elements of a true glass ionomer : • Acid-base setting reaction • Ion-exchange adhesion with underlying tooth structure • Continuing ion activity, with mobility of fluoride, calcium and phosphate ions
  7. 7. • Definition (Akinmade & nicholson, 1993) water based cement where-in following mixing, the glass powder & polyalkenoic acid undergo an acid/base setting reaction. The acid attacks the surface of powder particles, releasing calcium & aluminium ions, thus developing a diffusion-based adhesion between powder & liquid
  8. 8. Types of glass ionomer cements 1. Based on chemical composition 2 types of glass ionomer : • Glass-ionomer cement • Glass polyalkenoates • Glass polyphosphonates • Glass-ionomer hybrid materials • Resin modified glass-ionomer 2. Based on types of cure : • Autocure : Chemical cure – acid-base reaction • Dualcure : Light initiation followed by acid-base reaction • Tricure : Autocure resin reaction in remaining uncured resin
  9. 9. Glass-ionomer hybrid materials • The term “Resin-modified glass-ionomer” originally used by Antonucci et al, is the trivial name. • Systematic name, for precise chemical nomenclature as in ISO standards is “Resin-modified glass- polyalkenoate” • Consists of components of glass ionomer, modified by inclusion of a small quantity of additional resin, mostly HEMA. • They set partly by acid-base reaction & partly by photochemical polymerization.
  10. 10. Other polymerizable restorative materials : Polyacid modified composite resins (Compomers) • Donot belong to glass-ionomer category. • The correct ingredients are present (acid decomposable glass & possibly some polymeric acid) but in an insufficient amount to promote acid-base cure in dark • Donot set without light activation. • Donot bond to tooth structure through ion-exchange mechanism. • Fluoride reservoir effect of glass ionomer is not available.
  11. 11. Diagram showing theoritical composition of various resin-modified materials & the potentialeffect of modifying the relative percentage of the contents As resin component increases – acid-base reaction reduces ; benefits of glass ionomer are lost & the material becomes light activated only Compomers would belong in one of the middle 2 bars (acid-base component is negated & therefore belong to composite resin end of table)
  12. 12. Compomer - – anhydrous resin-based material – not possible to have ion transport within it. Fluoride release is minimal At 20 min ; compomer does not show signs of set if not light activated Resin modified glass ionomers -By 7-10min show signs of chemical set -Over the next 15020min becomes quite hard Mix under a light proof cover
  13. 13. SCIENTIFIC & CLINICAL DEVELOPMENT • INVENTION : • Resulted directly from basic studies on dental silicate cements & studies where the phosphoric acid in dental silicate cements were replaced by organic chelating acids.
  14. 14. EARLY DEVELOPMENT • 1966 : A.D.Wilson – examined cements prepared by mixing dental silicate glass powder with aqueous solutions of various organic acids (including poly(acrylic acid) - unworkable, set slowly, sluggish, not hydrolytically stable.Silica glass : Highly cross linked network of connected silicon & oxygen atoms; does not carry an electric charge Impervious to acid attack Ionomer glass : ionic polymer ; contains negative sites which are vulnerable to attack by positive hydrogen ions of acid
  15. 15. • 1968,1969 : A.D.Wilson + Kent & Lewis – found that hydrolytically stable cements could be produced by employing novel glass formulations. • 1968 : Kent – found that setting of these cements was controlled by Al2O3/ SiO2 ratio in the glass. • 1973,1979 : Kent et al – found a glass that was high in fluoride that gave a usable cementASPA 1 (aluminosilicate polycrylates).
  16. 16. • 1972 (reported in 1976):Wilson & Crisp – key discovery – tartaric acid – modified the cement-forming reaction, thus improving manipulation, extending working time & greatly sharpening setting rate. • This refinement of ASPA I was termed ASPA II & constituted the first practical GIC. • 1975 : Crisp et al – the disadvantage for general practice was that its liquid tended to gel. • 1975,1977 : Crisp &Wilson – developed copolymer of acrylic & itaconic acid that did not gel at high (50%) concentration in aqueous solution • ASPA IV. But this was inferior in other properties to ASPA II
  17. 17. • 1974 : McLean &Wilson – used it for fissure sealing & filling • 1977c : McLean &Wilson – ideal for restoration of classV erosion lesions. • 1979 : Crisp et al – ASPA X – with excellent translucency. • 1977 :Wilson et al – ASPA IVa – fine grained version for luting. • With less viscous polyacid, lacked the mobility of traditional zinc phosphate cement. • 1977 : Mclean &Wilson – in a review article suggested use in pediatric dentistry & as a liner in composite – resin / ionomer laminate.
  18. 18. LATER DEVELOPMENT • 1973 :Wilson & Kent – reported use of poly(acrylic acid) in dry powder form blended with glass powder. • The cement was formed by mixing this powder with water or tartaric acid solutions. • 1984 : Prosser et al – re-examined the above & resulted in development of ASPAV • ASPAVa – a water-hardening luting agent – proved to have the mixing qualities & mobility of zinc phosphate cement. • 1985 : McLean et al – the original 1977 idea of using composite resin / ionomer laminate was revived in a modified form. • GIC & enamel was etched – double etch technique (composite resin was attached micromechanically to enamel & GIC bonded indirectly to dentin).
  19. 19. • 1984 : Hunt & Knight – tunnel preparation for Class II • The reasoning behind the technique – GIC core bonds enamel shell together, preventing fracture (described by Hunt 1984, & Mclean 1987) • 1980 : Sced & Wilson & 1983 : Simmons – incorporated metallic oxides & metal alloy fillers, to improve strength of GIC. • 1985 : McLean & Gasser – fused silver particles onto ionomer glass, giving cement radioopacity, burnishability, smoother surface, increased wear resistance (reported by Moore et al 1985) • 1986 : McLean – Developed new Cermet cements for clinical use.
  20. 20. • 1988 :Wilson & McLean – Highly viscous glass ionomer cements • Late 1980’s : Resin-modified glass ionomer cements
  21. 21. COMPOSITION
  22. 22. Glass ionomer cement is defined as an acid-base reaction cement (Wilson 1978, Wygant 1958) Basic component Acid component Calcium aluminosilicate glass containing fluoride Polyelectrolyte which is a homopolymer or copolymer of unsaturated carboxylic acids known scientifically as alkenoic acids.
