Dental Polymers.pptx

POLYMERS USED IN DENTISTRY

1. Dental Polymers

2. Contents Introduction Basic nature of polymers Classification of polymers Polymerization and Types Stages of polymerization Prosthetic dental polymers Properties of polymers Uses of polymeric materials Types of polymers Molecular weight Structure of polymer

3. Intoduction Before introduction of acrylic polymers to dentistry the principle polymers used was vulcanized rubber.Polymers introduced in 1937 included vinylacrylics and poly acrylic acids. The primary use of polymers has been construction of prosthetic appliances such as denture base. However they are also used in artificial tooth,restoration,cements,elastics,inlay patterns,implants,impression materials,dies,temporary materials,endodontic filling etcs . Polymers are formed through chemical reactions that convert large number of low molecular weight(LMW) molecules known as monomers into a large very high molecular weight chain macro molecules known as polymers. The form and morphology of this macro molecule determines whether the material is a fiber,a rigid solid or an elastomer .

4. DENTURE - An artificial substitute for missing natural teeth and adjacent tissues DENTURE BASE - the part of a denture that rests on the foundation tissues and to which teeth are attached DENTURE BASE MATERIAL - any substance of which a denture base may be made up of . Polymeric molecules may be prepared from a mixture of different types of monomers. Homopolyme r -If it contains one type of constitutional repeating chemical molecules. Eg -A-A-A-A-A. Terpolymers -If more than three chemical molecules. Stereo specific -Sometimes polymers is produced having “ mer ” units with a special spatial arrangement with respect to adjacent unit.

5. EVOLUTION Materials used before 18 th century 1. Wood 2. Bone 3. Ivory Materials used in the 18 th century 1. Gold 2. Porcelain Materials used in the 19th century . Tortoise Shell (1850) 2. Gutta Percha (1851) 3. Vulcanite (1851) 4. Cheoplastic (1856) 5. Rose Pearl (1860) 6. Aluminum (1867) 7. Celluloid (1870) Materials used in 20 Th century 1 . Bakelite (1909) 2. Stainless steel (1921) 3. Cobalt Chromium (1930) 4. Vinyl Resin (1932) 5. Acrylic Resin (1937) 6. Self cure Acrylic Resin 7. Epoxy Resin (1951 ) 8. Polystyrene (1951) 9. Nylon (1955) 10. Polycarbonates(1967) 11. High impact acrylic (1967) 12. Polysulphones (1981) 13. Visible L.C.(1947)Acrylic (1986) 14. Pure Titanium (1998) PMMA most accepted for use in dentistry Khindria S K, Mittal S, Sukhija U. Evolution of denture base materials. J Indian Prosthodont Soc 2009;9:64-9

6. Desirable properties BIOLOGICAL - should be tasteless, odourless , non- toxic,non -irritating to the biological structures. impermeable to biological structures discourage the microbial growth. PHYSICAL – must have adequate strength and resilient to resist masticatory , impact and wear forces. must have dimensional stability and resistance to thermal changes. low specific gravity for less bulkiness. ESTHETICS - must have sufficient translucency and should allow coloring and pigmentation. must not change colour over time. HANDLING - must not produce toxic fumes or dust. must be easy to mix, insert, shape and cure. Should not change in presence of oxygen,saliva and blood contamination. must be easy to polish and repair. ECONOMIC- cost of the material and processing should be practical and feasible.

7. Basic nature of polymer The term polymer means a molecule which is made up of many “ mers”.Thus PMMA is a polymer composed of many mers.polymers may be prepared from a mixture of different types of monomers Eg-Polymethylmethacrylate is derived from methyl methacrylate . Dental uses of polymers- The various use of polymers in dentistry are as follows:- • Prosthodontics : “Denture bases and teeth, delicate liners, custom plate, impression materials, core build up  materials, temporary restoratives, establishing/ luting materials, and maxillofacial prostheses”.  • Operative Dentistry: “Dentin bonding agents, cavity fillings, resin and glass- ionomer cements, pit and fissure sealants, bracing materials and veneers”.  • Orthodontics: “Brackets, bracket holding adhesives and cements and spacers”.  • Endodontics : “Gutta-percha , root canal sealants and elastic dams”.  • Equipment: “Mixing bowls and spatulas, mouth guards (athletic gear) and defensive eyewear”.  

