SEMINAR
ON
DENTURE BASE RESINS
INDIAN DENTAL ACADEMY
Leader in continuing dental education
www.indiandentalacademy.com
www...
Contents
Introduction
History
Requirements
Classification
Composition
- heat cure
- autopolymerising resin
-other resin ma...
Introduction
Denture base is that part of a denture
that rests on the foundation tissues and
to which teeth are attached.A...
History
1851 – Vulcanite was developed.
1853-1st
denture base from vulcanite was
constructed by Nelson Charles Goodyear,
1...
1910-1940
Other polymers:vinyl acrylics,Polystyrene,
Epoxy,Nylon, Vinyl styrene, Polycarbonates,
Polysulfonates-unsaturate...
1936- Vernonite or
poly methylmethacrylate(PMMA).
1st
practical replacement for Vulcanite.
1946- 95% of dentures were made...
Plastic other than acrylic resins
Nylon: found unsatisfactory owing to its poor ability to
resist oral conditions-swelled ...
Polycarbonates:Contains 10% glass fibers of
150um length and 10 um diameter.
•Good impact strength- nine times more than
P...
Requirements
1. Biological:
- non toxic and non-irritant.
2. Chemical:
- inert , in-soluble and non-absorbent.
3. Physical...
- High value of thermal conductivity: to maintain the
healthy mucosa,and to retain normal reaction to hot
and cold stimuli...
- Sufficient flexural strength to resist fracture.
- An adequate fatigue life and a high fatigue limit.
- Good impact stre...
CLASSIFICATION
I. According to ISO 1567
Type Class Description
1 1 Heat processing (powder and liquid)
1 2 Heat processing...
II. According to material system
1. Metallic – stainless steel denture base
2. Non-metallic – acrylic resins, etc.
III. Ac...
Acrylic resin materials
Polymerisation reaction:
The polymerisation of PMMA involves the
conversion of low molecular weigh...
Initiation
Free radical
Monomer moleculewww.indiandentalacademy.com
Propagation
www.indiandentalacademy.com
Termination
www.indiandentalacademy.com
Chain transfer
www.indiandentalacademy.com
Composition of heat cure denture base resin
Powder
a. Prepolymerised polymethyl methacrylate in the form
of beads or granu...
f. Inorganic particles-Glass fibers zirconium silicate,
silicone carbide etc. to increase the stiffness and
decrease the c...
d. Plasticizer- Dibutylpthalate, to produce a softer and
more resilient polymer.
Gel types – e.g. Vinyl acrylics
•Liquid a...
Self cure resins:
Dispensed as powder and monomer liquid.
Composition:
Polymer: PMMA in the form of beads.
Copolymer-PEMA
...
Monomer:
Methylmethacrylate monomer.
Inhibitor- hydroquinone
Cross linking agent- glycol dimethacrylate
Plasticizer- dibut...
R° + M RM°
Liberation of heat.
The rate of polymerisation is influenced by
particle size.
Properties:
Free of residual mon...
Shorter working time due to gradual increase in
viscosity.
Curing is done at room temperature. So better
fit and more stab...
Benefits:
- Eliminates the processing stresses.
- Less thermal contraction.
Disadvantages:
More residual monomer
Low mecha...
property Heat cure Self cure
Method of
activation
heat Chemical
Composition No DMPT Present
Polymerisation
reaction
Heated...
Compressive
strength(Mpa)
75 65
Impact
strength(MPa)
1.5x106
at
17.2MPa
Less
Tensile
strength(MPa)
65 lesser
Residual
mono...
Water solubility 0.02 mg/cm 2
0.05mg/cm 2
Water
sorption(mg/cm 2
)
0.6 0.7
Aesthetic quality Good color
stability
No good ...
Aspects of manipulation
1. Preparation of the mould
2. Selection of separating medium
3. Powder liquid ratio
4. Polymer mo...
1. Preparation of the mould
CAP
COPE
DRAG
www.indiandentalacademy.com
2. Selection of separating medium
Used to separate the denture base material from the
mould surface.
Formerly, Tin foil wa...
- Soap
- Sodium silicate
- Starch
The most commonly used separating medium are
water soluble alginates.
Composition:
1. So...
Setting reaction:
Potassium alginate + calcium sulphate calcium
alginate + potassium sulphate
Functions:
1. To prevent the...
: Powder liquid ratio
It controls the workability of the mix and the
dimensional change on setting.
