Polyvinyl siloxane (PVS) impression materials represent the state of the art in elastomeric impression materials in prosthodontics and restorative dentistry [2-5] used for recording the impressions of dentulous and edentulous arches, duplication of casts and bite registrations.
Polyvinyl siloxane materials are a modification of the original condensation silicones.
Several authors have reported hydrogen gas bubble formation on the surface of gypsum dies poured immediately from polyvinyl siloxane impressions [3, 13].
It reacts with the platinum catalyst in the polyvinyl siloxane to cause a delay or total inhibition of polymerization [15, 19, 22] reported that even in concentrations as low as 0.005 per cent, total inhibition of polymerization of polyvinyl siloxane can be observed.
Polyvinyl siloxanes are available in viscosities ranging from very low (for pouring, syringing or wash use), to medium, high and very high.
Modern polyvinyl siloxanes have a working time of two minutes and a setting time of six minutes (with slight variation) [3, 13].
Polyvinyl siloxanes are currently considered to reproduce the greatest detail of all the impression materials.
Polyvinyl siloxanes show the smallest dimensional changes on setting of all the elastomeric impression materials.
Polyvinyl siloxanes are frequently reported to be the most ideally elastic impression materials because they exhibit better elastic recovery and less permanent deformation than the other elastomers.
Lacy et al  investigated the time dependant accuracy of elastomeric impression materials and concluded that polyvinyl siloxanes were the most stable of elastomers.
Polyvinyl siloxanes have the least viscoelastic qualities thus requiring the least time for recovery from viscoelastic deformation.
Shillingburg et al  tested an experimental polyvinyl siloxane material containing 20 per cent barium sulphate to improve radiopacity.