8. Properties Of Polymers- Fig-1-Rigidity,strength and melting temperature increases with increase with molecular weight and chain length(courtesy- phillips science of dental material) The mix of polymer composition, chain length, branching, cross linking and atomic direction can deliver an assortment of properties. To address the issues of different dental applications, these highlights are controlled to create a balanced properties. These properties can be gathered into four interrelated classifications: Mechanical, Rheological (Flow), Dissolution And Thermal.

9. Mechanical Properties—Deformation and Recovery When forces are applied to the polymer they  produce stress which causes materials to deform or stretch from its original shape and size  ( i.e , undergo strain) via either elastic strain, plastic strain or a combination of elastic plus plastic strain. •  Plastic  strain Plastic strain is irreversible distortion that can't be recouped and brings about another, perpetual shape as the after effect of slippage (flow) among polymer chains. •  Elastic  strain is a reversible,versatile strain that is rapidly and totally recouped when the stress is eliminated, as the result of polymer chains uncoiling and then recoiling. •  Viscoelastic strain is a blend of both flexible and plastic disfigurement, yet just the versatile part is recouped when the pressure is reduced.

10. Rheometric properties- The rheometry or flow behaviour of rigid polymers involves a mix of elastic and plastic deformation followed by elastic recovery after the stresses are removed.This combination of elastic and plastic changes are called visco elastic property. The length of chain,cross link numbers,temperature and rate of force application determines which type of behaviour dominates. Plastic flow- Irreversible strain conduct that happens when polymer chains slide more than each other and gets moved inside material bringing about perceptual distortion. Elastic recovery- reversible strain behaviour that occurs in amorphous regions of polymers when randomly coiled chains straighten and then recoil like springs.

11. Solvation and Dissolution properties- Polymers are usually slow to dissolve.the sovation characteristic are very sensitive to polydispersity,cross linking,crystallinity and chain branching.the following characteristic properties exhibited by polymer which is relevant in dentistry- The longer  the chains with high molecular weight the less is the solubility of polymer. Polymers engross a solvent and soften, but they never dissolve. The cross connecting of the chain forestalls chain detachment and retards disintegration and exceptionally cross connected chains can't be broken down.  Elastomers swell more effectively than plastics. Absorbed molecules spread the polymer chain within the polymer thus facilitating the slippage of chains and this property is called plasticization. Swelling of dental polymers affect the fit of dental polymeric prosthesis.

12. Thermal properties- The property of a polymer changes with change in  temperature and composition ,structure and molecular weight.Thus higher is the temperature the softer and weaker the polymers become.polymers can be formed into desired shapes using type of polymeric material used.According to its thermal setting polymer can be divided into thermoplastic polymers and thermosetting polymers . Thermoplastic polymers- Soften on heating and hardens on cooling.Thermoplastic polymers are made up of branched or linear chains and they soften when heated above the “glass transition temperature( Tg )”. Eg -polyamides (nylon),  acetal resins, epoxy resins,impression compound,polystyrene , polycarbonate resins, polyurethane and acrylic. Thermosetting polymers- Thermoplastic material undergoes a series of chemical changes and hardens when heated above the glass transition temperature.They don't soften again on re heating.They usually are cross linked in this state and don't melt.Eg -PMMA.

13. Co polymers -If it contains two or more different chemical molecules.It can be of two types- Random Block When monomer A is mixed with monmer B A and b monomeric units is formed. A-B-A-B-A-B Sequence of a monomer followed by another sequence of another monomer. A-A-A-B-B-B

14. Molecular Weight One polymer consists of various “ mers ” multiplied by number of “ mers ” and many range from thousand to millions of molecular units.( mers ).

