Download NON METALLIC DENTURE BASE MATERIALS

NON METALLIC DENTURE BASE
MATERIALS
DENTURE BASE: that part of a denture which rests on the oral
mucosa and to which artificial teeth are attached.
IDEAL PROPERTIES OF DENTURE BASE MATERIALS:
1.
2.
3.
4.
It should be compatible with absence of odor and taste.
It should be unaffected by oral fluids (insoluble, non absorbent,
and inert)
It should have adequate mechanical properties; including high
modulus of elasticity, high proportional limits, high transverse
strength, high impact strength, high fatigue strength, sufficient
resilience, hard and with good abrasion resistance.
It should have other physical properties including; thermal
expansion matches that of artificial teeth, high thermal
conductivity, low density, and softening temperature higher than
the temperature of foods and liquids in the mouth.
5. It should be esthetically satisfactory.
6. It should be easy to process with the minimum of expense
and equipments.
7. It should be easy to repair.
8. It should be radio opaque; if a denture or fragment of a
broken denture is accidentally inhaled or ingested, it
should be capable of detection by x-ray.
9. It should have dimensional stability on processing the
denture and in service.
10. It should be easy to clean and resistant to microbial
growth.
11. It should be good shelf life.
 No denture material that adequately fulfills all these
requirements was known.
Denture Base Materials
Classified into 3 classifications:
Denture base materials
Temporary
denture base
Self cured
acrylic
Shellac base
plate
Base plate
wax
Permanent
denture base
Injection
molded resin
Metallic base
Heat cured
resin
Denture base materials
Metalic
Non metalic
Light cured
resin
Poured typed
ANSI/ADA Classification(Sp.No.12/ISO 1567)
Type 1-Heat polymerizable polymers
• Class 1-Powder & liquid
• Class 2-Plastic cake
Type 2-Autopolymerizable polymers
• Class 1-Powder & liquid
• Class 2-Powder & liquid pour-type resins
Type 3-Thermoplastic blank or powder
Type 4-Light activated materials
Type 5-Microwave-cured materials
DENTURE BASE MATERIALS
1. metallic: Gold, Ni/Cr, Co/Cr, Ti alloys.
2. nonmetallic: acrylic resins, flexible denture base materials.
• POLYMERS
Polymers used in dentistry include; vinyl acrylics, polystyrene, epoxies,
polycarbonates, polyvinyl acetate polyethylene, cis- and transpolyisoprene, polysulfides, silicones, polyethers, polyacrylic acids and
others.
• CHEMICAL COMPOSITION
The term polymer denotes a molecule that is made up of many (poly)
parts (mers) . The molecules from which the polymer is constructed
are called monomers (one part). Copolymers means polymers contain
two or more different types of monomers.
Eg. Monomer : methylmethacrylate
•
Polymer : polymethylmethacrylate
•
Copolymer : methylmethacrylate- ethylmethacrylate copolymer
POLYMERS' USES :
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Denture bases
Artificial teeth
Tooth restoratives
Cements
Orthodontic space maintainers and elastics
Facings on fixed metal crowns and bridges
Obturators for cleft palate
Impressions
Dies
Provisional restorations
Root canal filling materials
Athletic mouth protectors.
Maxillofacial prostheses
Custom impression trays
Soft denture lining materials.
Polymers are either thermoplastic or thermosetting.
• Thermoplastic refers to polymers that may be
softened by heating and solidify on cooling , the
process being repeatable. Eg, polyestyrene .
• Thermosetting refers to polymers that solidify
during fabrication but cannot be softened by
reheating .eg, cross-linked polymethylmethacrylate,
silicons.
• Cross-linked molecules are a network structure that
may result in the polymer's becoming one giant
molecule .
ACRYLIC RESINS: Acrylic resins is the most widely used and
accepted plastic material in dentistry.
