From: Comparison between two methods of working length determination and its effect on radiographic extent of root canal filling: a clinical study [ISRCTN71486641]
Variable
Group I
Group II
Number
Mean
SD
Mean distance from tip of root canal filling to radiographic apex (mm)
67
-0.5
0.5
84
-0.4
Number of Radiographs (mean)
2.0
0.1
3.2