Re: Glass ionomer

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HIGlass-Ionomer CementsIntroductionThese materials were formulated in the 1970s by bringing together the silicate andpolyacrylate systems. The use of an acid-reactive glass powder together withpolyacrylic acid solution leads to a translucent, stronger cement that can be used forluting and restorative materials.ApplicationsGlass-ionomer cements are used for the cementation of cast-alloy and porcelainrestorations and orthodontic bands, as cavity liners or base materials, and asrestorative materials, especially for erosion lesions. They are being replaced by hybridionomer cements, which allow better handling.Composition and settingThe powder in these materials is finely ground

calcium aluminum fluorosilicate glasswith a particle size around 40 um for the filling materials and less than 25 um for theluting materials. One brand (Zionomer Liner, Den-Mat) also contains zinc oxide.Silver powder is fused into the glass in Ketac-Silver (3M/ESPE) for improvedphysical properties. The liquid is a 50% aqueous solution of a polyacrylic-itaconicacid or other polycarboxylic acid copolymer that contains about 5% tartaric acid.Some other materials contain 10% to 20% added silver, silver alloy, or stainless steel.In some materials the solid copolymer is added to the powder, and the solutioncontains tartaric acid; in others, all the ingredients are in the powder, and the liquid iswater.On mixing, the polyacrylic and tartaric acids react with the glass, leaching calciumand aluminum ions from the surface, which cross-link the polyacid molecules into agel. The tartaric acid serves to increase

working time and gives a sharp setting byforming metal ion complexes. Differences in composition between brands affect thehardening rate and properties. Some recent evidence suggests that a polysilicatematrix may also form within the polygel over time.ManipulationThe material should be carefully proportioned and the freshly dispensed componentsmixed rapidly in 30 to 40 seconds. Some brands are encapsulated, mechanicallymixed, and injected. The powder/liquid ratio for luting is about 1.3:1 for theconventional types of glass-ionomer cement. This ratio appears to be critical withthese cements to obtain optimal cementation properties. Best results are obtained bymixing the chilled powder with the liquid on a chilled slab. The correct cementingmix is fluid, similar to zinc phosphate. The lining mix is somewhat more viscous,depending on the brand. The restorative mix should have a puttylike consistency and

aglossy surface. Tooth surfaces should be clean and free from saliva but notdehydrated. Restoration surfaces should be free from debris and contamination. Thecement hardens slowly and should be protected from loss or gain of moisture when setclinically. Restoration margins or filling surfaces should be protected with a varnishor a light-curing sealant. This is less important with light-cured materials.PropertiesFor the luting materials, the setting time is in the range of 6 to 9 minutes. The liningmaterials set in 4 to 5 minutes, and the restorative materials set in 3 to 4 minutes.Materials that are light-cured set in approximately 30 seconds when exposed to avisible light source. The acid-base reaction continues slowly and properties improveover time.Film thickness is in the range of 25 to 35 um, which is adequate to seat castingssatisfactorily, although the flow properties are quite dependent on the

powder/liquidratio.For the luting cements, the compressive strength increases over 24 hours to 90 to 140MPa (13,000 to 20,000 psi) depending on the brand. The tensile strength increasessimilarly to 6 to 8 MPa (900 to 1,100 psi). The compressive modulus of elasticity isabout 7 GPa (900,000 psi). The lining materials have compressive and tensilestrengths in the same range with some light-cured materials at the higher end of therange reaching 150 to 160 MPa (21,000 to 23,000 psi) in compression and 10 to 12MPa (1,400 to 1,700 psi) in tension. The light-cured materials are significantlytougher in some brands, with a lower modulus. The restorative materials range from140 to 180 MPa (20,000 to 26,000 psi) in compression and 12 to 15 MPa (1,700 to2,100 psi) in tension. The light-cured restorative materials may have strengths as highas 200 MPa in compression and 20 MPa in tension. Some silver-containing

