Denture base materials

The ppt contains resin based and metal based denture base materials.

1. DENTURE BASE MATERIALS Neeraja M Menon Dept. Of Prosthodontics Coorg Institute of Dental Sciences

2. CONTENTS Definition Ideal denture base Classification History Resin denture base materials Types of denture base polymers Metal denture base material Types of partial denture base Methods of attaching denture bases Methods of attaching artificial teeth Relining and rebasing Review of litrature

3. DEFINITION Denture base: the part of a denture that rests on the foundation tissues and to which teeth are attached - GPT9 Denture base material: any substance of which a denture base may be made - GPT 9

4. Ideal denture base: Accuracy to adaptation to the tissue with low volume change Dense, non-irritating surface capable of receiving and maintain good finish Thermal conductivity Low specific gravity Sufficient strength Self cleansing Aesthetic acceptability Potential for future relining Low cost

5. Classification Metallic denture base materials Cobalt-chromium Gold, Titanium Stainless steel, Aluminium Non-metallic denture base materials Acrylic resin Vinyl resin

6. Formerly used materials Materials used before 18 th century Wood Bone Ivory Materials used in 18 th century Gold Porcelain Materials used in the 19th century 1. Tortoise Shell (1850 ) 2 . Gutta Percha (1851 ) 3. Vulcanite (1851 ) 4. Cheoplastic (1856 ) 5. Rose Pearl (1860) 6 . Aluminum (1867) 7 . Celluloid (1870)

7. Materials used in the 20 th century 1. Bakelite (1909) 2 . Stainless steel (1921 ) 3 . Cobalt Chromium ( 1930) 4 . Vinyl Resin (1932 ) 5 . Acrylic Resin (1937) 6 . Self cure Acrylic Resin 7 . Epoxy Resin (1951) 8 . Polystyrene (1951 ) 9. Nylon (1955) 10 . Polycarbonates (1967 ) 11 . High impact acrylic (1967 ) 12 . Polysulphones (1981) 13 . Visible L.C (1947)Acrylic (1986) 14 . Pure Titanium (1998)

8. Resin denture base materials 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. Goodyear Hyatt Bakeland

9. Polymers 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-9).

10. USES IN DENTISTRY Denture bases and artificial teeth. Denture liners and tissue conditioners. Composite restorative and pit and fissure sealant . Impression materials Custom trays for impression Mouth guards. Maxillofacial prosthesis. Space maintainers. Veneers.

11. 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

12. INDUCTION 1)ACTIVATION 2)INITIATION 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.

13. Initiator Activator Heat activated Benzoyl peroxide Heat Chemical activated Benzoyl peroxide Tertiary amine Light activated Champhoroquinone Visible light

14. 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.

15. Initiation BPO MMA

16. Propogation 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.

17. 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.

18. 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

19. 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 added. 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.

20. TYPES OF DENTURE BASE POLYMERS

21. 1) CONVENTIONAL HEAT CURED POLYMETHYL METHACRYLATE Powder form PMMA and other co polymers - Principal Constituent Benzoyl peroxide 0.2-0.5 % - Initiator Compounds of mercuric sulphide , - Dyes cadmium sulphide etc 1% Zn or Ti oxide - Opacifier Dibutyl phthalate - Plastisizer Dyed organic filler and inorganic - For aesthetics particles like glass fibers or beads & enhance physical properties Composition

22. Commercial names Acron Stellon Trevelon Lucitone Mediodont

23. 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 Rubbery or elastic Stiff Dough forming time The time required for the resin mixture to reach a dough like stage. In clinical use, the majority of resin reach a dough like consistency 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.

