dental polymers

1. DENTAL POLYMERS WITH
RECENT ADVANCEMENTS IN
DENTAL BASE TECHNIQUES

2. Polymers are chemical compound consisting of large organic
molecule (macromolecule) formed by the union of many smaller
repeating units (mers).
Polymerization : Chemical reaction in which monomers of low
molecular weight are converted into chains of polymers with a high
molecular weight.
monomer+monomer+monomer+monomer Mer-mer-mer-mer-

3. HISTORY OF DENTAL POLYMERS

4. During the 20th century a wide variety of synthetic elastomers - polysulfides, silicone
rubbers, polyethers and polyvinyl siloxanes were developed.
1936 - Polymethylmethacrylate (PMMA), a heat-processed thermosetting material.
Late 1950s - Dr. Ray Bowen of ADA research foundation introduced self-curing
dimethacrylates reinforced by a dispersed phase ceramic ‘filler’ particle. These resin-
based “composites” form a highly crosslinked, durable and aesthetically pleasing
polymer network.
Self cured resins UV photo cured resins Blue light photo polymerising resins

5. Dental uses of polymeric material and resins
• Prosthodontics: denture bases and teeth, soft liners, custom trays, impression
materials, core build up materials, temporary restoratives, cementing/luting
materials, and maxillofacial prostheses
• Operative Dentistry: dentin bonding agents, cavity fillings, resin and glass-ionomer
cements, pit and fissure sealants, splinting materials, and veneers
• Orthodontics: brackets, bracket bonding resins and cements, and spacers
• Endodontics: gutta-percha points, root canal sealants, and rubber dams
• Equipment: mixing bowls and spatulas, mouth guards (sports equipment), and
protective eyewear

6. Components and composition
Fundamental Nature of Polymers
Polymers consist of very large macromolecules and that their chainlike molecular
structure is capable of virtually limitless configurations and conformations. Chain
length, the extent of chain branching and crosslinking, and the organization of the
chains among themselves, determine the properties of polymers.
In addition to the carbon-chain organic polymers, macromolecules may also consist
of inorganic polymer networks such as those formed by silicon dioxide repeating
units.

7. Chain Length and Molecular Weight
The longer the polymer chain, the greater are the numbers of entanglements that
can form along it. Therefore, the longer the chain, the more difficult it is to distort
the polymeric material; thus, such properties as rigidity, strength, and melting
temperature increase with increasing chain length.

8. Chain Branching and Crosslinking
Linear macromolecules, polymer chains are often connected together to
form a nonlinear, branched, or crosslinked polymer.

9. Copolymer Structures
Polymers that have only one type of repeating unit (mer) are homopolymers;
those with two or more types of mer units are known as copolymers. There are
three different types of copolymers:
● Random copolymer—.
● Block copolymer—
● Graft or branched copolymer—

10. Molecular Organization
Amorphous structure - disordered or randomly arranged polymer chains.
Crystalline structure - highly ordered polymer chains.

11. Properties of polymers

12. 1. Mechanical Properties—Deformation and Recovery
• Plastic strain is irreversible deformation and results in a new, permanent
shape as the result of slippage (flow) among polymer chains.
• Elastic strain is reversible deformation and will be quickly and completely
recovered when the stress is eliminated, as the result of polymer chains
uncoiling and then recoiling.
• Viscoelastic strain is a combination of both elastic and plastic deformation.

13. 2. Rheometric properties
Stretching only No additional stretching Full recovery
loaded
Continued loading
Loading
continued
Partial recovery with permanent
deformation
Slipping occurred (Quantity of slippage
depends on the duration of loading)

14. 3. Solvation and dissolution properties
● Polymers are usually slow to dissolve.
● Solvation characteristics are sensitive to Mw,Mw/Mn (piolydispersty), cross-
linking, crystallinity & chain branching.
● Longer chain- polymer dissolve slowly.
● Polymers absorb a solvent, swell, &soften, rather than dissolve
● Elastomers swell more than plastics.
● Absorbed molecules (e.g., water-) spread polymer chains apart and facilitate
slip between chains. This lubricating effect is called plasticization.

