Dental Cements III PDF

Dental Cements III By Dr. Dina Sami Associate Professor of Dental Biomaterials Contents 1. Glass ionomer cements  Uses  Types 1. Conventional glass ionomer cement 2. Modified glass ionomer Metal reinforced glass ionomer Re...

Dental Cements III By Dr. Dina Sami Associate Professor of Dental Biomaterials Contents 1. Glass ionomer cements  Uses  Types 1. Conventional glass ionomer cement 2. Modified glass ionomer Metal reinforced glass ionomer Resin modified glass ionomer Nanoionomer cement 2. Resin cements 3. Calcium hydroxide cement Glass Ionomer cements Uses 1. Luting agent for crown and bridge. 2. Restoration of non-stress bearing areas e.g. class III and V cavity preparation. 3. Restoration of primary teeth. 4. Base 5. Endodontic sealers Types 1. Conventional GICs. 2. Metal reinforced GICs. 3. Resin modified GICs. 4. Nanoionomer cements  1. Conventional glass ionomer cements Forms 1. Powder and liquid 2. Anhydrous cements: liquid is dried and added to the powder which is mixed with water 3. Capsules: contain both the powder and liquid with the correct ratio separated by a membrane Mechanical mixing is done by by an amalgamator that only takes few seconds Composition 1. Powder  Calcium flouro alumino silicate glass which consists of calcium flouride (CaF2), sodium fluoride (NaF), silica (SiO2) and alumina (Al2O3). 2. Liquid: It is an aqueous solution of 1. Polyacrylic acid: main reactant 2. Itaconic acid: decreases the viscosity of the liquid, 3. Tartaric acid: increases the working time and decreases the setting time.  Setting reaction It is an acid base reaction 1. The acid in the liquid attacks and dissolves the surface of glass particles leading to the release of Ca2+, Al3+ and Fl- ions 2. Na+ form silica gel on the surface of the powder particles 3. Ca2+ ions react with the carboxylic groups of the acid forming a cross- linked carboxylic acid salt leading to initial setting 3. Al3+ ions react with the carboxylic groups of the acid forming cross- linked carboxylic acid salt resulting in a stronger cross-linked cement because Al is trivalent i.e. reacts with 3 carboxylic groups while Ca is divalent so reacts with 2 carboxylic groups. 4. Al3+ migrates much slower than Ca2+ and reaction of Al3+ takes longer time than Ca2+ 5. The setting reaction can take 24 hours so the material should be protected against premature saliva contamination un  Microstructure of set material Unreacted glass surrounded by silica gel embedded in a matrix of crosslinked calcium and aluminum polycarboxylate salts Role of water It is the medium in which the reaction occurs It hydrates the formed cross-linked matrix forming a stable gel which increases the strength of the set material If the cement is subjected to dryness before setting, the reaction will stop and the surface will crack decreasing the strength of the material If it is subjected to moisture contamination before setting dissolution of the matrix may occur decreasing the strength of the material So the cement must be protected by a layer of varnish during the setting process Properties of glass ionomer: 1. Anticariogenic effect (fluoride release and recharge): Glass ionomer cements can inhibit secondary caries due to fluoride release which reacts with hydroxyapatite to form flouroapatite which is more resistant to acid attacks from cariogenic bacteria GICs can reuptake fluoride (recharge) from a fluoride rich source and release it again 2. Bonding: Chemical bonding to tooth structure occurs by reaction of polyacrylic acid with calcium present in the tooth structure 3. Biological properties: They have a mild irritating effect on the pulp so in case of deep cavities, calcium hydroxide lining must be used. 4. Solubility and disintegration They have good resistance to dissolution under oral conditions and improved by varnish protection. 5. Film thickness is similar to that of zinc phosphate cement. 6. Mechanical properties: a. Compressive strength: similar to that of ZnPO4 cement. b. Tensile strength: slightly higher than that of ZnPO4 cement but still brittle. c. Modulus of elasticity: less than that of ZnPO4 cement, i.e. less rigid and more prone to elastic deformation. These materials are used in low stress bearing areas 7. Working and setting times Working time is shorter than that of ZnPO4 cement and setting time is longer than ZnPO4 cement 8. Optical properties They are translucent so can be used in anterior restorations in low stress bearing areas, but they have inferior esthetics when compared to composite resin materials  Manipulation Powder and liquid ratio is 1.3:1 or as recommended by the manufacturer. Mixing is done on glass slab or waxed paper pad. Powder is divided into two halves then incorporated into the liquid with a stiff spatula. A plastic spatula is used because the the silica in the cement can abrade a stainless steel spatula leading to the discoloration of the mix Proper mix is glossy which means the presence of unreacted polyacrylic acid which is important to form a bond with calcium in tooth structure In case of loss of gloss it is preferred not to use the mixed material Advantages of glass ionomer materials 1. Chemical bonding to tooth structures 2. Long-term fluoride release 3. Biocompatible 4. Good compressive strength 5. Low solubility in oral fluids Disadvantages of glass ionomer materials 1. Technique sensitive to either water contamination or dehydration. 2. Low abrasion resistance 3. Short working time and long setting time 4. Brittleness (low tensile strength) and low fracture toughness Modifications of glass ionomer cements Modifications were done to improve the mechanical properties, sensitivity to dehydrartion and moisture contamination, abrasion resistance and optical properties of conventional glass ionomer materials. 