The variety of impression materials available to dentists is very wide, ranging from elastic to rigid materials, two large categories that include multiple possible options.
The most commonly used typology is that of elastic materials, which are classified in turn into hydrocolloids and elastomers. For example, the first group includes alginates, while the second group includes all impression silicones, which are further divided into addition and condensation silicones.
The first to be developed were condensation silicones, invented in the 1950s and also known as polydimethylsiloxanes or first-generation silicones.
They react due to the use of an activator—whether in liquid or paste form—which is added and mixed manually.
The Characteristics of Condensation Silicones
While the disadvantages of condensation silicones include reduced processing times and less-than-perfect dimensional stability, the advantages include excellent mechanical properties, low costs, and detailed definition.
The Characteristics of Addition Silicones (or Second-Generation Silicones)
Addition silicones, also called polyvinylsiloxanes or second-generation silicones, were developed in the 1980s. The difference is mainly due to the vulcanization process, with the formation of the polymer occurring by addition, thanks to the cross-link between the vinyl groups of the polymer and the silane groups activated by a platinum salt catalyst.
One of the primary and most appreciated advantages of addition silicones is their great dimensional stability, which is made possible by the absence of by-products of the addition process.
They are also considered to be easier to mix than condensation silicones due to the convenience of self-mixing cartridges and automatic mixing systems. There are also various types of these materials with different consistencies and polymerization times to accommodate best the clinician's preferences.
Clinicians' Preferences
It should be emphasized that the techniques for obtaining precision impressions using quality impression materials, such as those proposed by Zhermack, are generally usable in the same way with either polydimethylsiloxanes or polyvinylsiloxanes.
Due to their high dimensional stability, good tear resistance, improved timing, the presence of self-mixing systems, and excellent wettability, addition silicones are often the clinician's choice.
It is, in fact, possible to obtain precise impressions with minimal distortion when removing the material; it is also worth highlighting the good compatibility with plaster material typical of hydrocompatible polyvinylsiloxanes.
More Comfort for the Patient
The benefits of using silicones for the patient should also not be overlooked. In fact, many studies have shown how impression materials can be uncomfortable, increasing psychological stress in patients.
By using silicones, thanks also to their reduced working and hardening times, we can significantly improve this aspect, even further reducing the time spent in the oral cavity when using fast-set impression materials.
The Great Versatility of Silicones
Based on what has been said so far, it is not surprising that silicones are very versatile and can be used in a variety of ways in the dental field.
Consider, for example, the taking of impressions for fixed and removable prostheses, with the best addition of silicones that guarantee high smoothness so as to be able to reach even the less easily accessible points of the gingival sulcus: the reference product in this case is the Elite HD+ Addition Silicone by Zhermack.
Silicones can also work perfectly for taking impressions for implant-based prosthetics if a radiopaque and scannable addition silicone specifically for implantology, such as Hydrorise Implant, is used. This impression material, which guarantees a high final hardness, makes it possible to obtain an impression capable of detecting the three-dimensional position of the implant very precisely.
Radiopacity helps the investigation.
It should be added that the radiopacity allows the clinician to radiographically verify the presence of the material under the gum, even in the event of breakage. In guided surgery, a radiopaque material allows the soft tissue profile to be identified in CBCT compared to the bone structure. And thanks to the possibility of being scanned directly without the use of opacifying powders, the material can be digitized without difficulty by either intraoral or extraoral scanners. This is also particularly useful in clinical situations, such as in totally edentulous patients, where the use of the intraoral scanner may encounter problems.
Other Uses
The use of addition silicones is also recommended to ensure high precision in the delicate duplication of the master model in the laboratory.
Silicones are also frequently used in the case of bite registration and during rehabilitation with fixed or removable prostheses. Even among silicone bite registration materials, there are more or fewer rigid variants that can be used depending on the clinical case. The advantages of using special addition silicones should not be overlooked—for example, the Elite Transparent—when creating transparent masks, with the possibility of replicating the diagnostic wax-up created by the dental technician in a dimensionally stable way and allowing the operator to transfer the previously created project into the mouth.
So, it is not surprising that silicones, and especially addition silicones, are consistently among the most widely used materials in dentistry, thanks to the advantages they ensure and their great ductility. The constant evolution of impression materials in step with new technologies also opens up previously unknown and unexpected scenarios, which may lead to better clinical outcomes and more predictable protocols. This is another way, thanks to the latest properties of these materials, such as scannability and radiopacity, that the digital world will also be able to benefit from impression materials within its workflows.
