COMPOSITE RESINS

Types

• Amount of filler-25% to 65% volume, 45% to 85% weight
• Filler particle size (diameter in microns)
  • Macrofill 10 to 100 µm (traditional composites)
  • Midi fill- 1 to 10 µm(small particle composites)
  • Minifill— 0.l to 1 µm
  • Microfill-: 0.01 to  0.1 µm (fine particle composites)
  • Hybrid--blend (usually or  microfill and midifill or minifill and microfill)
• Polymerization method
  • Auto-cured (self-cured)
  • Visible light cured
  • Dual cured
  • Staged cure
• Matrix chemistry
  • BIS-GMA type
  • Urethane dimethacrylate (UDM or UDMA) type
  • TEGDMA-diluent monomer to reduce  viscosity

METALLURGICAL TERMS

a. Cold Working. This is the process of changing the shape of a metal by rolling, pounding, bending, or twisting at normal room temperature.

b. Strain Hardening. This occurs when a metal becomes stiffer and harder because of continued or repeated application of a load or force. At this point, no further slippage of the atoms of the metal can occur without fracture.

c. Heat Softening Treatment (Annealing). This treatment is necessary in order to continue manipulating a metal after strain hardening to prevent it from fracturing. The process of annealing consists of heating the metal to the proper temperature (as indicated by the manufacturer's instructions) and cooling it rapidly by immersing in cold water. Annealing relieves stresses and strains caused by cold working and restores slipped atoms within the metal to their regular arrangement.

d. Heat Hardening Treatment (Tempering). This treatment is necessary to restore to metals properties that are decreased by annealing and cold working. Metals to be heat hardened should first be heat softened (annealed) so that all strain hardening is relieved and the hardening process can be properly controlled. Heat hardening is accomplished in dental gold alloy by heating to 840^o Fahrenheit, allowing it to cool slowly over a 15-minute period to 480^o Fahrenheit, and then immersing it in water.

Stages of manipulation

Definitions of intervals

• Mixing interval-length of time of the mixing stage.
• Working interval-length of time of the working stage
•  Setting interval-length of time of the setting stage

Definitions of times

• Mixing time-the elapsed time from the onset to the completion of mixing
• Working time-the elapsed time from the onset of mixing until the onset of the initial setting time
• Initial setting time-time at which sufficient reaction has occurred  to cause the materials to be resistant to  further manipulation
• Final setting time-time at which the material practically is set as defined by its resistance to indentation

[All water-based materials lose their gloss at the time of setting]

CRUCIBLE FORMER

It serves as a base for the casting ring during investing .Usually convex in shape.
May be metal , plastic or rubber .
Shape depends on casting machine used .
Modern machines use tall crucible to enable the pattern to be positioned near the end of the casting machine .

Mouth Protectors

Use - to protect against effects of blows to chin, top of the head, the face, or grinding of the teeth

Types

o    Stock protectors-least desirable because of poor fit
o    Mouth-formed protectors-improved fit compared with stock type
o    Custom-made protectors-preferred because of durability. low  speech impairment, and comfort

I. Components

a. Stock protectors-thermoplastic copolymer of PYA-PE (polyvinyl acetate-polyethylene copolymer)
b. Mouth-formed protectors-thermoplastic copolymer
c. Custom-made protectors- thermoplastic copolymer, rubber. or polyurethane
2. Reaction-physical reaction of hardening during cooling
3. Fabrication

Alginate impression made of maxillary arch. High-strength stone cast poured immediately. Thermoplastic material is heated in hot water and vacuum-molded to cast .

Mouth protector trimmed to within ½ inch of labial fold, clearance provided at the buccal and labial frena, and edges smoothed by flaming. Gagging, taste, irritation. and impairment of speech are minimized with properly fabricated appliances

4. Instructions for use

a. Rinse before and after use with cold water
b. Clean protector occasionally with soap and cool water
c. Store the protector  in a rigid container
d. Protect from heat and pressure during storage
e. Evaluate protector routinely for evidence of deterioration

Properties

1. Physical-thermal insulators
2. Chemical-absorbs after during use
3. Mechanical-tensile strength, modulus, and hardness decrease after  water absorption, but elongation, tear strength, and resilience increase
4. Biologic-nontoxic as long as no bacterial, fungal, or viral growth occurs on surfaces between uses
 

Impression Material

Manipulation

Mixture of powder and liquid is painted onto working cast to create shape for acrylic appliance à  After curing of mixture, the shape and fit are adjusted by grinding with burrs and stones with a slow-speed handpiece .Acrylic dust is irritating to epithelial tissues of nasopharynx and skin and may produce allergic dermatitis or other reactions.  Grinding may heat polymer to temperatures that depolymerize and release monomer vapor. which may be an irritant