Contents Introduction Rationale for Establishing Tooth Contacts during Fixed Prosthodontics Concepts of Occlusion Occlusion in fixed dental prosthesis Occlusal treatment Conclusion References Introduction Maxillary and mandibular teeth should contact uniformly on closing to allow optimal function, minimize trauma to the supporting structures and allow for uniform load distribution throughout the dentition. Occlusion - The static relationship between the incising or masticating surfaces of the maxillary and mandibular teeth. GPT -9 Centric relation - a maxillomandibular relationship, independent of tooth contact, in which the condyles articulate in the anterior-superior position against the posterior slopes of the articular eminences; in this position, the mandible is restricted to a purely rotary movement; from this unstrained, physiologic, maxillomandibular relationship, the patient can make vertical, lateral or protrusive movements; it is a clinically useful, repeatable reference position. Centric Occlusion [CO] - the occlusion of opposing teeth when the mandible is in centric relation; this may or may not coincide with the maximal intercuspal position. Maximum Intercuspation [MI] - It is the maximum interdigitation of the maxillary teeth with the mandibular teeth independent of condylar position. GPT 9 Anatomy Temporomandibular joint

1. DENTURE BASE
RESINS
GUIDED BY: Dr. SUDHEER ARUNACHALAM
Dr. TUSHAR TANWANI
Dr. ANUPAM PURWAR
Dr. RUCHI GUPTA
Dr. SUDEEPTI SONI
PRESENTED BY: Dr. MEGHA NASHINE

2. CONTENTS
• Introduction
• Types
• Classification
• Ideal requirements
• Polymerization
• Types and chemical stages
• Heat activated denture base resins
• Chemically activated denture base resins
• Specialized poly (methylmethacrylate) materials
• Physical properties
• Conclusion
• References

3. INTRODUCTION
• DENTURE BASE: the part of the denture that rests on the
foundation tissues and to which teeth are attached.
• ACRYLIC RESINS: any group of thermoplastic resins made by
polymerizing esters of acrylic or methylmethacrylate acids.
(GPT 9)

4. TYPES
ADA SPECIFICATION NO.12 FOR DENTURE BASE RESINS
• Type 1- Heat polymerizable polymers
• Type 2- Autopolymerizable polymers
• Type 3- Thermoplastic blank or powder
• Type 4- Light activated materials
• Type 5 - Microwave-cured materials

5. CLASSIFICATION OF RESINS
Based on thermal behaviour they are classified as:
Thermoplastic
Repeatedly softened and molded under heat and pressure.
Eg: polymethylmethacrylates, polystyrene.
Thermosetting
Can be moulded only once
Eg: polyester, viny ester, polyurethane.

6. IDEAL REQUIREMENTS OF
DENTAL RESINS
1) Tasteless, odourless,nontoxic and nonirritant to oral tissues.
2) Esthetically satisfactory, i.e. Should be transparent or
translucent and easily pigmented.The colour should be
permanent.
3) Dimensionally stable.
4) Adequate strength, resilience and abrasion resistance.
5) Insoluble and impermeable to oral fluids.

7. 6) Its softening temperature should be well above the
temperature of any hot foods or liquids taken in the mouth.
7) Easy to fabricate and repair.
8) Good thermal conductivity.
9) Radiopaque.
10) Adhesion to plastics, metals, and porcelain
11) Low specific gravity

8. STRUCTURE OF POLYMERS
LINEAR
BRANCHED
CROSS-LINKED

9. POLYMERIZATION
The term polymerization refers to a chemical reaction in
which monomers of low molecular weight are converted into
chains of polymers with a high molecular weight.

10. TYPES OF POLYMERIZATION REACTION
CONDENSATION REACTION
• Divided into 2 groups :
Those in which polymerization is accompanied by repeated
elimination of small molecules, i.e. the primary compounds
react with the formation of by-products such as water,
halogen acids, etc. called condensation polymerization.
 Those polymers, whose repeating units are joined by
functional group without the formation of the by-product.
These should be called as the step growth polymerized resins.
Eg: Polyurethane

11. ADDITION POLYMERIZATION
• Most dental resins are polymerized by addition
polymerization.
• There is no change in the chemical composition & no by-
products are formed.
• Starting from an active center, one molecule at a time is
added and a chain rapidly builds up, which can grow almost
indefinitely as long as the supply of building blocks is
available.