Acrylic denture base materials are classified into five groups (types):
Table: Classification of acrylic denture base materials according to ISO 1567 :
Type
Description
1
Heat- processing polymers, (powder and liquid or plastic cake)
2
Autopolymerized polymers,( powder and liquid)
3
Thermoplastic ( blank or powder)
4
Light-activated materials
5
Microwave-cured material
Chemical Composition of type 1 and type 2 Acrylic Resins
Most materials are supplied as a powder and liquid.
powder
polymer
The major component of the acrylic powder is beads of PMMA
which are produced by polymerizing methylmethacrylate in specific
methods. The PMMA is a clear, glass-like material.
initiator
it is decomposed either by heating (over than 65 ºC), or by an
accelerator, or by light. A peroxide such as benzoyl peroxide
(approximately 0.5% ) is used.
inorganic pigments, usually pink, and small red fibers are
incorporated to simulate the natural oral mucosa with its minute
blood vessel. Salts of cadmium or iron or organic dyes are used.
pigments
liquid
Inorganic particles
to improve acrylic properties
Opacifiers
to increase the radio opacity of the acrylic
monomer
Cross-linking agent
inhibitor♦
activator
Methylmethacrylate: it is a clear, colorless, volatile liquid with a
distinct odor that is toxic if inhaled for a prolong period.
Ethylene glycoldimethacrylate: to improve the physical properties
Hydroquinone (trace ): to prevent the premature polymerization of
the material.
N N' –DIMETHYL-P-TOLUIDINE (approximately 1% ) ): is
added only to self curing material to activate the polymerization at
room temperature i.e. without heating.
• ♦ Note: to prevent the premature polymerization
of monomer:
• An inhibitor is added to the liquid
• The liquid must be stored in a dark- brown, locked bottle.
POLYMERIZATION (CURING )
It is a chemical process which involves the generation of relatively long
molecules (polymer) from small component units ( monomer), or;
The process consists of the monomer units becoming chemically linked together
to form high molecular weight molecules.
Polymerization stages: Polymerization of acrylics usually occurs in 4
chemical stages summarized as follows:
1. ACTIVATION STAGE : the chemical reaction is activated by one of the
following techniques:
1. thermal activation by heating over than 65ºC by either a water bath or
microwave oven.
2.chemical activation: the reaction is activated by a chemical agent (accelerator)
which is incorporated in the liquid.
3. visible-light activation: by light of a specific wave length.
2.INITIATION STAGE: the reaction is initiated,
i.e. the curing starts.
3.PROPAGATION STAGE: the reaction
continues and growing long molecules or chains
of polymer are produced.
4.TERMINATION STAGE: the molecules
reaction is terminated, but the polymerization is
ever never be stopped as monomer residue is still
present in the final set acrylic material.
MANIPULATION OF CHEMICAL-CURED RESINS:
A powder-liquid ratio of 3:1 is used or according to manufacturer
instructions. The powder and liquid are mixed in a glass jar and covered.
The mixture passes through the following physical
changes:
1. sand stage: the mixed material.
2.stringy stage: the material is sticking to the spatula and fingers and sides
of mixing vessel.
3.dough stage: the mixture is more cohesive and less stickiness and can be
separated easily from the side of the mixing jar. The material now is
moldable and workable and can be shaped according to use.
4.rubber stage: the material is rubber-like.
5.hard solid stage.
Doughing time: the time taken to reach the dough stage.
Working time of acrylic: the time in which the material remains at the
dough stage and it is moldable and workable.
MANIPULATION OF HEAT-CURED RESINS:
The procedure is same as that of chemical-cured resin, but when the
mixture reaches the dough stage, the material is packed into a flask
and then cured in a water bath using one of these cycles:
Water bath curing cycles;
1. long cycle: is to heat the water of the bath containing the flask for 7
hours at 700C followed by 3 hours at 1000C.
2. short cycle: tap water is placed in the bath containing the flask. The
water is gradually brought to the boil over a period of 1 hour. Then
the water is allowed to boil for 1 hour.
Then the flask is cooled slowly on pang, and deflasked. The hard
acrylic denture cleaned, finished and polished.
Polymerization of heat cured acrylic resins by microwave
energy:
This process required :
1.a specially formulated resin.
2.non metallic flask
3.a conventional microwave oven to supply the thermal energy.
Advantages of microwave acrylic resins :
1.speed of polymerization
2.the physical properties of microwave resins are comparable to
conventional resins
3.the fit of microwave denture bases are comparable with
conventional ones.
Light activated denture base resins:
Chemical composition: this material has been
described as a composite having the following
composition:
1.urethane dimethacrylate
2.microfine silica
3.high-molecular weight acrylic resin monomer
4.organic filler (acrylic resin beads)
5.initiator (camphoroquinone)
Polymerization of Light activated denture base resins:
This type of denture base is supplied as a single
component in sheet and rope forms and is packed in
light-proof pouches to prevent inadvertent
polymerization.
