‹#› 1 Dental materials © Department of Biochemistry LF MU (E.T.) 2010 ‹#› 2 Dental Materials Restorative • metals and metal alloys •ceramics •cements •plasts Auxiliary • impression materials • model materials • casting investments • acrylic resins • dental waxes • finishing and polishing abrasives ‹#› 3 Metalls, alloys and amalgams in dentistry Metalls are only exceptionally used in pure form. Most often alloys are used that have better properties. Using Crowns, bridges, partial dentures, implants….. Requirements Chemical stability, malleability ‹#› 4 Metals Metalic bond •Metal atoms have large numbers of electrons in their valence shell. These become delocalized and form a "sea" of electrons surrounding a giant lattice of positive ions. metalbond ‹#› 5 Metallic bond •Metallic bonds are something like covalent bonds except that large numbers of electrons are shared by massive numbers of atoms. •This trading back and fourth of electrons is what holds metallic crystals together •Each metal forms a specific type of crystalline structure based upon the internal atomic properties for that metal. •Electrons acts as conductors for both thermal energy and electricity • ‹#› 6 Metalls Typical properties luster opacity toughness (an ability to absorb energy and inhibit crack propagation) compactness stiffnes thermal and electric conductivity ductility Salt ‹#› 7 Corrosion and tarnish of metals Tarnish •surface discoloration on a metal •slight loss or alteration of the surface or luster Often occurs from the formation of hard or soft deposits (calculus, plaques, films) Corrosion –deterioration of metal due to chemical reaction with enviroment Caused by action of moisture, atmospere, acid or alkaline solutions, certain chemicals, tarnish ‹#› 8 Types of metal corrosion •Chemical corrosion Processes of oxidation, halogenation, sulfurization etc. Less common in dental materials • •Electrochemical corrosion Metals behave as electrodes of galvanic cell in the presence of saliva. • ‹#› 9 Electrochemical corrosion of metals • •The corrosion is the dissolution of metals in the mouth •The corrosion tendencies of metals are related with their position in the electromotive series (standard potentials). •Depends on the composition of saliva •Some metalls have tendence to be easy oxidized and their ions go into solution (anode) •The other metalls have little tendency to go into the solution, but ions of the electrolyte try to accumulate on the surface of the metal (cathode) •Catodic and anodic reaction can take place simuntaneously on the surface of the metal ‹#› 10 AOX/ARED E° (V) Li+/Li K+/K Ca2+/Ca Na+/Na Mg2+/Mg Al3+/Al Zn2+/Zn Fe2+/Fe Sn2+/Sn Pb2+/Pb 2H+/H2 Sn4+/Sn2+ Cu2+/Cu Ag+/Ag Hg2+/Hg Pd2+/Pd Pt3+/Pt Au3+/Au -3,00 -2,92 -2,87 -2,71 -2,37 -1,66 -0,76 -0,44 -0,14 -0,13 0,00 0,15 0,34 0,80 0,85 0,99 1,2 1,5 Standard reduction potentials of selected metals Noble metals Resistant against corrosion Metals placed in an electrolyte have various tendency to go into solution. E.g.aluminium alloy has a strong tendency to go into solution. Gold has little tendency to go into solution > ‹#› 11 amalgam M0 ® M+ + e- Ionts of a metal are released into the solution, the electrode become positivelly charged (=anode) Gold alloy Reduction reaction. E.g.: M+ + e- ® M0 2H+ + e-® H2 2H2O + O2 + 4e- ®4 OH- Saliva as electrolyte Elektrochemical corrosion anoda katoda Ions are provided by electrolyte e- ‹#› 12 Galvanic shock Tissue fluid Saliva Tissue fluid Two different restorations e.g. gold and amalgam Possible path of galvanic current in the mouth When the two restorations are brought into direct contact, sudden short-circuit occurs and the patient experiences pain G A The same effect can be experienced