24. 2) AUTOPOLYMERIZING/COLD CURE POLYMETHYL METHACRYLATE Composition Powder Poly (methyl methacrylate) and other co-polymer(5 %) - Dissolves the monomer to form dough Benzoyl Peroxide  - Initiator Compounds of Mercuric sulphide - Dyes cadmium sulfide , etc. Zinc or titanium oxide - Opacifiers Dibutyl phthalate - Plasticizer Dyes organic fillers and inorganic particles like - Esthetics and to enhance glass bead fibers or beads physical properties

25. Liquid Methyl methacrylate - Dissolves/Plasticizes the polymer polymerization Dimethyl-p-toluidine - Activator Dibutyl phthalate - Plasticizer Glycol Dimethacrylate 1 to 2% - Cross - Linking agent (reduces Crazing) Hydroquinone (0.006 %)   - Inhibitor, prevents premature polymerization

26. ` 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 Fluid resin and compression molding technique can be employed for the fabrication of denture. Also used as repair material

27. 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. Eg : Hi-Impact Pourable( Excel Formula ®), Trevalon Hi and Lucitone 199

28. 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

29. 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 . Eg : QC 20, Meliodent and Trevalon

30. 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 packed flask is placed inside a microwave oven and irradiated using the following cycle: 13 minutes on low power at 90 watts, 1.2 minutes on high power at 500 watts, and then bench cool for 30 minutes [16]. The advantages are that it greatly reduced curing time (3 min.), 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

31. 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. In the visible light-cured material, camphorquinone and an organic amine (e.g. dimethylaminoethyl methacrylate) generate free radicals when irradiated by light in the blue to violet region . Light with a wavelength of about 400-500nm is needed to trigger this reaction. Then the denture base is exposed to a high-intensity visible light source for an appropriate period . 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.

32. 8) FIBER –REINFORCED POLYMER Glass , carbon/graphite, aramid and ultrahigh molecular weight polyethylene have been used as fiber reinforcing agents . Carbon Fibers : The advantages are increase in transverse and impact strength of PMMA, increased fatigue resistance when treated with silane coupling agent Kevlar (Synthetic Aramid Fiber ): The advantages are increase in modulus of elasticity, increase in fracture resistance. The use of 2% by weight Kevlar reinforcement fibers increases the fracture resistance of acrylic resin. Its disadvantages are poor esthetics because of yellow color , difficulty in polishing . Eg : StickTM , Novodent , Alldent

33. Alternatives to methacrylate materials Most alternatives to polymethacrylate are vinyl acrylic, polysterene , acrylic styrene, acrylonetrile copolymers . NEW PLASTIC MATERIAL High impact methacrylates : These are basically similar to standard methacrylate but have a higher impact and fatigue strength. Epoxy resins : 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

34. 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 : This is an elastomer graft copolymer with styrene. It is basically similar to polysterene and injection molded in a similar way. High density polythene : This is stiffer, stronger variety of polyether. Polypropylene : this is a hydrocarbon polymer similar to polyethylene but stiffer and stronger. Polyacetal : Also called polyformaldehyde . It has lower water absorption with good resilience and toughness, and resistance to fatigue

35. Polycarbonate : 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 .

36. VALPLAST Valplast is a flexible denture base resin that is ideal for partial dentures and unilateral restorations. The material is a specialized form of nylon in the family of superpolymides (a very pure nylon) that will not deteriorate chemically when it comes into contact with the fluids, bacteria, and physical environment of the mouth. The resin is a biocompatible nylon thermoplastic, it eliminates the concern about acrylic allergies. Flexibility of the material allows it to engage the undercut beneath the bony exostoses , that is not possible in rigid partial dentutres .

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

38. Advantages of Metal Bases over Resin Bases: (1) Accuracy and permanence of form- Cast more accurately than denture resins and maintain their accuracy of form without change in mouth . Internal strains released later to cause distortion not present. Accuracy – metal base provides intimacy of contact, help in retention of denture prostheses. Such intimate contact not seen in acrylic resin bases.

39. (2) Comparative tissue response- Inherent cleanliness of cast metal base contributes to health of oral tissue. Bacteriostatic activity – ionization and oxidization of metal base. Metal base is naturally cleaner than an acrylic resin base .

40. (3) Thermal conductivity- Temperature changes transmitted though metal to the underlying help to maintain health of that tissue . Patient acceptance .

41. (4) Weight and bulk- Metal alloy may be cast 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.

