Waxes are a group of ubiquitous materials that play a significant part in both restorative dentistry and in the dental laboratory. They are used extensively in the denture-making process, in making interocclusal records, as a splinting material in denture repairs, for boxing impressions when casting models, and forming the wax pattern in the lost wax technique to produce removable and fixed prostheses. A range of waxes with different properties are required to carry out these varying functions. A number of natural and mineral waxes, gums, fatty acids, oils and resins (both synthetic and natural) are blended together to produce the wax with specific properties required for its intended use (Table 16.1).

The common constituents of most dental waxes are hydrocarbons and esters with a high molecular weight. The use of natural waxes does present the manufacturer with a problem as these waxes have variable properties depending on their source and also the time at which they were obtained. The common plant waxes include carnauba, ouricury, candelilla (Figure 16.1) and Japan wax. Japan wax is really a fat containing glycerides of palmetic and stearic acid. It is derived from the berries of the sumac tree found in Japan and China and is regarded as a form of lacquer. The animal and insect waxes include spermaceti from the sperm whale and beeswax (Figure 16.2).

Fig. 16.1 Carnauba wax (A) is derived from the leaf of the Copernicia palm (B) found primarily in Brazil. Ouricury wax is obtained from the leaves of the feather palm (C) by scraping the surface of the leaves while candelilla is sourced from the leaves of a shrub Euphorbia antisyphilitica (D).

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Fig. 16.2 (A) Beeswax cake and (B) beeswax being scraped off the honeycomb.

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Mineral waxes are more consistent in their properties and presentations. They are usually derived from the refining of petroleum products. One of the most commonly available is paraffin wax (Figure 16.3) with a melting point of 40–70 °C. This wax has a tendency to show substantial volumetric contraction (in the region of 10–16%) during the cooling and solidification process.

Fig. 16.3 (A) Paraffin wax. (B) Close-up view of the flakes of paraffin wax.

The primary source of microcrystalline wax is the heavier oil fractions produced during the petroleum distillation process. These have higher melting points and are formed into plates. They are much tougher than paraffin waxes and show much less volumetric change when changing from liquid to solid. Their properties may be adapted by adding oil, making the wax less hard. The common microcrystalline waxes include ozokerite, ceresin (Figure 16.4), montan and barnsdahl. The first three waxes are all derived from shale and lignites found near petroleum deposits. Other waxes which may be incorporated into dental wax include synthetic waxes which have been produced for other purposes, such as polyethylene waxes and polyethylene glycol waxes. While the use of synthetic waxes in dental waxes is increasing, the natural waxes still predominate.

Fig. 16.4 (A) Ceresin wax and (B) ozokerite in its natural form.

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The handling properties of the individual waxes may be adjusted by the addition of gums, fats and resins. The resins may be either synthetic or naturally occurring. Dammar, rosin and sandarac (Figure 16.5) are three examples in the latter group and are derived from plants. Another common naturally occurring material is shellac (Figure 16.6), which is produced by insects. It is commonly obtained from India and Thailand. Shellac is a thermoplastic material and is used to make baseplates, which are used in the denture-making process. It is a rigid material when solid and other waxes may be added to it, for example to make occlusal rims. As it is more stable at mouth temperature, it is less likely to distort when used in the mouth.

Fig. 16.5 Examples of resins used in dental waxes: (A) different types of shellac, (B) sandarac tears, (C) rosin, and (D) dammar.

Fig. 16.6 Shellac used to make the baseplate for an occlusal rim.

In order to produce a wax which may be used in dentistry, a number of properties need to be considered:

Melting range

It is already apparent that the melting temperatures of the various constituents of the wax will affect the melting range of the final product. By adding waxes of high melting temperatures, the melting range of the paraffin wax-based materials can be increased significantly. This is of importance if the wax is to be used in the mouth as the melting range needs to be higher than mouth temperature. In the dental laboratory the wax needs to change rapidly from solid to liquid to in order to manipulate it. The melting range can be narrowed as well as raised. To manipulate the wax effectively, it must be maintained at the correct temperature. This may be done using a flame or induction coil (Figure 16.7).

Fig. 16.7 The dental technician using an induction coil to maintain the correct temperature of the wax when a wax pattern is being made so that it can be manipulated effectively.

Use of waxes in dentistry can be divided into three distinct areas:

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