4Main chemical which will polymerize Hydroquinone (o.Oo3-o.1%) COMPOSITION OF MONOMERMethyl methacrylateMain chemical which will polymerizeHydroquinone (o.Oo3-o.1%)Inhibitor while storageDibutyl phthalatePlastisizerGlycol dimethacrylate (1-2%)Cross linking agentStyrene vinyl acetate or ethyl methacrylateAs copolymers
5PROPERTIES OF MONOMERTypical smell of its ownClear, transparent liquidBoiling point 100.3*cGood organic solventCan get evaporatedInflammableStored in dark colored bottleLight weightVolumetric shrinkage of 21%It is a known allergen
6LIQUIDMethyl methacrylate monomerCross 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.
7Composition of polymer Polymethyl methacrylatemain ingredientBenzoil peroxide%, initiatorDibutyl phthalate8-10%, plasticizerZinc or tetanium oxideopacifier
8Composition of polymer Mercuric sulfide or iron oxide or titanium oxide- pigments and dyesGlass fibres or beads or zirconium sulfate- to increase stiffnessNylon or acrylic fibres- in veined type- capillaries of gum
9Different types of polymer powder Normal pink-which resembles the normal pinkcolor of gumClear polymer- no coloring agents are added- indicated in palatal areaTranslucentVeined or deep veined
10Properties of polymer powder Stable at room temperature- has long shelf lifeSoftening temperature- 125 * c- 125*-200*cdepolymerization occurs- 450 *cconverted back to monomerAbsorbs water and soluble in chloroform
11Properties of polymer powder Tensile strength- 600 kg/sq cmAppearance- shiny- transparentProduced in two shapes- spherical- granular
12Properties of polymer powder Control of particle size- no.52 sieve mesh- 300 micrometerIf particle size is smaller- softening will be quicker- granular shape softens faster
13Manufacturing of polymer powder Spherical particlesBy suspension polymerization- monomer and water are mixed with an emulsifier i.e, powder talc.- then the mixture is heated and stirred- at the end talc is washed off toget polymerized polymer particlesGranular particles- solid block- then it is grinded or milled
14A Recommended curing cycles overnight water-bath cures: 1) 7hr at 70 C CURING CYLES EMPLOYEDA Recommended curing cyclesovernight water-bath cures:1) 7hr at 70 C2) 14hr at 70 C3) 7hr at 70 C +1hr at 100C4) 14hr at 70C + 1hr at 100CDry heat cure:5)temp in excess of 100C using dry heat system
15B Short curing cycles 6) 7hr at 60C 7) 7hr at 60C +1 hr at 90C
16(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.Specific gravity: It should have low value of specific gravity in order that dentures should be as light as possible.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 conductivityRadiopacity: It is the inhibition of passage of radiant energy.It should be ideally radiopaque
17Effect of molecular weight on properties 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 TgEffect of molecular weight on propertiesIn 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.
18Effect 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 fillersModulus of elasticity and strength are generally increased.A degree of anisotropy exist, that is the strength depends on the orientation of fibres in the polymers.Viscoelasticity : Polymers show viscoelastic behavior. Elastic behavior is caused by uncoiling of polymer molecules. Plastic behavior is caused by breaking of intermolecular Vander Waals forces
19(III) MANIPULATIONShould not produce toxic fumes or dustEasy to mix, insert, shape and cure and short setting timeOxygen 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 PROPERTIESShould be translucent to match oral tissuesCapable of pigmentationNo change in color after fabrication.(v)ECONOMIC CONSIDERATIONCost should be lowProcessing should not require complex and expensive instruments.
20(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.
212)AUTOPOLYMERIZING/COLD CURE POLYMETHYL METHACRYLATE (POUR RESIN) Composition same as the heat cure version with following differences1)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.
22Upon 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
23Fluid resin and compression molding technique can be employed for the fabrication of denture. Also used as repair material
243)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 dentureBase showing size and shape of polystyrene-butadieneRubber inversion phase.
254) 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 moldEquipment 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
265) 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.
