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Denture Base Resin

  1. 1. Denture Base Resin -Dr. Soham Prajapati 1st Year Post Graduate, Dept. of Prosthodontics & Maxillofacial Prosthesis Including Oral Implantology. 7/12/2013 & 9/12/2013 1
  2. 2. • Definition • History • Classification • Dental polymers • Ideal requirements of Denture Base Resin • Principal ingredients of Denture Base Resin • Different Types Denture Base Resins • Properties of PMMA • Cytotoxicity of Denture Base Acrylic Resins • Recent Advances • Conclusion • References 2
  3. 3. Definition • DENTURE BASE: The part of a denture that rests on the foundation tissues and to which teeth are attached. • RESIN: A broad term used to describe natural or synthetic substances that form plastic materials after polymerization. - GPT 8 3
  4. 4. Key Points of DENTAL RESINS • ADA/ANSI Specification no 12 - Denture base resins. • ISO 1567 4
  5. 5. History • Skillfully designed dentures were made as early as 700 BC using ivory and bone. • Till 1800s, dentures were hand carved and tied in place with silk threads. • Queen Elizabeth I and George Washington suffered from tooth loss and unfit dentures. 5
  6. 6. History • In 1774, Duchateaus and Dubois de Chemant designed a full set of dentures that would not rot.(made of porcelain.) 6
  7. 7. History • Giuseppangelo Fonzi created a single porcelain tooth held in place by a steel pin in 1808. • Claudius Ash made an improved porcelain tooth in 1837. • Porcelain dentures moved to US in 1800s and marketed on a large scale. Fit was eventually improved as well. 7
  8. 8. History • In 1700s, plaster of paris was introduced. It was used to make a mold of the patient’s mouth. This helped to make the dentures precise. • Swaged Gold was used as denture base for those who could afford it. 8
  9. 9. • Real breakthrough when vulcanized rubber was discovered by Charles Goodyear in 1840. – Cheap – Easy to work – Hold the denture • Vulcanite dentures were available in India under British rule by British and other European Dentists. History 9
  10. 10. Vulcanite • Contains 32 % sulphur and metallic oxides for color. Advantages Disadvantages Nontoxic Non-irritant Excellent Mechanical Properties Quiet hard to polish Absorbs Saliva Becomes unhygienic. Unpleasant odor(when processed) Poor esthetics (opacity of rubber) Dimensional changes. 10
  11. 11. Nitrocellulose • Dimensionally stable • Excessive Warpage • High water absorption • Poor color stability • Contains unpleasant tasting plasticizer • Highly flammable 11
  12. 12. Other • Celluloid – Was tried in place of rubber but didn’t prove best of the material. • Porcelain – It was tolerate by denture bearing mucosa, but difficult to fabricate and easily broken. • Phenol Formaldehyde – Becomes dicolored and unesthetic and being thermosetting, it is difficult to repair 12
  13. 13. History • In 1937 Dr. Walter Wright gave dentistry its very useful resin. • It was polymethyl methacrylate which proved to be much satisfactory material tested until now. • By 1946, 98% of all denture bases were fabricated from PMMA. 13
  14. 14. Classification • According to ISO 1567 – Type 1 • Class 1 Heat processing polymers, powder and liquid • Class 2 Heat processed (plastic cake) – Type 2 • Class 1 Autopolymerized polymers, powder and liquid • Class 2 Autopolymerized polymers (powder and liquid pour type resins) – Type 3 Thermoplastic blank or powder – Type 4 Light Activated Materials – Type 5 Microwave-Cured Material 14 Applied Dental Materials, 8th edition, John F McCabe & Angus W. G. Walls
  15. 15. Classification • Based on the usage:- – Temporary Denture Base Resin • E.g. Self Cure Acrylics • Shellac base plate • Base plate wax • Injection Molded resins • Metallic Bases – Permanent Denture Base Resin • E.g. Heat Cure Denture Base • Light Cures Resins • Pour Type Resins 15
  16. 16. Classification • Based on the METHOD USED FOR ITS ACTIVATION:- – Chemically activated – Heat activated – Light activated 16
  17. 17. DENTAL POLYMERS • Polymer is chemical compound consisting of large organic molecules formed by the union of many repeating smaller monomer units. 17
  18. 18. • Polymerization occurs through a series of chemical reactions by which the macromolecule, or the polymer, is formed from large numbers of molecules known as monomers. • TYPES:- – CONDENSATION POLYMERIZATION – ADDITION POLYMERIZATION 18
  19. 19. CONDENSATION POLYMERIZATION • TWO GROUPS – Those in which polymerization is accompanied by repeated elimination of small molecules. The process repeat itself and form macromolecules. E.g. water, halogen acids, ammonia, etc. 19
  20. 20. – Those in which functional groups are repeated in the polymer chains. The polymers are joined by functional groups. Formation of a by-product is not necessary. E.g. polyurethane. Not widely used in DENTISTRY 20
  21. 21. ADDITION POLYMERIZATION • All resins employed extensively in dental procedure are produced by addition polymerization. • No change in chemical composition and no by- products are formed. 21
  22. 22. How?? • Starting from an active centre, one molecule at a time is added and a chain rapidly builds up, which can grow almost indefinitely as long as the supply of building blocks are available. 22
  23. 23. Chemical Stages of Polymerization 4 Stages:- • Induction • Propagation • Chain Transfer • Termination 23
  24. 24. INDUCTION • Induction or initiation period is the time during which the molecules of the initiator becomes energized or activated and start to transfer the energy to the monomer. 24
  25. 25. • Three induction systems:- – Heat Activation – Chemical Activation – Light Activation • Heat Activated:- The free radical liberated by heating benzoyl peroxide will initiate the polymerization of methyl methacrylate monomer. e.g. Denture base Resins 25
