disinfection of the root canal system during root canal re-treatment

Disinfection of the root canalsystem during root canalre-treatmentMATTHIAS ZEHNDER & FRANK PAQUE

In this narrative review, the differences between primary root canal treatments and re-treatments are explored in

view of optimal disinfection of the root canal system. A critical appraisal of the literature raises doubt as to whether

the microbiota found in re-treatment cases per se is more resistant to antiseptics than the counterpart found in

primary infections. In reality, primary, refractory, and persisting endodontic infections are all biofilm-related; their

microbial composition is dictated by local ecological factors rather than treatment history. Furthermore, their

resistance to antimicrobials is most likely similar. The true difficulty in disinfecting root canal systems during re-

treatment cases is to achieve access to the infected areas. Iatrogenic alterations in canal anatomy and the presence of

root filling material hamper the diffusion of disinfectants to these target areas. Consequently, cleaning the canal

systems of foreign material and creating a canal shape that can properly be disinfected should be the initial aims.

Ways of achieving these goals are discussed. Subsequently, the disinfection regimen can be similar to that in primary

root canal infections. However, time is a crucial factor in re-treatments, and thus a multiple-visit approach is

preferable in more complex cases in order to ensure more complete disinfection has been achieved.

Received 16 November 2009; accepted 3 November 2010.

Introduction

Cross-sectional studies suggest that more teeth are

being preserved, fewer teeth are being extracted, and

more endodontic treatments are being performed

today than ever before (1). However, as indicated by

the high prevalence of root-filled teeth with apical

radiolucencies, the quality of root canal treatment

rendered to the average dental patient is insufficient in

most countries (2). The number of root-filled teeth

with apical pathosis may even be underestimated. Thus

far, no epidemiological studies on the prevalence of

apical periodontitis have used sensitive methods such as

cone beam computerized tomography (3). Never-

theless, even with current diagnostic tools, root canal

re-treatments are commonly undertaken and are one of

the main drivers for the development of the endodon-

tic specialty. In theory, failed cases could be treated

surgically without further conventional coronal access

into the canal system. However, as discussed below, the

infection is usually inside the root canal space (4).

Based on the limited evidence currently available, it

appears that conventional orthograde re-treatment

offers a higher success rate in the long term than

endodontic surgery (5). This, however, depends

largely on the type of case that requires re-treatment

and the skills of the individual operator.

Strictly speaking, apical surgery is not a re-treatment

of a pre-existing root canal intervention. In the

following text, the term ‘‘re-treatment’’ is used for

the conventional orthograde treatment of a filled root

canal system with persistent apical periodontitis or

where new disease has emerged after root filling. To

render the best possible re-treatment, one should

understand the reasons for the persistence or develop-

ment of inflammatory lesions in the periapical area of

root-filled teeth. Apical periodontitis in both teeth with

a necrotic pulp and root-filled counterparts is a biofilm-

related disease (6–8). Microbial communities em-

bedded in a polysaccharide matrix in the protein-rich

environment of the necrotic root canal space trigger an

inflammatory host reaction in the periapical space (9).

58

Endodontic Topics 2011, 19, 58–73All rights reserved

2011 r John Wiley & Sons A/S

ENDODONTIC TOPICS 20111601-1538

From cross-sectional studies, there is a clear correlation

between the technical quality of root fillings apparent on

radiographs and periapical health (10–23). Furthermore,

the quality of the restoration as judged radiographically

appears to have an impact on the prevalence of periapical

pathosis (11, 13, 15, 16, 22, 24). A meticulous review of

randomized trials and cohort (follow-up) studies has

shown that, while there is substantial variation in the

studies (25), the quality of the root filling and the

coronal restoration, together with the periapical status

before treatment, are the main predictors of treatment

outcome (26). Given the microbial etiology of endo-

dontically-derived periapical lesions (27), these studies

suggest that (i) micro-organisms (re-)entering the root

canal system through leaking restorations and root

fillings and (ii) inadequate infection control in teeth

with primary infections are the two main reasons for root

canal treatments to fail. The impact of the coronal seal on

periapical health was shown in a cohort of 616 randomly-

selected patients who were recalled 6 years after the initial

survey: the quality of coronal restorations was associated

with the incidence of apical periodontitis (28). However,

with a high-quality root filling, periapical health can be

achieved or maintained even if a coronal seal is missing

(29). The importance of infection control during root

canal treatment has been substantiated by most of the

follow-up studies, which related culture results to

treatment outcome (30–40) (Table 1). It is therefore

not surprising that histological assessment of failed cases

from a case series 4 to 10 years after orthograde root

canal treatment revealed that 6 out of 9 cases with

persisting apical radiolucencies contained micro-organ-

isms in the apical area (4). Overall, and whatever the

reason for the presence of micro-organisms in filled root

canal systems, disinfection is the main issue when dealing

with re-treatment cases.

It was the goal of this communication to review root

canal disinfection in the context of re-treatment. For

this purpose, the nature of root canal infections in re-

treatment cases was critically inspected, and technical

problems inherent to re-treatments was discussed. In

light of this, the chemistry and application of topical

disinfectants was reviewed.

Root canal infections inroot-filled teeth

To understand disinfection of the root canal system

during re-treatment, it appears important to first

review possible infection types in endodontic re-

Table 1. Radiographic treatment outcome in relation to culture result before root fillingn

Reference Positive culturew Negative culture P-valuez Recall interval

Bender et al. (32) 175/38 (82%) 404/89 (82%) 40.1 2 years

Engstrom et al. (33) 95/42 (69%) 140/29 (83%) o0.01 4–5 years

Heling & Shapira (35) 14/6 (70%) 48/12 (80%) 40.1 1–5 years

Molander et al. (40) 12/15 (44%) 49/12 (80%) o0.01 2 years

Oliet et al. (34) 127/34 (79%) 187/12 (94%) o0.01 6 to 12 months

Peters & Wesselink (38) 7/1 (87.5%) 22/8 (73%) 40.1 Up to 4.5 years

Rhein et al. (30) 130/22 (84%) 319/21 (94%) o0.01 2 years

Sjogren et al. (36) 15/7 (68%) 29/2 (94%) o0.05 5 years

Sundqvist et al. (37) 2/4 (33%) 35/9 (80%) o0.05 Up to 5 years

Waltimo et al. (39) NS NS 52 weeks

Zeldow & Ingle (31) 35/7 (83%) 14/1 (93%) 40.1 2 years

nOnly studies performed on humans are included in this table.wNumber of cases with favorable/counterparts with unfavorable or uncertain outcome (success rate).zRecalculated (Chi-square and Fisher’s exact tests as appropriate) because some of the studies did not use appropriate statistical tests.NS: not stated; original data are not listed in communication, merely changes in periapical index scores.

Disinfection during re-treatment

59

treatment cases. Unfortunately, many texts found in

the endodontic literature have not differentiated

between persisting and new infections found in filled

root canals, and consequently paradigms have evolved

that may be partially or completely wrong (41). For

instance, it is a commonly-held belief that the

facultative microbiota associated with filled root canals

was somehow ‘‘selected’’ during the primary treatment

because facultatives such as enterococci were harder to

eliminate than the strictly anaerobic part of the

microbiota which was originally predominant (42).

The source for potential systematic error lies in the

designs of the studies used by some authors to support

this theory (Table 2). Micro-organisms which survived

after chemomechanical infection (i.e. persistent infec-

tions) and new infections in root-filled teeth have not

been differentiated in any human study. The only study

design that can explain the species which are more

likely to survive current disinfection protocols than

others are longitudinal studies with controlled asepsis

and sampling after each treatment step. In the well-

controlled culture study performed by Kvist and co-

workers (43), the number of micro-organisms was

reduced after instrumentation and irrigation, and again

after inter-visit medication with calcium hydroxide or

intra-visit medication with iodine potassium iodide.

However, there was no quantitative or qualitative

difference between the two medications with respect to

the micro-organisms that survived. There were more

cases which solely harbored either strict or facultative

anaerobes after medication as compared to the mixed

microbiota encountered at the initiation of treatment,

but that was most likely because of the low absolute

number of bacteria remaining in the canal and the

relatively high detection limit of culture methods.

It can thus be concluded that what survives is what was

there before treatment, without much specific selection

(Fig. 1). Well-controlled studies using culture-inde-

pendent methods for bacterial quantification and

identification draw a similar picture (44–46). Conse-

quently, there probably is no clinically-relevant resis-

tance of any species or phylum to the currently-used

antiseptics, but rather a general resistance by the mixed

root canal microbiota. The reason for joint survival of

the taxa present at treatment initiation could be two-

fold: first, parts of the infected area can be remote from

the active field of the antiseptics and thus individual

resistance does not play a decisive role; second, the

microbiota is organized as a biofilm. The latter point

had already been suggested in earlier studies on

associations between different microbial species recov-

ered from the same root canal system (47).

