📖 Dental Materials
Casting of glass or ceramic
Dental MaterialsCasting 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 MaterialsWETTABILITY
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 MaterialsMercury 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 MaterialsSpruing 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