  26. 26. • Light Activated:- – Photons of light energy activate the initiator to generate free radicals. e.g. composite resin. Chemical Activated:- – System consists of at least two reactants, when mixed they undergo chemical reaction and liberate free radicals, e.g. Self Cured Resin 26
  27. 27. INDUCTION 27
  28. 28. INDUCTION 28
  29. 29. 29
  30. 30. PROPAGATION • Once the growth has started, the process continues with considerable velocity. • Theoretically, the chain reactions should continue with evolution of heat until all the monomer has been changed to polymer. • Actually, the polymerization is never complete. 30
  31. 31. PROPAGATION 31
  32. 32. 32
  33. 33. CHAIN TRANSFER • The chain termination can also result from chain transfer. Here, the activated state is transferred from an activated radical to an inactive molecule, and a nucleus of growth is created. 33
  34. 34. CHAIN TRANSFER 34
  35. 35. CHAIN TRANSFER 35
  36. 36. TERMINATION • The chain reaction can be terminated either by direct coupling or by exchange of hydrogen atom from one growing chain to another. 36
  37. 37. Termination 37
  38. 38. Termination 38
  39. 39. 39
  40. 40. COPOLYMERIZATION • The macromolecule may be formed by polymerization of a single type of structural unit. • In order to improve the physical properties, it is often advantageous to use two or more chemically different monomers as starting materials. 40
  41. 41. • The polymer thus formed may contain units of these monomers. Such a polymer is called a copolymer and its process of formation is known as copolymerization. 41
  42. 42. Types of COPOLYMER • There are three different types:- • RANDOM TYPE • GRAFT TYPE • BLOCK TYPE 42
  43. 43. RANDOM TYPE • In random type of copolymer the different monomers are randomly distributed along the chain. ……ABBABABAAAAAABBABABABBBBBABBABBAB…. 43
  44. 44. GRAFT TYPE • Sequence of one of the monomers are grafted onto the ‘backbone’ of the second monomer species. 44
  45. 45. • Identical monomer units occur in relatively long sequences along the main polymer chain. …..AAAAABBBBBAAAAABBBBBAAAAABBBBBAAAAA….. BLOCK TYPE 45
  46. 46. IMPORTANCE OF COPOLYMERIZATION • It is to better the physical properties of resins. • Many useful resins are manufactured by copolymerization. 46
  47. 47. CROSS-LINKING • The formation of chemical bonds or bridges between the linear polymer is referred to as CROSS-LINKING. • It forms a three-dimensional (3D) network. 47
  48. 48. Application Of Cross-Linking • The more recent acrylic resins are of cross- linked variety. It improves the strength, and decreases the solubility and water sorption. • Acrylic teeth are highly cross-linked to improve its resistance to solvents, crazing and surface stresses. 48
  49. 49. Requirements Of Denture Base Materials 49
  50. 50. ADA Specification General Requirements of the non-processed Materials Liquid Clear as Water Free of Extraneous Material 50
  51. 51. Specification General Requirements of the non-processed Materials POWDER, PLASTIC CAKE OR PRECURED BLANK FREE OF IMPURITIES SUCH AS DIRT AND LINT 51
  54. 54. 54
  55. 55. Ideal Requirements Of Denture Base Materials Final report of the workshop on clinical requirements of ideal denture base material 1. Physiologic compatability • Nontoxic • Noncarcinogenic • Nonallergenic • Compatible with physiologic requirements of mucous membranes Optimum consistency to maintain or promote tissue health • Not deleterious to adjacent and underlying tissues • Conducive to normal salivary flow 55ATWOOD:JPD 1968 (20) 101-105
  56. 56. 2. Acceptability to patients' senses • Acceptable to all five senses-sight, sound, smell, taste, and touch • Able to duplicate and simulate oral tissues as nearly as possible • Possessing wide selection of color • Possible for esthetics to be easily modified • Color stable • Odorless • Tasteless • Possessing instantaneous temperature conductivity • Light weight • Possessing sensation of natural texture 56
  57. 57. 3. Functional usefulness • Rigid enough so that teeth penetrate the bolus • No interference with oral functions of chewing, swallowing, self cleansing, singing, speech, sneezing, breathing, laughing, coughing, etc. 57
  58. 58. 4. Hygienic factors • Sterilizable • Resistant to stain, calculus, and adherent substances • Nonporous to microorganisms • Low fluid absorption • Wettable (low surface tension) • Easily cleaned 58
  59. 59. 5. Durability • Not affected by oral environment-bacteria, food, medicines, etc. Unbreakable (not brittle) • Not crazing • Dimensionally stable and statically stable • Minimal internal strain • Good bond between different base materials • Good bond between base and teeth • Not flammable • Resistant to weak acids and alkalis • Resistant to abrasion and wear • Resistant to strain • Long lasting 59
  60. 60. 6. Adaptability to clinical problems • Adjustable • Easily polished • Easily repaired • Easily relined • May need more than one type of material • May use combinations of materials (soft for tissues, hard for teeth) Choice of hardness or softness (various materials for different situations 60
  61. 61. 7. Cost factors • Simple to manipulate • Simple to process • Inexpensive equipment for processing Average skill required for processing No separation medium required Easily separated from cast • Moderate cost of fabrication • Good shelf life • Predictable properties 61
  63. 63. PRINCIPAL INGREDIENTS OF ACRYLIC DENTURE BASE RESIN POWDER LIQUID Acrylic polymer (or Copolymer) beads Initiator Pigments Dyes Opacifiers Plasticizer Dyed organic fibers Inorganic particles Monomer Inhibitor Accelerator Plasticizer Cross-linking agent 63CRAIG RESTORATIVE DENTAL MATERIAL
