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12 TPDI • January and July 2019, Vol. 10, No. 1 & 2
A study on flexible dentures
soon it has become an alternative to fabricate RPDs that
do not contain metallic elements. Since 2007, a number
of thermoplastic resins were made available in the market
exclusive for RPD fabrication.5, 6. Some of the commer-
cially available products are Valplast, Sunex, Duraex,
Flexite, Proex, Lucitone, and Impak. Valplast, Sunex
and Lucitone are monomer free. Presently available ex-
ible materials are listed below.
Table I. Flexible resins
Generic Name Product Name
Polyamide Valplast
Flexiplast
Flexite
Flexite plus
Sunex
Leucitone FRS
Ultimate
Polyester Estheshot bright
Estheshot
Polycarbonate Reigning N
Reigning
Acrylic resin Acrytone
Polypropylene Unigum
Revuru Pradusha
Post graduate student, Department of Prosthodontics,
Vishnu Dental College,Bhimavaram
M.C. Suresh Sajjan
Professor of Prosthodontics and Principal, Vishnu Dental
College,Bhimavaram
A.V. Ramaraju
Professor of Prosthodontics and Vice Principal,
Vishnu Dental College,Bhimavaram
Bheemalingeswara Rao D.
Professor, Department of Prosthodontics,
Vishnu Dental College,Bhimavaram
K. Chandrasekharan Nair
Scopus Author ID 51564168300
Professor Emeritus,
Department of Prosthodontics,
Vishnu Dental College,Bhimavaram
Address for correspondence: Dr. Revuru Pradusha
Postgraduate Student, Department of Prosthodontics,
Vishnu Dental College, Bhimavaram
Email: pradusha09@gmail.com
Accepted: 30/05/2019
Edentulism is an indicator of oral health. More than
70% of Indian population especially the rural population
suffers partial edentulism which is an alarming situation
because of the limited facilities available in rural areas.
Partially edentulous situations can be treated with differ-
ent options viz. removable dentures, xed dentures and
dental implant supported. Support status of abutment
teeth, duration of edentulousness, general health prole
and patient’s affordability are major inuencing factors
that decide the treatment in partial edentulism1,2. Remov-
able dentures always had unquestionable popularity in
India because of the affordability acceptable to most of
the socioeconomic classes3,4. Conventional RPD designs
with metallic retainers, especially those appearing in the
aesthetic zone has been the primary deterrent to many
patients in accepting removable dentures. Attachments
have high aesthetic quotient but the technique sensitivity
and the necessity of large quantity of tooth tissue loss
has reduced the popularity. Common man’s partial den-
ture is acrylic based but its mechanical properties pose
a limitation for long term use.
Era of exible dentures was ushered in ever since
the introduction polyamide resin (nylon) in 1950’s. Very
TPDI • January & July 2019, Vol. 10, No. 1 & 2 13
A study on flexible dentures
Some of the advantages and disadvantages of these
materials are mentioned below6, 7, 8.
Advantages
• Denture wearers, both men and women, are highly
concerned about the aesthetic appearance. With
exible dentures it is possible for the retentive parts
to actively utilize a vital tooth, increasing the op-
portunities for both patients and dentists to choose
RPDs.
• More acceptable aesthetics, since there are no metal
clasps.
• Translucency of the material picks up underlying
tissue tones, making it almost impossible to distin-
guish in the mouth.
• The material is exceptionally strong and exible.
Free movement is allowed by the overall exibility.
Therefore, even if there is a little bit of bending, it
comes back to the original shape and position.
• The resins currently in use have a lower elastic
modulus and a softer surface compared with acrylic
resin9, 10, meaning that patients feel better when
worn. There also appears to be no problem with t.
As there is a low risk of breakage of dentures which
are highly elastic and not at all rigid, the denture base
can be made thinner. This makes them lighter and
thinner than RPDs using an acrylic resin or metal
framework to ensure rigidity.
• Ease of insertion in the mouth with alveolar under-
cuts because of the exibility.
