Biophysics of Dental Polymers PDF

International Balkan University Skopje Faculty of Dental Medicine Biophysics of DENTAL POLYMERS Asst. Prof. Eljesa Murtezi 1 POLYMER is a large molecule (known as a macromolecule) constructed of multiple repeating subu...

International Balkan University Skopje Faculty of Dental Medicine Biophysics of DENTAL POLYMERS Asst. Prof. Eljesa Murtezi 1 POLYMER is a large molecule (known as a macromolecule) constructed of multiple repeating subunits. These simple subunits that make up each polymer are known as monomers. The term polymer means many monomers! Monomers are the building blocks for each polymer. The formation of a polymer is called polymerization. This reaction involves the formation of covalent bonds between the monomers, resulting in long-chain or network structures. Polymerization can occur through various mechanisms, broadly classified into two categories: I. Addition Polymerization II. Condensation Polymerization 2  On the basis of type of -mer units, polymers are of two types: - HOMOPOLYMERS Polymers containing same type of monomer unit - COPOLYMERS Polymers containing 2 or more types of monomer unit Eyrilmez GO, Doran S, Murtezi E, Demir B, Demirkol DO, Coskunol H, Timur S and Yagci Y. Macromolecular Bioscience. 2015, 15, 1233-1241. Puglisi A., Murtezi E., Yilmaz G., Yagci Y., Polymer Chemistry, 2017, 8, 7307-7310. Murtezi E, Yagci Y. Macromolecular Rapid Communication. 2014, 35, 1782-1787. Murtezi E, Ciftci M, Yagci Y. Polymer International, 2015, 64(5), 588-594. 5 POLYMERIZATION The forming of a compound by the joining together of molecules of small molecular weights into a compound of large molecular weight. Polymerization is the process of linking monomers to form polymer chains. Based on the polymerization process, monomers link through functional group reactions or by creating reactive reaction intermediates (free radical propagation). 6 I. Chain-Reaction (Addition) Polymerization Addition polymerization is when a monomer and catalyst react with each other in a three-step process. The three steps are initiation, propagation, and termination. 7 I. Chain-Reaction (Addition) Polymerization Radical chain-growth Polymerization 9 PHOTOPOLYMERIZATION LIGHT Other forms of free radical production include the use of 1. UV in conjunction with a benzoic methyl ether 2. Visible light with an alpha- diketone and an amine 10 I. Chain-Reaction (Addition) Polymerization Cationic chain-growth Polymerization 11 I. Chain-Reaction (Addition) Polymerization Anionic chain-growth Polymerization 12 I. Chain-Reaction (Addition) Polymerization I.1. INITIATION The first step, involves the monomer undergoing an alkene addition reaction. Radical initiation works best on the carbon–carbon double bond of vinyl monomers and the carbon–oxygen double bond in aldehydes and ketones Initiation has two steps. In the first step, one or two radicals are created from the initiating molecules. In the second step, radicals are transferred from the initiator molecules to the monomer units present. 13 I. Chain-Reaction (Addition) Polymerization I. 2. PROPAGATION During polymerization, a polymer spends most of its time in increasing its chain length, or propagating. After the radical initiator is formed, it attacks a monomer. Once a chain has been initiated, the chain propagates until there are no more monomers (living polymerization) or until termination occurs. Phenyl initiator from benzoyl peroxide (BPO) attacks a styrene molecule to start the polymer chain. 14 I. Chain-Reaction (Addition) Polymerization I. 3. TERMINATION Chain termination is inevitable in radical polymerization due to the high reactivity of radicals. Termination can occur by several different mechanisms. I. 3. 1 COMBINATION Termination by the combination of two poly(vinyl chloride) (PVC) polymers. 15 I. Chain-Reaction (Addition) Polymerization I. 3. TERMINATION I. 3. 2 RADICAL DISPROPORTIONATION Termination by disproportionation of poly(methyl methacrylate). I. 3. 3 COMBINATION OF AN ACTIVE CHAIN END WITH AN INITIATOR RADICAL Termination of PVC by reaction with radical initiator. 16 Addition polymerizations 17 II. Step-Reaction (Condensation) Polymerization Instead of the free-radical propagation step, condensation polymerization involves monomers with two reactive functional or end groups that directly react with each other. These reactions often create bi-products such as water, ammonia, or HCl. For example, monomers in polyesters (a polymer category) are linked by the ester functional group. 19 20  Dental Polymers Dental polymers are a specialized class of polymers used in dentistry to restore, protect, or replace oral tissues. They offer properties like biocompatibility, aesthetics, durability, and ease of application. Dental polymers are used in various forms, such as composites, adhesives, impression materials, and prosthetics. 