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Denture Base Resins

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					Prosthetic Resin Polymers




         Dr Layla Abu-Naba’a
            PhD, MFDRCS
 Assistant Professor of Prosthodontics
                                         1
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                               Demographic changes
    Means an increased need for Prosthetic treatments

                                60
        % population over 50




                                50


                                40


                                30


                                20
                                     1941   1982   2025   2050

                                                                 2
6
            Prosthetic Uses

   Denture bases            Fluoride and
                              bleaching trays
   Denture teeth
                             Facing on esthetical
   Relining Materials        crowns
   Repair of dentures       Provisional
   Provisional acrylic       restorations
    partial dentures         Removable tooth
   Custom impression         movement devices
    trays                    Orthodontic retainers
   Mouth guards

                                                 3
6
           Denture base function

     Distributes pressure over a wider area
    So reducing bone resorption
     Retains artificial teeth
     Replaces missing tissue
     Forms a seal for retention


                                         4
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          Denture Base materials

    Carved ivory
    Carved Wood
    Vulcanite; dark, opaque
    (Vulcanised rubber)
    Highly cross-linked Acrylic resin
    Other Resin and plastic
    alternatives

                                        5
6
      Plastic acrylic teeth

    Bind chemically to the denture
    Can be adjusted
    Not cause wear of opposing tooth
    Good colour match
    Minor resiliency
    Wear under high force occlusion
    May stain with time

                                       6
6
          Other Teeth Materials

    Porcelain (high fusing ceramic)

    Isosit (composite; xlinked acrylic) –

    heavily xlinked

    Experimental fiber-reinforced teeth


                                            7
6
         Maxillofacial prosthesis

    Needed
        After trauma
        Surgical defects
        Birth defects


    Other materials
        Silicone rubber
        Vinyls with
        plasticizers

                                    8
6
         Acrylic repair

    Materials
     Chemically cured acrylic
     Light cured acrylic




                                9
6
    Relining Materials




                         10
6
    Provisional partial dentures




                              11
6
    Impression trays




                       12
6
        Record bases

    Materials
     Cold-curing acrylic resin
     Other material
       Shellac
       Vacuum formed vinyl or polystyrene
       Baseplate wax.



                                            13
6   Occlusal Splints
    Night guards
    Bleaching and fluoride
    application trays




                             14
6
    Mouth guards




                   15
6
         Orthodontic applications

     Removable tooth movement devices
     Orthodontic retainers




                                         16
6           Facing of crowns
            Provisional restorations
    Other materials:
    •Polycarbonate
    •Aluminum
    •Stainless steel
    •celluloid




                                       17
Polymer principles



                     18
6
      Terminology
    Monomer + monomer = polymer
    Monomer1 + monomer2 = copolymer
    Oligomonomer= 2-4 monomers

      Poly    = many
      Mono    = single
      Mer     = unit
      Oligo   =several
                                  19
6
      Types and molecular weight

    Addition polymerisation:
     No by products
     Polymer mwt = Σ mwt monomers
    Condensation polymerisation:
     By products are produced and lost in
     thefinal product
     Polymer mwt ≠ Σ mwt monomers


                                            20
6      Morphology
       of spatial arrangements
    Linear or chain polymerisation
       Easily manipulated, stretched, bent,
       thermoplastic, Hard
       e.g. fitting surface of acrylic teeth- better
       binding to denture base
    Branched polymerisation
       Easily manipulated, stretched, bent,
       thermoplastic, More hard




                                                       21
6
            Morphology
            of spatial arrangements
    Cross-linked polymerisation
      Strong, stiff, thermoset, wear resistant
      E.g. Denture base materials, Occlusal
      surfaces of actylic teeth

    Coiled chains
      Flexible
      e.g. impression materials



                                                 22
6
          Morphology
          of spatial arrangements
    Crystalline polymers
      Very regular arrangement in space:
        strong,
        stiff,
        absorb less water.
    Amorphous or glassy polymers
      Irregular arrangement
      Behaves as a brittle solid


