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Non metallic denture base material / dental crown & bridge courses


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Non metallic denture base material / dental crown & bridge courses

  2. 2. CONTENTS  Introduction  History  Disadvantages of earlier denture base materials  Polymers -Definition and use -Chemistry-Addition polymerization  Requisites for dental resins -Biological compatibility -Physical properties -Manipulation -Aesthetic properties -Economic consideration -Chemical stability  Types of denture base resins 1 Conventional heat cured Polymethyl methacrylate
  3. 3. 2 Cold cure /Autopolymerizing Polymethyl methacrylate (Pour resins). 3 High impact –resistant Acrylic 4 Injection molded polymers 5 Rapid heat polymerized polymers 6 Microwave- Polymerized polymers 7Light activated polymers 8 Fiber Reinforced polymer  Review of literature  Recent advancement  Conclusion  References
  4. 4. INTRODUCTION All through the history of the making of dentures,we find a constant struggle of the dentist to find a suitable denture base material
  5. 5. Definition : According to GPT - VI, Denture Base is defined as the part of Denture that rests on the foundation tissue and to which teeth are attached. Denture Base Material is any substance of which denture base may be made
  6. 6. HISTORY  Skillfully designed dentures were made as early as 700 BC.and  Talmud a collection of books of hebrews in 352-407 AD mentioned that teeth were made of gold ,silver,and wood.  Egypt was the medical center of ancient world, the first dental prosthesis is believed to have been constructed in egypt about 2500 BC. Hesi-Re Egyptian dentist of about 3000 BC
  7. 7. ront and back views of mandibular fixed bridge, four natural incisor teeth and two carved ivory teeth ound With gold wire found in Sidon-ancient Phoenicia about fifth and fourth century BC.
  8. 8.  During medieval times dentures were seldom considered ,when installed they were hand carved and and tied in place with silk threads.  Those wearing full denture had to remove them before eating.  Upper and lower teeth fit poorly and were held together by steel springs.  Earlier pictures of dental prosthesis are delivered to us by ABUL- CASIM an Arab born in Cordova Spain. Persian dentist of late eighteen century Indian surgeon of mid nineteenth century
  9. 9. WOOD  For years, dentures were fashioned from wood .  Wood was chosen -readily available -relatively inexpensive -can be carved to desired shape  Disadvantages -warped and cracked in moisture -esthetic and hygienic challenges -degradation in oral environment
  10. 10. Wooden denture believed to be carved out of box wood in 1538 by Nakoka Tei a Buddist priestess Wooden dentures
  11. 11. Bone  Bone was chosen due to its availability, reasonable cost and carvability .  It is reported that Fauchard fabricated dentures by measuring individual arches with a compass and cutting bone to fit the arches .  It had better dimensional stability than wood, esthetic and hygienic concerns remained.
  12. 12. IVORY  Denture bases and prosthetic teeth were fashioned by carving this material to desired shape  Ivory was not available readily and was relatively expensive.  Denture bases fashioned from ivory were relatively stable in the oral environment  They offered esthetic and hygienic advantage in comparison with denture bases carved from wood or bone. Carved ivory upper denture retained in the mouth by springs with natural human teeth cut off at the Neck and riveted at the base.
  13. 13.  Since ancient times the most common material for false teeth were animal bone or ivory,especially from elephants or hippopotomus.  Human teeth were also used,pulled from the deceased or sold by poor people from their own mouths.  Waterloo dentures  1788 A.D. Improvement and development of porcelain dentures by DeChemant. G.Fonzi an italian dentist in Paris invented the Porcelain teeth that revolutionized the construction Of dentures.Picture shows partial denture of about 1830,porcelain teeth of fonzi’s design have been Soldered to a gold backing.
  14. 14. CERAMICS  Porcelain denture bases were relatively expensive  During subsequent years secrets of porcelain denture became known and it became common and inexpensive.  ADVANTAGES over wood, bone , ivory were -Could be shaped using additive technique rather than subtractive (carving). -Additive technique facilitated correction of denture base surface. -this permitted more intimate contact with underlying soft tissues. -Could be tinted to simulate the colors of teeth and oral soft tissues. -stable in oral environment. -Minimal water sorption, porosity, and solubility. -Smooth surface provided hygienic properties.  Among the drawbacks BRITTLENESS was most significant, fractures were common, often irreparable.
