Requirements for modeling materials
To create precise details of the future prosthesis that will later be replaced with metal or plastic, dentists use wax compositions and ashless polymers. The main requirement for such materials is ashlessness. This means that during calcination, the mass must burn out completely so that the metal or plastic casting turns out defect-free.
In addition, a quality modeling material must:
- Layer well onto the gypsum model and possess adhesive properties.
- Have a contrasting color for visual control of the relief against the gypsum background, without staining the gypsum after removal.
- Exhibit minimal shrinkage (no more than 0.1–0.15% per degree upon cooling).
- Maintain plasticity and hardness at 37–40 °C, but neither break nor delaminate during processing at room temperature.
- Be easily and cleanly removable from the mold.
Classification of dental waxes
According to their origin, waxes are divided into four groups:
- Animal: beeswax (Cera), spermaceti, stearin, lanolin.
- Vegetable: Japanese (fruit), carnauba.
- Mineral: paraffin, ozokerite, peat wax, petroleum wax.
- Synthetic.
Characteristics of main waxes
- Beeswax. Melts at 62–64 °C. Not used in pure form due to excessive softness at room temperature. Serves as an additive to lower the melting point and increase the plasticity of dental mixtures.
- Stearin. A translucent product of animal fat hydrolysis. Forms soap when boiled with alkali. Used as a base for polishing pastes and thermoplastic impression materials.
- Vegetable waxes. Japanese wax becomes very sticky when heated. Carnauba wax is unique for its octacosanol content. It is brittle but high-melting (up to 96 °C). Adding it to beeswax sharply increases the overall hardness of the composition.
- Mineral waxes. Inert paraffin is used for denture bases. Ozokerite (mountain wax, purified variant — ceresin) has a kerosene odor and makes mixtures viscous and ductile.
Purpose and types of abrasives
Processing of the finished prosthesis requires the use of abrasive materials — hard crystalline or powdered minerals. They are necessary for rough metal grinding, polishing, lapping, tool sharpening, and final surface finishing.
The classification of abrasives includes several parameters:
- By purpose: divided into grinding (for rough and fine processing) and polishing (to impart smoothness and gloss).
- By binder: embedded in ceramic, bakelite, or vulcanite matrices, as well as free — in the form of pastes.
- By tool shape: wheels (cup-shaped, dish-shaped), lenticular burs, cone-shaped and pear-shaped heads, sandpaper and sheets.
- By origin: natural and artificial (electrocorundum, silicon and boron carbides, graphite).
Natural abrasive materials
Natural minerals are widely used to create dental instruments and polishing agents:
- Corundum and emery. Corundum is crystalline aluminum oxide. An important rule: the more iron impurities it contains, the worse it cuts. Emery is a rock where corundum is mixed with quartz, hematite, and magnesite. Grinding stones and abrasive papers are made from them.
- Quartz and flint. Varieties of silica. Suitable for abrasive paper sheets and tool dressing wheels.
- Pumice. A porous volcanic rock containing silica, alumina, and alkalis. Ideal for specialized abrasive papers and cleaning blocks.
- Garnet and sandstone. Garnet consists of lime and magnesia aluminosilicates. Both minerals are used for tool sharpening.
- Diamond. The hardest natural mineral made of pure carbon. Technical diamonds (unsuitable for jewelry) are used in dentistry. They are used to dress grinding wheels and sharpen carbide instruments.
To remember the mineral waxes, use the phrase “Pure Oils Protect Beautiful Nature”: Paraffin, Ozokerite, Peat, Brown coal, Naphtha.
Class and exam questions
Why is beeswax not used in its pure form?
It has too low a softening temperature (37–38 °C) and insufficient hardness. It is used only in mixtures to impart plasticity.
What is ceresin?
This is purified mountain wax (ozokerite), which is added to wax compositions to increase their viscosity and melting point.
How do impurities affect the properties of corundum?
As the iron oxide impurity content increases, the hardness and cutting ability of corundum decrease significantly.
What else to study on this topic
- Properties of artificial abrasives (silicon carbide, electrocorundum)
- Composition and application of polishing pastes
- Artificial thermoplastic impression materials
- Effect of temperature changes on the shrinkage of wax compositions
- Mechanism of interaction between carnauba and beeswax in mixtures
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Other topics in "Chapter 8. Dental Materials"
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