10 - DENTAL WAXES, CASTING INVESTMENTS, AND CASTING PROCEDURES

NOT ALL

Clinical Products

include bite registration wax, disclosing wax (also known as pressure-indicating paste), utility waxes for altering and adapting impression trays, and low-melting type I inlay waxes used in the mouth for direct-waxing processes for pattern production

Laboratory Products

include boxing wax, baseplate wax, sticky wax, beading wax, utility wax, and hard, medium, and soft type II inlay-type waxes for making patterns on patients’ models using the indirect wax technique

Synthetic Waxes

are chemically synthesized from natural molecules; most synthetic waxes are homogeneous than pure natural waxes

Natural Waxes

are derived from mineral, vegetable, and animal origins

40-60%

most dental waxes contain ___-___% paraffin by weight, which is derived from high-boiling fractions of petroleum

Paraffin Wax

→ flakes when trimmed

→ does not produce a smooth, glossy surface, which is a desirable requisite for an inlay wax o thus, other waxes and natural resins must be added as modifying agents

Gum Dammar or Dammar resin

→ natural resin

→ added to the paraffin to improve the smoothness in molding and to render it more resistant to cracking and flaking

→ increases the toughness of the wax and enhances the smoothness and luster of the surface

Carnauba Wax

→ occurs as a fine powder on the leaves of certain tropical palms

→ very hard, has a relatively high melting point and has an agreeable odor

Candelilla Wax

→ provides the same general qualities as carnauba wax but its melting point is lower and it is not as hard as carnauba wax

Ceresin

→ white wax extracted from ozokerite, a waxy mineral mixture of hydrocarbons that is colorless or white when pure, but it has a somewhat unpleasant odor

→ may replace part of the paraffin to modify the toughness and carving characteristics of the wax

WAX PATTERN REMOVAL

→ Wax pattern should be removed from the die without any distortion of wax → Any motion that might distort the wax pattern should be avoided during removal

SPRUE DIAMETER

→ Select a sprue former with a diameter that is approximately the same size as the thickest are of the wax pattern

SPRUE POSITION

→ The position of the sprue former attachment is often a matter of individual judgment and intuition, based on the shape and form of the wax pattern

greatest bulk

→ Ideal position for the sprue formes is the point of _____________ in the pattern to avoid distorting thin areas of wax during attachment to the pattern and permit complete flow

SPRUE ATTACHMENT

→ The sprue former should be directed away from any thin or delicate parts of the pattern because the molten metal may abrade of fracture investment in the area and result in a casting failure

SPRUE LENGTH

→ The length of the sprue former depends on the length of casting ring. Sprue too short = wax pattern will be removed from the ring due to porosities

→ Gypsum bonded – 6 mm from the top; phosphate bonded – 3-4 mm

Phosphate-Bonded

these investments are designed primarily for alloys used to produce copings or frameworks for metal-ceramic prosthesis and some base metal alloys; it can also be used for pressable ceramics

Ethyl Silicate-Bonded

investments used principally for the casting of removable partial dentures made from base metals (Cobalt and Nickel based alloys)

Gypsum-Bonded

-based materials type represent for the traditionally used conventional casting of gold alloy inlays, onlays, crowns, and larger fixed dental prostheses (FDPs)

High Heat Casting Technique

1 min. can pass without noticeable change

Low Heat Casting Technique

the alloy should be cast right after removal from the oven

Clay Crucibles

crown and bridge alloys, such as the high noble and noble types

Carbon Crucibles

high noble crown and bridge alloys but also for the higher-fusing gold-based metal-ceramic alloys

Air Supply for the Lower Frame

→ incomplete combustion and a lower temperature will result → this type of flame is likely to be favored by the beginner because the roaring sound that accompanies this flame adjustment “sounds” hot

Upper Brush Flame

→ indicates the proper adjustment for maximal efficiency and temperature

Non-Combustion Zone

→ no heat is present

Combustion Zone

→ green and immediately surrounding the inner cone

→ the gas and air are partially burned

→ this zone is oxidizing and should always be kept away from the molten alloy during fusion

Reducing Zone

→ dimly blue and located just beyond the tip of the green combustion zone

→ this is the hottest part of the flame and it should be kept constantly on the alloy during melting

Oxidizing Zone

→ outer cone is the area in which combustion occurs with the oxygen in the air

→ under no circumstances should this portion of the flame be used to melt the alloy

→ not only is its temperature lower than that of the reducing zone but it also oxidizes the alloy

base metal alloys

the highest temperatures are required for

750 C to 1030 C

burnout temperatures for phosphate-bonded investments range from