                                           23
6
           Plasticizers effects
     Added to stiff, glassy uncross-linked
    polymers
     Lowers glass transition temperature (Tg)
     Become
        rubber-like,
        Flexible
        less brittle



                                                24
6
             Dimensional and thermal
             changes

    Expansion on polymerization, exothermic
    Contraction on polymerization
      21vol.% If unfilled acrylic resin
      6% denture resin
      1-3% composites
    Expansion on swelling in water
    Expansion or warpage on thermal change
    and reheating
                                              25
Acrylic Resin Types




                      26
Ideal properties
Natural appearance          •Low density
Easy processing             •Radiopaque
Easy to clean               •High thermal
Easy to repair              conductivity
Inexpensive                 •High modulus of
Biocompatible               elasticity, impact
Resistant to bacterial      strength
contamination               •Abrasive resistance
High strength, stiffness,   •Dimensionally stable
hardness, toughness,
                            •Accurate reproduction
fatigue resistance
                            of surface detail
                                                     27
 Curing methods
Chemically cured
  Tertiary amine ( dimethyl-p-toluidine or sulfinic acid)
  (accelerator)
  Benzoyl peroxide (initiator)
  Hydroquinone (inhibitor)
Heat cured
  Heat and pressure control
     Avoids porosity
     Maximizes conversion of monomer to polymer
Light cured
  Photo-initiators (camphorquinone),
  Blue light,
     Used for: record bases, custom tray, denture repair

                                                            28
  Heat cured acrylic resin
Powder ( can have limitless life)
   Beads or granules of polymethyl methacrylate
   Initiator (benzoyl peroxide)
   Pigments/dyes (colour vitality as cadmium, iron, organic dyes)
   Optical opacifiers (tio2/zno)
   Plasticizers (ethyl acrylate (internal), dibutylphthalate (external) to
   make dough easier)
   Synthetic fibres (nylon)
                                               Bead Polymer
   Coloured fibres (blood vessels)

Liquid ( in dark bottle, avoid contamination by
               powder)
   Methyl methacrylate monomer
   Inhibitor (hydroquinone)
   Crosslinking agent
       (diethylene glycol dimethacrylate, (1,4 butylene glycol dimethacrylate)


                                                                           29
 Chemical cured resin
Cure is initiated by a tertiarv amine (e.g. Dimethyl-
p-toluidine or sulfinic acid)
Absence of heat:
   Lower molecular weight material
   Lower strength properties
   Higher residual monomer in the resin
   Color stability is not as good- yellowing
   Less contraction on cooling to room temp

Polymer beads are smaller
   Faster dissolution in the monomer to produce a dough
   Doughy stage is reached before the addition curing reaction –
   mix viscosity is high and prevents the adaptation of the mix to
   the mould walls or cast -keep readapting

Lowering of the glass transition temperature
   Less build-up of internal strain
   Highly susceptible to creep- distortion when in use.
                                                                     30
 Light activated materials
Components:
   Urethane dimethacrylate matrix
   Acrylic copolymer
   Silica filler to control rheology
Forms
   Sheets
   Ropes
Curing
   Light chamber- 400-500 nm
   Photo-initiators (camphorquinone),
   Teeth added in a second exposure over the base
Used for
   Record bases
   Custom tray
   Denture repair
Hardness and impact strength ≈ heat cured resin
Elastic modulus < heat cured resin; deform under
mastication
Less shrinkage (3%) better fit                      31
Less residual monomer
 Auto-polymerizing, pour acrylic
Reducing agent (tertiary aromatic amine or barbituric
acid derivative, NN’-dimethyl-p-toluidine) reacts with
peroxide at room temp.
Excellent detail reproduction
To be able to pour in mold, balanced size, mwt,
plasticizers and xlink agents
Reversible hydrocolloid (agar) mold can’t resist teeth
movement during pouring
Hydro pressure flask reduces air bubbles and
monomer porosities
Difficult to dewax, less monomer binding to teeth
Shortcomings:
   residual monomer
   ↓ Cross link densities
    Creep
    Variety of products
                                                         32
  High-impact acrylic
A rubber phase is added (phase inversion)
   Uniformly distributed
   Rubber cored polymer
Types
   Butadiene + styrene = polystyrene butadiene rubber
   Butadiene + MMA
   PMMA + polystyrene butadiene rubber + poly(2,3-
   dibromopropyl methacrylate) for opacity
PMMA = lucitone 199
Lightly xlinked or no cross linking agent is added
Rubber has a craze inhibitory effect                    33
     Experimental types of acrylic
All aim to increase impact strength and stiffness
  Glass reinforced acrylic (failed)
     Fibers may irritate patient if denture fitting surface was
     abraded
  Carbon fibers
     Black color- used only in lingual areas
  Kevler fibres (poly-p-phenylene terephthalamide)
     Straw color
     Poor bond between fibers and matrix
     Difficult to pack
     Black shadow- used only in lingual areas


