Denture Base Materials

INTRODUCTION
HISTORY
REQUISITES FOR IDEAL DENTURE BASE MATERIAL
CLASSIFICATION
METAL DENTURE BASE
DENTURE BASE POLYMERS
RECENT ADVANCES
CONCLUSION
REFERANCES

1. DENTURE BASE MATERIALS

2. 2 CONTENTS INTRODUCTION HISTORY REQUISITES FOR IDEAL DENTURE BASE MATERIAL CLASSIFICATION METAL DENTURE BASE DENTURE BASE POLYMERS RECENT ADVANCES CONCLUSION REFERANCES

3. I N TRODUCTION

4. 4 DEFINITIONS Denture : An artificial substitute for missing natural teeth and adjacent structure. (GPT 9) Denture Base: The part of a denture that rests on the foundation tissues and to which teeth are attached. (GPT 9) 4 Denture Base Material: Any substance of which a denture base may be made. (GPT 9)

5. HISTORY

6. FORMERLY USED MATERIALS Before 18 th century In 18 th century 6 WOOD IVORY BONE GOLD PORCELEIN

7. Materials used in the 19 th century Tortoise Shell (1850) Gutta Percha (1851) Vulcanite (1851) Cheoplastic (1856) Rose Pearl (1860) Aluminum (1867) Celluloid (1870) 7 VULCANITE CELLULOID GUTTA PERCHA

8. Materials used in the 20th century Bakelite (1909) Stainless steel (1921) Cobalt Chromium (1930) Vinyl Resin (1932) Acrylic Resin (1937) Self cure Acrylic Resin Epoxy Resin (1951) Polystyrene (1951) Nylon (1955) Polycarbonates (1967) High impact acrylic (1967) Polysulphones (1981) Visible L.C (1947)Acrylic (1986) Pure Titanium (1998) 8 ACRYLIC RESIN STAINLESS STEEL POLYSTYRENE BAKELITE

9. Requisites For Ideal Denture Base Material

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12. CLASSIFICATION

13. According To Uses 13

14. According To Material System 14

15. According to mode of polymerization 15

16. According to Method of activation 16

17. According to ANSI/ADA (Sp. No. 12/ ISO 1567) 17

18. METAL DENTURE BASE MATERIAL

19. Single maxillary complete denture opposing natural mandibular teeth Unfavorable occlusion Heavy anterior contacts Heavy masticatory force 19 Metal denture base material Indication

20. Advantages of Metal Bases over Resin Bases: (1) Accuracy and permanence of form More Accurate and maintain their accuracy of form without change in mouth. Internal strains released later to cause distortion not present. Accuracy - provides intimacy of contact, help in retention of denture prostheses (2) Comparative tissue response- Inherent cleanliness of cast metal base contributes to health of oral tissue. Bacteriostatic activity - Ionization and oxidization of metal bases 20

21. Advantages of Metal Bases over Resin Bases: (3) Thermal conductivity- Temperature changes transmitted though metal to the underlying tissue so prevent accidental burning by hot food. Patient acceptance. (4) Weight and bulk- Thinner than acrylic resin and still have adequate strength. Certain situations demands use of acrylic denture base. Extreme loss of residual alveolar bone- fullness to denture base to restore facial contours. 21

22. Disadvantages of Metal Bases over Resin Bases: Aesthetically not acceptable Relining difficult Restoration of normal facial contour can not be achieved 22

23. COBALT-CHROMIUM ALLOYS : As early as 1949 nearly 80% of all partial denture were cast from Co-Cr alloys. NICKEL CHROMIUM ALLOYS : Nickel 70% , Chromium 18% CHROMIUM : Responsible for the tarnish resistance and stainless. Should not contain more than 28% or 29% chromium Technique sensitive. 23 Different metallic denture base materials

24. 24 COBALT AND NICKEL : Cobalt increases the elastic modulus, strength and hardness more than Nickel . CARBON : Carbon content increases hardness of Co-based alloys. More than 0.2% results in a too hard and too brittle alloy not suitable for dental appliances. Decrease of 0.2% will decrease the tensile and the yield strength. MOLYBDENUM : (3% to 6% ) Contributes to the strength of the alloy. Initially tungsten was used , but it reduced the elongation. ALUMINIUM : Forms a compound with Ni and Al (Ni3Al) which increases the tensile and the yield strength of the alloys.

25. 25 B ERYLIUM : About 1% lowers the fusion temperature range of the alloy by about100 degrees C. SILICONE AND MANGANESE : Increase the fluidity and cast ability NITROGEN : Contributes to the brittle qualities of these alloys TITANIUM : Ti was developed by William Gregor of England in 1791 , and was named by Martin H. Kalproth of Germany in 1795 . Welhelm Kroll 1930 invented useful metallurgical processes for Ti and considered to be the FATHER of Ti dentistry . It has the advantage of light-weight, strength and biocompatibility but requires an inert casting environment and casting defects can be a problem.