Although yeasts, archaea, and viruses contribute to

the microbial diversity of endodontic infections,

Table 2. Study types that led to the potentially aberrant conclusion that facultative micro-organisms including enterococciresist chemomechanical treatment better than anaerobic counterparts, and potential systematic error in these studies

Type of study Potential bias

Infection and disinfection of bovine dentin blocks � Human apical root dentin in adults does not contain patent tubules

� (Coronal) tubular infection may be clinically meaningless, as mantle dentin and

cementum seal off bacteria from the periodontium

� What grows well in the laboratory is not necessarily dominant in the root canal

Culture or culture-independent assessment of

filled root canals with persisting apical lesions

� The presence of certain taxa in the root canal years after the root was filled does not

mean that they survived treatment (coronal recontamination of the canal is just as

likely)

Analysis of root canal samples sent in by private

practitioners after canal preparation/medication

� Personnel not familiar with microbiological sampling procedures are unlikely to

apply proper protocols

� Salivary contamination is likely

Fig. 1. Recovery of culturable bacteria after differenttreatment steps, taken from the longitudinal study byKvist and co-workers (43). Results between the inter-(calcium hydroxide) and intra- (iodine potassium iodide)visit medication groups were merged because there wereno significant differences.

Zehnder & Paque

60

bacteria are the most common micro-organisms

encountered in infected root canals (48). It should be

realized that the original source of any endodontic

infection is always the same: transient or resident taxa in

the oral cavity which enter the root canal system.

Hence, it would appear that the method or pathway of

entry and the local ecological factors in the root canal

are the two main factors driving the course and the

composition of the mixed infection which is typically

found in pulpless root canal systems (49). However,

there appears to be a striking similarity between

primary root canal infections in teeth with apparently

exposed pulp spaces compared to counterparts that are

apparently non-exposed (50). Infection and disinfec-

tion was compared between root canals with necrotic

pulps and counterparts with a root filling in teeth with

apical periodontitis in only one study (45). Using

TaqMans PCR to detect total bacterial loads and

the presence of 9 target species (Aggregatibacter

actinomycetemcomitans, Fusobacterium nucleatum,

Table 3. Longitudinal studies on disinfection of root-filled teeth associated with periapical lesions

Reference

Assessment

method

Initial Growth

or DNA � Treatment

Residual

growth

or DNA �

Blome et al. (45) PCR 20/0 Rotary Ni–Ti instrumentation, irrigation for 30 min

with either 0.1% CHX or 2% NaOCl, which were

then activated with an ultrasonic tip for 1 min

(delivery undisclosed, results not divided between

irrigants)

Calcium hydroxide dressing for 14 days, delivered

with a syringe

20/0n

20/0n

Peculiene et al. (141, 142) Culture 53/12 SS hand instrumentation, 2 mL of 2.5% NaOCl and

5 mL of 17% EDTA (delivery sequence and method

undisclosed, results merged between both studies)

17/36

Schirrmeister et al. (144) Culture and

PCR

12/8 (culture)

13/7 (PCR)

Ni–Ti hand instrumentation, 2.5% NaOCl during

instrumentation, 5 mL of 17% EDTA for 1 min after

instrumentation, then 10 mL of 2.5% NaOCl,

delivered 1 mm from WL using a 30-gauge needle

Irrigation with 2% aqueous CHX solution,

delivered as above

Calcium hydroxide dressing for 2 to 3 weeks

(delivery method undisclosed)

0/12 (culture)

0/13 (PCR)

0/12 (culture)

0/13 (PCR)

2/10 (culture)

0/13 (PCR)

Sundqvist et al. (37) Culture 24/30 SS hand instrumentation, 0.5% NaOCl irrigation

(volume and delivery method undisclosed), calcium

hydroxide dressing delivered using a spiral paste

filler, left for 7 to 14 days

6/18

Zerella et al. (143) Culture 40/0 Hand instrumentation, 1% NaOCl during

instrumentaion (volume and delivery method

undisclosed)

Canal irrigation with 5 mL of 1% NaOCl, then

calcium hydroxide dressing with or withoutw 2%

CHX for 7–10 days (delivery methods undisclosed)

Instrumentation and mechanical removal of

dressing with MAF and irrigation as above

Dressing as above

9/31

17/23

5/35

12/28

Abbrevations: CHX 5 chlorhexidine digluconate; MAF 5 master apical file; NaOCl 5 sodium hypochlorite; Ni–Ti 5 nickel–titanium; PCR 5 polymerase chain reaction; SS 5 stainless-steel; WL 5 working length.nCounts were significantly reduced compared to baseline, but no negative sample was obtained.wThis was a randomized study. As the outcomes did not differ, the results of both groups are merged in this table for the sake ofsimplicity.


61

Porphyromonas gingivalis, Prevotella intermedia, Tan-

nerella forsythia, Treponema denticola, Enterococcus

faecalis, Peptostreptococcus micros, and Porphyromonas

endodontalis), it was found that the initial bacterial load

was higher in primary than in secondary infections.

Whether this is truly the case or based on the difficulty

of sampling in previously-filled root canals remains

unclear. Nevertheless, there was neither a difference in

the initial composition of the microbiota between the

two groups nor in the reduction achieved by the

antimicrobial treatment (Table 3). However, it should

be considered that the surrogate outcome ‘‘microbial

load after treatment’’ may yield false negative results

(51). A micro-organism which cannot be reached by a

disinfectant because of alterations in the canal anatomy

or remaining filling material is also unlikely to be

sampled. Probably one of the most interesting studies

in this context is that by Gorni & Galiani (52). In re-

treatment cases with violated anatomy, the healing rate

was roughly half of that obtained with those cases with

apparently unaltered anatomy. This indicates that the

main problem with re-treatments is not a specifically

resistant microbiota but rather anatomy which cannot

be reached by disinfectants. Based on current knowl-

edge, biofilm in canal recesses and ramifications is also

the main clinical problem in teeth with primary apical

periodontitis (6, 53). However, in re-treatment cases,

reaching and eliminating microbial communities in

contact with the host defense may be rendered even

more difficult by canal obliterations, ledging, and

perforations. In addition, there is evidence to suggest

that canal filling material and debris are being

compacted into previously untouched areas during

the mechanical attempt to remove the root filling

(Fig. 2). These mechanical impediments may further

hamper the attempt to disinfect a previously filled root

canal system.

General treatment considerations

First and foremost, consideration should be given as to

whether or not the tooth in question is of strategic

importance to oral health and function and is worth re-

treating. This largely depends on an informed decision

by the patient based on the known prognostic factors

which influence treatment outcome (54) and the

prosthetic value of the tooth (55). Again, in terms of

the prognosis of the root canal treatment per se, the

question of whether or not and to what extent

the anatomy was violated by the dentist performing

the primary treatment remains the core issue (52).

Teeth with a short root filling and/or unaltered

Fig. 2. Three-dimensionally reconstructed images based on micro-computed tomography scans of a mandibular firstmolar after rotary canal instrumentation (a), root canal filling using the lateral compaction technique (b), and theattempt to mechanically remove the root filling using the last rotary instrument which was used for preparation (c).Using pre-determined gray value ranges for gutta-percha and sealer, these can be separated from each other and depictedin false colors (b), sealer in yellow, gutta-percha in pink; note the accessory cones and areas devoid of sealer which werevisualized). Note that a considerable amount of filling material was pushed into the isthmus area (c, arrows), where nofilling materials were present after root filling (b). In addition, filling material was extruded over the apical constrictions(c, arrowheads) during the attempt to remove it.

Zehnder & Paque

62

anatomy appear to be the easiest to re-treat with the

highest chance for success. In these teeth, there is no

biological reason why a success rate similar to that of a

primary treatment should not be expected once the

root filling has been removed. Consequently, a re-

treatment typically consists of two stages: (i) access to

the canal(s) followed by the attempt to completely

remove foreign materials from the canal system; and (ii)

instrumentation and disinfection as is recommended

for primary cases.

Numerous techniques have been advocated to

physically remove posts and other objects including

the root filling from the canal space (56). While this is

not the general topic of this communication, compact-

ing materials into canal recesses during attempts to

remove them must be avoided. Using rotary instru-

ments at high speeds as is recommended by some will

warm gutta-percha, thus rendering the old root filling

soft with a distinct risk of it compacting into canal fins,

recesses, and ramifications. As stated above, this may

make it harder to disinfect the canal system after

mechanical debridement (Fig. 1). The same apparently

holds true for the use of solvents to ease the removal of

gutta-percha. Solvents such as chloroform liquefy the

polyisoprene or polycaprolactone in gutta-percha and

resin-bonded root filling materials, respectively. As

has been shown in extracted teeth, re-treatment

without a solvent leaves canal walls cleaner compared

to the use of chloroform or eucalyptol (57). It may thus

be prudent to use hand instruments or slowly revolving

rotary instruments to mechanically remove the bulk

of the old root filling without the use of any solvent or

the melting effect caused by friction heat (58, 59).

