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Regulatory testing of hydraulic cements used in dentistry and standard test methods for root-end filling materials do not exist. The aim of this study was to identify a simple, reproducible method for testing the solubility of materials that set with water (hydraulic) used as root-end filling materials in dentistry. Commercial and prototype hydraulic cements were characterized by scanning electron microscopy and X-ray diffraction analyses and their solubilities were determined using ISO 6876; 2012 standard, a modified ISO 6876 method with media alternative to water and a new method measuring the percentage mass loss and volume change of materials (micro-CT method) from a single surface exposed to three solutions. The solubility testing was performed by three operators to enable an intra-laboratory comparison. The solubility data obtained from the two commercial and two prototype materials varied depending on the method used, with the ISO 6876 method identifying differences in solubility of the materials (p < 0.05) but when modified with alternative solutions, no differences were found (p > 0.05). The changes in solution thus effected the solubility of the tested materials. Inter-operator differences were observed with the weight changes determined from the new method indicating this method was not robust. The weight and volume assessments using the new method were not solution-dependent. The advantage of the proposed method compared with the ISO standard is its simplicity, enabling a number of tests to be performed on the same set of samples that also more closely mimics the clinical environment.