Objective      To study the sealing ability of Portland Cement (PC) as apical barrier in vitro

and to compare the sealing ability of PC with that of mineral trioxide aggregate (MTA)

glass ionomer cement (GIC) and amalgam (Am).        Methods        Sixty-four premolars with single root canal were instrumented and set as open root apex modle. The premolars were randomly divided into an experimental group and a control group. The experimental group were subdivided into  group A

  group B

  group C and  group D (n=15)

and each group of teeth were filled with PC

MTA

GIC and Am

respectively. The control group was subdivided into a negative control group and a positive control group (n=2). Coomassie brilliant blue was applied for quantitative determination of protein leakage using 4% bovine serum albumin for continuous 60 d.       Results       The protein leakage between group A and group B had no significant statistically difference (P0.05). The protein leakage of group A showed significant statistically difference when compared with that of group C and D (P0.05)

and the same results were found in group B compared with group C and group D (P0.05). The increase of protein leakage with time in the group A showed no significant statistically difference (P0.05).        Conclusion       Sealing ability of PC is better than that of GIC and Am

and is the same as that of MTA when used as apical barrier filling materials.