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Biomaterials in dentistry Department of General Chemistry Poznań University of Medical Sciences DDS 2011/12 Biomaterials in dentistry 1. Composites 2. Polymers: - acrylic and methacrylic acids - epoxy systems - polyethers - silicones 3. Impression materials: - rubbers (polysulfides, silicones), - alginate and agar hydrocolloids 4. Waxes 5. Gypsum 6. Cements (ZnO-phosphate, ZnO-eugenol, glass-ionomers) 7. Metals alloys, amalgams 8. Ceramics Biomaterials in dentistry Composites Composites can be defined as a compound containing two or more distinctly different phases with properties superior or intermediate between the individual components A composite has at least two distinct phases: - a continuous matrix (polymer/resin) - dispersed, discontinuous (filler) Examples: - natural: bone, dentine, enamel - synthetic: fiberglass, dental restoratives Dental composites - major constituents : - high molecular weight monomers, - fillers, - minor constituents : - diluents or viscosity modifiers (monomers with low molecular weight and viscosity), - inhibitors, stabilizers, - silane coupling agents. Polymers Polymers Biomaterials in dentistry Polymers Polyacrylic and polymethacrylic acids Biomaterials in dentistry The epoxy systems Biomaterials in dentistry The polyether system Biomaterials in dentistry Silicones Biomaterials in dentistry Biomaterials in dentistry Composites in dentistry Biomaterials in dentistry Impression materials Rubbers - polysulfides Biomaterials in dentistry Biomaterials in dentistry Impression materials - silicone rubbers Biomaterials in dentistry Impression materials – alginate, agar-agar The elastic impression materials, alginate and agar hydrocolloids, and the rubber materials, are the most widely used today. Alginate hydrocolloid Dental alginate impression materials change from the sol phase to the gel phase because of chemical reaction. Once gelation is completed, the material cannot be reliquefied to a sol. These hydrocolloids are called irreversible. Alginic acid is prepared from a marine plant and is a linear polymer of anhydro-β-Dmannuric acid of high molecular weight. Solutions of potassium and sodium salts of alginic acid, when reacted with a calcium salt, produce an insoluble elastic gel: Potassium alginate + calcium sulfate dihydrate + water → calcium alginate gel + potassium sulfate Biomaterials in dentistry Alginic acid Biomaterials in dentistry Agar hydrocolloids The agar hydrocolloid impression materials are compounded from reversible agar gels. When heated, they liquefy or go into the sol state, and on cooling they return to the gel state. This process can be repeated, and the gel of this type is described as reversible. Biomaterials in dentistry Waxes Dental waxes may be composed of natural and synthetic waxes, gums, fats, fatty acids, oils, natural and synthetic resins, and pigments of various types. Waxes have been classified according to their origin: - mineral - plant - insect - animal The two principal groups of organic compounds contained in waxes are hydrocarbons and esters, some waxes contain free alcohols and acids. Most mineral waxes contain hydrocarbon chains ranging from 17 to over 44 carbon atoms. Plant and animal waxes contain considerable concentrations of esters. Carnauba (a plan wax) contains 85% alkyl esters of various kinds. The principal ester in beeswax is myricyl palmitate: C15H31 COO C30H61 Biomaterials in dentistry Montan wax (an earth wax) contains large amounts of esters, the main compound being: C28H57 COO C24H49 Synthetic waxes – become available in recent years. The following represent some of the synthetic waxes: - polyethylene waxes - polyoxyethylene glycol waxes - halogenated hydrocarbon waxes - hydrogenated waxes - wax esters from the reaction of fatty alcohols and acids. Biomaterials in dentistry Gypsum Most gypsum products are obtained from natural deposits. Gypsum is the dihydrate form of calcium sulfate CaSO42H2O. On heating it loses 1.5 mol of water and is converted to hemihydrate CaSO4 ½ H2O When hemihydrate is mixed with water, the reverse reaction takes place: CaSO4 ½ H2O + 1 ½ H2O → CaSO4 2H2O + 3,9 kcal/mol Plaster of paris water gypsum The reaction is exotermic. The term plaster of paris got its name because it was obtained by burning the gypsum from deposits near Paris, France. Gypsum products are used for several different purposes: - model laster - dental stone Biomaterials in dentistry Cements Cements are employed for two primary purposes: - to serve as a restorative filling