  15. 15. One piece porcelain upper denture crafted by Dr John Scarborough,Lambertville,New Jersey 1868.
  16. 16.  In 1794 John Greenwood began to swage gold bases for dentures. Made George Washington's dentures. George washington’s last dental prosthesis. The palate was swaged from a sheet of gold and ivory teeth riveted To it.The lower denture consists of a single carved block of ivory. The two dentures were held togther by steel Springs.
  17. 17.  In 1839 an important development took place CHARLES GOODYEAR discovered VULCANIZATION of natural rubber with sulphur(30%) and was patented by Hancock in england in 1843.  NELSON GOODYEAR (brother of charles goodyear) got the patent for vulcanite dentures in 1864.  . They proceeded to license dentists who used their material, and charged a royalty for all dentures made. Dentists who would not comply were sued.  The Goodyear patents expired in 1881, and the company did not again seek to license dentists or dental products.  Vulcanite dentures were very popular until the 1940s, when acrylic denture bases replaced them.
  18. 18. A set of vulcanite dentures worn by Gen. John J. (Blackjack) Pershing, commander of the American Expeditionary Forces in France during the First World War Set of complete dentures having palate of swaged Gold and porcelain teeth set in vulcanite.
  19. 19.  In 1868 John Hyatt, A US Printer, discovered the first plastic molding compound, called celluloid. He made it by dissolving nitrocellulose under pressure  In 1909, another promising organic compound was found. This was phenol formaldehyde resin discovered by Dr. Leo Backeland . Celluloid upper denture 1880,celluloid as a Substitute for vulcanite was unsuccessful as It absorbs stains and odors in the mouth, Gradually turns black and was flammable.
  20. 20.  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. Dentures made of polymethyl methacrylate
  21. 21. Disadvantages of different denture base 1. Vulcanite : In 1839 Vulcanized rubber was discovered and introduced as a Vulcanite and Ebonite. For the next 75 years Vulcanite rubber was the principal Denture base Material. But failed because of following reasons : Disadvantages It absorbs Saliva and becomes unhygienic due to bacterial proliferation. Esthetics were poor. Dimensionally unstable. Objectionable taste and odor
  22. 22. 2. Celluloid Although it was having tissue like color but having principal disadvantages like Disadvantages  Lack of stability  Unpleasant taste  Unpleasant odor  Stainability  Flammable
  23. 23. 3. Bakelite It was formed by heating and compressing a mixture of phenol and formaldehyde. Disadvantages  Lack of uniform quality  Variable strength  Variable color  Dimensional unstability.
  24. 24. POLYMERS Chronology of events  Charles Goodyear discovery of vulcanized rubber in 1839.  John hyatt discovered celluloid in 1868  Dr Leo Bakeland discovered phenol-formaldehyde resin (Bakelite).  In the 1930’s Dr Walter Wright and the Vernon brothers working at the Rohn and Haas company in Philadelphia developed Polymethylmethacrylate (PMMA), a hard plastic.  Although other materials were used for dental prosthesis, none could come close to PMMA and by the 1940;s 95% of all dentures were made from this acrylic polymer.
  25. 25.  Natural polymers include:  Proteins (polyamides or polypeptides) containing the chemical group (-Co-NH-); this is known as an amide or peptide link.  Polyesoprenes such as rubber and gutta percha.  Polysaccharides, such as starch, cellulose, agar and alginates.  Polynucleic acids, such as deoxyribonuclei acids (DNA) and ribonucleic acids (RNA).  Synthetic polymers are produced industrially or in the laboratory, by chemical reaction. Synthetic polymer : Defined as a non metallic compound synthetically produced (usually from organic compounds) which can be molded into various useful forms and then hardened for use.
  26. 26. DEFINITION: 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-7th edition). USES IN DENTISTRY  Denture bases and artificial teeth.  Denture liners and tissue conditioners.  composite restorative and pit and fissure sealent.  Impression materials  Custoum trays for impression  Temporary restoratives.  Mouthguards.  Maxillofacial prosthesis.  Space maintainers.  Veneers.  Cements and adhesives.
  27. 27. CHEMISTRY OF POLYMERIZATION  Monomers react to form polymer by a chemical reaction called polymerization.  The most common polymerization reaction for polymers used in dentistry is addition polymerization. ADDITION POLYMERIZATION  INDUCTION  PROPOGATION  CHAIN TRANSFER  TERMINATION INDUCTION 1)ACTIVATION 2)INITIATION
  28. 28. ACTIVATION Free radicals can be generated by activation of radical producing molecule using.  Second chemical  Heat  Visible light  Ultraviolet light  Energy transfer from another compound that acts as a free radical.