12. CHEMICAL STAGES OF POLYMERIZATION
INDUCTION
To start the addition polymerization process, free radicals
must be present.
• The free radical chemical that is used to start the
polymerization enters into the chemical reaction & becomes
the part of of the final product. Termed as initiator.
• The initiator may be activated to provide the free radicals by 3
methods.

13. a. Heat activation.
• The free radicals liberated by heating benzoyl peroxide will
initiate the polymerization of methyl methacrylate monomer.
b. Chemical activation
• Two reactants when mixed, liberate free radicals.
• Eg: the use of benzoyl peroxide & an aromatic amine
(dimethyl-p-toluidine) in self cure dental resins.
c. Light activation.
• The photons of light energy activate the initiator to generate
the free radicals, e.g. camphorquinone & amine will react to
form free radicals, when they are irradiated with visible light.

14. PROPAGATION
Because little energy is required once the growth has started,
the process continues rapidly and is accompanied by
evolution of heat.
Theoretically, the polymerization should continue with
evolution of heat, until all the monomer has been converted
to a polymer. However, the polymerization is never complete.
TERMINATION
The chain reactions can be terminated either by direct
coupling or by exchange of hydrogen atom from one growing
chain to another.

15. CHAIN TRANSFER
• The active state is transferred from an activated radical to an
inactive molecule, & a new nucleus of growth is created.
• In the same manner, an already terminated chain might be
reactivated by chain transfer, & will continue to grow.

16. HEAT ACTIVATED DENTURE BASE
ACRYLIC RESINS

17. • Mode of supply
1. Powder and liquid
2. Gels-sheets and cake
• The powder may be transperent or tooth coloured or pink
coloured.
• The liquid is supplied in tightly sealed amber coloured bottles .
• Commercial names: E.g. Stellon (DPI)
Luiciton(Bayer)
Trevelon (Dentsply)

18. COMPOSITION
LIQUID
• Methyl methacrylate : Major constituent
• Dibutyl pthalate : Plasticizer
• Glycol dimethacrylate(2-14%) : Cross-linking agent
• Hydroquinone(0.003-.01%) : Inhibitor-prevents setting

19. POWDER
• Poly methyl methacrylate : Major constituent
• other copolymers – 5%
• Benzoyl peroxide : Initiator
• Compounds of mercuric
Sulphide, cadmium sulphide : Dyes
• Zinc or titanium oxide : Opacifiers
• Dibutyl phthalate : Plasticizer
• Dyed organic filler & inorganic : For esthetics
particles like glass fibres or beads

20. POLYMERIZATION REACTION
• Polymerization is achieved by application of heat and pressure. The
simplified reaction is :
• Powder + Liquid + Heat Polymer + Heat
(External) (Reaction)

21. COMPRESSION MOLDING TECHNIQUE
1) PREPARATION OF MOLD

22. On completion of setting process, the record base & the
softened wax should be removed from the mold. To accomplish
this, denture flask is immersed in boiling water for 4 min.

23. 2) APPLICATION OF SEPARATING MEDIA
This medium must prevent direct contact between the denture
base resin & the mold cavity.
The most popular separating agents are water soluble alginate
solution.

24. 3) POLYMER MONOMER RATIO
The accepted polymer monomer ratio is 3:1 by volume or 2:1 by
weight.
4) POLYMER-MONOMER INTERACTION
When polymer & monomer are mixed in proper proportions,
a workable mass is produced
On standing, it passes through 5 distinct stages :
Sandy: no interaction at molecular level. consistency of
mixture—coarse or grainy.
Stringy: the monomer attacks the polymer by penetrating into
the polymer. The mass is sticky or stringy when touched or
pulled apart.

25. Doughlike: an increased number of polymer chain enter solution. A
sea of monomer & dissolved polymer is formed. The physical
& chemical characteristics exhibited during the later phases of this
stage are ideal for compression molding.
Rubbery or elastic: monomer is dissipated by evaporation & by
further penetration into remaining polymer beads. Mass rebounds
when compressed or stretched.
Stiff: this may be attributed to evaporation of the free monomer.
Clinically, the mixture appears very dry & is resistant to mechanical
deformation.

26. 5) DOUGH FORMING TIME
ADA specification no. 12 requires that dough like consistency be
attained in less than 40 min from start of mixing process.
Clinically, most resins reach doughlike stage in less than 10
min.
6) WORKING TIME.
ADA specification no. 12 requires the dough to remain moldable
for atleast 5 min. The working time of the resin may be
extended by refrigeration.