  64. 64. Acrylic Resins used In Dentistry • Derivatives of Ethylene and contains a vinyl group in their structural formula. • Acrylic resin used in dentistry are the esters of :- – Acrylic acid, CH2 = CHCOOH – Methacrylic acid, CH2 = C(CH3)COOH 64
  65. 65. DENTURE BASE RESINS HEAT ACTIVATED DENTURE BASE RESINS • Most widely used resins for the fabrication of complete dentures. • Available as:- – Powder and liquid • Powder may be transparent or tooth colored or pink colored (to stimulate the gum, some even contain red fibers to duplicate blood vessels). • Monomer is supplied in tightly sealed amber colored bottles (to prevent premature polymerization by light or ultraviolet radiation on storage). 65
  66. 66. • Commercial Names:- – Stellon (DPI) – Lucitone (Bayer) – Travellon (Dentsply) 66
  67. 67. Composition 67 POWDER Poly (methyl methacrylate) Ethyl or butyl Methacylate (5 %) Benzoyl Peroxide Compounds of Mercuric sulfide, cadmium sulfide, etc. Zinc or titanium oxide Dibutyl phthalate Inorganic fillers like glass fibers, zirconium silicate, alumina, etc. Dyes synthetic nylon or acrylic fibers Major component Copolymers – improved properties Initiator Dyes Opacifiers Plasticizer Improves physical properties like stiffness, etc. To simulate small capillaries
  68. 68. Composition 68 LIQUID Methyl methacrylate Dibutyl phthalate Glycol Dimethacrylate Hydroquinone (0.006%) Plasticizes the polymer Plasticizer Cross-Linking agent (reduces Crazing) Inhibitor – prevents premature polymerization
  69. 69. 69 Chemical Basis
  71. 71. TECHNIQUE • Primary impressions • Secondary impressions • Jaw relations • Try in stage • Acrylization – Flasking – Dewaxing – Packing- under pressure – Curing 71
  72. 72. Flasking • The Art of Investing in a Flask ” - GPT • Flask “ a metal case or tube used in investing procedure” - metal - brass - 3 or 4 parts 72
  73. 73. 73 3 PART FLASK
  74. 74. 4 PART FLASK 74
  75. 75. PRESSURE CLAMP 75
  77. 77. COMPRESSION MOLDING TECHNIQUE  Periphery of flask should be in level with the rim of the flask  Occlusal plane – parallel to the base of the flask 77
  78. 78. • Tilting of the casts • Retromolar pads and tuberosity should be protected • Checking the seating of flask members • Distance from top lid – 6 mm 78
  79. 79. • Paint on separating media like cellulose lacquers, solution containing alginate compounds, calcium oleate ,soaps, sodium silicate, starches were introduced….. Tin foil substitutes. • Most popular… water soluble alginate solution • Produce thin, relatively insoluble calcium alginate films….. 79
  80. 80. Sodium Alginate Solution • Water soluble. • Reacts with the calcium of plaster or stone to form a film of insoluble calcium alginate. • Composition – 2 % sodium alginate in water – Glycerine – Alcohol – Sodium phosphate – Preservatives 80
  81. 81. Sodium Alginate Solution • Application – Applied using brush, coating only the plaster surfaces. – One or two coats are applied. 81
  82. 82. Sodium Alginate Solution • Precautions to be taken – Waxes or oils remaining on the mold surface will interfere with the action of the separating medium. – Mold should not be warm, not hot. Continuity of the film will break if the mold is steaming hot. – Avoid coating on teeth. 82
  83. 83. • Second mix is mixed • Lid is closed • Flask is clamped 83
  84. 84. Polymer – Monomer Interaction • Sandy, stringy, dough like, rubbery or elastic, stiff • During sandy stage, little or no interaction occurs on a molecular level. Polymer beads remain unaltered. • Later, mixture enters stringy stage. Monomer attacks the surfaces of individual polymer beads. Stage characterized by stringiness. 84
  85. 85. Polymer – Monomer Interaction • Subsequently the mass enters a dough like stage. On molecular level increased number of polymer chains are formed. Clinically the mass becomes as a pliable dough. It is no longer tacky • This stage is ideal for compression molding. • Hence material is inserted into mold cavity during dough like stage. 85
  86. 86. • Following dough like stage, the mixture enters rubbery or elastic stage. Monomer is dissipated by evaporation and by further penetration into remaining polymer beads. In clinical use the mass rebounds when compressed or stretched. • Upon standing for an extended period, the mixture becomes stiff. This may be attributed to the evaporation of free monomer. From clinical point, the mixture appears very dry and resistant to mechanical deformation 86
  87. 87. DOUGH FORMING TIME • The time required for the resin mixture to reach a dough like stage is termed the dough forming time. • In clinical use, the majority of resin reach a dough like consistency in less than 10 min. 87
  88. 88. PACKING • Placement and adaptation of denture base material within the mold cavity is termed packing. Over packing- leads to excessive thickness and malposition of prosthetic teeth Under packing- leads to noticeable denture base porosity • Trial packing is done to ensure proper packing of resin mass in the mold. • After the final closure of the flasks, they should remain at room temperature for 30- 60 min. it is called bench curing 88
  89. 89. Bench curing • It permits equalization of pressure throughout the mold • Allows more time for uniform dispersion of monomer throughout the mass of dough • If resin teeth are used, it provides a longer exposure of resin teeth to the monomer producing a better bond of the teeth with the base material 89
  90. 90. POLYMERIZATION PROCEDURE / CURING • When heated above 60 °C, molecules of benzoyl peroxide decompose to yield free radicals. • Each free radicals, rapidly reacts with an available monomer molecule to initiate polymerization. • Heat is required to cause decomposition of benzoyl peroxide. Therefore heat is termed as activator. • Decomposition of benzoyl peroxide molecule yields free radicals that are responsible for initiation of chain growth. Hence it is termed as initiator 90
