Denture Resins, Dental Alloys, and Ceramics

Denture Base Materials Classification

Liner: The polymeric material used to replace the tissue contacting the surface of an exist- ing denture.

Rebasing: Process of replacing an entire denture base on an existing complete partial denture.

Relining: Process of replacing the tissue contacting the surface of existing dentures.

Tissue Conditioner: Chemically activated polymeric material that tends to degrade more rapidly than heat-activated resin.

Polymerization: Refers to a series of chain reactions by which a macromolecule of polymerization is formed from a single molecule known as a monomer.

Polymerization Types:

• Condensation polymerization
• Addition polymerization

Chemical Stages of Polymerization

• Induction/initiation
• Heat activation
• Chemical activation

Light activation:

• Propagation
• Termination
• Chain transfer
• Inhibition of Polymerization
• Impurities Oxygen

Plasticizers: Substances added to resins

• To increase the solubility of the polymer in the monomer
• To decrease the brittleness of polymers

Plasticizers Types:

• External and
• Internal

Physical Stages of Polymerization

• Stage 1: Wet Sand Stage
• Stage 2: Sticky Stage
• Stage 3: Dough / Gel Stage
• Stage 4: Rubbery Stage
• Stage 5: Stiff

Technical Consideration/Fabrication of Acrylic Resin Dentures

• Compression molding techniques
• Injection molding technique

Fabrication of Acrylic Resin Dentures Stages:

• Preparation of wax pattern
• Preparation of split mold
• Application of separating medium most commonly used sodium alginate solution

Fabrication of Acrylic Resin Dentures Others: Tinfoil, soap, cellulose lacquers, sodium silicate.

• • Mixing of powder and liquid 3:1 by vol. or 2:1 by weight (Polymer: monomer).
  • If too much monomer – Polymerization shrinkage, porosity
  • If too much little monomer – Cured acrylic will be granular
• Packing

Polymerization Cycle Curing/bench curing:

Curing cycle/polymerization cycle – Technical name for the heating process, employed to control the initial propagation of polymerization in the denture mold.

• One-step procedure: Curing at a constant temperature in a water bath at 74°C for eight hours or more without terminal boil.
• Two-step procedure: Curing at 74°C for 1.5 hours and then increasing the temperature of the water bath to boiling temperature for an additional hour.
  • Cooling
  • Deflasking
  • Finishing and polishing

Heat Cure Denture Base Resins [SPOTTER]

Heat Cure Denture Base Resins Composition

Self Cure/Cold Cure/Auto Polymerizing Resin [SPOTTER]

Auto Polymerizing Resin Uses:

• Restorative material
• Denture repair, relining, and rebasing
• Construction of special trays Advantages

Comparison of Heat Cured and Self Cured Resins

Light Activated [Spotter]

Consists of a urethane dimethacrylate matrix with an acrylic copolymer, micro-fine silica fillers, and camphor quinone photoinitiator, supplied in premixed sheets having clay-like consistency polymerized in a light chamber with tube light of 400- 500 nm from high-intensity quart halogen bulbs.

Material Used In Maxillofacial Prosthesis

• Poly methyl methacrylate
• Latex
• Plasticized polyvinyl chloride
• Silicone rubber
• Poly urethane polymers

Temporary Crown and Bridge Material

• Polycarbonate
• Cellulose acetate
• Aluminum
• Tin Silver
• Nickel chromium.

Casting Procedure For Dental Alloys

Steps:

• Tooth preparation
• Impression
• Die preparation
• Wax pattern
• Sprue former
• Casting ring liner
• Investing
• Wax elimination and heating
• casting by casting Machine {Centrifugal force systems, Air Pressure type}
• Quenching
• Recovery of casting
• Sandblasting

Pickling: by either 50% hydrochloric acid or sulfuric acid.

• Polishing

Defects In Casting

Distortion

Surface roughness

Porosity:

• Shrink spot porosity
• Back pressure porosity
• Irregular voids
• Spherical voids

Dental Ceramics

Dental Ceramics: An inorganic compound with nonmetallic properties typically consisting of oxygen and one or more metallic or semi-metallic elements that are formulated to produce the whole on the part of a ceramic-based dental prosthesis.

Glaze Ceramics: A specially formulated ceramic powder, that when mixed with a liquid applied to a ceramic surface, and heated to an appropriate temperature for a sufficient time forms a smooth glassy layer on a dental ceramic surface.

Sintering: The process of heating closely packed particles to a specified temperature to density and strengthen structures as a result of bonding, diffusion ad flow phenomena.

Application of Ceramics:

• Single unit ceramics, porcelain jacket crowns, porcelain fuse to metal
• Veneers for crowns and bridges.
• Artificial teeth
• Inlays and Onlays

Ceramics Classifications:

1. According to the firing temperature
   • High fusing-1290-1370°C
   • Medium fusing-1095-1260°C
   • Low fusing-1870-1065°C
2. According to use
   • Construction of artificial teeth
   • Fabrication of jacket crowns and inlays
   • As veneers.
3. According to the method of firing
   • Air fired
   • Vacuum fired
4. According to application
   • Core porcelain
   • Dentine/body porcelain
   • Enamel porcelain
5. Recent Porcelains
   • Magnetic core
   • Extrusion-molded or infection molded aluminous core material
   • Fluoride – mica glass or castable ceramics.

Manufacture Of Porcelain Fitting – Manufacturing Process

• [The components are mixed and fused and then quenched in water]

Method of Strengthening (of brittle porcelain)

1. Introduction of residual compression stresses into the surface of the material
   • Ion exchange
   • Thermal tempering
   • Thermal expansion coefficient mismatch
2. The intersection of crack propagation through the material

Fabrication Building up of Porcelain

Condensation – Methods

• Vibration
• Spatulation
• Brush technique
• Ultrasonic
• Gravitational
• Whipping

Firing -Stages

• Low bisque
• Medium bisque
• High bisque