276) 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
287)Light activated denture base resins This material is a composite having a matrix of urethane dimethacrylate, microfine silica and high molecular wt acrylic resin monomersAcrylic 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 polymerizingDimethacrylate
298) 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.
30Polymer – monomer interaction When mixed in proper proportions, the resultant mass passes through five distinct stages1.Sandy2. stringy3. Dough like4. rubbery5. StiffDuring sandy stage, little or no interaction occurs on a molecular level. Polymer beads remain unaltered.This stage is ideal for compression molding.Hence material is inserted into mold cavity during dough like stage.
312. Stringy stageLater, mixture enters stringy stage. Monomer attacks the surfaces of individual polymer beads.Stage charcterized by stringiness,…3. dough like stageThe mass enters a dough like stage.On molecular level increased number of polymer chains are formed. Clinically the mass becomes as a pliable dough. It is no longer tacky ( sticky)
324.Rubbery or elastic stage Following dough like stage, the mixture enters rubbery or elastic stage. Monomer is dissipated by evaporation and by further penetration into remaining polymer beads. In clinical use the mass rebounds when compressed or stretched5. Stiff StageUpon standing for an extended period, the mixture becomes stiff.This may be due to the evaporation of free monomer. From clinical point, the mixture appears very dry and resistant to mechanical deformation
41Checking the seating of flask members Invested flask & cast is washed in clear slurry waterSurface tension reducing agent is applied to the exposed waxSeparating medium is applied
42Second mix is mixedHand spatulationMechanical spatulation-Under reduced atmospheric pressure-Minimum air inclusion-Reduces finishing timeStone is coated in occlusal & inter-Proximal areas with stiff brush
43Stone is poured in flask Vibrator can be usedIn absence of vibratorFlask is filled till approximately ¼ of the flaskStone is removed in incisal & occlusal surfacesStone is allowed to set
44After the stone is set separating medium is coated Occlusal & incisal surfaces shouldn’t be coated with the separating mediumClear slurry is poured till the stone is mixedSlurry is poured off, flask is filled with the stone
48porosity Presence of voids within structure of resin Porosity can be of two typesInternalExternalInternal porosity is due to voids within the structure usually at thicker portionCause – due to vaporization of the monomer (100.8C)Solution- long low temperature curing cycle is recommended.
49External porosity is due porosities which occur near the surface of denture. CauseLack of homogeneity of dough.Lack of adequate pressure.Prevention – use proper monomer – powder ratio, packing in dough stage.
50Crazing Crazing is formation of surface cracks on denture base resin. Causes –Incorportion of stressAttack by solvent (alcohol)Incorporation of water during processing.PreventionAvoidance of solventProper use of separating mediaMetal mouldsUse of cross linked acrylic
52Denture warpage Denture warpage is change in shape or fit of denture. Cause is incorporation of stress in deturePacking in late dough or rubbery stage.Stress induced during curingImproper deflaskingRise in temp while polishingImmersion of processed denture in hot water.
54Denture fracture Improper deflasking Denture base excessively thin Accidental dropping at time of polishing
55Change in tooth position Care to taken at time of dewaxing procedureRearticulation to be done after processing the denture to check of occllusal discrepancy.
56The cured polymer should be stiff enough to hold the teeth in occlusion during mastication and to minimize uneven loading of the mucosa, underlying the denture should not creep under masticatory loads should not deteriorate in the aqueous oral environment and crazes should not form The cured polymer should be biologically inert and slow to foul
57For an allergic patient, low free-monomer content may be thought more important than stiffness. For a patient requiring a soft lining, stiffness is very important if the reduced cross sectional area of the denture, may lead to stability or loading problems.
58HEAT CURECuring the dough before the monomer has diffused to the core of the beads may result in reduced flexural strength and a tendency for cracks to propagate.The curing cycle is designed to raise the temperature to a point at which(1) sufficient benzoylperoxy radicals are produced to overcome the scavenging effect of oxygen,(2) polymer chains form by free-radical addition polymerization.
59Too rapid a risein temperature produces large numbers of radicals or radical avalanche, as a result, many growing polymer chains. These chains collide either with other radicals or with polymer chains, producing an increase in branching and cross-linking of the interstitial polymer. This in turn reduces toughness.