15. 4. Thermal properties
● Polymer chains are held together by- weak secondary bonds( Vander wall bonds)
- entanglement of chains if they are sufficient long.
● The higher the molecular weight ,the more entanglements there will be, giving a
stiffer & stronger polymer.
● Glass transition temperature (Tg) is the temperature in which macromolecule
molecular motion begins to force the molecular chains apart. thus, polymeric
material softens when heated above this temperature.

17. Chemistry of polymerisation
The process of polymerization were divided by Flory (1953) and Carothers
(Mark 1940) into two groups.

18. ADDITION POLYMERISATION
(CHAIN POLYMERISATION)
CONDENSATION POLYMERISATION
(STEP GROWTH POLYMERISATION)
Monomers are activated one at time and together in
a sequence to form growing or smaller chains.
Chemical reaction takes place with the release of
by-product or smaller units and there is change in
the final composition.
Types : free radical, Ring opening, ionic
polymerisation.
The by-product such as water or an alcohol to
be condensed out.
Eg.heat cured or autopolymerizing poly methyl
methacrylate etc.
Eg. Proteins, carbohydrates
Fast process
Slow process

19. Addition polymerisation
● It occurs among the molecules containing double or triple bonds. No small
molecules are liberated and reaction is rapid chain type reaction.
● Monomers add sequentially to the end of a growing chain
● Is very fast and exothermic
● Produces high molecular weight polymers
● The macromolecules are formed from smaller units, or monomers, without
change in composition because the monomer and the polymer have the same
empirical formulas.

20. Stages in addition polymerisation
The process of free radical additional polymerization to produce the polymers
involves 4 stages
1. Induction
2. Propagation
3. Chain transfer
4. Termination

21. Induction
The process of producing free radical is called activation.
Free radicals can be generated by activation of radical producing molecule using
1. Chemical agents
2. Heat
3. Visible light
4. Ultra Violet Light
5. Energy transferred from another compound which acts as a free radical. Of these
: Chemical agents, Heat & Visible light are most often used in dentistry.
Benzoyl peroxide commonly used in dentistry.

22. The Activation is done by the decomposition of the benzoyl peroxide.
A. Heat : When heated above 50 -100oC , benzoyl peroxide decomposes to form a
free radical. Heat cure acrylic resins
B. Chemical Compounds :
1. Benzoyl peroxide can also be activated when brought into contact with a tertiary
amine.
2. This method is used in cold cure acrylic resins, in chemically cured composite
restorative materials , which consists of a base paste ( tertiary amine activator)
& a catalyst paste (containing benzoyl peroxide initiator)
C. Light :
1. Ultra violet light in conjunction with a benzoic methyl ether.
2. Visible light with camphorquinone and an organic amine.

23. Initiation
The free radicals will react with a monomer such as ethylene and initiate the
polymerization process.
When this occurs ,the remaining unpaired electron makes the new molecule & a
free radical

24. Propagation
The free radicals are transferred to the monomer which in turn reacts with other
monomer
Repeating this process again and again generates the polymer chain until the
growing chains collide or all the free radicals have reacted.

25. Chain transfer
In this process, the active free radical of a growing chain is transferred to
another molecule and a new free radical for further growth is created.

26. Termination
The chain reactions can be terminated by :
1. Direct coupling of two free radical chain ends or by
2. Exchange of a hydrogen atom from one growing chain to another.
3. Collision of a growing chain with an initiation radical.
4. Collision of a growing chain with inhibitor.

27. Inhibition of addition polymerisation
Any impurity if it is present, it reacts with the monomer and inhibit polymerization .
eg. Hydroquinone 0.006%
Eugenol , Oxygen.
Main functions:
1. Aids in prevention of polymerization during storage
2. In case of two parts(self cure) system provides adequate time for mixing &
placement

28. 1. Free- radical polymerization
Initiator releases free- radicals which bring about the Polymerization reaction.
Eg : Benzoyl peroxide releases free- radicals to bring polymerization in acrylic resins.
1. Ring- opening poymerization
Ring structure in the polymer chain is opened & crossing- linking occurs.
Eg : Epoxy resin, Polyether impression material.
1. Ionic polymerization :
Catalyst bring about exchange of ions
resulting in cross- linked polymer. l Eg : Addition silicones

