Denture Base Resins Question and Answers

Denture Base Resins Important Notes

1. Composition Of Heat-Activated Resin

2. Heat Cure And Self-Cure Resins

3. Porosity

• Internal porosity
• Occurs in central thick areas of the denture if the resin is heated above the boiling point of the monomer
• External porosity
• Occurs due to inadequate pressure, application, and improper mixing of monomer and polymer

Read And Learn More: Dental Materials Question and Answers

4. Stages In The Mixing of Heat Cure Resin

• Wet sandy stage
• Sticky stage
• Dough stage
• Rubbery stage
• Stiff stage

5. Tissue Conditioners

• They are highly plasticized acrylic resins used as temporary soft liners to condition the inflamed and distorted tissues caused by ill-fitting dentures
• It contains polymer powder and a liquid containing aromatic ester in ethanol

Denture Base Resins Long Essays

Question 1. What are denture base rosins? Describe the properties and manipulation technique of heat-cure acrylic resin.
Answer:

Denture Base Resin Properties:

• Monomer
  • Clear, transparent, volatile liquid
  • Sweetish odor
  • Melting point–48° C
  • Boiling point-iOO°C
  • Density -0.945 gm/ml at 20° C
  • The heat of polymerization is 12.9 Kcal/mol
  • Volume shrinkage-21%
• Polymer
• Tasteless, odorless
• Aesthetic acceptable
• Density-1.19 m/cm3
• Strength-low
• Compressive strength -75 MPa
• Tension strength -52 MPa
• Impact strength – increases by plasticizer
• Hardness -18-20 KHN
• Modulus of elasticity -2400 MPa
• Well-processed acrylic has good dimensional stability
• It shrinks due to
• Thermal shrinkage
• Polymerization shrinkage
• Water sorption-0.6 mg/cm2
• Insoluble in water and oral fluids
• Thermal properties -Softenat 125 C
• Poor conductor of heat and electricity
• High coefficient of thermal expansion
• Has good color stability
• Biocompatible
• Adhesion to metal and porcelain is poor
• Adhesion to denture teeth is good
• Shelf life varies

Denture Base Resin Manipulation Techniques:

• Compression molding technique
  • Commonly used technique
  • Steps
  • Preparation of wax pattern
  • Preparation of split mold
  • Application of separating media
  • Mixing of powder and liquid
  • Parking Curing Cooling Deflasklng
  • finishing and polishing
• Injection molding technique
  • Mold space Is filled by injecting Resin under pressure
  • A sprue hole and vent are formed in the mold
  • Soft resin Is forced into the mold space through Injector
  • It Is kept under pressure until it hardens
• Fluid resin technique
  • Resin is mixed to form a thin dough
  • This can be poured into the mold space
  • Kept In a pressure chamber for 30-60 min
  • Light cure denture base technique
  • Visible light of 468 nm is used as an activator and a complete denture is cured in a light chamber for .10 min

Acrylic Denture Base Resins 

Question 2. Write in detail about the composition and the properties of denture base resin and add a note on light-activated denture base resins
Answer:

Denture Base Resin Powder:

Denture Base Resin Liquid:

Light Activated Denture Base Resin:

• Consist of
• A urethane methacrylate matrix
• Microfine silica fillers
• Camphoroquinone amine photoinitiator system
• N.N. Dimethyl paratoludineacceleritor

Denture Base Resin Technique:

Denture Base Resin Disadvantages:

• Complicated
• Expensive
• No improvement in properties

Question 3. What are soft liners? Write composition, properties, and uses of tissue conditioners
Answer:

Soft Liners Types:

• Temporary soft liners
• Permanent soft liners
• Plasticized acrylic resin
• Vinyl resin
• Silicone rubber

Soft Liners Purpose:

• To protect soft tissues by acting as a cushion
• Used when irritation of the mucosa occurs
• Used in areas of severe undercut and congenital or acquired defects of the palate

Soft Liners Tissue Conditioner:

Tissue conditioners are materials whose useful function is very short

Soft Liners Composition:

• Powder-poly ethyl methacrylate and its copolymers
• Liquid-aromatic ester in ethanol or alcohol of high molecular weight