                                                                  34
  Experimental types of acrylic
Added Bis-GMA and fiber
  Flexural strength ≈ ceramics
  Can be used as lingual bars and connectors
Experimental (mwt polyethylene fiber-reinforced)
  Neutral color
  Low density
  Biocompatibility
  Surface treated to enhance fabrication
  Time consuming




                                                    35
  Types of acrylic

Other (polystyrene,epoxy, SS)

PMMA Adhesion to
  Metal- use adhesive primers
  untreated porcelain teeth with organo
  silane compounds




                                          36
Heat Cured Resin



                   37
   Polymethyl methacrylate
 MMA
 Liquid
                       Heat and pressure



                    PMMA
                                (entanglements)
                   Powder
PMMA            Particle swells                   Old and new
                                      MMA         polymer chains
Powder                                            Intertwined at the
                                      Liquid      molecular level.


Activation       Acrylic dough (Cohesive gel)
             Initiation
                              Propagation
                                                  Termination
                                                                   38
    Setting reaction
Mixing of powder and liquid cause monomer diffusion and
 softening of the surface of the powder producing the following
 gelling stages:
Ratio P/L (2/1 wt%, 1.6 -1 vol%)
 Sandy- initial melting of beads              (not used)
 Stringy or sticky- entanglements with swollen beads and
 thickened interstitial monomer              (not used)
 Dough- gelation                              (used)
 Rubbery- monomer penetrates to the core of beads,
 plasticizing them, ↓Tg                   (not used)


                                                           39
 Manipulation issues

P/L
   Inadequate filling by monomer
   Weak material properties
   Porosity
↓P/L
   Excessive polymerisation shrinkage
   Poor fit
   Light color as powder holds the pigments




                                              40
  Manipulation issues
Curing before monomer diffuse to bead
(before dough stage)
    ↓ flexural strength
    cracks between linear polymerised interstitial gel and cross
  linked beads
    More shrinkage contraction by the loss of pressure produced
  by the dough to compensate for it
Curing in dough stage
   monomer penetrate the beads
   dissolves beads allows cross-linking agent to penetrate
   interpenetrating polymer network IPN.
Packing in the rubber stage
   Less extrusion of excess acrylic from flask
   Extra pressure in the mould
       Fracture the cast
       less flow around teeth                                 41

       Dislodgment of teeth into mould
Manipulation issues
Control of color
   Pigments position
      Inside beads
      surface of beads
        – polymer should be added to the monomer slowly so it will not
          washed off by too rapidly
   Blood vessel resembling Fibers aggregate in the bottom
   of bottle
        – Shake powder well before use
Mould Lining
   resin may penetrate rough plaster and adhere
   a separating medium must be employed
      solution of sodium alginate
      tin foil.



