Factors affecting the viscosity of the root canal irrigant sodium hypochlorite and their effect on irrigant flow

For Peer Review

Factors affecting the viscosity sodium hypochlorite and

their effect on irrigant flow

Journal: International Endodontic Journal

Manuscript ID: IEJ-12-00733.R2

Manuscript Type: Original Scientific Article

Keywords: irrigation, sodium hypochlorite, surfactant, critical micellar concentration, dynamic viscosity, Reynolds number, laminar flow, turbulent flow

International Endodontic Journal


For Peer Review

Factors affecting the viscosity sodium hypochlorite and their effect on irrigant

flow

F. Bukiet1, T. Soler2, M. Guivarch2, J. Camps2, H. Tassery1, F. Cuisinier1, N. Candoni3

1Laboratoire biologie santé et Nanosciences, UFR Odontologie de Montpellier 1,

Montpellier, 2Laboratoire Interface Matrice Extracellulaire Biomatériaux, UFR

Odontologie de Marseille, Aix Marseille Université, Marseille, 3CNRS, Centre

Interdisciplinaire de Nanosciences de Marseille, Aix Marseille Université, Campus de

Luminy, Marseille, France.

Running Title: Endodontic irrigant viscosity and flow properties

Keywords: irrigation, sodium hypochlorite, surfactant, critical micellar concentration,

dynamic viscosity, Reynolds number, laminar flow, turbulent flow.

Correspondence:

Dr Bukiet Frédéric

Laboratoire biologie santé et Nanosciences, UFR Odontologie de Montpellier 1, 545

Av du Prof J.L. Viala 34193, Montpellier Cedex 5, France.

Phone number: +336-43-95-21-83

E-mail : [email protected]

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Abstract

Aim To assess the influence of concentration, temperature and surfactant addition to a

sodium hypochlorite solution on its dynamic viscosity and to calculate the

corresponding Reynolds number in order to determine the corresponding flow regimen.

Methodology The dynamic viscosity of the irrigant was assessed using a rotational

viscometer. Sodium hypochlorite with concentrations ranging from 0.6% to 9.6% was

tested at 37°C and 22°C. A wide range of concentrations of 3 different surfactants was

mixed in 2.4% sodium hypochlorite for viscosity measurements. The Reynolds number

was calculated under each condition. Data was analysed using two-way ANOVA.

Results There was a significant influence of sodium hypochlorite concentration

(p<0.001) and temperature (p<0.001) on dynamic viscosity: the latter significantly

increased with sodium hypochlorite concentration and decreased with temperature. A

significant influence of surfactant concentration on dynamic viscosity (p<0.001)

occurred especially for high surfactant concentrations: 6.25% for benzalkonium

chloride, 15% for Tween 80 and 6.25% for Triton X-100. Reynolds number values

calculated for a given flow rate (0.14 mL.s-1) and root canal diameter (sizes 45 and 70)

clearly qualified the irrigant flow regimen as laminar.

Conclusions Dynamic viscosity increased with sodium hypochlorite and surfactant

concentration but decreased with temperature. Under clinical conditions, all viscosities

measured led to laminar flow. The transition between laminar and turbulent flow may be

reached by modifying different parameters at the same time: increasing flow rate and

temperature while decreasing irrigant viscosity by adding surfactants with a high value

of critical micellar concentration.

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Introduction

It is generally accepted that periapical pathosis is due to the presence of

microorganisms or bacterial byproducts in the root canal (Kakehashi et al. 1965)

which must be removed to achieve success (Sjögren et al. 1997). However, root

canal anatomy is complex with irregularities areas that contain pulpal tissues and

microorganisms that cannot be approached by instruments (Paqué et al. 2011).

Therefore, an antiseptic and proteolytic fluid is necessary to disinfect and clean these

areas. The way this irrigant spreads onto the canal and reaches the non-

instrumented areas is of primary importance in root canal treatment.

Much research has been undertaken to reveal the mechanisms underlying irrigant

penetration so as to draw clinical conclusions. For example, poor penetration depth

of the irrigant beyond the needle tip (Boutsioukis et al. 2009), limiting the disinfection

of the apical part of the root canal, has been reported. However, there is still a lack of

knowledge concerning irrigant penetration because various physical parameters and

complex mathematical calculations oblige researchers to create simulators in order to

approach clinical conditions (Gulabivala et al. 2010). Recently, irrigant flow has been

studied using a Computational Fluid Dynamics model (Boutsioukis et al. 2009,

2010a, 2010b). In these publications, flow was analyzed according to irrigation

technique, needle design, anatomical characteristics of canals and flow rate.

