Endodontic ‘solutions’ part 1: a literature review on the use of endodontic lubricants, irrigants and medicaments

Sodium hypochlorite

Sodium hypochlorite (NaOCl) is a caustic solution with a pH of 12–13 which, if diluted and stored out of the light at room temperature, is stable for only one week.21 It is efficient in dissolving organic components of dentine, but its ability to remove inorganic components is limited. It has a broad antimicrobial spectrum against bacteria, bacteriophages, spores, yeasts and viruses. At high concentrations, however, it can damage soft tissues and dentine.22 Conflicting evidence exists as to the most effective non-toxic concentration of NaOCl for endodontic usage. Several clinical studies have shown that, even after irrigation at 5% concentration during instrumentation, nearly one third to one half of the root canals remained contaminated.23,24 Berber et al25 found that only higher concentrations of NaOCl were able to disinfect E faecalis infected canals independent of the canal preparation technique used. The proteolytic effect of NaOCl is dependent on the amount of free available chlorine. The chlorine is exhausted by reacting with inorganic reducing substances, so frequent irrigation with a lower concentration can equate with higher concentrations.24 It is apparent from the current available evidence that there is no rationale for using NaOCl at concentrations over 1%26 as this offers the best balance of tissue dissolution capacity, antimicrobial activity and biocompatibility. Copious irrigation with l% concentration can achieve the desirable clinical effects.27

The question then is what volume per canal? Yamada et al28 found that 20 ml per canal, 10 ml 17% EDTA and 10 ml 5.25% NaOCl, produced the cleanest canal. In an in vitro study analysing the quantity of dentine debris remaining following irrigation with different volumes of 2% NaOCl and flushing methods, the authors found that there was no significant difference between 6 ml or 12 ml at a rate of 2 ml/30 s or 50 ml continuous flow.29 This is twice the concentration advocated above so it may be reasonable to assume that, from these two papers, 10–20 ml per canal would suffice. However, there is insufficient evidence to date to support this.

It has also been shown in a number of in vitro studies that warming NaOCl improves its efficiency.30,31 A 1% solution at 45 °C has the equivalent effect as 5.25% at 20 °C, according to Sirtes et al.31 However, there are no clinical studies to support these findings and, in addition, it is unknown what effect this heat has on adjacent tissues.

Another method of increasing the temperature of NaOCl is with acoustic microstreaming caused by ultrasonic activation. This removes more organic and inorganic debris plus bacteria.32 According to Al-Jadaa et al,33 pulp dissolution occurs in the main plus accessory canals and temperatures of 55 °C were measured. Zeltner et al,34 however, found no temperature increase if a continuous flow was used.

Chlorhexidine (CHX)

Chlorhexidine digluconate is a bisguanide antiseptic with broad antimicrobial action and substantivity of more than 12 hours.11,12 The microbial flora associated with primary endodontic infections is largely gram negative anaerobes, unlike that of secondary cases where gram positive organisms such as E faecalis and yeast predominate. CHX is more effective against gram positive bacteria12 and therefore may have a role as an endodontic irrigant in retreatment cases. In vitro studies have shown it to be effective against Candida albicans and E faecalis.13,14 CHX solution at 1% and 2% concentrations was shown to be as fast as 5.2% NaOCl in killing E faecalis.14 According to Zamany et al35 the 2% concentration is best for endodontic use. In some clinical studies, CHX was shown to be as effective as NaOCl in root canal disinfection,36 although it lacks the ability to dissolve organic tissue and therefore is less effective in removing necrotic pulps.37 Improved disinfection was obtained when combined with NaOCl.35 CHX cannot be advocated as a main irrigant in endodontic cases but it may be useful as a final rinse following NaOCl, especially in retreatment cases.27 It should, however, be noted that combined use of chlorhexidine and NaOCl can cause discoloration,38 so the use of sterile water or paper points is indicated following NaOCl and before CHX.

Iodine

Iodine preparations can also help eliminate E faecalis and C albicans,39 which are often associated with persistent endodontic infections. Iodine potassium iodine (IKI) is known for its ability to diffuse through dentinal tubules and kill bacteria in vivo.40 However, the duration of its antimicrobial effect is short. It has been shown that 5 min irrigation with 5% IKI reduces the number of E faecalis recovered from root canals in cases of chronic apical periodontitis associated with both primary and secondary infection.41 Iodine is also antiviral42 and viruses have recently been implicated in the pathogenesis of periradicular periodontitis.4 It is important only to consider the use of iodine in patients with no reported allergy to iodine or seafood.