26. DENTURE BASE POLYMERS

27. POLYMER 27 A polymer is a long chain organic molecule. It is produced by the reaction of many smaller molecules called monomers, or mers . If reaction occurs between two different but compatible monomers the polymeric product is called a COPOLYMER . RESIN : A broad term used to describe natural or synthetic substances that form plastic materials after polymerization (GPT-9)

28. CLASSIFICATION 28

29. Monomers react to form polymer by a chemical reaction called POLYMERIZATION . The most common polymerization reaction for polymers used in dentistry is ADDITION POLYMERIZATION. 29 CHEMISTRY OF POLYMERIZATION

30. INDUCTION ACTIVATION Free radicals, can be generated by activation of radical producing molecule . INITIATION 30 INITIATOR ACTIVATOR Heat Activated Benzoyl Peroxide Heat Chemical Activated Benzoyl Peroxide Tertiary Amine Light Activated Champhoroquinone Visible Light

31. Resulting free radical-monomer complex then acts as a new free radical center when it approaches another monomer to form a dimer. 31 PROPOGATION

32. The active free radical of a growing chain is transferred to another molecule (e.g., a monomer or inactivated polymer chain) and a new free radical for further growth is created. 32 CHAIN TRANSFER

33. Chain termination can result from chain transfer. Addition polymerization reactions are most often terminated. By direct coupling of two free radical chain ends. By the exchange of a hydrogen atom from one growing chain to another. 33 TERMINATION

34. CLASSIFICATION 34 Light Activated

35. HEAT ACTIVATED DENTURE BASE RESINS 35

36. Polymer Monomer Ratio & Interaction 36 POLYMER : MONOMER 3 : 1 (By wt.) 2 : 1 (By vol.)

37. Dough Forming Time : ADA specification no. 12 requires that dough like consistency be attained in less than 40 min . from start of mixing process Clinically, most resins reach dough like stage in less than 10min Working Time : ADA specification no. 12 requires the dough to remain moldable for atleast 5 min The working time of the resin may be extended by refrigeration. 37 Dough Forming Time & Working Time

38. HEAT ACTIVATED DENTURE BASE RESINS Advantages Good appearance High glass-transition temperature Ease of fabrication Low capital costs Good surface finish Disadvantages Free-monomer can cause sensitization Low impact strength Flexural strength low enough to penalize poor denture design Fatigue life too short Radiolucency 38

39. Rubber reinforced (butadiene-styrene polymethyl methacrylate) Rubber particles grafted to MMA for better bond with PMMA. Indicated for patients who drop their dentures repeatedly e.g. parkinsonism. Available as powder-liquid system & processing is same as heat cure resin 39 HIGH IMPACT RESIN Advantages Good impact strength Disadvantages Reduced stiffness

40. Metal fiber reinforced Carbon / graphite fiber reinforced Aramid fiber reinforced Polyethylene fiber reinforced Highly drawn linear polyethylene fibers (HDLPF) Glass fibres (have best aesthetics) 40 FIBER REINFORCED RESINS Advantages High stiffness & Very high impact strength Good fatigue life Polypropylene fibers: Good translucency & surface finish Disadvantages Carbon and Kevlar fibers: Poor color Poor surface

41. Polyethylene > glass > thick Kevlar >carbon >thin Kevlar > unreinforced 41 Comparison Of Impact Strength Of Resins Reinforced With Different Fibers

42. Same as conventional material except that they contain altered initiation system. (heat + chemical) These initiator allow them to be processed in boiling water for 20min. A problem with these is that areas of the base thicker than approx. 6mm have a high level of porosity. Short duration of heating also leaves a higher level of residual monomer, 3-7 times greater than conventional heat cured denture base. Eg :- QC 20, Meliodent , trevalone 42 RAPID HEAT POLYMERIZED POLYMER

43. Resins are the same as used with conventional material and are processed in a microwave. Denture base cures well in Special Polycarbonate flask(instead of metal). The advantages are that it greatly reduced curing time (3min) at 450 watts shortened dough-forming time, minimal colour changes, less fracture of artificial teeth and resin bases and superior denture base adaptability, lower residual monomer ratio, most stable. Eg : Material: Nature- cryl Microwave curing resin: Acron MC 43 MICROWAVE POLYMERIZED POLYMERS