However, the influence of the physico-chemical properties of the irrigant on its

penetration depth has not yet been evaluated.

Two essential parameters must be taken into account to understand fluid dynamics in

root canals. First, fluid surface tension as it influences the spreading properties of the

irrigant on dentine surfaces (De Gennes et al. 2004, Bukiet et al. 2012). When adding a

surfactant to an irrigant, the liquid surface tension decreases with increasing surfactant

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concentration, until reaching the critical micellar concentration (CMC). Above the CMC,

the addition of surfactant contributes to the formation of micelles in the liquid, and the

surface tension remains relatively constant; the best wetting properties are achieved at

this concentration (Bukiet et al. 2012).

Second, fluid viscosity as it describes the internal resistance to root canal irrigant flow

(Viswanath 2007), deformed by either shear or tensile stress. When flowing, the

different layers of the liquid slide against each other at different velocities with a transfer

of energy. In fluid dynamics, two main types of flow exist: laminar flow, characterized by

smooth and constant fluid motion, and turbulent flow which has chaotic eddies, vortices

and other flow instabilities. The type of flow is related to the Reynolds number (Re), a

dimensionless number quantifying the relative importance of inertial and viscous forces

(Guyon et al. 2001). In the case of a root canal, similar to a tube, Re is given by:

Re=(ρ v D)/µ [1]

Where:

ρ is the fluid density (kg.m-3)

v is the fluid velocity (m.s-1)

D is the root canal diameter (m)

µ is the fluid dynamic viscosity (Pa.s or kg.s-1.m-1)

Since Re is inversely related to fluid viscosity, this factor must be taken into account

when assessing the type of flow of the irrigant in a root canal. At a low Reynolds

number (Re<2,300), viscous forces are dominant leading to laminar flow whereas at

high Reynolds number (Re>4,000), inertial forces are dominant leading to turbulent

flow (Holman 2002). Theoretically, laminar flow may be associated with a higher

penetration depth of the irrigant while turbulent flow may allow better removal of debris.

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The factors affecting irrigant viscosity may influence its flow within the root canal in

function of the Re value. For instance, viscosity could be expected to increase with the

concentration of sodium hypochlorite and decrease with its temperature. Similarly,

adding chemical products such as surfactants, often displaying viscous properties, may

increase the viscosity. It would appear that no previous publication has studied the

viscosity of endodontic irrigants. The purpose of the present work was thus to assess

the influence of sodium hypochlorite concentration, temperature and addition of the

surfactants Benzalkonium Chloride (BAK), Tween 80 (TW), Triton X-100 (TR) on the

viscosity of sodium hypochlorite in order to determine the effect of these parameters on

the Re value and therefore on flow properties. The Couette’s method, which is known

to be reliable and accurate in order to determine viscosity measurement (Couette

1890), has been used in the present work. The null hypothesis was that surfactant

addition to NaOCl did not significantly influence the viscosity of irrigant and the Re

value.

Materials and methods

Dynamic viscosity measurement

Dynamic viscosity (µ) was measured using a rotational viscometer (Elcometer 2300,

Manchester, UK). According to the manufacturer’s operating instructions, a constant

temperature (37 or 22°C) was maintained using a thermostat connected to a specific

adaptor wrapped around the sample. The torque required to rotate the spindle in the

fluid depended on fluid viscosity. Thus, the measurements corresponded to the torque

necessary to rotate a cylinder plunged into a constant volume of liquid (18mL) at a

known constant speed (100 rpm). The validity of the protocol was verified recording the

viscosity of pure water warmed at 22°C and 37°C as references.

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To obtain accurate and precise data, an optional spindle dedicated to low viscosity

fluids was used. Stable flow conditions were reached quickly and the dynamic viscosity

(µ) readings on the screen were recorded after 30 s (in mPa.s). The process was

repeated 10 times per solution tested (n=10 per group and per concentration). Between

each measurement, the container, spindle and thermal adaptator were thoroughly

cleaned with acetone then ethanol before flushing with ultrapure water (milli-Q,

Millipore, Billerica, MA, USA) and dried.

The mean values and standard deviations were calculated from the 10 values obtained

from each test parameter for further statistical analysis.

Factors affecting dynamic viscosity: concentration, temperature and surfactant

addition

Effect of NaOCl concentration on dynamic viscosity

Different NaOCl solutions at various concentrations (CNaOCl): 0.6%, 1.2%, 2.4%, 4.8%

and 9.6% obtained from the dilution of 9.6% NaOCl with ultrapure water were stored at

37°C prior to measurement (group 1).

