The invention relates to a kit of parts for preparing a glass ionomer cement, the kit comprising a Part A and a Part B, Part A being a powder and comprising an acid-reactive filler in an amount above about 60 wt. %, the acid-reactive filler having a mean particle size in the range of 3.5 to 10 μm, an non acid-reactive filler in an amount above about 1 wt. %, the non acid-reactive filler having a mean particle size in the range of 1.0 to 3.5 μm, Part A not comprising a polyacid in an amount above about 1 wt. %, wt. % with respect to the weight of Part A, Part B being a liquid and comprising a polyacid in an amount above about 30 wt. %, water, a complexing agent, wt. % with respect to the weight of Part B. The invention also relates to a process of producing a hardenable or hardening composition and use thereof in the dental field.