  23. 23. Types of Calcium fluoroaluminosilicate glass: SiO2 - Al2O3 - CaF2 (Simple 3-component system) SiO2 - Al2O3 - CaF2 - AlPO4 SiO2 - Al2O3 - CaF2 - AlPO4 – Na3AlF6 Components are fused between 1100°C - 1500°C Melt poured onto metal plate / into water Glass then ground to fine powder (Maximum particle size: 50µm for restorative & 20µm for luting) Chemical composition of original ionomer glass (G-200) (Modified from Barry et al 1979) SiO2 30.1% Al2O3 19.9% AlF3 2.6% CaF2 34.5% NaF 3.7% AlPO4 10.0%
  24. 24. Fluoride – Lowers temperature of fusion Improves working characteristics of cement paste Increases markedly strength of set cement Enhances translucency Contributes to cements therapeutic value Cryolite (Na3AlF6) - Supplements fluxing action of CaF2 Reduces temperature at which glass will fuse Increases translucency of set cement AlPO4 - Increases translucency Adds body to set cement
  25. 25. Visual appearance of glass – clear / opal / opaque Glasses high in SiO2 (>40%) - transparent Glasses high in Al2O3 - opaque Al2O3 / SiO2 ratio : Crucial , required to be 1:2 Increase in ratio • Decreases setting time • Clear to opaque • Compressive strength increases • Determines the rate at which breakdown of glass matrix occurs Negative sites are vulnerable to acid attack ; if enough Al atoms, all the connecting links in network will be completely decomposed ; such a glass has cement forming potential
  26. 26. VARIATION ON BASIC GLASS COMPOSITION 1. Calcium may be replaced by strontium / barium / lanthanum 2. Disperse phase glasses Flexural strength 3. Fibre re-inforcement (eg. Alumina fibres ) Flexural strength 4. Metallic inclusions Radioopaque glass
  27. 27. POLYELECTROLYTES • Are both electrolytes and polymers • includes copolymers of unsaturated mono-, di-, and tri- carboxylic acids, particularly those of acrylic acids. • The more important carboxylic acids in ionomer include acrylic acid, maleic acid and itaconic acid. • The polyacids may be • in the form of concentrated aqueous solution (40-50% by mass) • Blended dry with glass powder
  28. 28. COMPOSITION OF ASPA CEMENTS • ASPA I – G-200 + 50% polyacrylic acid • ASPA II – G-200 + 47.5% polyacrylic acid + 5% tartaric acid • ASPA III – G-200 + 45% polyacrylic acid + 5% tartaric acid + 5% methyl alcohol • ASPA IV – G-200 + 47.5% copolymer of acrylic & itaconic acid 2:1 ratio + 5% tartaric acid
  29. 29. Different configurations affect adhesion ?? • Polyacrylic acid cements – bond more strongly to enamel & dentin (Aboush & Jenkins, 1986) • Copolymer cements – less resistant to acid attack than Polyacrylic acid cements (Setchell et al, 1985) • Copolymer cements – harder than polyacrylic acid aids early finishing (Mount & Makinson 1982, Matis & Philips 1986)
  30. 30. Effect of molecular weight and concentration of polyacrylic acid • Increase in molecular weight and concentration • Shortens setting time • Increases strength • Increased viscosity of mix
  31. 31. Water • Reaction medium • Plays role in hydrating reaction products i.e metal polyalkenoate salts and silica gel
  32. 32. Tartaric acid • The principal obstacle in developing practical GIC was • Sluggish nature of set • Working time was minimal • Slow hardening • In 1976Wilson et al reported addition of tartaric acid made glass ionomer cement a practical one • It enabled reduction of fluoride • Delayed onset of viscosity
  33. 33. Other additives Working time Setting time Polyphosphates Metals Stannous fluoride
  34. 34. SETTING REACTION
  35. 35. Cement forming reaction of glass ionomer cement Showing extraction of ions from the glass, migration into aqueous phase, & subsequent precipitation as polyanion hydrogels
  36. 36. There are 4 overlapping stages that can be identified but not clearly separated out Unattacked glass particles dispersed in polyacid liquid Outer layer of glass particles is depleted of metal ions & degraded to silica gel. Metal ions migrate to liquid, where they remian in soluble form (red dots) Initial gelation Soluble metal ions remain .. The cement is still vulnerable to moisture Fully hardened glass ionomer in an insoluble form Cement is no longer vulnerable to attack by moisture Decomposition Migration Gelation Further slow maturation Post-set hardening
  37. 37. Glass structure unattacked (electrically charged network) H ions attack network dwelling ions, Ca 2+ & Na+ H ions attack the charged aluminosilicate network, destroying the glass network & liberating Al ions 1 st s t a g e 2 n d s t a g e 3 r d s t a g e Silicic acid formed condenses to form silica gel
  38. 38. Setting reaction of auto cure cements Only the surface of each particle is atacked by the acid Releasing Ca & Al ions, & F ions which remain free & are not part of the matrix The calcium polyacrylate chains form first then the aluminium polyacrylate chains follow immediately By stage 3, there is a degree of maturity, with more calcium & aluminium chains Also a halo of siliceous hydrogel surrounding each glass particle, which increases resistance to acid attack Note : these chains can break & reform throughout the life of the restoration
  39. 39. Stage 1 : Decomposition of glass & migration of metal ions (Dissolution) • 20-30% of glass is attacked by polyacid • Surface of the glass particles decompose • Releasing metal ions (Al 3+ , Ca 2+ ) • Glass network breaks down into silicic acid which polymerises at surface of the glass powder • As pH of aqueous phase increases, polyacrylic acid will ionize & create electrostatic field that will aid the migration of liberated cations into the aqueous phase • The ions thus migrate into the aqueous phase • As the negative charge increases, polymer chains unwind, viscosity increases
  40. 40. Stage 2 : Precipitation of salts; gelation & hardening • At a critical pH & ionic concentration, precipitation of insoluble polyacrylates begins • Ca 2+ &Al 3+ bind to polyanions via carboxylate groups • The initial set is achieved by the cross-linking of the more readily available Ca 2+ (forming clinically hard surface within 4minutes of start of mix) • Maturation occurs over the next 24hours when the less mobile Al 3+ become bound within the cement matrix, leading to more rigid cross- linking between poly (alkenoic acid) chains • Aluminium polyacrylate ultimately predominates in the matrix
  41. 41. Few points to remember …. 1. Why not sodium ions ??? 2. What happens to fluoride & phosphate ions?? 3. Do all COOH convert to COO- 4. Period of vulnerability ?? 5. Causes of gelation
  42. 42. 1.Why not sodium ions ??? • They cannot displace the hydrogen sphere • They are not site bound, because of their low ionic charge • They do not precipitate as polyacrylates What happens to them ?? • They contribute to formation of orthosilicic acid on the surface of particles • As pH rises, this converts to silica gel which assists in binding the powder to matrix
  43. 43. 2.What happens to fluoride & phosphate ions?? • They form insoluble salts and complexes
  44. 44. 3. Do all COOH convert to COO-?? …. No 1. When most of the carboxylic acid groups have ionized • Negative charge on polymer chain increases • Positively charged H ions now become very strongly bound to remaining un-ionized carboxylic acid group & not easily replaced by metal ions 2. As density of cross-links increase • Hinders movement of metal ions towards carboxyl sites
  45. 45. 4. Period of vulnerability ?? • Till soluble ions insoluble matrix • After material is set, but not fully hardened; a proportion of ions (Ca 2+ ,Al 3+ polyacrylate ions ) are in soluble form • Can be dissolved out by aqueous fluids • Weakened cement • Softened surface • Opaque restoration [In a freshly set cement, calcium polyacrylate predominate, they are more vulnerable to water than aluminium polyacrylates]
  46. 46. 5. Causes of gelation • Multivalent Ca 2+ ,Al 3+ ions displace various hydration spheres that interpose themselves between cation-anion pairs • Cation-polyacrylate ion pairs are formed • Desolvation of hydration spheres renders ionic pairs more hydrophobic and precipitation occurs Chain entanglement Ionic cross-linking Hydrogen bonds Involved in matrix formation
  47. 47. Ca 2+ bridge 2 chains ; so do Al 3+ bridge 3?? Stearically unlikely because of presence of negatively charged ligands Coordination number of Al is 6 in water, therefore it should be attached to 6 ligands In glass ionomer cement, ligands are COO-, F-, OH-, water molecules Possible molecular structure of the set glass ionomer cement A- represents F- / OH- Fig 3-4
  48. 48. Stage 3 : Hydration of salts ; Hardening & Slow maturation • Progressive hydration of matrix salts, leading to sharp improvement in physical properties • Continues for about 24hours • Slight expansion under high humidity • Further changes occur for >= 1 year What are the underlying chemical changes ? What are the indicators of these slow changes ?
