Evolution of denture base materials and reveiw of current ones

Timelines in the Development
of Denture Base Materials and
a Review of Current Ones
Dr. Silas M. Toka
MDS I (PROS)
12th November, 2015

Introduction
• The earliest complete upper and lower denture appear
to date from circa 1500 and was dug up in Switzerland
(Rath 1958).
• It consists of two arch shaped templates of bone,
crudely carved from an ox’s femur and tied together at
their posterior extremities to form a hinge.
• There are no bases as such and retention must have
been from the remaining natural teeth.
• Highly likely the prosthesis must have been cosmetic
rather than functional.

Historic Finds
• Dentures carved from wood and ivory are claimed to
have been discovered by Belzoni in Egyptian tombs,
but no proof of any of these discoveries exists (Guerini
1909, Ambler 1909).
• Guerini and Ambler quoted the Roman poet Martial
(80AD), to support the view that complete dentures
were provided in ancient Rome.
• Ambler (1906) stated that a complete set of false teeth,
fabricated in gold, was found in a Roman tomb a few
years before his writing (an unsubstantiated report).

Historic Finds
• The fabrication of a denture was first described by
Purmann in 1684 (Guerini 1909).
• A lump of wax was partly carved, and partly moulded
to the desired shape and contour, so that it reproduced
the missing teeth, fitted snugly against those
remaining, and adapted to the palate and residual
alveolar ridge.
• This model was then used by a craftsman for
reproduction in bone or ivory.

Historic Finds
• However, such a denture is unlikely to have derived its
retention from a denture base, as a large wax pattern
would have been impossible to withdraw from the
mouth without distortion.
• The pattern was therefore kept as small as was
reasonably possible.
• Springs were introduced as means of retention most
probably by Fauchard (1728), but these dentures
probably caused soft tissue injuries and were not
functionally optimum.

Complete Denture Impression
• What was yet to be appreciated, was that a broad
denture base to distribute occlusal loads, and one
which, by its extension, would also assist in stability
and retention.
• According to Guerini (1909), Frederick the Great’s
dentist, Philip Pfaff (1756), developed a more effective
way of impression taking.
• His method was to take a wax impression of the entire
jaw in two separate pieces, which are re-assembled
outside the mouth to make a plaster cast.

Complete Denture Ivory Bases
• With a reasonably accurate, dimensionally stable cast,
the carver proceeded to fabricate an ivory denture
without frequent recourse to the patient.
• To give the denture a more lifelike appearance, human
teeth were added to the front on the ivory base
(Guerini 1909, Ash 1920, Woodforde 1968).
• Both ivory and human teeth however, deteriorated in
the mouth.

Complete Denture Ivory Bases
A letter of 1798 to George
Washington from his dentist,
contained detailed advice on
countering the stains and for
plugging holes in the President’s
dentures.
The dentist seemed
to believe that the
stains were coming
from portwine and
“other acids”
(Woodforde 1968).

Complete Denture Porcelain Bases
• Alexis Duchateau, a French apothecary wore
hippopotamus ivory dentures that had become stained
due to occupational repercussions.
• He succeeded in fabricating a denture made of
porcelain in one piece, both the base and the teeth,
after partnering up with Paris Dentist, Dubois de
Chémant.
• Duchateau’ s efforts were acknowledged by the Royal
Academy of Surgeons, Paris, in 1776, despite the fact
that he was never able to fabricate a similar denture
for anyone else.

Complete Denture Porcelain Bases
• Meanwhile, Dubois de Chémant perfected the
porcelain technique.
• By 1804, he claimed that 12,000 of his sets were in
use, denoting a wide patient acceptability of his
methods.
• However, his methods were not reproducible by other
dentists, given the unpredictable shrinkage of
porcelain during firing.
• Porcelain was however found to be ideal for making
individual teeth separate from the base (Ash1920,
Bremner1954).

Complete Denture Vulcanite Bases
• By 1814, porcelain bases had fallen out of favour
(Bremner1954).
• Greater accuracy could be achieved by hand carving of
ivory.
• Vulcanite was discovered by Charles Goodyear in 1839
and he was granted a patent for using it as a denture
base material in 1855 (Lufkin1948).
• Ivory bases however still continued to be favoured
even after the discovery of vulcanite.