if a piece of aluminium foil becomes wedged between two teeth and contacts gold restoration ‹#› 13 Concentration cell corrosion A pit on a dental alloy as corrosion cell The region of a pit is an anode, and surface around the rim of the pit is cathode The ionic current flows through the electrolyte and the electronic current flows through the metal It is a consquence of accumulation of food debris in the pit. The debris produces an electrolyte in that area that is different from the electrolyte that is produced by normal saliva. ‹#› 14 Noble (precious) metals ‹#› 15 • corrosion resistance • tarnish resistance • expansive Au aurum Pt platinium Pd palladium Os osmium Ir iridium Ru ruthenium Most common noble metals in dental casting alloys – Au, Pt Noble (precious) metals ‹#› 16 Element Atomic number Density (g/cm3) Melting point(K) Boiling point (K) Ru 44 12,2 2583 4173 Pd 46 12 1825 3413 Ir 77 22,5 2683 4403 Pt 78 21,4 2045 4100 Au 79 19,3 1338 3080 Characteristic properties of noble metals ‹#› 17 Gold (Au) •Tarnish and corrosion resistance •Highest ductility and malleability of all metals (29g/100 km) •Relatively soft •Can be used for direct filling in pure state •Pieces of gold are placed in the prepared cavity •Welding by pressure at the mouth temperature (compaction) • In alloys with Cu, Ag, Pt, Pd, Ni, Zn ‹#› 18 Platinum (Pt) •Chemical and thermal resistance •Using in fixed protetics. •Pt in alloys with gold has whitening effect. Paladium (Pd) •Using only in alloys, increases the corrosion resistance •Contributes to strength. Whitening effect. •Similar to Pt, more effective and less expensive therefore has replaced Pt in most alloys Iridium (Ir) •Is combined with Pt for preparation of tough and hard alloys ‹#› 19 Base metals • used in alloys, increase strength, elasticity • lower cost Ti titanium Ni nickel Cu copper Ag silver Zn zinc ‹#› 20 Element Atomic number Density (g/cm3) Melting point(K) Boiling point (K) Ti 22 4,51 1993 3560 Ni 28 8,9 1726 3008 Cu 29 8,96 1357 2840 Ag 47 10,5 1235 2485 Zn 30 7,14 693 1180 Characteristic properties of base metals ‹#› 21 Titanium (Ti) •Mechanic properties are close to bone. Nearly completely biocompatible, corrosion resistant. Suitable for dental implants. •Can be used in pure state. Copper (Cu) • increase the strength • in pure state used for impression materials • principle hardener in gold alloys. • imparts reddish color ‹#› 22 Silver (Ag) • the best heat and electricity conductor • formation of AgS with sulfur from food • soluble in HNO3, conc. H2SO4, HCl •Using mostly in alloys •Increases ductility and hardness of alloys •Antimicrobial effect • Controls color (neutralizes the red color imparted by Cu). •Promotes ductility • ‹#› 23 Element Atomic number Density (g/cm3) Melting point(K) Boiling point (K) Hg 80 13,6 234,3 630 -39oC 357oC Mercury •Dense metal that is liquid at room temperature •II.B group = Hg+, Hg2+ •High vapour pressure •Monoatomic in vapour ‹#› 24 Alloys - formed, when two or more molten metals are mixed together and allowed to cool to a solid crystalline state Physical properties • Characteristic properties of metals – metallic luster, thermal and electric conductivity, given arrangement in crystaline lattice •Properties depend on the nature of its internal microscopic crystalline structure •affected by factors such as the speed of the cooling Metal Alloy Structure ‹#› 25 Alloys Binary alloy – an alloy containing two chemical components Tertiary, quaternary….. Phase diagram – a graphs of the phase field they express dependence of phase state and composition on the temperature during cooling ‹#› 26 Phase diagram = solidus line (solid phase is bellow) and liqidus line (above is only melt), follows