Seems sometimes dentists use both! Read below:
A major goal in endodontic treatment is to obtain a clean
root canal. Toward this end the instrumentation is generally
supported by the use of a solution for irrigation. Root canals
have a complex anatomy and there are areas that may not be
accessible for instrumentation. Therefore, agents capable of
dissolving necrotic tissue are used (1).
Sodium hypochlorite was successfully used in wound treatment
during World War I (2)
and later it was introduced in endodontic therapy as an antibacterial tissue-dissolving irrigant
(3-6). It is extensively used and its tissue dissolving
capability has been studied under varying test conditions (7).
Favorable results have been obtained when using calcium
hydroxide as an intracanal dressing between visits (8, 9). Also,
it has been found that the use of calcium hydroxide as a long-term intracanal dressing enhances the prognosis for treatment of young human teeth (10). The reason for this beneficial effect is not thoroughly understood. However, it has been
demonstrated in monkey teeth that the use of calcium hydroxide
results in considerably cleaner root canals compared
with root canals where calcium hydroxide had not been used
(11). As strong bases are able to denaturate and hydrolyze
proteins (12), calcium hydroxide may contribute to a breakdown
of intracanal soft tissue remnants thus rendering a
cleaner root canal.
In clinical practice, calcium hydroxide and sodium hypochlorite are often used in the same root canals.
The purpose of this study was to assess in vitro, the separate and combined effects of calcium hydroxide and sodium hypochlorite on the dissolution of necrotic tissue.
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CONCLUSIONS
In this study, using necrotic porcine muscle tissue, it was found that:
1. Calcium hydroxide was capable of dissolving tissue.
2. The tissue dissolving effect of sodium hypochlorite was
enhanced by pretreatment with calcium hydroxide..
endodonticcentre.ca/Sites/EndodonticCentre/uploads/documents/28110413115519.pdf 