However, irrigation with an aqueous antiseptic is still

indicated during that treatment stage in order to rinse

out the mechanically loosened filling material. In the

following section, a discussion concerning which type

of irrigant is most suitable for each treatment step is

provided.

Treatment steps and recommendedirrigants

1. Instrumentation and removal of bulk filling

As mentioned above, it may be unwise to attempt to

dissolve the entire root filling as this may create rather

than solve problems, especially in teeth with complex

anatomy and isthmus areas. Instead, an irrigant should

be administered that rinses out the filling components

which have been mechanically loosened. Amongst the

common and readily available endodontic irrigants, it

would appear that calcium-complexing (chelating)

solutions such as EDTA (60) or citric acid (61) make

the most sense during this step. While there is no

research backing this up, it can be observed when using

a dental microscope during re-treatment that con-

siderably more filling material is rinsed from the canal

system with a chelating solution compared to, for

instance, a sodium hypochlorite solution. The reason

for this may be two-fold. First, EDTA (and most likely

also citric acid) has a slight dissolving effect on most

sealers (62). Second, aggressive chelating solutions

dissolve the inorganic components from the root canal

walls (63) and thus may make it easier to mechanically

remove the root filling.

Regarding their antimicrobial effect, chelating solu-

tions are probably underestimated. While they do not

demonstrate a substantial direct effect on microbial

viability, they do interfere with biofilm cohesion (64).

In addition, complexing agents may attack the

cell wall and/or prevent cell wall synthesis (65). This

may explain their inhibitory effect on yeasts (66, 67).

EDTA prevents the growth of yeasts presumably by

causing alterations in the formation of the cell

wall (68). The role of chelators such as EDTA and

citric acid as permeabilizing agents of the outer

membrane of Gram-negative bacteria has also been

discussed (69). EDTA has shown a considerably

better reduction of viable counts in infected

human teeth compared to physiological saline solution

(70). The latter observation, however, may be biased

because of the inhibitory carry-over effect of

EDTA in low dilutions on viable counts observed on

agar plates (71).

For root canal irrigation, a 17% EDTA solution

(maximum strength) is recommended. A 10% citric

acid solution will have similar properties (71, 72) and

may be cheaper and easier to obtain. Alternatively, a

commercially available chelating solution containing

citric acid, doxycycline and a detergent (Tween-80)

sold as BioPure MTAD (Dentsply Tulsa Dental, Tulsa,

OK, USA) could be used. However, the addition of a

surfactant to chelating solutions shows little benefit in

hard tissue debridement (73). Furthermore, the use of

an antibiotic such as doxycycline to treat biofilm is

questionable (74).


63

2. Dissolution of remaining filling materialand sealer

Once the bulk of the filling material has been

mechanically removed, switching to a solvent may be

indicated. The danger of pressing softened material

into canal recesses is thus minimized, as the mechanical

treatment is almost completed. Amongst the solvents

which have been used in endodontics, chloroform has

the best track record: it is highly efficient in dissolving

the polyisoprene in gutta-percha (75), the polycapro-

lactone in resin-bonded systems (76), and most sealers

(77). It has been claimed that the risk of harming the

patient is minimal when chloroform is administered

into the root canal (78, 79). Chloroform also has some

antibacterial effect and may further reduce the

intracanal infection (80). However, chloroform is

extremely toxic and (indirectly) carcinogenic (81). A

fatal oral dose of chloroform may be as low as 10 mL

(14.8 g), with death due to respiratory or cardiac arrest

(US Environmental Protection Agency, http://www.

epa.gov/iris/subst/0025.htm). Chloroform in chlori-

nated drinking water, despite its extremely low

concentration, is suspected to be a potential cause for

male infertility (82). Dichloromethane (methylene

chloride) is a slightly less toxic alternative which

is still a relatively good solvent (83). However, based

on the toxicity of these organic solvents, it may be

advisable to refrain from their usage in endodontic

practice.

Highly viscous (oily) solvents based on eugenol are

readily available but their effect is far below that

observed with chloroform (77, 84). A solvent should

have a relatively low viscosity so that it can be applied

like an aqueous irrigant. Furthermore, it should be as

biocompatible as possible. Ideally, this solvent should

have some antimicrobial effect. Essential oils in peel

extracts from lime fruits contain about 90% D-

limonene. This compound is comparatively cytocom-

patible (85) and is used systemically in alternative

medicine (86). Orange oil (sold as ‘‘Orange Solvent’’

by various manufacturers) is readily available, inexpen-

sive, and displays a solvent effect which is close to that

of chloroform (87). In addition, it has antimicrobial

activity (88). This, however, has never been investi-

gated in the context of endodontic infections. Orange

solvent has the advantage over other plant-derived

solvents such as eucalyptus oil in that its viscosity is

closer to that of water and it can thus easily be

administered through an endodontic irrigating

syringe (see below). In addition, orange solvent

has a pleasant smell which will not disturb the

patient. Orange solvent is not soluble in water, so it

may be wise to rinse the canal system with alcohol

(ethanol) before the subsequent application of aqueous

disinfectants.

3. Disinfection and chemical debridement

As indicated above, the difference between a re-

treatment case and a case with a necrotic pulp is mainly

that in the former, much work has to be done to expose

the infected canal space to disinfectants. Once the bulk

of the root filling material has been removed and the

original canals have been negotiated, however, a re-

treatment case can be disinfected just as a case with a

primary infection. In primary root canal treatments,

sodium hypochlorite (NaOCl) is the first choice

endodontic irrigant for many reasons: availability,

price, and antimicrobial efficacy (89). The chemical

features of sodium hypochlorite and other root canal

irrigants used for root canal disinfection have been

reviewed in detail (90). In the context of re-treatment,

chlorhexidine (CHX) is often mentioned as a possible

alternative to NaOCl. However, the evidence on CHX

is based largely on results from laboratory studies of

dentinal tubules infected with E. faecalis, a species

erroneously associated with resistance to sodium

hypochlorite. CHX is a disinfectant which has been

used with a relatively good success rate in periodontics

and preventive dentistry. However, in endodontics, it

should be considered that, unlike sodium hypochlorite,

CHX is not a cleaning agent. Instead, CHX will adhere

to cleaned surfaces and prevent or delay their

recontamination (91). CHX solutions have a compara-

tively minor effect on biofilm (92–94) and do not

dissolve necrotic tissue (95). It thus comes as no

surprise that 2.5% CHX performed significantly worse

compared to 2.5% NaOCl in reducing cultural and

PCR counts in primary root canal infections in a

randomized clinical trial (96). The usability of CHX in

endodontics is further hampered by the effect of

NaOCl on CHX (90). The CHX precipitate contains

potentially mutagenic compounds such as 4-chloroani-

line (97, 98). Consequently, CHX should not be

administered in conjunction with or immediately after

NaOCl. Nevertheless, CHX may have some usefulness

as a final irrigant once the canal walls are thought to be

Zehnder & Paque

64

http://www.epa.gov/iris/subst/0025.htm











clean. The clinical trial which showed a beneficial effect

of a final CHX rinse on bacterial reduction, however,

compared CHX against saline and not NaOCl (99). A

recent randomized trial could not demonstrate any

additional effect of MTAD irrigation, or inter-visit 2%

CHX gel medication after instrumention and 1.3%

NaOCl irrigation (100). As stated by the authors, their

study ‘‘. . . confirmed the critical role of canal prepara-

tion – instrumentation and irrigation with NaOCl – in

achieving disinfection. Beyond this critical step, it

remains questionable whether additional procedures, if

any, add significant antibacterial advantage.’’

The two most unique features of sodium hypochlo-

rite compared to other known disinfectants are its

ability to dissolve necrotic tissue remnants (95) and its

outstanding effect on biofilm (64, 92, 101). While the

first feature may not be that important in re-treatment

cases, the second surely is. Consequently and until

other evidence emerges, NaOCl solutions should

remain the first choice for the disinfection stage in re-

treatments. Regarding the concentration of sodium

hypochlorite solutions, there is much dispute amongst

clinicians. Concentrated solutions (5% and higher) are

caustic if inadvertently extruded into periradicular

tissues (102). Furthermore, concentrated solutions

are extremely hypertonic (103). This may explain their

higher disruptive effect on biofilm compared to diluted

counterparts (92, 104), but also their untoward effects

on vital host tissue and the dentin matrix (105, 106).