27. 7) PACKING.
• Introduction of denture base resin into mold cavity is
termed as packing
• Overpacking:
• Exhibits excessive thickness & resultant malpositioning
of prosthetic teeth.
• Underpacking:
• Leads to noticeable denture base porosity
Steps in resin packing
A) Properly mixed resin is bent in
horse shoe shape & placed into
the mold cavity

28. B)The flask assembly is placed into a flask press,
& pressure is applied.
C) Excess material is carefully removed from
the flask.
D) The flask is transferred to a flask carrier that
maintains pressure on the assembly during
processing.

29. 8) CURING
• The two stages involved in curing cycle for compression molding
method are bench and heat curing.
• Bench curing :
This is done at room temperature for 30-60 min after packing.
• Heat curing :
This is done by placing the packed dental flask in a boiling water bath
• Three curing cycle may followed;
• a) 74 degree C for 8 hr
• b) 74 degree C for 8 hrs followed by 100 degree C for 1 hr
• c) 74 degree C for 2 hrs followed by 100 degree C for 1 hr

30. 9) DEFLASKING
• On completion of the process, the flask should be cooled
slowly and then the denture is retrieved from the flask and
finished and polished.

31. INJECTION MOLDING TECHNIQUE
• For this a specially designed flask is used with Placement of
sprues for introduction of resin. Wax elimination is
performed and Flask is reassembled
• The soft resin is contained in the injector and
is forced into mold space as needed
The flask is placed into water bath for
polymerization of denture base resin.
As material polymerizes, additional resin is
Introduced. Continuous feeding of material
compensates for shrinkage

32. • The debate exists regarding the comparative accuracy of denture
bases fabricated by compression molding & those fabricated
injection molding.
• Nogueira et al in 1999 compared incisal pin opening &
dimensional accuracy for dentures constructed by compression
molding & injection molding. They used lucitone 199 material
with long curing cycle.
• They concluded that injection molding method produced a
significantly smaller pin opening over the standard compression
molding technique. The injection molding technique, using
polymethyl methacrylate, was more accurate method for
processing dentures.
• ( J Prosthet Dent 1999;82:291-300 )

33. POLYMERIZATION PROCEDURE
• Denture base resins generally contain benzoyl peroxide. When
heated above 60oC, molecules of benzoyl peroxide decompose
to yield electrically neutral species containing unpaired
electrons. These species are called free radicals.
• Each free radical reacts with an available monomer molecule to
initiate chain growth polymerization. The reaction product also
possesses unpaired electron so it remains chemically active.
Consequently, additional monomer molecule become attached
to individual polymer chains

34. • The process occurs rapidly & terminates by
 Coupling of two grouping chains (combination).
 Transfer of single hydrogen ion from one chain to another.
Heat is required to cause decomposition of benzoyl peroxide
molecules, therefore, heat is termed as activator. Benzoyl
peroxide is termed as the initiator.

35. CHEMICALLY ACTIVATED DENTURE
BASE ACRYLIC RESINS

36. • The chemically activated acrylic resin polymerize at room
temperature . They also known as ‘self-cure’ , ‘cold cure’ or
‘Auto-polymerizing’ resin.
• In cold cure acrylic resins, the chemical initiator benzoyl
peroxide is activated by another chemical (dimethyl para
toludine which is present in the monomer), instead of heat as
in heat cure resin. Thus polymerization is achieved at room
temperature.
• Available as
Powder and liquid

37. COMPOSITION
Liquid
• Methyl methacrylate monomer : dissolves polymer
• Dimethyl-p-toludine : Activator
• Dibutyl pthalate : Plasticizers
• Glycol dimethacrylate 1-2% : Cross linking agent
• Hydroquinone : Inhibitor

38. Powder
• Poly methyl methacrylate : Dissolved by monomer
to form dough
• other copolymers – 5%
• Benzoyl peroxide : Initiator
• Compounds of mercuric
Sulphide, cadmium sulphide : Dyes
• Zinc or titanium oxide : Opacifiers
• Dibutyl phthalate : Plasticizer
• Dyed organic filler & inorganic : For esthetics
particles like glass fibres or beads

39. POLYMERIZATION REACTION
The simplified reaction is :
Powder + Liquid Polymer + Heat
(Peroxide initiator) (Amine accelerator) (reaction)

40. ADVANTAGES
Ease of manipulation
Less shrinkage
Better initial fit, which is because the curing is carried out at room
temperature. Thus there is less thermal contraction.
For repairing dentures, self curing resins are preferable to heat cured.
DISADVANTAGES
Slightly inferior properties
Poor colour stability
Tissue irritation from residual monomer

41. MANIPULATION
SPRINKLE ON TECHNIQUE
• Powder(Polymer), liquid(monomer) are added onto the cast
which has been already treated by separating medium.
• The powder is sprinkled on the cast and monomer is added
until the desired thickness obtained.
• To improve the strength of constructed prosthesis, the resin
can further be cured in hot water under pressure for around 20 min
in a pressure pot.
• The advantage of this technique are better adaptation and
ease of fabrication.

