The Lost Wax Technique and Dental Waxes

The Lost Wax Technique: From Impression to Restoration
Centuries old technology used in jewelry making, art, and many other applications.

William H. Taggart demonstrates the method for use in dentistry in 1907.

1. Impression
2. Die/Die Spacer
3. Wax Pattern
4. Sprue/Investing
5. Burn-out
6. Casting
7. Finishing/Polishing

Usually an elastomeric material with clean, readable margins.

Poured up in die stone in a vacuum unit to minimize bubbles and create the strongest model possible.

Die and Die Spacer
The die is a very accurate replica of the prepared tooth or teeth. A die spacer is painted on to allow room for the crown to fit over the tooth and for the luting agent (cement).

Wax-Up or Wax Pattern
“Wax-up” on the die will replicate the final restoration and then be converted into metal, ceramic and metal, or all ceramic restorations.

This wax likeness of the final product will be converted by the lost wax process.

Margins, occlusion, and contours must be finalized at the completion of the wax-up.

Wax patterns are then ready to invest.

The wax up on the die which is part of a die model which is on an articulator to help determine occlusion.

Sprung and Investing
The sprue forms a channel through which the molten metal is cast.

Investment is a gypsum-like product that can stand up very high heat and is poured around the wax entombing the pattern in the stone.

Burn Out Oven
When the investment dries, the ring is then placed in an oven that burns away the wax, leaving a cavity (pattern) in the ring the exact shape of the restoration

There is no residue left as the wax burns out completely.

Metal is melted with a torch and flung through the sprue channel into the space left behind by the melted wax

Finishing and Polishing
Removing the sprue
Finish contours
Polish to high lustre

Uses of wax in dentistry
Adjunct material used in varied ways to create restorations directly and indirectly.

Patterns for castings (Lost-Wax technique)
Help hold restorations while being repaired.
Lute restorations together when soldering.
Laboratory work (models/articulator)
Denture fabrication (impression/records/ processing).

Types of Wax
I. Pattern Wax
II. Processing Wax
III. Impression Wax

Pattern Wax
The waxes that are used to create a likeness of the restoration to be cast in metal or ceramic, or processed into acrylic in the case of dentures.

A. Inlay B. Casting C. Base Plate

Inlay Wax
Used to create inlays, onlays, crowns, bridges, posts, implant abutments or any restoration to be cast in metal.

Preformed patterns for the creation of partial denture frame-works.

Base Plate
Versatile sheets of brittle wax that hold denture teeth when preparing a denture set up and provide a model of gingiva, soft tissue, and many other functions.

Processing Wax
Used in laboratory procedures to help fabricate or repair restorations.

Boxing/Beading wax is used on models when fabricating dentures.
Periphery wax- used on impression trays to add an area or help create the periphery of the impression.
Sticky wax-used for luting together pieces when soldering, performing a repair, or mounting models on an articulator.

A. Boxing B. Periphery C. Sticky

Impression Wax
Used to transfer information from the patient to the lab to facilitate fabrication of the restoration.

Bite Registration Wax

Used to border mold a denture impression producing a clean clear impression of the mucobuccal fold.

border molding

Bite Registration Wax
Recording the interarch relationship: taking a bite record. Warm the wax until its soft. Put it in the mouth – have the patient bite down and stay close until the wax cools and is stable.

Recording the interarch relationship:
Waxes are mostly replaced by elastomeric impression materials used as bite registration materials.

Waxes in Dentistry
Mixture of natural (beeswax/paraffin/ carnauba) and synthetic waxes.
Provides a mixture of properties (stiffness/ flow/ softness, etc,) for the particular job at hand.
There are many different products for a wide range of applications.

Properties of Dental Waxing

Melting Range
Since all dental products are a combination of different waxes, they melt over a range of temperatures. They become soft, pliable, and usable before they become liquid.

Excess Residue
When burned out in an oven, certain waxes leave no ash or residue. They burn-out completely and cleanly. This is the key to the lost-wax technique.

The change in shape in response to applied force. At low temperatures, there is very little flow. As temperature rises (nearing or entering melting range), flow increases. This is key when working with wax for restorations.

Thermal Expansion
Waxes expand greatly when heated-more so than any other material- Another key factor when considering wax-ups for restorations.

Residual Stress
Stresses build up in the mass of wax as a result of handling – carving, heating, cooling – which can distort the shape of the mass if left too long. (think of dimensional stability of impression materials). Need to invest it in investment gypsum soon after completing the wax-up.

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