It thus may not be advisable to use a solution which

contains more than 2.5 wt% NaOCl, at least not for the

entire course of a re-treatment procedure. Instead,

activation schemes for the solution should be con-

sidered (see below).

NaOCl irrigation alone will leave a smear layer and

inorganic debris in the canal system (107). Conse-

quently, a flush with a strong chelating solution for

approximately 3 minutes should be administered after

instrumentation and NaOCl irrigation (107, 108).

Alternatively, etidronate (ethane-1-hydroxy, 1-diphos-

phate or 1-hydroxyethylidene, 1-bisphosphonate or

HEBP) powder (Cublen K 8514 P; Zschimmer &

Schwarz, Burgstadt, Germany) can be mixed into the

sodium hypochlorite irrigant at a weight/volume ratio

of 10% to 18% directly before application to obtain a

chelating NaOCl solution (63, 71). This solution can

be used throughout the disinfection stage, and,

because of its decalcifying properties, has the potential

to be used during instrumentation as well.

Irrigation and irrigant activation

Before working length has been established, it is

advisable to use a short 27-gauge needle. This will

deliver more irrigant into the canal system. The

pressure will be higher and more material can be

flushed out. Once working length has been established

and the canal is adequately widened, a slim (301-

gauge) irrigating needle with a safety tip can be

introduced to the full working length. It should be

realized that the irrigant does not pass far in front of the

tip of the irrigating needle (109–111). Consequently,

apical preparation size becomes an important issue.

However, in re-treatment cases, canals are usually

widened to remove the original filling material to a size

that allows proper placement of the irrigating tip.

Irrigation of the apical area is of utmost importance in

the treatment of any form of apical periodontitis,

because it is precisely in that area where the root canal

infection encounters the host defense system (9).

Given the superior effect of sodium hypochlorite

irrigation over all other treatment steps during disin-

fection, the necessity to get the hypochlorite close to

the target area cannot be overstated.

The use of sonic/ultrasonic activation of the irrigant

has gained popularity. Sonic activation of the irrigant is

of questionable value (112, 113). However, there

appears to be a clear additive effect of ultrasonic

activation and sodium hypochlorite in water (114–

116). The term ‘‘passive ultrasonic irrigation’’ or PUI

refers to the fact that a tip is used not to instrument the

root canal walls but rather to activate the irrigant in

the canal system (117). In theory, the irrigant can be

delivered through or along the activated tip, or

be placed using normal syringe irrigation and then be

activated. The latter method bears the advantage that it

is more controllable. The exact effect which conveys

the ultrasonic enhancement of the NaOCl effects in the

root canal are not entirely clear (118). Acoustic

streaming and most likely also cavitation, i.e. the

formation and subsequent collapse of vapor bubbles of

a flowing liquid in a region where the pressure of the

liquid falls below its vapor pressure, both appear to play a

role (115, 117). Cavitation is related to the generation of

high heat in the microenvironment of the collapsing

bubble, which may explain the synergistic effect of

ultrasonic activation and NaOCl (119, 120).

Due to the fact that ultrasonic activation will generate

heat in the irrigant (121), PUI should not be used in


65

conjunction with solvents because these are easily

flammable and their vapors are potentially hazardous.

The activation of chelating agents with an ultrasonic tip

is also of questionable value. While the streaming of the

solution will be enhanced, the generation of heat and

the possibility of cavitation may not be beneficial.

Chelators have a clear temperature range at which they

work best. Heating from 201C to 901C, for instance,

will decrease the calcium binding capacity of EDTA

and citric acid from 219 to 154 and from 195 to 30 mg

CaO/g, respectively (122).

Alternative irrigant activation methods could or

should also be considered. Among these, systems

which work with alternating low pressure are the most

promising (123, 124). However, there is no informa-

tion available at this point regarding the usefulness of

these devices in the context of re-treatment. Extrusion

of irrigant through the apex (124) and general

controllability are concerns that need to be evaluated

carefully before any clinical advice can be given.

Topical inter-visit antisepticsto be considered

In primary endodontic infections, there appears to be

little evidence to support the absolute necessity of a

two-visit approach (40, 125, 126). In re-treatment

cases, however, the time to properly disinfect the root

canal system in the first visit is often lacking. The

debridement stage and the attempt to remove all

foreign materials from the canal system are time-

consuming. For the sake of the patient, it may thus be

advisable to postpone the disinfection stage to the

second visit. But there is no evidence to suggest that re-

treatment of a simple case could or should not be

performed in one visit (54).

Two topical disinfectants should be considered for

re-treatment cases: calcium hydroxide suspensions

and 2% CHX gel. Calcium hydroxide should be the

first choice because of its good compatibility with

sodium hypochlorite. Indeed, calcium hydroxide

powder can even be mixed with the NaOCl irrigant

used beforehand to obtain an inter-visit dressing with

combined short- and long-term antimicrobial power

(127). As can be shown in tissue-dissolution experi-

ments, calcium hydroxide exerts a dissolution capacity

which is comparable to that of sodium hypochlorite

(128). However, calcium hydroxide suspensions have a

slow-onset long-lasting effect, which contrasts to

the fast but relatively short-lived action of sodium

hypochlorite solutions (127). Calcium hydroxide

suspensions have this so-called ‘‘depot’’ effect or, in

chemical terms, high alkaline capacity because of the

low solubility of calcium hydroxide in water. Fresh

hydroxyl ions continuously enter the aqueous phase.

Alkaline capacity is responsible for the antimicrobial

effect of calcium hydroxide (129) and for its tissue-

dissolving capacity (127). Because both the tissue-

dissolving and the antimicrobial effects of calcium

hydroxide and sodium hypochlorite are related to their

proteolytic capacity (130), observations on tissue

dissolution can be extrapolated to antimicrobial

capacity. Indeed, it has been shown that a 10-minute

application of calcium hydroxide does not reduce

viable counts in infected root canals while a one-week

application has a major effect (131). As with any other

antiseptic which is tested after NaOCl application, the

additional microbial reduction caused by calcium

hydroxide is hard to determine in clinical studies

because measurements occur at or around the detec-

tion limit (39). Nevertheless, calcium hydroxide per se

is a strong disinfectant, as has been shown when

it was applied clinically after irrigation with an inert

irrigant (132).

A negative effect of calcium hydroxide on mechanical

tooth properties via degradation of the dentin matrix

has been suspected (133). As with sodium hypochlo-

rite, the proteolytic effect of calcium hydroxide

suspensions does not stop at the pulp–dentin interface

and thus collagen is degraded. However, laboratory

experiments on human root dentin have suggested that

the long-term effect of calcium hydroxide on mechan-

ical properties is self-limiting and much less than the

short-term effect of sodium hypochlorite solutions of

� 2.5% NaOCl (134, 135). Nevertheless, it may not

be advisable to leave calcium hydroxide in the root

canal system for months, especially not in teeth with

incomplete root formation.

CHX gel (2% weight/volume) used as a topical inter-

visit medication has a similar antimicrobial effect as a

calcium hydroxide/saline dressing (136). Effects on

clinical outcomes such as the flare-up rate also appear

to be similar between CHX and calcium hydroxide

dressings (137). However, in contrast to calcium

hydroxide, there is no direct effect of CHX on

endotoxin (138). Nevertheless, CHX can reduce host

reactions to endotoxin by binding to these lipopoly-

saccharides (139). Based on their similar effectiveness

Zehnder & Paque

66

and the low compatibility of CHX with sodium

hypochlorite, calcium hydroxide remains the root canal

dressing of choice. However, there is one potential

application for CHX gel that has not been discussed in

the literature but can sometimes show good clinical

results. In root canal systems which continuously have

exudates in the canal after proper instrumentation,

irrigation, and calcium hydroxide placement, adminis-

tering CHX gel through the apex can sometimes be

beneficial. In these cases, a chronic periapical infection

is to be suspected and the placement of a relatively

tissue-friendly antiseptic such as CHX gel makes sense.

In this context, it should be realized that the absolute

necessity to stay short of the apical constriction when

instrumenting root canals of teeth with apical perio-

dontitis is a paradigm which has recently been proven

wrong (140).

Human studies on disinfection inre-treatment cases

Thus far, only six studies (37, 45, 141–144) have

specifically assessed the effectiveness of antimicrobial

protocols in root-filled teeth with apical lesions (Table

3). The results of these investigations are influenced by

various factors. First and foremost, assessment meth-

ods and the thus-resulting detection limits differ

between studies, and results can thus not be compared.

