Differential Zoledronate Adsorption by Commercially Available Biphasic Calcium Phosphate Bone Substitutes

Background/Objectives: Osteonecrosis of the jaw, a non-healing wound, is a side effect in patients treated with nitrogen-containing bisphosphonates (e.g., zoledronate) after some oral procedures. Considering zoledronate toxicity in surgical wounds and the capacity of calcium phosphate synthetic compounds to adsorb it, the aim of this work was to demonstrate and elucidate the mechanism underlying this adsorption. Methods: Four different calcium phosphate synthetic bone substitutes were used in this study: AdBone® BCP (0.5–1 mm), Guidor® easy-graft (0.5–1 mm), Maxresorb® (0.5–1 mm) and Maxresorb® (0.8–1.5 mm). The materials were incubated in aqueous zoledronate solutions. Samples of the solutions obtained after 1, 2, 3, 6, 24, 48, 72 and 120 h of conditioning were then analyzed by spectrophotometry to measure their absorbance and subsequently characterized by micro-elemental analysis. Results: All four materials demonstrated time-dependent zoledronate adsorption. AdBone® BCP achieved the most rapid and sustained sequestration, reaching 80% reduction at 24 h and stabilizing at 85% from 72 h onwards without re-release. Maxresorb® formulations showed comparable kinetics through 72 h (70–75%) but exhibited partial re-release at 120 h. Guidor® easy-graft showed negligible adsorption through the first 24 h, consistent with the physical barrier effect of its PLGA coating. Spectrophotometric findings were independently confirmed by elemental analysis. Conclusions: This work confirms zoledronate adsorption by calcium phosphate synthetic biomaterials. Among the tested materials, AdBone® BCP demonstrated the most favorable adsorption profile, with kinetics well matched to the critical window of alveolar wound healing. These findings support the use of biphasic calcium phosphate bone substitutes as a local strategy to reduce free zoledronate bioavailability at the surgical site, potentially lowering the risk of MRONJ in patients undergoing dentoalveolar procedures under bisphosphonate therapy.