15. Spatial Structure Property of polymers is also determined by the spatial structure. Three basic types- Linear Branched Cross linked Linear polymer has monmer unit of same type.the linear and branched molecules are separate and discrete whereas cross linked are network structure results in a giant molecule .

16. Classification Based on their thermal behaviour- Thermoplastic Thermosetting Based on polymerization Addition Condensation Based on origin Natural Synthetic Based on architecture Linear Branched Cross linked Based on chemistrty Homopolymer Co-polymer- random,block or graft

17. Poymerization and Types Polymers are prepared by a process called polymerization where many no. Of monomer undergo chemical reaction and gets attached to itself by cross linking and together form high molecular weight macro molecule called polymer.This series of chemical reaction is called “ polymerization” Polymerization takes place in 2 Types:- Addition Condensation

18. Addition polymerization Monomer unit add sequentially to the end of growing chain.the chain grows indefinitely untill all monomer is exhausted.the process is simple but not easily control.eg-Vinyl polymers and MMA. The process occurs in two steps- Carbon carbon double bond(c=c) opens and joins to form single bond. Ring open reaction in which 3 atom ring is broken and joins with other bond which again break to form single bond.

19. Free radical polymerization Initiator releases free radicals which bring about polymerization reaction. Eg -benzyl peroxide release free radicals to bring polymerization in acrylic resins Ring opening polymerization Ring structure in the polymer chain is opened and cross linking occurs. Eg -polyether resins Ionic polymerization Catalyst bring about exchange of ions resulting in cross linked polymer Eg -addition silicones

20. Stages in addition polymerization Induction Activation Initiation Propagation Chain transfer Termination

21. Induction First a free radical is formed denoted by R. This free radical is a atom possesing unpaired electron. Activation is the process of producing free radical. Free radical is generated by chemical agent- benzoyl peroxide. Heat-tertiary amine Visible light Uv light. This free radical reacts with monomer and initiates the polymerization reaction. When at one end this initiation occurs the other end the remaining molecule unpaired electron will make new molecule and free radical which further will proceed the reaction. Free radical converts monomer into polymer.the lower moleculer pair with higher molecule resulting in atomic bonding.

22. Propagation Free radical are transferred to the monomer which in turn reacts with other monomer. M+M DIMER. This Process Continues With Evolution Of Heat And Leads To Large No Of Polymer Molecules. Increase in chain requires energy

23. Chain Transfer The active free radical is transferred to another molecule and a new free radical for further growth is created. Chain transfer occurs when a free radical approaches a MMA molecule and donates a hydrogen atom to MMA.There forms a double bond and free radical become inactive. A new nucleus growth is created.

24. Termination The chain reaction terminates by direct coupling of free radical or by exchange of hydrogen atom. Inhibition of addition polymerization may also be due to impurities which reacts with free radicals.eg-hydroquinone.

25. Condensation polymerization Also called step growth polymerization.by products is formed. The formation of by product which gradually evaporates is the reason for step growth. Two molecules react to form a large molecule with elimination of smaller molecule such as water , alcohol,halogen acids and ammonia. The reaction proceeds in a step wise fashion from monomer to dimer to trimer . The polymer formed is of low molecular weight .

26. Requisite properties of polymers Strength and durability Satisfactory thermal properties Processing accuracy & dimensional stability Chemical stability ( unprocessed & processed) Insolubility in and low sorption of oral fluids Absence of taste and odor Biocompatible Natural appearance Color stability Adhesion to plastics, metals, and porcelain Ease of fabrication and repair Moderate cost

27. Poly methyl metha acrlyate The most popular material used for denture fabrication since its introduction in 1937 “ Walter wright ” introduced [PMMA] Clear and colourless polymer. polymer of methyl methacrylate , with chemical formula (C5H8O2)n Belongs to the important acrylic family of resins.

