CASTING: casting is the process by which the wax pattern of a restoration is converted to a replicate in a dental alloy. The casting process is used to make dental restorations such as inlays, onlays, crowns, bridges and removable partial dentures.

Objectives of casting

1) To heat the alloy as quickly as possible to a completely molten condition.
2) To prevent oxidation by heating the metal with awell adjusted torch .
3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.

STEPS IN MAKING A CAST RESTORATION
1. TOOTH PREPARATION
2. IMPRESSION
3. DIE PREPARATION
4. WAX PATTERN FABRICATION
5. SPRUING

Physical reaction-cooling causes reversible hardening

Chemical reaction-irreversible reaction during setting

Root canal sealers

Applications

Cementation of silver cone gutta-percha point
Paste filling material

Types

Zinc oxide-eugenol cement types
Noneugenol cement types
Therapeutic cement types

properties

Physical-radiopacity
Chemical-insolubility
Mechanical-flow; tensile strength
Biologic-inertness

Gingival tissue packs

Application-provide temporary displacement of gingival tissues
Composition-slow setting zinc oxide-eugenol cement mixed with cotton twills for texture and strength

Surgical dressings
1.Application-gingival covering after periodontal surgery
2. Composition-modified zinc oxide-eugenol cement (containing tannic, acid. rosin, and various oils)

Orthodontic cements

Application-cementation of orthodontic bands
Composition-zinc phosphate cement 

Manipulation

Zinc phosphate types are routinely mixed with cold or frozen mixing slab to extend the working time
Enamel bonding agent types use acid etching for improved bonding
Band, bracket, or cement removal requires special care
 

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 

Casting of glass or ceramic

A castable ceramic is prepared in a similar manner as metal cast preparation .
Glass is heated to 1360 degrees & then cast.
Phosphate bonded investments are used for this purpose .

COMPOSITE RESINS

Components

• Filler particles-colloidal silica, crystalline silica (quartz), or silicates of various particle sizes (containing Li, AI, Zn, Yr)
• Matrix-BIS-GMA (or UDMA) with lower molecular weight diluents (e.g., TEGDMA) that correct during polymerization
• Coupling agent- silane that chemically bonds the surfaces of the filter particles to the polymer matrix