•Too much powder: Unde...
Polymer monomer interaction
The powder is slowly added to the liquid to get a
workable mass which passes thro five distinc...
(4) Rubbery or elastic stage:dissipation of monomer.
clinically, rebound and stretches.
(5) Stiff stage:evaporation of fre...
Packing
The dough is packed into the mould
cavity.
•Packed at sandy or stringy stage,
too much monomer will be present
bet...
Bench curing
After the final closure of the flask , it is allowed to
stand for 1 hour.
Objective: For more uniform dispers...
Polymerisation cycle or Curing cycle:
The heating process used to control polymerisation is
termed polymerisation cycle.Th...
3.Processing the resin at 74°C for approximately 2 hour
and increasing the temperature of the water bath to
100°C and proc...
Processing defects of dentures
Rough or irregular surface.
Porosity
Dimensional changes
Processing stresses
Crazing
Fractu...
Rough or irregular surface
Improper wetting of wax denture by plaster mix.
Entrapment of air bubbles in investing plaster....
porosity
Undesirable effect on the strength and optical,
hygienic properties.The causes are:
Polymerisation shrinkage term...
Granular porosity-granular effect on the
denture surface, due to low powder liquid
ratio.
Blotchy, opaque surface – when m...
Processing stresses
Polymerisation shrinkage.
Mechanical stresses on repeated drying and
wetting of the denture, causing a...
Crazing
May appear on the surface and has weakening effect.
Delayed packing.
Constant cycle of drying and wetting done by ...
fractures
Dentures may break:
On impact(extra orally)
Due to fatigue, form repeated bending
of the denture in service.(if ...
INJECTION MOULDING TECHNIQUE
In this technique, for injection of resin, a hollow
sprue connects the mould cavity created b...
www.indiandentalacademy.com
Advantage:
-increased dimensional accuracy.
-Elimination of trial closures.
-It can be used for microwavable and pour type...
Pour type denture resins/ pour and cure
resins/ fluid resins
These are cold cure resins.
Difference in the size of polymer...
Fluid resin technique
Employs a pour able resins,
chemically activated resin.
Dispensed as a powder
liquid system.(2.5:1by...
www.indiandentalacademy.com
Uses:
Three methods of duplicating dentures with pour
type autopolymerising resin.The method differ
in the type of flask a...
Advantages:
- Improved adaptation to underlying soft tissues
- Decreased probability of damage to prosthetic
teeth and den...
Modified acrylics
Objective is to improve the impact strength,
fatigue resistance, or radiopacity.
The impact strength or ...
THE FATIGUE RESISTANCE:or fibre
reinforced acrylics
1. adding carbon fibers:
Positioning of fibers is critical,placed in t...
Advantages:
-Increase in impact and flexural strength
-Improvement in fatigue resistance.
-Minimizing denture fractures.
D...
RADIOPACITY:Incorporating atoms of high
atomic numbers than the C,H, and O atoms of
which acrylic resin is made.
Radiopaqu...
Co-monomer containing heavy
metals e.g barium acrylate
Polymer has poor
mechanical
properties
Halogen - containing Co-
mon...
ALTERNATIVE POLYMERS:
Polycarbonates and certain vinyl polymers.
Indications: allergic patient.
when greater impact streng...
procedure: after placing the denture in boiling
water , boiled for 20 mins and then bench
cooling .
The initiator is formu...
Hydrophilic acrylics
consist of co-polymer of methylmethacrylate
and hydroxyethyl methacrylate.
This material is easily we...
Microwave activated resins
Electromagnetic waves.
A special glass fibre reinforced plastic flask.
Processing technique: co...
Disadvantages:
- high capital cost.
- Flasks easily fracture.
- Porosity if condition are not controlled.
www.indiandental...
Light activated denture base resins
Single component denture base resin
supplied in pre mixed sheet or rope forms
It is a ...
www.indiandentalacademy.com
The acrylic is polymerized in a light chamber
with blue light of 400 to 500nm.
The denture base rotates in the chamber.
Se...
Disadvantages:
High capital cost.
Inferior bond to resin denture.
Lower elastic modulus and slightly
lower flexural streng...
