Dental cement Topic General requirements for dental cements Classification of dental cements Component and properties Setting reaction Mixing process The uses of dental cements Definition Dental cements : materials made from two components, powder and liquid, mixed together. Powder + Liquid Pastelike or flowable material Hardens to a rigid solid Uses of dental cements Luting agent • • Temporary cement Permanent cement Pulp protection or cavity sealer Cavity varnish Liner Base Uses of dental cement Filling Temporary filling Permanent filling Others Root canal sealer Calciumhydroxide cement Bite registration material Luting agent Luting : the use of moldable substance to seal a space between two component. Most dental treatment necessitate attachment of prostheses to the teeth by means of luting agent. General requirements for luting agents Biocompatibility Retention High tensile strength, fracture toughness, fatique strength Good marginal seal General requirements for luting agents Low film thickness Ease of use Radiopacity Aesthetics Film thickness The thickness of film between two flat surface The maximum allowable thickness is 25 µm (ADA specification No. 96) Low film thickness value is preferred Cement base A thick layer of cement (>0.75mm) is applied under restoration to protect pulp against injuries. The base should be strong enough to resist the condensation force during the placement of restoration. Well insulation ability Good sealing Classification of dental cements Conventional cement Zinc phosphate cement Zinc oxide-eugenol cement Polycarboxylate cement Glass ionomer cement Resin-base cement Resin cement Resin modified glass ionomer cement Conventional cement Typically powder/liquid system Liquid is an acid Powder is a base ; insoluble in oral fluid When mixed together Acid-base reaction Zinc Phosphate cement Zinc phosphate cement Powder Zinc oxide Magnesium oxide Liquid Phosphoric acid Water Alumenium phosphate ZnO ZnO Zn+ ZnO Zn+ Zinc aluminophosphate gel Unreacted ZnO Unreacted ZnO Unreacted ZnO Zinc aluminophosphate matrix Unreacted ZnO Setting reaction Exothermic reaction Adding of water can accerlate the reaction. Loss of water can lengthen the setting reaction. Working time and setting time Working time commonly is 3-6 minute Setting time is 2.5-8 minute(ADA specification No.96) Depending on the manufacturer instruction How to extend the setting time ? Reducing powder/ liquid ratio recommended} {not Mixing on the cool glass slap {no moisture} Mixing over a large area. Mixing cements in increments. Mixing procedure There are three steps: First : add the small amount of powder into the liquid To achieve the slow neutralization of the liquid. To control the reaction. Mixing procedure Second : Larger amount of powder is added to liquid For further saturation of liquid to newly form zinc phosphate. This steps may not effect by heat released from the reaction. {because of the less amount of unreacted acid} Mixing procedure Finally: the small amount of powder is added again To control the optimum consistency 4 2 1 5 3 7 8 6 4 2 1 5 3 7 8 6 Characteristic properties Setting time at 37O 5 – 9 minutes Minimum compressive strength 75 MPa Maximum film thickness Maximum Solubility 25 µm (for luting the prostheses) 0.2% by weight ADA specification NO.8 for Zinc phosphate cement Effects of manipulation on some properties. Manipulative variables Decreased powder/liquid ratio Increase rate of powder incorporation Increase mixing temperature Water contamination Properties Copressive Film strength thickness Solubility Initial acidity Setting time Biocompatibility Acid can penetrate into the dentinal tubule irritate pulp pH of cement Liquid = 2.0 3 minutes after mixing = 4.2 1 hour = 6 48 hours = 7 Modified zinc phosphate cement Fluoride cement Add Stannous fluoride Higher solubility/ Lower strength Zinc silicophosphate Zinc phosphate + Silicate Higher strength/ lower solubility Fluoride released Translucency Clinical applications Zinc phosphate cement