29. Step growth polymerisation
● When two molecules react to form a large molecule with the elimination of a
smaller molecules such as water, alcohol, halogen acids & ammonia.
● Polymers are formed more slowly than by addition polymerization because the
reaction proceeds in a stepwise fashion from monomer to dimer to trimer until
large polymer molecule containing many monomer molecule are eventually
formed
● Polymers are generally of lower molecular weight
● E.g in dentistry - polysulphide impression material (by-product water),
condensation silicone (by-product ethyl alcohol)

30. Copolymerisation
Polymer chain contains 2 or more chemically different types of monomer units.
Three types of copolymerisation
● Random type
● Block type
● Graft type

33. Acrylic dental resins
● Mostly used in fabrication of all complete dentures.
● Dr. Walter Wright (1937) introduced Polymethylmethacrylate as a denture base
material .
● ADA/ANSI specification no. 12 - Denture base resins.
● Are derivatives of ethylene (-C=C-) and contain vinyl group -CH2=CHR in their
structural formula.

34. Ideal requirements of dental Polymers

35. Methylmethacrlyate
The liquid monomer methyl methacrylate is mixed with the polymer, which is supplied
in the powdered form. The monomer partially dissolves the polymer to form a plastic
dough.
Transparent at room temperature.

36. POWDER LIQUID
Acrylic polymer (or copolymer)
beads
Initaitor
Pigments
Dyes
Opacifiers Plasticizers
Dyed organic fillers
Inorganic particles
Monomer
Inhibitor
Accelerator
Plasticizer
Cross-linking agent
Principal ingredients of acrylic denture base resin

37. Compositions of heat activated PMMA

38. Commercial names :
● Stellon (DPI)
● Lucitone (Bayer)
● Travellon (Dentsply)

39. Composition of chemically activated PMMA
I

40. POLYMER –TO- MONOMER RATIO
● The polymer to monomer ratio is 3:1 by volume.
● Using this ratio the volumetric shrinkage can be limited to 7%
● Polymer – monomer interaction
When mixed in proper proportions, the resultant mass passes through five distinct
stages
1. Sandy
2. Stringy
3. Doughlike
4. Rubbery
5. Stiff

41. SANDY STAGE:
- Little or no interaction at molecular level. - polymer beads remain unaltered (coarse
or grainy)
STRINGY STAGE:
- Monomer attacks the individual polymer beads and is absorbed into the beads. -
Some polymer chains are dispersed into monomer.
- characterized by Stringiness or Stickiness- touched
DOUGH STAGE:
- At the molecular level, an increased number of polymer chains enter the solution,
thus monomer and dissolved polymer- formed.
- It is no longer tacky or and will no longer adhere to the mixing vessel or spatula . -
The later phase of this stage are ideal for compression molding. Hence material is
inserted into the mould cavity during dough like stage.

42. RUBBERY STAGE:
- Because the monomer is dissipated by evaporation and by
further penetration into remaining polymer beads. - Mass rebounds when compressed or
stretched.
STIFF STAGE:
- Continued evaporation of unreacted monomer.
- Material looks dry and resistant to mechanical deformation

43. DOUGH FORMING TIME
● The time required for the resin mixture to reach a dough like stage.
● In clinical use, majority of the denture base products reach dough stage
consistency in less than 10 min.
WORKING TIME
● Defined as the time a denture base material remains in the dough like stage. This
period is critical to the compressive molding process.
● Ambient temperature affects the working time. Working time 5 minutes.

44. Residual Monomer
● Residual monomer decreases rapidly during the time of polymerisation
and more slowly after the most polymerisation is over.
● Residual monomer content in heat cure resins is around 0.3-0.5% and in
self cure it is around 3-5%
● This residual monomer might leach out & contact oral mucosa ,specially
denture bearing mucosa
● Irritant or allergic reaction by MMA monomer
● Light cure resins released comparatively less residual monomer than heat
or self cured
● For minimizing monomer released heat cure & chemical cured dental
resins must be immersed for 1 day in water before wearing

45. Polymerization shrinkage
● It is the volumetric shrinkage that occurs during the polymerization of MMA to
PMMA polymer.
● Density of the mass changes from 0.94 to 1.19gm/cm3
● Volumetric shrinkage of 21%
● Along with volumetric shrinkage linear shrinkage occurs during the cooling
process.
● It can be minimized by
1. A correct proportioning of the monomer &
2. The polymer packing in the dough stage .