  29. 29.  Commonly employed initiator is Benzoyl peroxide which is activated rapidly between 50 degree and 100 degree C to release two free radicals per benzoyl peroxide molecule.  Second type is chemically activated ,consists of two reactants when mixed undergo reaction eg tertiary amine (the activator) and benzoyl peroxide (the initiator). Amine forms a complex with benzoyl peroxide which reduces the thermal energy (and thus the temperature) needed to split it into free radicals.  Third type is light activated .The visible light light cured dental restoratives,camphorquinone and an organic amine (dimethylaminoethylmethacrylate) generate free radicals when irradiated by light in the blue to violet region.  Light with a wavelength of about 470nm is needed to trigger this reaction.
  30. 30. INITIATION
  31. 31. The resulting free radical monomer complex acts as a new free radical center which is approached by another monomer to form a dimer, which also becomes a free radical. PROPOGATION
  32. 32. CHAIN TRANSFER  The active free radical of a growing chain is transferred to another molecule (eg monomer or inactivated polymer chain) and a new free radical for further growth is created termination occurs in the latter.
  33. 33. TERMINATION  Can occur from chain transfer.  Addition polymerization reaction is terminated by -Direct coupling of two free radical chains ends -Exchange of hydrogen atom from one growing chain to another.
  34. 34. INHIBITION OF ADDITION REACTION  Addition of small amount of Hydroquinone to the monomer inhibits spontaneous polymerization if no initiator is present and retards the polymerization in the presence of an initiator.  Amount added is 0.006% or less  Methyl ether of hydroquinone is generally present. COPOLYMERIZATION  When two or more chemically different monomers each with desirable properties can be combined to yield specific physical property of a polymer .eg small amount of ethyl acrylate may be co-polymerized with methyl methacrylate to alter the flexibility and fracture resistance of a denture.
  35. 35. METHYL METHACRYLATE  The acrylic resins are derivative of ethylene and contains a vinyl group (-c=c-)  Polyacids tends to imbibe water, due to polarity related to carboxyl group.  Water tends to separate the chain and cause softening and loss of strength.  Methyl methacrylate is a transparent liquid at room temp.  Physical properties -Molecular wt=100 -Melting point=-48 C -Boiling point=100 C -Density=0.945g/ml at 20 C -Heat of polymerization=12.9 Kcal/mol Methyl methacrylate molecule
  36. 36. POLYMETHYL METHACRYLATE  Transparent resin, transmits light in uv range to a wavelength of 250 nm. it has got remarkable clarity.  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)  It is chemically stable and softens at 1250 C  It can be molded as a thermoplastic material between 125 and 200 C  Depolarization takes place at approx 450 C .  Absorbs water by imbibition  Non crystalline structure possess high internal energy.  Polar carboxyl group can form hydrogen bridge to a limited extent with water.
  37. 37. REQUISITES FOR DENTAL RESINS (I)BIOLOGICAL COMPATIBILITY  Tasteless  Odorless  Nontoxic, non-irritating  Insoluble in saliva or any other fluids taken into the mouth.  Impermeable to oral fluids. MONOMER TOXICITY A review of clinical studies and patients reports on reaction to acrylic resin dental prosthesis by William M. Goebel in Feb 1980 have shown the following facts  Fischer patch tested groups of patients with heat cured and autopolymerizing acrylic resin disks, monomer, powdered polymer, and patients own acrylic resin prosthesis. From the results he concluded that methyl methacrylate monomer is a sensitizer which can cause an allergic contact eczematous reaction on skin and oral mucoa He also concluded when completely polymerized it is no longer a sensitizer
  38. 38. Or elicitor of allergic reaction.  Crissey also concluded that stomatitis venenata is a possible but uncommon result of monomer allergy.  Danielewicz- A. stysiak found similar results leading to conclusion that denture sore mouth caused by hypersensitivity is possible but rare.  Axelsson and Nyquist performed a longitudinal study to determine the biological effect of the leaching of monomer on the oral mucosa. Deliberately under cured dentures were followed for up to 3 years . Clinical examination revealed what was determined to be hyperkeratosis during the first week with no signs of inflammation,it resolved by end of one month Investigations concluded that results did not substantiate the opinion that residual monomer plays an essential role in denture sore mouth.  Spealman and associates performed cutaneous sensitization tests for monomer on 50 medical students, one third developed mild erythema at the site of contact due to local irritation, when tested 10 days later evidence of allergic sensitivity was obtained in 20% of the subjects. This demonstrated that monomer can be both a local irritant and an allergic sensitizer.