44. 44 CHEMICALLY ACTIVATED DENTURE BASE RESIN

45. Advantages Easy to deflask Dimensional accuracy Capable of higher flexural strength than heat cured Disadvantages Increased creep Increased free-monomer content Color instability Reduced stiffness Tooth adhesion failure Uses For making temporary crowns & FPDs Construction of special trays For denture repair , relining & rebasing For making removable orthodontic appliances 45 CHEMICALLY ACTIVATED DENTURE BASE RESIN

46. Techniques Sprinkle on technique Adapting technique Fluid resin technique Compression molding technique 46

47. 47 LIGHT ACTIVATED DENTURE BASE RESINS Supplied in- premixed sheets with claylike consistency Packed in - light proof pouches Light with a wavelength of about 400-500nm Visible light Blue to violet

48. LIGHT ACTIVATED DENTURE BASE RESINS Advantages No methacrylate monomer Decreased polymerization shrinkage Possible improved fit compared to conventional material Requires little equipment Disadvantages Decreased elastic modulus Requires high artistic skills Technique sensitive 48

49. These are made of Nylon or Polycarbonat e. The material is supplied as a gel in the form of a putty . It has to be heated and injected into a mold Equipment is expensive. Craze resistance is low. The SR- Ivocap system uses specialized flasks and clamping presses to keep the molds under a constant pressure of 3000 lbs 49 INJECTION MOLDED RESINS

50. INJECTION MOLDED RESINS Advantages Dimensional accuracy Low free-monomer content Polycarbonate and nylon Good impact strength Disadvantages High capital costs Difficult mold design problems Less craze resistance Less creep resistance 50

51. Polymerization shrinkage Porosity Water absorption Solubility Strength Processing stresses Crazing 51 Physical Properties of Denture Base Resins

52. During polymerization shrinkage the density of the mass changes from 0.94 g/cm3 - 1.19 g/cm3 Volumetric shrinkage – 7% , exhibit Linear shrinkage – 2% Linear shrinkage – denture base adaptation and cuspal interdigitation Greater linear shrinkage  greater discrepancy in initial fit Initial cooling – resin is soft- contraction at the same rate as that of dental stone At glass transition temperature – contraction occurs – faster rate than the surrounding stone 52 POLYMERISATION SHRINKAGE Volumetric shrinkage – 21% Glass transition temperature It is a thermal range in which the resin passes from a soft, rubbery stage to a rigid glassy state Beyond this  rigid mass

53. 53 Accepted linear shrinkage for heat activated resin – 0.12%-0.97% Processing shrinkage Chemically activated resin- 0.26% Heat activated resin- 0.53% Fluid resin Technique - VD Heat & chemically activated resin - VD

54. Contraction porosity Generalized Localized Gaseous porosity Granular porosity Air inclusion porosity 54 POROSITY

55. 55 CONTRACTION POROSITY GASEOUS POROSITY Insufficient pressure Rapid heating Insufficient mixing

56. Absorbs relatively small amount of water when placed in water . Water molecules penetrate the PMMA and occupy positions between polymer chains forces them apart . Slight expansion in polymerized mass. Water acts as plasticizer. Water absorption value – 0.69 mg/cm2 Interferes with the polymer chain making them more mobile – relaxation of stresses Changes in shape (insignificant) WATER SOLUBILTIY : Insoluble in oral cavity 56 WATER ABSORBTION 1%increase in weight 0.23% linear expansion in acrylic

57. During polymerization – tensile stresses are sustained Stresses relaxed – distortion occurs 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 0.2 mm 57 PROCESSING STRESSES Inhibition of natural dimensional change Thermal change causing shrinkage (cooling to glass transition temperature) STRESS

58. Crazing is formation of surface Microcracks on denture base resin . Causes Incorporation of stress (Tensile) Attack by solvent (alcohol) Incorporation of water during processing. Prevention Avoidance of solvent Metal moulds Use of cross linked acrylic 58 CRAZING HAZY / FOGGY APPEARANCE

59. STRENGTH CREEP Load application – stresses within the resin – change in shape Strength α degree of polymerization. Chemically activated resin – lower degree of polymerization. Acts as rubbery solids that recover from elastic deformation once stresses are eliminated – VISCO-ELASTIC BEHAVIOR. If load is not removed additional plastic deformation occurs – CREEP. Rate at which this deformation occurs – CREEP RATE (9Mpa) 59

60. Recent Advances

61. Lower residual monomer content than PMMA, thus act as alternatives to Poly Methyl Methacrylate in allergic patients. Diurethane dimethacrylate , Polyurethane, Polyethylenterephthalate and Polybutylenterephthalate . Enterephthalate based ( Promysan , thermoplastic) show low water solubility than PMMA. 61 HYPOALLERGENIC RESINS

