One of the main origins of unsuccesful endodontic treatment is coronal leakage. In the prevention of coronal leakage a good sealing restoration seems mandatory. The effect of 2 types lining cement used as coronal barrier on filled root canals was studied over time. Fifty extracted human canines were prepared and filled by gutta-percha with a quantifiable initial coronal leakage. After placement of the lining cements in 2 groups of 20 canines, leakage was assessed at 96 hours and at 26 weeks and compared with the leakage in a control group of 10 canines. Placement of a coronal barrier of lining cement on the orifice of the root canal after endodontic treatment revealed a significant reduction of coronal leakage. In this study leakage decreased over time.