pH changes in external root surface cavities after calcium hydroxide is placed at 1, 3 and 5 mm short of the radiographic apex

The purpose of this study was to test the null hypothesis that there is no difference in the pH on the external apical dentin surface when the canal is completely filled with calcium hydroxide or when it is placed 3 or 5 mm short of the apical foramen in extracted human teeth. The root canals of single-rooted anterior human teeth were cleaned and shaped after decoronation. Cavities about 0.50 mm deep and 1.0 mm wide located at 1, 3 and 5 mm from the radiographic apex were prepared on the external root surface and the teeth were randomly divided into four groups. The roots were filled with calcium hydroxide at 1, 3 and 5 mm from the radiographic apex, and the control group was left empty. pH readings were obtained at intervals over a 28-day study. The roots which were filled within 1 mm of the radiographic apex had the greatest increase in pH in each of the cavities. These results demonstrate that the greatest pH change on the external root surface near the apex is obtained when the canal is more completely filled with calcium hydroxide.