Luting agent Base and temporary filling Modified zinc phosphate Luting prostheses Luting the orthodontics band Zinc oxide-eugenol cements Lower strength than Zinc phosphate cement. Sedative effect Usually used as temporary filling Zinc oxide-eugenol cement Simple ZOE Reinforced ZOE EBA cement Compositions of simple ZOE Powder Zinc oxide Rosin : reduce the brittleness of the set cement Zinc stearate : plastcizer Zinc acetate : improve strength Liquid Eugenol and olive oil Setting reaction First ZnO + Eugenol -- water Zn(OH)2 Second Zn(OH)2+2HE ZnE2+H2O Setting reaction Water accelerates the reaction Zinc eugenolate is easily hydrolized by moisture Manipulation Paste/paste Mix two equal pastes together until it obtains the homogeneous color. Powder/liquid Usually 4/1 for maximum strength Mix the large increment, firstly Not require cool glass slap Classification Type I Type II Permanent cementation Type III Temporary luting cement Temporary restoration [for a few days] Type IV Cavity liner Specification requirements Type Setting Compressive Solubility Film time strength thickness [%] [min] [MPa] [µm] Type I 4-10 35 maximum 2.5 25 Type II 4-10 35 maximum 1.5 25 Type III 4-10 35 maximum 1.5 - Reinforced ZOE Used as the intermediate restorative materials (IRMTM) Add 10-40% resin polymer in the powder for strengthening the set cement Compressive strength 35-55 MPa EBA cement Powder Liquid Add 20-30% of aluminium oxide Add 50-60% ethoxybenzoic acid in eugenol Compressive strength 55-75 MPa Clinical applications Base Temporary cementation Permanent cementation If cement contains eugenol, it is not to use with resin restorative material. Zinc polycarboxylate cement Or called Zinc polyacrylate cement The first adhesive cement More biocompatibility than zinc phosphate cement Bond to tooth structure and metal Polyacrylic acid have more molecular weigth Moderate strength/ moderate solubility Composition Powder [the same as zinc phosphate cement ] Zinc oxide Magnesium oxide Stannous fluoride Liquid Aqueous solution of polyacrylic acid Other carboxylic acid Manipulation Mix first half of powder to liquid to obtain the maximum length of working time. The reaction is thixotropic The viscosity decreases when the shear rate increases Setting reaction Like zinc phosphate cement Retarded by cool environment Bonding to tooth structure The polyacrylic acid is believed to react with calcium ion via the carboxyl group. The adhesion depends on the unreacted carboxyl group. Specification requirements Setting time at 37OC: 9 minutes Maximum film thickness: 25µm Minimum compressive strength: 50 MPa Maximum solubility: 0.2% Applications Cement inlays or crowns Used as base Temporary filling Lute the stainless steel crown Glass ionomer cement Or called Polyalkynoate cements Conventional glass ionomercement Resin-modified glass ionomer cement [RMGICs] Powder + Liquid/ Powder + water/ Encapsulated Composition Powder Calcium aluminum fluorosilicate glass Liquid Polyacid Copolymer of polyacrylic / itaconic acid Copolymer of polyacrylic / maleic acid Add tartaric: accelerator Setting reaction There are three stages: Dissolution Gelation Hardening. Water hardening or water setting Polyacid liquid Hydrogen ions Ca2+ Al3+ Glass core FSilica gel Polyacid liquid Ca2+ Al3+ F- -COOH Cross-linked polyacid Gelation Calcium ions have more reactivity than aluminium ions. This is critical phase of contamination. Polyacid liquid Al3+ -COOH Cross-linked polyacid Hardening Last as long as 7 days. The reaction of aluminium ions provides the final strength of set cement. Glass core Cross-linked polyacid Silica gel Properties Film thickness is similar or less than zinc phosphate cement. Setting time 6 to 8 minutes from start of mixing. Less pulpal irritation. Bacteriocidal or bacteriostatic. Prevent caries. Strength The 24-hour compressive strength is greater than zinc phosphate cement. The compressive strength increase to 280MPa between 24 hours to 1 year after initial setting. Bonding It can be chemically