This document provides information on denture base resins. It defines denture bases and materials, and classifies resins according to ISO 1567 and usage. The main types discussed are heat-cured, chemically-cured, light-cured, and microwave-cured resins. The document outlines the composition, polymerization process, properties, and cytotoxicity of these resins. It also discusses ideal requirements, water absorption, strength, and cleaning of denture bases.

2. DENTURE BASE
RESINS
Dr.Anju Sree Durga.B
Department of Prosthodontics

4. Introduction
• Denture prosthesis is composed of artificial teeth attached to a denture base
• Although individual denture bases may be formed from metals or metal alloys, the
majority of denture bases are fabricated using common polymers
• Such polymers are choosen based on availability, dimensional stability, handling
characteristic, color and compatability with oral tissues.

5. Contents
• Definition
• Classification
• Dental polymers
• Ideal requirements of denture base resin
• Ingredients
• Types
• Properties
• Cytotoxicity
• Conclusion
• References

6. Definition
• Denture base- the part of a denture that rest on the
foundation tissues and to which the teeth are attached
(GPT- 9)
• Denture base material – any substance of which a denture
base may be made.(GPT-9)

7. History

8. • Polimers :- chemical compound of huge organic or
inorganic molecules formed by large number of
repeating smaller structural units
• Monomer :- simple chemical compounds or
repeating units reacting to form a polymer.

9. Classification
• According to ISO 1567
• Type 1 – Heat processed denture base material
• Type 2 – Autopolimerised denture base material
• Type 3 Thermoplastic blank
• Type 4 Light activated materials
• Type 5 Microwaved cured materials.

10. • Based on usage:-
• Temporary denture base resin
• Self cure acrylic
• Shellac base plate
• Permanent denture base resin
• Heat cure denture bases
• Light cure resins

11. Polymerisation

12. • Powder
 Prepolymerised spheres of polymethyl
methacrylate
 Ethyl or butyl methacrylate(5%)
 Benzoyl peroxide
 Dibutyl phthalate
 Compounds of mercuric sulphide or cadmium
sulphide
 Zinc or titanium oxide
 Dyed synthetic nylon or acrylic fibres
Liquid
 Nonpolymerised
methylmethacrylate
 Dibutyl phalate
 Glycol dimethacrylate
 Hydroquinone

13. Chemical stages of
polymerisation

14. Copolymerization
• Macromolecules may be formed by polymerization of single
type of structural units.
• To change the inherent properties of the homopolymer, two or
more chemically different monomer are used
• Act as internal plasticizer.

15. Types of copolymer
• Random type
• Monomers are randomly distributed
• Graft type
• Sequence of one of the monomer are grafted onto the
backbone of second monomer.
• Block type
• Identical monomer units occur in relatively long
sequence along the main polymer chain

16. Types of polymers
 Linear polymers

17.  Cross linked polymers
The backbone chains are cross
linked by covalent bonding , by
adding a cross linkng agent.
This improves the physical
properties of the polymer
Eg :- Ethyleneglycol dimethacrylate

18. Polymerisation
Condensation polymerization
Chemical reaction between bifunctional or trifunctional
molecules resulting in stepwise growth to form polymers.
Some byproducts of small molecules are formed
Polymerization is not fast
Low degree of polymerization
Low molecular weight

19. Addition Polymerization
Ionic addition
• Hydrogen ion
transfer from
one to another
Ring opening
addition
• Monomer
containing
terminal rings
are opened by
amines
Free radical
addition
• Polymerisation
begins from an
active centre
like a free
radical

20. Stages of polymerization
Induction
• Free radicals are produced by dissociation of certain
chemicals by different activation energy system.
• Free radicals may later combine with monomer and
initiates polymerization.
• This interval is known as induction period.

21. Propagation
• Radical monomer complex act as free radical and combines with
another monomer and forms dimer radical
• This process repeats one after other to form a polymer chain
• This takes place instantaneously until all monomers are
exhausted
• Reaction is exothermic.

22. Chain transfer
• Active free radical energy of the growing chain, can get
transferred to another monomer or already terminated
polymer .
• The first polymer chain gets terminated and next one starts
growing by this hydrogen ion transfer .

23. Termination
• Chain reaction can be terminated either by direct coupling or by
exchange of hydrogen atoms from one growing chain to the
other.