Summary and conclusion
Denture bases are responsible for
artificial tooth fixation,stability and
distribution of masticato...
References
Anusavice Kenneth J.: Phillips Science of Dental
Materials. 10th
edition, W.B. Saunders, 1999.
Combe E.C.: Note...
Austin AT, Basker RM. Residual monomer levels in
denture bases. Br Dent J 1982;153:424
McCabe JF and Walls AWG: Applied de...
•Consani RLX, Dometti SS and Consani S. effect of new
tension system, used in acrylic resin flasking, on the
dimensional s...
Keenan PL,Radford DR & Clark RKF.dimensional
change in complete dentures fabricated by injection
moulding and microvave pr...
Thank you
For more details please visit
www.indiandentalacademy.com
www.indiandentalacademy.com
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Transcript of "Denture base resins/ cosmetic dentistry training"

  1. 1. SEMINAR ON DENTURE BASE RESINS INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  2. 2. Contents Introduction History Requirements Classification Composition - heat cure - autopolymerising resin -other resin materials Aspects of manipulation Recent advances(modified acrylics) Summary and conclusion References www.indiandentalacademy.com
  3. 3. Introduction Denture base is that part of a denture that rests on the foundation tissues and to which teeth are attached.Although individual denture bases may be formed from metals or metal alloys, the majority of denture bases are fabricated using polymers. www.indiandentalacademy.com
  4. 4. History 1851 – Vulcanite was developed. 1853-1st denture base from vulcanite was constructed by Nelson Charles Goodyear, 1891- use of vulcanite as a denture base material was considered “universal”. 1869- Celluloid was introduced, developed from plant framework. It had natural gingival colour but short shelf life.therefore, NEW MODE CONTINOUS combination product, of rubber denture base material, a celluloid gum work area and porcelain teeth. www.indiandentalacademy.com
  5. 5. 1910-1940 Other polymers:vinyl acrylics,Polystyrene, Epoxy,Nylon, Vinyl styrene, Polycarbonates, Polysulfonates-unsaturated Polyester, Polyurethane,Polyvinyl acetate- ethylene, Hydrophilic polyacrylate,Silicones,Light activated urethane dimethacrylate,Rubber reinforced acrylics, and Butadiene- reinforced acrylics. 1930-1940 the Phenol formaldehyde products were 1st to compete with vulcanite. Self cure were introduced after world war II. www.indiandentalacademy.com
  6. 6. 1936- Vernonite or poly methylmethacrylate(PMMA). 1st practical replacement for Vulcanite. 1946- 95% of dentures were made with Vernonite www.indiandentalacademy.com
  7. 7. Plastic other than acrylic resins Nylon: found unsatisfactory owing to its poor ability to resist oral conditions-swelled badly. -if left outside water will shrink. The epoxy resins:drawbacks -high rate of water sorption with dimensional change,fracture,loss of posterior teeth,heavy deposition of various stains and calculus,colour change and some fouling odour. -Phenol formaldehyde(Bakelite):proved too difficult to process. •Color instability. Vinyl resins:low resistance to fracture. •Failure were common. www.indiandentalacademy.com
  8. 8. Polycarbonates:Contains 10% glass fibers of 150um length and 10 um diameter. •Good impact strength- nine times more than PMMA. •More difficult to mould dentally, since injection moulding technique is required. •Greater water sorption,higher flexibility,lower hardness,lower adhesion to acrylic teeth. Acrylics: Better aesthetic quality •Easy to process using inexpensive techniques. •Shrink at the rate of 1um in eight hours. if left outside www.indiandentalacademy.com
  9. 9. Requirements 1. Biological: - non toxic and non-irritant. 2. Chemical: - inert , in-soluble and non-absorbent. 3. Physical: - Aesthetically satisfactory. - The softening temperature should be higher than the temperature of liquids and food ingested. - Dimensionally stable. - Low value of specific gravity or density. www.indiandentalacademy.com
  10. 10. - High value of thermal conductivity: to maintain the healthy mucosa,and to retain normal reaction to hot and cold stimuli. - It should be radio-opaque. 4. Mechanical properties: - A high value of modulus of elasticity- For greater rigidity. - A high value of elastic limit to prevent permanent deformation. - A combination of both above would allow the base to be fabricated in thin sections. www.indiandentalacademy.com