42. Disadvantage Aesthetics Enhancement of retention not possible – lack of weight of metal base Relining difficult Restoration of normal facial contour can not be achieved

43. Different metallic denture base materials Cobalt-chromium alloys : As early as 1949 it was estimated that nearly 80% of all partial denture appliances were cast from Co- C r alloys . C omposition Principle elements (approx . 90 %): Cobalt 60% Chromium 25% to 30 %   Other components :Molybdenum silicone, Aluminium nitrogen, Berylium carbon & manganese

44. Nickel chromium alloys : Nickel 70 % Chromium 16% Chromium : Responsible for the tarnish resistance and stainless. When the chromium content of an alloy is more than 30% it is more difficult to cast ; and therefore dental alloys should not contain more than 28% or 29% chromium These alloys are considered to be technique sensitive.

45. Cobalt and nickel : Cobalt increases the elastic modulus, strength and hardness more than Nickel does CARBON : Increase in carbon content increases hardness of Co-based alloys. If the carbon content is increased by 0.2% more than the desired amount –results in a too hard and too brittle alloy not suitable for dental appliances. Whereas a decrease of 0.2% will decrease the tensile and the yield strength.

46. MOLYBDENUM : (3 % to 6% ) Contributes to the strength of the alloy. Initially tungsten was used , but it reduced the elongation , was therefore replaced by other hardening elements like molybdenum ALUMINIUM Forms a compound with Ni and Al (Ni3Al) which increases the tensile and the yield strength of the alloys.

47. BERYLIUM : About 1% lowers the fusion temperature range of the alloy by about 100 degrees C . SILICONE AND MANGANESE : Increase the fluidity and castability of these alloys. NITROGEN : If present contributes to the brittle qualities of these alloys

48. T itanium Ti was developed by William Gregor of England in 1791,and was named by Martin H. Kalproth of Germany in 1795 . Welhelm Kroll1930 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

49. Types of partial denture base Tooth Supported Partial Denture Base Distal Extension Partial Denture Base

50. Tooth supported partial denture base In tooth supported prostheses denture base is primarily a span between 2 abutments supporting artificial teeth. Occlusal forces transferred to abutments via rests. It prevent horizontal migration of all abutment teeth in partially edentulous arch and vertical migration of teeth in opposing arch.

51. Distal extension partial denture base It is close to the terminal abutment, only a framework supporting occlusal surface is necessary. Support from the underlying ridge tissues is very important. Maximum support is obtained by using broad accurate denture bases, which transmit the occlusal load equally over the entire area Support should be of primary important in selecting designing & fabricating distal extension partial denture base.

52. Methods of Attaching Denture Bases : Resin bases are attached to the partial denture framework by means of a minor connector designed so that a space exists between it and underlying tissues of the residual ridge. Relief at least a 20 gauge thickness over basal seat areas of master cast is used to create raised platform on the investment cast. Thus after casting the portion of retentive framework to which the resin base will be attached will stand away from the tissue surface sufficiently to permit a flow of resin base material beneath the surface. The retentive framework for the base should be embedded in the base material with sufficient thickness of resin. (1-5mm).

53. Thickness of the resin is essential during the denture adjustments or during relining procedures also to avoid weakness and subsequent fracture of resin base materials. Metal bases –cast as integral parts of partial denture framework . May also be assembled and attached to framework with acrylic resin.

54. Methods of Attaching Artificial Teeth : Artificial teeth may be attached denture bases With acrylic resin. Cemented. Processed directly to metal. Cast with framework

55. 1. Porcelain or resin artificial teeth attached with resin . Porcelain teeth are mechanically retained. Posterior teeth are attached retained by acrylic resin in their diatonic holes. Anterior porcelain teeth are retained by acrylic resin surrounding the lingually placed retention pins. Resin teeth are retained by chemical union of the acrylic resin of denture base. Attachment of resin to the metal base may be accomplished by nail head retention, retention loop, or diagonal spurs placed at random. Any junction of resin with metal should be at an undercut finishing line or associated with some retentive undercut.