                                                                    42
Manipulation issues
Control of Processing strains
  Shrinkage in restricted mould cause internal strain
  On release of stress (flask opening) it may give
     Crazing
     Warpage
     Distortion
  These are reduced by the slightly extra packed material
  that flow into shrinkage spaces when temperature is
  higher than Tg (heated flask)
  Manipulation further reduces strains by
     Using acrylic teeth
     Cooling the flask slowly


                                                            43
Flasking steps

Flasking
Dewaxing
Putting a separating medium
Placing acrylic dough
Packing
Heat curing


                              44
                   Flasking
 Wax-up



Melt out the wax




                    Packing


                       Curing

                                45
Flasking for heat cured resin
Flasking options with acrylic dough:
  Trial-packing, trimming, repacking
  Packing-only
  Poured resin (e.G., Lucitone fas-por)
  Injection moulding

Heat and pressure control
  Aim to produce radicals and initiate polymerization
  Reaction is thermally activated and generates heat as
  well
  Reaction conversion is about 98 to 99.5%
  MMA: tbp = 100c (p= 1 atm); 140c (p= 2 atm)


                                                      46
 Heat curing cycles
Fast cycle
  Cure at 71-72°C for 30-90 min
  100°C for 30 min.
Slow cycle = cure at 71-72°c for 10 hrs
  [A slow cycle is better with larger amounts of
  material.]
  [Generally, slow cures result in better
  dimensional accuracy.]
Other cycles are done as recommended
by manufacturers


                                                   47
Heat curing cycles

Rapid heating:
  Excess radical release
  Extra xlinking and branching of interstitial
  polymer
  More residual monomer
  Reduced toughness
  Heat builds up from exothermic rxn
  Porosity
     Loss of strength
     Bad esthetics (opaque and cloudy color)
     Possible fouling

                                                 48
Heat curing cycles

Slow :
  Sufficient radical release
  Adequate xlinking and branching between high
  mwt polymer chains
  Increased toughness
  Sufficient radical ends increase monomer
  incorporation in growing chains
  Xlinking agents polymerized, reducing their
  plasticizing effect (in their non bound state) and
  reduce creep
  Produce an annealing effect easing stresses
  produced from shrinkage, reducing crazing and
  distortion
                                                   49
Heat curing cycles

Pressure control
  Places compressive force
  Compensates for polymerization shrinkage
  Increase flow of dough around teeth, more
  monomer wetting and surface dissolution,
  stronger bond
  Oozes out excess dough
  Some hybrid systems begin polymerization
  from one side to allow dough to cover for
  shrinkage

                                              50
Heat curing cycles

Microwave curing
  Uses a microwave
  Flasks are non metalic
  Reduced time




                           51
Denture shortcomings




                       52
 Denture Radiolucency
Problems when accidents displace fractured
segments
   Lungs
   Skull
   stomach
Salts and fillers reduce esthetics, strength
Organo-metalics are toxic
   Bromine containing organics lack heat stability, must be
   added in quantities that plasticize the denture, causing creep
   and water sorption
   Phase separating bromo-polymer in beads reduce the
   previous effects
                                                            53
 Mechanical properties
Failure to Moderate strengths:
  impact resistant denture is low
  Low elastic and flexural modulus
  lack of fracture toughness
  30% of denture repairs involve midline fractures
which are most prevalent among upper dentures.
  dropped denture does not necessarily break instantly
  a crack continue to grow and failure due to flexural
  fatigue.
Failure due to poor quality processing
  Lack of bonding between the resin and the acrylic teeth
  and weak interface
  Crazes due to processing faults or exposure to solvents
  is another possibility.
Creep
  Reduced by cross linking
                                                            54
  Heat cured < cold cured
   Internal denture porosity
Inherent porosity:       Minimized by
    Not seen by vision     Use heat cured resin
    1-2% of residual       Pack denture under
    monomer                correct pressure
    Leaks                  Use correct P/L
    Replaced by fluids     Use the glaze after
                           polishing




                                                  55
  Internal denture porosity

Irregular porosity:     Minimized by
    Seen by vision        Use correct P/L
                          Add liquid first
    Not regular on
                          Mix well
    denture surface
                          Cover the mix before
    P/L heterogeneity     dough stage
    Air incorporation     Can use the vibrator
      (spherical pores)



