Components 

a. Fillers added to most to control shrinkage
b. Matrix

Dental Solders

Applications-bridges and orthodontic appliances

Terms

Soldering -joining operation using filler metal that melts below 500° C

Brazing -joining operation using filler metal that melts above 500°C

Welding-melting and alloying of pieces to be joined

Fluxing
 -Oxidative cleaning of area to be soldered
 - Oxygen scavenging to prevent oxidation of alloy being soldered
16- 650 -- 650 fineness solder to be used with 16-karat alloys; fineness refers to the gold content

Classification

a. Gold solders-bridges
b. Silver solders-gold-substitute bridges and orthodontic alloys

Structure of gold solders

Composition-lower gold content than of alloys being soldered

Manipulation-solder must melt below melting temperature of alloy

Properties

1. Physical-similar to alloys being joined
2. Chemical-more prone to chemical and electrochemical corrosion
3. Mechanical-similar to alloy  being joined
4. Biologic-similar to alloys being joined
 

SELECTION OF SPRUE 

1 . DIAMETER :
It should be approximately the same size of the thickest portion of the wax pattern .
Too small sprue diameter suck back porosity results .

2 . SPRUE FORMER ATTACHMENT :
Sprue should be attached to the thickest portion of the wax pattern .
It should be Flared for high density alloys & Restricted for low density alloys .

3 . SPRUE FORMER POSITION

Based on the
1. Individual judgement .
2. Shape & form of the wax pattern .

Patterns may be sprued directly or indirectly .
Indirect method is commonly used

Effects of Amalgam.

(1) The combined effects of the properties of its ingredients should provide the most satisfactory restorative material.

(2) Quantity of mercury. Too little mercury in the mix results in a grainy, weak, readily tarnished, and corroded amalgam. Too much mercury will cause excessive expansion and weakened amalgam.

 (3) Composition of the alloy. Composition of the alloy must include a minimum of 65 percent silver, a maximum of 29 percent tin, a maximum of 6 to 13 percent copper, and a maximum of two percent zinc by weight

 (4) Correct proportion important. Before use, the silver alloy is mixed with pure and uncontaminated mercury. There are some alloys that are completely zinc free. They can therefore be used more successfully in a moisture-contaminated environment.

 (5) Properties of the finished product.

Silver imparts strength, durability, and color, gives the alloy desirable setting expansion, decreases flow, and accelerates (decreases) the setting time.

Tin makes the amalgam easier to work, controls excessive setting expansion, and increases both flow and setting time.

Copper increases hardness, contributes to setting expansion, reduces flow, and decreases setting time.

Zinc increases workability, and unites with oxygen and other "impurities" to produce a clean amalgam.

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 

Model. Cast. and Die Materials

Applications
- Gold casting, porcelain and porcelain-fused–to metal fabrication procedures
- Orthodontic and pedodontic appliance construction
- Study models for occlusal records

Terms
a. Models-replicas of hard and soft tissues for study of dental symmetry
b. Casts-working replicas of hard and soft tissues for use in the fabrication of appliances or restorations
c. Dies :-  working replicas of one tooth (or a few teeth) used for the fabrication of a restoration
d. Duplicates-second casts prepared from original  casts

Classification by materials

a Models :- (model plaster or orthodontic stone; gypsum product)
b. Stone casts (regular stone; gypsum product)
c. Stone dies (diestone; gypsum product)-may electroplated
d. Epoxy dies (epoxy polymer)-abrasion-resistant dies