the equilibrium composition of melt and co-existing solid phase at various temperatures during cooling T(K) Composition (%B) Binary mixture A, B S-solidus curve L-liquidus curve ‹#› 27 Dental alloys •Hardness, toughness x plasticity •Corrosion and abrasivity resistance •Color •Biological compatibility x toxicity ‹#› 28 Two types: • high noble alloys (the content of of gold and platinum metals min.75%) • noble alloys (25-75% of gold and noble metals) Other metals contained in gold alloys: Cu, Ag, Pt, Pd, Ni, Zn. Most often (Au,Cu), (Au,Cu,Pt,Zn) (Au,Pd,Cu) Cu increases hardness but decreases the corrosion resistance Very expansive The amount of gold in an alloy is expressed in carats Pure gold is defined as 24 carat (24K). An alloy with 50% gold is 12K, an alloy with 75% gold is 18K Gold alloys ‹#› 29 Examples of gold alloys www.vscht.cz/met/aki/kom_48/48_11_14.pdf Examples of alloys containing minimally 75% of gold and platinum metals Examples of alloys containing 25-75% of gold and platinum metals ‹#› 30 a) Co based alloys Examples of composition: -Co, Cr, Mo, Si, Mn -Co, Cr, Mo, W, Si (addition of Cr and Mo increses hardness) -Co, Cr, Mo, Ti Predominantly base metal alloys (> 75% base metals) b) Ni based alloys Examples of composition: - Ni, Cr, Mo, Si (Cr – min. 20%, Mo – min. 4%) Total content of Ni + Cr + Mo – min 85% ‹#› 31 Biocompatibility of alloys It is related to ability of their corrosion If alloys corrodes more, it releases more of its elements into the mouth and increases the risk for unwanted reactions in the oral tissues (unpleasant tastes, irritation, allergy… Alloys are tested – e.g. in a solution of lactic acid for 7 days – the changes on the alloy surface and in the solution are analyzed. ‹#› 32 Amalgam still the most commonly used filling material Amalgam fillings Alloys containing mercury mixture of mercury (from 43% to 54%) and powdered alloy made mostly of silver, tin, zinc and cooper (amalgam alloy). ‹#› 33 1826 – Auguste Taveau developed his own dental amalgam from silver coins and mercury History This amalgam contained a very small amount of mercury and had to be heated in order for the silver to dissolve at an appreciable rate. When the French Crawcour brothers emigrated to the United States in 1833, they introduced Taveau's amalgam. Because of the amalgam's poor quality, many dentists refused to use it. Numerous experiments were carried out from the 1860s through the 1890s to develop improved amalgam filling materials. Chicago, Illinois, dentist G. V. Black (1836-1915) finally standardized both cavity preparation and amalgam manufacture in 1895. ‹#› 34 •approximately equal parts •50% of liquid mercury + 50% of an alloy powder •Typical components of dental amalgam alloy: Ag,Sn,Cu •Low copper alloys: Cu max. 6% •High copper alloys: Cu>6% •Alloy powder composition: •> 40% silver (Ag) •< 32% tin (Sn) •< 30% copper (Cu) •< 2% zinc (Zn) •< 3% mercury (Hg) • Modern dental amalgams ‹#› 35 Reaction of silver alloy with mercury Amalgamation Setting reaction of amalgam alloy with mercury ØWhen high-copper alloy particles contact the mercury, they begin to dissolv in the mercury ØHowever, once some of the alloy particles has dissolved, new solid products begin to crystallize as the chemical reaction occurs ØAs the crystallization of new products continues, the amalgam becomes stiffer and eventually hardens completely ‹#› 36 Hardening of the amalgam The hardening of the amalgam occurs before all the original alloy particles can dissolve The set amalgam contains much of the original silver alloy particles surrounded by the new products The amalgamation reaction: Silver alloy (g) + mercury → silver alloy (g, unreacted) + silver-mercury (g1) + copper-tin(h) g- silver