28. METHYL METHACRYLATE METHYL METHACRYLATE is the methyl ester of methacrylic acid. It polymerizes easily to form polymethyl methacrylate . Colorless liquid with an acrid, fruity odor . Slightly soluble in water and floats on water. Vapors heavier than air. Boiling point 100.8 degree celcius

29. The monomer tends to self-polymerize if subjected to heat, polymerization catalysts , strong oxidizers, or ultraviolet light. An inhibitor such as  hydroquinone ,is added to keep the chemical from initiating polymerization Polymerize exothermically uses in the fields of medicine and dentistry to make prosthetic devices and as a ceramic filler or cement. Vapors irritate the eyes and respiratory system. Studies have shown [ european commission, esis ; iuclid dataset, methyl methacrylate (80-62-6) p.275 (2000 CD-ROM edition )] that dermal exposure is greater than inhalational exposure and is excreted in urine, but quantifiable analysis could not be made.

30. Polymer – Monomer Interaction Sandy stage Stringy stage Dough like stage Rubbery or elastic stage Stiff stage

31. Synthetic resins are used in a variety of dental applications:- Dentures (bases, liners and artificial teeth) Cavity-filling materials ("composites") Sealants Impression materials Equipment (mixing bowls) c ements (resin-based ) Dental resins used mainly to restore and replace tooth structure and missing teeth APPLICATIONS OF RESINS IN DENTISTRY

32. Applications of polymers in dentistry Denture Base Material- Most denture bases and acrylic teeth are fabricated using (poly methyl methacrylate ) PMMA.pmma is frequently used due to its  various advantages like low cost,biocompatibility,ease of processing,stability in oral environment and acceptable esthetics.How ever the properties of pmma is enhanced by incorporating many fillers and fibers. Soft Lining Materials-    These are consistent materials which are placed between the denture and the oral mucosa so as to diminish torment and distress brought about by hard dentures. These materials are additionally applied in maxillofacial reconstruction and as obturators . soft lining materials are classed in two types: soft acrylics and silicone rubbers .   Heat or room temperature polymerized methacrylates with included plasticizers, hydrophilic acrylic polymers, silicones and elastomer / methacrylate copolymers are ordinarily utilized as soft lining materials. A basic prerequisite is a glass temperature beneath 37 °C, with the end goal that the polymer stays delicate in the oral pit. The polymers ought to be biocompatible, non aggravation to oral tissues, have satisfactory mechanical quality and have low liquid take-up. soft acrylics show great bond to PMMA denture bases true to form anyway the joining of plasticizers adds to, the solidifying over some stretch of time and they additionally experience the ill effects of enormous water take-up. There is a developing worry about the utilization of Pthalate plasticizers, because of their harmfulness. Silicones experience the ill effects of absence of bond to the acrylic denture bases and have a low protection from tear.  

33. Some silicone delicate liners assimilate a lot of liquids and water take-up of hydrosilanized silicone rubbers is affected by added substances, for example, hydrophobic or hydrophilic silica and is identified with the dissolvability of the added substance, more prominent solvency offering ascend to a drawn out water take-up with bigger deviation from traditional dissemination attributes.  Dental Composites- Dental composites are tooth hued filling materials made out of synthetic polymers, particulate ceramic fillers , polymerization promoters and coupling agents.They are progressively being utilized as restorative materials set straightforwardly, in a roundabout way or as a cement, inbonded restorations. Dental composites are supplied as single paste formulations also termed visible light cure (VLC) materials and as two pastes for the self-cure systems.