• Vulcanite is the product of vulcanization of rubber to
yield very hard rubber.
• The occurring reaction is basically addition of sulfur at
the double bonds, forming intramoleculer ring
structures, so a large portion of the sulfur is
highly cross-linked in the form of intramoleculer
addition.
• High sulphur content up to 40% may be used for
greatest resistance to swelling and minimal dielectric
loss.

• Vulcanite had advantages over all other materials then
available despite its largest drawback of poor taste and
smell because of its sulphur component.
• However, it was cheap and could easily be adapted to a
cast of the mouth.
• It could accurately reproduce the dimensions and
surface details of the cast when cured.
• Ash (1920) reports that after 1868, vulcanite dentures
became the order of the day and a property of the
multitude.

• Vulcanite gained popularity when plaster became
available as an impression material in the mid 19th
century.
• Up to then, only wax had been used.
• Plaster now offered a reliable impression technique,
vulcanite: a cheap and accurate base material, and
porcelain: realistic and durable teeth.
• And when in 1844, Wells discovered nitrous oxide as
an inhalational anaesthetic, extractions were now
more tolerable and patients could seek denture care.

• Vulcanite however, despite being a considerable
improvement from other denture base materials was
still not readily available to all.
• It was protected by patents and dentists had to pay
royalties to use it, with whoever it was that infringed
on the laws, being ruthlessly prosecuted.
• Alternative materials were thus still being sought.
• Tin and aluminium were tried but none superseded
the properties of vulcanite, despite the fact that
vulcanite was sometimes porous, absorbent, opaque
and lifeless in appearance (Miner1973).

• Vulcanite use intensified after 1879, when, on Easter
Sunday, an irate dentist, Dr. Samuel Chalfant DDS,
murdered Josiah Bacon, the treasurer of the Goodyear
Dental Vulcanite Company, who had been the patent
enforcer (Woodforde1968).
• Vulcanite became the
standard denture base
material after the patent
expired.

Complete Denture Gold Bases
• Before the advent of vulcanite, the other principal
material present was gold, which was both
intrinsically expensive and demanding of lengthy and
skilled technique.
• Richardson described the process of swaging gold
dentures and attaching teeth on them.
• It is expected in all likelihood that both gold and ivory
dentures were for the very rich.
• Corbett in 1888 pointed out that it took 6 weeks to
make ivory denture bases with natural teeth.

Wood and Gutta Percha Denture Bases
• Attempts were made to carve cheap dentures from
wood, which was easily worked but was unaesthetic
and subject to rapid fouling in the mouth.
• Gutta percha was also tried but was not durable.

Celluloid Denture Bases
• Invented in 1868 by Hyatt.
• Employed from about 1890 as a denture base material
(Peyton 1975).
• Its colour was better than vulcanite but the need to use
camphor as a plasticizer gave it an unpleasant taste
and odour.
• It also lacked dimensional stability tending to distort
in service, and so whatever popularity it enjoyed was
brief.

Celluloid Denture Bases
• Celluloid marked the introduction of plastics whose
history dates from 1832, when Braccanot developed
Xyloidine from starch cotton and wood fibres
(Schwartz 1950).
• Various other modifications of cellulose nitrate were
found wanting because of poor dimensional stability.
• Cellulose was however a precursor to inventions of
materials better than vulcanite.

Bakelite Denture Bases
• A phenol-formaldehyde resin discovered in 1909.
• By 1924, such resins were being produced
commercially, and between then and 1939, as many as
fifteen products of this kind were introduced in
dentistry.
• They were technique sensitive and quality control was
difficult, with wide variations in colour, dimensional
stability, and strength, dependent on processing
conditions (Sweeney 1939).

Methacrylate Denture Bases
• In 1901, Rohm produced commercial products of
acrylic acid.
• There is a conflict in dates but consensus seems to
suggest the following:
1. 1935: First appearance of acrylics for dental use.
2. 1936: Polymethyl methacrylate (PMMA) in the form
of transparent sheet introduced by Rohm and Haas
(Schwartz 1950).
3. 1937: Sheet and powder PMMA introduced by Du
Pont De Nemours.

• In 1937, Vernonite, a methacrylate acrylic resin was
clinically evaluated by Wright (Peyton 1975), and was
found to fulfill virtually all the requirements of an
ideal denture base material.
• By 1945, it was estimated that 95% of all dentures
were constructed of methacrylate polymers with
porcelain teeth (Peyton 1975).