  11. 11. - Sufficient flexural strength to resist fracture. - An adequate fatigue life and a high fatigue limit. - Good impact strength. - Sufficient abrasion resistance to prevent excessive wear. 5. Miscellaneous - Relatively inexpensive. - Easy to manipulate and fabricate. - Easy to clean. - Easy to repair. www.indiandentalacademy.com
  12. 12. CLASSIFICATION I. According to ISO 1567 Type Class Description 1 1 Heat processing (powder and liquid) 1 2 Heat processing (plastic cake) 2 1 Self cure (powder and liquid) 2 1 Self cure (powder and liquid pour type resins) 3 - Thermoplastic blank or powder 4 - Light-activated materials 5 - Microwave materialswww.indiandentalacademy.com
  13. 13. II. According to material system 1. Metallic – stainless steel denture base 2. Non-metallic – acrylic resins, etc. III. According to mode of polymerization 1. Addition polymer – e.g. acrylic resins, polyvinyl chloride, polymethyl methacrylate 2. Condensation polymer – e.g. bakelite, nylon IV.According to method of activation 1. Thermal – heat cure acrylics 2. Chemical- self cure acrylics 3. Light activated 4. Microwave energywww.indiandentalacademy.com
  14. 14. Acrylic resin materials Polymerisation reaction: The polymerisation of PMMA involves the conversion of low molecular weight monomer to high molecular weight polymer. Free radical addition polymerisation which involves activation, initiation ,propagation and termination. www.indiandentalacademy.com
  15. 15. Initiation Free radical Monomer moleculewww.indiandentalacademy.com
  16. 16. Propagation www.indiandentalacademy.com
  17. 17. Termination www.indiandentalacademy.com
  18. 18. Chain transfer www.indiandentalacademy.com
  19. 19. Composition of heat cure denture base resin Powder a. Prepolymerised polymethyl methacrylate in the form of beads or granules. b. Initiators – Benzoyl peroxide (0.5-1.5%), to initiate the polymerization of the monomer c. Plasticizer – Dibutylpthalate (8-10%), increases the rate of dissolution of polymer in monomer. d. Pigments – Cadmium selenide (pink), Mercuric sulfide (red),Rouge/ Ferric oxide(brown). e. Synthetic fibers:Acrylic or nylon to give veined appearance. www.indiandentalacademy.com
  20. 20. f. Inorganic particles-Glass fibers zirconium silicate, silicone carbide etc. to increase the stiffness and decrease the coefficient of thermal expansion. g. Opacifiers-Heavy metal compounds, e.g. salts of Barium and Strontium. Liquid a. Methyl methacrylate monomer- It has a limited shelf life b. Inhibitor- Hydroquinone, added to improve the shelf life of monomer c. Cross linking agent- Ethylene glycoldimethacrylate, it improves the mechanical properties, more resistant to surface crazing. www.indiandentalacademy.com
  21. 21. d. Plasticizer- Dibutylpthalate, to produce a softer and more resilient polymer. Gel types – e.g. Vinyl acrylics •Liquid and powder have been mixed to form a gel and shaped into a thick sheet. •Chemical accelerators cannot be used. www.indiandentalacademy.com
  22. 22. Self cure resins: Dispensed as powder and monomer liquid. Composition: Polymer: PMMA in the form of beads. Copolymer-PEMA Initiator (< 2%) Benzoyl peroxide Plasticizer dibutyl phthalate Colour pigments: salts of Mercury and Iron Dyed synthetic fibers Inorganic particles glass fibers, Zirconium Silicate Radio-Opacifiers-salts of Barium . www.indiandentalacademy.com
  23. 23. Monomer: Methylmethacrylate monomer. Inhibitor- hydroquinone Cross linking agent- glycol dimethacrylate Plasticizer- dibutylpthalate Activator- dimethyl para toludine Setting reaction: PMMA +initiator+MMA+inhibitor+activator (powder) (liquid) free radicals(R°) www.indiandentalacademy.com
  24. 24. R° + M RM° Liberation of heat. The rate of polymerisation is influenced by particle size. Properties: Free of residual monomer- 3-5% Polymerisation of self cure is never completed. The effects of free residual monomer:released from the denture thus irritate the mucosa. it will act as plasticizer and make the resin weaker and more flexible. The degree of polymerisation is inferior.www.indiandentalacademy.com
