Cultures were evaluated as follows: (i) fixed OC were stained for TRAP activity using Naphtol AS-MX phosphate (3-hydroxy-2-naphtho-2′,4′-xylidide phosphate, Sigma-Aldrich) and Fast red (Sigma-Aldrich) dissolved in 0.1 M acetic buffer (pH 5.0) containing 1% tartaric acid.