Comparison of the transfer precision of three different impression materials in combination with transfer caps for the Frialit (R)-2 system

Transfer of the precise position of implants to a master cast is a prerequi site for accurate and passive fit of the superstructure. Implants lack the mobility of natural teeth and, therefore, inaccurate frameworks result in s tress within the mechanical parts and the implant-bone interface. Various i mpression methods have been described to achieve accurate reproduction of t he intra-oral relation of the implants. The aim of this experimental study was to compare three different impression materials (polyether, polyvinyl s iloxane, hydrocolloid) with the Frialit(R)-2 system and with the indirect t echnique. In addition, the use of transfer caps (TCs) to improve transfer p recision was tested with all three materials. All measurements were perform ed using a three-dimensional (3D) co-ordinate measuring machine that is cap able of locating points in space and calculating the relative distortions a s angles of tilt (rot-XY, rot-XZ, rot-YZ) and 3D displacement. The results suggest that addition-silicone (a-silicone) and polyether are the materials of choice for implant transfer procedures. The use of TCs resulted in a si gnificantly reduced rotation in the XY-plane but did not improve the absolu te 3D displacement. A-silicone with the use of TCs proved to be most precis e. Comparison between polyether and polyvinyl siloxane showed significant d ifferences in the XY-rotation and the 3D displacement in favour of the sili cone. Because the mean distortions between the original model and the maste r casts were about 100 mu m, absolutely precise fit may be unattainable owi ng to the physical properties of the materials. Further studies will have t o evaluate the amount of tolerable stress at the implant-bone interface.