The range of impression materials available to dentists is, as is known, extremely vast, and ranges from elastic materials to rigid materials, two large categories that include various possible options. It is also known that the most used is the elastic materials category, which in turn consists of hydrocolloids and elastomers. Whereas the former group includes, for example, alginate, the latter includes impression silicones that in turn consist of addition silicones and condensation silicones.
Condensation and Addition Silicones
The first to be developed were condensation silicones, which were invented in the 1950s, and are also known as polydimethylsiloxanes or first-generation silicones. They react thanks to the use of an activator – which can be a liquid or a paste – that is added and mixed manually. Although the disadvantages of condensation silicones include their short working times and sub-optimal dimensional stability, their advantages include excellent mechanical properties, limited costs and hydrophobia.
Addition silicones, which are also known as polyvinylsiloxanes or second-generation silicones, were developed in the 1980s: the main difference is the vulcanisation process, with the formation of the polymer by addition, thanks to the cross-linking between the vinyl group of the polymer and the silane groups activated by a platinum salt catalyst. One of the main and most appreciated advantages of addition silicones is their great dimensional stability, which is possible thanks to the absence of addition reaction byproducts. They are also said to be easier to mix than condensation silicones, due to the convenience of self-mixing cartridges and automatic mixing systems.
Before going any further, it should be emphasised that the techniques for obtaining silicone master impressions, using quality impression materials such as those offered by Zhermack, are usually similar for polydimethylsiloxanes and polyvinylsiloxanes. Dentists often prefer addition silicones thanks to their high-dimensional stability, good tear resistance, improved times, presence of self-mixing systems and excellent wettability. Indeed, they make it possible to obtain precise impressions with minimum distortion when the material is removed and also have a good compatibility with gypsum typical of hydrocompatible polyvinylsiloxanes.
Uses of Dental Impression Silicones
The use of silicones also brings non-negligible benefits for patients. Many studies have shown that impression material can be uncomfortable for patients and therefore increase their psychological stress. By using silicones, thanks also to the limited working and setting times, this aspect can be considerably improved and further reduces the time in mouth when using fast-set impression materials.
From what has been said so far, it is therefore not surprising that silicones are extremely versatile and suitable for different uses in dentistry. Think, for example, of impression taking for fixed and removable prostheses, with the best addition silicones ensuring high fluidity, making it possible to reach even the less readily accessible points of the gingival sulcus: the product of election in this case is Zhermack’s Elite HD+ addition silicone.
Silicones can also be perfect for taking impressions for implant-retained prostheses, by opting for a radio-opaque and scannable addition silicone developed specifically for use in implantology, such as Hydrorise Implant; with this impression material, which ensures a high final hardness, the impression obtained is capable of recording the three-dimensional position of the implant very precisely. Use of addition silicones is also recommended for ensuring high precision in the delicate duplication of master models in the laboratory.
Silicones are also commonly used in the case of bite registration, for rehabilitation with fixed or removable prostheses; the advantages of using special addition silicones – such as Elite Transparent – for the fabrication of transparent masks must not be overlooked, since they make it possible to reproduce the diagnostic wax-up in a dimensionally stable manner, and allow the practitioner to transfer the previously fabricated project into the patient’s mouth. It is therefore no surprise that silicones, especially addition silicones, are consistently amongst the most commonly used materials in dentistry, thanks to the advantages ensured and their great ductility.