56. Plastic mesh work Open lattice Beads Nail heads

57. 2.Porcelain or resin tube teeth and facings cemented directly to metal bases : Some disadvantages of this type of attachment are the difficulties in obtaining satisfactory occlusion, lack of adequate contours for functional tongue and cheek contact and unaesthetic display of metal at gingival margins. This can be avoided when the tooth is butted directly to the ridge and by selecting tube teeth for width but with occlusal surfaces slightly higher than required. Recent advance include an attachment of readymade resin teeth to the metal base with acrylic resin of same shade. This is called pressing on a resin tooth. It is particularly applicable to anterior replacements. After a labial index of the position of the teeth is made. The lingual portion of the tooth may be cut away or a posthole is prepared in the tooth for retention on the casting. Subsequently the tooth is attached to the denture with acrylic resin of the same shade. Since this is done under pressure, the acrylic attachment provides hardness and strength.

58. 3 . Resin teeth processed directly to metal bases : Modern cross linked copolymer enable the dentist to process a crylic resin teeth that have satisfactory hardness and abrasion resistance for many situation. Occlusion may be created without restoring to the modification of readymade artificial teeth. Recesses in the denture pattern are either carved by hand or may be created around manufactured teeth that are only used to form recess in the pattern. Occlusal relationship may be established on mouth and then to the articulator and then the teeth are carved and processed in acrylic resin of proper shade.

59. 4. Metal teeth Occasionally a second molar tooth may be repaired as part of partial denture casting. This is usually done when space is too limited for the attachment of an artificial tooth and yet the addition of second molar is desirable to prevent migration of an opposing second molar . Before casting occlusal surface should be waxed properly and the area of occlusal contact should be held minimum the avoid damage to the periodontium of opposing tooth and the associated discomfort to the patient. They should be used only to fill a space and to prevent tooth migration and no more as they are difficult to adjust and objectionally hard for use as occlusal surface.

60. 5. Chemical bond : Direct chemical bonding of acrylic resin metal framework Sections of metal framework that are to support replacement teeth can be roughened with abrasives, then treated with vaporized silica coating. Upon this surface a resin-bonding agent is applied, followed by thin film of resin to act as a substrate for latter attachment of replacement resin or for processing of acrylic resin tissue replacement.

61. RELINING RESIN DENTURE BASES Involves replacement of the tissue surface of an existing denture Indication Whenever the denture loses or has poor adaptation to the underlying tissues, while all other factors as occlusion; aesthetics; centric relation; vertical dimension at rest and denture base material are satisfactory: – Loss of retention. – Instability. – Food under denture. – Abused mucosa

62. Heat cured relining The fitting surface is cleaned . The undercuts are removed and the flanges are shortened . Minor defects and extensions can be corrected with self cured acrylic. A wash impression is then taken on the fitting surface of the denture with impression paste, with the patient in light occlusal contact . Later the impression paste is replaced with heat cured acrylic which is more durable than the materials used for direct relines.

63. Chemically cured relining Cold cured acrylic or tissue conditioner are used The flanges are trimmed (to reduce danger of over extension) and the undercuts removed . The new relining is then mixed and applied to the fitting surface . The denture is inserted and the patient asked to bite gently on the denture to ensure that the occlusion is not altered by the procedure . Border moulding can then be carried out . The denture is kept in situ for about 5 minutes after which it is removed and carefully examined

64. REBASING RESIN DENTURES It’s a process of readaptation of a denture to the underlining tissues by replacing the denture base material with a new one without changing its occlusal relation . Indications: When the existing denture base is unsatisfactory; crazed or porous.

65. An impression is made with the denture and a cast is obtained. An occlusal and incisal index of the teeth is made in plaster using HOOPER DUPLICATOR, the posts of the lower part of the duplicator are seated in the upper part to maintain the relationship of the casts to the plaster index. The denture with the impression material are removed from the cast . Artificial plastic teeth are sectioned from the denture and all base material around the teeth is removed  Teeth are placed and held in position in the index using sticky wax on the labial and buccal surface . A layer of base plate wax is placed over the ridge of the cast . The upper part of the duplicator is closed and denture teeth are waxed to the proper thickness and counter to the cast. The cast is removed; flasked and processed in the usual manner. After deflasking , the cast is reattached to the upper part of the duplicator to adjust any occlusal errors. Occlusion of rebased denture is further perfected by clinical remount.