  49. 49. What are the underlying chemical changes ? • Increase in bound water (Wilson et al) • Slow increase in cross-linking (Hill,1986) • Slow replacement of residue carboxyl hydrogen ions by ,metal ions, increasing cross-linking • Increasing predominance of Al over Ca in the matrix What are the indicators of these slow changes ? • Translucency improves • Becomes more resistant to dessication • Strength continues to increase for atleast 1 year • Ability to absorb / loose water decreases with age • Initially the cement is plastic, then as it ages rigidity increases, approaching that of phosphate bonded cements
  50. 50. Cement structure Hydrogel matrix : Ca & Al polyacrylates + fluorine as fluoroaluminium polyacrylate Water – in bound & free form Glass core pitted by selective etching Siliceous hydrogel (with fluorite crystallites) Smaller filler particles; contain only siliceous hydrogel Cohesive forces binding matrix together : mixture of ionic cross-links, hydrogen bridges, chain entanglement This framework is porous ; ions with small dimensions (Eg. OH- & F-) are free to move through the material
  51. 51. Role of water
  52. 52. Glass ionomer cements are water based cements - they contain water - make water during setting reaction Role of water / Significance  Water plays an important role in Setting reaction Final structure -Reaction medium -Coordinating species -Hydrating species -plasticizer  In the set cement 24% is water Loosely bound Tightly bound As it ages tightly bound : loosely bound increases
  53. 53. Early contamination Loss of calcium polyacrylate chains Absorption of water Loss of translucency Loss of physical properties Leaves cement susceptible to erosion Dehydration Cracking & fissuring of cement Softening of surface Loss of matrix-forming ions
  54. 54. Factors affecting setting characteristics • Role of fluoride • Role of tartaric acid Role of fluoride Fluoride forms metal complexes They retard the binding of cation to anion sites on polyacrylate chain Delays gelation & prolongs working time Release of H+ Acidity of paste increases Delays pH dependant gelation
  55. 55. Role of tartaric acid • Tartaric acid is stronger than polyacrylic acid Forms stronger complex with Al Therefore increases extraction of Al from glass • Initially tartaric acid alone complexes cations As neutalisation proceeds & pH ~ 3 Polyacrylic acid becomes neutralised by metal ions until cement sets at pH ~ 5-5.5 • Also ionization of polyacrylic acid is suppressed & unwinding of the chain is retarded, resulting in decrease in viscosity & delaying gelation • Once gelation occurs, tartaric acid accelerates hardening • Tartaric acid & calcium react preferentially therefore initial set may be due to formation of calcium tartarate • Tartaric acid controls initial setting of cement • Improves manipulation • Increases working time • Sharpens set by accelerating precipitation • Increases strength
  56. 56. Factors affecting rate of setting 1. Glass composition : increase in Al/Si ratio – faster set 2. Particle size : finer – faster set 3. Tartaric acid – sharpens set without shortening working time 4. Relative proportion of constituents – Powder : Liquid 5. Temperature of mixing – increase – faster set Among these the factors within the province of the clinician are Temperature of mixing Powder : Liquid
  57. 57. Factors within the province of the clinician 1.Temperature of mixing • Chilling powder & mixing pad – increases working time up to 25% (Mc Lean 1970) • Increase in working time occurs without loss of physical properties (Makinson 1978) • Word of warning – • Chilling of liquid will cause gelation • Increase in humidity & temperature below dew point – weakens the cement 2. Powder : Liquid • Increase in powder – faster set • But insufficient liquid – decrease in translucency of the set cement
  58. 58. Setting reaction of resin-modified light cured materials • 2 distinct mechanisms : • The original acid – base setting reaction • Vinyl polymerisation of acrylate groups that can be activated through the presence of photo initiators such as camphorquinone
  59. 59. When mixed, original acid base reaction appears to continue without interruption Resin component provides as umbrella effect Some degree of cross linking may be present between 2 matrices ; both reactions may proceed without interference Over time, any remaining resin not affected by light - activation may undergo further chemical setting reaction A “Dark – cure reaction” Lead to the term “Tricure” or “Triple-cure” Light activation
  60. 60. Is depth of cure an important factor??? …Yes… 1. Lack of water inhibition of acid-base reaction 2. Residual HEMA in lower levels, closest to pulp 3. Fully light activated restoration is notably superior in physical properties Therefore, depth of cure is important ; incremental build up recommended Unless, a mechanism for chemical curing of methacrylate groups is incorporated “Redox” catalyst Allows for continuing polymerisation in absence of light activation, thus ensuring activation of any remaining HEMA Micro – encapsulated potassium persulphate & ascorbic acid
  61. 61. The red chains represent fully activated resins to the depth of penetration of activator light Showing influence of resins incorporated into the glass ionomer Note : there is already a degree of cross-linking between the polyalkenoic acid chains and the polymer chains Showing progress of setting reaction of resin component of RMGIC Autocure redox reaction continues until entire mass is set Red chains represent completion of auto cure setting Note complete cross linking between polyalkenoic acid chains & polymer chains
  62. 62. To summarise.. 2 distinct types of setting reaction occur : Acid-base neutralisation reaction Free-radical metharylate cure Relationship between the 2 reactions may take one of 2 forms Formation of 2 separate matrices  Ionomer salt hydrogel  Poly-HEMA matrix Multiple cross-linking pendant methacrylate groups may replace a small fraction of carboxylate groups of polyacrylic acid, thus preventing separation of 2 potential matrices Cross – linking of polymer chains may take place through 1/more of the following reactions Acid – base reaction Light – cure mechanism Oxidation – reduction reaction Full physical properties are not achieved till acid – base reaction continues for some days
  63. 63. Structure of set cement • RMGIC is presumed to have either • A multiple cross – linked matrix or • Matrix containing 2 separate phases Depth of cure 3-4mm
  64. 64. Criticisms against RMGI 1. HEMA – monomer – toxic – relative lack of biocompatibility, potential for allergic response 2. HEMA – hydrophilic – set material takes up water – expansion + less resistance to wear & erosion 3. Potential for color change over time (Doray 1994) 4. HEMA – low molecular weight monomer – more polymerisation shrinkage + substantial exotherm that can last for sometime
  65. 65. Setting reaction of resin – modified auto cure material • Mixing of powder + liquid • Usual acid base reaction initiated • Catalyst in powder will initiate polymeristaion of HEMA & cross-linkable monomers • Ultimately, there will be cross-linking between 2 systems & the entire mass will set hard with uniform physical properties
  66. 66. Setting reaction of light initiated auto cure material • Involves enhancing speed of acid-base reaction by utilizing a simple physical principle • No resin is added • The glass ionomer is colored (Eg. red) ; on irradiation with a blue halogen activator light , acid-base reaction will take place more rapidly • Setting time is reduced dramatically • No heat generation • Physical properties not downgraded • Highly bactericidal • Flows easily • Easily identified Uses : Fissure sealant Uncooperative patient Root surface protection Lining/ base in very deep cavities Transitional restoration during stabilization phase Temporary seal for endodontics
  67. 67. ADHESION
  68. 68. • Glass ionomer cements are the only restorative materials that depend primarily on chemical bond to tooth structure. • They form an ionic bond to the hydroxyapatite at the dentin surface and also obtain mechanical retention from microporosities in the hydroxyapatite.