                                                 56
   External denture porosity
Irregular surface            Minimized by
   deficiencies:               Mold dough by hand
   Seen by vision              into small areas
   Insufficient pressure       Place sufficient
   Dough was not molded        material in flask
   correctly by hand leaving Pack under correct
   surface blisters and pores pressure
   Insufficient dough




                                                    57
   External denture porosity
Irregular porosity:         Minimized to by
   Shrinkage by               Pack under pressure
   polymerisation (5-8% vol   Slight extra denture
   or 0.2 -0.5% linear)       material can overcome
   Further shrinkage by       shrinkage and
   cooling to room            maintain pressure
   temperature                (single packing)
   Can compensated for by     Pack in dough stage
   the post dam technique




                                                 58
  Internal denture porosity
                        Minimized by
  Gaseous porosity        Avoid high processing
 Seen by vision           temperatures
                          Avoid extra monomer
 Volatisation of          than recommended for
monomer by                P/L
Localized MMA boiling     Raise heat slowly and
 Common in thicker        evenly around the
portions                  flask




                                              59
      Gaseous porosity

     Avoid high processing temperatures
                             160
                             140
            Temperature 0C




                             120
                             100

Incorrect                    80
cycle                        60
                             40
                             20                                                        Correct
                                                                                       cycles
                              0
                               0




                                                                                   0
                                   10

                                        20

                                             30

                                                   40

                                                        50

                                                             60

                                                                  70

                                                                       80

                                                                            90
                                                  Time (min)                     10         60
Crazing

Area of localised region of high plastic
deformation which may fill by voids
   Crazed region can still support stress
   As the voids in the crazed region grow, they become
   separated only by thin fibrils of polymer
   Fibrils fail and a crack is formed
   Crack will grow under an externally applied load
   Cause denture failure by brittle fracture.
Caused by
   Internal strains in flask
   Heat (due to polishing)
   Differential contraction around porcelain teeth       CRAZE               CRACK

   Attack by solvents such as alcohol

                                                                      61
                                                         Reversible        Irreversible
Crazing

Avoid internal strain during polymerisation
   Slow cooling of the flask
   Use single trial packing
   Use cross linked polymer types
Avoid extra stress during function
   Use acrylic rather than porcelain teeth
   Do not overheat on polishing
   Keep denture away from solvents
                                             CRAZE             CRACK
   Avoid denture drying
   Polish after each adjustment
   Use glazes for surface

                                             Reversible   Irreversible
                                                          62
   Dimensional changes on
   processing
  Expansion on heating flask; heat evenly
  Expansion on polymerization, exothermic
  Contraction on polymerization (21vol.%);
  Contraction on cooling to room temperature;
  Expansion on swelling in water;
  Expansion on thermal change to 32c.

Net result– should be near zero
                                            63
Warpage on drying

Contraction on evaporation of
absorbed water
Don’t leave denture outside the mouth
dry




                                    64
    Adverse reactions to PMMA
                   Most common in dental
                   laboratories
                   Associated with regular
                   contact with monomer
                   when handling the
Irritant contact   dough
dermatitis         Must avoid direct
                   contact
                   Rubber gloves may not
                   provide sufficient
                   protection
                   Barrier creams can help
                                         65
   Adverse reactions to PMMA
                                 Must ensure full cure of denture
Allergic contact dermatitis
   Usually associated with       Avoid relining procedures
   release of                    May use an extra cycle of
      residual monomer
      Benzoic acid               polymerisation – but denture
   Types                         may warp
      Immediate
      Delayed hypersensitivity   May need to consider
      (type IV)
   Heat cured resin < chemical   alternative material such as
   cured                         polycarbonate if Delayed
                                 hypersensitivity


                                                         66
  Adverse reactions to PMMA

Further reading:
Hensten-petterson & jacobsen. J prosthet dent
   1991; 65: 138
Kaber. Int dent J 1990; 40: 359
Http://www.Shef.Ac.Uk/uni/project/arrp/




                                                67
 Thermal properties
Low Thermal conductivity

  during denture processing heat cannot escape – prone to
  gaseous porosity
  isolates from any sensation of temperature – throat burns



