16: Waxes and occlusal registration materials

Chapter 16 Waxes and occlusal registration materials

Constituents of Dental Waxes

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).

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.

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.

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.

Properties

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

Jan 31, 2015 | Posted by in Dental Materials | Comments Off on 16: Waxes and occlusal registration materials
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