Soft Liners Properties:

• Viscous properties
• Allow excellent adaptation to the irritated denture-bearing mucosa
• Elastic behavior
• Cushions the tissues from the forces of mastication and bruxism

Soft Liners Uses:

• Reclining of ill-fitting dentures
• As an impression material

Advantages Of Acrylic Denture Base Resins

Question 4. Classify denture base resins. Write the composition and action of each constituent of heat cure acrylic. Add a note on porosity and its causes in dental acrylic resins.
Answer:

Denture Base Resins Classification:

• Temporary
• Shellac base plate
• Base plate wax
• Permanent
• Light cure resin
• Pour type resins
• Injection molded resins

Denture base resins porosity:

Denture Base Resins Short Essays

Question 1. Resilient denture liners
Answer:

Resilient Denture Liners

• A denture recliner is a polymeric material placed on the tissue-contacting surface of a denture base to absorb some of the energy produced by masticatory impact
• Act as a shock absorber between the occlusal surfaces of a denture and the underlying oral tissues

Resilient Denture Liners Types:

• Hardliners
  • The materials used are either cold cure or heat cure acrylic with a composition similar to denture base resin
  • They should chemically bond to the old denture base
  • Retain dimensional stability
  • Cold-cure acrylic is preferred
• Soft Resilient Liners
  • They are of two types
  • Permanent -Temporary
  • Purpose
  • To protect soft tissues by acting as a cushion
  • Used when irritation of the mucosa occurs
  • Used in areas of severe undercut and congenital or acquired defects of the palate
  • Short-term resilient liner or tissue conditioner

Question 2. Tissue conditioners
Answer:

Tissue Conditioners

• Tissue conditioners are chemically activated polymeric materials that tend to degrade more rapidly than heat-activated resin
• Supplied as powder of polymethylmethacrylate or its higher copolymers
• Liquid has plasticizers like aromatic esters such as butyl phthalate, butyl glycolate in alcohol or ethanol
• They can be formed directly in the patient’s mouth

Tissue Conditioners Disadvantages:

• Poor mechanical bonding
• Dimensionally unstable
• No permanent resilience
• Difficult to polish

Question 3. Separating media
Answer:

Separating Media Uses

• To prevent water from the mold from entering the acrylic resin
• To prevent monomers from penetrating into the mold
• Helps in the easy retrieval of dentures from the mold

Separating Media Types:

• Tinfoil
• Cellulose
• Solution of alginate compound
• Calcium oleate
• Soft soaps
• Sodium silicate
• Starches

Separating M

edia Applications:

• Applied using a brush, coating only the plaster surfaces and not acrylic teeth
• One or two coats may be applied

Question 4. Curing
Answer:

Curing

• It is the heating process employed to control the initial propagation of polymerization in the denture mold
• The selection of the curing cycle depends on the thickness of the resin
• Curing cycles are
• Heating the flask in water at 60-70T. for 9 hours
• Heating the flask at 65T, for 90 min
• Removing the flask from the water bath, bench cooling it for 30 min and pacing it in cold tap water for 13 min is satisfactory

Classification Of Denture Base Materials

Question 5. Requirements Of Denture Base Materials
Answer:

Requirements of Denture Base Materials

• Should be tasteless, odorless, non-toxic and non-irritant
• Be esthetic
• Be dimensional stable
• Have enough strength, resilience, and abrasion resistance
• Be insoluble and impermeable to oral fluids
• Have low specific gravity
• Tolerate temperature well
• Be easy to fabricate and repair
• Have good thermal conductivity
• Be radiopaque
• When used as filling material it should
• Bond chemically to the tooth
• Have a coefficient of thermal expansion matching that of tooth structure
• Be economical

Question 6. Curing Cycles Of Heat Cure Acrylic Resin
Answer:

Curing Cycles Of Heat Cure Acrylic Resin

• The curing cycle is the heating process used to control the initial propagation of polymerization in the denture mold
• It is selected according to the thickness of the resin

Curing Cycles Of Heat Cure Acrylic Resin Types:

