Absorption of mucin on the surface of the hydroxyapatite disks with coating was evaluated. The disks were immersed in 10 mg/mL of mucin obtained from bovine submaxillary glands (Sigma–Aldrich, Co., St. Louis, MO, USA) for 90 min. They were rinsed with phosphate buffer solution (PBS) to remove the residual mucin before they were stained with Alcian blue solution (pH = 2.5). The absorbed mucin was then extracted using 30% hydrogen peroxide. The optical density of the supernatant (200 mL) was measured spectrophotometrically at 595 nm . The expected difference is at least 10°. Six hydroxyapatite disks per group were studied.