  39. 39.  There are well documented reports of both hyper sensitivity reaction and local irritation caused by methyl methacrylate monomer .Autopolymerizing acrylic resin contains a higher concentration of residual monomer and could cause chemical injury , sensitization or allergic reaction in a previously sensitized individual.  A Harrison and R Huggett in 1992 did a study to find out the effect of the curing cycle on residual monomer levels of acrylic resin denture base polymers. Levels of residual monomer were determined on a homopolymer and co-polymer using Gas-liquid chromatography. A wide range of recommended and short cut curing cycles were investigated which produced values ranging from 0.56 to 18.46%.From the ranges examined an optimum cycle of 7hr at 70 C and 1 hr at 100 C was established which was used to polymerize 23 available synthetic denture base polymers and only small difference were found with the material tested with a range of 0.54 to 1.08% of residual monomer.
  40. 40. CURING CYLES EMPLOYED IN THE STUDY A Recommended curing cycles overnight water-bath cures: 1) 7hr at 70 C 2) 14hr at 70 C 3) 7hr at 70 C +1hr at 100C 4) 14hr at 70C + 1hr at 100C Short and reverse cures: 5) Boil water,insert flask , remove heat for 20 min return to boil for 10 min. 6) Boil water ,insert flask ,return to boil, boil for 10 min. Dry heat cure: 7)temp in excess of 100C using dry heat system B Short curing cycles 8) 7hr at 60C 9) 7hr at 60C +1 hr at 90C 10) Boil water, insert flask remove heat for 20 min return to 90 C hold at 90C for 5 min 11) Boil water insert flask return to 90C hold at 90C for 5min.
  41. 41. RESIDUAL MONOMER CONTENT OF TREVALON POLYMERIZED BY 11 DIFFERENT CYCLES CURING CYCLE RESIDUAL MONOMER(%) I 2.91 2 2.14 3 0.79 4 0.82 5 1.32 6 3.97 7 0.91 8 15.65 9 1.39 10 2.01 11 17.72
  42. 42. CONCLUSION 1 A curing cycle of 7hr at 70C followed by a terminal boil at 1hr at 100C is the optimum curing cycle resulting in max monomer conversion. 2 Short cut curing cycles are undesirable and result in significantly raised levels of residual monomer. 3 The residual monomer levels of 23 available denture base polymers cured using the optimum cycle ranged from 0.54 to 1.08%.
  43. 43. (II)PHYSICAL PROPERTIES  Should possess adequate strength and resiliency and resistance to biting and chewing forces impact forces and excessive wear in oral cavity.  Should be dimensionally stable under all conditions of service including thermal changes and variations in loading. I) Specific gravity: It should have low value of specific gravity in order that dentures should be as light as possible. II) Thermal conductivity: It is defined as the number of calories per second flowing through an area of 1cm2 in which the temperature drop along the length of the specimen is 1°C/cm.  It should have high value of thermal conductivity  Radiopacity: It is the inhibition of passage of radiant energy.  It should be ideally radiopaque
  44. 44.  Glass transition temperature:  It is the temperature at which molecular motions become such that whole chains are able to move. It is close to softening temperature. At this temperature sudden change in elastic modulus occurs.  Amorphous polymer below Tg behave as rigid solids while above Tg they behave as viscous liquids, flexible solids or rubbers.  Increased chain branching  Decreased Tg. Increased number of cross links  Increased Tg Effect of molecular weight on properties In many polymers the chains are held together by secondary, or Vander Waals forces and molecular entanglement. Materials of high molecular weight have a greater degree of molecular entanglement, and have greater rigidity and strength and higher values of Tg and melting temperature than low molecular weight polymers.
