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NEET MDS Synopsis - Lecture Notes

📖 Dental Materials

Showing page 1 of 22 (86 total records)

Casting of glass or ceramic

Dental Materials

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 .

WETTABILITY

Dental Materials

WETTABILITY
To minimise the irregularities on the investment & the casting a wetting agent can be used .

FUNCTIONS OF A WETTING AGENT

1 . Reduce contact angle between liquid & wax surface .
2 .Remove any oily film left on wax pattern .

Mercury hygiene

Dental Materials

Mercury hygiene

  • Do not contact mercury with skin
  • Clean up spills to minimize mercury vaporization
  • Store mercury or precapsulated products in tight containers
  • Only triturate amalgam components-in tightly- sealed capsules
  • Use amalgam with covers
  • Store spent amalgam under water or fixer in a tightly sealed jar
  • Use high vacuum suction during amalgam alloy placement, setting, or removal when mercury may be vaporized
  • Polishing amalgams generally causes localized melting of silver-mercury phase with release of mercury vapor, so water cooling and evacuation must be used

Spruing Technique

Dental Materials

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