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Denture base resins

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Denture base resins

  1. 1. 1
  2. 2. 2  Introduction  History  Requirements of an ideal denture base material  Introduction to PMMA  Polymerisation reaction  Types of denture base resin  Heat activated resins  Chemically activated resin  Light activated resin  Physical properties of resins  Recent advancements  Summary  Bibliography
  3. 3. 3  Dentures – mode of replacement of natural teeth since 700 BC  Increased patient awareness lead to increased expectations  Significant advances in development of new materials for replacement of lost teeth  Acrylic resin is the most widely accepted and used Denture base material.
  4. 4. 4  First Dental prosthesis – Egypt in 2500 BC TORTOI SE SHELL PORCE -LAIN CELLUL OID WOOD CHEOP LASTIC ALUMI NIUM BONE GUTTA PERCH A BAKELI TE PVC SS & alloys GOLDIVORY VULCA NITE PMMA
  5. 5. 5  WOOD:  Readily available and inexpensive  Easily carvable X Cracked in moisture X Lacked aesthetics X Degraded in oral environment
  6. 6. 6  BONE  Available at reasonable costs  Carvable  Better dimensional stability X Aesthetic and hygiene concerns  IVORY  Stable in oral environment  Aesthetic and hygienic X Not readily available X expensive First fabricated by FAUCHARD
  7. 7. 7  PORCELAIN  Shaped easily  Ensured intimate contact with underlying tissue  Stable  Minimal water sorption  Smooth surface  Less porosity  Low solubility X Brittle X Difficult in grinding and polishing ALEXIS DUCHATEAU in 1774 - first to fabricate porcelain denture
  8. 8. 8 18 – 20 karat gold alloyed with silver and teeth riveted to it
  9. 9. 9  TORTOISE SHELL • It was the first thermoplastic denture base material • Formed by CF HARRINGTON in1850  GUTTA PERCHA • Unstable • First formed by EDWIN TRUMAN in 1851
  10. 10. 10  CHEOPLASTIC • It is a low fusing alloy of silver, bismuth and antimony • First formed by ALFRED A BLANDY in 1856
  11. 11. 11  VULCANITE • First self retaining dentures • Functional • Affordable • Durable • Dark red colour • Unhygienic NELSON GOODYEAR in 1864
  12. 12. 12  ALUMINIUM • By Dr Bean in 1867 ( he also invented the casting machine  CELLULOID • Discolours easily • Has a residual camphor taste • Difficult to repair • Obtained by plasticizing cellulose nitrate with camphor J. SMITH HYATT in 1869
  13. 13. 13  BAKELKITE • Stains easily • Residual phenol taste • Brittle • Difficult to repair • Short shelf life  POLY VINYL CHLORIDE • Pleasing colour but difficult processing methods Dr. LEO BAKELAND in 1909
  14. 14. 14  STAINLESS STEEL and BASE METAL ALLOYS • Low density • Low metal cost • Higher resistance to tarnishing and corrosion • High modulus of elasticity • Allergy to nickel  POLYMETHYL METHACRYLATE • Most satisfactory material tested till date. Dr. WALTER WRIGHT (1937)
  15. 15. 15
  16. 16. 16
  17. 17. 17  PMMA/Acrylic resin is the material of choice for full denture bases  Chemical model for many other material developments – restorative materials  The most satisfactory denture base material used till date REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  18. 18. 18 Acrylic resins are prepared by a free radical addition polymerisation chain reaction REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  19. 19. 19  INITIATION RECTION • Vinyl group susceptible to attack by free radical • Opening of π bond, and formation of σ bond • Shift of electron takes place Initiation reaction REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  20. 20. 20  PROPAGATION REACTION • Process of repeated reaction of the same type - chain propagation • Steric hindrance effects – increased effects on attack on next double bond • Polymer chains with free radical – growing or live chains REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  21. 21. 21  TERMINATION REACTION • Not a function of the chain length already created • Depends on the concentration of free radicals in the system • Self limitation of the reaction – mutual annihilation of free radicals REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  22. 22. 22  CHAIN TRANSFER • Hydrogen abstraction - simple transfer of an H2 atom to attacking radical • Leaves a free radical residing on attacked species REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  23. 23. 23  Based on the mode of activation • Heat activated PMMA  High impact resin  Rapid heat polymerising resin  Microwave – activated PMMA • Chemical activated PMMA • Light activated PMMA
  24. 24. 24
  25. 25. 25  COMPOSITION: • Polymer:  pre-polymerised spheres of PMMA  Benzoyl peroxide – initiator • Monomer:  Hydroquinone – Inhibitor  Glycol dimethacrylate – cross linking agent (1% - 2% by vol) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  26. 26. 26 BENZOYL PEROXIDE is not a catalyst!!!