• Complete biocompatibility is achieved because the
material is free of monomer and metal, these being
the principal causes of allergic reactions in conven-
tional denture materials11.
• Flexible dentures will not cause sore spots due to
negative reaction to acrylic resins and will absorb
small amounts of water to make the denture more
soft tissue compatible.
• There is very limited need of modication of the
remaining teeth to receive occlusal rests as in the
case of metallic clasps.
• Rebasing (Changing the entire plastic / tissue area
except the acrylic teeth) is possible.
• A real boon for patients with compromised oral
conditions anomalies such as ectodermal dysplasia.
Disadvantages
• Flexible dentures tend to absorb water content and
tend to discolour very often12.
• Surface roughening after a few months of denture
delivery was identied. As the surface is not as hard
as that of acrylic resin, the depths and the widths
of marks were greater than in the acrylic resins by
the scratch test, thus the polished surface loses its
lusture.
• Debonding of acrylic teeth from nylon denture base
since teeth in these exible dentures are bonded
mechanically (diatorics) and not chemically.
• It does not conduct heat and cold like metal.
• The resin clasp covers the cervical area of the abut-
ment teeth over a wide area on both the crown and
root sides, being designed to be part of the gingiva.
This means that the area covered by the resin clasp
is large, and the undercut and relief regions may
easily become dead space, with the risk of exacer-
bating periodontal conditions. Meticulous cleaning
is therefore essential.
• Breakage of retentive elements from denture is not
uncommon.
• Mobile teeth are not splinted by exible dentures.
• The laboratory charges are on the higher side.
• Flexible denture is very hard to repair if fractured.
No additions can be made onto it. In such cases,
rebasing is recommended.
• Lacks important elements of conventional RPD like
occlusal rests and rigid framework hence transmis-
sion of functional load is not very efcient.
• Difculty in polishing.
• Requires more chair-side time for adjustment.
• Requires special instruments (knives and polishing
kit) to make the adjustment.
• When grinding this prosthesis, proper ventilation,
masks and vacuum systems should be used and the
procedure is technique sensitive.
• Extreme caution is necessary when processing to
avoid skin contact with the heated sleeve, cartridge,
furnace, heating bay, hot cartridge, injection insert,
piston head adapter, hot asks, and heat lamps.
14 TPDI • January and July 2019, Vol. 10, No. 1 & 2
Revuru Pradusha
Indications
• In every partially edentulous situation.
• They utilize the undercuts in the ridge for retention
so it is indicated in ridges where bilateral undercuts
are present and where pre-prosthetic surgery is
contraindicated.
• The unique physical properties of the material also
make it more adaptable in challenging cases and
situations involving paediatric patients, cancerous
mouths and cleft palates.
• A patient with systemic sclerosis and microstomia.
• Because of its excellent biocompatibility, it is also
an ideal replacement for acrylic when patients are
allergic to denture acrylics.
• Flexible partials could be a treatment of choice in
cases of patients having a history of repeated partial
denture frame breakage.
• They can also be used as an easy and affordable
alternative to implants or xed partial dentures
• Flexible Partials are ideal for people in high-risk
situations like: Athletes, Police and Fire-ghters,
Military Personnel, Prison Ofcers, Any person who
might be exposed to physical harm or injury etc.
Additional applications of Flexible denture material include:
o Cosmetic gum veneers
o Bruxism appliances
o Implant retained over-dentures and full dentures for
patients with protuberant bony structures or large
undercuts
o Unilateral Space Maintainers
o Temporary Prostheses (short and long-term)
o Obturators and speech therapy appliances
o Orthodontic Devices
o Occlusal splints and sleep apnea appliances
o Anatomical bite restorer (Used during full mouth
rehabilitations)
Contraindications
• Inter-arch space (<4mm space for placement of
teeth), prominent residual ridges where there is less
space for placement of teeth.
• Flat abby ridges with poor soft tissue support
which require more rigid prosthesis.