  69. 69. Bond strength to dentin : (Richard S. Schwartz et al JOE,vol.31,no.3,March2005,156) • Lower initial bond strength compared to resins (around 8MPa) • Despite this they succeed clinically because of the following factors: • They form “dynamic” bond. As the interface is stressed, bonds are broken, but new bonds are formed. • Low polymerization shrinkage • Coefficient of thermal expansion similar to tooth structure
  70. 70. Barriers to adhesion : 1. Water – aqueous fluids in dentin & enamel • Hydrophilic, highly ionic GIC competes successfully with water because of its multiplicity of carboxyl groups that form H bonds with the substrate 2. Dynamic nature of tooth material • Enamel : ion exchange • Dentin : living material subject to change • The adhesive bond must have dynamic character • Polymeric nature of glass ionomer ensures multiplicity of bonds between GIC and substrate. Scission of single bond does not lead to failure because the bond can reform. Bonding to these is like trying to bond to shifting sand
  71. 71. Mechanism of adhesion to enamel & dentin • Smith (1968): Chelation of calcium contained in apatite – involved in adhesion • Beech (1973): Suggested interaction of polyacrylic acid & apatite. • Bonding only to apatite, therefore weaker adhesion of GIC to dentine and non existence of adhesion to decalcified dentine. • Wilson (1974):Considered possibility of polyacrylates bonding to collagen. • Initially, when paste is fluid, adhesion is by H-bonding provided by free carboxyl groups present in fresh mix. • As cement ages, H bonds are progressively replaced by ionic bonds, the cations coming from cement or hydroxyapatite. • McLean &Wilson (1977): Hypothesized presence of an intermediate later between cement 7 tooth surface. • Wilson, Prosser & Powis (1983): Postulated the adsorption phenomenon of bond to mineralized tissue.
  72. 72. Adhesion Bond to mineralized tissue • Diffusion • Adsorption phenomenon Bond to collagen • H bonding • Metallic ion bridging Bond to mineralized tissue Phosphate ions are displaced from apatite by carboxyl groups. To retain electrical neutrality, phosphate takes with it calcium. Setting of the material + dissolution of enamel & dentin surface results in buffering of polyacid. Rise in local pH & reprecipitation of minerals at cement-tooth interface occurs. Therefore chemical bond is achieved by a calcium phosphate polyalkenoate crystalline structure acting as an interface between enamel or dentin & the set material. Bond to collagen May occur by H bonding or metallic ion bridging between carboxyl groups on polyacid & collagen molecules of dentine. Chain length may also be an important factor in adhesion. The GIC is based on a polymer chain that is capable of bridging gaps between the cement body and the substrate.
  73. 73. The poly (alkenoic acid ) chains actually penetrate the surface of both enamle & dentine & displace phosphate ions, releasing them into the cement Each phosphate ion takes with it a calcium ion to maintain electrolytic balance, leading to an ion-enriched layer at the interface As the acid is buffered by the release of ions the pH will rise & the interface will set as a new ion-enriched material between the tooth & the restoration.
  74. 74. Bond strength & nature of polyacid • Cements based on polyacrylic acid appear to bond more strongly than those based on copolymers of acrylic acid with itaconic & maleic acids (Aboush & Jenkins, 1986) • Adhesion of cermet cements is inferior to conventional GIC (Thorton et al, 1986) • Pretreatment of enamel & dentin with polyacrylic acid, which is not washed off, so that intermediary bonding is formed. (Powis, 1986)
  75. 75. Improving adhesion – surface conditioning : • Surface conditioning – McLean &Wilson (1977) first used the term, to differentiate from acid etching. • Powis et al (1982);Aboush & Jenkins (1986) – smoother the surface stronger the bond. • Surface irregularity --- air entrapment + stress concentration • Ideal requirement of surface conditioners (Mount, 1984) • Isotonic (to decrease osmotic effect) • The Ph = 5.5 – 8 (neutral) • Nontoxic • Compatible with chemistry of cement • Water soluble, be easily removed • Not deplete enamel & dentine chemically • Enhance surface chemically in preparation for bonding.