66. Review Of Literature Repair strength of autopolymerizing , microwave, and conventional heat-polymerized acrylic resins Rached RN et al, J Prosthet Dent  2004 Aim: This study evaluated the transverse repair strength of a conventional heat-polymerized ( Lucitone 199, ‘‘L’’) and a microwave-polymerized ( Acron MC, ‘‘A’’) acrylic resin that were repaired with these same resins and with an autopolymerizing acrylic resin ( Acron MC/R, ‘‘AR’’).

67. Twenty-four rectangular specimens (65.0 3 10.0 3 3.3 mm) of L or A and 6 of AR were manufactured and stored in distilled water at 37 degree C for 7 days. Eighteen specimens of L or A were selected randomly. Six specimens of each material remained intact (control), each 6 were sectioned in the middle to create a 10-mm gap and repaired with the materials L, A, or AR. After an additional 7 days of storage at 37 degree C , the transverse strength ( MPa ) of the repaired and intact specimens was measured using a 3-point bending test. Conclusion: The autopolymerizing resin exhibited a repair strength similar to those found for the conventional heat- and microwave-polymerized materials.

68. In vitro evaluation of the influence of repairing condition of denture base resin on the bonding of auto polymerizing resins Hiroyuki et al, J Prosthet Dent  2003 Aim: This study evaluated the influence of water absorbed in denture base resin on the bond strength and resistance to cyclic thermal stresses of autopolymerizing resins bonded to denture base resin

69. Denture base resin disks were fabricated from heat-polymerized acrylic resin ( Lucitone 199). The disks were divided into groups with 3 conditions of water content: (1) complete water saturation (control), (2) superficial desiccation by blowing air on the specimen , (3) complete desiccation . Each denture base specimen received 1 of 3 surface treatments including: (1) no treatment, (2) airborne-particle abrasion, or (3) methylene chloride application . An autopolymerizing repair resin (Repair Material) or reline resin ( Tokuso Rebase Normal set ,) was applied to the bonding area (5 mm diameter) and polymerized at 37°C for 10 minutes. The resistance to cyclic thermal stress was determined after subjecting the specimens to 50,000 thermal cycles between 4°C and 60°C water baths with a 1-minute dwell time. Bond strength ( MPa ) was measured by shear bond testing at a 1.0 mm/min crosshead speed until the applied resin debonded from denture base resin. Data were statistically analyzed by 3-way analysis of variance and multiple comparisons among the groups were performed with Bonferroni test (.05).

70. Result: Bond strengths of autopolymerizing resin to denture base resin were not significantly influenced by water content of denture base resin but were significantly influenced by resin type, thermal cycling, and surface treatment.

71. The effect of reinforcement with woven E-glass fibers on the impact strength of complete dentures fabricated with high-impact acrylic resin Sung-Hun Kim et al, J Prosthet Dent  2004 Aim: The purposes of this study were to measure the impact strength of maxillary complete dentures fabricated with high-impact acrylic resin and to evaluate the effect of woven E-glass fiber -reinforcement on the impact strength of the complete dentures.

72. Preimpregnated woven E-glass fibers (Stick Net) were used to reinforce 10 complete denture bases fabricated with a heat-polymerized high-impact acrylic resin ( Lucitone 199). Ten unreinforced complete dentures served as a control group . All specimens were stored in water at 378 degree C for 2 months before testing. The impact strengths (J) of the dentures were measured with a falling-weight impact test. The impact strengths of both groups were compared by a repeated measures analysis of variance (a=.05). The Weibull distribution was also applied to calculate the cumulative fracture probability as a function of impact strength.

