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Dental Materials

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
 

Spruing Technique:

Direct Spruing:

The flow of the molten metal is straight(direct) from the casting crucible to pattern area in the ring. Even with the ball reservoir, the Spruing method is still direct. A basic weakness of direct Spruing is the potential for suck-back porosity at the junction of restoration and the Sprue.

Indirect Spruing:

Molten alloy does not flow directly from the casting crucible into the pattern area, instead the alloy takes a circuitous (indirect) route. The connector (or runner) bar is often used to which the wax pattern Sprue formers area attached. Indirect Spruing offers advantages such as greater reliability & predictability in casting plus enhanced control of solidification shrinkage .The Connector bar is often referred to as a “reservoir .

Armamentarium :
1 . Sprue
2 . Sticky wax
3 . Rubber crucible former
4 . Casting ring 
5 . Pattern cleaner 
6 . Scalpel blade & Forceps 
7 . Bunsen burner

Properties of Acrylic Resins.

  • They have a low thermal conductivity. These resins are not easily washed out by the acids of the oral cavity (low solubility). Acrylic resins are also resilient, which allows them to be used in stress-bearing areas.
  • Acrylic resins exhibit a moderate shrinkage of from 3 to 8 percent. This shrinkage and low marginal strength can lead to marginal leakage. Acrylic resins have a low resistance to wear. Acrylic resins cannot be used over a zinc oxide and eugenol-type base because eugenol interferes with the acrylic curing process.
  • Mixing. Insufficient mixing will cause an uneven color or streaks in the mixture. Overmixing will cause the material to harden before it can be placed
  • Poor distortion resistance at higher temperatures, therefore dentures should not be cleaned in hot water
  • Good resistance to color change
  • Absorbs water and must be kept hydrated  (stored in water when not in mouth) to prevent dehydration cycling and changes in dimensions
  • Not resistant to strong oxidizing agents
  • Low strength; however, flexible, with good fatigue resistance
  • Poor scratch resistance; clean tissue-bearing surfaces of denture with soft brush and do not use abrasive cleaners

Physical reaction-cooling causes reversible hardening

Chemical reaction-irreversible reaction during setting

PROPERTY

INGREDIENT

 

Silver

Tin

Copper

Zinc

Strength

Increases

 

 

 

Durability

Increases

 

 

 

Hardness

 

 

Increases

 

Expansion

Increases

Decreases

Increases

 

Flow

Decreases

Increases

Decreases

 

Color

Imparts

 

 

 

Setting time

Decreases

Increases

Decreases

 

Workability

 

Increases

 

Increases

 

 

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