  76. 76. Agents Proposed by Conc entr ation D u r at io n Advantage Disadvantage Polyacrylic acid Powis et al (1982) 25% Enamel – etches slightly & removes polishing marks. Dentin - Removes debris, smoothes irregularities & opens up tubules May cause sensitivity with luting agents Mount (1984) 1 0 se c Long et al (1986) 30- 35% Tannic acid Powis et al 3 0 se c Enamel – smooth featureless surface without etching/ decalcification Dentine – Tubules not opened Mineralizing solutions (Eg. Levine et al solution & ITS solution) 2- 3 m in Smear layer will be included in ion-exchange layer & will not interfere with adhesion Forms calcium & phosphate rich layer between GIC & tooth - ineffective
  77. 77. CLASSIFICATION 1. ByWilson & McLean (1988) 2. By McLean et al (1994) 3. By Smith /Wright (1994)
  78. 78. Classification by Wilson & Mclean (1988) • Type I : Luting & bonding materials • Type II : Restorative • Type II.1 : Restorative aesthetic (autocure & resin-modified) • Type II.2 : Restorative reinforced / Bis-reinforced filling materials • Type III : Lining or Base
  79. 79. Classification by Mclean et al (1994) • Glass ionomer cement • Resin modified glass ionomer cement • Polyacid modified composite resin
  80. 80. Classification by Smith / Wright (1994) • Type I – Luting cement • Type II – a) aesthetic filling material b) reinforced resin filling material • Type III – Fast setting lining cement • Type IV – Fissure sealing cements • TypeV – Orthodontic cements • TypeVI – Core build up material
  81. 81. Type I : Luting & Bonding
  82. 82. Factors in favor of glass ionomer lute 1. Tensile strength – as high as zinc phosphate 2. Solubility – lower 3. Thixotropic flow properties – allow easier placement ; without need to vent casting / retain pressure during setting 4. Fine film thickness 5. Fluoride release 6. Potential for postinsertion sensitivity – same as for other cements 4. Fine film thickness2. Solubility – lower
  83. 83. Significant factors • Powder particle size - 4-15 µm • Film thickness – 10-20 µm • P/L ratio – 1.5:1 • pH – newly mixed cement – 1.8 ; within 30min – 4.5 • Dispensing & mixing – P/L system & 2 paste system • Time to mature – less time desirable; break away excess when cement is crisp & firm • Adhesion to enamel & dentin – cementation of crown – hydraulic pressure – penetartion of polyacrylic acid into tubules – post-insertion sensitivity – therefore seal surface of dentin ; do not remove smear layer •Adhesion to noble metals – by electroplating the fitting surface with 2-5µm tin oxide immediately prior to placement
  84. 84. •Cementation on vital teeth - 25% tannic acid (for 2min) or dentin bonding agent containing polalkenoic acid applied just before cementation Remove temporary cement Washed only ; not conditioned / seal Mixing time – 25 seconds String up 2-3 cm Apply to inside, especially margins Seat crown with positive pressure ; no need to maintain pressure Paint small quantity on tooth Remove excess when cannot be indented with sharp instrument Remove debris from gingival crevice Cemented crown
  85. 85. •Cementation on non vital teeth – 10% polyacrylic acid conditioning (for 10-15sec) to remove smear layer Preparation cleaned Root surface & post hole conditioned Washed & dried with alcohol Cement painted on post Canal filled to top with cement Post seated Inside of crown painted with cement Seat crown with positive pressure ; no need to maintain pressure Cemented crown
  86. 86. Bonding with glass ionomer - Bonding composite resin Glass ionomer used as bonding agent in small shallow cavities (Yamada et al 1996) • Prepare cavity • Condition for 10sec ; wash & dry • Paint thin layer of Glass ionomer bonding agent over entire cavty including walls • Blow off excess • Light activate for 20sec • Place composite incrementally ; finish, contour & polish Advantage :acid-base reaction of glass ionomer will continue & compensate for shrinkage of glass ionomer Prepare cavity Condition Glass ionomer bonding agent Light activate Place composite finish, contour & polish SEM showing interaction layer / ion-exchange layer Low viscosity, low P/L ratio, resin- modified glass ionomer used
  87. 87. Bonding with glass ionomer - Bonding amalgam Long term results – not available Short term results suggest – reduced post-insertion sensitivity to temperature changes in newly placed restoration Greatest hazard – potential for incorporation of fragments of glass ionomer into amalgam during condensation – reducing the physical properties ; unlikely to be sufficient to prevent cusp loss Similar clinical technique
  88. 88. Type II.1 : Restorative aesthetic materials
  89. 89. Factors in favor : Adequate aesthetics & translucency Sufficient physical properties in fully supported restoration Adhesion achieved Fluoride reservoir
  90. 90. Significant factors P/L ratio – 2.9:1 to 3.6:1 (if polyacrylic acid is liquid) 6.8:1 (in anhydrous cements) Time to mature : Autocure - Initial snap set - 4min from start of mix Resin modified Require atleast 1 week to mature Light activation - 20-40sec Resin glaze : to paint over finished restoration ; no effect on continuing maturation ; will seal voids / porosities on surface
  91. 91. Matrix checked for accuracy of fit Pumice slurry - 5 seconds ; flushed & dried 10% polyacrylic acid - 10-15 sec Cement placed excess removed after 4 min After matrix removed ; bonding resin applied Bonding resin light activated Erosion lesion Finished restoration
  92. 92. Type II.2 : Restorative reinforced materials
  93. 93. Reasons for use : When fast setting material is desirable With increased physical property But where color match not important Significant factors: • Resistant to uptake of water in 5min • But first 2 weeks water loss is a problem Following material earlier marketed as reinforced ; now considered a misnomer • Because physical properties not significantly improved • Adhesion & fluoride release reduced • Need another material to cover for esthetics 1. Silver cermet 2. Amalgam alloy admix 3. Silver alloy admix Newer generation high strength glass ionomers
  94. 94. Silver cermet • Manufactured by incorporating 40% by weight of microfine silver particles < 3.5µm in diameter in which powdered glass particles • The 2 were then sintered under pressure • Unreacted silver was washed out • 5% titanium dioxide added to modify color Advantages : Surface could be burnished High density & low porosity restoration High abrasion resistance High compressive strength & fracture resistance Disadvantage : Earlier used for “core build-up“ but their physical properties cannot be relied on Less adhesion (mechanical retention required) Uses : In repairing chipped & faulty margins of existing restorations ; alternative to replacement Color : closer to tooth Radioopacity : same as amalgam
  95. 95. Amalgam alloy admix Spherical amalgam alloy particles incorporated with a fast-setting glass ionomer powder (Simmons 1983) Amalgam alloy was incorporated in proportion of 8 parts cement powder : 1 part alloy by volume This was then mixed with polyacrylic acid (3:2 by weight) • black restoration •Physical properties slightly improved •Early resistance to water uptake •Set rapidly •Adhesion & fluoride release less than unfilled •Difficult to mix to required consistency by hand ; capsules were later available
  96. 96. Silver alloy admix Include silver containing alloy in flat brokenpieces rather than spheres ; flakes would offer larger surface area for reaction with polyacrylis acid Higher abrasion resistance because when subjected to wear, the preparation developed a Beilby – type smear layer on its surface Physical properties, color, fluoride release, adhesion – better than above 2 But material has had limited market
  97. 97. New generation High strength / Condensable glass ionomers Fast setting Auto cure 10-15% better physical properties than resin modified glass ionomer Available as “normal set” or “fast-set” Particularly useful as transitional restoration Changes : powder particle size particle size distribution heat history of glass (improvement in surface reactivity of powder )
  98. 98. Significant factors : • P/L ratio : 3:1 to 4:1 • Time to mature : resistant to water uptake / loss as soon as set • Adhesion : stronger because cement is stronger • Release of ions : similar to other types of autocure, therefore useful for root surface caries, tunnels Physical properties : • Tensile strength & fracture resistance substantially better than autocure, marginally better than resin modified glass ionomer • Abrasion resistance – as they mature they match that of amalgam, composite resin • Radioopacity – adequate Main application : 1. Minimal lesions 2. Transitional restoration
  99. 99. Type III :Lining & Base cements