Ozone

The use of strong oxidizing agents, such as ozone, are being investigated as potential antimicrobial root canal solutions. Although manufacturers (KaVo Dental, Bismarckring, Germany) claim that effective treatment can be completed in a single visit using gaseous exposure to ozone, the available research evidence is still controversial. Nagayoshi et al43 observed that ozonated water had nearly the same antimicrobial activity as 2.5% NaOCl during irrigation, especially when combined with the use of ultrasonics. Huth et al44 also reported potential benefits of using ozone in root canal treatment when used in high concentrations. Hems et al,45 however, on evaluating the ability of ozone to kill an E faecalis strain, found that its antibacterial efficacy was not comparable to that of NaOCl. Estrela et al46 found ozone to have no antimicrobial activity against E faecalis. These findings and others have cast doubts on the efficacy of ozone as an antimicrobial agent in endodontic infections.

Photo-activated disinfection (PAD)

Photo-activated disinfection involves the placement of a dye into the RCS, which is then activated by lasers causing disruption of bacterial cell walls and subsequent bacterial death. At present, there is insufficient evidence to support this method.47

Ethylenediaminetetraacetic acid (EDTA)

EDTA (a chelator) 15–17%, with pH 7, is widely used as a root canal irrigant in both primary and secondary cases. It effectively removes the smear layer15 but has limited antibacterial properties.16 The smear layer is debris that covers the root canal walls formed by root canal instrumentation. It can protect the biofilm and reduce sealer adaptation to canal walls so its removal should improve treatment outcome. It is important to note that strong chelators can cause dentine erosion over time.48 Kuah et al49 found that a relatively short (1 min) application with ultrasonics was effective in the apical region. When EDTA is used in combination with NaOCl, both the inorganic and the organic elements are removed, achieving patent dentinal tubules and clean surfaces even in the apical portion.50 Superior results have been reported when NaOCl is used as the last irrigant.50 EDTA, however, interacts with NaOCl and this can reduce the amount of chlorine available in solution, thereby compromising the tissue dissolving ability and antimicrobial effect of NaOCl.51 In an alternating irrigating regimen, copious amounts of NaOCl should be administered to wash out remnants of the EDTA, to ensure effective use of NaOCl as a final rinse, especially in multiple visit treatments.27

Citric acid

Citric acid 10–50% is another demineralizing solution which can remove the smear layer following canal instrumentation. Zehnder et al52 demonstrated that the less toxic 10% strength was effective. Citric acid like EDTA also interacts with NaOCl, but at a faster rate, reducing the availability of chlorine and therefore the effect on bacteria and organic tissue.52 Most studies have not found a significant difference between the chelation properties of citric acid and EDTA.53,54

Bio Pure^TM MTAD^TM

A relatively new irrigant Bio Pure^TM MTAD^TM Cleanser (Dentsply International, York, PA, USA) was briefly introduced to the market as a potential replacement for EDTA. This product has three components: doxycycline, an antibiotic from the tetracycline family; citric acid, a chelating agent; and a detergent. The recommended protocol for use is irrigation with 1.3% NaOCl for 20 min followed by MTAD for 5 min. Torabinejab et al55 found that it successfully removed the smear layer. Beltz et al56 found high dentine binding of doxycycline. According to Davis et al57 MTAD is more effective than 5.25% NaOCl against E faecalis and Zhang et al58 found MTAD to be less cytotoxic than 5.25% NaOCl, EDTA and Ca(OH)₂. MTAD, however, is not currently available owing to concerns regarding a risk of intrinsic staining of dentine caused by the oxidation of MTAD following the use of NaOCl, and other effects on dentine.59 As with any product containing antibiotics, there is also a risk of bacterial resistance.

Electrochemically-activated water

Electrochemically-activated water (ECA), such as Sterilox® is known to reduce microbial contamination, endotoxins and the biofilm in dental unit water lines.60 When applied to endodontics, however, Marais and Williams61 found ECA to be a less effective antimicrobial agent than 3.5% NaOCl. Owing to the reduced toxicity and tissue damage associated with these solutions, future research is indicated.