  91. 91. Temperature rise • Because resin and dental stone are relatively poor thermal conductors, the heat of reaction cannot be dissipated. Therefore the temperature of resin rises well above the temperature of investing stone and surrounding water. • It should be noted that temperature of resin not allowed to exceed the boiling point of the monomer (100.8oC) – which produces significant effects on the physical characteristics of the processed resin. 91
  92. 92. Curing cycle • Following curing cycle have been quite successful – Processing in a constant temperature water bath at 74oC for 8 hours or longer with no terminal boil. – Processing in a 74 0C water bath for 8 hours and then increasing the temperature to 100oC for 1 hour. – Processing resin at 74oC for approximately 2 hours and increasing the temperature of water bath to 100oC for 1 hour. 92
  93. 93. Polymer – Monomer Ratio • Polymerization of MMA to PMMA yields 21% decrease in the volume of material, which would create difficulties in denture base fabrication and clinical use. • To minimize dimensional changes, Resin manufacturers prepolymerize a significant fraction of the denture base resin. • The accepted polymer to monomer ratio is 3:1 by volume. • Using this ratio the volumetric shrinkage is limited to 6% and 0.5% linear shrinkage. 93
  94. 94. Polymer – Monomer Ratio 94 If too much monomer is use:- If too little monomer is use:- Greater curing or polymerization shrinkage More time is needed to reach the packing consistency Porosity may occur in denture Not all the polymer bead will be wetted by monomer and the cured acrylic will be granular. Dough will be difficult to manage and it may not fuse into a continuous unit of plastic during processing
  95. 95. • First reported by Kimura et. al • This technique employs a specially formulated resin and a non metallic flasks. FRP Flask [ Fiber Reinforced Plastic flasks] 95 POLYMERIZATION VIA MICROWAVE ENERGY
  96. 96. Advantages: • Cleaner and faster polymerization. 3 minutes • Minimal color changes • Less fracture of artificial teeth and resin bases • Superior denture base adaptability 96
  97. 97. • No noticeable difference • Trade name – Keystone Diamond D • Disadvantages Flasks are expensive and have tendency to break down after processing several dentures. The polycarbon bolts tend to break if tightened too firmly. 97 Bernard Levin et al [ JPD 1989;61: 381-383]
  98. 98. Injection molded polymers • In mid 1970’s, Ivoclar introduced this system. • These are made of Nylon or Polycarbonate. • It has to be heated and injected into a mold 98 The SR-Ivocap system uses specialized flasks and clamping presses to keep the molds under a constant pressure of 3000 lbs
  99. 99. Injection molded polymers • Flask is then placed into water bath for polymerization as the material polymerizes addition resin is introduced into the mold cavity. This process offsets the effects of polymerization shrinkage. • Equipment is expensive. 99 The SR-Ivocap system uses specialized flasks and clamping presses to keep the molds under a constant pressure of 3000 lbs
  100. 100. Injection molded polymers • Advantages – Dimensional Accuracy – No increase in vertical dimension. – Homogenous denture base – Low free monomer content – Good impact strength • Disadvantages – High cost of equipment – Difficult mold design – Less craze resistant – Special flask is required. 100
  101. 101. 101
  102. 102. Technique 102
  103. 103. Technique 103
  104. 104. Chemically Activated Denture Base Resins • Does not require thermal energy. • Hence often referred to as cold curing, self curing or autopolymerizing resins. 104
  105. 105. Chemically Activated Denture Base Resins • Chemical activation is accomplished through the addition of a tertiary amine such as dimethyl- Para- toluidine to the liquid. • Upon mixing, the tertiary amine causes decomposition of benzoyl peroxide. Consequently, free radicals are produced and polymerization is initiated. 105
  106. 106. Composition 106 POWDER Poly (methyl methacrylate) and other co-polymer(5 %) Benzoyl Peroxide Compounds of Mercuric sulfide, cadmium sulfide, etc. Zinc or titanium oxide Dibutyl phthalate Dyes organic fillers and inorganic particles like glass bead fibers or beads. Dissolves the monomer to form dough Initiator Dyes Opacifiers Plasticizer Esthetics
  107. 107. Composition 107 LIQUID Methyl methacrylate Dimethyl-p-toluidine Dibutyl phthalate Glycol Dimethacrylate 1 to 2% Hydroquinone (0.006%) Dissolves/Plasticizes the polymer Activator Plasticizer Cross-Linking agent (reduces Crazing) Inhibitor – prevents premature polymerization
  108. 108. MANIPULATION OF AUTOPOLYMERIZATION RESINS • Sprinkle on technique • Adapting technique • Fluid resin technique • Compression molding technique 108
  109. 109. • There is greater amount of unreacted monomer which creates two major difficulties. 1. It acts as plasticizer that results in decreased transverse strength of denture resin. 2. Residual monomer serves as a potential tissue irritant, thereby compromising the biocompatibility of the denture base. 109
  110. 110. Technical considerations • Most often molded using compression technique. • Mold preparation and resin packing are essentially same. • Working time for self cure resin is shorter than heat cured resins. • Refrigerating the liquid component or mixing vessel before mixing process can prolong the working time. 110