• Deep overbites (4mm or more) where anterior teeth
can be dislodged in excursive movements
• Little remaining dentition with minimal undercuts
for retention.
• Bilateral free-end distal extensions with knife edge
ridges or lingual tori in the mandible7.
• Bilateral free-end distal extension on maxilla with
extremely atrophied alveolar ridges.
Flexible dentures vs cast partial dentures(Table 2,3)
Table 2: Comparison between exible and cast partial dentures
Flexible dentures Cast partial den-
tures (CPD)
Time period for
preparation
Less time Time consuming
Cost Less expensive
compared to CPD
More expensive
Weight Light weight heavier
Aesthetics Highly aesthetic Unaesthetic due
to metal clasps
Clasps Nylon clasps Metal clasps
Occlusal rest No preparation
required
Preparation re-
quired
Table 3. Comparison between Flexible dentures and Acrylic
dentures
Flexible dentures Acrylic dentures
Bilateral under-
cuts
Can be used Cannot be used
Easiness of
fracture
Wont fracture
easily
Fracture easily
Biocompat-
ibility
Excellent biocom-
patible
In some patients
allergic reactions
due to presence of
monomer
Lab procedures More stable Less stable
Comfort More comfort Less comfort
Irritation to
mucosa
No irritation irritant
Bonding of
teeth to denture
Mechanical bond-
ing
Chemical bonding
Hardness Less Higher hardness
Repair or reline Can’t be relined or
repaired
Can be relined or
repaired
TPDI • January & July 2019, Vol. 10, No. 1 & 2 15
A study on flexible dentures
The thermoplastic nylons are translucent material that al-
low the underlying tissue to be seen resulting in excellent
aesthetics and there are no metal clasps at all. Clasps are
also made up of thermoplastic nylons. So clasps can be
given on canines without compromising aesthetics which
is not possible in cast partial dentures. Flexible dentures
exhibit viscoelastic behaviour that lead to improvement
in masticatory function and patient’s comfort compared
with hard dentures. Flexible removable partial dentures
can adapt to the shape and movement of mouth and for
this reason, these are far more comfortable to wear. In
a study13, conducted by Singh et al about the preference
among the two types of denture base material; exible
dentures versus conventional acrylic, 100% patients
Fig 1a.Flexible dentures Fig 1b. Flexible denture
Fig 1c. Flexible denture Fig 1d.Flexible denture Fig 1d.Flexible denture
Fig 2.Valplast denture Fig 2a.Valplast denture Fig 2b.Valplast denture
Fig 3. Acetal resin clasp Fig 4. Sunflex denture
16 TPDI • January and July 2019, Vol. 10, No. 1 & 2
preferred the exible dentures over customary methyl
methacrylate dentures.
Material and its properties:
Thermoplastic resins which become pliable or
mouldable above a specic temperature and return to a
solid state upon cooling are used for the fabrication of
exible dentures. There are different kinds of thermo-
plastic resins available viz.
• Polyamide
• Acetal
• Polyesters
• Polycarbonate
• Polypropylene
• Acrylic
Polyamide
Polyamide resin was proposed as a denture base ma-
terial in the 1950s. Nylon is a generic name for polyam-
ides. These polyamides are produced by the condensation
reactions between a diamine and a dibasic acid. Nylon
is a crystalline polymer, whereas PMMA is amorphous.
This crystalline effect accounts for the lack of solubility
of nylon in solvents, as well as high heat resistance and
high strength coupled with ductility, higher elasticity than
common heat polymerizing resins, toxicological safety
for patients with resin monomer and metal allergy16,17.
Valplast (Fig 2)
Valplast is a pressure-injected, flexible denture
base resin that is ideal for partial dentures and unilateral
restorations. The resin is a biocompatible nylon ther-
moplastic with unique physical and esthetic properties.
Valplast is chemically a polyamide resin with 99.9% of
polylaur- olactam
Properties:
• It has lower elastic modulus than acrylic resins
• Its exural strength and exural modulus are 1/3rd
higher than that of acrylic resins
• It is soft, easily deformable, and elastic.