In addition, and perhaps even more importantly, the

exact method by which the irrigants and medications

were delivered was not mentioned. This aspect,

however, is crucial. In summary, the observations

made by the different authors again indicate that there

is only limited effect of an inter-visit medication after

proper irrigation with sodium hypochlorite. Further-

more, the reduction in culture and PCR counts was

comparable in these re-treatment cases with corre-

sponding observations in primary endodontic infec-

tions. This, as stated above, suggests that the

microbiota found in re-treatment cases per se is not

more resistant to antiseptics than the counterpart

found in primary infections. Interestingly, the irrigat-

ing scheme which has been proposed for primary root

canal infections (90) also appears to be the most

effective in secondary infections (144). However, it

must be stressed that this is merely speculative because

results cannot be compared between studies.

Suggested irrigation and medication

As indicated above, there is limited information

regarding a truly ‘‘evidence-based’’ regimen to disin-

fect previously filled root canals. It is in the nature of

the subject that there will always be different ways to

reach the same goal, i.e. maximum biofilm reduction in

the root canal system. Nevertheless, based on basic

research observations and the chemistry of the agents

involved, it is possible to provide guidelines regarding

the use of the antimicrobials currently available. As

stated above, time is a crucial factor and thus, indirectly,

chemical compatibility of the irrigants and inter-visit

antiseptics which are applied become key issues. A

possible irrigation scheme is summarized in Table 4.

If there is no time to disinfect the canal properly in

the first visit (which is usually the case), the patient

should be scheduled for a second appointment focus-

ing on disinfection. Ideally, calcium hydroxide suspen-

sions should be applied for the interim. They should be

administered as thin slurries using a spiral-type filler

(145). Thin slurries enable ionic (calcium and hydroxyl

Table 4. Suggested application of irrigants during re-treatment

Treatment step Irrigant Application

Mechanical removal of root filling 17% EDTA or 10% citric acid 27-gauge needle

Preparation of canal system � 2.5% NaOCl 301-gauge needle to full working length

Removal of remaining root filling materials Orange solvent 301-gauge needle to full working length

Removal of orange solvent � 95% Ethanol 301-gauge needle to full working length

Removal of smear layer and accumulated debris 17% EDTA or 10% citric acid 301-gauge needle to full working length

Final disinfection � 2.5% NaOCl 301-gauge needle to full working length,

then activation with passive ultrasonic tip for

20 s; repeat 2 times


67

ion) flow, which is only possible in an aqueous

environment and responsible for the calcium hy-

droxide effect (146). Thin slurries have a better

antimicrobial effect than thick counterparts, at

least in the in vitro disinfection of dentinal tubules

(147). Consequently, excessive drying before calcium

hydroxide placement and compaction of the material as

has been recommended in apexification procedures is

unnecessary or even counter-productive if disinfection

is the aim in a canal system with a fully developed apex.

Mixing pure calcium hydroxide powder with the

sodium hypochlorite solution used for irrigation will

save chair time because the sodium hypochlorite

contained in the aqueous phase will continue to act

on the canal microbiota, at least for several minutes.

How long it takes until the available chlorine is used up

(reduced) under these circumstances, however, is

unclear and should be evaluated in the spatial environ-

ment of human root canals.

To remove the calcium hydroxide at the initiation of

the second visit, calcium-chelating agents are useful. In

addition, it makes sense to re-enter each canal with the

master apical file or rotary instrument to agitate

the chelating solution and thus enhance calcium

hydroxide removal (148). The irrigation scheme

depicted in Table 4 can thus be repeated in the second

visit, starting with an EDTA or citric acid flush to the

full working length.

Concluding remarks

New disinfectants have recently appeared including

octinedine as a possible replacement for CHX (149),

peracetic acid as a possible replacement for EDTA/

citric acid (63), and ultrafine bioactive glass particle

suspensions to replace calcium hydroxide (129).

However, until further evidence is available, the

practitioner is well advised to use the currently available

irrigants and materials.

References

1. Bj�rndal L, Reit C. The annual frequency of rootfillings, tooth extractions and pulp-related proceduresin Danish adults during 1977–2003. Int Endod J 2004:37: 782–788.

2. Eriksen HM. EndodontologyFepidemiologic consid-erations. Endod Dent Traumatol 1991: 7: 189–195.

3. Wu MK, Shemesh H, Wesselink PR. Limitations ofpreviously published systematic reviews evaluating the

outcome of endodontic treatment. Int Endod J 2009:

42: 656–666.4. Nair PN, Sjogren U, Krey G, Kahnberg KE, Sundqvist

G. Intraradicular bacteria and fungi in root-filled,asymptomatic human teeth with therapy-resistant peri-

apical lesions: a long-term light and electron micro-scopic follow-up study. J Endod 1990: 16: 580–588.

5. Torabinejad M, Corr R, Handysides R, Shabahang S. Out-

comes of nonsurgical retreatment and endodontic surgery:a systematic review. J Endod 2009: 35: 930–937.

6. Nair PNR, Henry S, Cano V, Vera J. Microbial status ofapical root canal system of human mandibular first

molars with primary apical periodontitis after ‘‘one-visit’’ endodontic treatment. Oral Surg Oral Med OralPathol Oral Radiol Endod 2005: 99: 231–252.

7. Carr GB, Schwartz RS, Schaudinn C, Gorur A,

Costerton JW. Ultrastructural examination of failedmolar retreatment with secondary apical periodontitis:

an examination of endodontic biofilms in an endodon-tic retreatment failure. J Endod 2009: 35: 1303–1309.

8. Schaudinn C, Carr G, Gorur A, Jaramillo D, Costerton

JW, Webster P. Imaging of endodontic biofilms bycombined microscopy (FISH/cLSM - SEM). J Microsc2009: 235: 124–127.

9. Nair PNR. Apical periodontitis: a dynamic encounter

between root canal infection and host response.Periodontol 2000 1997: 13: 121–148.

10. Imfeld TN. Prevalence and quality of endodontic

treatment in an elderly urban population of Switzer-land. J Endod 1991: 17: 604–607.

11. Ray HA, Trope M. Periapical status of endodonticallytreated teeth in relation to the technical quality of the

root filling and the coronal restoration. Int Endod J1995: 28: 12–18.

12. Weiger R, Hitzler S, Hermle G, Lost C. Periapicalstatus, quality of root canal fillings and estimatedendodontic treatment needs in an urban German

population. Endod Dent Traumatol 1997: 13: 69–74.13. Sidaravicius B, Aleksejuniene J, Eriksen HM. Endo-

dontic treatment and prevalence of apical periodontitisin an adult population of Vilnius, Lithuania. EndodDent Traumatol 1999: 15: 210–215.

14. De Moor RJ, Hommez GM, De Boever JG, Delme KI,

Martens GE. Periapical health related to the quality ofroot canal treatment in a Belgian population. Int EndodJ 2000: 33: 113–120.

15. Kirkevang LL, Ørstavik D, H�rsted-Bindslev P, WenzelA. Periapical status and quality of root fillings and

coronal restorations in a Danish population. Int EndodJ 2000: 33: 509–515.

16. Dugas NN, Lawrence HP, Teplitsky PE, Pharoah MJ,Friedman S. Periapical health and treatment quality

assessment of root-filled teeth in two Canadianpopulations. Int Endod J 2003: 36: 181–192.

17. Segura-Egea JJ, Jimenez-Pinzon A, Poyato-Ferrera M,

Velasco-Ortega E, Rios-Santos JV. Periapical statusand quality of root fillings and coronal restorations

in an adult Spanish population. Int Endod J 2004: 37:525–530.

Zehnder & Paque

68

18. Georgopoulou MK, Spanaki-Voreadi AP, Pantazis N,Kontakiotis EG. Frequency and distribution of root

filled teeth and apical periodontitis in a Greek popula-tion. Int Endod J 2005: 38: 105–111.

19. Kabak Y, Abbott PV. Prevalence of apical periodontitisand the quality of endodontic treatment in an

adult Belarusian population. Int Endod J 2005: 38:238–245.

20. Siqueira JFJ, Rocas IN, Alves FR, Campos LC.Periradicular status related to the quality of coronalrestorations and root canal fillings in a Brazilian

population. Oral Surg Oral Med Oral Pathol OralRadiol Endod 2005: 100: 369–374.

21. Tsuneishi M, Yamamoto T, Yamanaka R, Tamaki N,Sakamoto T, Tsuji K, Watanabe T. Radiographic

evaluation of periapical status and prevalence ofendodontic treatment in an adult Japanese population.Oral Surg Oral Med Oral Pathol Oral Radiol Endod2005: 100: 631–635.

22. Kayahan MB, Malkondu O, Canpolat C, Kaptan F,

Bayirli G, Kazazoglu E. Periapical health related to thetype of coronal restorations and quality of root canalfillings in a Turkish subpopulation. Oral Surg Oral MedOral Pathol Oral Radiol Endod 2008: 105: e58–e62.