Effect of NaOCl solution temperature on dynamic viscosity

The same experimental procedure was followed with NaOCl solutions at the same

concentrations as group 1 but stored at 22°C (group 2).

Effect of surfactant concentration on dynamic viscosity

A 2.4% NaOCl solution stored at 37°C was mixed with one of the following surfactants:

• group 3: Benzalkonium Chloride (BAK) (Sigma-Aldrich B1383 - Semisolid, St

Louis, MI, USA), cationic surfactant at concentrations (CBAK) from 0% to 12.5%.

• group 4: Tween 80 (TW) (Sigma-Aldrich P1754 viscous liquid), non ionic

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surfactant at concentrations (CTW) ranging from 0% to 25%.

• group 5: Triton X-100 (TR) (Sigma-Aldrich X100 laboratory grade), non ionic

surfactant at concentrations (CTR) ranging from 0% to 25%.

All solutions were freshly prepared and energetically homogenized using a magnetic

stirrer immediately before measurements. This was maintained through spindle rotation

throughout the experimentation.

The 2.4% NaOCl solution without surfactant was used as the negative control

(surfactant 0%). Extreme surfactant concentrations (inappropriate for clinical activity)

were tested as positive controls (12.5% for CBAK and 25% for CTW and CTR).

Reynolds number calculation

An irrigant flow rate of 0.14mL.s-1 previously used by Boutsioukis et al. (2009) was

chosen for Reynolds number calculation. The needle tip must be placed about 3mm

short of the working length. Thus, for a given root canal preparation (6% taper with an

apical diameter of 0.25 mm or 0.50 mm), the canal diameter at the needle tip level was

of 0.45 mm or 0.70 mm. Then, the Reynolds number was calculated using these values

according to the equation [1] given in the Introduction.

Statistical analysis

First, after verifying the assumptions for analysis of variance (ANOVA), a two-way

ANOVA, at 5% confidence level, was performed to determine the influence of

concentration (way 1) and temperature (way 2) on the viscosity values. A Duncan

multiple range test was carried out at the same confidence level to create groups which

were not statistically different.

Second, after verifying the assumptions, an ANOVA, at the 5% confidence level, was

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performed for each surfactant, completed by a Duncan multiple range test to evaluate

the influence of each surfactant concentration on NaOCl viscosity. It was not possible

to compare the surfactants between each other because the surfactant concentrations

were adapted to each surfactant and therefore varied from one group to another. The

viscosity was plotted against the surfactant concentration to demonstrate the general

feature of the relationship.

Results

Influence of NaOCl concentration and temperature on dynamic viscosity (Groups

1 & 2) (Table 1)

The two-way ANOVA test revealed a significant influence of CNaOCl (p<0.001) and

temperature (p<0.001) on µ: viscosity statistically increased with NaOCl concentration

and decreased with increasing temperature.

In group 1 tested at 37°C, µ decreased from 1.31 ± 0.01 mPa.s for CNaOCl 9.6%

(positive control) to 1.15 ± 0.009 mPa.s for CNaOCl 0.6% (negative control). The Duncan

test could distinguish four different subgroups: 0.6% NaOCl and 1.2 % NaOCl were

similar while the following concentrations – 2.4%, 4.8% and 9.6% – were each

statistically different from each other. Re decreased respectively from 379 to 332 and

from 244 to 214 when sodium hypochlorite concentration increased from 0.6% to 9.6%

for both the 0.45 mm canal diameter and the 0.70 mm canal diameter.

In group 2 tested at 22°C, µ decreased from 1.77 ± 0.01 mPa.s for CNaOCl 9.6%

(positive control) to 1.20 ± 0.007 mPa.s for CNaOCl 0.6% (negative control). The Duncan

test distinguished four different subgroups: 0.6% NaOCl displayed the lowest value,

1.2% and 2.4% concentrations were statistically equivalent, 4.8% concentration was

slightly higher and finally 9.6% concentration showed the highest viscosity. Re

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decreased respectively from 363 to 246 and from 233 to 158 when sodium hypochlorite

concentration increased from 0.6% to 9.6% for a 0.45 mm canal diameter and 0.70 mm

canal diameter.