  111. 111. Processing considerations • Following final closure of the denture flask, pressure must be maintained throughout polymerization process. • Initial hardening of resin occurs within 30 minutes of final closure. • To ensure sufficient polymerization, the flask should be held under pressure for minimum 3 hours • Resins polymerized via chemical activation generally display 3-5% free monomer where as heat activated resins 0.2-0.5% free monomer. 111
  112. 112. Uses • Temporary crowns and FPDs. • Construction of special tray. • For denture repair, relining and rebasing. • Making removable orthodontic appliances. • For adding a post dam to an adjusted upper denture. • For making temporary and permanent denture bases. 112
  113. 113. FLUID RESIN TECHNIQUE • Special resin is available. • Chemical composition is similar to polymethyl methacrylate materials. • Principal difference is they have high molecular weight powder particles that are much smaller and when they are mixed with monomer, the resulting mix is very fluid. • Significantly lower power: liquid ratio ranges from 2:1 to 2.5:1. 113
  114. 114. Method of Flasking and Curing • Agar hydrocolloid is used for the mold preparation in place of the usual gypsum. • Fluid mix is quickly poured into the mold and allowed to polymerize under pressure at 0.14 MPa . 114
  115. 115. Fluid Resin Technique • Employs a pourable chemically activated resin Advantages • Improved adaptation to underlying soft tissues. • Decreased damage to prosthetic teeth and denture base during deflasking. • Reduced material costs. • Simplification of flasking, deflasking, finishing procedure 115 Walter Shepard [ JPD 1968;19: 562-564]
  116. 116. Fluid Resin Technique Disadvantages • Noticeable shifting of prosthetic teeth during processing • Air entrapment • Poor bonding between denture base and acrylic teeth • Technique sensitivity 116 Walter Shepard [ JPD 1968;19: 562-564]
  117. 117. • Fluid denture resin processing in a rigid mold • Koblitz FF et al described a fluid resin processing technique using rigid, modified gypsum investment as replacement for hydrocolloid investment. • Advantages • Method requires no specialized equipment such as metal flasks or hydrocolloid conditioning apparatus • The technique eliminates the time consuming step of sorting and replacing artificial teeth in as hydrocolloid mold. 117[ JPD 1973; 30; 339-345 ]
  118. 118. 118
  119. 119. 119
  120. 120. Self Cured Heat Cured Heat is not necessary for polymerization Porosity is greater Has lower average molecular weight (not Strong) Higher residual monomer content Rheological properties - Shows greater distortion - More initial deformation - Increased creep and slow recovery Poor color stability Easy to flask Heat is necessary Porosity is less Higher molecular weight Lower residual monomer content - Shows less distortion - Less initial deformation - Less creep and quicker recovery Color stability is good Difficult to deflask Increased rate of monomer diffusion at higher temperature. 120
  121. 121. Light Activated Denture Base Resins • This material has been described as a composite having a matrix of urethane dimethacrylate and microfine silica • Visible light is the activator • Camphoroquinone serves as the initiator for polymerization • Supplied in sheets and rope forms and is packed in light proof pouches. 121
  122. 122. Light Activated Denture Base Resins • Can be used as repair material and as custom tray material. • Single component denture base is supplied as sheet and rope form in light proof pouches. 122
  123. 123. • Technique – Teeth are arranged, and the denture base is molded on an accurate cast. – Subsequently the denture base is exposed to high intensity visible light source for an appropriate period – Following polymerization, the denture is removed from the cast, finished and polished in a conventional manner. 123
  124. 124. Properties Of Denture Base Resins • METHYL METHACRYLATE  Methyl methacrylate is a transparent liquid at room temp.  Physical properties -Molecular weight = 100 -Melting point = - 48 C -Boiling point = 100.8 C -Density = 0.945g/ml at 20 C -Heat of polymerization=12.9 Kcal/mol 124
  125. 125. POLYMETHYL METHACRYLATE • Transparent resin, transmits light in UV range to a wavelength of 250 nm. • Hard resin knoop hardness no of 18 to 20. • Tensile strength is 60 MPa • Density is 1.19 g/cm cube. • Modulus of elasticity 2.4 GPa(2400 MPa) 125
  126. 126. POLYMETHYL METHACRYLATE • It is chemically stable and softens at 1250C • It can be molded as a thermoplastic material between 125oC and 200oC. • Depolarization takes place at approx. 450oC . • Absorbs water by imbibition • Non crystalline structure possess high internal energy. 126
  127. 127. Strength • Resins are typically low in strength, however they have adequate compressive and tensile strength for complete or partial denture applications. • Compressive strength- 75 Mpa • Tensile strength- 52 Mpa Affected by:- • Composition of the resin • Technique of processing • Degree of polymerization • Water sorption • Subsequent environment of the denture 127
  128. 128. Hardness • Resins have low hardness. They can be easily scratched and abraded. • Heat cured resin- 18-20 KHN • Self cured resin- 16-18 KHN 128
  129. 129. Modulus of elasticity • Resins have sufficient stiffness [ 2400MPa] for use in complete and partial dentures. Impact Strength • It is the measure of energy absorbed by a material when it is broken by a sudden blow. • Addition of plasticizers increase the impact strength. 129
  130. 130. 130
  131. 131. Polymerization shrinkage • When MMA monomer is polymerized to form PMMA.. Results in 21% volumetric shrinkage. • To reduce this high % of shrinkage… polymer powder is supplied in prepolymerized beads form which accounts for only 7% of volumetric shrinkage. • Distributed uniformly to all surfaces, hence the adaptation of denture bases to underlying soft tissues is not significantly affected. Processing shrinkage Due to stresses induced during processing • 0.26% for self cure resin • 0.53% for heat activated resin 131