1. Metal reinforced glass ionomer a. Silver alloy admix b. Cermet glass ionomer 2. Resin modified glass ionomer 1. Metal reinforced glass ionomer a. Silver alloy admix Made by the incorporation of the amalgam alloy powder with the glass powder. e.g. miracle mix b. Cermet glass ionomer: Made by sintering or fusing silver particles to the glass ionomer powder Advantages of metal reinforced GICs 1. Increase in abrasion resistance 2. Little increase in compressive strength 3. Reduction in solubility Disadvantages of metal reinforced GICs 1. Reduction in fluoride release 2. Reduction in bond strength with tooth structures 3. Reduction in esthetic Uses of metal reinforced GICs 1. Core build up material core 2. Posterior filling material for deciduous teeth 2. Resin modified glass ionomer (hybrid ionomer) They are hybrids of the two types of materials; glass ionomer and composite resin Methacrylate resins similar to to those used in composite resin materials are added to the glass ionomer liquid to allow setting by polymerization. Setting reactions of the Hybrid GICs 1. Conventional acid-base reaction between powder and liquid 2. Free radical polymerization reaction of the resin component. Tricure glass ionomer -These materials contain chemical initiators and activators in addition to photoinitiators so that the resin part of the material can undergo chemically activated polymerization in absence of light. Setting reactions of the tricure resin modified glass ionomers: a. Conventional acid-base reaction between powder and liquid b. Light cure polymerization of the resin c. Chemical cure polymerization of the resin Properties of resin modified GICs cement 1. Release of fluoride 2. Ability to bind adhesively to tooth structures 3. A prolonged working time and a rapid setting time 4. High strength 5. Higher resistance to desiccation and acid attack 3. Nanoionomer cements It is a resin-modified glass ionomer cement combined with nanofiller technology. Fillers used are 1. Fluoroaluminosilicate glass of size less than 3 micron (average 1 micron) 2. Nanofillers (5–25 nm) 3. Nanocluster fillers (1.0–1.6micron) derived from silica and zirconia Resin cements These materials have a similar composition to that of restorative composites but with lower filler content to decrease the viscosity and film thickness. Types: 1. Conventional composite resin cements a. Self-cured resin cements b. Light cured resin cements c. Dual cured resin cements 2. Adhesive resin cements. 1. Conventional composite resin cements a. Self-cured resin cements Available as a two component system to be mixed together  Powder and liquid  Two paste system Composition:  diacrylate oligomers diluted in dimethacrylate monomers  Fillers: Silanated silica or glass  Peroxide-amine initiator activator system b. Light cured resin cements Available as a single paste that needs no mixing Composition: Urethane dimethacrylate or Bis-GMA diluted in dimethacrylate monomers Fillers: Silanated silica or glass Champhroquinone as photointiator c. Dual cure resin cements Are resin cements that polymerize by both light and chemical curing at the same time. Supplied as base and catalyst to be mixed before use. After mixing, chemically activated polymerization occurs slowly and provides longer working time. When the cement is exposed to light, it solidifies rapidly by light activated polymerization 2. Adhesive resin cements Are self-cured resin cements that contain an adhesive promoter such as 4-methacryloxy ethyl trimellitic anhydride (4-META). Contains both hydrophilic and hydrophobic groups facilitating a bond between hydrophilic tooth and hydrophobic materials 4-META Properties of resin cements 1. Unreacted monomers can be irritating to the pulps, so pulp protection using calcium hydroxide is important if the remaining dentin thickness is small. 2. These cements are insoluble in water. 3. Compressive strength and fracture toughness are high compared to other cements 4. Bonding: micromechanical bonding in conventional types and chemical in adhesive resin cements. 5. Good optical properties as these cements are translucent  The material of choice for luting ceramic restorations and indirect composite restorations due to their translucency and high compressive strength and fracture toughness and low solubility.  2. Calcium hydroxide They are characterized by 1. High pH value (alkaline)  Stimulate pulp to lay down 2ry dentin.  Have antibacterial effect against micro-organisms found in carious lesions 2. Good Biocompatibility Uses 1. Used as a liner in deep cavity to seal the dentinal tubules and prevent penetration of chemicals into the pulp. 2. Used in direct pulp capping 3. Used as intra-canal medicaments in endodontics  2. Calcium hydroxide Forms 1. Calcium Hydroxide Suspension 2. Two-paste system (chemically cured) (Dycal) 3. One-paste system (light cured) Composition Paste 1 Paste 2 Calcium hydroxide Glycol salicylate. Zinc oxide Titanium dioxide. Zinc stearate. Calcium sulphate sulphonamide. Calcium tungstate Manipulation and setting reaction Equal volumes of the two pastes are mixed on waxed paper pad for 30 seconds. The cements will set in 2 minutes Acid base reaction named Chelation Properties 1. Alkaline pH so stimulates pulp to lay down 2ry dentin and has an antibacterial effect. 2. High solubility and disintegration 3. Low compressive strength (5 Mpa) so in a deep cavity, a thin liner of Ca (OH) cement and then a base of Zinc phosphate cement should be placed before condensation of amalgam.