The influence of the mixing technique on the content of voids in two polyether impression materials

One of the most critical problems related to hand mixing of an elastomeric impression material is air entrapment during spatulation. This leads the formation of both surface and subsurface bubbles which in turn may result in inaccurate dental impressions and/or jeopardize their physical properties. In the present study the influence of the mixing technique has been determined by evaluating the surface area and the number of voids in two polyether materials (Permadyne and Impregum, Espe, Seefeld, Germany). The techniques tested were the stropping technique as hand-mixing and the Pentamix device (Espe) as mechanical mixing. Eighty special trays (10 mm x20 mm x43mm) featuring 10 transverse slots were fabricated and divided into four groups of twenty units. Groups 1 and 2 received the hand-mixed materials Permadyne high viscosity and Impregum F, respectively. Groups 3 and 4 (Pentamix group) received the mechanically mixed materials Permadyne Penta H and Impregum Penta, respectively. After polymerization, 10 slices of material were obtained for each tray by sectioning through the tray slots with a surgical blade. The slices were glued on a card and black and white photographs were taken. Subsequently, the negative films were placed on a viewing box and digitized with a video camera. A special software program allowed to identify and calculate the total surface area and the number of voids. Significant differences between the "stropping" groups (groups 1 and 2) and "Pentamix" groups (groups 3 and 4) were found. The mechanical mixing (Pentamix) generated the smallest number and total surface area of voids, while no significant differences were detected between Permadyne Penta H and Impregum Penta. Clearly, mechanical mixing represents a marked improvement over the traditional hand-mixing methods.