34. Dentin Bonding Agents-   Other than GIC bulk filling material do not adhere to tooth exclusively and Dentine bonding agents provide a phenomenal attaching to tooth structures as well as the new age materials likewise permit bonding between composite resins and substrates, for example, base metal combinations, solidified amalgam, cured composites and porcelain.adhesion to enamel isn't as troublesome as to dentine inferable from the unpredictable and variable arrangement of dentine. Dentine bonding agents can be considered to include three segments:”a primer, a coupling agent and an unfilled resin” significant so as to acquire a precise impression followed by its flexible recuperation and mechanical quality . More recently, a therapeutic adhesive was synthesized that contained three agents: “a QAM named dimethylaminododecyl methacrylate (DMADDM) with antibacterial activity, nanoparticles of silver ( NAg ) and NACP for remineralization ”. There was no decrease in dentin bond quality from one day to a half year of when placed in water, while the commercial control bonding agent lost strength roughly 33% of its dentin bond quality at six months.This bonding agent indicated a drawn out toughness in dentin bond quality.   Impression  Materials-  Numerous methods in restorative dentistry require an exact replica model of the oral delicate and hard tissues so as to build appliances  outside the mouth; a few models being dentures ,crowns and bridges and orthodontic appliances. Impression materials are presented in the oral cavity in a plastic or fluid state which subsequently undergo a series of chemical reaction.The flow properties are significant so as to get a precise impression followed by its flexible recuperation and mechanical strength. Impressions are frequently stored at room temperature and subjected to high tensile stresses on removal from undercut areas. Eg -natural polymers agar – agar,silicone impression material,polyethers,polysulphide .

35. Peek And Peak- PEEK ( polyetheretherketone ) is a synthetically manufactured polymeric material and  the most significant representative of polyaryletherketone (PAEK). This is a partially crystalline, thermoplastic high temperature- resistant, high-performance plastic with a melting temperature of 334°C. Therefore, PEEK can be used in pressurized compression systems like “for 2 press” system, while the factory pressed product can be processed with different cutters and used in “CAD/ CAM”technology .  PAEK is a moderately new group of high temperature thermoplastic polymers comprising of a fundamental sweet-smelling aromatic molecular chain linked by “ ketone and ether”.The synthetic structure of polyaromatic ketones gives stability at high temperatures (more than 300 ° C), making it amazingly alluring for modern applications. Before the finish of 1990, PEEK had developed as the fundamental thermoplastic polymer and was utilized to supplant metal parts in the orthopaedics.PEEK can without much of a stretch be altered by including different materials carbon fiber addition may build the elastic modulus to 18 GPa . The carbon-fortified PEEK module is compared to the cortical bone and the dentin. The elasticity of PEEK is like that of bone, enamel and dentin subsequently making it an ideal material for perpetual prosthetic rebuilding efforts.

36. Bio HPP- Bioactive PEEK with ceramic filler (Bio-High Performance Polymer) is a part of the “PEEK” family and is applied in surgeries since a considerable length of time. Because of its fantastic stability, its ideal polishing properties and its low plaque affinity, BioHPP is generally excellent for exact prosthetic reclamations manufacture. “The biopolymer has a modulus of flexibility closer to the human bone and this reality improves the masticating performances. BioHPP (High Performance Polymer) is an innovative thermoplastic polymer dependent on PEEK”. It was made and upgraded for dental use. It contains ceramic microparticles for better polishing of the restorations. These ceramic fillers have a size of about 0.3-0.5 microns and possess 20% of the all out volume of BioHPP .  BioHPP is as close as conceivable deep down, on account of its coefficient of versatility (around 4 GPa ). This is significant in implant treatment in situations when winding powers may happen. The biting pressure is transmitted as tenderly as could be expected under the circumstances, and the danger of fracture is decreased, because of the BioHPP modulus of flexibility near that of the spongiose bone.  BioHPP is especially appropriate for patients with sensitivities on the grounds that the solvency of the polymer in water is low <0.3 ìg /mm3.Studies exhibits high protection from abrasion.BioHPP can be an option in contrast to chromium-cobalt dental alloys (Cr-Co) since it is lighter and doesn't cause erosion. BioHPP developments can be built utilizing both current CAD/CAM innovation and standard wax substitution innovation.   Application of Bio-HPP:-Removable Partial Dentures, Crown And Bridge Fabrication, Individual Implant Abutments.

37. DENTURE BASE RESINS Dr.Rasmita Samantaray

38. Contents Introduction Some terminologies Types of denture base resins Heat Cure Self Cure Light Cure Techniques used in processing DBR. Physical Properties Of DBR.

