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By

Ahmed Mostafa Hussein

Assisstant lecturer

Dental Biomaterial Department

Faculty of Dentistry, Mansoura University

2013

FLEXIBLE DENTURE

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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

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Indications of nylon flexible denture

Contraindications of nylon flexible denture

Main composition

Manipulation

Commercial products

Uses of thermoplastic resins

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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

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7 .High water sorption

8 .Dimensional changes and polymerization shrinkage

9. There are many factors in the laboratory procedure

that can lead to alteration of denture occlusion and

results in significant increase in vertical dimension

after processing.

10. Denture wearers use dentures adhesive which

causes its own problems.

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VALPLAST FLEXIBLE DENTURE BASE

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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.

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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.

9. Less bulky (thinner) and lighter weight

10 .Better chewing efficiency

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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.

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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.

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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.

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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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Controversial and/or need more research

اّد�عاء – : Claimed to have.1يّد�عى

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

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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 such as ectodermal dysplasia.

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Contraindications of nylon flexible denture

1 .Unilateral distal extension

2 .Low vertical dimension and closed bite

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Nylon flexible denture Conventional rigid acrylic denture

Not brittleClinically unbreakable

Brittleness of PMMA, so frequent fracture occurs

Good biocompatibility: because it is free of monomer and metal

Allergy to MMA monomer

More comfortable, not irritant to mucosa

Irritation of mucosa

Soft and inherent flexibilityAbility to engage undercuts for retention

RigidDifficult to insert in undercut areas

Better esthetics, esthetic clasp Less esthetics, metal claspShorter fabrication time Longer fabricaion time

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Nylon flexible denture Conventional rigid acrylic denture

Temporary only PermanentMechanical retention between acrylic teeth and nylon denture.De-bonding is a major disadvantage.

Chemical bond between acrylic teeth and acrylic denture

Lower hardness Higher hardnessHigh surface roughness.Brushing increases surface roughnessUsually cannot be relined and repaired

Can be relined and repaired

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Main composition

Polyamide nylon thermoplastic material

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Manipulation

Injection molding technique:

It is highly sensitive to the position and size of sprue

placement.

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1. Investing in a special flask (e.g valplast 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.

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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.

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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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FLEXIBLE DENTURE INJECTION SYSTEM

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INJECTION CASTING PROCEDURE

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FLEXIBLE DENTURE RETRIEVED

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Commercial products

Valplast, Flexiplast, Duraflex, Impak, Lucitone FRS,

Flexite, Flexite M.P., Flexite Plus, Sunflex and Proflex.

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1.Valplast (Valplast Int. Corp. - USA)

Nylon polyamide thermoplastic.

Light weight

Monomer free

 

 

2.Flexiplast (Bredent - Germay)

Nylon polyamide

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3.Lucitone FRS (DENTSPLY Trubyte, New York, PA, USA)

Nylon linear polyamide

Monomer free

 

4.Flexite

Thermoplastic fluoropolymer (Teflon) 1962

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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 .

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7.Sunflex

Nylon thermoplastic

Tissue-colored clasps

More stain-resistant than other flexible acrylics.

Can be relined & repaired.

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8.Pro-flex

Full and partial flexible denture since 1998.

Can be repaired.

Can be relined using Pro-flex soft liner material.

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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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Comparison between:

Acrylic soft liner (soft acrylic resin e.g Vertex)

Nylon flexible denture (e.g Valplast)

FOR RESEARCH

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الله ) رسول وسلم قال عليه الله (صلى :

نافعا لما ع* الله لوا س+

ينفع ال ع*لم من بالله تعو�ذوا و

الجامع : صحيح ، حسن 3635إسناّده

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References

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of the hardness of flexible denture base resins: original

study. Health Sci 2012; 1: 1–8.

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