The use of synthetic bone graft substitutes to repair bone defects has dramatically increased over the last decade. Among these materials, calcium phosphates such as tricalcium phosphate or hydroxyapatite are amongst the most effective and the most used.1 Many chemical and physical factors have been identified to influence their reactivity and degradation rate upon implantation. Recently, we found that a simple thermal treatment at temperatures of 450–600 °C was able to strongly modify the reactivity of α-tricalcium phosphate powders [α-TCP; α-Ca3(PO4)2] with water without significant change of physical properties.2 The strong decrease of reactivity was attributed to the thermal removal of surface defects. Here, we demonstrate the potential of this treatment to control the onset of this particular setting reaction (defined by the start of the exothermic reaction) from a few minutes to a few hours. Furthermore, we show that the behavior of osteoclast lineage cells cultured in vitro on calcium phosphates is affected by the thermal treatment. We conclude that the presented findings may open up new strategies for engineering bone void fillers.