• Long curing cycle
• The flask is heated in water at 60*70’1C for 9 hours
• Short curing cycle
• The flask is heated at 65°C for 90 min
• Then boil for 1 hour for adequate polymerization of the thinner portions

Denture Base Resins Short Question And Answers

Question 1. Condensation polymerization
Answer:

Condensation Polymerization

• Condensation polymerization is of two types
• Those in which polymerization is accompanied by repeated elimination of small molecules with the formation of by-products such as water, halogen, acids, etc
• Those in which function groups are repeated in polymer chains. Example. polyurethane

Question 2. Chemical stages in polymerization
Answer:

Chemical Stages In Polymerization

• Induction
• Propagation
• Termination
• Chain transfer

Question 3. Cold cure acrylic
(or)
Autopolymerizing resin
Answer:

Autopolymerizing Resin

• The chemically activated acrylic resin polymerizes at room temperature
• They are known as self-curing cured or auto-polymerizing resins
• The chemical initiator benzoyl peroxide is activated by another chemical dimethyl para toluidine which is present in the monomer

Flexible Denture Base Materials 

Question 4. Light-activated denture base resin
Answer:

Light-Activated Denture Base Resin consists of:

• A urethane dimethacrylate matrix
• Microftne silica fillers
• Carnphoroquinone amine photoinitiator system
• N.N. Dimethyl paratoludtne accelerator

Light-Activated Denture Base Resin Disadvantages:

• Complicated
• Expensive
• No improvement in properties

Question 5. Denture cleansers
Answer:

Denture Cleansers

Dentures are cleaned by either immersion in the agent or by brushing with the cleanser

Denture Cleansers Types:

• Household cleanser
• Bleaches
• Vinegar
• Dentrifices
• Mild detergents

Denture Cleansers Composition:

• Alkaline compounds
• Detergents
• Flavoring agents
• Sodium perborate

Question 6. Tissue conditioners
Answer:

Tissue Conditioners

• Tissue conditioners are chemically activated polymeric materials that tend to degrade more rapidly than heat-activated resin
• Supplied as powder of polymethylmethacrylate or its higher copolymers
• Liquid has plasticizers like aromatic esters such as butyl phthalate, butyl glycolate in alcohol or ethanol
• They can be formed directly in the patient’s mouth

Tissue Conditioners Disadvantages:

• Poor mechanical bonding
• Dimensionally unstable
• No permanent resilience
• Difficult to polish

Question 7. Denture recliners
Answer:

Denture Recliners

• A denture recliner is a polymeric material placed on the tissue-contacting surface of a denture base to absorb some of the energy produced by masticatory impact
• Act as a shock absorber between the occlusal surfaces of a denture and the underlying oral tissues

Denture Recliners Types:

• Hard-liners
• Soft resilient liners
• Short-term resilient liner or tissue conditioner

Flexible Denture Base Materials 

Question 8. Purpose of soft liners
Answer:

Purpose Of Soft Liners

• To protect soft tissues by acting as a cushion
• Used when irritation of the mucosa occurs
• Used in areas of severe undercut and congenital or acquired defects of the palate

Question 9. Crazing in acrylic resin
Answer:

Crazing In Acrylic Resin

• Crazing is the formation of surface cracks on the denture base resin
• It can be microscopic or macroscopic in size

Crazing In Acrylic Resin Causes:

• Mechanical stresses
• Attack by a solvent
• Incorporation of water

Crazing In Acrylic Resin Prevention:

• Using cross-linked acrylics
• Tin foil separating media
• Metal molds

Question 10. Physical stages in the mixing of heat cure acrylic resins
Answer:

Physical Stages In The Mixing Of Heat Cure Acrylic Resins

• Wet sandy stage
• Sticky stage
• Dough stage
• Rubbery stage
• Stiff stage

Question 11. Functions of separating medium.
Answer:

Functions Of Separating Medium

• To achieve a clean surface for new dentures
• Prevent direct contact between denture base and model
• Prevent entry of water from mold Into resin
• Prevent penetration of monomer into the model
• Help in easy retrieval of dentures from mold