The properties of polymerizable luting cements

The properties of a polyacid‐modified composite resin and two resin‐modified luting cements have been studied. The polyacid‐modified composite resin had the slowest setting reaction and, in this respect, it did not conform to the current international standard for luting cements. The compressive strength of all of the materials was studied after varying periods of storage from 24 h to 1 year. The polyacid‐modified composite resin showed a distinct dip in strength at 1 month in all of the storage media, but otherwise it showed no significant variation with either age or storage medium. The resin‐modified glass–ionomers showed variation at 24 h with storage medium (deionized water, 0·9% NaCl or 20 mmol dm −3 lactic acid), but thereafter they showed little variation, until 1 year, when Vitremer® luting showed a significant decline in strength in pure water. However, at 24 h and when stored in water, all of the materials had strengths that easily exceeded the minimum requirement of the current standard (70 MPa). They all took up water on storage, with diffusion coefficients ranging from 1·32 to 17·19×10 −7  cm 2  s −1 . These values were found to depend on whether the specimens were stored in pure water or in physiological saline. However, equilibrium water contents varied only slightly between water and saline. The polyacid‐modified composite resin, Dyract‐Cem®, took up the least water, as well as showing the smallest variation in strength with age. By contrast, it was more difficult to mix than the other materials and the high viscosity of the paste led to the formation of voids and other imperfections in the specimens.