• PMMA denture bases initially presented with
difficulties in accurate processing, encouraging a brief
stint of use of metals and “mucostatic techniques”
(Bohannan 1954).
• However, PMMA had too many obvious advantages
and the early problems were soon overcome.

Positive Traits of PMMA
1. It has good stable colour which can be made to
correspond to either the gingiva or the teeth.
2. It is inert and translucent.
3. PMMA chemically bonds to teeth that are very life-
like also made of PMMA.
4. It is robust.
5. Can be simply repaired or added to.
6. Is inexpensive.

• Pure poly(methyl methacrylate) is a colorless,
transparent solid.
• To facilitate its use in dental applications, the polymer
may be tinted to provide almost any shade and degree
of translucency.
• Its colour and optical properties remain stable under
normal intraoral conditions, and its physical
properties have proven adequate for dental
applications.

PMMA Presentation
• Poly(methyl methacrylate) denture base material
usually is supplied as a powder-liquid system.
• The liquid contains nonpolymerized methyl
methacrylate.
• The powder contains prepolymerized poly(methyl
methacrylate) resin in the form of small beads.
• When the liquid and powder are mixed in the proper
proportions, a workable mass is formed.
• Subsequently, the material is introduced into a mold
cavity of the desired shape and polymerized.

Synonyms: Record Base, Base Plate

Definition
• A record base or base plate is a temporary form
representing the base of a denture.
• It is used in recording maxillo-mandibular
relations and in the arrangement of the teeth.

Requirements
• Should be rigid.
• Should be accurate.
• Should be dimensionally stable.
• The borders should be round and smooth as the
borders of finished dentures.
• Should be thin at the crest, labial and buccal
slopes to provide space for tooth arrangement.

Types
TEMPORARY RECORD BASES
• They are discarded and replaced by denture base
material, once their role in establishing jaw
relation, teeth arrangement and try in is
complete.
PERMANENT RECORD BASES
• They are not discarded and become part of the
actual base of the finished complete denture.

Types of Temporary Record Bases
• Shellac base plate
• Reinforced shellac base plate
• Cold cure acrylic resin
• Visible light cure acrylic resin
• Vacuum formed vinyl and polystyrene
• Base plate wax

Types of Permanent Record Bases
• Heat cure acrylic resin
• Gold
• Chromium-cobalt alloy
• Chromium-nickel alloy

COLD CURE ACRYLIC RESINS
• Heat and microwave energy may be used to induce
denture base polymerization.
• The application of thermal energy leads to
decomposition of benzoyl peroxide, and the
production of free radicals.
• The free radicals formed as a result of this process
initiate polymerization.
• Chemical activators also may be used to induce
denture base polymerization.

Composition of Cold Cured PMMA
• Chemical activation is completed at room temperature.
• They are also referred to as cold-curing, self-curing, or
autopolymerizing resins because chemical activation is
accomplished through the addition of a tertiary amine,
such as dimethyl-para-toluidine, to the denture base
liquid (i.e.,monomer).
• Upon mixing powder and liquid components, the tertiary
amine causes decomposition of benzoyl peroxide.
• Consequently, free radicals are produced and
polymerization is initiated.
• Polymerization progresses in a manner similar to that
described for heat-activated systems.

Cold Cure Acrylic Resins
POSITIVE ATTRIBUTES
• Good strength (no need for reinforcement ) as
compared to materials like shellac and baseplate wax.
• Display slightly less shrinkage than heat-activated
resin, therefore have greater dimensional

Cold Cure Acrylic Resins
DRAWBACKS
• The degree of polymerization achieved using chemically
activated resins is not as complete as that achieved using
heat-activated systems.
• Thus, there is a greater amount of unreacted monomer in
chemically cured denture bases.
• This unreacted monomer acts as a plasticizer that results
in decreased transverse strength of the denture resin.
• The residual monomer also serves as a potential tissue
irritant, thereby compromising the biocompatibility of the
denture base.

Fabrication of Cold Cure Acrylic Bases
METHODS
• Sprinkle on method
• Finger adapted dough method
• Flasking method
• Stone mold method
• Wax-confined method

Flasking Method
• A wax pattern is constructed over the cast with a
thickness and contour desired for complete
denture.
• The cast and pattern are flasked, the wax is
eliminated, acrylic resin is packed and allowed
to set under the pressure of clamps or press.
• The processed base is removed from the cast,
smoothed, and polished at the borders.