60Slow cures result in much tougher denture bases, producing fewer cross-links and branches, and having a higher overall molecular weight between cross-links becauseFree-monomer content is often loweralso, because the steadier rise in internal viscosity of the curing polymer allows the monomer easier access to the growing free radicals. The cross-linker is more completely polymerized in heat-cured systems; this results in significantly lower creep values due to removal of the plasticizing effect of unreacted pendant crosslinker groups.
61Heat-cured systems have one great advantage over autopolymerized and injection molding methods: an increased rate of monomer diffusion at the higher temperature.Conversely, an increased temperature of cure can also result in the annealing of stresses that build up in the structure due to polymerization shrinkage. If this stress is not released, it can act as the foci for crazes or distortions
62Autopolymerizing acrylic The pour technique for dentures, originally developed during the 1960s, reversible hydrocolloid. The fitting surface of the moldconsists of the plaster model itself; the acrylic teeth occupy their positions in the agar mold in the same way they do in a conventional plaster mold. In general, the creep of these products is greater than that of heat-cured acrylics.
65Acrylic soft linersacrylics that have a natural glass-transition temperature at least 25°C less than that of the mouth. The plasticizer used to soften the acrylic can either be unbound to the acrylic and hence free to diffuse out during use, resulting in a loss of resilience,
66Silicone soft linersThe silicones used as soft liners can be divided into two types:room-temperature vulcanizing (RTV)and heat curing.The RTV silicones' greatest drawback is their lack of adhesion, which is especially a problem around the edges of the attachment between acrylic and silicone
67Temporary Soft Liners and Functional Impression Materials it is their viscoelastic properties that are important,specifically their ability to flow under masticatory and linguistic forces, spreading the load on the mucosa evenly.
721) In heat cure denture base resins the monomer is a) methacrylate b) ethylmethacrylatec) metyl ethyl methacrylated) polymethylmethacrylate
732)If curing occurs at temperature more than 100 degree celsius porosity results in which are of denturea)hard thick central areab) thin palatal areac)thin area of flangesd) porosity is uniformly distributed
743)What is the shrinkage if 3:1 powder:liquid ratio is used b) 8%c) 10%d) 21%
754) Hydroquinone is added to methyl methacrylate monomer a) to prevent polymerization during storageb)to initiate release of free radiclesc) to enable polymerisation reaction at room temperatured)all of the above
765) cross linking of denture base is contributed by a)gylcol dimethacrylateb) benzoyl peroxidec) N para toluidine d) methyl methacrylate
776) use of dimethyl P toluidine is indicated for a) thermal polymerization of acrylicb) chemical polymerizationc) retarding the polymerizing reactiond) to inhibit the action of benzoyl peroxide
787)Porosity present in acrylic denture is usually the result of a) prolonged curing cycleb) lack of sufficient pressure applied to flaskc) insufficient acrylic resin monomerd) prolonged bench cooling after curing
798)The most important disadvantage of acrylic denture base is a) porosityb)shrinkagec)tooth breakaged)water absorption
809)In self cure acrylic resin the activator is a) toluidineb) quaternary ammonium compoundc) benzoyl peroxided) tertiary amine
8110) Which of the following may result if an excessive amount of monomer is incorporated into an acrylic resin mixturea) excessive expansionb) low impact strengthc) excessive shrinkaged) excessive brittleness
8211) Porosity of denture base is due to a) packing at dough stageb) curing at 160 degree Celsiusc) inadequate pressured) all of the above
8312) Subsurface porosity is due to a) thermal changesb) thickness of resinc) lack of temperatured) packing past the dough stage
8413) To prevent porosity in self cure acrylic resin curing should be carried in a) cold waterb) hot waterc) under tap waterd) under vaccum pressure
8514) Acrylic resins are used for a) anterior restorationsb) temporary brigdesc) denture basesd) all
8615) Packing of heat cure acrylic resin should be done in which stage a) Sandy stageb)Stringy stagec)Dough staged)Rubbery stage