• Its high amount of exion means it is unlikely to
fracture.
• It has lower specic gravity
• Its excellent elasticity means it can be used even in
abutment teeth with a large undercut.
Availability:
• Available in three basic shade categories (medium
pink, light pink and meharry). Valplast is uniquely
formulated to allow patient’s natural It easily blends
in with the colour of the gums, giving it the aesthetic
advantage that the border between base and gums
is difcult to distinguish.
Advantages
• It can be used to make thinner denture bases than
those possible with acrylic resins minimizing dis-
comfort when dentures are worn.
• It possesses sufcient strength and elasticity not to
fracture even under the application of maximum
stress
• It has no risk of allergy, and is highly resistant to
both acids and alkalis. There is almost no change
in its surface roughness even after immersion in
glutaraldehyde or sodium hypochlorite.
• It may also be used to provide retention when insert-
ing a denture base into the undercut of the residual
ridge.
• The material is a specialized form of nylon in the
family of superpolymides (a very pure nylon) that
will not deteriorate chemically when it comes into
contact with the uids, bacteria, and physical envi-
ronment of the mouth.
Disadvantages:
• Its surface is easily damaged and the polished surface
gradually loses its lusture thought limited repolishing
is a possibility.
• It does not bond to acrylic resins and hence reline
and repair are difcult to carry out at the chair side.
This problem has reportedly been addressed by
methods such as the use of resin repair materials
or treating the surface with 4-META/MMA-TBB
resin after sandblasting to enable bonding to acrylic
resins.
Indications:
• It is the most suitable for patients with intermediary
defect of 1–2 incisors that require only a retentive
area and a minimalized denture base.
Revuru Pradusha
TPDI • January & July 2019, Vol. 10, No. 1 & 2 17
A study on flexible dentures
• It may also be used for patients with intermediary
defect of molars.
• The low elastic modulus of Valplast means that
dentures are lacking in rigidity, but this can be
overcome by using it in combination with a metal
framework.
Lucitone FRS exible denture resin
Designed for use with injection System. Lucitone
FRS Flexible Denture Resin is a temporary thermoplastic
injectable resin that offers customizable exibility, high-
impact resistance and transparency, delivering aesthetic
removable partial dentures and clear or colored clasps.
Lucitone FRS enables dental laboratories to provide a
range of exibility from a rmer more resilient design
(2mm thickness) all the way to a super exible partial
(1.5mm thickness) for an individualized restoration.
This is made of semi-crystalline nylon composition for
improved color stability and stain resistance. It is easy to
nish and polish due to the microcrystalline structure. It
is monomer free and non-irritating. Available in Original,
Light Pink, Light Reddish Pink, Dark Pink and Clear
shades. Clear shade is used for fabrication of clear clasps,
occlusal splints, and night guards.
Acetalresins (Fig 3)
Acetal as a homo-polymer has good mechanical
properties, but as a co-polymer has better long-term
stability. Acetal resin is very strong, resists wear and
fracturing, and is quite exible18. These characteristics
make it an ideal material for pre-formed clasps for par-
tial dentures, unilateral partial dentures, partial denture
frameworks, provisional bridges, occlusal splints, and
even implant abutments. Acetal resins resist occlusal wear
and are well suited for maintaining vertical dimension
during provisional restorative therapy.
While stronger, Acetal does not have the natural
translucency and vitality of thermoplastic acrylic and
polycarbonate, and these materials might offer better
results for short-term temporary restorations.
Polyesters
There are two types of polyester material Esthe Shot
and Estheshot bright. According to the manufacturer’s
published gures, EstheShot Bright has a exural modu-
lus of 1490 MPa, close to that of polyamides, making it
softer yet with an impact resistance eight times greater
than that of EstheShot One important characteristic of
polyesters is that they bond well to self-curing resins.
