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
 

Applications

a. Dentulous impressions for casts for prosthodontics

b. Dentulous impressions for pedodontic appliances

c. Dentulous impressions for study models for orthodontics

d. Edentulous impressions for casts for denture construction

Manipulation

Mixing

o    P/L types mixed in bowl (plaster and alginate)
o    Thermoplastic materials not mixed (compound and agar-agar)
o    Paste/paste types hand mixed on pad (zinc oxide-eugenol, polysulfide rubber, silicone rubber, polyether rubber. and poly-vinylsiloxane)
o    Paste/paste mixed through a nozzle on an auto-mixing gun (poly-vinylsiloxane)

Placement

o    Mixed material carried in tray to mouth (full arch tray, quadrant tray. or triple tray)
o    Materials set in mouth more quickly because of higher temperature

Removal - rapid removal of impression encourages deformation to take place elastically rather than permanently (elastic deformation requires about 20 minutes)

Cleaning and disinfection of impressions 

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

Tooth Polishing and Cleansing Agents

1. Cleansing-removal of exogenous stains, pellicle, materia alba, and other oral debris without causing undue abrasion to tooth structure
2. Polishing-smoothening surfaces of amalgam, composite, glass ionomers, porcelain, and other restorative materials

Factors influencing cleaning and polishing

-    Hardness of abrasive particles versus substrate
-    Particle size of abrasive particles
-    Pressure applied during procedure
-  Temperature of abrasive materials

Structure

 Composition

-contain abrasives, such as kaolinite, silicon dioxide, calcined magnesium silicate, diatomaceous silicon dioxide, pumice. Sodium-potassium
-aluminum silicate, or zirconium silicate; some pastes also may contain sodium fluoride or stannous fluoride, but they have never been shown to produce positive effects
 

Reactions-abrasion for cleansing and polishing

Properties -  Mechanical
 
- Products with pumice and quartz produce more efficient cleansing but also generate greater abrasion of enamel and dentin
-Coarse pumice is the most abrasive
-The abrasion rate of dentin is 5 to 6 times faster than the abrasion rate of enamel, regardless of the product
-Polymeric restorative materials, such as denture bases, denture teeth, composites, PMMA veneers, and composite veneers, can be easily scratched during polishing
-Do not polish cast porcelain restorations (e.g., Dicor) that are  externally characterized or the color will be lost