Influence of surfactant concentration at 37°C

Benzalkonium chloride: Group 3 (Table 2)

The ANOVA test revealed a significant influence of CBAK on µ (p<0.001): µ increased

with increasing CBAK. Viscosity increased from 1.186 ± 0.008 mPa.s for CBAK 0%

(negative control) to 2.081 ± 0.008 mPa.s for CBAK 12.5%. The Duncan test

distinguished three different subgroups with non-statistical different values of µ within

each subgroup: the first from 0 to 3.125%, the second at 6.25% and the third at 12.5%.

A clear increase of viscosity appeared from CBAK of 6.25%. Re decreased with

increasing CBAK, respectively from 368 to 209 and from 236 to 135 for a 0.45 mm canal

diameter and a 0.70 mm canal diameter.

Tween 80: Group 4 (Table 3)

The ANOVA test revealed a significant influence of CTW on µ (p<0.001): µ increased

with increasing CTW. Viscosities ranged from 1.186 ± 0.008 mPa.s for CTW 0 %

(negative control) to 4.943 ± 0.009 mPa.s for CTW 25%. The Duncan test distinguished

four different subgroups with non-statistically different values of µ in each subgroup:

from 0 to 6%, 15%, 20% and finally 25%. A significant increase in viscosity occurred

from CTW of 15% and above. Re decreased from 368 to 88 and from 236 to 57 with

increasing CTW for a 0.45 mm canal diameter and a 0.70 mm canal diameter,

respectively.

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Triton X-100: Group 5 (Table 4)

The ANOVA test revealed a significant influence of CTR on µ (p<0.001): µ increased

with increasing CTR. Viscosity increased from 1.186 ± 0.008 mPa.s for CTR 0 %

(negative control) to 24.218 ± 0.06 mPa.s for CTR 25%. The Duncan test distinguished

6 different subgroups: 0.000035%, 0.00007%, 0.50%, 0.80%, 1% and 3.12 % none of

which were statistically different from the negative control. The viscosities recorded with

concentrations from 0.0001428% to 0.25% were significantly lower. Finally the viscosity

shown by the following concentrations – 6,25%, 15%, 20% and 25% – were much

higher and significantly different from each other. Re decreased from 368 to 18 with

increasing CTR for a 0.45 mm canal diameter and from 236 to 12 for a 0.70 mm canal

diameter, respectively.

Plotting of µ versus CBAK, CTw and CTR showed that µ generally increased with the

concentration of surfactants. However, when examining low range surfactant

concentration, an initial decrease of µ was observed for all of the surfactants before µ

increased with concentration (Fig. 1). This minimum value of µ was reached for

different concentrations according to the surfactant: 0.004% for CBAK, 0.02% for CTW

and 0.0001428% for CTR. These concentrations are twice the CMC of each surfactant.

Discussion

The purpose of the present study was to assess the impact of NaOCl concentration,

temperature and surfactant addition on the dynamic viscosity of the irrigant to calculate

the corresponding Reynolds number. It can be concluded that dynamic viscosity

statistically increased with NaOCl concentration and with surfactant concentration

beyond the critical micellar concentration but decreased with temperature. The

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Reynolds number values calculated from the data corresponded to laminar flow and

were a long way from the threshold for a turbulent flow (Guyon et al. 2001).

Calculation of the Reynolds number (Re) was carried out by applying the equation [1]

under “typical” endodontic conditions: an irrigant flow rate of 0.14mL.s-1 and mean root

canal diameter of 0.45 mm (Boutsioukis et al. 2009). The 2.4% NaOCl viscosity at 37°C

was 1.186 mPa.s, leading to a Reynolds number of 277 which means a laminar flow.

According to equation [1], this flow could be switched to turbulent by increasing the flow

rate or decreasing the root canal diameter. When working with µ=1.186 mPa.s, the

calculations showed that Re could be increased beyond 4000, either by using a flow

rate larger than 1.6mL.s-1 or when working on root canals with a diameter smaller than

0.04 mm. Unfortunately, a flow rate of 1.6mL.s-1 is inappropriate for clinical activity due

to the risk of NaOCl extrusion, which has been observed for flow rates higher than 0.3

mL s-1 (Chow 1983). Concerning the canal diameter, only lateral canals and

ramifications have diameters smaller than 0.04 mm. Therefore, neither the irrigant flow

nor the canal diameters are sufficient to switch from a laminar to a turbulent flow. A

substantial decrease in viscosity combined with these parameters may be required to

change the flow regimen. With this aim in mind, the present work focused on the effects

of temperature, NaOCl concentration and surfactant concentration on irrigant viscosity.

