An explanation of the mineralization mechanism in osteoblasts induced by calcium hydroxide

Calcium hydroxide (Ca(OH)2) has been broadly used in endodontics, including apexification to obtain apical closure by mineralization. However, the detailed mechanism of mineralization induced by Ca(OH)2 is still unclear. This study focuses on the function of calcium and hydroxyl ions which dissociate from Ca(OH)2 during the mineralization process. Though primary osteoblasts cultured in the medium without or with 0.025 mg ml−1 Ca(OH)2 did not show mineralization, they did exhibit mineralization when they were cultured with a higher concentration of Ca(OH)2 (0.25 mg ml−1). Mineralization induced in the presence of 0.25 mg ml−1 Ca(OH)2 was greater at pH 7.4 than at pH 8.5. The high mineralization activity observed under neutral conditions was caused by the prolonged activation of p38 and JNK. Hydroxyl ions did not have any effect on the mineralization. The results demonstrate that calcium ions dissociated from Ca(OH)2 are critical for inducing the mineralization of osteoblasts.