  25. 25. Shorter working time due to gradual increase in viscosity. Curing is done at room temperature. So better fit and more stable. The color stability is not good. Easy to manipulate. Manipulation: Compression moulding technique -Allowed to polymerize at room temperature in a pressure chamber. -Dough forming time is 5 mins. -Trial closure only 1 or 2 . -For complete polymerisation kept for 2 ½ hrs or overnight. www.indiandentalacademy.com
  26. 26. Benefits: - Eliminates the processing stresses. - Less thermal contraction. Disadvantages: More residual monomer Low mechanical properties. Colour instability. Uses: Occasionally used for denture bases. -Preparation of special trays. -Denture repairs, relining and rebasing. -For removable orthodontic appliances. www.indiandentalacademy.com
  27. 27. property Heat cure Self cure Method of activation heat Chemical Composition No DMPT Present Polymerisation reaction Heated to 60 to 70°C On mixing Degree of polymerisation high low Mechanical Superior inferior www.indiandentalacademy.com
  28. 28. Compressive strength(Mpa) 75 65 Impact strength(MPa) 1.5x106 at 17.2MPa Less Tensile strength(MPa) 65 lesser Residual monomer .2-.4% 3-5% Thermal shrinkage higher Lesser crazing greater Better dimensional stabilitywww.indiandentalacademy.com
  29. 29. Water solubility 0.02 mg/cm 2 0.05mg/cm 2 Water sorption(mg/cm 2 ) 0.6 0.7 Aesthetic quality Good color stability No good color stability Processing shrinkage 0.53% 0.26% www.indiandentalacademy.com
  30. 30. Aspects of manipulation 1. Preparation of the mould 2. Selection of separating medium 3. Powder liquid ratio 4. Polymer monomer interaction 5. Dough forming time 6. Packing 7. Bench curing 8. Polymerization cyclewww.indiandentalacademy.com
  31. 31. 1. Preparation of the mould CAP COPE DRAG www.indiandentalacademy.com
  32. 32. 2. Selection of separating medium Used to separate the denture base material from the mould surface. Formerly, Tin foil was used, but it was a time consuming and difficult process. Causes: a. Dimensional inaccuracy b. Poor reproduction of details Tin foil substitutes: -Cellulose lacquers -Evaporated milk -Solutions of alginate compoundswww.indiandentalacademy.com
  33. 33. - Soap - Sodium silicate - Starch The most commonly used separating medium are water soluble alginates. Composition: 1. Sodium/potassium alginate- 2-3% 2. Di/tri sodium phosphate- 0.7% 3. Preservatives- 0.3% 4. Glycerin- 4% 5. Alcohol- 7% 6. Balanced with water- 85% www.indiandentalacademy.com
  34. 34. Setting reaction: Potassium alginate + calcium sulphate calcium alginate + potassium sulphate Functions: 1. To prevent the diffusion of water from the mold into the un polymerized packed dough. 2. To prevent the diffusion of the monomer from the unpolymerised packed dough into the mould material. Precautions: The coating should be uniform. -De waxing must be done thoroughly. -The resin teeth should not be coated.www.indiandentalacademy.com
  35. 35. : Powder liquid ratio It controls the workability of the mix and the dimensional change on setting. •Too much powder: Under wetting of the polymer beads •Too much of monomer-Excessive Polymerisation shrinkage and loss of quality of fit. •To reduce the volumetric Polymerisation shrinkage from 21% to 7% and linear shrinkage to 0.5% - Use of prepolymerised resin is recommended - 3:1 polymer and monomer ratio. www.indiandentalacademy.com
  36. 36. Polymer monomer interaction The powder is slowly added to the liquid to get a workable mass which passes thro five distinct stages: (1) Wet, sand like stage (2) Stringy stage/ a tacky fibrous stage. (3) A smooth Dough like stage:On molecular level:Increase in no. of polymers chains, a large amount of undissolved polymer remains. clinically, no longer tacky and does not stick to mixing spatula.The latter phases of this stage is ideal for compression moulding. www.indiandentalacademy.com
  37. 37. (4) Rubbery or elastic stage:dissipation of monomer. clinically, rebound and stretches. (5) Stiff stage:evaporation of free monomer. clinically, the mixture appears dry and is resistant to mechanical deformation. DOUGH FORMING TIME: The time required for resin mixture to reach a dough like stage.According to ADA-12 it is less than 40 mins & clinically it reaches in 10 mins. WORKING TIME:According to ADA-12,the dough to remain moldable for atleast 5 mins. www.indiandentalacademy.com
