In Vivo Assessment of the Apatite-Forming Ability of Second-Generation Hydraulic Calcium Silicate Cements Using a Rat Subcutaneous Implantation Model

Abstract

Hydroxyapatite formation on endodontic hydraulic calcium silicate cements (HCSCs) plays a significant role in sealing the root canal system and elevating the hard-tissue inductivity of the materials. This study aimed to evaluate the in vivo apatite-forming ability of 13 second-generation HCSCs using a representative first-generation HCSC (white ProRoot MTA: PR) as a positive control. Thirteen second-generation HCSCs and PR were loaded into polytetrafluoroethylene tubes and implanted in subcutaneous tissue of 4-week-old male Wistar rats. At 28 days after implantation, hydroxyapatite formation on the HCSC implants was assessed with micro-Raman spectroscopy, surface ultrastructural and elemental characterization, and elemental mapping of the material–tissue interface. A Raman band for hydroxyapatite (v1 PO43- band at 960 cm−t) and hydroxyapatite-like calcium-phosphorus-rich spherical precipitates were detected on six second-generation HCSCs and PR. In the elemental mapping, calcium-phosphorus-rich hydroxyapatite-layer-like regions were not observed on the seven HCSCs that showed neither the hydroxyapatite Raman band nor hydroxyapatite-like spherical precipitates. These results indicated that only 6 of the 13 second-generation HCSCs produced a detectable amount of hydroxyapatite in rat subcutaneous tissue within 28 days, similar to PR. The seven second-generation HCSCs that did not exhibit hydroxyapatite formation may not be suitable alternatives to PR due to their weak in vivo apatite-forming ability.