alloy Ag3Sn g1- silver-mercury Ag2Hg3 h´- copper tin Cu6Sn5 g2 phase Sn7Hg – only in low-copper amalgams ‹#› 37 Hardening of the amalgam g1- Ag2Hg3 g2- Sn7Hg h´- Cu6Sn5 ‹#› 38 Amalgam is a complex metallurgical structure, containing up to six phases ‹#› 39 Dental amalgam alloys ØPowder is produced by milling or the lathe cutting a part of ingot (particles are irregulary shaped) ØAtomizing of liquid alloy (particles are spherical) ØMixtured- lath-cut + spherical particles Powder can be suppplied in the form of pellets ultra_capsules ‹#› 40 amalgamator Amalgamation (trituration) ØAmalgam alloy is mixed with mercury in ratio 1:1, mixing (cca 10 s) – amalgamators ØPlastic phase – (5-10 min) - condenzation under the firm pressure in the cavity of prepared teeth ØHardening – increase in strength and hardness – 1-2 h ®24 h ØAmalgam become sufficiently strong within first hour Ø Setting reaction of amalgam alloy with mercury ‹#› 41 Properties of amalgam • Strenght •Dimensional change •Creep •Tarnish •Corrosion ‹#› 42 Amalgam corrosion Sn7Hg (g 2) + ½ O2 + H2O + Cl- ® Sn4(OH)6Cl2 + Hg Half-life cca 6 years High copper amalgam Cu6Sn5 + ½ O2 + H2O + Cl- ® CuCl2.3Cu(OH)2 + SnO Half-life cca 20 years g 2 phase is attached by chlorides ‹#› 43 Toxicity of amalgams There is some controversy about the use of amalgams Although mercury by itself is classified as a toxic material, the mercury in amalgam is chemically bound to other metals to make it stable. Once the amalgam reaction is complete, little or no mercury remains unreacted In practice, minute amounts of mercury vapor (appr.1-2 mg/day) are released from dental amalgams as a result of chewing Higher release may occur during the setting reaction, during removal of old amalgams or if the amalgam is heated above 80o. ‹#› 44 Mercury hygiene Process of handling mercury to minimize health risks: ØNever touche mercury even with gloved hands ØMask should be worn to decrease exposure to particulate amalgam ØUsing precapsulated amalgam ØUsing high-volume evacuation during placement and removal amalgam restorations ØAmalgam scrap should be stored in containers and capped tightly and kept cool ‹#› 45 Dental ceramics Structure: Usualy amorphous glass with crystaline phase –both components are bonded by covalent or ionic bonds. Diferent properties in comparision with other materials (metals, cements, resins) • do not conduct electricity and heat • long time resistant to corrosion and chemical effects, hard • flexure strenght and fracture toughness • color stability • biocompatibility •brittle ‹#› 46 Crystaline structure of silicates The main unit is tetrahedron with composition SiO4-. SiO4- reacts with cations or other SiO4-. Zuby2 ‹#› 47 zuby3 Formation of linear and branched networks. Dental ceramicscomprises crystaline and amoufphous phase on the base of silicates structure Depending on temperature different minerals are formed . By heating of quartz structure of tridymite is formed, after it cristobalite and at the temperature hugher than 1700oc amorphous melt is formed. Structure of quartz ‹#› 48 Composition of dental ceramics Base component Mostly oxides Conventional dental porcelain: feldspar (aluminosilicates) and silica (SiO2) In modern ceramics alumina(Al2O3 ) spinell (MgO.Al2O3 ), leucit (KAlSi2O6 ) or zirkonium oxide (ZrO2). Fluxes The fluxes cause the other raw ingradients to form a glass that is not crystalline and melts at a relatively low temperature . Borax, Na2CO3 or K2CO3 Pigments e.g. NiO2 (brown), CuO (green), CoO2(blue) ‹#› 49 Processing of dental ceramics These crystalline ingredients are heated together with fluxes such Na2CO3 or K2CO3 The fluxes cause the other raw ingradients to form a glass that is