  38. 38. Packing The dough is packed into the mould cavity. •Packed at sandy or stringy stage, too much monomer will be present between the powder particles. •If too early : porosity. •If done at rubbery or stiff stage, material too viscous to flow. •Over packing:Excessive thickness and mal positioning of prosthetic teeth. •Under packing: Noticeable porosity. •The acrylic dough is packed into the flask by use of pneumatic, hydraulic or mechanical press. www.indiandentalacademy.com
  39. 39. Bench curing After the final closure of the flask , it is allowed to stand for 1 hour. Objective: For more uniform dispersion of monomer throughout the mass. www.indiandentalacademy.com
  40. 40. Polymerisation cycle or Curing cycle: The heating process used to control polymerisation is termed polymerisation cycle.This process should be well controlled to avoid the effects of uncontrolled temperature rise, such as boiling of the monomer, or denture base porosity.The following techniques are there: 1.Involves processing the denture base resin in a constant temperature water bath at 74°C(165°F) for 8 hours or longer, with no terminal boiling treatment.(slow curing) 2.Processing in a 74°C water bath for 8 hour and then increasing the temperature to 100°C for 1 hour. www.indiandentalacademy.com
  41. 41. 3.Processing the resin at 74°C for approximately 2 hour and increasing the temperature of the water bath to 100°C and processing for 1hr.(fast curing) BENCH COOLING: It is cooled slowly as rapid cooling may result in warpage because of differences in thermal contraction of resin and investing stone. Bench cooled for 30mins and subsequently immersed in cool tap water for 15mins. www.indiandentalacademy.com
  42. 42. Processing defects of dentures Rough or irregular surface. Porosity Dimensional changes Processing stresses Crazing Fractures www.indiandentalacademy.com
  43. 43. Rough or irregular surface Improper wetting of wax denture by plaster mix. Entrapment of air bubbles in investing plaster. Low liquid powder ratio. Incomplete de waxing. Insufficient or improper coating of separating agent. delayed packing. Insufficient material in the mold. www.indiandentalacademy.com
  44. 44. porosity Undesirable effect on the strength and optical, hygienic properties.The causes are: Polymerisation shrinkage termed contraction porosity-appear as irregular voids throughout, and on the surface of denture. causes:insufficient material, insufficient pressure. Gaseous porosity shows fine uniform bubbles. Particularly in thicker regions. Localised porosity-improper mixing of components or early packing.www.indiandentalacademy.com
  45. 45. Granular porosity-granular effect on the denture surface, due to low powder liquid ratio. Blotchy, opaque surface – when mixing vessel’s lid is not covered. Rapid heating Insuffiecint mixing Insuffient pressure www.indiandentalacademy.com
  46. 46. Processing stresses Polymerisation shrinkage. Mechanical stresses on repeated drying and wetting of the denture, causing alternate contraction and expansion. During deflasking internal stresses are developed. Difference in the coefficient of thermal expansion of acrylic resin and investing material. www.indiandentalacademy.com
  47. 47. Crazing May appear on the surface and has weakening effect. Delayed packing. Constant cycle of drying and wetting done by patient. it is around the tooth neck Difference in the coefficient of thermal expansion of porcelain teeth and acrylic resin.(1:10) Solvent action-Use of MMA monomer during denture repair. Sudden cooling. During polishing . www.indiandentalacademy.com
  48. 48. fractures Dentures may break: On impact(extra orally) Due to fatigue, form repeated bending of the denture in service.(if parallel cracks).(intra orally) Presence of notches. Inadequate curing time. Excessive grinding and polishing www.indiandentalacademy.com
  49. 49. INJECTION MOULDING TECHNIQUE In this technique, for injection of resin, a hollow sprue connects the mould cavity created by wax boil out to an external opening on the flask and a high pressure injection cylinder is connected to the opening. The pressure is maintained during the polymerisation cycle. www.indiandentalacademy.com
  50. 50. www.indiandentalacademy.com