62. 62 Resins With Modified Chemical Structure FILLERS FUNCTION Hydroxy-apatite Increases Fracture Toughness Al2o3 Fillers Increases The Flexural Strength & Thermal Diffusivity 2% Quaternary Ammonium Silver nanoparticals , Zinc oxide, gentamycin Antiseptic Properties Ceramic Or Sapphire Whiskers Thermal Diffusivity 11-14% Bismuth Or Uranium 35% Organo-zirconium Triphenyl Bismuth (Ph3Bi) Impart Radiopacity Equivalent To Aluminum. cytotoxicity

63. Fully polymerized basic material is softened by heat (without chemical changes) and injected afterwards. 63 THERMOPLASTIC RESINS

64. Advantages Excellent esthetics. Unbreakable ,flexible, light weight. Stable high fatigue endurance. Increased creep & wear resistance. Non Porous: no bacterial growth but retains enough moisture to keep it comfortable for gums. Can be relined and repaired. Materials Used Thermoplastic Nylon Thermoplastic Acetal Thermoplastic Acrylic Thermoplastic Polycarbonate 64 THERMOPLASTIC RESINS

65. Inj. Temp 274-293 degree centigrade Translucent Tissue colored clasps instead of metal clasps Unbreakable, does not wrap & lightweight No discoloration over time ( colour fast) & is non-porous so no growth of bacteria. LIMITATIONS Flexible in nature difficult to polish and adjust Not strong enough for normal tooth borne rest seats eg : valplast , lucitone FRS (more impact resistance) 65 (A) THERMOPLASTIC NYLON : POLYAMIDE (VALPLAST, FLEXIPLAST) 1950

66. Clasps engage first third of undercuts: 3-4 times more retention. Can be placed more gingivally: better aesthetics. 18 vita +3 pink shades: for simulating lifelike appearance. Metal clasps and bars can be replaced. Flexible & monomer free- hypoallergic. Teeth and clasps can be added on existing denture bases. 66 (B) THERMOPLASTIC ACETAL: POLYOXYMETHYLENE 1971

67. 67 Limitations Cannot be used as major connector Does not seal the base of the denture which allows seepage of fluid Can not be used as crib and clasp where diastema is Absent Application Preformed clasp for RPDS Partial denture framework Provisional bridge Occlusal splints Implant abutment

68. Decreased wear resistance Poor impact resistance Adequate tensile & flexural strength Easy to polish Repairable and relineable at chair side EXCEPTION : Flexite and M.P.-A -highest impact resistance among acrylics (very popular in bruxism and parkinsonism patients) 68 (C) THERMOPLASTIC ACRYLIC

69. Strong, flexible and fracture resistant Low wear resistant- vdo wont be maintained over long term Used as provisional bridge and crown only Clinical advantage Minimal residual monomer-can be used in allergic patients Very little water absorption-less smell and bacterial growth Good adherence and coherence 69 (D) THERMOPLASTIC POLYCARBONATE: POLYMER OF BISPHENOL-A

70. 70 ENIGMA GUM TONING Custom shade matching of natural gingival tissue using ‘Enigma’ color tones. Gives extra confidence to patient in appearance of their dentures. Available in Ivory, Light Pink, Natural Pink, Dark Pink & Light Brown. Different colors are mixed to get the desired gum tone.

71. New method of fabricating dentures from Dentsply International . Marketed as an indirect build-up method for fabricating dentures that is monomer-free and flask-free. Light-cured system that does not contain any ethyl-, methyl-,butyl-, or propyl-methacrylate monomers. Uses three resins to form the denture: Baseplate Resin, Set-up Resin and Contour Resin. Handle like wax, yet be cured into a denture base material without investing and flasking . 71 ECLIPSE PROSTHETIC RESIN SYSTEM https://www.youtube.com/watch?v=4PzKPuTU3pg

72. The general properties of these materials are strength, hardness, toughness, low curing shrinkage and good adhesion to metals. The disadvantages for dental use are the toxicity, the yellow colour which darkens further, high water absorption, poor adhesion to vinyl polymers 72 EPOXY RESINS :

73. CONCUSION There is a wide variety of denture base materials and the ever growing urge to find the best and the most feasible material will always bring an evolution in denture base material sciences. As clinicians, we must understand the basic nature of each of these, to provide the best possible treatment to our patient. 73

74. Phillips - science of dental materials – 11 th ed. William J O’Brien Dental materials Selection 3 rd edition NEW ERA IN DENTURE BASE RESINS: A REVIEW Dental Journal of Advance Studies Vol. 1 Issue III-2013 Denture Base Resins From Past to New Era European Journal of Molecular & Clinical Medicine ISSN 2515-8260 Volume 07, Issue 06, 2020 https://www.youtube.com/watch?v=4PzKPuTU3pg 74 REFERENCES

75. Thanks ! 75