This document discusses and compares the advantages and disadvantages of various types of removable partial dentures (RPDs), including cast metal RPDs, conventional rigid acrylic RPDs, and nylon flexible dentures. It provides details on the composition, manipulation, and commercial products of nylon flexible dentures. While flexible dentures are more comfortable and esthetic than other options, they also have limitations such as being intended only for temporary use, difficulty in repairing or relining, and lack of occlusal rests. The document analyzes factors to consider when selecting between RPD materials based on a patient's needs and dental situation.

1. By
Ahmed Mostafa Hussein
Assisstant lecturer
Dental Biomaterial Department
Faculty of Dentistry, Mansoura University
2013
1

2. 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
2

3. Indications of nylon flexible denture
Contraindications of nylon flexible denture
Main composition
Manipulation
Commercial products
Uses of thermoplastic resins
3

4. 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
4

5. 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
5

6. 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.
6

7. 7

8. 8

9. 9

10. 10

11. 11

12. Advantages of nylon flexible denture (1955)
:Soft and inherent flexibility.1
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.
12

13. 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
13

14. : Translucent, so it allows naturalBetter esthetics.11
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)
14

15. 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.
15

16. 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.
16

17. 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.
17

18. 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.
18

19. 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.
19

20. Controversial and/or need more research
–:Claimed to have.1
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
20

21. 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.
21

22. Contraindications of nylon flexible denture
1. Unilateral distal extension
2. Low vertical dimension and closed bite
22

23. Nylon flexible dentureConventional rigid acrylic
denture
Not brittle
Clinically 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 flexibility
Ability to engage undercuts for
retention
Rigid
Difficult to insert in undercut
areas
Better esthetics, esthetic claspLess esthetics, metal clasp
Shorter fabrication timeLonger fabricaion time
23

24. Nylon flexible dentureConventional rigid acrylic
denture
Temporary onlyPermanent
Mechanical retention between
acrylic teeth and nylon
denture.
De-bonding is a major
disadvantage.
Chemical bond between acrylic
teeth and acrylic denture
Lower hardnessHigher hardness
High surface roughness.
Brushing increases surface
roughness
Usually cannot be relined and
repaired
Can be relined and repaired
24

25. Main composition
Polyamide nylon thermoplastic material
25

26. Manipulation
Injection molding technique:
It is highly sensitive to the position and size of sprue
placement.
26

27. 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.
27

28. 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.
28

29. 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.
29

30. 30

31. 31

32. 32

33. Commercial products
Valplast, Flexiplast, Duraflex, Impak, Lucitone FRS,
Flexite, Flexite M.P., Flexite Plus, Sunflex and Proflex.
33

34. 1.Valplast (Valplast Int. Corp. - USA)
Nylon polyamide thermoplastic.
Light weight
Monomer free
2.Flexiplast (Bredent - Germay)
Nylon polyamide
34

35. 3.Lucitone FRS (DENTSPLY Trubyte, New York, PA,
USA)
Nylon linear polyamide
Monomer free
4.Flexite
Thermoplastic fluoropolymer (Teflon) 1962
35

36. 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.
36

37. 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.
37

38. 7.Sunflex
Nylon thermoplastic
Tissue-colored clasps
More stain-resistant than other flexible acrylics.
Can be relined & repaired.
38

39. 8.Pro-flex
Full and partial flexible denture since 1998.
Can be repaired.
Can be relined using Pro-flex soft liner material.
39

40. 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
40

41. 41

42. 42

43. 43

44. 44

45. Comparison between:
Acrylic soft liner (soft acrylic resin e.g Vertex)
Nylon flexible denture (e.g Valplast)
45

46. 46

47. References
Kaira LS, Dayakara HR, Singh R. Flexible denture for
partially edentulous arches – A case report.
www.journalofdentofacialsciences.com 2012; 1: 39–42.
Arafa KA. Evaluation the physical properties between
flexible, cold-cued and hard heat-cured acrylic resin (in
vitro study). Life Sci J 2012; 9: 1707–10.
Gladstone S, Sudeep S, Arum Kumar G. An evaluation
of the hardness of flexible denture base resins: original
study. Health Sci 2012; 1: 1–8.
47

48. Ito M, Miyamoto T, Kawai Y. The combination of a nylon
and traditional partial removable dental prosthesis for
improved esthetics: a clinical report. J Prosthet Dent
2013; 109: 5–8.
Hundal CM, Madan BR. Comparative clinical evaluation
of removable partial dentures made of two different
materials in Kennedy Applegate class II partially
edentulous situation. MJAFI 2012; 1–7.
Yavuz T, Aykent F. Temporary flexible removable partial
denture: a clinical report. Clinical Dentistry and
Research 2012; 36: 41–4.
48

49. Singh JP, Dhiman RK, Bedi RPS, Girish SH. Flexible
denture base material: a viable alternative to
conventional acrylic denture base material. Contemp
Clin Dent 2011; 2: 313–7.
Dhiman CR, Chowdhury LCSR. Midline fractures in
single maxillary complete acrylic vs flexible dentures:
original article. MJAFI 2009; 65: 141–5.
Negrutiu M, Sinescu C, Romanu M, Pop D, Lakatos S.
Thermoplastic resins for flexible framework removable
partial dentures: review articles. TMJ 2005; 55: 295–9.
49

50. Shamnur SN, Jagadeesh KN, Kalavathi SD, Kashinath
KR. Flexible dentures – an alternate for rigid dentures.
Journal of Dental Sciences & Research; 1: 74–9.
50