Extrusion Force Of Impression Materials Supplied In Self-Mixing Cartridges P. Bottenberg* (1), R. Marx (2) (1: Dept. Of Restorative Dentistry, Free University Of Brussels, Laarbeeklaan 103, B-1090 Brussels, Belgium; 2: Dept Of Dental Materials Science, Rwth Aachen, Germany) Objectives Presenting impression materials for indirect restorations in self-mixing cartridges has the advantage of shorter mixing time and less inclusion of air bubbles. Some mixing catridges are supplied with an intraoral application tip in order to perform mixing and impression taking in one step. In the present study the force needed to extrude a given quantity of low- or regular body impression materials as well as the plunger speed were measured.   Materials and Methods 6 different brands of addition silicone impression pastes were tested (Extrude light body, President light and regular body, Provil light and medium body, Dimension light body). The cartidge was held in a stative and placed in a tensile/compressive strength testing machine (Zwick, Ulm, Germany). The automixing cannula and the intraoral application tip was placed on the cartridge. The plunger supplied with the cartridges was replaced by a metal bar connected to the crosshead of the testing machine. The maximum force (Fmax) was determined at a crosshead speed of 0.25 mm s-1. In a second experiment, the plunger was advanced at a constant force of 500 N for a way of 10 mm and a way-time diagram was recorded. The plunger speed was determined as the slope of the curve. A difference was made between the speed before (speed 1) and after reaching of the application tip (speed 2).   Results Fmax varied between 370 and 810 N (p<0.05, excepted President light and regular). A 3-10-fold increase of the extrusion force was recorded as the material reached the application tip. Speed 1 varied between 3.75 mms-1 (Provil LB) and 1.63 mms-1 (President LB). Speed 2 varied more dramatically between 0.14 mms-1 (Dimension LB) and 0.48 mms-1 (Provil LB); all slopes different (p<0.01).   Conclusions The resistance offered by self-mixing cartidges, especially when equipped with an intraoral application tip is considerable, even when a 6:1 or 8:1 transmission in the complete syringe system is taken into account. This reduces the precision of the operator, especially in complex intracoronal preparations. The classification in light and medium body is not related to the flow properties of the materials.