  51. 51. Advantage: -increased dimensional accuracy. -Elimination of trial closures. -It can be used for microwavable and pour type resins. Drawbacks: -inadequate spr uing will lead to under filled moulds. -Expensive equipment. -Injector is difficult to clean. www.indiandentalacademy.com
  52. 52. Pour type denture resins/ pour and cure resins/ fluid resins These are cold cure resins. Difference in the size of polymer. Slurry mixed which is poured into agar- hydrocolloid mold and allowed to polymerize under pressure at 0.14MPa for 30 –45 mins.. Centrifugal casting and injection molding techniques are used. www.indiandentalacademy.com
  53. 53. Fluid resin technique Employs a pour able resins, chemically activated resin. Dispensed as a powder liquid system.(2.5:1by wt.) www.indiandentalacademy.com
  54. 54. www.indiandentalacademy.com
  55. 55. Uses: Three methods of duplicating dentures with pour type autopolymerising resin.The method differ in the type of flask and the investing media. 1. Modified denture flask method (Brewer and morrow, 1975) 2. The pour –resin flask method(Boos and carpenter 1974) 3. The cup and flask method(Wagner, 1970 Singer, 1975) -in the preparation of the saddles for partial dentures, in which trial packing is difficult. www.indiandentalacademy.com
  56. 56. Advantages: - Improved adaptation to underlying soft tissues - Decreased probability of damage to prosthetic teeth and denture bases during deflasking - Reduce material cost - Simple procedure Disadvantages: - Noticeable shifting of teeth - Air entrapment within the denture base material - Poor bonding between the denture base material and teeth - Technique sensitive www.indiandentalacademy.com
  57. 57. Modified acrylics Objective is to improve the impact strength, fatigue resistance, or radiopacity. The impact strength or high impact strength materials -improved by adding -Elastomers: able to absorb energy. -Use of acrylic-elastomer copolymer e.g. methylmethacrylate-butadiene or methylmethacrylate- butadiene-styrene copolymers. Increased by 10 fold. Drawback is greater cost.www.indiandentalacademy.com
  58. 58. THE FATIGUE RESISTANCE:or fibre reinforced acrylics 1. adding carbon fibers: Positioning of fibers is critical,placed in that part of denture which is under tensile stress. bonding between the fibres and acrylics is difficult to achieve, further weaken the denture therefore the technique is a complicating factor. Unaesthetic. 2.other reinforcing fibres: Kevlar (aramid),nylon, glass fibres Ultra high modulus polyethylene polymers(UHMPE) 3. Metal inserts(wires,plates,fillers) www.indiandentalacademy.com
  59. 59. Advantages: -Increase in impact and flexural strength -Improvement in fatigue resistance. -Minimizing denture fractures. Drawbacks: -Tissue irritation from glass fibres -Straw colored Kevlar fibres. -Increase in production time. -difficulties in handling. -Metal inserts failure due to stress concentration. www.indiandentalacademy.com
  60. 60. RADIOPACITY:Incorporating atoms of high atomic numbers than the C,H, and O atoms of which acrylic resin is made. Radiopaque additives comments Metal inserts or powdered metals May weaken the base & is unaesthetic. Inorganic salts(barium sulphate), Bismuth(10 to 15%) At 8% insufficient radiopacity At 20% weaken the basewww.indiandentalacademy.com
  61. 61. Co-monomer containing heavy metals e.g barium acrylate Polymer has poor mechanical properties Halogen - containing Co- monomer or additives e.g. Tribromophenylmethacrylate Bromine containing Co- monomers. Additives may act as plasticizer Co-monomers are expensive. Most promising ones. www.indiandentalacademy.com
  62. 62. ALTERNATIVE POLYMERS: Polycarbonates and certain vinyl polymers. Indications: allergic patient. when greater impact strength is required. Processing: Injection molding. So special equipment is required. RAPID HEAT POLYMERISED RESINS OR HYBRID ACRYLICS:polymerized in boiling water immediately after being packed into a denture flask. www.indiandentalacademy.com
  63. 63. procedure: after placing the denture in boiling water , boiled for 20 mins and then bench cooling . The initiator is formulated form both chemical and heat activated initiators to allow rapid polymerisation. Polymerisation shrinkage-0.97-0.43% double the conventional ones. www.indiandentalacademy.com
