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[Effect of root canal curvature on canal length measurement on digital image of human lower mandibular permanent incisor].

OBJECTIVE
To investigate the effect of canal curvature on measured precision in canal length of human lower mandibular permanent incisors imaged by direct digital radiograph.


METHODS
With Trophy digital X-ray system, 299 Chinese lower mandibular permanent incisors were selected to take the direct digital X-ray photography in both facial to lingual (L-T) and proximal directions (M-D). Two operators familiar with endodontic knowledge estimated the canal length by means of on-screen DDR with 2-and 3-click measurements.


RESULTS
The true canal length of Chinese lower mandibular permanent incisors was (19. 54 +/- 1.62) mm. The tooth root canal length on digital image was overestimated with 3-click measurement (P < 0.05), and the canal length with 2-click measurement was almost similar to the true canal length from the facial-lingual direction X-ray photography (P > 0.05). The less than 1 mm difference between the estimated canal and the true canal length was above 95%. The canal length was underestimated with 2-click measurement as the curvature severity increased.


CONCLUSION
Direct digital radiography system is applicable to estimate the canal length in clinic as the accuracy is very good. The curved canal length should be estimated with 3-click measurement.