39. Heat activated resins Activated by heat Above 60 degree celcius , benzoyl peroxide decomposes Free radicals polymerization reaction initiated Unreacted monomer [0.2%-0.5%] Exothermic reaction Polymer to monomer ratio – 3:1 Dough forming time – less than 40 min manufacturers provide – less than 10 min Working time – 5min [extended via refrigeration] As a rule uses compression molding technique

40. composition Powder Pre-polymerized poly (methyl methacrylate ). Copolymers of of PMMA (5%) E.g.: Ethyl or Butyl methacrylates Initiator (0.2-1.5%) E.g.:benzoyl peroxide. Plasticizer E.g.: Dibutyl phthalate. Color pigments E.g : Mercuric sulphide, Cadmium Opacifiers E.g.: Zinc or titanium oxides Dyed synthetic fibers [nylon or acrylic] Inorganic particles E.g.: Glass fibers , zirconium silicate. Heavy metal compounds E.g.Barium , bismuth, etc . Liquid Methyl methacrylate Co-monomers Inhibitor E.g.:Hydroquinone (0.003%-0.1%). Plasticizers E.g.: Butyl or Octyl methacrylate Dibutyl Phthalate. Cross-linking agent E.g.: Ethylene glycol dimethacrylate

41. Compression Molding Technique

42. Dewaxing Immersed in boiling water for 4 min Appropriate parts of flask removed Softened residual wax removed using wax solvent or by dropping of hot water. Mold cavity cleaned with mild detergent and rinsed with boiling water Packing

43. Injection molding technique

44. Compression vs injection Various studies suggest that the injection molding technique produces dentures with higher dimensional accuracy. It compensates the polymerisation shrinkage due to high pressure and extra influx of resin for the unreacted monomer Also called curing cycle Should be controlled to avoid effects of temp rise above the boiling point of monomer [100.8 degree celcius ] Boiling of monomer yields internal porosity Can control by heating the resin more slowly Polymerization cycle Also called curing cycle Should be controlled to avoid effects of temp rise above the boiling point of monomer [100.8 degree celcius ] Boiling of monomer yields internal porosity Can control by heating the resin more slowly

45. Research suggests 3 techniques: DBR in constant temp. Of 74 degree celcius for 8 hrs or longer, no terminal boiling treatment Processing in 74 degree celcius water bath for 8 hrs and increasing temp. To 100 for 1 hr Processing at 74 degree celcius for 2 hrs and raise the temp to 100 for 1 hr. Cooling slowly Rapid cooling causes warping Thus bench cooling for 30 min, then under cool tap water for another 15 min Denture stored in water till delivery to the patient to avoid dimensional changes

46. Chemically activated resins Cold curing, self curing, autopolymerising resins

47. Degree of polymerisation incomplete Greater amount of unreacted monomer [ 3%-5%] Unreacted monomer acts as plasticizer – decreases transverse strength Residual monomer – potential tissue irritant- compromises biocompatibility Slightly less shrinkage than heat activated Greater dimensional accuracy Inferior color stability due to the presence tertiary amines ready for oxidation Two techniques used:- Compression molding technique Fluid resin technique

48. Fluid resin technique

49. Advantages Improved adaptation to underlying tissues Decrease probability of damage during deflasking Reduced material costs Simplified procedure Disadvantages Shifting of prosthetic teeth Air entrapment Poor bonding of teeth to DBR Technique sensitivity Light Activated Resins Composite – matrix of UDMA,microfine silica, high mol.wt . Monomer,resin beads as organic fillers, Visible light – activator, Camphorquinone – initiator Resin placed inside light chamber & polymerized Bluelight – 400-500 nm High intensity quartz-halogen bulbs Rotated continuously for uniform polymerisation

50. Advantages developed to surpass contact allergies,laboratory vapours, and the traditional lengthy lost wax technique of investing, flasking and boil-out used with the conventional PMMA materials biocompatibility, ease of fabrication and manipulation, low bacterial adherence, and ability to bond to other denture base resins. use of UDMA was limited by the low impact resistance and brittleness of the material [TRIAD] New MMA free material developed by dentsply [ECLIPSE] – superior physical and mechanical properties