  64. 64. Hydrophilic acrylics consist of co-polymer of methylmethacrylate and hydroxyethyl methacrylate. This material is easily wetted so enhanced denture retention. Drawback: Poorer mechanical properties than PMMA when material is saturated with water. www.indiandentalacademy.com
  65. 65. Microwave activated resins Electromagnetic waves. A special glass fibre reinforced plastic flask. Processing technique: compression moulding. microwave energy in an oven at 500-600W curing time as short as 3 mins. Advantages: -short processing time.,easy and clean . -Dimensional accuracy. - comparable physical properties.www.indiandentalacademy.com
  66. 66. Disadvantages: - high capital cost. - Flasks easily fracture. - Porosity if condition are not controlled. www.indiandentalacademy.com
  67. 67. Light activated denture base resins Single component denture base resin supplied in pre mixed sheet or rope forms It is a composite having a matrix of urethane dimethacrylate, microfine silica and high molecular weight acrylic resin monomer; no methyl methacrylate is present a) Organic filler- acrylic resin beads b) Activator- visible light c) Initiator- camphoroquinone www.indiandentalacademy.com
  68. 68. www.indiandentalacademy.com
  69. 69. The acrylic is polymerized in a light chamber with blue light of 400 to 500nm. The denture base rotates in the chamber. Setting reaction is free radical addition polymerisation. A bonding agent – mixture of acrylic monomers, including methyl methacrylate;cured by visible light. Advantages: No flask required. Short processing time. Improved fit, comparable impact strength & hardness www.indiandentalacademy.com
  70. 70. Disadvantages: High capital cost. Inferior bond to resin denture. Lower elastic modulus and slightly lower flexural strength-increase deformation. Recently, they have been trying the use of lasers for polymerisation of resins. www.indiandentalacademy.com
  71. 71. Summary and conclusion Denture bases are responsible for artificial tooth fixation,stability and distribution of masticatory forces over a large tissue bearing area.so far acrylic resins are most commonly used and still the research is going on the resins which will fill all the requirements of dentist and patient. www.indiandentalacademy.com
  72. 72. References Anusavice Kenneth J.: Phillips Science of Dental Materials. 10th edition, W.B. Saunders, 1999. Combe E.C.: Notes on dental materials: 6th ed. Churchill Livingstone, 1992. Craig Robert G. and Powers J.M.: Restorative dental materials. 11th ed. Mosby Inc. 2002. Gladwin Marcia, Bagby Michael: Clinical aspects of dental materials, Lippincott, 2000. Vermilyea SG, Powers JM and Koran A. the rheological properties of fluid denture base resins. J www.indiandentalacademy.com
  73. 73. Austin AT, Basker RM. Residual monomer levels in denture bases. Br Dent J 1982;153:424 McCabe JF and Walls AWG: Applied dental materials, 8th ed. Blackwell Science Limited, 1998. O’Brien WJ: Dental material and their selection, 2nd ed. Quintessence, 1997. Van Noort Richard: Introduction to dental materials, Mosby 1994. Devlin H, Watts DC. Acrylic “allergy”. Br Dent J 1984;157:272 Elahi JM, Abdullah MA. Effects of different polymerisation techniques on dimensional stability of record bases. J Prosthet Dent 1994;71:150-3 www.indiandentalacademy.com
  74. 74. •Consani RLX, Dometti SS and Consani S. effect of new tension system, used in acrylic resin flasking, on the dimensional stability of denture bases. J Prosthet Dent 2002;88:285-9 •Morata H, Toki K, Hong G and Hamda T.effect of tissue conditioners on the dynamic viscoelastic properties of a heat polymerised denture base. J Prosthet Dent 2002;88:409-14 •Yannikakis S,Zissis A,Dent,Polyzios G & Andreopuolos A.Evaluation of porosity in microwave-processed acrylic resin using a photographic method.J Prosthet Dent 2002;87:613-9 •Rueggeberg FA.From vulcanite to vinyl, history ofwww.indiandentalacademy.com
  75. 75. Keenan PL,Radford DR & Clark RKF.dimensional change in complete dentures fabricated by injection moulding and microvave processing. J Prosthet Dent 2003;89:37-44 Zappini G,Kammann A & Wachter W.comparison of fracture tests of denture base materials. J Prosthet Dent 2003;90:578-85 www.indiandentalacademy.com
  76. 76. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com

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