material either alone or with other materials - to retain restorations or appliances in a fixed position within the mouth Certain other cements are used for specialized purposes in the following fields of dentistry : - restorative - endodontic - orthodontic - periodontic - surgical Biomaterials in dentistry The classification of dental cements based on their chief chemical ingredients: - zinc oxide - phosphates - zinc oxide – eugenol - zinc oxide – non-eugenol - zinc polyacrylate - glass and hybrid ionomers - resin, composite and adhesive resin cements - calcium hydroxide Biomaterials in dentistry Typical composition of zinc phosphate cement powder and liquid Biomaterials in dentistry Components of zinc oxide – eugenol cement Biomaterials in dentistry Zinc polyacrylate cement Biomaterials in dentistry Glass ionomers Glass ionomers (GI) are restorative materials, used as a cavity liner and dentin bonding, a core material to support cast metal or ceramic restorations. Glass ionomer cements are supplied as a powder and a liquid. The powder is a calcium fluoroaluminosilicate glass with a formula: SiO2 – Al2O3 – CaF2 – Na3AlF6 – AlPO4 and composition: Biomaterials in dentistry The liquid is a 47.5% solution of 2:1 polyacrylic acid/itaconic acid copolymer in water. The itaconic acid in liquid reduces viscosity and inhibits gelation. Tartaric acid (5%) in the liquid is an accelerator and facilitates the extraction of ions from the glass powder. The setting reaction is an acid-base reaction between the acidic polyelectrolyte and the glass: GI set by a hardening reaction between glass powder and polymers and copolymers of acrylic acid. Protons released from the polymer acid attack the surface of the glass particles, and release Al3+ and Ca2+ ions. Salt bridges are formed between the polymer acid and gel matrix formed. Similar reaction can take place between the ionomer mix and calcium ions on the surface of tooth structure, resulting in an adhesive bond. The glass ionomer cements chemically bond to enamel and dentin during the setting process. Biomaterials in dentistry Metals Metal alloys: - cobalt-chromium alloys - nickel-chromium alloys - titanium and titanium alloys (Ti-6Al-4V) Dental amalgam alloys: - low copper alloys - high copper alloys - silver-tin alloys (intermetallic compound Ag3Sn - -phase Biomaterials in dentistry Titanium alloys Ti-6Al-4V Ti – 12 Mo – 6Zr – 2Fe Ti – 15Mo – 5Zr – 3Al Ti – 15Mo – 3Nb – 3O Ti – Zr – 4Nb – 2Ta – 0.2Pd Ti – 15Sn – 4Nb – 2Ta – 0.2Pd Ti – 13Nb – 13 Zr (high biotolerance) Ti – 35Nb – 5Ta – Zr (low Young’s coefficient) Biomaterials in dentistry Amalgams An amalgam is an alloy of mercury with one or more other metals. Dental amalgam is produced by mixing liquid mercury with particles of an alloy of silver, tin, copper and sometimes zinc, palladium, indium, and selenium, a combination of soild metals known as the amalgam alloy. Composition of amalgam alloy must consist essentially of silver and tin. Other metals may be included in lesser amounts. The alloys are classified as low-copper alloys (5% or less copper) and hohg-copper alloys (13-30% of copper). A high-copper alloy is selected to obtain a restoration with high early strength, low creep, and good corrosion resistance. Composition of low- and high-copper amalgam alloys Biomaterials in dentistry The equilibrium silver-tin phase diagram. An alloy containing approx. 27% tin is slowly cooled below a temp. 4800 C, and an intermetallic compound (Ag3Sn), known as the gamma (γ) phase, is produced. This compound (phase) is an important ingredient in the amalgam alloy and combines with mercury to produce a dental amalgam of desired mechanical properties and handling. Biomaterials in dentistry Low-Cu amalgam formation: Ag3Sn() + Hg(l) → Ag2Hg3(1) + Sn7-8Hg(2) + Ag3Sn() High-Cu amalgam formation: Ag3Sn() + AgCu (eutectic) + Hg(l) → Ag2Hg3(y1) + Sn7-8Hg(2) + Ag3Sn() + AgCu (eutectic, unreacted) followed by the reaction: Sn7-8Hg(2) + AgCu → Cu6Sn5() + Ag2Hg3(1) Biomaterials in dentistry Ceramics Dental porcelains are made mainly with potash feldspar, heated with alkali metal carbonates to about 1000C. The feldspar decomposes to form a glass and leucite KAlSi2O6 (or K2O Al2O3 4SiO2). Pure quartz crystals (SiO2) are used in dental porcelain, contributes to the mass during heating by providing a framework for the other ingredients. Kaolin is a clay represented by the formula Al2O3 2SiO2 2H2O. Kaolin gives porcelain its properties of opaqueness. Biomaterials in dentistry Composition of dental ceramics for fusing to high temperature alloys