51. Microwave activated resins Microwave energy Specially formulated resin [ethylene glycol dimethacrylate ] Non metallic flask Conventional microwave oven Less time consuming Physical properties and dimensional accuracy is comparable with conventional resins. cleaner, more time-efficient, more cost-effective, and less cumbersome method of polymerisation of denture base resins Rapid heating may cause porosity minimal residual monomer levels attainable with the water bath system were not achieved. Microwave curing at 70W for 25 min minimized porosity problems associated with rapid heating in sections not thicker than 3 mm. offers no advantage in time saving over rapid water curing systems

52. Physical properties

53. POLYMERIZATION SHRINKAGE MMA polymerises into PMMA, density changes from 0.94g/cm3 -1.19 g/cm3 Volumetric shrinkage -21% Shrinkage is uniformly distributed Clinically satisfactory denture In presence of linear shrinkage, discrepancy in initial fit of a denture TENSILE & COMPRESSIVE STRENGTH Have adequate tensile & compressive strength Fracture may happen accidentally or due to faulty fabrication & flexural fatigue. Eg :-Heat cure DBR ELONGATION Elongation combined with strength indicates the toughness of the material. Materials having low elongation are tough materials and vice versa It is important as gives an idea about the workability of the materials Mostly regarding alloys Eg polyvinyl acrylics

54. PROPORTIONAL LIMIT Its a function of the rate of stress applied For a denture base it should be sufficiently high To prevent permanent deformation due to masticatory forces This may result in loss of retention and/or loosening of teeth from Denture base .

55. IMPACT STRENGTH It is the measure of the energy absorbed by a material when it breaks by a sudden blow Addition of plasticizers increases impact strength But is followed by decrease in hardness, proportional limit, elastic modulus & compressive strength Therefore , a DB cannot have excellent impact strength at the cost of other properties Eg : rubber reinforced acrylic has higher impact strength

56. FLEXURAL STRENGTH Closely represents type of loading in vivo When compared with metal the elastic moduli of all the plastics are low FATIGUE STRENGTH It represents the no. of cycles before failure at a certain stress Eg : rubber reinforced has superior strength, pour type has the least. FRACTURE TOUGHNESS It is a property which describes the ability of a material containing a crack to resist  fracture. Highest for rapid heat cured acrylic Lowest for pour type acrylic. Is higher when specimens are saturated with water rather than dry. COMPRESSIVE CREEP Time dependant When DBR are kept under a load, it will deform with time Lowest – heat cure resins Higher - self cured resins RECOVERY AFTER INDENTATION Recovery is greater in dry specimen [86%-89%] than wet specimen[84%-88%] Time allowed was 10 min Demonstrate viscoelastic properties.

57. Thermal properties

58. THERMAL CONDUCTIVITY Poor conductors of heat and electricity Acts as insulators in mouth against hot & cold food THERMAL COEFFICIENT OF EXPANSION describes how the size of an object changes with a change in temperature.  Temperature change from processing to room temperature or mouth temperature indicates importance High [71-81x10-6/degrees celcius ] Addition of fillers may reduce this HEAT DISTORTION TEMPERATURE Measure of ability of a plastic To resist dimensional distortion by heat For PMMA – 71-91 degrees Repair temperature low Use self cure or light cure

59. Need for advancements Well fitting dentures which are repeatedly fracturing A complete denture opposing natural dentition Patients with heavy bites Implant supported over dentures Limited vertical space Thin dentures Technique sensitivity Denture Stomatitis [ candida induced] HIGH IMPACT REINFORCED RESINS 1000% strength increase over non-reinforced greater impact strength and fatigue properties Hence HIGH IMPACT Reinforcements by : Fibres [continuous parallel, chopped and woven] Carbon / graphite fiber Aramid fiber [aromatic polyamide/ kevlar ] Polyethylene Glass fiber E – glass fiber Rubber [butadiene-styrene PMMA] Metal