  27. 27. 27  STORAGE • Specific time and limits for storage • May undergo changes • Causes changes in working properties • Change in Chemical and physical properties of processed denture REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  28. 28. 28 MANIPULATION COMPRESSION MOLD TECHNIQUE INJECTION MOLD TECHNIQUE REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  29. 29. 29 • Preparation of the mold • Selection of separating medium • Polymer -to-monomer ratio • Polymer –monomer interaction • Dough forming time • Working time • Packing • Polymerization procedure • Temperature rise • Internal porosity • Polymerisation cycle REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  30. 30. 30 Three part flask
  31. 31. 31 Pressure Clamp
  32. 32. 32  Proper finishing  Periphery should be sealed  Apply petroleum jelly on the inner surface of the flask and on the casts  Adjustment of the plaster model  Plaster models are wetted - soaked with slurry water REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  33. 33. 33  Flask is filled with freshly mixed stone  Place cast on to the mixture  Contour the stone  coated with separating media (after initial set)  Another mix of stone is poured into the flask REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  34. 34. 34  Incisal and occlusal surfaces of teeth should be slightly exposed  Allow to set and coat with separating media  Additional increment of stone filled  Lid is gently tapped in place  Apply pressure with pressure clamp REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  35. 35. 35 REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  36. 36. 36
  37. 37. 37  Place the flask in boiling water for 4 mins  Remove and separate segments  Baseplate and softened wax are removed  Prosthetic teeth remain firmly  Cleaned with mild detergent and rinsed in boiling water Dewaxing REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  38. 38. 38  Prevent direct contact between denture base resin and the mold Failure Water may affect polymerisation rate and alter optical and physical properties Presence of Monomer or free polymer may fuse the investment to denture base REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  39. 39. 39  Water soluble alginate solution – most popular separating agents  Produce thin film of calcium alginate Water soluble alginate solution + Calcium sulphate dihydrate Calcium alginate REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  40. 40. 40  Application • Applied on the exposed surfaces of a warm, clean stone mold • Carefully applied in the interdental surfaces • Should not contact exposed tooth surfaces REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  41. 41. 41  Polymerisation results in volumetric and linear shrinkage (21% decrease)  Manufactures pre-polymerize – pre shrinking  Powder + liquid = dough like mass  3:1 is accepted monomer : polymer ratio (0.5% linear shrinkage) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  42. 42. 42  A workable mass is produced, which passes through 5 stages Sandy Stringy Dough- like Rubbery Stiff REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  43. 43. 43  SANDY • Coarse or grainy • Polymer beads remain unaltered  STRINGY • Increased viscosity • Monomer attacks polymer beads  DOUGH-LIKE (ideal for compression molding) • Pliable dough • Increased number of polymer chains REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  44. 44. 44  RUBBERY OR ELASTIC • Mass rebounds when compressed or stretched • Excess monomer is dissipated by evaporation  STIFF • Due to complete evaporation of free monomer REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  45. 45. 45  Time required to reach a dough like stage  According to ADA spec.no.12 , required consistency should be reached in <40mins (clinically - <10min) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  46. 46. 46  Defined as the time that a denture base material remains in the dough like stage  According to ADA spec. 12, material should remain in dough like stage for atleast 5 min  Refrigerating increases working time  Presence of moisture degrades physical and aesthetic properties REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  47. 47. 47  Placement and adaptation of denture base resin within the mold cavity Denture with excessive thickness and resultant mal- positioning Noticeable denture porosities OVERPACKING UNDERPACKING REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  48. 48. 48  Resin should be in dough-like state  Bent into an horse-shoe shape and placed in position  Polyethylene sheet placed over resin – incremental pressure applied REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  49. 49. 49  Excess material – flash  Trial closures are repeated till no flash remains  No polyethylene sheet to be placed for final closure  Flask is transferred to a flask carrier – maintains pressure REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  50. 50. 50 Cross sectional representation of the flask and its contents REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  51. 51. 51  When heated above 60⁰C, benzoyl peroxide decomposes  Yields free radicals  Acts rapidly with monomer – chain growth polymerisation REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  52. 52. 52  Additional monomer molecules attach to individual polymers – rapid  Heat required - activator  Benzoyl peroxide - initiator Coupling of 2 grouping chains Transfer of H2 ion from one chain to another REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  53. 53. 53 Temperature - time heating curves for the water Bath, investing plaster and acrylic resin during polymerisation ofa thick denture base REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  54. 54. 54  Initially heating is slow - resin occupies I the centre of the mold  Temperature >70C – begin to increase rapidly  Decomposition rate of benzoyl peroxide is significantly increased  Resin and dental stone are poor conductors – heat not dissipated Temperature rises from that of the boiling point of monomer (100.8 C) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  55. 55. 55