24. Inhibition of polymerization
• Certain impurity atoms can react with free radicals or
neutralize the growing chain.
• Eg:- hydroquinone

25. Physical stages of polimerisation

26. Polymer – monomer interaction
Sandy stage
• Little or no interaction occur on a molecular
level
• Consistency of mixture is coarse or grainy
Stringy stage
• Monomer attacks surfaces of individual polymer
beads
• These polymer chains uncoils, therby increasing the
viscosity of the mix
• This stage is characterized by stringiness or
stickiness
Doughlike stage
• Increased number of polymer chains enter the
solution
• Mass behaves as a pliable dough.
• Ideal for compression molding

27. Rubbery stage
• Monomer is dissipated by evaporation and
penetration into remaining polymer beads
• Mass rebounds when compressed or streched
Stiff stage
• Evaporation of free monomer
• Mixture appears very dry and resistant to
mechanical deformation

28. Ideal requirements of denture base resins

33. Uses
Splints
Temporary crowns
Dentures

34. Types of denture resins
• Heat activared denture resins
• Chemically activated denture resins
• Light activated denture resins
• Microwave activated resin

35. Heat activated denture base resins
• Heat activated materials are used in the fabrication of nearly all
denture bases.
Powder
 Prepolymerised polymethyl
methacrylate
 Ethyl or butyl methacrylate(5%)
 Benzoyl peroxide
 Dibutyl phthalate
 Compounds of mercuric sulphide
or cadmium sulphide
 Zinc or titanium oxide
 Dyed synthetic nylon or acrylic
fibres
Liquid
 Nonpolymerised
methylmethacrylate
 Dibutyl phalate
 Glycol dimethacrylate
 Hydroquinone

36. Compression molding technique
Heat activated denture base resins are shaped via compression
molding.
Steps:-
• Preparation of split mold
• Application of separating medium
• Packing
• Curing
• Finishing and polishing

38. Polymer to Monomer ratio
• Polymerisation of methylmethacrylate to form
polymethylmethacrylate yields 21% decrease in
volume of material
• Using 3:1 ratio , volumetric shrinkage may be limited
to approximately 7% and 0.5% linear shrinkage

39. Injection molding technique
• Wax sprues are attached to wax denture base.
• Flask is placed into a carrier that maintain pressure during resin introduction and processing.
• Resin mixture is introduced into room temperature mold
• Flask is then placed on the water bath for polymerization
• As the material polymnerises , additional material is introduced into mold cavity.
• Upon completion denture is recovered, finished and polished.

41. • Advantages
• Dimensional accuracy
• Homogenous denture bases
• No increase in vertical dimension
• Low free monomer content
• Good impact strength
• Disadvantages
• Higher cost of equipment
• Less craze resistance

42. Polymerisation procedure
 Polymerisation of denture base resin is exothermic process
 Above 70°c benzoyl peroxide decompose and gives of free
radicals for the reaction
 As the reaction proceeds , temperature of resin will rises.
 Temperature of resin should not be allowed to rise above
100.8°c as this may leads to internal porosity.

43. Polymerisation cycles
• A constant temperature waterbath at 74°c for 8hrs or longer,
with no terminal boiling treatment.
• Processing in a 74°c waterbath for 8hrs and then increasing the
temperature to 100°c for 1hr.
• Processing the resin at 74°c for approximately 2hrs and
increasing the temperature of waterbath to 100°c and processing
for 1hr.
• Following completion of polymerization cycle , denture flask
should be cooled slowly to room temperature.

44. Polymerization via microwave
energy
This technique employs a specially formulated resins and a
nonmetallic flask.
Polymerization heat is dispersed more efficiently and polymerization
is rapid with minimal porosity.
Microwave acts only on the monomer, which decreases in the same
proportion as the polymerization decreases.

45. Advantage:-
• Greatly reduced curing time
• Shortened dough forming time
• Minimal color changes
• Less fracture
• Lower residual monomer ratio
• Most stable

46. Disadvantages
• Less bond strength of resin to denture teeth
• Plastic flask and policarbon bolts are very expensive

47. Chemically activated resin
Heat activated resin
Heat
Benzoyl peroxise
Production of free radical
Polymerisation
Chemically activated resin
Dimethyl-para-toluidine (tertiary amine)
Benzoyl peroxide
Production of free radical
Polymerisation

48. Techniques
Sprinkle on
technique
Fluid resin technique Compression
mold technique

50. • There is greater amount of monomer which creates 2
difficulties:-
• A) It act as a plasticizer which decrease the transverse strength
of denture base .
• B) Residual monomer act as a tissue irritant, therby
compromising the biocompatibility of the denture base.

51. Light activated denture base resin
• This material has been described as a composite having a
matrix of urethane dimethacrylate and microfine silica
• Visible light is activator.
• Camphoroquinones act as initiator for polymerization.
• Single component denture base resin is available in sheet and
rope form in light proof pouches.

52. Technique
• After teeth arrangement, denturebase is molded on accurate cast
• Then the denture base is exposed to high intensity visible light
source for an appropriate period.
• Following polymerization denture is removed from the cast,
finished and polished in a conventional manner.

53. Advantages
• Less porosity than chemically activated resin
• Facilitates final fabrication in mouth
• Lighter
• Decreased polymerization shrinkage
• Non toxic

54. Disadvantage
Cannot be flasked in conventional manner.
Factors such as light intensity, angle of illumination, distance of
resin from light source can affect number of free radicals formed
making this system technique sensitive.