23. Tavares PB, Bonte E, Boukpessi T, Siqueira JF Jr,Lasfargues JJ. Prevalence of apical periodontitis in rootcanal-treated teeth from an urban French population:influence of the quality of root canal fillings and coronalrestorations. J Endod 2009: 35: 810–813.

24. Georgopoulou MK, Spanaki-Voreadi AP, Pantazis N,Kontakiotis EG, Morfis AS. Periapical status and qualityof root canal fillings and coronal restorations in a Greekpopulation. Quintessence Int 2008: 39: e85–e92.

25. Ng YL, Mann V, Rahbaran S, Lewsey J, Gulabivala K.Outcome of primary root canal treatment: systematicreview of the literatureFPart 1. Effects of studycharacteristics on probability of success. Int Endod J2007: 40: 921–939.

26. Ng YL, Mann V, Rahbaran S, Lewsey J, Gulabivala K.Outcome of primary root canal treatment: systematicreview of the literatureFPart 2. Influence of clinicalfactors. Int Endod J 2008: 41: 6–31.

27. Sundqvist G. Bacteriological studies of necrotic dentalpulps. Umea: Dissertation, 1976.

28. Kirkevang LL, Vaeth M, H�rsted-Bindslev P, BahramiG, Wenzel A. Risk factors for developing apical

periodontitis in a general population. Int Endod J2007: 40: 290–299.

29. Ricucci D, Lin LM, Spangberg LS. Wound healing ofapical tissues after root canal therapy: a long-term

clinical, radiographic, and histopathologic observationstudy. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 2009: 108: 609–621.

30. Rhein ML, Krasnow F, Gies WJ. A prolonged study ofthe electrolytic treatment of dental focal infectionFa

preliminary report. Dent Cosmos 1926: 68: 971–981.31. Zeldow BJ, Ingle JL. Correlation of the positive culture

to the prognosis of endodontically treated teeth: aclinical study. J Am Dent Assoc 1963: 66: 9–13.

32. Bender IB, Seltzer S, Turkenkopf S. To culture or notto culture? Oral Surg Oral Med Oral Pathol 1964: 18:527–540.

33. Engstrom B, Hard af Segerstad L, Ramstrom G,Frostell G. Correlation of positive culture with the

prognosis of root canal treatment. Odontol Revy 1964:15: 257–270.

34. Oliet S, Sorin SM. Evaluation of clinical results based

upon culturing root canals. J Brit Endod Soc 1969: 3:3–6.

35. Heling B, Shapira J. Roentgenologic and clinicalevaluation of endodontically treated teeth, with or

without negative culture. Quintessence Int Dent Dig1978: 9: 79–84.

36. Sjogren U, Figdor D, Persson S, Sundqvist G. Influence

of infection at the time of root filling on the outcome ofendodontic treatment of teeth with apical perio-dontitis. Int Endod J 1997: 30: 297–306.

37. Sundqvist G, Figdor D, Persson S, Sjogren U.Microbiologic analysis of teeth with failed endodontictreatment and the outcome of conservative re-treat-ment. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 1998: 85: 86–93.

38. Peters LB, Wesselink PR. Periapical healing of endo-dontically treated teeth in one and two visits obturated

in the presence or absence of detectable microorgan-isms. Int Endod J 2002: 35: 660–667.

39. Waltimo T, Trope M, Haapasalo M, Ørstavik D.

Clinical efficacy of treatment procedures in endodonticinfection control and one year follow-up of periapicalhealing. J Endod 2005: 31: 863–866.

40. Molander A, Warfvinge J, Reit C, Kvist T. Clinical and

radiographic evaluation of one- and two-visit endo-dontic treatment of asymptomatic necrotic teeth withapical periodontitis: a randomized clinical trial. J Endod2007: 33: 1145–1148.

41. Zehnder M, Guggenheim B. The mysterious appear-ance of enterococci in filled root canals. Int Endod J2009: 42: 277–287.

42. Molander A, Reit C, Dahlen G, Kvist T. Microbio-logical status of root-filled teeth with apical period-ontitis. Int Endod J 1998: 31: 1–7.

43. Kvist T, Molander A, Dahlen G, Reit C. Microbio-logical evaluation of one- and two-visit endodontictreatment of teeth with apical periodontitis: a ran-

domized, clinical trial. J Endod 2004: 30: 572–576.44. Siqueira JFJ, Guimaraes-Pinto T, Rocas IN. Effects of

chemomechanical preparation with 2.5% sodium hypo-chlorite and intracanal medication with calcium hy-

droxide on cultivable bacteria in infected root canals.J Endod 2007: 33: 800–805.

45. Blome B, Braun A, Sobarzo V, Jepsen S. Molecular

identification and quantification of bacteria fromendodontic infections using real-time polymerasechain reaction. Oral Microbiol Immunol 2008: 23:384–390.

46. Rocas IN, Siqueira JFJ. Identification of bacteriaenduring endodontic treatment procedures by acombined reverse transcriptase-polymerase chain


69

reaction and reverse-capture checkerboard approach.

J Endod 2010: 36: 45–52.47. Sundqvist G. Associations between microbial species in

dental root canal infections. Oral Microbiol Immunol1992: 7: 257–262.

48. Siqueira JFJ, Rocas IN. Diversity of endodontic

microbiota revisited. J Dent Res 2009: 88: 969–981.49. Sundqvist G. Taxonomy, ecology, and pathogenicity of

the root canal flora. Oral Surg Oral Med Oral Pathol1994: 78: 522–530.

50. Chu FC, Tsang CS, Chow TW, Samaranayake LP.

Identification of cultivable microorganisms from pri-

mary endodontic infections with exposed and unex-

posed pulp space. J Endod 2005: 31: 424–429.51. Sathorn C, Parashos P, Messer HH. How useful is

root canal culturing in predicting treatment outcome?

J Endod 2007: 33: 220–225.52. Gorni FG, Gagliani MM. The outcome of endo-

dontic retreatment: a 2-yr follow-up. J Endod 2004:

30: 1–4.53. Nair PNR. On the causes of persistent apical perio-

dontitis: a review. Int Endod J 2006: 39: 249–281.54. Ng YL, Mann V, Gulabivala K. Outcome of secondary

root canal treatment: a systematic review of the

literature. Int Endod J 2008: 41: 1026–1046.55. Zitzmann NU, Krastl G, Hecker H, Walter C, Weiger

R. Endodontics or implants? A review of decisive

criteria and guidelines for single tooth restorationsand full arch reconstructions. Int Endod J 2009: 42:757–774.

56. Ruddle CJ. Nonsurgical retreatment. J Endod 2004:

30: 827–845.57. Horvath SD, Altenburger MJ, Naumann M, Wolkewitz

M, Schirrmeister JF. Cleanliness of dentinal tubules

following gutta-percha removal with and without

solvents: a scanning electron microscopic study. IntEndod J 2009: 42: 1032–1038.

58. Gergi R, Sabbagh C. Effectiveness of two nickel–

titanium rotary instruments and a hand file for

removing gutta-percha in severely curved root canals

during retreatment: an ex vivo study. Int Endod J 2007:40: 532–537.

59. Aydin B, Kose T, Caliskan MK. Effectiveness of HERO

642 versus Hedstrom files for removing gutta-percha

fillings in curved root canals: an ex vivo study. Int EndodJ 2009: 42: 1050–1056.

60. Nygaard Østby B. Chelation in root canal therapy.

Odontol Tidskr 1957: 65: 3–11.61. Loel DA. Use of acid cleanser in endodontic therapy.

J Am Dent Assoc 1975: 90: 148–151.62. Keles A, Koseoglu M. Dissolution of root canal sealers

in EDTA and NaOCl solutions. J Am Dent Assoc 2009:

140: 74–79; quiz 113.63. Lottanti S, Gautschi H, Sener B, Zehnder M. Effects of

ethylenediaminetetraacetic, etidronic and peracetic acid

irrigation on human root dentine and the smear layer.

Int Endod J 2009: 42: 335–343.64. Bryce G, O’Donnell D, Ready D, Ng YL, Pratten J,

Gulabivala K. Contemporary root canal irrigants are

able to disrupt and eradicate single- and dual-species

biofilms. J Endod 2009: 35: 1243–1248.65. Brul S, Coote P. Preservative agents in foods. Mode of

action and microbial resistance mechanisms. Int J FoodMicrobiol 1999: 50: 1–17.

66. Grawehr M, Sener B, Waltimo T, Zehnder M.Interactions of ethylenediamine tetraacetic acid with

sodium hypochlorite in aqueous solutions. Int Endod J2003: 36: 411–417.