  132. 132. 132
  133. 133. Denture Warpage • It is the deformity or change of shape of the denture which affect the fit of the denture. • Stresses incorporated during processing. 133
  134. 134. Denture Warpage • Caused by:- • Stress causes by curing shrinkage or uneven or rapid cooling. • Packing of resin in rubbery stage. • Improper flasking. • During polishing, a rise in temperature occurs. 134
  135. 135. Denture Warpage • Caused by:- • Immersion of the denture in hot water. • Recuring of the denture after addition of relining material, etc. 135
  136. 136. Porosity • May compromise physical, aesthetic and hygienic properties of processed dentures. 136
  137. 137. Porosity Internal Porosity: • Is in form of voids or bubbles within the mass of processed resin. It is confined to thick portions of denture base. • Results from vaporization of unreacted monomer and low molecular wt. polymers, 137
  138. 138. Porosity External Porosity: • Inadequate mixing of powder liquid components. • Inhomogeneity of resin mass • Inadequate pressure or insufficient material • Air inclusions incorporated during mixing procedures. 138
  139. 139. Water Sorption • Absorption is primarily by diffusion mechanism. • Water molecules occupy positions between polymer chains forcing the polymer chains apart. • The introduction of water molecules in the polymerized mass produces two important effects • Acts as plasticizers • It causes slight expansion of polymerized mass 139
  140. 140. Water Sorption • PMMA exhibits a water sorption value of 0.69mg/cm2 • Fortunately these changes are relatively minor and do not exert significant effects on the fit or function of processed bases. 140
  141. 141. Crazing • Is formation of surface cracks on denture base resin. • Due to -Stress relaxation -Solvent action e.g. Ethyl alcohol • Crazing in a transparent resin imparts a hazy or foggy appearance. • These surface cracks predispose a denture resin to fracture. 141
  142. 142. Plaque Adhesion • An invitro study done on the adhesion and penetration of C. Albicans proved that adhesion of C. Albicans occur, but they cant penetrate the Denture Base Resin. 142 A COMPARATIVE IN-VITRO STUDY ON THE ADHERENCE AND PENETRATION OF C. ALBICANS TO THREE DIFFERENT RESIN DENTURE BASE SURFACE -Dr. Divyang Patel
  143. 143. Other Microorganisms • Streptococcus Oralis, Bacteroides gingivalis, B. Intermedius And S. Sanguis. • It was found, they adhere to rougher surface than those that are highly polished. 143
  144. 144. Solution for Plaque Adhesion • Chlorhexidine apparently can bind to acrylic surfaces for atleast 2 weeks. • Treating acrylic with Nystatin, followed by drying, produced similar results. 144
  145. 145. Resistance to Acids, Bases And Organic Solvents • Weak acids or bases = Excellent • Quiet resistant to Organic Solvents • Soluble in aromatic hydrocarbons, ketones and esters. • Alcohol will cause crazing in Denture plastic. • Incorporating ethylene glycol dimethacrylate as a cross linking agents significantly improves solvent resistance. 145
  146. 146. DENTURE CLEANSER 146 • Most immersion denture cleansers are effective in the removal of mucin, stains, and loosely attached food debris. • A solution consisting of 1 tsp of a hypochlorite such as Clorox, and 2 tsp of calgon in half glass has been recommended for occassional overnight immersion of plastic dentures.
  147. 147. DENTURE CLEANSER 147
  148. 148. Cytotoxicity of Denture Base Acrylic Resins [ JPD 2003: 90; 190-195 ] • Residual monomer, resulting from incomplete conversion of monomers into polymer, has the potential to cause – irritation, – inflammation, – and an allergic responses of oral mucosa. • Clinical signs and symptoms reported include – erythema, – erosion of oral mucosa, – burning sensation of mucosa and tongue. 148
  149. 149. Cytotoxicity of Denture Base Acrylic Resins [ JPD 2003: 90; 190-195 ] Effect of polymer : monomer ratio • More monomer added to the mixture, the greater amount of residual monomer and therefore more potential for cytotoxicity . Effect of storage time and water immersion • Sheridan et al reported that cytotoxic effect of acrylic resins was greater in first 24 hours after polymerization and decreased with time. • Therefore it is recommended that dentist soak the resin prosthesis in water for atleast 24 hours before placing them in the patients mouth. 149
  150. 150. • Effects of polymerization cycle • Reduced amount of residual monomer when polymerization time extended was observed. • Auto polymerized resins exhibited higher content of residual monomer than heat polymerized resins. 150
  151. 151. • Lamb et al observed that levels of residual monomer were higher for specimens polymerized at 200C as compared with those at 550C. • Therefore it is suggested that the Autopolymerized acrylic resins should be heat treated to decrease cytotoxic effects. 151
  152. 152. Occupational Hazard • Plastic dough should not be manipulated excessively with bare hands. • The monomer is a good solvent for body oils and may pick up dirt from the hands, resulting in a non esthetic denture. • Monomer may also enter blood stream through the skin. 152 Restorative Dental Materials, Robert G. Craig & John M Powers, 11th edition
  153. 153. Recent Advances HIGH IMPACT RESISTANT ACRYLIC • Butadiene- styrene rubber is incorporated with copolymer of vinyl and hydroxyethyl monomer. • These materials are slightly stiffer twice the impact strength absorbs less water lower linear shrinkage. But are not entirely color stable. 153
  154. 154. Recent Advances HIGH IMPACT RESISTANT ACRYLIC Phase inversion resulting in dispersion throughout the beads of tiny islands of rubber containing small inclusions of rubber/PMMA graft polymer. 154