46. NEW ERA IN DENTURE BASE RESINS- A REVIEW
1. Reinforced resins
a. High impact resins
b. Fiber-reinforced
2. Hypoallergenic resins
3. Resins with modified chemical structure
4. Thermoplastic resins
5. Enigma gum toning in denture bases

47. REINFORCED RESINS:
1. HIGH IMPACT RESINS
• Rubber reinforced (butadiene tyrene polymethyl methacrylate).
• Rubber particles grafted to MMA for better bond with PMMA.
CLINICAL APPLICATION:
• They are so called because of greater impact strength & fatigue
properties, hence indicated for patients who drop their dentures
repeatedly e.g. parkinsonism, senility. Available as powder liquid system
E.g Lucitone 199 , D.P.I Tuff

48. 2. FIBRE REINFORCED
Fiber reinforcement result in a 1000% strength increase over non-reinforced (if there is
proper bonding)
1. METAL REINFORCEMENT: Not widely used because unesthetic, expensive, poor
adhesion between wire & acrylic resin & metal being prone to corrosion. Metals can
be added in the form of wires, plates or fillers.
METAL MESH
METAL PLATE
METAL REINFORCED
WIRE

49. 2. CARBON/GRAPHITE FIBRE REINFORCEMENT:
● Carbon fibers (65-70 mm length, 5 % by weight & treated with silane coupling
agent) are placed during packing.
● Anisotropic and provides greatest reinforcement of denture base resin in terms
of flexural strength.
● Carbon Graphite fibres are available as-chopped, continuous, woven, braided
& tubular.
● ADVANTAGES: Increases flexural strength, impact strength, prevents fatigue
and strengthens the resin.
● DISADVANTAGES: Unesthetic because of black colour but this can be
covered by an opaquer. The polishing is difficult & also weakens the finished
prosthesis. In addition, there is problem of lateral spreading of fibers during
pressing.

50. ARAMID FIBER REINFORCED
An aramid is an organic compound
called polyparaphenylene terephthalamide and is marketed as Kevlar.
Aramid fiber reinforcement increases the strength but again they are unesthetic &
difficult to polish so limited to locations where aesthetics is not important.

51. POLYETHYLENE FIBER REINFORCED
● Multi fibered polyethylene strands cut to 65 mm length & surface treated with
epoxy-resin (to improve adhesion) are placed in resin during packing.
● They develop anisotropic properties to the composite (i.e. increase strength and
stiffness in one direction).
ADVANTAGE:
1. Highest impact strength
2. High modulus of elasticity
DISADVANTAGE :
1. Decreased transverse strength
2. Finishing and polishing is difficult
3. Does not bond well to the resin

52. HIGHLY DRAWN LINEAR POLYETHYLENE FIBERS (HDLPF)
● Patterns of continuous parallel fibers provide maximum reinforcement to both
maxillary & mandibular bases.
● horizontally positioned fibers in anterior part of labial flange & in region
immediately behind central incisors.
● Reinforcement done with 4 layers of fibers (2 in lateral direction sandwitched
between 2 layers at 45 degree from middle ones )
● In mandible, maximum stresses appear in labial & lingual second premolar
region & fracture occurs in middle region.
● Thus mandibular bases are reinforced with fibers at right angle to ridge located
close to polished & fitting surface
ADVANTAGES :
1. high tensile stiffness & strength
2. notch insensitivity & cracks do not propagate through array of fibers.
3. The coherence is maintained even after a large number of testing cycles.

53. GLASS FIBRES (HAVE BEST AESTHETICS)
● Chopped fibers mixed with denture base acrylic resin enhance isotropic mechanical
properties.
● 6 mm chopped glass fibers with 5% fiber in combination with injection moulding
technique result in increase in transverse strength, elastic modulus& impact
strength.
● Glass fibers may be modified by plasma polymerization technique using HEMA,
TEGDME
ADVANTAGES
These are the fibres of choice because of well documented improvement in :
Flexural properties, Fatigue resistance, the best aesthetics, excellent polishing
characteristics.
In addition, they resist extreme temperature, moisture, oil.