  45. 45. Effect of plasticizers  Plasticizers penetrate between the randomly oriented chains of polymer as a result of which molecules are further apart and forces between them are less. They soften the material and make it more flexible by lowering its Tg. They lubricate the movements of polymer chains and are sometimes added to help molding characteristics. This principle is used in producing acrylic soft lining materials.  Effect of fillers  Modulus of elasticity and strength are generally increased.  A degree of anisotrophy exist, that is the strength depends on the orientation of fibres in the polymers.  Viscoelasticity : Polymers show viscoelastic behaviour. Elastic behaviour is caused by uncoiling of polymer molecules. Plastic behaviour is caused by breaking of intermolecular Vander Waals forces
  46. 46. (III) MANIPULATION  Should not produce toxic fumes or dust  Easy to mix, insert, shape and cure and short setting time  Oxygen inhibition, saliva and blood contamination should have little or no effect.  Final product should be easy to polish and easy to repair in case of breakage. (IV) AESTHETIC PROPERTIES  Should be translucent to match oral tissues  Capable of pigmentation  No change in color after fabrication. (v)ECONOMIC CONSIDERATION  Cost should be low  Processing should not require complex and expensive instruments.
  47. 47. (VI) CHEMICAL STABILITY  Conditions in mouth are demanding and only the most chemically stable and inert materials can withstand such conditions without deterioration. “No resin has yet met all of these ideal criteria”. Methacrylate polymers fulfill the aforementioned requirement reasonably well.
  48. 48. TYPES OF DENTURE BASE POLYMERS 1)CONVENTIONAL HEAT CURED POLYMETHYL METHACRYLATE  Supplied as powder and liquid POWDER  Polymer of PMMA in the form of spheres or beads.  Benzoyl peroxide is attached to it (initiator) 0.5%  Plasticizer is incorporated (methacrylate or acrylate monomer).  Coloring pigments cadmium/ organic dyes/ iron are added for esthetics.
  50. 50. LIQUID  Methyl methacrylate monomer  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.  When MMA polymerizes it shrinks 21% by volume.  Using a 3:1 powder liquid ratio it could be minimized to 6%.  A correctly heat processed denture base could have as little as 0.3% to 2% residual monomer.
  51. 51.  As a rule,heat activated denture base are shaped via compression molding technique. Polymer monomer interaction When polymer and monomer are mixed it passes through following stages  Sandy  Stringy  Dough like  Rubbery or elastic  Stiff Dough forming time  According to ANSI/ADA specification no 12 for denture base resins requires that this consistency be reached in less than 40 min from start of mixing time.  In clinical use it is achieved in less than 10 min. Working time  Time that a denture base remains in a dough like stage.ANSI/ADA specification no 12 requires the dough to remain moldable for 5 min.
  52. 52. 2)AUTOPOLYMERIZING/COLD CURE POLYMETHYL METHACRYLATE (POUR RESIN)  Composition same as the heat cure version with following differences 1)The powder contains beads of polymer that have a lower molecular wt. and benzoyl proxide (initiator) 2) The liquid contains a chemical activator ,tertiary amine such as dimethyl-para-toluidine.  Upon mixing tertiary amine causes decomposition of benzoyl peroxide.  Dentures processed have more residual monomer (1-4%),but lower dimensional change.  Decreased transverse strength (residual monomer act as plastisizer).  Compromised biocompatibility (residual monomer)  Color stability inferior (teriaty amine susceptible to oxidation), stabilizing agents should be added
  53. 53.  Fluid resin and compression molding technique can be employed for the fabrication of denture.  Also used as repair material
  54. 54. 3)HIGH IMPACT RESISTANT ACRYLIC  Similar to heat cured material but less likely to be broken if dropped.  Produced by substituting the PMMA in the powder with a copolymer.  Copolymer of butadiene with styrene or methyl methacrylate are incorporated into the beads.  Phase inversion resulting in dispersion throughout the beads of tiny islands of rubber containing small inclusions of rubber/PMMA graft polymer. Electron micrograph of high impact denture Base showing size and shape of polystyrene-butadiene Rubber inversion phase.
  55. 55. 4) Injection molded polymers  These are made of Nylon or Polycarbonate.  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
  56. 56. 5) RAPID HEAT POLYMERIZED POLYMER  Same as conventional material except that they contain altered initiation system.  These initiator allow them to be processed in boiling water for 20 min.  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.
  57. 57. 6) MICROWAVE POLYMERIZED POLYMERS  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 properties and the accuracy of these materials have been shown to be as good or better than those of the conventional heat cured material.  Processing time is much shorter (4-5 min). Microwave resin and non metallic microwave flask
  58. 58. 7)Light activated denture base resins  This material is a composite having a matrix of urethane dimethacrylate, microfine silica and high molecular wt acrylic resin monomers  Acrylic resin beads are included as organic fillers.  Visible light is the activator, whereas camphorquinone serves as the initiator for polymerization.  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. Light curing unit for polymerizing Dimethacrylate
  59. 59. 8) FIBER –REINFORCED POLYMER  Glass, carbon/graphite, aramid and ultrahigh molecular wt 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.