High Coefficient of Thermal Expansion

  Porcelain teeth may be lost due the differential expansion
  and action
  Warpage if denture is cleaned with hot water


                                                          68
  Water Sorption
 PMMA will absorb water by polar nature (1.0-2.0%
 wt)
  May compensate for processing shrinkage
 Weeks of continuous immersion in water to reach a
 stable weight


Solubility
 Solvents (e.G. Chloroform, alcohol)
 Xlinked are insoluble in most of fluid intakes
 Weight loss will occur, due to leaching of the
    Monomer
    Pigments and dyes.
                                                  69
   Ideal properties achieved?
Natural appearance                              
Easy processing                                 
Easy to clean                                   
Easy to repair                                  
Inexpensive                                     
Biocompatible                                   
Resistant to bacterial contamination            x
High strength, stiffness, hardness, toughness   X
Low density                                     
Radiopaque                                      X
High thermal conductivity                       X
Dimensionally stable                            X
                                                
                                                70
Accurate reproduction of surface detail
 More

DB bonding to alloy framework
Acrylic-metal leakage




                                71
Other Denture Base materials




                           72
 Injection molded plastic
Types
  Polycarbonates
  Nylon
Advantage:
  Consistent mwt
  Substitute acrylics in sensitive patients
Disadvantage
  Must use dry mold, slow heating and cooling
  Under filled molds by inadequate spruing or underheating
  Low melt temp cause high injection forces, moving teeth in
  mold
  Cost of equipment
  Difficult to attach to teeth
  Small market segment
  Can explode if high heat and wet molds
  Overheating cause depolymerization, oxidation, porosties
     Loss of strength
     Bad esthetics (opaque and cloudy color)                   73

     Possible fouling
Polycarbonates

Tough plastic
Injected in dry molds
A high melt viscosity
  Problems in binding to teeth

May de-polymerize explosively in the
presence of heat and water
No cross linking –
  Poor solvent resistance
  Poor craze resistance

                                       74
Nylons and polyamides

Polyamide = diacid + diamine
Conventional nylon failed
  Excessive water sorption
  Poor creep resistance
  Biodegradation

Glass (beads or fibers) reinforced nylon
  Less water sorption
  Fibers better in stiffness(≈ acrylic) than beads
  Fibers may irritate patient if denture fitting surface was abraded


                                                                   75
Cellulose product

Camphor used as plasticiser
Warpage in mouth
Camphor leached out
  Loss of color
  Taste
  Blistering
  Staining


                              76
Phenol Formaldehyde (Bakelite)

Difficult to process
Lost its color with function




                               77
Vinyl resins

Low resistance to fracture
Fatigue failure




                             78
Relining Materials




                     79
   Denture base reprocessing:

Hard and soft tissue changes every 5-8 years
  Require modifying denture base:
  Relining  resurfacing of the tissue surface
  Rebasing  replacement of entire denture
  base



                                             80
 Soft denture lining material

Uses:
  After surgery
  Immediate dentures
  Sores
  Undercuts which are not removed by surgery
  Ill fitting denture
can be done
  In lab
  Chair side


                                               81
Ideal lining material properties
   Durability: but hardens in short time
(1-4w, 1-3 y)
   Dimensional stability
   Resistance to fouling
   Water absorption
   Osmotic presence of soluble material
   Resistance of Biodegradation
   Could it bond old acrylic
   Inhibit candida growth
                                           82
  Lining materials–acrylic based
Glassy MMA + high conc. of plasticizers
 Plasticizers:
    Free: diffuse out reducing the resiliency
    Bound in cured matrix – failed clinically
      Has lower rate of polymerization
      Phase separation
      Water accumulate in plasticizer rich phase
      Soluble impurities cause more osmotic pressure
      Swells and distorts
      Discoloration
      Bad taste
      Exothermic rxn
                                                       83
      Bad taste
    Lining materials–acrylic based
Soft acrylics that have ↓Tg
 EMA (ethylmethacrylates)
    Beads coploymer
       Ethyl methacrylate + isobutyl methacrylate
       Ethyl methacrylate + ethoxyethyl methacrylate
         – Have unpleasant odour
    Monomer
       MMA Tg > room temp Less irritant to patients
       Isobutyl methacrylate Tg < room temp (polished after placing
       in iced water), Dimensional instability
     Plasticizer in monomer trapped in beads (25-50%)
       Phthalate ester – leach out by time
       Avoid heat, strong bleaching agents that reduce resilience
                                                               84
  Lining materials–acrylic based
Soft acrylics that have ↓Tg
 Hydroxy EMA
    Water is the plasticizer
    Swelling of liner may make it distort
    Ions enter and may crystallize inside matrices thus
    hardening the liner