  155. 155. Recent Advances RAPID HEAT POLYMERIZED POLYMER • These are hybrid acrylics which have had the initiator formulated to allow for very rapid polymerization without nearly as much porosity. • The flasks are placed in boiling water immediately after being packed. The water is then brought back to a boil for 20 min to complete the curing cycle. • Fast, high temperature cure makes this material stiffer than conventional acrylic processing. • E.g. travelon 155
  156. 156. FIBER –REINFORCED POLYMER • Glass, carbon/graphite, aramid and ultrahigh molecular weight polyethylene have been used as fiber reinforcing agents. • Metal wires like graphite has minimal esthetic qualities. • Fibers are stronger than matrix polymer thus their inclusion strengthens the composite structure. • The reinforcing agent can be in the form of unidirectional, straight fiber or multidirectional weaves. 156
  157. 157. Acrylic resins with improved thermal conductivity • Thermal conductivity of PMMA is three times less than metals. • Thermal conductivity of denture base materials is found to have an important effect on gustatory sensitivity. • Thermal conductivity of acrylic based materials can be improved by introducing a more thermally conducting phase within the insulating acrylic resin matrix. • E.g. Al2O3, porcelain whiskers JPD 1998: 20; 278- 157
  158. 158. BPS (Biofunctional Prosthetic System) • BPS is the system designed to work with the body in a biologically harmonious way, maximizing function, and giving comfort and natural appearance to the patient. 158
  159. 159. 159 Resorbed ridges Occlussal centric tray loaded with impression for recording initial vertical dimension Biofunctional prosthetic system impression trays
  160. 160. 160 Bite registration through Gnathometer M Secondary impression-making with zinc oxide eugenol past Wax-up trial for the patient
  161. 161. 161 Acrylized Denture
  162. 162. Flexible Denture • First introduced in 1956. • Trade name:- – Flexiplast – Valplast • Superpolyamides, which belong to nylon family, which inherent property of flexibility. • Flexibility depends on the thickness • Good retention 162
  163. 163. Flexible Denture Advantage • Good retention Disadvantage • Acrylic teeth do not bond chemically with flexible denture base. 163
  164. 164. VALPLAST • Nylon like material • Nearly unbreakable, pink colored like gum • Can be built quite thin, can form not only denture base but the clasp as well. • Valplast is a flexible denture base resin that is ideal for partial dentures and unilateral restorations. 164
  165. 165. VALPLAST – • The resin is a biocompatible nylon thermoplastic ,it eliminates the concern about acrylic allergies. • Quite hygienic. It is not possible for Valplast to absorb the remnants of food or other stains. So there will be no odor. 165
  166. 166. Conclusion 166
  167. 167. Conclusion 167
  168. 168. 168
  169. 169. 169
  170. 170. References • Kenneth j. Anusavice ; Phillips Science of dental material .Eleventh edition, Elsevier,2004. • Robert C. Craig John M. Powers, John C.Wataha ;Dental materials properties and manipulation,. Eleventh edition,2002. • Applied Dental Materials, 8th edition, John F McCabe & Angus W. G. Walls • Rudd and morrow; dental laboratory procedures: 1986 2nd edition • Vk subbarao ; notes on dental materials : 4th edition 170
  171. 171. • Basic Dental Materials – John J. Manappallil, 3rd edition • Walter Shepard : fluid resin technique; JPD 1968 (19) 561- • Koblitz F.F et al: Fluid denture resin processing in a rigid mold JPD1973 (30) 339- • Dimensional accuracy of pour acrylic resin and conventional processing of cold cure resin JPD 1970 (24) 662- • Atwood et al: final report of the workshop on clinical requirements of ideal denture base material ; JPD 1968(20) 101-105 171
  172. 172. • EW Skinner; acrylic denture base material their physical properties and manipulation. JPD 1951 (1) 161- • Comparison of self curing and heat curing denture base resins JPD 1953 (3) 332- • FA Peyton; evaluation of dentures processed by different technique JPD 1963 (13) 269- • Cytotoxicity of denture base acrylic resin JPD 2003 (90) 190- • Bernard Levin et al; use of microwave energy for processing acrylic resins JPD 1989 (61) 381- 172
  173. 173. • Robert EO; Comparison of accuracy between compression and injection molded complete denture JPD 1999 (82) 291- • Glossary of Prosthodontic Terms 8 • A comparative in-vitro study on the adherence and penetration of c. ALBICANS TO THREE DIFFERENT RESIN DENTURE BASE SURFACE - Dr. Divyang patel 173
  174. 174. 174

Hinweis der Redaktion

  • The scope, requirements and procedures for evaluating denture base plastics are listed in ANSI/ADA Specification No. 12
    The specification includes acrylic, vinyl and styrene polymers, or mixtures of any of these polymers as well as copolymers.
  • 2nd point. Retention of false teeth became more difficult as the number of teeth diminished in the mouth and those that wore full set of dentures had to remove them before eating.
  • In ancient times, the most common material for false teeth were animal bone or ivory , especially from elephants or hippopotamus.
    Human teeth were also used, pulled from the dead or sold by poor people from their own mouths.

  • Dimensional changes WhY:-
    Thermal expansion during Heating in the vulcanizer
    Contraction of 2 to 4% by volume during addition of the sulphur to the rubber.
  • John Hyatt
  • Prior to 1940, vulcanite was most widely used denture based polymer
    Highly cross linked natural rubber which was difficult to pigmen and tend to become unhygienic due to uptake of saliva
  • Any impurity present increases the length of this period.