  60. 60. REVIEW OF LITERATURE  F.A. Peyton and D.H. Anthony(1963) evaluated and compared denture bases of different types of materials as well as techniques of processing. Materials selected were: • 4 different self – cure type • 7 heat cure acrylic resins • 3 special injection products • 2 chromium cobalt alloys • 1 epoxy type of denture plastic • 1 vulcanite denture material • 1 all porcelain denture base -for purpose of comparison.  . In this study comparisons of only three principal types of materials were presented with results reported being primarily to maxillary dentures. After the dentures were deflasked they were stored in water for 24hours at room temperature before the measurements were recorded, to simulate interval of time before delivery to the patient. The dentures were evaluated for changes in contour and fit due to the effect of aging, influence of repair, the effect of fracture along midline, effect on contour after repairs and effect on contour due to processing
  61. 61.  Based on the observations they concluded that:- - The most accurate dentures were of self- cure type, followed by the heat- cure and then the injection molded group. - The contours of heat cured and self- cured dentures after 20 months of water storage as compared with 24 hours and 8 months of water storage showed few changes in contour. - The heat cure dentures exhibited considerable change in contour after repair by heat – curing method, but few changes with self- curing repair. Self – cure dentures showed no changes during repairs by either method.
  62. 62.  M. Braden (1964) described the absorption of water by acrylic resins and other materials. He enumerated the kinetics of water absorption to follow the mathematical laws of diffusion. The effect of material thickness and temperature of water, influencing the water absorption were studied. Based on the observations they concluded that:- - 1.The temperature had a marked effect on the diffusion coefficient (i.e. it increased by factor of two to three) in temperature range of 22.5ºC to 37.4ºC, but had no effect on equilibrium water content. 2.The time required to saturate or dry- out an appliance depended markedly on temperature. 3.The water absorption and desorption processes were shown to obey the mathematical laws of diffusion. The time for accompanying dimensional changes could be predicted.
  63. 63. J.M Berrong, R.M Weed, J.M. Young (1990)  Studied the reinforcing effect of Kevlar (synthetic aramid) fibers incorporated in processed poly(methyl methacrylate) resin samples using 0%(control), 1%, and 2% by weight of the added fibers. The samples were subjected to impact testing to determine the fracture resistance, and sample groups were statistically compared using ANOVA (analysis of variance)and Duncan’s multiple comparisons. Impact strength of each reinforced sample was significantly greater than the control (3.0 kg/cm) and 2% by weight (6.3 kg/cm) showed the highest resistance to fracture. However the Kevlar fibers had the following disadvantages 1.Yellowish color limits its use in esthetic regions 2. Difficulty to incorporate the fibers in middle of resin and its subsequent exposure limited its polishability in that region. 3. An advantage was that Kevlar fiber reinforced resin when fractured, the fracture ends were united which facilitated easy repair.
  64. 64. John E.Ward et al in 1992 studied the effect of repair surface design ,repair material and processing method on the transverse strength of repaired acrylic resin.  Transverse strength (three point bend test) of heat cured acrylic resin( lucitone) was tested after being repaired by 1.Autopolymerizing monomer and polymer 2.Autopolymerizing monomer and heat cured polymer  Three repair joints were studied 1 Butt 2 Round 3 45 Degree bevel  Three processing method were used 1 Bench cure 2 Hydroflask with hot water for 10 min 3 Hydroflask with hot water for 30 min
  65. 65.  The strength of the repairs made with round and 45-degree bevel joint design were similar and significantly greater than those with a butt joint design.  the strength of the repairs processed in a hydroflask for 10 min and 30 min were similar and significantly greater than those cured on bench top.  There was no difference in the strength of repairs made with autopolymerizing monomer and heat-cured polymer. Andreas G and G L. Polyzois in 1994 Compared the repair strength of a heat cured and a visible light cure denture resin with an autopolymerizing (control) and four VLC resins used as repair material.  Flexural properties were measured and revealed that the highest strength and toughness of joint are obtained by autopolymerizing repair material.  VLC material exhibited lower repair strength.and toughness.  No interaction between base and repair material was detected which was attributed to poor adhesive bonding created at the interface.
