Bleeding from root canal: Am I 'over' or 'under'?

In a root canal with ongoing endodontic treatment, both over instrumentation and under instrumentation may be the cause of persistent oozing of blood. Finding out which side of the apical constriction you are on is critical to the success of root canal treatment as well as patient comfort.

• Firstly, confirm the working length using an electronic apex locator. If you have already violated the apical constriction leading to the bleeding canal, tactile sensation may not help. Radiograph will only be helpful if you are more than 2 mm short of the radiographic apex or anywhere beyond it - which is a wide range from the apical constriction.
• If you are not using or not getting a reliable reading from the apex locator, the working length has to be determined using radiograph and tactile sensation. Flare the canals coronally till the root canal curvature; and use successively larger K-files to the apical area till binding is obtained 1-2 mm short of the radiographic apex. You now know whether you were 'over' or 'under'.
• If you were over-instrumenting, you only need to create an apical stop with a larger diameter instrument. This will both help in stopping the bleeding as well as getting a good apical seal. While if the reason was under-instrumentation, you can now proceed to clean and shape the remaining apical root canal. 
• If the working length you re-determine is the same as before, it is most likely that the bleeding is occurring from pulp remnant. Studies have shown that to thoroughly clean the apical root canal, you need to go at least 4 sizes larger than the initial apical file. Moreover, the root canal anatomy is more ovoid or elliptical than circular - the shape of an endodontic instrument; allowing pulp remnants along the root canal walls as well. Insert a barbed broach all the way to the working length, rotate it clockwise and pull it out. Then use H-file of the last apical size in circumferential filing motion to disengage any remnant still adhering to the root canal walls and irrigate copiously. 

SEM micrographs of the first K-files to bind at the root canal apex showing wide discrepancy between apical foramen and file size (Relationship between files that bind at the apical foramen and foramen openings in maxillary central incisors - a SEM study; Ronaldo et al. Braz Dent J; vol 22:6)

• The type of bleeding is also a good indicator of the source. Fresh, thin bleed is more likely to come from periapical trauma while oozing, dark bleed is more likely to originate from pulp remnants. 
• If the bleeding still persists, it is best to forego any further instrumentation. Dry the canals using paper points. Generally, if the bleeding is periapical it will dry out with the paper points while if there is a pulp remnant, the paper points will continue to absorb the bleed. 
• In such cases, it is always better to schedule a second sitting for completing the cleaning and shaping rather than a single sitting root canal treatment. Place a proper intracanal medicament along with a good coronal seal and prescribe a suitable non steroidal analgesic for any pain likely to result from over instrumentation. 

Additional Reading: The morphology of the apical foramen in posterior teeth in a North Indian population. Arora, Tiwari. IEJ,42, 930-939,2009.