    The higher the temperature, the shorter is the length of the induction period.
    2 processses are needed :- activation and initiation
  • 50 to 100 c temp BPO 2 free radicals (benzoyl peroxide)
    Chemicall activated tertiary amine (activator) and BPO initiator
    Light activated camphorquinone and organic amine (dimethylaminoethyamine) blue to violet region (470 nm light wavelenght)
  • Light activated camphorquinone and organic amine (dimethylaminoethyamine) generate free radicals...blue to violet region (470 nm light wavelenght)
    Chemically activated tertiary amine (activator) and BPO initiator
  • Energy sourceforms free radical which opens up double or triple bond in the monomer
  • Rapid addition of monomer molecules to free radicals – free radical shifted to end of chain
  • Realigning of molecules leading to addition of monomer molecules
  • The active free radical of growing chain is transferred to another molecule (e.g monomer or inactive polymer chain) and a new free radical for further growth is created. Termination occurs in the later.
  • The active free radical of growing chain is transferred to another molecule (e.g monomer or inactive polymer chain) and a new free radical for further growth is created. Termination occurs in the later.
  • The chain reaction can be terminated either by direct coupling of two free radical chains
  • Termination by exchange of hydrogen atom from one growing chain to another
  • Depletion of free radicals and formation of polymers
  • Small amount of ethyl acrylate may be copolymerized with methyl methacrylate to alter flexibility.
    Block and graft polymers show improved impact strength. In small amount, also modify the adhesive properties of resin and surface characteristic.
  • Crazing is formation of surface cracks on the denture base resin
  • short, fine fibers that separate from the surface of cloth or yarn, esp. during processing.
  • 3rd point:- to stimulate the gum, some even contain red fibers to duplicate blood vessels.
  • Cross linking agent Ethylene glycol dimethacrylate(5-15%).they are added to avoid crack or craze produced by stresses during drying.
    Inhibitor Hydroquinone (trace) to avoid premature polymerization and enhance shelf life.

  • Devoid of undercut

    Shaping of the stone – blade or knife
  • When mixed in proper proportions, the resultant mass passes through five distinct stages.
  • When mixed in proper proportions, the resultant mass passes through five distinct stages.
  • The polymerization of denture base resin is exothermic and the amount of the heat evolved may affect the properties of the processed denture bases.
  • Following the completion of curing, the denture flasks should be cooled slowly to room temperature
    Rapid cooling may result in warping of denture base because of difference in thermal contraction of resin and investing stone.
    Hence flasks should be removed from the water bath and bench cooled for 30 min.
  • Of considerable importance
  • If too much monomer is use:-
  • Resins can also be polymerized by microwave energy
  • Resins can also be polymerized by microwave energy
  • 700 W microwave oven
  • The material is supplied as a gel in the form of a putty
  • The material is supplied as a gel in the form of a putty
  • Spru channels 7 mm
    Vent channels 3 mm
  • Chemical activators are used to induce polymerization
  • Chemical activators are used to induce polymerization
  • Supplied in form of powder and liquid. Mixed according to manufacturer’s instructions.
  • , 1. The cast with denture wax-up has been attached to the surface of the plastic base. Fig. 2. The sprues for the maxillary denture extend so that they are even with the inner step; of the plastic base. Fig. 3. The sprues for the mandibular denture are attached to the most distal point 4 each heel area.
  • The stress at which fracture occurs is called the ultimate strength.
    Compresive strength – the resistance of a material to breaking under compression.
    Tensile strength -the resistance of a material to breaking under tension.
  • Hardness is the resistance of a material to indentation.
    The knoop hardness is obtained by measurement of the length of an indentation from an diamond indenter and calculating the number of kilograms required to give an indentation of 1mm2.
  • It is the measure of stiffness of a material. It is equal to the ratio of the stress to the strain.
    It is the measure of energy absorbed by a material when it is broken by a sudden blow.

  • It is fortunate that many types of denture base materials are available that will produce satisfactory dentures. The requirements may vary for different patients, and the process- ing facilities can dictate which material to use. There are also significant differences between products in each category, and it is wise to choose materials that have passed ANSI/ADA Specification No. 12
  • Porosity may be
  • Absorption is primarily by diffusion mechanism.
    PMMA absorbs relatively small amounts of water when placed in aqueous environment.
  • PMMA absorbs relatively small amounts of water when placed in aqueous environment.
  • Alcohol not used for cleaning and storing dentures.
  • Cobalt chromium alloys not used
  • HIEA :- senility and parkinsonism patients
    less likely to be broken if dropped.
    Incorporated into beads

  • Rubber inversion phase
  • Gustatory :- concerned with tasting or the sense of taste
    a single crystal of a material in the form of a filament with no dislocations.
  • Low-density impression material (syringe Acc Gel) was syringed into the vestibular area and the occlusal centric tray was loaded with high-density hydrocolloid and inserted into the patient’s mouth to get the initial vertical dimension [
  • http://valplastpartial.com/valplast-partial-cleaner.html
    Why biocompatible, because no monomer
  • http://valplastpartial.com/valplast-partial-cleaner.html
    Why biocompatible, because no monomer
  • http://valplastpartial.com/valplast-partial-cleaner.html
    Why biocompatible, because no monomer
  • http://valplastpartial.com/valplast-partial-cleaner.html
    Why biocompatible, because no monomer
  • Fatigue strength :-0 dentures are subjected to large amount of cyclic stresses during mastication
    Fatigue strength represents the number of cycles before failure at a certain stress.