The light activated denture resins cannot be flasked in
a conventional manner because opaque investing media
prevents the passage of light. Instead teeth are arranged
and the light-activated resin is molded on an accurate
cast. Then it is exposed to a high-intensity visible light
source for an appropriate period. After polymerization
the denture is finished and polished in a conventional
manner.
Properties of denture base acrylic resins:
1. Adequate appearance with various pigments, allowing
tissue color matching.
2. light weight.
3. low thermal conductivity.
4. low abrasive resistance.
5. They have residual monomer that may develop allergy in
some patients.
6. Suffecient thickness of the material provides adequate
rigidity and strength.
7. Insignificant dimensional changes.
8. Water absorption followed by drying may cause crazing.
Therefore, the dentures should be kept moist at all times.
Thermoplastic materials for dental prostheses,
Valplast and Flexiplast, were first introduced to
dentistry in the 1950s. Both materials were
similar grades of Polyamides (nylon plastics).
Advantages of nylon flexible denture (1955)
1. Soft and inherent flexibility: Ability to engage undercuts for retention. No
need for periodic adjustment of clasp to keep them tight. Low modulus of
elasticity
2. Will not warp or become brittle.
3. clinically unbreakable.
4. Good biocompatibility: because it is free of monomer and metal.
5. No porosity, so no bacteria can build up within it.
6. No gingival inflammation
7. More comfortable
8. Absorb small amounts of water to make the denture more soft and tissue
compatible.
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9. Less bulky (thinner) and lighter weight
10. Better chewing efficiency
11. Better esthetics: Translucent, so it allows natural gum to show
through, making it invisible.
Clasps rest on the gums surrounding the natural teeth.
They are indistinguishable from the gums.
No metal framework
12. More retention and stability
13. Retention depends mainly on the tissue and only a small portion of
abutment tooth. No evidence of excessive abutment mobility
14. Ease of fabrication (in comparison with cast RPD)
15. Reduces chair side time (shorter fabrication time)
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Disadvantages of nylon flexible denture
1.Intended only for provisional or temporary applications. Flexible dentures are generally only
used when traditional dentures cause discomfort to the patient and cannot be solved
through relining.
2. A major drawback is de-bonding of the acrylic teeth from nylon denture base. Nylon
polyamide denture base material does not bond chemically with acrylic resin/porcelain, so
mechanical undercuts (diatorics) are made in each tooth. It cannot be used with patients
having low vertical dimension and closed bite.
3.Tend to absorb the water content and will discolor often.
4.Discoloration and gradual fading of denture base color are reported after 1-2 years.
5.High surface roughness. This may lead to bacterial and fungal colonization. ??!!
N.B: Brushing a Valplast appliance is not recommended as this may remove the polish and
roughen the surface over time.
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6.The procedure is technique sensitive. Extreme caution is necessary when processing to
avoid skin contact with the heated sleeve, cartridge, furnace, hot cartridge, injection
insert, hot flasks and heat lamps.
7.Difficult to adjust and polish.
8.When grinding this prosthesis, proper ventilation, masks and vacuum systems should
be used.
9.Lower hardness
10.Lacks important elements of RPD, in particular, occlusal rests and a rigid
framework, So it won't maintain vertical dimension. It is contraindicated for
unilateral distal extension.
11.Usually cannot be relined, so stability is a concern if the alveolar ridge resorbs.
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Usually cannot be repaired.
Conventional rigid acrylic
denture
Brittleness of PMMA, so
frequent fracture occurs
Nylon flexible denture
Not brittle
Clinically unbreakable
Allergy to MMA monomer Good biocompatibility: because
it is free of monomer and metal
Irritation of mucosa More comfortable, not irritant
to mucosa
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Rigid
Difficult to insert in undercut
areas
Soft and inherent flexibility
Ability to engage undercuts for
retention
Less esthetics, metal clasp
Longer fabricaion time
Better esthetics, esthetic clasp
Shorter fabrication time
Conventional rigid acrylic
denture
Permanent
Chemical bond between acrylic
teeth and acrylic denture
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Nylon flexible denture
Temporary only
Mechanical retention between
acrylic teeth and nylon
denture.
De-bonding is a major
disadvantage.
Higher hardness
Lower hardness
High surface roughness.
Brushing increases surface
roughness
Can be relined and repaired
Usually cannot be relined and
repaired