bonded to the tooth structure. The mechanism of bonding is the same as polyacrylate cement. The dentine bond strength may be lower than polyacrylate because of technique sensitivity. Modified GI Cermet Combination of glass and metal No significantly improve the strength More wear resistance and short setting time Resin-modified GI Resin-modified glass ionomer cement Add polymerizable function groups Both chemical & light curing Overcome moisture sensitive & low early strength Names: Ligth cured GICs, Dual-cured GICs, Tri-cured GICs, Hybrid ionomer, Compomers, Resin-ionomers Setting reaction Polymerization Acid-base reaction initial setting maturing process & final strength Heat released from the polymerization reaction. Properties Higher strength than conventional GI Higher adhesion to resin material Less water sensitivity Can be polished after curing Relative properties of a glass ionomer and a resin-modified GI cements Property GIC RMGIC Working time 2 min 3 min 45 sec Setting time 4 min 20 sec Compressive strength 202 MPa 242 Mpa Tensile strength 16 Mpa 37 Mpa Applications Type I : Luting agent Type II : Filling material Type III : Base and liner Conventional GI for cementation GI filling material Adhesive resin cement Occur later from the direct filling resin Become popular because of the improved properties, high bond strength. Resin cement is flowable composite resin. Composite resin cement Composite : Resin matrix + inorganic filler Silane coated Composition Filler Silica Matrix Bis-GMA (polymer) The fillers binds with matrix by silane coupling agent Setting reaction Polymerization Chemical activation Light activation Dual activation [chemical and light] Preparations Powder / liquid Chemical, light, or dual cure 2 paste system [base / catalyst] Chemical, light, or dual cure Single paste Light cure Bonding system Bond with the tooth surface by enamel an dentine bonding system. Bond with metal by using metal primer. Bond with ceramic restoration by treating the surface of porcelain with silane coupling agent Properties Very good bond strength High compressive strength Water sensitive Might irritate pulpal tissues Applications Tooth color filling materials Luting cements Calcium hydroxide cement Used as base and liner High pH value Good biocompatibility Composition 2 Pastes system Base Salicylate reaction Calcium tungstate and barium sulfate radiopacity Catalyst Calcium hydroxide Properties Lower compressive strength than others Resist to the condensation force of amalgam filling High pH 9.2-11.7 [Alkaline] Bactericidal High solubility Properties Stimulate the secondary dentine formation in the area of thin dentine [<0.5mm] Stimulate the dentine formation in the exposed-pulp lesion [Direct pulp capping] Comparable properties of cements Compressive strength [MPa] 160 140 120 100 80 60 40 20 0 Zinc phosphate Polycarboxylate Zhen Chun Li and Shane N. White, 1999 GIC RMGIC Resin cement Bond strength Separation forces [MPa] 300 250 200 150 100 50 0 Zinc phosphate GIC Sule Ergin and Deniz Gemalmaz, 2002 RMGIC Resin Film thickness [µm] 50 40 30 20 10 0 Zinc phosphate Polycarboxylate Shane N. White, Zhaokun Yu, 1992 GIC RMGIC Resin Others Solubility ZOE > Polycarboxylate > Zinc phosphate~GIC > Resin cement Irritation to pulp tissues Resin~Zinc phosphate > GIC > Polycarboxylate > ZOE~Calcium hydroxide References Textbooks Kenneth J. Anusavice Phillips’ science of dental materials 11th edition W.B. Saunders company 2003 References Textbook Robert G. Craig Restorative dental materials 9th edition Mosby company 1993 References Textbook Richard van Noort Introduction to dental materials 2nd edition Mosby company 2002 References Journals Li ZC, White SN. Mechanical properties of dental luting cements. J Prosthet Dent 1999;81(5):597609 White SN, Yu Z. Film thickness of new adhesive luting agents. J Prosthet Dent 1992;67(6):782-90 Ergin S, Gemalmaz D. Retentive properties of five luting cements on base and noble metal copings. J Prosthet Dent 2002;885:491-97