67. Ates M, Akdeniz BG, Sen BH. The effect of calciumchelating or binding agents on Candida albicans. OralSurg Oral Med Oral Pathol Oral Radiol Endod 2005:

100: 626–630.68. Brul S, Stratford M, van der Vaart JM, Dielbandhoesing

SK, Steels H, Klis FM, Verrips CT. The anti-fungal action of 1,10-o-phenanthroline and EDTA is

mediated through zinc chelation and involves cellwall construction. Food Technol Biotechnol 1997: 35:267–274.

69. Helander IM, vonWright A, Mattila-Sandholm TM.

The role of lactic acid bacteria and novel antimicrobialsagainst Gram-negative bacteria. Trends Food Sci Technol1997: 8: 146–150.

70. Yoshida T, Shibata T, Shinohara T, Gomyo S, Sekine I.

Clinical evaluation of the efficacy of EDTA solution asan endodontic irrigant. J Endod 1995: 21: 592–593.

71. Zehnder M, Schmidlin P, Sener B, Waltimo T.Chelation in root canal therapy reconsidered. J Endod2005: 31: 817–820.

72. Reis C, De-Deus G, Leal F, Azevedo E, Coutinho-Filho

T, Paciornik S. Strong effect on dentin after the use ofhigh concentrations of citric acid: an assessment with

co-site optical microscopy and ESEM. Dent Mater2008: 24: 1608–1615.

73. Zehnder M, Schicht O, Sener B, Schmidlin P. Reducingsurface tension in endodontic chelator solutions has

no effect on their ability to remove calcium from

instrumented root canals. J Endod 2005: 31: 590–592.74. Norrington DW, Ruby J, Beck P, Eleazer PD.

Observations of biofilm growth on human dentin andpotential destruction after exposure to antibiotics. OralSurg Oral Med Oral Pathol Oral Radiol Endod 2008:105: 526–529.

75. Tamse A, Unger U, Metzger Z, Rosenberg M. Gutta-percha solventsFa comparative study. J Endod 1986:

12: 337–339.76. Ezzie E, Fleury A, Solomon E, Spears R, He J. Efficacy

of retreatment techniques for a resin-based root canalobturation material. J Endod 2006: 32: 341–344.

77. Schafer E, Zandbiglari T. A comparison of theeffectiveness of chloroform and eucalyptus oil in

dissolving root canal sealers. Oral Surg Oral Med OralPathol Oral Radiol Endod 2002: 93: 611–616.

78. Margelos J, Verdelis K, Eliades G. Chloroform uptakeby gutta-percha and assessment of its concentration in

air during the chloroform-dip technique. J Endod1996: 22: 547–550.

79. Chutich MJ, Kaminski EJ, Miller DA, LautenschlagerEP. Risk assessment of the toxicity of solvents of gutta-

Zehnder & Paque

70

percha used in endodontic retreatment. J Endod 1998:

24: 213–216.80. Edgar SW, Marshall JG, Baumgartner JC. The anti-

microbial effect of chloroform on Enterococcusfaecalis after gutta-percha removal. J Endod 2006: 32:1185–1187.

81. Komulainen H. Experimental cancer studies of chlori-

nated by-products. Toxicology 2004: 198: 239–248.82. Veeramachaneni DN. Impact of environmental pollu-

tants on the male: effects on germ cell differentiation.

Anim Reprod Sci 2008: 105: 144–157.83. Wennberg A, Ørstavik D. Evaluation of alternatives to

chloroform in endodontic practice. Endod Dent Trau-matol 1989: 5: 234–237.

84. Michaud RA, Burgess J, Barfield RD, Cakir D, McNeal

SF, Eleazer PD. Volumetric expansion of gutta-percha in

contact with eugenol. J Endod 2008: 34: 1528–1532.85. Hosseinimehr SJ, Karami M. Citrus extract modulates

genotoxicity induced by cyclophosphamide in mice bone

marrow cells. J Pharm Pharmacol 2005: 57: 505–509.86. Sun J. D-Limonene: safety and clinical applications.

Altern Med Rev 2007: 12: 259–264.87. Hansen MG. Relative efficiency of solvents used in

endodontics. J Endod 1998: 24: 38–40.88. O’Bryan CA, Crandall PG, Chalova VI, Ricke SC.

Orange essential oils antimicrobial activities against

Salmonella spp. J Food Sci 2008: 73: M264–M267.89. Frais S, Ng YL, Gulabivala K. Some factors affecting the

concentration of available chlorine in commercial

sources of sodium hypochlorite. Int Endod J 2001:

34: 206–215.90. Zehnder M. Root canal irrigants. J Endod 2006: 32:

389–398.91. Sekino S, Ramberg P, Uzel NG, Socransky S, Lindhe J.

The effect of a chlorhexidine regimen on de novo plaque

formation. J Clin Periodontol 2004: 31: 609–614.92. Muller P, Guggenheim B, Schmidlin PR. Efficacy of

gasiform ozone and photodynamic therapy on a

multispecies oral biofilm in vitro. Eur J Oral Sci2007: 115: 77–80.

93. Arias-Moliz MT, Ferrer-Luque CM, Espigares-Garcia

M, Baca P. Enterococcus faecalis biofilms eradication by

root canal irrigants. J Endod 2009: 35: 711–714.94. Williamson AE, Cardon JW, Drake DR. Antimicrobial

susceptibility of monoculture biofilms of a clinical isolate

of Enterococcus faecalis. J Endod 2009: 35: 95–97.95. Naenni N, Thoma K, Zehnder M. Soft tissue dissolu-

tion capacity of currently used and potential endodon-

tic irrigants. J Endod 2004: 30: 785–787.96. Vianna ME, Horz HP, Gomes BP, Conrads G. In vivo

evaluation of microbial reduction after chemo-mechan-

ical preparation of human root canals containing

necrotic pulp tissue. Int Endod J 2006: 39: 484–492.97. Basrani BR, Manek S, Sodhi RN, Fillery E, Manzur A.

Interaction between sodium hypochlorite and chlor-

hexidine gluconate. J Endod 2007: 33: 966–969.98. Basrani BR, Manek S, Fillery E. Using diazotization to

characterize the effect of heat or sodium hypochlorite

on 2.0% chlorhexidine. J Endod 2009: 35: 1296–1299.

99. Zamany A, Safavi K, Spangberg LS. The effect of

chlorhexidine as an endodontic disinfectant. Oral SurgOral Med Oral Pathol Oral Radiol Endod 2003: 96:578–581.

100. Malkhassian G, Manzur AJ, Legner M, Fillery ED,

Manek S, Basrani BR, Friedman S. Antibacterial efficacyof MTAD final rinse and two percent chlorhexidine

gel medication in teeth with apical periodontitis: arandomized double-blinded clinical trial. J Endod2009: 35: 1483–1490.

101. Clegg MS, Vertucci FJ, Walker C, Belanger M, BrittoLR. The effect of exposure to irrigant solutions

on apical dentin biofilms in vitro. J Endod 2006: 32:434–437.

102. Hulsmann M, Hahn W. Complications during rootcanal irrigationFliterature review and case reports. IntEndod J 2000: 33: 186–193.

103. Zehnder M, Kosicki D, Luder H, Sener B, Waltimo T.

Tissue-dissolving capacity and antibacterial effect ofbuffered and unbuffered hypochlorite solutions. OralSurg Oral Med Oral Pathol Oral Radiol Endod 2002:94: 756–762.

104. Ozok AR, Wu MK, Luppens SB, Wesselink PR.

Comparison of growth and susceptibility to sodiumhypochlorite of mono- and dual-species biofilms of

Fusobacterium nucleatum and Peptostreptococcus (mi-cromonas) micros. J Endod 2007: 33: 819–822.

105. Driscoll CO, Dowker SE, Anderson P, Wilson RM,Gulabivala K. Effects of sodium hypochlorite solution

on root dentine composition. J Mater Sci Mater Med2002: 13: 219–223.

106. Marending M, Luder HU, Brunner TJ, Knecht S, Stark

WJ, Zehnder M. Effect of sodium hypochlorite onhuman root dentineFmechanical, chemical and struc-

tural evaluation. Int Endod J 2007: 40: 786–793.107. Baumgartner JC, Mader CL. A scanning electron

microscopic evaluation of four root canal irrigationregimens. J Endod 1987: 13: 147–157.

108. Yamada RS, Armas A, Goldman M, Lin PS. A scanning

electron microscopic comparison of a high volume finalflush with several irrigating solutions: part 3. J Endod1983: 9: 137–142.

109. Hsieh YD, Gau CH, Kung Wu SF, Shen EC, Hsu PW,

Fu E. Dynamic recording of irrigating fluid distributionin root canals using thermal image analysis. Int Endod J2007: 40: 11–17.