not crystalline and melts at a relatively low temperature Dental porcelain is then refired with metal oxides to add color and fluorescence.After the porcelain is cool, it is ground to a fine powder. Processing: powder is mixed with water , pressed into the mold, heat treated (sintering), overglazing, shading. ‹#› 50 Zirconia ceramics ZrO2 is important modern material for production of ceramics ZrO2 is brittle (during sintering tetragonal phase changes to monoclonal ) Change of the phase can be supressed by addition of other oxides (např.MgO, Y2O3, CaO, CeO) Y-ZTP –yttrium stabilized tetragonal zirconia polycrystals ‹#› 51 Dental cements Temporary filling materials, thermal insulation, mechanical support to teeth restored with lother materials, protection to the pulp from iritants, special using in andodontics and ortodontics Most dental cements are supplied as two component – powder and liquid (or two pastes) The liquid partially dissolves the powder particles and forms a matrix. Reaction occurs on the surface of unreacted particles of powder that become covered by the layer of reaction product.During setting it becomes hard enough to act as a "glue" and is used to cement crowns and posts. ‹#› 52 Types of dental cements •Zinc-phosphate •Silicate •Polyalkenoate •Calcium-hydroxide •Zinc oxide - eugenol •Resine Aqueous cements: zincphosphate, silicate, polyalkenoate Non-aqueous cements: calcium-hydroxide, zincoxide- eugenol, resine ‹#› 53 Classification acording to process of setting Setting by acid-base reaction (formation of a salt) • Zinc phosphate •Silicate •Polyalkenoate •Calcium-hydroxide •Zinkoxide- eugenol Setting by radical polymeration •Hybrid glass-ionomer •Resine ‹#› 54 Examples of Cements Zinc phosphate cement powder: ZnO (+ MgO + traces SiO2) liquid: H3PO4 (+ buffered by aluminium phosphate, zinc phosphate and magnesium phosphate) Chemical reaction of setting: ZnO + H3PO4 + H2O ® Zn(H2PO4)2 . H2O 2 ZnO + Zn(H2PO4)2 . H2O ® Zn3(PO4)2 . 4 H2O The set cement is a cored structure consisting primarily of unreacted zinc oxide particles embedded in a cohesive amorphous matrix zinc-aluminium phosphate ‹#› 55 Zinc oxide eugenol cement zuby4 Eugenol –oil from rose-apple Zinc-eugenolate (chelate) Has sedative effect on the pulp Useful for cementation on prepared teeth Moderate strength and low acidic quality Powder: ZnO, Liquid: eugenol ‹#› 56 Modification of zincoxide-eugnol cements Addition of ethoxybenzoate Mixture of 62,5% ethoxybenzoate, 37.5% eugenol, powder max. 30% Al2O3 ‹#› 57 powder: aluminium silicate glass prepared by fusing of SiO2, Al2O3 , CaO, NaF and sodium fluorosilicate at 1400oC liquid: cca 50% H3PO4 (+ buffering salts aluminium phosphate, zinc phosphate and magnesium phosphate) Silicate cements Structure after setting is formed by amorphous AlPO4 and particles of glass covered by the layer of SiO2 ‹#› 58 Zinc polycarboxylate cements Water based-cements used as final cements for retention of crowns and bridges Powder: Zinc oxide + Al2O3, SnF2 Liquid: 40-50% polyacrylic acid in water They react to form zinc polyacrylate that surrounds the partially reacted zinc oxide powder particles Properties: moderate viscosity, moderate strength, ability to bond enamel, mild acidity. ‹#› 59 ‹#› 60 Glass Ionomers Cements (GIC) mixture of aluminosilicate glass and aqueous solution of polymers and copolymers of organic acids (acrylic acid, maleinic, itaconic) Composition: Powder: particles of 10-20mm alkaline fluorosilicate glass with the high content of Ca,Al,P,F- (prepared from SiO2, Al2O3, CaF2, AlPO4, Na3[AlF6], AlF3, addition of polyacid) Liquid: polymer soluble in water e.g. polyacrylic, polymaleinic acid, adition of tartaric acid water as a reaction medium ‹#› 61 Maleinic acid Itaconic acid Acrylic acid ‹#› 62 Reaction principle: The material sets as a result of the metalic salt bridges between the Al3+ and Ca2+ ions and the acidic groups on the polymers a small amount of tartaric acid is added to the water to provide a sharper, better defined setting reaction ‹#› 63 Structure of GIC after setting Matrix of Ca,Al polyalkenoates Glass particles Gel of SiO2 ‹#› 64 Possible inter- and intramolecular interactions in glassionmer cements (X = OH- , F-,) ‹#› 65 Hybrid Ionomer Cements or Resin-modified Glass Ionomers The powder is similar to that of glass ionomers The liquid contains monomers (HEMA – hydroxymetacrylate), polyacids and water Hybrid ionomers set by acid-base and resin polymerization reaction (light-cured or self-cured) ‹#› 66 Acid-base reactions are supplemented by a second resin polymerization ‹#› 67 Resin cements Used for bonding of ceramic and indirect composite crowns, inlays and onlays Temporary resin cements are used for temporary cementation of část crowns and restorations Composed of dimethacrylate resin and glass filler (see the composite fillings) ‹#› 68 Metal-reinforced glass ionomer cements GIC can be reinforced by physically incorporating silver alloy powder with glass powder (silver alloy admix) or by fusing glass powder to silver particles through sintering (cermet) ‹#› 69 Gypsum in dentistry production: from mineral gypsum CaSO4 . 2H2O by removal of crystaline water (calcining). Dental plaster = calcium sulfate hemihydrate CaSO4 . ½ H2O Plaster setting: reverse reaction with H2O to CaSO4 . 2H2O – setting is caused by different solubility of hydrate and hemihydrate in water. Volume changes during plaster setting: after mixing of water volume contraction, during setting volume expansion. Dental plaster: expansion < 0,25%. Addition of borax or K2SO4 ‹#› 70 Plaster setting 2 CaSO4 . ½ H2O + 3H2O ® 2 CaSO4.2H2O solubility 0,2 g/100g water Solubility 0,9 g/100g water Setting accelerators: K2SO4, NaCl Setting retarders: Na2B4O7, sodium citrate, CH3COOH, gelatin ‹#› 71 Macromolecular compounds and plastics in dentistry natural syntetic ‹#› 72 Polymers are macromolecules composed of regulary repeated units. The building unit is monomer . The molecular weight of monomers is about 100, the molecular weight of polymer ~10 000 Carbon atom with the tendency to form chains has in macromolecular chemistry dominant role. Polymers ‹#› 73 Types of polymeration reactions · radical polymeration · ionic polymeration · polyadition · polycondensation ‹#› 74 Radical polymeration - From unsaturated hydrocarbons (monomers) macromolecules (polymers) are formed RO. + CH2= CH2 –—® RO – CH2– CH2. initiator ROCH2CH2. + CH2 = CH2 —® ROCH2CH2CH2. propagation CH2= CH2 –—® [CH2– CH2]n ‹#› 75 Monomers and products of polymeration - examples x x x x x polyethylene PE polyvinylchloride PVC polystyrene PS polymethyl-acrylate teflon ‹#› 76 Acrylate polymers most common plasts in stomatology (95%) Metacrylic acid methyl-acrylate Acrylic acid methyl-metacrylate ‹#› 77 Initiator: organic peroxide dibenzoylperoxide it is activated by the heat or organic accelerator ¯ ‹#› 78 Cross-linked polymers Produced in the presence of small amounts of different monomer units with reactive double bonds on each end of the molecule Eg.. glycoldimetacrylate Advantage: higher resistance against surface cracking or crazing in the mouth. ‹#› 79 Crosslinking using glycoldimetacrylate ‹#› 80 Copolymers – two or more different monomers both units are spaced randomly along the chain butyl metacrylate more resistant to fractures Hydroxyethyl metacrylate Oktyl metacrylate - increases softness and flexibility Examples of monomers added to methylmetacrylate ‹#› 