  100. 100. Definition : Lining – thin layer of a neutral material placed on the floor of a cavity, prior to final restoration, to make good a deficiency in the cavity design or to provide thermal protection to the pulp Base – is identified as a dentine substitute that is placed to make up for major area of dentine loss prior to lamination of an enamel substitute over the top Significant factors : Lining cements : • Low P/L 1.5 :1 (do not act as bonding agent ; should not be left exposed ; low physical properties) • used in thin sections to fill voids in cavity design ; act as thermal insulator Base / dentin substitute : • P/L : 3:1
  101. 101. Properties • Physical Properties • Erosion & Longevity • Aesthetic properties • Biologic properties
  102. 102. Cement type Settin g time (min) Film thickness (µm) 24hr compressive strength (MPa) 24 hr Diametral tensile strength (MPa) Elastic modulus (GPa) Solubility in water (wt%) Pulp response Glass ionome r luting 7.0 24 86 6.2 7.3 1.25 Mild to moderat e Properties of glass ionomer luting cement Compressive strength is comparable to zinc phosphate Diametral strength is slightly higher Modulus of elasticity is ½ of zinc phosphate Thus, it is less stiff & more susceptible to elastic deformation It is thus not as desirable as zinc phophate to support an all ceramic crown, because greater tensile stress would develop in the crown under occlusal loading
  103. 103. Properties of restorative glass ionomers Compressive strength (MPA) Diametral tensile strength (MPa) Knoop hardness (KHN) Solubility (ANSI/ADA test) Anticariogenic/ Pulp response Glass ionomer type II 150 6.6 48 0.4 YES/MILD Cermet 150 6.7 39 - YES/MILD Hybrid Ionomer 105 20 40 - YES/MILD
  104. 104. Material Fracture toughness (MPa.m1/2) Admixed amalgam 1.29 Light cured glass ionomer 1.37 Hybrid composite 1.17 Glass ionomer lining cement 0.88 Cermet 0.51 Metal-reinforced glass ionomer 0.30 Fracture toughness – a measure of energy required to cause crack propagation that leads to fracture Restorative glass ionomers are much inferior to composites Also more vulnerable to wear
  105. 105. Erosion & Longevity 1. Dissolution & erosion 2. Durability & longevity
  106. 106. Dissolution & erosion 2 aspects Leaching of soluble constituents from cement Actual erosion Because of chemical & mechanical wear Disintegration only if they are matrix formers Short term aspects Long term aspects Because of acids from plaque, food & beverages Damage in technique Moisture contamina tion before cement hardened Desiccation before cement fully matured
  107. 107. In glass ionomer cement, anion is a polymer where the active carboxylic groups are connected by covalent linkages impervious to acid attack. Only cross-links are ionic, and many of these have to be broken before the matrix would decompose Fig 7.4 wilson & mclean Acid erosion : Glass ionomer < silicates < zinc phosphate < zinc polycarboxylate
  108. 108. Durability & longevity • Depends on • Adequate preparation of cement • Adequate protection • Conditions of mouth
  109. 109. Aesthetic properties • Translucency • Glass ionomer cements has a degree of translucency • Because its filler is a glass (not opaque) • Because of slow hydration reactions, glass ionomer cements take at least 24hrs to fully mature & develop translucency • Early contamination with water reduces translucency • Dark shades are less translucent • Glass ionomer remain unaffected by oral fluids • Opacity • Opacity is also termed as contrast ratio (Cr) • If Cr=1 – material is opaque • If Cr = 0 – perfectly translucent • To match enamel Cr < 0.55 • Glass ionomers Cr < 0.9 • Scattering power & reflectance • Opacity also depends on the scattering coefficient • Light reflectance • Thickness of specimen
  110. 110. Biologic properties
  111. 111. Biocompatibility • They elicit greater pulp reaction than ZOE (Plant et al 1984) • But less than zinc phosphate (Tobias 1978) • With any glass ionomer cement, it is wise to place a thin layer of protective liner, such as Ca(OH)2 , within 0.5mm of pulp chamber (Anusavice) • Inflammatory response of pulpal tissues resolves within 30 days & there is no enhancement of reparative or secondary dentine formation (G J Mount) • Response of gingival tissues is minimal (Garcia et al 1981) Effect on pulp & cells
  112. 112. Reasons for blandness of polyacrylic acid (McLean & Wilson, 1974) • Polyacrylic acid – weak acid • Dissociated H+ ions remain in neighbourhood of polyanion chain because of electrostatic attraction from multiple negative charges. • When partly neutralized, the negative charge on the chain increase, tendency of polyacylic acid to dissociate into H+ ions & polyacrylate ion decreases. • Diffusion of polyacrylic acid into dentinal tubules is unlikely because of its high molecular weight & chain entanglement. • Polyacrylic acid is readily precipitated by Ca+2 in tubules. • Therefore sensitivity under luting GIC may be due to faulty technique than chemistry of cement.
  113. 113. Fluoride release
  114. 114. Biological potential of glass ionomer cements • Significance of water in glass ionomer cements • Glass ionomer – water based material • Water plays important part in • Setting reaction • Final structure • Water is the reaction medium • Hydrates siliceous hydrogel
  115. 115. Once GI sets, Loosely bound – easily lost shrinkage& cracking & undue stress on ion exchange adhesion Tightly bound - cannot be removed ; associated with hydration shell of cation-polyacrylate bond Increase in strength & modulus & decrease in plasticity One important factor in these materials being water based lies in the chemical principle that it is only possible to have ion mobility in presence of water Which is essential for demineralization-remineralisation of tooth (anhydrous material can play no part ) Water is in the form of As material ages, ratio of tightly bound water : loosely bound water increases
  116. 116. • Ionic components of GIC • Calcium • Strontium • Aluminium • Silica • Fluoride • All ions are available for transfer from matrix into surrounding because of presence of water. • Lower the pH, greater the release of ions. • Note: (i) Calcium & strontium have similar polarity & atomic size, therefore they can replace each other in cement & hydroxyapatite. • (ii) Strontium imparts radioopacity • (iii) Strontium has anticariogenic properties. • Therefore strontium can participate effectively in remineralisation.
  117. 117. Mineral phase of enamel & dentin Enamel & Dentin are porous to migrating ions especially dentin Enamel : Each crystal of hydroxyapatite is surrounded by a layer of tightly bound water – hydration shell – which shows that the crystal is electrically charged & can attract ions that are able to play a part in remineralization Remaining water fills spaces between rods – main diffusion pathway into & thru enamel Dentin : 23% water by volume Water filled pores + inter-tubular lateral microtubules + dentinal tubules Increased potential for ion transfer By weight By volume By weight By volume
  118. 118. • Enamel rods are tightly packed • Pores are not large enough to allow bacteria • Only when sufficient disintergration has occurred, process becomes irreversible • Outer apatite crystals dissolve from surface • Increase porosity • Facilitating acid transport & demineralisation • Also, ions can return along the same pathway
  119. 119. Carious lesion • 1960’s – Massler, Fusayama & Brannstrom wrote detailed reports on science of demineralisation & remineralisation ; & theoritical value of ion exchange Carious dentin 1st decalcified layer 2nd decalcified layerFusayama et al 1966 Massler 1967 Infected layer Affected layer Pitts 1983, Mertz – Fairhurst et al 1992 Actively carious Pre-carious
  120. 120. • This concept was reinforced by a clinical study • Heavily carious 1st molars taken • Minimal caries removal • Restored using strontium based high strength glass ionomer cement • Harvested • Fl & Sr penetrated both layers of dentin & became part of normal apatite crystals beyond • 2 distinct zones identified Outer layer of non- remineralised dentine with minimal Fl & Sr uptake Deeper zone of well re-mineralised dentine Postulated that Collagen network in outer zone is totally devoid of mineral Lack of seeding sites Preventing uptake of mineral ions Remineralisable dentine contained atleast 20% by weight of mineral onto which incoming ions were able to absorb
  121. 121. External ion exchange • Glass ionomer acts as fluoride reservoir • Movement of fluoride out of glass ionomer • Electrolytic imbalance on surface of restoration • Cations from plaque & salive are taken up by the restoration • Balanced state • Increase in maturation & strengthening of restoration (Nicholson et al, 1999) • Also, plaque on surface of glass ionomer will have reduced count of S.mutans, therefore tissue tolerance of glass ionomer is more & less inflammation is seen.