  56. 56. 56  Porosities are formed when the temperature of the resin exceeds that of the unreacted monomer  resin is poor thermal conductor - heat generated cannot be dissipated REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  57. 57. 57  Heating process used to control polymerization – curing cycle Constant temp – 74C For 8 hrsor longer with no Terminal boiling treatment Processing at - 74 C for 8hrs and then increasing to 100 At 74 C for 2 hrs and then Increasing to 100 C for 1 hr REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  58. 58. 58 Temperature changes in acrylic resin when subjected to various curing schedules REFERENCE : Material science for dentistry, B. W. Darwell, 9th Ed
  59. 59. 59  Denture flask should be bench cooled for 30mins before retrieval  Rapid cooling – warpage – differences in thermal contraction of resin and investing material  Immersed in cool tap water for 15 mins  Deflasked  Stored in water until delivery REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  60. 60. 60  Half of the flask is filled with stone  Contoured and permitted to set  Sprues are attached to the wax denture base REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  61. 61. 61  Investment process is completed.  Wax elimination is performed  Flask is placed under pressure  Resin mix is introduced into the mold  polymerised REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  62. 62. 62  High-impact strength resin • Reinforced with butadiene-styrene rubber. • Rubber particles are grafted to methyl methacrylate to bond to the acrylic matrix • Supplied in powder-liquid form • Conventionally processed
  63. 63. 63  Rapid heat-polymerized resin • Hybrid acrylics, with both chemical and heat-activated initiators - allow rapid polymerization • No porosity expected • polymerized in boiling water for 20 minutes
  64. 64. 64  Microwave-activated PMMA: • Nishii (1968) first used microwave energy to polymerize denture base resin in a 400 watt microwave oven for 2.5 minutes. This research was later carried on by Kimura et al (1983) and De Clerk.
  65. 65. 65
  66. 66. 66  Chemical activators used to induce polymerisation  Cold curing / self curing/ auto- polymerising resin  Chemical used – dimethyl –para- toluidine (to monomer) Initiates breakdown of benzoyl peroxide to produce free radicals and Hence polymerisation REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  67. 67. 67  Degree of polymerisation is not complete – greater amount of unreacted monomer  Less colour stability due to the presence of the amine – susceptible to oxidation Plasticizer - Results in decreased transverse strength Potential tissue irritant REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  68. 68. 68  Less shrinkage and greater dimensional accuracy compared to heat activated PMMA REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  69. 69. 69  Supplied in monomer – polymer form  Mixed according to manufacturer’s instructions to attain dough like consistency  Working time is shorter  Refrigerating monomer increases working time – rate of polymerization decreases REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  70. 70. 70  Pressure must be maintained throughout  Initial hardening – 30 min  Flask should be held under pressure for min. 3 hrs  Low degree of polymerisation – dimensional instability – soft tissue irritation REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  71. 71. 71  Employs a pourable, chemically activated resin  When mixed – low viscosity resin  Completed tooth arrangement is sealed to the underlying cast  Flask is filled with reversible hydrocolloid – allowed to cool REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  72. 72. 72  After gelation – cast is removed and sprues and vents are cut on the external surface  Wax is eliminated using hot water  Teeth are carefully retrieved and placed in position  Resin is mixed and poured via sprue channels REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  73. 73. 73  Placed in pressurised chamber at room temperature  Allowed to polymerize for30 – 45minutes  Denture is retrieved, sprues are removed  Returned to articulator for correction of processing changes REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  74. 74. 74
  75. 75. 75  Advantages • Improved adaptation • Decreased probability to damage to the teeth • Reduced cost • Simplification of procedure REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  76. 76. 76  Disadvantages • Noticeable shift of teeth • Air entrapment • Poor bonding • Technique sensitive REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  77. 77. 77