81 Modified polymers Modification by the addition of compounds that do not enter into the polymerization Oily organic esters, rubbers, inorganic fillers E.g.: addition of dibuthyl phtalate plasticize the polymer ‹#› 82 Components of the powder and liquid of an acrylic denture base Powder Liquid Polymer (polymethylmetacrylate) Monomer (methylmetacrylate) Organic peroxide Hydrochinon (inhibitor) 0,1%* TiO2 (translucence) Cross-linking monomer Anorganické pigmenty Organic accelerator (amine)** Dyed synthetic fibers for esthetics *prevention of polymeration during storage ‹#› 83 Vinyl plastics Copolymers of vinylacetate and ethylene + x y Using in preventive dentistry as mouth protectors vinylacetate-ethylene copolymer ‹#› 84 Resin-Based Fillings Consist of three phases: •Resin matrix •Dispersed inorganic filler particles •Silane coupling agent ‹#› 85 Natural composite materials Enamel Dentin 95% anorganic component (mainly hydroxyapatite) 1% organic component (enamelin) 4% water 75% anorganic component (hydroxyapatite) 20% organic component 5% water The differences in properties are given by matrix/filler ratio ‹#› 86 Resin matrix The most common resins Oligomers based on: bis(phenyl-glycerol-metacrylate)-propane (bis-GMA) urethane dimethacrylate (UDMA) The reactive double bonds udergo to polymerization after appropriate initiation. R-large organic group (phenyl, carboxyl, amide … ‹#› 87 bis(fenyl-glycerol-metacrylate)-propane urethametacrylate 2,2-bis-[4-(2-hydroxy-3-methacryloxy-propyloxy)phenyl]-propane (1-methylethylidene)bis[4,1-phenyleneoxy(2-hydroxy-3,1-propanediyl)] bismethacrylate Bisphenol A-glycidyl methacrylate bis-GMA ‹#› 88 Resin matrix Bis-GMA and UDMA oligomers are viscous liquids to which low molecular weight monomers (dimethacrylates) are added to control the consistency of the composite paste EDMA ‹#› 89 Filler composition Conventional fillers – silica or glass (aluminium/borosilicates) (diameter 1-50 mm) Fine fillers (diameter 0,2-3 mm) Quartz lithium aluminium silicate Barium, strontium, zinc or ytterbium glasses Microfine fillers (diameter 0,04 mm) Colloidal silica particles Hybrid fillers – mixture of macroparticles grind glass>1 mm and SiO2 0,01-0,1mm ‹#› 90 •class of organosilane compounds having at least two reactive groups of different types bonded to the silicon atom in a molecule. •One of the reactive groups of different types (ex. methoxy, ethoxy and silanolic hydroxy groups) is reactive with various inorganic materials such as glass, metals, silica sand and the like to form a chemical bond with the surface of the inorganic material •the other of the reactive groups (vinyl, epoxy, methacryl, amino and mercapto groups) is reactive with various kinds of organic materials or synthetic resins to form a chemical bond. Silane coupling agents ‹#› 91 silaneformulas_1 silaneformulas_2 silaneformulas_4 silaneformulas_6 silaneformulas_7 Examples of silane coupling agents ‹#› 92 H2O + 3 CH3OH Effect of coupling agent ‹#› 93 Light curing systems – polymerization is initiated by the blue light Self-cure systems – polymerization is initiated by chemical way. Polymerization of composite Polymerization is based on radical reaction. Two types of iniciation: ‹#› 94 Light curing systems For inciation is used camphorquinone It is excited by blue light (468 nm) and interacts with tertiary amine to form free radicals that initiate polymerization ‹#› 95 Self-curing systems Two pastes. One of which contains the dibenzoylperoxide (initiator) and the other an aromatic tertiary amine (N,N-dimethyltoluidine) (activator) When the two pastes are mixed together, the amine reacts with dibenzoylperoxide to form free radicals Dual-cure resins Combination of both principles