This means that repair, adding lost teeth, and reline can
be performed at the chair side. EstheShot is a polyester
resin that has polyethylene terephthalate copolymer as
its main ingredient
Esthe Shot Bright has lower exural modulus than
Esthe-Shot, and has been developed as a novel polyester
resin that combines strength and exibility. Both have
outstanding safety, esthetic appearance, and functional-
ity. Shear bond strength tests comparing EstheShot and
acrylic resins have shown that this product has higher
bond strength than polyamide, polycarbonate, or acetyl
resins. This is regarded as the most important advantage
of Esthe-Shot, and in practice it can be easily repaired
with self-curing resins. Fitting tests also indicated better
results than polyamide or polycarbonate resins. In clinical
practice, it is easier easier to polish the polyester dentures.
Polycarbonates
Polycarbonates have superior exural strength and
exural moduli which are higher than those of poly-
amides and polyesters. According to the manufacturer’s
published gures, JET CARBO-S® and Reigning N®
have lower elastic moduli and can be used effectively in
patients with large undercuts. Fracture risk is seldom
reported and the material has high impact resistance.
Although their t is poorer than EstheShot®, it is better
than Valplast®. Their bonding to self-curing resins is
around the same level as that of acrylic resins. The color
change when exposed to heavily coloured food materials
is observed to be similar to acrylic resins.19
Acrylic resin
ACRY TONE is the only acrylic resin currently
used for exible dentures. This product uses an acrylic
resin that is much softer than other thermoplastic resins.
Sunex (Fig 4)
Sunex Partial Dentures are made from a strong
biocompatible nylon thermoplastic, and are unbreakable,
yet lightweight and translucent which allows natural tis-
sue to show through. The sunex exible denture base
18 TPDI • January and July 2019, Vol. 10, No. 1 & 2
materials are virtually Invisible, unbreakable, metal free,
lightweight and comfortable to wear20.
Proex
Pro-ex is a exible denture base material which
can be used for complete and partial dentures. Pickett
Dental Laboratory has been offering Pro-ex full and
partial exible dentures since 1998. This can engage
undercuts effectively. It is hypo-allergenic and hence
recommended for patients with known acrylic or metal
sensitivities. Aesthetically the material is semi translu-
cent, allowing the prosthesis to blend with natural gum
tissue. Proex full and partial exible dentures are easily
adjusted by the dentist. Simply warm the denture with
running water to bring it up to body temperature before
inserting it. It can engage undercuts and hold the teeth
under masticatory load.
Biodentplast (Bredent)
It is a semi-crystalline thermoplastic material with
a linear structure characterized by high crystallinity. The
material shows good physical and chemical properties
such as increased hardness, tensile strength, and good
dimensional stability. The high rigidity and full restoring
capacity of Bio Dentaplast allows usage of the material
for a wide indication range. Classic indications recom-
mended by bredent are:
• clasp free partial dentures
• tooth coloured clasps
• temporary (max. 2 years) crowns and bridges
• tooth-coloured occlusal appliances
Manipulation and Design
a. The laboratory manipulation of these thermo-
plastic materials is done by injection moulding technique.
Figure 5.1 Continous Circumferential clasp Figure 5.2 Circumferential clasp for a mesially-tip tipped distal molar
Figure 5.3 Combination clasp Figure 5.4 circumferential clasp
Revuru Pradusha
TPDI • January & July 2019, Vol. 10, No. 1 & 2 19
Acrylic teeth do not bond chemically with the thermo-
plastic nylon so diatorics are prepared. Clasps are also
made up of exible thermoplastic material with excellent
esthetics. Different clasp designs that are used area.
continuous circumferential clasp (Fig.3.1) b. Circumfer-
ential clasp for a mesially-tipped distal molar (Fig.3.2) c.
Combination clasp (Fig.3.3) and d. Circumferential clasp
(Fig.3.4)14
Flexible dentures have challenged the basic prin-
ciples of conventional designs. However constant im-
provements on the properties of exible resins might
improve the acceptability.
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A study on flexible dentures