materialsare in this range, and even higher strengths have been achieved in recent materials.In general, with light-cured materials, properties are dependent on the depth of cure.The solubility of the cements in water is about 1% for a luting material, and this ishigher in lactic acid. Good resistance to dissolution is observed under oral conditions.Resistance to dissolution and disintegration is improved by varnish protection forconventional cements.Erosion of clinical restorations of conventional cements by acid phosphate fluoridepreventive-treatment solutions has been observed, making these solutionscontraindicated.Some studies show that light-cured glass-ionomer materials continue to absorb waterover several months, with swelling and reductions in strength and stiffness. Theclinical significance of this behavior is not yet clear.Glass-ionomer cements exhibit bonding to enamel, dentin, and alloys in

a mannersimilar to zinc polycarboxylates. In vitro and in vivo the adhesion is variable and isaffected by surface conditions. Slight and variable marginal leakage has beenobserved. Bonding to dentin for conventional materials is not improved bypretreatment with polyacrylic acid solutions, whereas with light-cured materials it isdependent on the use of dentin primers.Biologic effectsPulpal response to the lining and restorative materials appears generally favorable.Variable behavior has been reported for the various luting materials with instances ofpostoperative sensitivity. This has been attributed to a prolonged initially low pHcoupled with the effects of the toxic ions. This may be accentuated by dehydration ofdentin and marginal leakage of bacteria. Leaching of fluoride and uptake by adjacentenamel occurs with these cements, and this continues for at least a year withpotentially cariostatic

effects. Antibacterial action has been attributed to low initialpH, leaching, release of silver and other ions, or a combination of these. Light-curedmaterials have been observed to show greater cytotoxicity.Advantages and DisadvantagesThe advantages of glass-ionomer cement materials include easy mixing, high strengthand stiffness, leachable fluoride, good resistance to acid dissolution, potentiallyadhesive characteristics, and translucency.The Disadvantages include initial slow setting and moisture sensitivity, variableadhesive characteristics, radiolucency, and possible pulpal sensitivity.BEST REGARDSEBTISAM From: "Mokaamr@..."

<mokaamr@...> Ore < > Sent: Monday, 26 March 2012, 11:30 Subject: Glass ionomer

Does it have a setting contraction?where does ca of the setting reaction come from?

Thanks

[Guest guest]

Thank you.On 26 Mar 2012, at 11:52, ebtessam elhamalawy <ebtessamhamalawy@...> wrote:

HIGlass-Ionomer CementsIntroductionThese materials were formulated in the 1970s by bringing together the silicate andpolyacrylate systems. The use of an acid-reactive glass powder together withpolyacrylic acid solution leads to a translucent, stronger cement that can be used forluting and restorative materials.ApplicationsGlass-ionomer cements are used for the cementation of cast-alloy and porcelainrestorations and orthodontic bands, as cavity liners or base materials, and asrestorative materials, especially for erosion lesions. They are being replaced by hybridionomer cements, which allow better handling.Composition and settingThe powder in these materials is finely ground

calcium aluminum fluorosilicate glasswith a particle size around 40 um for the filling materials and less than 25 um for theluting materials. One brand (Zionomer Liner, Den-Mat) also contains zinc oxide.Silver powder is fused into the glass in Ketac-Silver (3M/ESPE) for improvedphysical properties. The liquid is a 50% aqueous solution of a polyacrylic-itaconicacid or other polycarboxylic acid copolymer that contains about 5% tartaric acid.Some other materials contain 10% to 20% added silver, silver alloy, or stainless steel.In some materials the solid copolymer is added to the powder, and the solutioncontains tartaric acid; in others, all the ingredients are in the powder, and the liquid iswater.On mixing, the polyacrylic and tartaric acids react with the glass, leaching calciumand aluminum ions from the surface, which cross-link the polyacid molecules into agel. The tartaric acid serves to increase

working time and gives a sharp setting byforming metal ion complexes. Differences in composition between brands affect thehardening rate and properties. Some recent evidence suggests that a polysilicatematrix may also form within the polygel over time.ManipulationThe material should be carefully proportioned and the freshly dispensed componentsmixed rapidly in 30 to 40 seconds. Some brands are encapsulated, mechanicallymixed, and injected. The powder/liquid ratio for luting is about 1.3:1 for theconventional types of glass-ionomer cement. This ratio appears to be critical withthese cements to obtain optimal cementation properties. Best results are obtained bymixing the chilled powder with the liquid on a chilled slab. The correct cementingmix is fluid, similar to zinc phosphate. The lining mix is somewhat more viscous,depending on the brand. The restorative mix should have a puttylike consistency and

