Irrigation in Endodontics - The Endoexperience

Irrigation in Endodontics 299
than NaOCl/MTAD. 54,55 Comparative studies on MATD and Tetraclean have indicated
better antibacterial effects by the latter. 56 Although a mixture containing an antibiotic
may have good short-term and long-term effects, concerns have been expressed
regarding the use of tetracycline (doxycycline) because of possible resistance to the
antibiotic and staining of the tooth hard tissue, which has been demonstrated by exposure
to light in an in vitro expreriment. 57 However, no report of in vivo staining has been
published.
CHALLENGES OF IRRIGATION
Smear Layer
Removal of the smear layer is straightforward and predictable when the correct
irrigants are used. Relying on EDTA alone or other irrigants with activity against the
inorganic matter only, however, results in incomplete removal of the layer. Therefore,
use of hypochlorite during instrumentation cannot be omitted (Fig. 8). The smear layer
is created only on areas touched by the instruments. Delivery of irrigants to these
areas is usually unproblematic, with the possible exception of the most apical canal,
depending on canal morphology and the techniques/equipment used for irrigation.
However, careless irrigation, with needles introduced only to the coronal and middle
parts of the root canal, is likely to result in incomplete removal of the smear layer in
the apical root canal.
Dentin Erosion
One of the goals of endodontic treatment is to protect the tooth structure so that the
physical procedures and chemical treatments do not cause weakening of the dentin/
root. Erosion of dentin has not been studied much; however, there is a general
consensus that dentin erosion may be harmful and should be avoided. A few studies
have shown that long-term exposure to high concentrations of hypochlorite can lead
to considerable reduction in the flexural strength and elastic modus of dentin. 19 These
studies have been performed in vitro using dentin blocks, which may allow artificially
deep penetration of hypoclorite into dentin. However, even short-term irrigation with
hypochlorite after EDTA or CA at the end of chemomechanical preparation causes
strong erosion of the canal-wall surface dentin (Fig. 9). 20 Although it is not known
for sure whether surface erosion is a negative issue or if, for example, it could improve
dentin bonding for posts, it is the authors’ opinion that hypochlorite irrigation after
Fig. 8. Instrumented canal wall after removal of the smear layer by NaOCl and EDTA.