For sure Impression materials are related and integrated in the dentistry field. That’s why we observe so many changes in the materials itself just like the polyether and additional silicone. Briefly, impression materials are divided into rigid and elastic impression materials in which generally the rigid one is used for edentulous patients with mild or moderate undercuts whereas the elastic one is used for dentulous or edentulous patients with severe undercuts. Now both polyether and additional silicone (PVS) are subgroups of the elastomeric elastic impression materials and have a variety of functions and properties which distinguish each other.
To understand why polyether is out and why additional silicone is the most commonly used impression material we need to know the different uses and properties of each elastomeric material. Starting with the advanced and the newest impression material which is the polyether(PE). In (Figure 1) we already know that the polyether comes in variety of colours which can give a beautiful and fantastic surface details. Polyether is used mainly to control moisture. Some patients in different cases might have increased salivary action in which saliva might interfere with the impression material and result in poor surface details. Not only saliva that causes the issue but blood, water and gingival fluids can interfere with the outcome.
Properties of PE:
- Hydrophilic material which has an exceptional flow and wettability
- High surface details which is achieved by the hydrophilicity nature of the material
- Good dimensional stability
- Stock or special trays can be used
- Multiple delivery methods
Mainly hydrophilicity and flowability are the main properties that gives the polyether the advantage against the other impression materials. The polyether has a variety of delivery methods which simplifies the usage of this material. including AUTOMATIC MIXING SYSTEM such as the 3M ESPE Pentamix 3 Automatic Mixing Unit or a hand-dispensed cartridge mixing system. Check the video below for further details about the Pentamix 3.
Although all these feature and advancements present in the polyether impression material, dentists still like to use the additional silicone Impression material.
Vinylpolysiloxane (VPS) or Additional Silicone
Dentists still use today the VPS in various cases as this material consists of two pastes the first one consists of polymethylhydrosiloxane, divinylpolysiloxane and fillers (remember that the presence of fillers gives somehow a viscous property to the material). Whereas the second paste consists of divinylpolysiloxane, platinum salts and fillers as well.
The (VPS) comes in different consistencies light, medium, heavy and very heavy bodied (putty).
Properties of VPS:
- Excellent surface details, which can be used in secondary impressions
- Dimensional stability
- Gives multiple casts
- Stock and custom trays can be used
- Variety of delivery methods
VPS delivery methods include: 1- hand mixing, 2- cartridges of base and catalyst (mixing gun), 3- syringes (injectable) 4- sausages (Motorized mixer).
Both with multiple almost similar properties. Then WHY PE?
The main issue that some dentists face during their cases in the moisture control. The VPS has hydrophobic properties that creates a struggle while doing the impression and this can be replaced by the PE with the hydrophilicity nature! On the other hand, dentists prefer the VPS because it is cheaper, can perform the same surface details as the PE, can control the hydrophobic nature by placing a barrier between the material and the patient mouth. Still the VPS can be delivered in variety of methods as mentioned above to exploit the costs of using the PE in automatic mixing unit. Still the VPS is provided with an automatic mixing unit to fulfil the needs of dentists. Some dentists prefer VPS because PE May cause allergic reaction due to the sulphonic acid ester/poor taste, Stiff set material (sometimes hard to remove from mouth), impressions may swell and distort because of the absorption of water, should therefore be stored dry, more expensive and need tray-special adhesives. At the end clinicians in the past faced too much troubles to fabricate a denture or a bridge without having an accurate impression materials. Now advancements in the chemical makeup of each impression material category give the dentist options that can work well in cases that are routine or in the most challenging clinical situations. It is up to the clinician to understand the different characteristics of the various impression materials and to choose one that is best matched to the specific clinical situation at hand