aglossy surface. Tooth surfaces should be clean and free from saliva but notdehydrated. Restoration surfaces should be free from debris and contamination. Thecement hardens slowly and should be protected from loss or gain of moisture when setclinically. Restoration margins or filling surfaces should be protected with a varnishor a light-curing sealant. This is less important with light-cured materials.PropertiesFor the luting materials, the setting time is in the range of 6 to 9 minutes. The liningmaterials set in 4 to 5 minutes, and the restorative materials set in 3 to 4 minutes.Materials that are light-cured set in approximately 30 seconds when exposed to avisible light source. The acid-base reaction continues slowly and properties improveover time.Film thickness is in the range of 25 to 35 um, which is adequate to seat castingssatisfactorily, although the flow properties are quite dependent on the

powder/liquidratio.For the luting cements, the compressive strength increases over 24 hours to 90 to 140MPa (13,000 to 20,000 psi) depending on the brand. The tensile strength increasessimilarly to 6 to 8 MPa (900 to 1,100 psi). The compressive modulus of elasticity isabout 7 GPa (900,000 psi). The lining materials have compressive and tensilestrengths in the same range with some light-cured materials at the higher end of therange reaching 150 to 160 MPa (21,000 to 23,000 psi) in compression and 10 to 12MPa (1,400 to 1,700 psi) in tension. The light-cured materials are significantlytougher in some brands, with a lower modulus. The restorative materials range from140 to 180 MPa (20,000 to 26,000 psi) in compression and 12 to 15 MPa (1,700 to2,100 psi) in tension. The light-cured restorative materials may have strengths as highas 200 MPa in compression and 20 MPa in tension. Some silver-containing

materialsare in this range, and even higher strengths have been achieved in recent materials.In general, with light-cured materials, properties are dependent on the depth of cure.The solubility of the cements in water is about 1% for a luting material, and this ishigher in lactic acid. Good resistance to dissolution is observed under oral conditions.Resistance to dissolution and disintegration is improved by varnish protection forconventional cements.Erosion of clinical restorations of conventional cements by acid phosphate fluoridepreventive-treatment solutions has been observed, making these solutionscontraindicated.Some studies show that light-cured glass-ionomer materials continue to absorb waterover several months, with swelling and reductions in strength and stiffness. Theclinical significance of this behavior is not yet clear.Glass-ionomer cements exhibit bonding to enamel, dentin, and alloys in

a mannersimilar to zinc polycarboxylates. In vitro and in vivo the adhesion is variable and isaffected by surface conditions. Slight and variable marginal leakage has beenobserved. Bonding to dentin for conventional materials is not improved bypretreatment with polyacrylic acid solutions, whereas with light-cured materials it isdependent on the use of dentin primers.Biologic effectsPulpal response to the lining and restorative materials appears generally favorable.Variable behavior has been reported for the various luting materials with instances ofpostoperative sensitivity. This has been attributed to a prolonged initially low pHcoupled with the effects of the toxic ions. This may be accentuated by dehydration ofdentin and marginal leakage of bacteria. Leaching of fluoride and uptake by adjacentenamel occurs with these cements, and this continues for at least a year withpotentially cariostatic

effects. Antibacterial action has been attributed to low initialpH, leaching, release of silver and other ions, or a combination of these. Light-curedmaterials have been observed to show greater cytotoxicity.Advantages and DisadvantagesThe advantages of glass-ionomer cement materials include easy mixing, high strengthand stiffness, leachable fluoride, good resistance to acid dissolution, potentiallyadhesive characteristics, and translucency.The Disadvantages include initial slow setting and moisture sensitivity, variableadhesive characteristics, radiolucency, and possible pulpal sensitivity.BEST REGARDSEBTISAM From: "Mokaamr@..."

<mokaamr@...> Ore < > Sent: Monday, 26 March 2012, 11:30 Subject: Glass ionomer

Does it have a setting contraction?where does ca of the setting reaction come from?

Thanks