  122. 122. Internal remineralization • Dental pulp demonstrates very high level of tolerance to glass ionomer. • Very mild inflammatory response to freshly mixed GIC seen, with rapid recovery. • Snuggs et al, 1993 – dentin bridging in mechanical exposure of pulp sealed with GIC • Brannstrom, 1982 – Pulpal irritation is direct result of bacterial activity. Therefore, if no irritation, no inflammation will occur. • Glass ionomer demonstrates ion-exchange adhesion, which could be an ideal sealant, thus preventing ingress of bacterial nutrients. • Therefore GIC can be placed in very close proximity to pulp without risk of irreversible pulp inflammation & CaOH sub-lining is not justified.
  123. 123. Entire margin of cavity cleaned down to sound dentine Axial wall still in softened demineralised affected dentine is retained 10% polyacrylic acid 10 second conditioning Light initiated autocure glass ionomer over axial wall (sublining) High strength autocure glass ionomer then placed Cut back to expose enamel walls Entire cavity covered with thin layer of Resin modified adhesive glass ionomer composite Suggested clinical technique
  124. 124. Glass ionomer as bone substitute • Rober Purrmann – originated the work • Owing to its properties of bioactivity & biocompatibility, glass ionomer has been tried as bone cement & bone replacement material. • Through ion-exchange mechanism, it can cause stable integration with bone & can affect both its growth & development adjacent to surface of material. • Note : unset GI is strictly contraindicated to be contacted with neural tissues (because of controversy over Al release)
  125. 125. Glass ionomer as bone cement • Prof. Charnley’s, 1960’s – Use of PMMA to provide stable mechanical anchor for metallic prosthesis. • Morphologic fixation / cement fixation • Owing to disadvantages of PMMA, glass ionomers replaced them • Advantage : • - No exotherm setting reaction • Chemically bond to bone & some metals & less shrinkage • Osteoconductive property of material • In oral surgery, • Applied to prevention of bone loss following extraction • Used as filler for bone donor sites & cyst cavities.
  126. 126. Clinical applications of glass ionomer cements
  127. 127. Uses Conservative • Luting & bonding • Restorative • Lining & base • Minimal intervention – the place of glassionomer • Transitional restoration Endodontics • Root canal sealing • Orthograde root canal sealing • Root-end filling material • Repair of perforations and root resorption defects • Perforation repair • Repair of root resorption cavities • Treatment of vertically fractured teeth • Coronal seal
  128. 128. Use of glass ionomer in conventional & surgical endodontics • Pitt Ford (1979) - Use in root canal first introduced • Stewart (1990) - made modifications • to increase working time • added barium sulphate : increase radioopacity • Ray & Seltzer (1991) – usable experimental formulation • Adequate working time • Adequate radioopacity • Adequate adhesion to root canal wall These modifications led to commercialization of Ketac – Endo (ESPE, Germany) in 1991 RMGIC – Vitrebond (RM) More recent developments : KT- 308 (GC) ZUT
  129. 129. Minimal intervention cavity designs – The place of glass ionomers
  130. 130. Site 1 Size 0 lesions Site 1 : pit & fissure on occlusal surface of posterior teeth Size 0 : initial lesion ; not yet resulted in cavitation Concept of fissure seal – 1st discussed by Simonsen (1989) The anatomy of enamel within a fissure is covered with a layer of enamel rods that appear to run parallel with the surface rather than at right angles. When etched, it will not develop the usual pattern of porous enamel that allows penetration of unfilled resin Wilson & McLean (1988) show that a glass ionomer will successfully occlude fissure This is now termed “fissure protection” to differentiate it from a “resin seal”
  131. 131. Neither resin nor glass ionomer will flow into a fissure beyond the point where fissure narrows to 200µm Retention thus mainly depends on adhesion to enamel at the entrance to fissure rather than mechanical interlocking into complexities of fissure Even though enamel rods lie in different orientation, glass ionomer will develop ion exchange adhesion & show acceptable longevity (Mount & Hume, 1998) 8 years 12 years Technique involved In young patient fast set autocure like light initiated autocure glass ionomer used
  132. 132. Site 1 Size 1 lesions Size 1 : smallest minimal lesion requiring operative intervention Fissures are explored using small tapered diamond bur #8107 at intermediate high speed under air water spray then lightly polished with #3107 Technique involved Satisfactory adaptation of entire fissure
  133. 133. Site 1 Size 2 lesions Size 2 : Moderate size cavities Technique involved Why glass ionomer used as base ? If resin composite used, might require removal of more dentin which would otherwise remineralize
  134. 134. Site 2 Size 0 lesions Site 2 – contact areas between anteriors / posteriors Size 0 : initial lesion ; not yet resulted in cavitation
  135. 135. Site 2 Size 1 lesions If lesion 3 mm below the crest of marginal ridge – “Tunnel” cavity design If lesion < 2mm from the crest of marginal ridge – “ Slot ” cavity design If proximal surface accessible – “Proximal approach” Site 2 – contact areas between anteriors / posteriors Size 1 : smallest minimal lesion requiring operative intervention
  136. 136. Access through occlusal surface Triangular access cavity Clean enamel margins “Tunnel” cavity design Glass ionomer syringed mylar strip in place Completed restoration Note : internal dimension of cavity Glass ionomer will flow readily into a small cavity & has the ability to remineralise “ Slot ” cavity design Glass ionomer is a sound option because occlusal load will not be great “Proximal approach” Fast set, high strength auto cure used because radioopaque & will not be under occlusal load
  137. 137. Site 2 Size 2 lesions Site 2 – Contact areas between anteriors / posteriors Size 2 : Moderate size cavities Laminate technique / bilayered restoration with glass ionomer as the base If resin modified is used; no need to etch after placement because enough resin content to provide adhsion with composite Substantial layer of glass ionomer across the entire floor is exposed to oral environment at gingival proximal box
  138. 138. Site 3 lesions Cervical areas related to gingival tissues including exposed root surface Glass ionomer ideal : Because can withstand flexure Root surface not under occlusal load
  139. 139. INSTRUCTIONS FOR DENTAL ASSISTANTS
  140. 140. Storage Powder & liquid by different manufacturers should not be interchanged Both bottles firmly closed (water based) Polyacrylic acid liquid thickens over time, within 12 months viscosity increases. It can be thinned down by : immerse bottle with lid on in water at 75°C for 15minutes, place in rubber bowl, let water from hot tap run over it. Test at 15minutes for viscosity. Let it cool before use. Liquid should never be refrigerated. Mixing slab should cool, but never below dew point.
  141. 141. Full spoon, no excess Tip liquid bottle to side, then invert completely If water / tartaric acid, only 1 drop used. Hand dispensing
  142. 142. Hand mixingLiquid should not stay on paper pad longer than 1minute (some of it may soak into it) First half folded into liquid in 10-15seconds Second half incorporated in 15 seconds Small mixing area Don’t mix beyond 30 seconds The objective is – only wet the particle – no dissolving it.
