The optical density from Groups 1 to 4 were 0.058 ± 0.007 ng/cm2, 0.115 ± 0.014 ng/cm2, 0.093 ± 0.01 ng/cm2, and 0.1 ± 0.015 ng/cm2, respectively (p < 0.01). The mucin absorbed by the hydroxyapatite disks of Group 1 was significantly less than that of Groups 2, 3, and 4.