110. Boutsioukis C, Lambrianidis T, Kastrinakis E. Irrigant

flow within a prepared root canal using various flowrates: a computational fluid dynamics study. Int Endod J2009: 42: 144–155.

111. Gao Y, Haapasalo M, Shen Y, Wu H, Li B, Ruse ND,Zhou X. Development and validation of a three-

dimensional computational fluid dynamics model ofroot canal irrigation. J Endod 2009: 35: 1282–1287.

112. Al-Jadaa A, Paque F, Attin T, Zehnder M. Acoustichypochlorite activation in simulated curved canals.

J Endod 2009: 35: 1408–1411.113. Brito PR, Souza LC, Machado de Oliveira JC, Alves

FR, De-Deus G, Lopes HP, Siqueira JFJ. Comparison


71

of the effectiveness of three irrigation techniques in

reducing intracanal Enterococcus faecalis populations:

an in vitro study. J Endod 2009: 35: 1422–1427.114. Martin H. Ultrasonic disinfection of the root canal.

Oral Surg Oral Med Oral Pathol 1976: 42: 92–99.115. Martin H, Cunningham W. EndosonicsFthe ultra-

sonic synergistic system of endodontics. Endod DentTraumatol 1985: 1: 201–206.

116. Blume T, Neis U. Improving chlorine disinfection ofwastewater by ultrasound application. Water Sci Technol2005: 52: 139–144.

117. van der Sluis LW, Versluis M, Wu MK, Wesselink PR.

Passive ultrasonic irrigation of the root canal: a review

of the literature. Int Endod J 2007: 40: 415–426.118. Walmsley AD. Ultrasound and root canal treatment:

the need for scientific evaluation. Int Endod J 1987: 20:105–111.

119. Suslick KS. Sonochemistry. Science 1990: 247:1439–1445.

120. Sirtes G, Waltimo T, Schaetzle M, Zehnder M. The

effects of temperature on sodium hypochloriteshort-term stability, pulp dissolution capacity, and

antimicrobial efficacy. J Endod 2005: 31: 669–671.121. Al-Jadaa A, Paque F, Attin T, Zehnder M. Necrotic

pulp tissue dissolution by passive ultrasonic irrigation in

simulated accessory canals: impact of canal location andangulation. Int Endod J 2009: 42: 59–65.

122. Coons D, Dankowski M, Diehl M, Jakobi G, Kuzel P,Sung E, Trabitzsch U. Performance in detergents,

cleaning agents and personal care products: complexing

agents. In: Walther HJ, ed. J. Falbe: Surfactants inConsumer Products. Berlin: Springer, 1987: 256–262.

123. Lussi A, Messerli L, Hotz P, Grosrey J. A newnon-instrumental technique for cleaning and filling

root canals. Int Endod J 1995: 28: 1–6.124. Hauser V, Braun A, Frentzen M. Penetration depth of a

dye marker into dentine using a novel hydrodynamic

system (RinsEndo). Int Endod J 2007: 40: 644–652.125. Weiger R, Rosendahl R, Lost C. Influence of calcium

hydroxide intracanal dressings on the prognosis of

teeth with endodontically induced periapical lesions.Int Endod J 2000: 33: 219–226.

126. Penesis VA, Fitzgerald PI, Fayad MI, Wenckus CS,BeGole EA, Johnson BR. Outcome of one-visit

and two-visit endodontic treatment of necrotic

teeth with apical periodontitis: a randomized con-trolled trial with one-year evaluation. J Endod 2008:

34: 251–257.127. Zehnder M, Grawehr M, Hasselgren G, Waltimo T.

Tissue-dissolution capacity and dentin-disinfecting

potential of calcium hydroxide mixed with irrigatingsolutions. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 2003: 96: 608–613.

128. Hasselgren G, Olsson B, Cvek M. Effects of calcium

hydroxide and sodium hypochlorite on the dissolution

of necrotic porcine muscle tissue. J Endod 1988: 14:125–127.

129. Waltimo T, Mohn D, Paque F, Brunner TJ, Stark WJ,Imfeld T, Schatzle M, Zehnder M. Fine-tuning of

bioactive glass for root canal disinfection. J Dent Res2009: 88: 235–238.

130. McDonnell G, Russell AD. Antiseptics and disinfec-

tants: activity, action, and resistance. Clin Microbiol Rev1999: 12: 147–179.

131. Sjogren U, Figdor D, Spangberg L, Sundqvist G.

The antimicrobial effect of calcium hydroxide as ashort-term intracanal dressing. Int Endod J 1991: 24:119–125.

132. Ørstavik D, Kerekes K, Molven O. Effects of extensive

apical reaming and calcium hydroxide dressing onbacterial infection during treatment of apical perio-

dontitis: a pilot study. Int Endod J 1991: 24: 1–7.133. Cvek M. Prognosis of luxated non-vital maxillary

incisors treated with calcium hydroxide and filled withgutta-percha. A retrospective clinical study. Endod DentTraumatol 1992: 8: 45–55.

134. Marending M, Stark WJ, Brunner TJ, Fischer J,Zehnder M. Comparative assessment of time-related

bioactive glass and calcium hydroxide effects onmechanical properties of human root dentin. DentTraumatol 2009: 25: 126–129.

135. Marending M, Paque F, Fischer J, Zehnder M. Impact

of irrigant sequence on mechanical properties of humanroot dentin. J Endod 2007: 33: 1325–1328.

136. Manzur A, Gonzalez AM, Pozos A, Silva-Herzog D,

Friedman S. Bacterial quantification in teeth with apicalperiodontitis related to instrumentation and different

intracanal medications: a randomized clinical trial.J Endod 2007: 33: 114–118.

137. Gama TG, de Oliveira JC, Abad EC, Rocas IN, SiqueiraJFJ. Postoperative pain following the use of two

different intracanal medications. Clin Oral Investig2008: 12: 325–330.

138. de Oliveira LD, Jorge AO, Carvalho CA, Koga-Ito CY,Valera MC. In vitro effects of endodontic irrigants onendotoxins in root canals. Oral Surg Oral Med OralPathol Oral Radiol Endod 2007: 104: 135–142.

139. Zorko M, Jerala R. Alexidine and chlorhexidine bind to

lipopolysaccharide and lipoteichoic acid and preventcell activation by antibiotics. J Antimicrob Chemother2008: 62: 730–737.

140. Metzger Z, Huber R, Slavescu D, Dragomirescu D,

Tobis I, Better H. Healing kinetics of periapical lesionsenhanced by the apexum procedure: a clinical trial.

J Endod 2009: 35: 153–159.141. Peciuliene V, Balciuniene I, Eriksen HM, Haapasalo M.

Isolation of Enterococcus faecalis in previously root-

filled canals in a Lithuanian population. J Endod 2000:26: 593–595.

142. Peciuliene V, Reynaud AH, Balciuniene I, HaapasaloM. Isolation of yeasts and enteric bacteria in root-filled

teeth with chronic apical periodontitis. Int Endod J2001: 34: 429–434.

143. Zerella JA, Fouad AF, Spangberg LS. Effectiveness of a

calcium hydroxide and chlorhexidine digluconatemixture as disinfectant during retreatment of failed

endodontic cases. Oral Surg Oral Med Oral Pathol OralRadiol Endod 2005: 100: 756–761.

Zehnder & Paque

72

144. Schirrmeister JF, Liebenow AL, Braun G, Wittmer A,

Hellwig E, Al-Ahmad A. Detection and eradication of

microorganisms in root-filled teeth associated with

periradicular lesions: an in vivo study. J Endod 2007:

33: 536–540.145. Peters CI, Koka RS, Highsmith S, Peters OA. Calcium

hydroxide dressings using different preparation

and application modes: density and dissolution

by simulated tissue pressure. Int Endod J 2005: 38:889–895.

146. Gubler M, Brunner TJ, Zehnder M, Waltimo T, Sener

B, Stark WJ. Do bioactive glasses convey a disinfecting

mechanism beyond a mere increase in pH? Int Endod J2008: 41: 670–678.

147. Behnen MJ, West LA, Liewehr FR, Buxton TB,McPherson JC 3rd. Antimicrobial activity of severalcalcium hydroxide preparations in root canal dentin.J Endod 2001: 27: 765–767.

148. Salgado RJ, Moura-Netto C, Yamazaki AK, CardosoLN, de Moura AA, Prokopowitsch I. Comparison ofdifferent irrigants on calcium hydroxide medicationremoval: microscopic cleanliness evaluation. Oral SurgOral Med Oral Pathol Oral Radiol Endod 2009: 107:580–584.

149. Tandjung L, Waltimo T, Hauser I, Heide P, DeckerEM, Weiger R. Octenidine in root canal anddentine disinfection ex vivo. Int Endod J 2007: 40:845–851.


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disinfection of the root canal system during root canal re-treatment

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