73. Result: The impact strengths of maxillary complete dentures fabricated with high-impact acrylic resin increased by a factor greater than 2 when reinforced with woven E-glass fiber .

74. Studies on the effects of titanate and silane coupling agents on the performance of poly (methyl methacrylate)/barium titanate  denture base nanocomposites . Nidal W . et al, J Dent 2017 Aim: The study aimed to fabricate and characterise silanated and titanated nanobarium titanate (NBT) filled poly(methyl methacrylate) (PMMA) denture base composites and to evaluate the behaviour of a titanate coupling agent (TCA) as an alternative coupling agent to silane . The effect of filler surface modification on fracture toughness was also studied.

75. Silanated , titanated and pure NBT at 5% were incorporated in PMMA matrix. Neat PMMA matrix served as a control. NBT was sonicated in MMA prior to mixing with the PMMA. Curing was carried out using a water bath at 75°C for 1.5h and then at 100°C for 30min. NBT was characterised via Fourier transform-infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Brunauer -Emmett-Teller (BET) analysis before and after surface modification. The porosity and fracture toughness of the PMMA nanocomposites (n=6, for each formulation and test) were also evaluated.

76. Result: Formation of a monolayer on the surface of TCA enhanced the NBT dispersion, however agglomeration of silanated NBT was observed due to insufficient coverage of NBT surface. Such behaviour led to reducing the porosity level and improving fracture toughness of titanated NBT/PMMA composites. Thus, TCA seemed to be more effective than silane .

77. Effect of Nanodiamond Addition on Flexural Strength, Impact Strength, and Surface Roughness of PMMA Denture Base Al harbi et al, J Prosthet Dent 2018 Aim: To assess the effect of addition of different concentrations of nanodiamonds (NDs) on flexural strength, impact strength, and surface roughness of heat-polymerized acrylic resin .

78. 120 specimens were fabricated from heat-polymerized acrylic resin. They were divided into a control group of pure polymethylmethacrylate (PMMA; Major.Base.20) and three tested groups (PMMA-ND) with 0.5%wt, 1%wt, and 1.5%wt of added ND to PMMA. Flexural strength was determined using the three-point bending test. Impact strength was recorded by using a Charpy type impact test. Surface roughness test was performed using a Contour GT machine. One-way ANOVA and Tukey's post-hoc analysis (p ≤ 0.05) were used for statistical analysis.

79. Result: The addition of NDs to acrylic denture base improved the flexural strength and surface roughness at low concentrations (0.5%), while the impact strength was decreased with ND addition.

80. 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,. Eight edition,2004. Morrow R.M RUDD K.D :Dental Lab procedures CD Vol 3 edition Wang Russel .R : Titanium for complete application,Quintessence Int.1996,27:401application,Quintessence Int.1996,27:401  Winkler Sheldon : Esssentials Of Complete Denture Prosthodontics 3r edition 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

81. Rached , R. N., Powers, J. M., & Del Bel Cury , A. A. (2004). Repair strength of autopolymerizing , microwave, and conventional heat-polymerized acrylic resins. The Journal of Prosthetic Dentistry, 92(1), 79–82.  Minami, H., Suzuki, S., Minesaki , Y., Kurashige , H., & Tanaka, T. (2004). In vitro evaluation of the influence of repairing condition of denture base resin on the bonding of autopolymerizing resins. The Journal of Prosthetic Dentistry, 91(2), 164–170.  Kim, S.-H., & Watts, D. C. (2004). The effect of reinforcement with woven E-glass fibers on the impact strength of complete dentures fabricated with high-impact acrylic resin. The Journal of Prosthetic Dentistry, 91(3), 274–280. doi:10.1016/j.prosdent.2003.12.023 Al- Harbi , F. A., Abdel-Halim, M. S., Gad, M. M., Fouda , S. M., Baba, N. Z., AlRumaih , H. S., & Akhtar, S. (2018). Effect of Nanodiamond Addition on Flexural Strength, Impact Strength, and Surface Roughness of PMMA Denture Base. Journal of Prosthodontics. 

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