Visible Light Cured Acrylic Resin
• This material is a composite having a matrix of
urethane dimethacrylate, microfine silica, and
high molecular weight acrylic resin monomers.
Acrylic resin beads are included as organic filler.
• Visible light is the activator, whereas
camphorquinone serves as the initiator for
polymerization.

The single-component denture base resin is supplied in
sheet and rope forms and is packed in light-proof pouches
to prevent inadvertent polymerization.

Vacuum-formed Vinyl and
Polystyrene
Any undercuts are relieved, and
separating medium is applied to the cast.
A sheet of base plate material placed
over the cast and inserted in the vacuum
chamber.
Electric heater switched to heat the
sheet.
Turn on the vacuum. The sheet will
adapt closely to the cast.
Switch of the heater and allow the
record base to cool.
Remove the record base and cut the
excess material.

Vacuum-formed Vinyl and Polystyrene
Advantages
• Easy to fabricate
• Uniform thickness
• Accurate adaptation to the master cast
• Good rigidity
Disadvantages
• Expensive
• Difficult to form smooth rounded borders

HEAT-PROCESSED DENTURE BASE RESINS
• Heat-activated materials are used in the fabrication of
nearly all denture bases.
• The thermal energy required for polymerization of
such materials may be provided using a water bath or
microwave oven.
• Available information indicates that the physical
properties and fit of microwave resins are comparable
to those of conventional resins, despite their fast speed
of polymerization.

Composition of Heat Cured PMMA
POWDER
• Consists of prepolymerized spheres of poly(methyl
methacrylate) and a small amount of benzoyl
peroxide.
• The benzoyl peroxide is responsible for starting the
polymerization process and is termed the initiator.

Composition of Heat Cured PMMA
LIQUID
• The liquid is predominantly nonpolymerized methyl
methacrylate with small amounts of hydroquinone.
• Hydroquinone is added as an inhibitor and it prevents
undesirable polymerization or “setting” of the liquid
during storage.
• A cross-linking agent also may be added to the liquid.
• Glycol dimethacrylate is commonly used as a cross-linking
agent in PMMA denture base resins.
• Glycol dimethacrylate is chemically and structurally
similar to methyl methacrylate and therefore may be
incorporated into growing polymer chains.

Polymerization Cycle
• One technique involves processing the denture base
resin in a constant temperature water bath at 74˚ C
(165˚ F) for 8 hr or longer, with no terminal boiling
treatment.
• A second technique is consists of processing in a 74˚ C
water bath for 8 hr and then increasing the
temperature to 100˚ C for 1 hr.
• A third technique involves processing the resin at 74˚
C for approximately 2 hr and increasing the
temperature of the water bath to 100˚ C and
processing for 1 hr.

• Polymerization is an exothermic process.
• If the temperature of the resin exceeds the boiling
point of unreacted monomer and/or low molecular
weight polymer(s), these components may boil.
• Clinically, boiling yields porosity within the completed
denture base.
• Such porosity usually will not be seen at the surface of
the denture base.

• The heat generated as a result of polymerization is
conducted away from the surface of the resin and into the
surrounding dental stone.
• Consequently, heat is dissipated, and the surface
temperature of the resin does not reach the boiling point of
the monomer.
• Because resin is an extremely poor thermal conductor,
heat generated in a thick segment of resin cannot be
dissipated.
• As a result, the peak temperature of this resin may rise
well above the boiling point of monomer.
• This causes boiling of unreacted monomer and produces
porosity within the processed denture base.

• Following completion of the chosen polymerization cycle,
the denture flask should be cooled slowly to room
temperature.
• Rapid cooling may result in warping of the denture base
because of differences in thermal contraction of resin and
investing stone.
• The flask is removed from the water bath, bench cooled for
30 min, then immersed in cool tap water for 15 min.
• The denture base is then deflasked, prepared for delivery,
and stored under water to decrease the probability of
unfavourable dimensional changes.

References
1. Philips’ Science of Dental Materials by Kenneth J.
Anusavice, 11th Edition, 2003,Elsevier
2. Murray MD, Darvel BW; The Evolution of the
Complete Denture Base. Theories of Complete
Denture Retention – A Review. Part 1 Aust Dent J
1993 Jun;38(3):216-9

Evolution of denture base materials and reveiw of current ones

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