This document discusses flexible dentures as an alternative to conventional rigid acrylic dentures. It outlines the disadvantages of cast and acrylic dentures including brittleness, fracture, and irritation of tissues. Flexible dentures made of nylon are introduced in 1955 as having advantages like flexibility, light weight, and biocompatibility. Both advantages and disadvantages of flexible dentures are provided. Indications include bilateral undercuts and contraindications include unilateral extensions and low vertical dimension. The document describes the composition, manipulation through injection molding, and various commercial flexible denture products. Thermoplastic resins are discussed for uses beyond dentures.

1. 1
Flexible denture
Disadvantages of cast RPD
Disadvantages of conventional rigid acrylic RPD (PMMA 1930)
Advantages of nylon flexible denture (1955)
Disadvantages of nylon flexible denture
Controversial and/or need more research
Indications of nylon flexible denture
Contraindications of nylon flexible denture
Main composition
Manipulation
Commercial products
Uses of thermoplastic resins
References
Disadvantages of cast RPD
1. Expensive
2. Need high skill in preparation
3. Time consuming mouth preparation
4. Technique-sensitive casting
5. More difficult
6. Visibility of metal clasp
7. Heavy weight
8. Brittle
9. Difficult in relining & repairing

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Disadvantages of conventional rigid acrylic RPD (PMMA 1930)
1. Brittleness of PMMA, so frequent fracture occurs.
2. Allergy to MMA monomer
3. High porosity
4. Irritation of mucosa
5. Foul smell
6. Difficult to insert in undercut areas
7. High water sorption
8. Dimensional changes and polymerization shrinkage
9. There are many factors inthe laboratory procedure that can lead to alteration of denture
occlusion and resultsin significant increase in vertical dimension after processing.
10. Denture wearers use dentures adhesive which causes its own problems.
Valplast flexible denture base
Valplast flexible denture base

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Advantages of nylon flexible denture (1955)
: so it prevents the gum from being rubbed raw.Soft and inherent flexibility1.
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.
because it is free of monomer and metal.:Good biocompatibility4.
5. No porosity, so no bacteria can build up within it.??!!
6. No gingival inflammation
7. More comfortable
8. Absorb small amounts of water tomake the denture more soft and tissue compatible.
9. Less bulky (thinner) and lighter weight
10. Better chewing efficiency
Translucent, so it allows natural gum to show through, making it:stheticsBetter e11.
invisible.
Clasps rest on the gums surrounding the natural teeth.
They are indistinguishable from the gums.
No clasp on the tooth surface.
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 willdiscolor 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 notrecommended as this may remove the polish
androughen the surface over time.
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.
Usually cannot be repaired.

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:al and/or need more researchiControvers
–:.to haveClaimed1.
High creep resistance, fatigue endurance, wear characteristics, dimensional stability and
solvent resistance.
N.B: Injection moulded denture base material has better accuracy than compression moulded
PMMA
2. Bacterial and fungal colonization: Although it has no porosity, it has high surface
roughness.
3.Color stability
Indications of nylon flexible denture
1.Bilateral undercuts
2.Allergy to acrylic resin
3.Patients who do not want a fixed restoration and metal clasps.
4.No enough bone for fitting dental implant
5.Bruxism
6.Patients with compromised neuro-motor function
7.Single denture
8.Obturators
9.Rehabilitating the anomalies suchas ectodermal dysplasia.
Contraindications of nylon flexible denture
1. Unilateral distal extension
2. Low vertical dimension and closed bite

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Main composition
Polyamide nylon thermoplastic material
Manipulation
Injection molding technique:
It is highly sensitive to the position and size of sprue placement.
1. Investing in a special flask (e.gvalplast flask) and spruing.
Sprue designing:
For complete maxillary dentures, sufficient width sprue is attached to the posterior border
of the denture with an extension over the palate area to allow adequate flow of the material
throughout the palate area.
For partial dentures and mandibular complete dentures, the sprue is attached to both
lingual extensions as well as in the midline.
2.Wax elimination by boiling.
3. Undercuts (diatorics) are made (prepared) in the centre of each tooth so that the melted
fluid polyamide will flow into the undercuts for mechanical retention.
After preparation, each tooth is cemented back into its place in the top half of the flask with
valcement (cement provided with the valplast system).
N.B. Cyanoacrylate is contraindicated, because it bonds permanently with the teeth surface.
4. Thermoplastic nylon is melted at temperatures from 274 to 302°C for 11 min before
injection.
The opened flask is placed directly in a pre-heated oven maintained at 65-80°C. Furnace
timer was set for 17 minutes.
The flasks halves are assembled with brackets and together with the cartridge containing
melted nylon; they are placed on to the injection unit. The injection molding pressure is
maintained at 5 bars for 1 min. The dental flask is bench-cooled before deflasking.

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Fig.1: Flexible denture injection system
Fig.2: Injection casting procedure
Fig.3: Flexible denture retrieved

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Commercial products
Valplast,Flexiplast,Duraflex,Impak, Lucitone FRS, Flexite,Flexite M.P., Flexite Plus, Sunflex and Proflex.
1.Valplast(Valplast Int. Corp. - USA)
Nylon polyamide thermoplastic.
Light weight
Monomer free
2.Flexiplast (Bredent - Germay)
Nylon polyamide
3.Lucitone FRS (DENTSPLY Trubyte, New York, PA, USA)
Nylon linear polyamide
Monomer free
4.Flexite
Thermoplastic fluoropolymer (Teflon) 1962
5.Flexite M.P.
Thermoplastic acrylic, a special blend of polymers.
Highest impact rating of any acrylic.
Flexible
Can be relined and repaired.
Easy to adjust and repair.

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6.Flexite Plus
Nylon polamide thermoplastic material
Monomer free
Impervious to oral fluids
May be combined with a metal framework to eliminate the display of metal labial clasps.
7.Sunflex
Nylon thermoplastic
Tissue-colored clasps
More stain-resistant than other flexible acrylics.
Can be relined & repaired.
8.Pro-flex
Full and partial flexible denture since 1998.
Can be repaired.
Can be relined using Pro-flex soft liner material.
Uses of thermoplastic resins
1.Flexible RPD
2.Tooth colored clasps
3.Preformed RPD clasps
4.Flexite-metal combination
5.Obturators
6.Impression tray
7.Provisional crowns and bridges
8.Orthodontic brackets
9.TMJ’s, bruxism & anti-snoring devices
10.Sports mouth guards

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Notes
Conventional acrylic resin (PMMA): 1930
Nylon denture base: 1955
Teflon (thermoplastic fluoropolymer) e.gFlexite: 1962
Acetal thermoplastic resin: 1971
Acetal resin tooth-colored clasps: 1986, & entire RPD: early 1990s
Nylon preformed tooth-colored clasps (Clasp-Eze): 1992
Pro-flex: 1998

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