54. Types of glass fibres
● Different types of glass fibers are produced commercially; these include E-glass, S-
glass, R-glass and V-glass.
● Of these, E-glass fiber, (composition: SiO2,55%; CaO, 22%; Al203,15%; B2O3,6%;
which has high alumina and low alkali and borosilicate, is claimed to be superior in
flexural strength.
● Because the modulus of elasticity of glass fibers is very high, most of the stresses
are received by them without deformation.
● They are chemically stable and durable in the pH range 4-11

55. E-GLASS FIBERS
Each strand of this E-glass is computer impregnated with a PMMA (porous polymer) and
silane coupler that allows dissoloution bonding to acrylic. (e.g. Preat Perma Fiber )
ADVANTAGES
● Available in two forms (mesh & fiber)
● are translucent providing esthetics.
● Because of glass fiber bonding, they also have more strength.

56. POSITION & PLACEMENT OF FIBERS
1. Place the fiber in the weakest area (On tension side during
mastication)

57. 2. For repairs, place reinforcement 90 degree to the
fracture.

58. 3. Unidirectional fibers are stronger, especially when direction of
highest stress is known.

59. 4. Continuous, bidirectional fibres.

60. COMPARISON OF IMPACT STRENGTH OF RESINS REINFORCED WITH
DIFFERENT FIBERS:
Polyethylene > glass > thick Kevlar >carbon >thin Kevlar > unreinforced.

61. HYPOALLERGENIC RESINS
● Diurethane dimethacrylate, Polyurethane, Polyethylenterephthalate and
Polybutylenterephthalate.
● Hypoallergenic denture base materials exhibit significantly lower residual
monomer content than PMMA, thus act as an alternative in allergic patients
● Enterephthalate based (Promysan, thermoplastic) show low water solubility
than PMMA.
● Light activated indirect composite containing urethane dimethacrylate (UDMA)
is an alternative to PMMA for patients hypersensitive to PMMA

62. RESINS WITH MODIFIED CHEMICAL STRUCTURES
● Addition of hydroxy-apatite fillers increases fracture toughness.
● Al2O3 fillers increases the flexural strength & thermal diffusivity that could lead
to more patient satisfaction.
● 2% quaternary ammonium compound displays antiseptic properties & these
dentures may be used for geriatric patients to improve their oral health.
● Addition of ceramic or sapphire whiskers to improve thermal diffusivity.
● Addition of 11-14% of several compounds of either bismuth or uranium or 35%
of an organo-zirconium compound impart radiopacity equivalent to that of
aluminium.

63. THERMOPLASTIC RESINS:
● Fully polymerised basic material
● Softened by heat without chemical changes
ADVANTAGES
● Excellent esthetics
● Unbreakable, flexible, light weight
● Stable high fatigue endurance
● Increased creep and wear resistance
● Non porous: no bacterial growth but enough moisture to keep it comfortable
for gums.
● Can be relined and repaired

64. MATERIALS USED:
1. Thermoplastic nylon: polyamide (valplast, flexiplast)
2. Thermoplastic acetal
3. Thermoplastic acrylic
4. Thermoplastic polycarbonate: polymer of bisphenol-a

65. Thermoplastic nylon
Eg: valplast, lucitone frs (more impact resistance)

66. Thermoplastic acetal (polyoxymethylene)
18 VITA +3 PINK SHADES: FOR SIMULATING LIFELIKE APPEARANCE
Uses:
● Preformed clasps for RPD.
● Partial denture framework
● Provisional splints
● Occlusal splints

67. Thermoplastic acrylic
EXCEPTION: Flexite M.P. has the highest impact rating of any acrylic & does not
crack even if falls on floor thus very popular in bruxism and Parkinson's patients.

68. Thermoplastic polycarbonate - polymer of bisphenol A

69. ENIGMA GUM TONING
● Custom shade matching of natural gingival tissue using ‘Enigma’ colour
tones.
● Gives extra confidence to patient in appearance of their dentures.
● Available in Ivory, Light Pink, Natural Pink, Dark Pink & Light Brown.
Different colors are mixed to get the desired gum tone.

70. PEEK(NEWER MATERIAL)
POLYETHER ETHER KETONE (PEEK) BELONGING TO PAEK(POLYARYL-ETHER
KETONE) FAMILY
INTRODUCED IN DENTISTRY IN THE YEAR 1992