 Polymerisable plasticisers
    Beads ploymer
       Ethyl methacrylate + isobutyl methacrylate or
    Monomer
     Alkyl maleate or
     Alkyl itaconate + Tridecyl methacrylate +
     2-diethylhexyl maleate, ethylene glycol dimethacrylate
                                                              85
    Tissue conditioners
Differ from soft lining material by the following
    Different viscoelastic properties
       Flowable on insertion responding to
         – Masticatory forces
         – Lingual forces
         – Border moulding forces
       Increase viscosity on setting
       Flows slowly responding to persistent heavy masticatory
       forces after setting
         – Useful to fill space after tissue swellings resolve
         – Can be used as a functional impression
    Reaction
       Gel formation not polymerization
       Alcohol swells beads and ↓ their Tg
       Beads become tacky by entanglements and  cohesive
       strength                                                  86
    Tissue conditioners
Differ from soft lining material by the following
    Composition
     •   Old- plasticine
     •   Old- chewing gum
     •   Ethyl methacrylate copolymers
     •   Or small mwt polymers

    Plasticisers:
         ethyl alcohol or
         aromatic esters (butylphthalyl butylglycolate)
         hemical cleaning damages the liner
           – Use plain soap and water



                                                          87
    Tissue conditioners
Differ from soft lining material by the following
    Alcohol problems:
       Leak and replaced by water- so harden days up to 14 days
       High conc. Can give a sting sensation
       Can give a false positive on breathalyser test
       Reduce leach of plasticisers by glazing or semiset MMA
       Very susceptible to infection
         – Incorporate antimicrobials as
             » silver zeolite
             » itraconazole
       Chemical cleaning damages the liner
         – Use plain soap and water
                                                                88
Silicon - RTV
Room temperature vulcanizing silicones (RTV)
  Polymethyl siloxane polymer
  It sets by crosslinking of existing polymers
     Heat
     Tetraethyl silicate
Condensation minimal xlinking
  Poor tear resistance
  Poor abrasion resistance
  Poor adhesion to denture
     Use adhesive or coupling agent
  Osmotic pressure effects
     Buckling and swelling with water
  Poor resistance to cleansers
  Biocompatible
  Dimensional stability
  May foul by Candida
                                                 89
Silicon – Heat cured
 More xlinking
 Poor tear resistance
 Adequate adhesion to denture
     Can use siloxane methacrylate as a binder to heat
    cured additional silicon
 Resistant to aqueous environment and Osmotic
 pressure effects
 better resistance to cleansers
 Poor tear resistance
 Poor abrasion resistance
                                                         90
Other acrylic products




                         91
  Denture base hygiene

1. Clean with toothbrush and warm soap-
   and-water
2. Use low abrasive cleaners
2. Avoid oxidizing or Cl-containing
   materials
  •   Bleaching the color
  •   Reduces strengths of denture
  •   Reduces fatigue resistance
3. Diligently clean both the top and tissue-
   borne surfaces
4. Clean with benzalkonioum
                                           92
Thank you



            93
References

Philips Science of Dental Materials
Dental Materials and Their Selection
Applied Dental Materials
Dental Materials. Clinical Applications for
Dental Assistants and Dental
Introduction to Dental Materials
RPD acrylic materials by Dr Stephen C.
Bayne
Dr Layla Abu- Naba’a
                                   94

				
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