  143. 143. Mixing of capsules • To activate capsule apply pressure 3-4 seconds before placing in machine • Ultrahigh speed machine : 4000 cycles/minute • (< 3000 cycles/minute – not desirable)
  144. 144. Loss of gloss test This point is reached at 2minutes after start of mix 10sec in 4000cycles/minute
  145. 145. Correct consistency for hand mixed Type I : Luting : string up to 3-4cm from slab Type II : string 1cm + gloss Type III : for lining amalgam : 1.5:1 P/L ratio : 3-4cm string For base for composite : 3:1 P/L ratio : 1-1.5cm string
  146. 146. Clean – up Before it sets, immerse slab & spatula in water If set, chip off / place in water then clean
  147. 147. Summary & Conclusion
  148. 148. Review of literature
  149. 149. REFERENCES
  150. 150. REFERENCES : (Text books) 1. Glass-ionomer cement : Alan D.Wilson / JohnW. Mclean 2. An atlas of Glass Ionomer Cements – A Clinician’s guide (3rd edition) : Graham J. Mount 3. Preservation & restoration of tooth structure : Graham J. Mount 4. Phillip’s Science of Dental Materials (11th edition) : Kenneth J. Anusavice 5. Sturdevant’s Art & Sience of Operative Dentistry (4th edition):Theodore M. Roberson et al 6. Tylman’s theory & practices of fixed prosthodontics, chapter 21, page 394-406 : Franklin Garcia Godoy et al
  151. 151. REFERENCES : (Journals) 1. Proposed nomenclature for glass-ionomer dental cements & related materials. JohnW. Mclean et al.QI vol. 25, no. 9, 1994 ; 587-589. 2. GIC – Past, present & future. Graham J. Mount. Buonocore memorial lecture (Michael B.) Operative dentistry 1994, 19, 82-90. 3. Glass ionomer cements in restorative dentistry. JohnW. Nicholson et al. QI vol. 28, no.11, 1997, 705-714. 4. The need for caries preventive restorative materials.Gordon J. Christensen. JADA, vol. 131, sept. 2000, 1347-1349. 5. Composite resin & GIC : current status for use in cervical restorations – WilliamW. Brackett et al. QI 1990; 21: 445-447. 6. Longevity in glass-ionomer restorations: review of successful technique. Graham J. Mount. QI 1997 ; 28: 643-650. 7. Viscous GIC : a new alternative to amalgam in primary dentition. Roland frankenberger et al. QI 1997 ; 28:667-676. 8. Adhesion of GIC in clinical environment.G.J.Mount. operative dentistry 1991;16:141-148. 9. Glass ionomer : a review of their current status. G.J.Mount.Operative dentistry 1999 ; 24 : 115-124.
  152. 152. 10.The use of glass ionomer cements in both conventional & surgical endodontics. (review) M.A.A.De Bruyne et al. IEJ, 37; 2004: 91-104. 11.Pulpal consideration of adhesive materials. Harold R. Stanley.Operative dentistry, supplement 5, 1992, 151-164. 12. Glass ionomer cements used as fissure sealants with the atraumatic restorative treatment (ART) approach : review of literature. H.K.Yip et al. IDJ (2002)52, 67-70. 13. Demineralization & remineralization of dentine caries, and role of glass- ionomer cements.W. Gao et al. IDJ (2000) 50, 51-56. 14. Advances in restorative materials.CharlesW.Wakefield et al. DCNA,Vol. 45, no. 1, January 2001, 7- 27. 15.Direct & indirect restorative materials.ADA council on scientific affairs. JADA, vol.134,April 2003, 463-471. 16. Minimal intervention dentistry : Rationale of cavity design. G.J.Mount. Operative dentistry, 2003, 28, 92-99. 17.The sealant restoration : indications, success and clinical technique. D.C.Hassall et al. BDJ, vol. 191, no.7, October 13, 2001, 358-362. 18. Minimally invasive dentistry. CarolAnne Murdoch-Kinch et al. JADA, vol.134, January 2003, 87-94. 19.The influence of various conditioning agents on the interdiffusion zone & microleakage of a glass ionomer cement with a high viscosity in primary teeth.Y.Yilmaz et al.Operative dentistry 2005, vol. 30, no.1, 105-113
  153. 153. cements. S.S. Wu et al. Operative dentistry 2005; 30-2; 180-184 21. Invitro evaluation of cariostatic action of esthetic restorative materials in bovine teeth under severe cariogenic challenge. MLG Pin et al. Operative Dentistry 2005, 30-2, 368-375 22.The microtensile bond strength of Fuji IX GIC to antibacterial conditioned dentin. M.G.Botello. Operative Dentistry 2005, 30-3 ; 311-317 23. Fluoride release & neutralising effect by resin-based materials.T.Itota et al. Operative Dentistry 2005, 30-4, 522-527 24. Effect of neutral citrate solution on the fluoride release of conventional restorative glass ionomer cements. Roeland J.C.De Moor et al. Dental Materials 2005, 21-4, 318-323 25. Effect of cavity configuration & ageing on the bonding effectiveness of 6 adhesives to dentin. Kenichi Shirai et al. Dental Materials 2005, 21-2, 110-124 26. Salivary contamination & bond strength of glass ionomers to dentin. S.K.Sidhu. Operative Dentistry 2005, 30-6, 676-684 27. Early & long-term wear of “Fast-set” convetional GIC. A.Werner et al Dental Material 2005, 21-8, 716-720 28. Dental materials 2005, 21, 498-504 Steven R. Armstrong 29. Dental materials 2005, 21, 695-703 H.K.Yip et al 30. Dental materials 2005, 21, 704-708 Martin J.Tyas
  154. 154. 32. Restorative dentistry for pediatric teeth – state of the at 2001.Gordan J. Christensen, JADA,Vol. 132, March 2001, 379-381 33. Fluoride containing restorative materials. Edward J. Swift, Clinical Preventive Dentistry 1988, vol.10, no.6, 19-24 34. Root end filling materials- a review.Vasudev SK et al, Endodontology 2003, vol. 15, 12-18 35. Fluoride releasing restorative materials & secondary caries. John Hicks et al, DCNA 2002, 46, 247-276 36. Minimal intervention dentistry – a review, Martin J.Tyas, IDJ 2000, 50, 1- 12 37. Minimally invasive dentistry . CarolAnne Murdoch-Kinch et al, JADA 2003, vol 134, 87-94 38. Glass ionomer cements used as fissure sealants with the ART approach : review of literature. H.K.Yip et al, IDJ 2002, 52, 67-70
  155. 155. 39.The ART approach for primary teeth : review of literature. Roger J Smales et al, Pediatric Dentistry 2000, 22:4, 294-298 40.The ART approach for the management of dental caries. Roger J. Smales et al, QI 2002; 33: 427432 41. Direct & indirect restorative materials, JADA vol. 134, 2003, 463-471 42.The sealant restoration : indications, success and clinical technique. D.C.Hassall, BDJ 2001,VOL.191, NO.7, 358-362 43. Adhesive dentistry & endodontics : materials, clinical strategies and procedures for restoration of access cavities : a review. Richard S. Schwartz et al, JOE vol 31, no.3, march 2005, 151- 164

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