42. HAND ADAPTED DOUGH TECHNIQUE
• Powder and liquid are proportioned and mixed in a
porcelain jar.
• When the mix reaches the dough stage , it is
immediately placed between two glass slabs , removed and
adapted over the cast, and manually molded quickly to the
desired shape.

43. FLUID/ POUR TYPE RESIN
A special resin is available for this technique.
• The chemical composition of the pour-type of
denture resin is similar to the poly methyl methacrylate
materials.
• The principal difference is that the pour type of
denture resins have high molecular weight powder
particles that are much smaller and when they mixed
with the monomer, the resulting mix is very fluid.
• Therefore, they are reffered as ‘fluid resins’. They
are used with a significantly lower powder liquid ratio,
i.e it ranges from 2:1 to 2.5:1. This makes easier to mix
and pour.

44. The cast with the attached tooth
arrangement is removed from
the flask.
The sprues & vents to the mold cavity
are cut from the external surface of
the flask.
Wax is eliminated from cast using hot water.
The prosthetic teeth are retrieved &
carefully seated in their respective positions
within the hydrocolloid investing medium.
The resin is mixed according to
manufacturer’s directions & poured into
the mold cavity via sprue openings

45. • The flask is then placed in a pressurized chamber at room
temperature, & the resin is permitted to polymerize.
• Only 30 to 40 min is required for polymerization.
• Following the polymerization, the
denture is retrieved from the flask
& sprues are removed

46. ADVANTAGES
Improved adaptation to underlying soft tissues.
Decreased probability of damage to prosthetic teeth & denture base
during deflasking.
Simplification of flasking, deflasking & finishing procedures
DISADVANTAGES
Noticeable shifting of prosthetic teeth during processing.
Air entrapment within the denture base material.
Poor bonding between the denture base material & acrylic resin
teeth.

47. SPECIALIZED POLY (METHYL
METHACRYLATE) MATERIALS

48. MICROWAVE CURED DENTURE RESINS
Microwave energy may also be used to polymerize PMMA resin.
Curing time is 3 minutes in a standard household microwave oven.
Special nonmetallic polycarbonate or fibre-reinforced plastic
flasks are used instead of metallic flask, as microwave will reflect from
surface.
The microwave provides the required thermal
energy for polymerization reaction.
supplied as
Powder-liquid system similar to conventional resin.

49. ADVANTAGES
Drastic reduction in curing time
Good denture base adaptation
DISAVANTAGES
Poor bonding to denture teeth
Increase porosity
Expensive flask
Poor durability of flask

50. LIGHT ACTIVATED DENTURE BASE RESINS
• These materials have been described as a
composite having the matrix of
urethane dimethacrylate,
microfine silica,
high molecular weight acrylic resin monomer.
Acrylic resin beads are included as organic filler.
Visible light is activator, whereas
camphorquinone serves as initiator
AVAILABLE AS
The single component denture base resin is supplied in sheet &
rope forms & is packed in light proof pouches to prevent
inadvertent polymerization.

51. FABRICATION
The denture base material is adapted to the
cast while it is in plastic state. The denture
base can be polymerized without teeth &
used as base plate.
The teeth are arranged and denture base
Sculpted while the material is still soft.
Polymerized in light chamber at 400-500nm.

52. HIGH IMPACT ACRYLICS
• Commercially available high impact denture base materials
usually incorporate a microdispersed rubber phase (usually
butadiene styrene rubber) into polymer. This produces
improvement in both impact & fatigue strength but there may
be consequent reduction in rigidity.
• They are processed like heat cure resins.
• Indicated especially in patients who have difficulty in handling
their dentures. Example, very old patients, neuromuscular
disease with tremors, parkinsonism

53. RAPID HEAT POLYMERIZED RESINS
• These are hybrid acrylics that are polymerized in boiling water
immediately after being packed into a denture flask.
• After being placed into the boiling water, the water is brought
back to a full boil for 20 minutes. After the usual bench
cooling to room temperature, the denture is deflasked,
trimmed , and polished in the usual manner.
• The initiator is formulated to allow for rapid polymerization
without the porosity that one might expect.

