Dental practitioners choose the material to be used according to the work to be carried out and its specific purposes. They can now choose from a vast range of reference materials, being able to rely on the on-going progress achieved by manufacturers, with the aim, for example, of guaranteeing greater precision, rapid impression taking, reduced patient discomfort and improved dimensional stability. The developments worthy of note include those regarding elastomers, including addition silicones (also known as polyvinylsiloxanes or PVS) and condensation silicones.
The ideal material for bite registration
Silicones have come to be essential materials for both dentists and dental technicians. These materials have been developed over decades, indeed, centuries of refinement: it is worth remembering that the first bite registration dates back to 1756, the year in which Philipp Pfaff used gypsum. Since then, the crucial characteristics of the materials to be used for bite registration have been established in an increasingly detailed manner. It is undoubtedly necessary to be able to count on a material that sets rapidly, without undergoing significant dimensional changes; the ideal material must also have reduced resistance during the intercuspation phase, to allow registration in a natural position; the bite registration material must also be able to record even the smallest detail of the surfaces over which it is pressed and, lastly, it must be easy to handle.
And silicones certainly satisfy these requirements. In the world of bite registration materials, elastomeric materials are those that were most recently placed on the market. These materials are typically easy to handle and boast excellent dimensional stability. The advantages of elastomers also include their high fidelity in reproducing detail and the ease with which they can be modified once cured. However, elastomers do have one disadvantage: when the gypsum model is positioned, the material may be unintentionally forced, with the risk of it being deformed. To avoid this effect (known in jargon as the “spring effect”), it is advisable to modify the registrations.
However, this is not the only feasible option. Dentists may also choose waxes, which are unsurprisingly materials that have been consolidated by use and time. One of the strengths of waxes is undoubtedly their ease of use; on the other hand, one cannot overlook the reduced dimensional stability of this material, which can be adversely affected by changes in temperature. We will now focus on the use of condensation and addition silicones.
Use of condensation and addition silicones in dentistry
Silicones have come to be essential materials for both dentists and dental technicians.
Condensation silicones, for example, are developed not only for use in the dental practice for impression taking, but also to satisfy the specific requirements of dental laboratories; this is the case, for example, of Zhermack’s condensation silicones, which are characterised by good mechanical properties and a high degree of hardness, making them ideal for use as silicones for masks and for flask counter-moulds for dentures.
Dental technicians, on the other hand, may also opt for a highly fluid, transparent bicomponent addition silicone in order to fabricate transparent silicone masks, for light-curing composites and resins.
Addition silicones or polyvinylsiloxanes distinguish themselves among impression materials for their tear resistance, high wettability, rapid setting times and excellent dimensional stability. Dentists who opt for a PVS can therefore count on very limited distortion of the impression after removal from the patient’s oral cavity, high precision and long dimensional stability. It should also be pointed out that these silicones are also gypsum-compatible and therefore guarantee the creation, in the laboratory, of models affording excellent precision.
Dentists therefore favour addition silicones as impression material, due to their excellent performance and optimum results in many different applications. When taking impressions for prostheses on implants, for example, the ideal choice is a radio-opaque, scannable addition silicone that has been designed specifically for implantology.
However, as pointed out at the beginning, dentists cannot focus solely on aspects such as stability and precision when choosing the impression material to be used, and also have to consider the discomfort the patient may experience during the impression taking phase. As a matter of fact, certain dental impression silicones are able to minimise the psychological stress associated with the process thanks to their fast working and setting times.