  66. 66. K.Vallitu in 1997 Did a study to analyze the preliminary results from a clinical study of electrical glass (E-glass), partial fiber reinforcement ( PFR) of acrylic resin removable denture base.  E- glass fiber reinforcement was evaluated for 13 months after insertion of the fiber  12-CD, 10-RPD, with a history of recurrent fractures were selected.  The PFR was incorporated at the time of repair..  One CD and and one RPD fractured in the region of reinforcement during examination period.  Fractures were most likely caused by faulty placement of fiber reinforcement.  In six dentures new fracture occurred in region without PFR.  Result revealed the importance of correct positioning of the partial fiber reinforcement and use of accurate lab technique.
  67. 67. A study was done in our college Under The Able Guidance of Dr N.P.PATIL to see the” effect of fiber reinforcement on the dimensional changes of polymethyl methacrylate resin after processing and after immersion in water”.  Study was carried out to evaluate the effect of fiber reinforcement on the dimensional changes of heat cure poly(methyl methacrylate) resins and to compare the dimensional changes occurring in three types of heat cure poly (methyl methacrylate) resins after processing and after immersion on water  Thirty temporary denture bases of uniform thickness and peripheral extensions in respective areas were fabricated on identical maxillary edentulous cast for each of the three group.  Denture bases of all three groups showed contraction in the intercanine, intermolar, and canine to molar distances on right and left side after processing.  The dimensional changes observed in the three groups after processing are in the following decreasing order- Fiber glass reinforced heat cure PMMA, High impact heat cure PMMA, Non reinforced heat cure PMMA.
  68. 68.  The amount of space observed between the tissues was also in the above order.  The denture bases after immersion in water(17 days) of all the three groups showed expansion this comensated partly for processing shrinkage.  Fiber glass reinforcement can be used clinically since the magnitude of change was less than one % which seems to have little clinical significance.
  69. 69. A STUDY WAS DONE IN OUR COLLEGE UNDER THE ABLE GUIDANCE OF Dr N.P.PATIL TO SEE “ TRANSVERSE AND IMPACT STRENGTH OF A NEW INDIGENOUS HIGH- IMPACT DENTURE BASE RESIN DPI- TUFF AND ITS COMPARISON WITH MOST COMMONLY USED TWO DENTURE BASE RESINS”  Three heat cure denture base resins were compared;Three heat cure denture base resins were compared; 1.1. DPI – TUFFDPI – TUFF 2.2. Lucitone 199Lucitone 199 3.3. Conventional heat cure denture base resinConventional heat cure denture base resin  Total of 120 samples were prepared using short and long curing cyclesTotal of 120 samples were prepared using short and long curing cycles -- 73ºC and held for 90 minutes followed by boiling at 100 ºC for 30 minutes - In the long curing cycle the temperature was slowly raised from room temperature to 73ºC and held for 9 hours  They were furher divided into samples tested under dry and wet conditions.
  70. 70. Conclusion drawn were  The DPI- TUFF high impact denture base resin appears to be comparatively superior to the other two resins compared with mean transverse strength.  The dry strength of the samples of the materials tested show that it is greater than after immersion of the samples in water at 37ºC for 1 week.  The long curing cycle shows considerably higher values of transverse and impact strength as compared to short curing cycle.
  71. 71. Clinical Implications  In the study it was observed that the dry strength of samples was higher than that of the samples tested after immersion in water. This could probably reduce the chances of fracture during accidental dropping of the denture while polishing and before insertion of denture.  The denture may be more prone to fracture after use in mouth for considerable period of flexing or accidentally dropped during or after its removal from the mouth.  Lastly, although the use of long polymerizing cycle is time consuming, it results in dentures with more fracture resistance as compared with the use of short polymerizing cycle.
  72. 72. RECENT ADVANCEMENT  Modifications of acrylic resin materials designed to improve specific properties included. 1 plasticization, 2 copolymerization, 3.cross linking and reinforcement.  Internal plasticization by co-polymerization may improve strength properties.  Cross-linking is a special case of co-polymerization. In general cross-linking lowers strength and flexibility but increases solvent resistance, softening point and hardness
  73. 73.  One disadvantage of cross-linking is the reduction of bonding between acrylic resin teeth and the base which may occur particularly with a cold curing base material  Reinforcement by glass fibers is easily accomplished. This is done by mixing discrete fibers with dough or by combination with glass cloth.  Specially primed glass is necessary to bring out good adhesion to the resin and to maintain it particularly in wet conditions.  In the dough fiber method, the percentage of glass which can be incorporated is limited to about 20% by weight because of reduction of flow of the dough.