60. Indication Indicated for patients who drop their dentures repeatedly e.g. Parkinsonism. powder-liquid system processing is same as heat cure resins . HYPOALLERGEN RESINS Polyurethane , Polyethylenterephthalate and Polybutylenterephthalate [ phthalate based], light activated UDMA significantly lower residual monomer content RESIN WITH MODIFIED CHEMICAL STRUCTURE hydroxy -apatite fillers increases fracture toughness Al2O3 fillers increases the flexural strength and thermal diffusivity 2% quaternary ammonium compound polymerised with a denture acrylic resin displays antiseptic properties Addition of ceramic or sapphire whiskers improves thermal diffusivity Addition of Triphenyl Bismuth or uranium or organo -zirconium compound impart radiopacity equivalent to that of aluminium . PMMA MODIFIED HYDROXYAPATITE Hydroxyapatite whiskers added to [polymer matrix] reinforce acrylic resins Better mechanical properties Clinical effectiveness yet to be studied

61. Thermoplastic Resins Thermoplastic Nylon (Polyamide) Thermoplastic Acetal Thermoplastic Acrylic Thermoplastic Polycarbonate Excellent Esthetics Very Comfortable For The Patient. Non-porous So No Growth Of Bacteria [It Still Retains A Slight Amount Of Moisture To Keep It Comfortable Against Gums Thermoplastic Nylon Polymide Rapid Injection System 1962 -- the first flexite thermoplastic injected at temperatures from 274 to 293 degrees Celsius. Valplast and flexiplast and lucitone 1992, The Flexite Company, developed and patented the first pre-formed tooth colored clasps known as Clasp- Eze , made of nylon material and is available in pink and clear shades.

62. LUCITONE- High grade microcrystalline polyamide Excellent stability, aesthetics Soft – doesnt fracture easily on falling High resistance to abrasion Resistant to stains and calculus Lacks color stability Become loose with long term use Cannot be relined or repaired Bonding with acrylic teeth is not good THERMOPLASTIC ACETAL- Polyoxymethylene [POM] 1986, introduced as tooth colored clasps Superior aesthetics Available in about 17 shades Injection molding technique Acetal as a homo-polymer has good short-term mechanical properties, but as a co-polymer has better long-term stability. Clasps & framework material THERMOPLASTIC ACRYLIC- Commercially available as flexite MP Special blend of polymers – highest impact rating of any acrylic tooth and gingival colors & has both translucency and vitality, providing excellent esthetics easy to adjust, handle and polish It is relineable and repairable at the chair-side very popular for bruxism appliances and denture bases

63. THERMOPLASTIC POLYCARBONATE polymer chain of bisphenol -A carbonate very strong, resists fracturing, and is quite flexible does not wear well thus will not maintain vertical dimension long not suitable for full or partial dentures but ideal for provisional crown and bridges natural translucency and finishes very well, yielding excellent esthetics Temporary and provisional restorations available commercially as Reigning. DRUG RELEASING DENTURES Disks were prepared by grafting PNVP [poly(N-vinyl-2-pyrrolidinone)] onto PMMA loaded with miconazole Quenched disks could also be charged with chlorhexidine that displayed anticandidal activity. Long term management of candida induced denture stomatitis

64. References Craig’s 12 th edition, chapter-7,chapter 21. ANUSAVICE 11 th edition, chapter 6,chapter-19 . Progress in Natural Science: Materials International 2013;23(1): 89–93. Vivek R, Soni R (2015) Denture base Materials: Some Relevant Properties and their Determination. Int J Dent Oral Health 1(4) International Journal of Prosthodontics . May/Jun1990, Vol. 3 Issue 3, p249-255. 7p. Dental Materials Volume 4, Issue 1, Pages 1-48 (February 1988) OHDM - Vol. 13 - No. 2 - June, 2014. R.Bhola et al, trends biomater . Artif . Organs, vol 23(3), pp 129-136 (2010) biocompatible denture. Nogueira SS et al comparison of accuracy between compression- and injection- molded complete dentures.J prosthet dent. 1999 sep;82(3):291-300 .