  78. 78. 78  COMPOSITION: • Matrix : Urethane dimethacrylate, microfine silica • Filler : acrylic resin beads • Activator : visible light • Initiator : camphorquinone REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  79. 79. 79  Supplied in sheet and rope form  Packed in light proof pouches  Opaque investing material is required – no conventional method REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  80. 80. 80  Denture is moulded on an accurate cast  Exposed to a high intensity visible light for a period  Removed from the mold  Finished and polished REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  81. 81. 81
  82. 82. 82 The physical properties will be discussed under the following headings:  Polymerisation shrinkage  Porosity  Water absorption  Solubility  Processing stresses  Crazing REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  83. 83. 83  During polymerization the density of the mass changes from 0.94 g/cm3 to 1.19 g/cm3. thus a volumetric shrinkage of 21%  Linear shrinkage – denture base adaptation and cuspal interdigitation REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  84. 84. 84  Volumetric shrinkage – 7%, hence linear shrinkage 2%  Initial cooling – resin is soft – contraction occurs at the same rate as that of dental stone  At glass transition temperature – contraction occurs at a faster rate than the surrounding stone. REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  85. 85. 85
  86. 86. 86 Decreases in vertical dimension Increase in overall vertical dimension Fluid Resin technique Heat/chemically activated REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  87. 87. 87  Surface or subsurface voids compromise physical and aesthetic properties  More likely to develop in thicker portions  Due to vapourization of unreacted monomer and low molecular weight polymers  Does not occur equally REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  88. 88. 88  Can also be due to inadequate mixing of powder and liquid  Regions with more monomer, shrink more – resulting in voids  Using proper monomer – polymer ratio is essential REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  89. 89. 89  Also due to insufficient pressure or less material during polymerisation  Assume irregular shape  Resultant resin appears lighter REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  90. 90. 90  Final type is associated with fluid resins  Caused due to air inclusions during mixing and pouring REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  91. 91. 91  Absorbs relatively small amounts when placed in water  Water molecules penetrate the PMMA and occupy positions between polymer chains – forces them apart Slight expansion In polymerised mass Water acts as plasticizers REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  92. 92. 92 Water absorption value – 0.69 mg/cm2 Interferes with the polymer chain Making them more mobile by releasing stresses Changes in shape (insignificant) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  93. 93. 93  Insoluble in fluids in the oral cavity  Negligible loss REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  94. 94. 94  Natural dimensional change is inhibited - contains stresses  Stresses relaxed - distortion occurs  During polymerization tensile stresses are sustained  Stress is produced during thermal shrinkage also (cooling < glass transition temperature) REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  95. 95. 95  Additional factors include • improper mixing and handling of the resin • Poorly controlled heating and cooling of flask assembly  Dimensional changes due to small stresses - 0.1 to 0.2mm REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  96. 96. 96  Stress relaxation may produce flaws - CRAZING  Hazy or foggy appearance  Tensile stresses most often responsible and may result the denture to crack. REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  97. 97. 97  Produced due to mechanical separation of individual polymer chains – tensile stresses  Also due to solvent action  Begins at surface of the resin and oriented to right angles to the tensile forces. REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  98. 98. 98  Load application produces stresses within the resin – change in shape  Strength of the resin is directly proportional to the degree of polymerisation shrinkage  Heat activated resins display lower degree of polymerisation
  99. 99. 99  Act as rubbery solids that recover from elastic deformation once stresses are eliminated – viscoelastic behaviour  If load is not removed additional plastic deformation occurs – creep  Rate at which this deformation occurs – creep rate REFERENCE : Phillips' Science of dental materials, Anusavice, 11th Ed
  100. 100. 100
  101. 101. 101  The radiolucent nature of PMMA is one of its disadvantages as a denture base material.  Denture wearers can endure serious complications if their dentures fractures and a portion is inhaled or ingested.  Use of sophisticated ultrasound techniques also prove to be difficult for detection.
  102. 102. 102  The most promising material - Silanated barium fluoride impregnated powdered glass. (kasim 1998)  Barium sulphate (BaSO4) has also been added to denture base resins to improve radiopacity.  Lang et al. (2000) investigated the potential for triphenylbismuth incorporated into injection moulded heat cure resins to improve radiopacity.