55. Physical properties of denture
base resin

56. Physical properties
Methyl methacrylate
• It is a clear transparent, volatile liquid at room temperarure
• Melting point : -48°c
• Boiling point : 100.8°c
• Density : 0.94g/cm3
• Heat of polymerization : 12.9Kcal/mol
• Volume shrinkage : 21%
Polymethyl methacrylate
• It is an amorphous structure which is tasteless and odourless.
• Density is 1.19

57. Polymerisation shrinkage
• Volumetric shrinkage : 21%
• When prepolymerised polymer is used, volumetric shrinkage becomes
7%.
• Shrinkage exhibited by this material is distributed uniformly to all
surfaces.
• Based on projected volumetric shrinkage of 7%, linear shrinkage
should exhibit approximately 2%
• Thermal shrinkage is responsible for linear shrinkage phenomenon
• Processing shrinkage for
• Heat activated resin : 0.53%
• Chemically activated resin :0.26%

58. Porosity
• Causes
• Vapourisation of unreacted monomer and low molecular
weight polymer
• Inadequate mixing of powder and liquid components
• Inadequate pressure or insufficient material in the mold
cavity
• Air inclusion

59. Water absorption
• Cause of water absorption : diffusion, polarity of molecules
• Effect of water absorption : act as plasticizer
Expansion of polymerized mass.
• Water sorption value : 0.69mg/cm3
• It has been estimated that for each 1% increase in wt produced
by water absorption, acrylic resin expands by 0.23% linearly
• ANSI/ADA Specification No : wt gain should not be more than
0.8mg/cm2

60. Crazing
• It is suface flaws or microcracks on denture base
resin
• Causes : stress application
Solvent action(ethyl alcohol)
• Transparent resin : hazy or foggy appearance
• Tinted resin : whitish appearance
• Surface cracks predispose a denture resin to
fracture.

61. Strength
• Factors affecting strength
a) Composition of resin
b) Processing technique
c) Degree of polymerization
d) water sorption
e) condition presented by oral environment
• Compressive strength : 76MPa
• Tensile strength : 48 – 62 MPa

62. • Impact strength
• It is a measure of the energy absorbed by a material when
it is broken by a sudden blow
• Heat cure acrylic> Autopolymerising acrylic

63. Denture warpage
• It is the deformity or change of shape of the
denture which can affect the fit of the denture.
• Causes :-
• Stress caused by curing shrinkage or uneven
cooling
• Rise in temperature during polishing
• Immersion of denture in hot water
• Packing of resin in rubbery stage

64. Resistance to acids, bases, and
organic solvents
• Resistant to weak acids or bases and organic solvents
• Soluble in aromatic hydrocarbons, ketones and esters.
• Solution containing alcohols should not be used for
cleaning or storing the dentures
• Incorporating ethylene glycol dimethacrylate as a
crosslinking agent improves solvent resistance.

65. Solutions for microbial control
• Microorganisms like Candida albicans, Streptococcus oralis, Bacteroids
gingivalis, S. sanguis can adhere to denture base acrylic
• Chlorhexidine can bind to acrylic surfaces for atleast 2 weeks
• Treating acrylic with nystatin, followed by drying, produces similar
results.
• Using phenol disinfectant can cause surface damage to denture base
resin
• Several studies have identified that metal oxide nanoparticles (MgO,
TiO2, ZnO) reinforced dentures has antimicrobial property.

66. Denture cleansers
• Dentures are cleansed by either immersion in an agent
or brushing with cleanser.
• Immersion agents contains alkaline compounds,
detergents, sodium perborate and flavouring agents
• Perborate alkaline peroxide oxygen
• Vinegar is effective in dissolving calculus.

67. Cytotoxicity
• Residual monomer has the potential to cause
• Irritation
• Inflammation
• Allergic response to oral mucosa
• Clinical signs and symptoms includes
• Erythema
• Erosion
• Burning sensation of mucosa and tongue.

68. • They are most commonly manifested as type I
hypersensitivity reactions (anaphylaxis) or type IV
(contact stomatitis, dermatitis and, upon repeated
contact with the allergen).
• According to the standard (ISO 1567:
• 1999) the maximum allowed amount of residual
• MMA for hot polymerized acrylate is 2.2%, and
• for the cold polymerized is 4.5%.

69. Conclusion
• There are wide variety of denture base materials and the ever
growing urge to find the best and the most feasible material will
always bring an evolution in denture base material science.
• As clinicians, we must understand the basic nature of each of
these, to provide the best possible treatment to our patients.

71. Reference
• Kenneth J Anusavice; Philips science of dental materials 11th edition
• Robert C Craig , John M Powers, John C Wataha; Dental materials properties and manipulation;
11th edition
• V K Subbarao; notes on Dental materials 4th edition
• Basic dental materials – John J Manapallil 3rd edition

72. Evaluation of Cellular Toxicity of Three Denture Base
Acrylic Resins M. Ebrahimi Saravi, M. Vojdani, F.
Bahrani
Residual monomer content and its release into water
from denture base materials Pekka K. Vallittd, Varpu
Miettinen’, Pekka Alakuijala2
Adverse reactions to denture resin materials m Kostic,
A Pejcic, Gligorigevic