  74. 74. Alternatives to methacrylate materials  Most alternatives to polymethacrylate are vinyl acrylic, polysterene, acrylic styrene, acrylonetrile copolymers . NEW PLASTIC MATERIAL  High impact methacrylates (IM): These are basically similar to standard methacrylate but have a higher impact and fatigue strength.  Epoxy resins (E): 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
  75. 75.  Nylon materials: They were found to be unsatisfactory for denture base because of high molding shrinkage which led to warpage, high water absorption and yellowing.   High impact polystyrene (IS): This is an elastomer graft copolymer with styrene. It is basically similar to polysterene and injection molded in a similar way.  High density polythene (DE): This is stiffer stronger variety of polyether.  Polypropylene (PP): this is a hydrocarbon polymer similar to polyethylene but stiffer and stronger.  Polyacetal (A): Also called polyformaldehyde. It has lower water absorption with good resilience and toughness, and resistance to fatigue
  76. 76.  Polycarbonate (PE): It is thermoplastic material with low water absorption and very high impact strength and toughness.  Chlorinated polyether: It has very low water absorption and low mold shrinkage with excellent resistance to staining and chemical agents  Eclipse prosthetic resin system is a new method of fabricating dentures from Dentsply International. It is being marketed as an indirect build-up method for fabricating dentures that is monomer-free and flask-free. Eclipse is a light-cured system that does not contain any ethyl-, methyl-, butyl-, or propyl-methacrylate monomers.  System uses three resins to form the denture: Baseplate Resin, Set-up Resin and Contour Resin. The resins were developed to handle like wax, yet be cured into a denture base material – without investing and flasking.
  77. 77.  VALPLAST - Valplast is a flexible denture base resin that is ideal for partial dentures and unilateral restorations.  The resin is a biocompatible nylon thermoplastic ,it eliminates the concern about acrylic allergies.
  78. 78. Conclusion
  79. 79. REFERENCES:  Kenneth j. Anusavice ; Phillips Science of dental material .Eleventh edition, Elsevier,2004.  Jack L. Ferracane ; Materials in Dentistry principles and application. Second edition ,Lippincot williams, 1995.  William J. O’Brien; Dental materials and their selection. Third edition, quintessence Publishing co. 2002.  Robert C. Craig John M. Powers, John C.Wataha ;Dental materials properties and manipulation,. Eight edition,2004.  Robert L.Engelmeier; The dental clinics of North America-complete dentures, W B Saunders company jan 1996 vol.40 no.1  J.W. Nicholson; The chemistry of medical and dental materials, First edition RS.C 2002.  Peyton F.A., Anthony D.H., 1963: “Evaluation of dentures processed by different techniques”. J. Prosthet Dent.; March – April 13(2): 269-282.  Braden M., 1964: “The absorption of water by acrylic resins and other materials”. J Prosthet Dent.; March/April 14(2): 307-316  Vallitu .P.K 1997 “Glass fiber reinforcement in repaired acrylic resin removable dentures: Priliminary result of a clinical study.” Quintessence Int;28:39-44.
  80. 80.  Patil N .P and Hedge VK 1996,”comparative evaluation of the effect of palatal vault configuration on dimensional changes in complete dentures during processing as well as after water immersion”.Dissertation submitted to Rajiv Gandhi univ of health sciences,karnataka.  John E .Ward et al; 1992; effect of repair surface design, repair material,and processing method on the transverse strength of repaired acrylic resin.  Andreas G.A and G.L.Polyzois,1994;”Repair of denture base resin using visible light cured materials”.J Prostho Dent; 72:462-8  Patil N P and Arundhati N Raj 2004 “ TRANSVERSE AND IMPACT STRENGTH OF A NEW INDIGENOUS HIGH- IMPACT DENTURE BASE RESIN DPI- TUFF AND ITS COMPARISON WITH MOST COMMONLY USED TWO DENTURE BASE RESINS” Dissertation submitted to Rajiv Gandhi univ of health sciences,Karnataka.  Melvin E Ring ; ,An illustrated history of dentistry.1985
  81. 81. THANK YOU