  103. 103. 103  Inhibition of Candida albicans on denture resins could play a significant role in preventing the development of denture stomatitis  PMMA-silver nanoparticle discs were formulated, with the commercial acrylic resin
  104. 104. 104  The inner surface of the prosthesis is rough, and in addition to local (eg, poor hygiene, local trauma, tissue integrity loss) and systemic factors (eg, malnutrition, diabetes mellitus, human immunodeficiency virus infection, xerostomia), contributes to the proliferation of C. albicans
  105. 105. 105  Spherical silver nanoparticles were synthesized and added to a PMMA formulation, resulting in successful reduction of adherence of C. albicans
  106. 106. 106  Commercially pure (CP) titanium has appropriate mechanical properties  Lightweight (low density) compared with conventional dental alloys  Outstanding biocompatibility that prevents metal allergic reactions
  107. 107. 107  Flexible denture material is available in the form of granules in cartridges of varying sizes.  It was first introduced by the name of valplast and flexiplast to dentistry in 1956.  These are superpolyamides which belong to nylon family
  108. 108. 108  Advantages • Soft inherent flexibility • Will not warp • Clinically unbreakable • No porosity • Less bulky • Biocompatible • Better esthetics • Better chewing efficiency
  109. 109. 109  Disadvantages • De-bonding of acrylic teeth • Discolouration • High surface roughness • Cannot be relined • Difficult to polish • Technique sensitive • Cannot be repaired
  110. 110. 110
  111. 111. 111
  112. 112. 112  Contraindications : • Insufficient inter-arch space (< 4mm space for placement of teeth) • Prominent residual ridges • Flat, flabby ridges
  113. 113. 113  Management of xerostomia patients - soft and adapt well to the gums - comfortable for wearing.  retain moisture and give better lubrications than acrylic dentures  biocompatible - safe for patients with carcinoma.  lighter in weight, are not brittle, do not warp  suitable in conditions of inadequate vertical dimension
  114. 114. 114  One modification of the Valplast partial denture is called the Nesbit.  The Nesbit is used to replace one to three teeth on the same side of the mouth and is much smaller than a conventional partial denture.
  115. 115. 115  The procedure can be completed in two short visits, requires no anesthesia or drilling of teeth (in most cases), and the cost is substantially less than either a permanent bridge or dental implants.  A Valplast Nesbit is generally easy to get used to, and has a very realistic appearance
  116. 116. 116  Incorporation of a rubber phase  butadiene styrene  Improved impact strength
  117. 117. 117  The transverse strength of high-impact denture base resin can be increased significantly by a factor of 29% and 76% when reinforced with zirconia in a concentration of 5% and 15% respectively  In this process, expansion of ZrO2 crystals occurs and places the crack under a state of compressive stress and crack propagation is arrested
  118. 118. 118  To improve the physical and mechanical properties of acrylic resin, it was reinforced with fibres 1. Carbon fibres 2. Kevlar fibres 3. Glass fibres
  119. 119. 119  CARBON FIBRES: • The use of Carbon fibres as denture base strengtheners have been investigated by Larson et al and Sonit(1991) . • Carbon fibres have been shown to improve flexural and impact strength, prevent fatigue fracture and increased fatigue resistance on treating with silane coupling agent(Yazdanie-1985)
  120. 120. 120  KEVLAR FIBRES: • These fibres are resistant to chemicals, are thermally stable, and have a high mechanical stability, melting point, and glass transitional temperature • Studies conducted by Berrong et al(1990) have shown to significantly increase the impact strength and the modulus of elasticity of the resin but they are also unesthetic
  121. 121. 121  GLASS FIBRES: • Different types of glass fibres are produced commercially; these include E-glass, S-glass, R-glass, V-glass, and Cemfil. • E-glass fibre - high alumina and low alkali and borosilicate, is claimed to be superior in flexural strength • Because the modulus of elasticity of glass fibres is very high, most of the stresses are received by them without deformation
  122. 122. 122 No denture base material has yet been developed which completely fulfils all the criteria for success and conversely does not posses any of the above noted problems. Since PMMA was introduced, most dental material research has focused upon developing materials with higher strength, lower levels of residual methacrylate monomer after processing, improved dimensional stability, increased radiopacity and improved resistance to candidal infiltration
  123. 123. 123  Phillip’s Sciences of dental materials, Anusavice, 11th Ed  Material science for dentistry, B. W. Darwell, 9th Ed  Young, Beth C. (2010) A comparison of polymeric denture base materials.  Cytotoxicity of denture base acrylic resins: A literature review http://www.iosrjournals.org/iosr-jdms/papers/Vol13-issue3/Version-2/C013320709.pdf.  Denture base resins : From past to future http://ijds.in/article-pdf-RENU_TANDON_SAURABH_GUPTA_SAMARTH_KUMAR_AGARWAL-63.pdf
  124. 124. 124

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