HYBRID TECHNIQUE

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Properties of an Irrigant?
To effectively clean and disinfect the root canal system, an irrigant should be able to disinfect and penetrate dentin and
its tubules, offer long-term antibacterial effect (substantivity), remove the smear layer, and be nonantigenic, nontoxic
and noncarcinogenic. In addition, it should have no adverse effects on dentin or the sealing ability of filling materials.7
Furthermore, it should be relatively inexpensive, convenient to apply and cause no tooth discoloration.7 Other desirable
properties for an ideal irrigant include the ability to dissolve pulp tissue and inactivate endotoxins.13
What are the Types, Advantages and Disadvantages of Current Irrigants?
The irrigants that are currently used during cleaning and shaping can be divided into antibacterial and decalcifying
agents or their combinations. They include sodium hypochlorite (NaOCl), chlorhexidine, ethylenediaminetetraacetic
acid (EDTA), and a mixture of tetracycline, an acid and a detergent (MTAD).
Sodium Hypochlorite (NaOCl)
Sodium hypochlorite (household bleach) is the most commonly used root canal irrigant. It is an antiseptic and inexpensive
lubricant that has been used in dilutions ranging from 0.5% to 5.25%. Free chlorine in NaOCl dissolves vital and
necrotic tissue by breaking down proteins into amino acids.14 Decreasing the concentration of the solution reduces its
toxicity, antibacterial effect and ability to dissolve tissues.14 Increasing its volume or warming it increases its effectiveness
as a root canal irrigant.14
Advantages of NaOCl include its ability to dissolve organic substances present in the root canal system and its affordability.
The major disadvantages of this irrigant are its cytotoxicity when injected into periradicular tissues, foul
smell and taste, ability to bleach clothes and ability to cause corrosion of metal objects.15 In addition, it does not kill all
bacteria,12,16-18 nor does it remove all of the smear layer.19 It also alters the properties of dentin.20,21 The results of a recent
in vitro study show that the most effective irrigation regimen is 5.25% at 40 minutes, whereas irrigation with 1.3% and
2.5% NaOCl for this same time interval is ineffective in removing E. faecalis from infected dentin cylinders.22 Based on
the findings of this study, the authors recommend the use of other irrigants to increase the antibacterial effects during
cleaning and shaping of root canals.
Sodium hypochlorite is generally not utilized in its most active form in a clinical setting. For proper antimicrobial
activity, it must be prepared freshly just before its use.23,24 In the majority of cases, however, it is purchased in large
containers and stored at room temperature while being exposed to oxygen for
extended periods of time. Exposure of the solution to oxygen, room temperature
and light can inactivate it significantly.24
Extrusion of NaOCl into periapical tissues (Figures 5a and 5b) can cause
severe injury to the patient.25,26 To minimize NaOCl accidents, the irrigating
needle should be placed short of the working length, fit loosely in the canal
and the solution must be injected using a gentle flow rate. Constantly moving
the needle up and down during irrigation prevents wedging of the needle in
the canal and provides better irrigation. The use of irrigation tips with sideventing
reduces the possibility of forcing solutions into the periapical tissues.
Treatment of NaOCl accidents is palliative and consists of observation of the
patient as well as prescribing antibiotics and analgesics.
Chlorhexidine
Chlorhexidine gluconate has been used for the past 50 years for caries prevention,
27 in periodontal therapy and as an oral antiseptic mouthwash.28 It has a
broad-spectrum antibacterial action, sustained action and low toxicity.14 Because of these properties, it has also been recommended
as a potential root canal irrigant.14,27 The major advantages of chlorhexidine over NaOCl are its lower cytotoxicity
and lack of foul smell and bad taste. However, unlike NaOCl, it cannot dissolve organic substances and necrotic tissues present
in the root canal system. In addition, like NaOCl, it is unable to kill all bacteria and cannot remove the smear layer.29,30
Ethylenediaminetetraacetic Acid (EDTA)
Chelating agents such as ethylenediaminetetraacetic acid (EDTA), citric acid and tetracycline are used for removal of the
inorganic portion of the smear layer.7 NaOCl is an adjunct solution for removal of the remaining organic components. Irrigation
with 17% EDTA for one minute followed by a final rinse with NaOCl is the most commonly recommended method
to remove the smear layer.14 Longer exposures can cause excessive removal of both peritubular and intratubular dentin.31
EDTA has little or no antibacterial effect.32
MTAD
An alternative solution to EDTA for removing the smear layer is the use of BioPure™
MTAD™ (DENTSPLY Tulsa Dental Specialties, Tulsa, Okla.), a mixture of a tetracycline isomer,
an acid (citric acid) and a detergent.33 MTAD was developed as a final rinse to disinfect
the root canal system and remove the smear layer. The effectiveness of MTAD to completely
remove the smear layer (Figure 6) is enhanced when a low concentration of NaOCl (1.3%) is
used as an intracanal irrigant before placing 1 ml of MTAD in a canal for 5 minutes and rinsing
it with an additional 4 ml of MTAD as the final rinse.33 It appears to be superior to CHX in
antimicrobial activity.30 In addition, it has sustained antibacterial activity, is biocompatible and
enhances bond strength.14 Table 1 shows the advantages and disadvantages of current irrigants
utilized during root canal