54. PHYSICAL PROPERTIES OF
DENTURE BASE RESINS

55. METHYL METHACRYLATE MONOMER
• Clear, transparent, volatile liquid at room temperature.
• Melting point -48 degree celsius
• Boiling point 100 degree celsius
• Density 0.945 gm/ml at 20 degree celsius
• Heat of polymerization 12.9Kcal/mol
• Volumetric shrinkage during polymerization 21%

56. POLYMETHYLMETHACRYLATE
STRENGTH: These materials have adequate compressive (75 Mpa) &
tensile strength(48-62 Mpa) for complete or partial dentures
application.
Impact strength: it is measure of energy absorbed by a material when it
is broken by a sudden blow.
Chemically activated resin: 13(J/m)
Conventional heat cured acrylic resins 15(J/m)
Rubber modified acrylic resins 31 (J/m)
Polyvinyl resins 30 (J/m)

57. HARDNESS AND WEAR RESISTANCE
Acrylic resins are materials having low hardness
Heat cure acrylic resins: 18 KHN
self cure acrylic resin : 16 KHN
Rubber modified acrylic resin : 14 KHN
CREEP
• When denture base resin is subjected to sustained load, the
material exhibits an initial deflection or deformation. If this
load is not removed, additional deformation may occur over
time. This additional deformation is termed as creep.
• chemically activated resins have higher creep rates
COLOUR STABILITY
Heat cure acrylic resins have good colour stability while that of
self cure is slightly lower.

58. SOLUBILITY
Denture base resins are virtually insoluble in the fluids commonly
encountered in the oral cavity
WATER ABSORPTION
PMMA exhibits the water sorption value of 0.69 mg/cm2. The linear
expansion caused by water absorption is approximately equal to
thermal shrinkage encountered as a result of polymerization
process. Hence, these processes almost offset one another.
BIOCOMPATIBILITY
Completely polymerized acrylic resins are biocompatible.
DENSITY
The polymer has a density of 1.19 gm/cm square
RADIOOPACITY
By inclusion of heavy metal salts like bismuth or uranyl at
concentration of 10 to 15%

59. RESIDUAL MONOMER CONTENT
The highest residual monomer level is observed with chemically
activated denture base resins at 1 to 4% shortly after processing.
In heat cure acrylics before the start of curing the residual monomer
is 26.2%. In one hour at 70 degree celsius it decreases to 6.6% and
at 100 degree celsius it is 0.29%.
THERMAL PROPERTIES
Stability to heat: softens at 125 degree Celsius
Thermal conductivity: poor conductors of heat and electricity
Coefficient of thermal expansion: high coefficient of thermal
expansion. Addition of fillers reduces CTE

60. POLYMERIZATION SHRINKAGE
During polymerization, the density of the monomer changes from
0.94gm/cc to 1.19gm/cc. This results in shrinkage in the volume of
monomer polymer dough.
However, inspite of the high shrinkage, the fit of the denture is not
affected because the shrinkage is uniformly distributed all over the
surface of the denture. Thus, the actual shrinkage observed is low.
Self cure type has lower shrinkage. Its processing shrinkage is 0.26 %
Compared with 0.53% for heat activated resin
Dimensional changes do occur in the denture bases constructed from
various resins as illustrated in the fig

61. The illustration reveals that chemically activated resin processed
with pour type technique gives least dimensional changes

62. POROSITY
• Porosity is likely to develop in thicker portions of denture base.
A. Properly polymerized, no porosity.
B. & C. rapid heating, relatively small subsurface voids.
D. Insufficient mixing of monomer & polymer, large voids resulting
from localized polymerization shrinkage.
E. Insufficient pressure during polymerization, relatively large
irregular voids.

63. CONCLUSION
A widely used polymer in dentistry is acrylic resin.
The choice of material should be based on the purpose ,
properties, and the practicality of the clinical situation in hand .
PMMAs ,though they do not fulfil all the requirements of an
ideal denture base material, are widely used due to their
accepted esthetic, physical, and mechanical properties, ease of
use ,and biocompatibility.

64. REFERENCES
1. Craig Restorative dental material”8th edition.
2. “Philips science of dental materials” 11th edition.
3. Nogueira SS, Ogle ER, Davis LE. Comparison of accuracy between
compression & injection molded complete dentures. J Prosthet
Dent 1999;82:291-300