21 22 Based on their thermal behavior they can be divided into: 23 THERMOPLASTIC polymers Made of linear and or branched chains They may be softened by heating and solidify by cooling (Reversible reaction) The resin can then be shaped and molded upon temperature changes. E.g. -poly (methyl methacrylate) (PMMA), poly styrene (PS) etc… THERMOSETTING polymers Undergo a chemical change and become permanently hard when heated above the temperature which they begin to polymerize, and do not soften again on reheating. Thermosetting plastics have superior abrasion resistance and dimensional stability comparted the thermoplastics which have better flexural and impact properties E.g. cross linked PMMA, silicones etc. 24 PHYSICAL PROPERTIES OF POLYMERS Deformation and Recovery Applied forces produce stress within polymers that can cause: Plastic and/or elastic strain or both Plastic deformation, irreversible and results in new, permanent shape Elastic deformation is reversible and will be completely recovered when the stress is eliminated Viscoelastic deformation is a combination of elastic and plastic strain, but recovery of only elastic strain occurs as the stress is decreased… 25 RHEOMETRIC PROPERTIES Flow behavior of solid polymers involves combination of elastic & plastic deformation and the elastic recovery when the stresses are eliminated… Viscoelasticity Strain Chain length Elastomers do not always recover fully and retain a small degree of plastic deformation Viscoelastic recovery. 26  Effect of polymer chain length, branching and crosslinking on mechanical and physical properties. Rigidity, strength and melting temperature increase as polymer chain length grows and molecular weight increases 27 SOVLATION PROPERTIES The longer the chains (the higher the molecular weight), the more slowly a polymer dissolves Polymers tend to absorb a solvent, swell and soften, rather than dissolve Cross linking prevents complete chain separation and retards dissolution Highly cross-linked polymers cannot be dissolved Elastomers swell more than plastics A small amount of swelling of dental polymeric devices can have undesirable results on the fit of protheses. Absorbed molecules (e.g., water) spread polymer chains apart and facilitate slip between chains. This lubricating effect is called plasticization. 28 TYPES OF DENTAL POLYMERS 1. Acrylic Polymers: Used in dentures and orthodontic appliances. Polymethyl methacrylate (PMMA) is a common example. 29 TYPES OF DENTAL POLYMERS 2. Dental Composites Made from a matrix of resin (e.g., bis-GMA) reinforced with inorganic fillers. Used in restorative dentistry for fillings and bonding. 30 TYPES OF DENTAL POLYMERS 3. Elastomers Used as impression materials. Examples include polysulfides, polyethers and silicones 31 TYPES OF DENTAL POLYMERS 4. Resin-based Cements: Used for luting crowns, bridges, and orthodontic brackets. 32 33 Required properties of polymers for DENTAL purposes Biocompatibility Must not cause adverse reactions in the oral tissues. Mechanical Strength Able to withstand forces like chewing and grinding. Aesthetic Quality Mimics the natural appearance of teeth. Ease of Manipulation Allows dentists to shape and cure the material easily. 34 APPLICATIONS IN DENTISTRY 1. Restorative Materials Dental composites and resins are used to restore decayed teeth. Their tooth-like color and texture make them highly aesthetic. 2. Prosthetics Dentures, partials, and orthodontic appliances are fabricated using acrylic polymers. 3. Impression Materials Elastomers capture the fine details of teeth and oral tissues for making molds. 4. Adhesives and Sealants: Dental adhesives bond restorative materials to teeth. Sealants protect pits and fissures from cavities. 35 Advancements in Dental Polymers …include Nanocomposites Improved strength and reduced shrinkage during curing. Smart Polymers Respond to changes in pH, temperature, or stress, aiding in bioactive restorations. Antimicrobial Polymers Help prevent bacterial colonization and secondary caries. The development of high-performance dental polymers ensures improved patient outcomes, longer-lasting treatments, and more natural-looking restorations. 36 Residual Monomer in Dentistry Residual monomer refers to unreacted monomer molecules that remain in a polymerized dental material after the curing or setting process. These unreacted monomers are a concern in dentistry because they can affect the mechanical properties, biocompatibility, and long-term performance of dental materials. Additionally, residual monomers may leach out over time, potentially causing irritation, toxicity, or hypersensitivity in the surrounding tissues. 37 Methods to REDUCE Residual Monomer Improved Curing Protocols Post-polymerization Treatment Optimized Material Composition Application of Thin Layers 38 Thank you for your attention 39