Root canal irrigant temperature can be heated before using (Sirtes et al. 2005). In the

present study, when temperature increased from 22°C to 37°C, NaOCl viscosity

decreased. This well-known phenomenon may be explained by thermal agitation of the

molecules which move more easily at 37°C than at 22°C (Guyon et al. 2001). This

result must be related to those of other studies, which have evaluated the influence of

NaOCl temperature on its protein dissolving ability (Sirtes et al. 2005, Stojicic et al.

2010) and its antibacterial efficiency (Sirtes et al. 2005). Irrigant flow remains laminar

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because temperature only has a limited effect on NaOCl viscosity. The low viscosities

(near 0.2mPa.s for µ) required to switch from laminar to turbulent flow correspond to

higher temperatures not compatible with clinical applications.

Previous studies had reported that the irrigant viscosity statistically increased with

CNaOCl (Guerisoli et al. 1998). The result of the present study confirmed those given by

another methodology (Guerisoli et al. 1998). Despite significant differences between

the concentrations, viscosity only varied from 1.20 ± 0.007 mPa.s for 0.6% NaOCl to

1.77 ± 0.01 mPa.s for 9.6% NaOCl. Thus, the choice of CNaOCl influences the proteolytic

and antibacterial activities more than the flow properties. Consequently, a 2.4%

concentration within the recommended range between 1% and 5.25%, can be used as

irrigant without modifying irrigant flow properties.

The addition of a surfactant to NaOCl or EDTA in order to enhance wetting properties

has already been evaluated with encouraging results (Abou-Rass & Patonai, 1982,

Berutti et al. 1997, Pecora et al. 1998, Gambarini, 1999, Giardino et al. 2006, Stojicic et

al. 2010, Merivale et al. 2009, Palazzi et al. 2012, Bukiet et al. 2012). However, no data

is available concerning the modification of irrigant viscosity through surfactant addition,

despite the potential impact that viscosity may have on irrigant flow. In this study, 3

surfactants with a wide range of concentrations were studied. BAK is a cationic

detergent which has already been used in dentine bonding agents (Pashley et al.

2011), orthodontic resin (Othman et al. 2002) and in a commercial EDTA solution

(Salvizol, Pierre Rolland, Merignac, France). Moreover, a recent study showed that

BAK is an antiseptic which decreases bacterial adherence and biofilm growth (Jaramillo

et al. 2012). TW and TR are both non ionic surfactants with a syrupy appearance. They

have also been included in root canal irrigant products like Biopure™ MTAD (for TW)

and Chlor-Xtra™ (for TR) but with undisclosed concentrations. Although Gulabivala et

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al. (2010) asserted that the effect of additives would be to increase its viscosity and

reduce its Reynolds number, it has never been proven or invalidated before the present

work.

The study demonstrated that for low surfactant concentrations, viscosity first

decreased until a minimum value (Fig. 1). This decrease is likely related to the

neutralization of surfactant charges by the sodium cations present in NaOCl

solutions. As a result, the conformation of surfactants is more compact and viscosity

decreases (Onesippe & Lagerge 2009). The minimum µ value occurred for each

surfactant at different concentrations. It is interesting to note that these

concentrations are twice the CMC in 2.4% NaOCl solutions: 0.0076% for CMCBAK

(Bukiet et al. 2012), 0.01% for CMCTW and 0.00035% for CMCTR.

This relation between viscosity and CMC has already been used to determine CMC

through viscosity measurements (Tyuzyo 1960). So, while viscosity decreases due to

neutralization of surfactant charges, it then increases after formation of micelles. Thus,

it has been logically shown that the initial decrease in viscosity was more efficient for

TW which has the highest CMC. Consequently, adding a surfactant at concentration

near the CMC reduces irrigant viscosity and increases Re. On the contrary, adding a

surfactant at high concentration larger than CMC increases irrigant viscosity and

decreases Re.

In the present work, the increase in viscosity beyond CMC is more noticeable at very

high concentrations of surfactants not used in endodontics: 6.25% for BAK, 15% for TW

and 6.25% for TR. However, regardless of the surfactant and the concentration,

viscosity was high enough to give Reynolds numbers lower than 250 corresponding to

a laminar flow (Re<2500).

The clinical significance of irrigant flow regimen is still undetermined. Laminar flow is

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due to friction forces and likely more appropriate for allowing the irrigant to flow into the

unshaped areas and ramifications due to its regularity. However, a previous work

clearly highlighted a stagnation of the irrigant beyond the needle tip (1.5mm), whatever

the flow rate (Boutsioukis et al. 2009). This contradiction is due to gas bubble formation

in the apical area, acting as a vapor lock when the irrigation needle is placed deeply

(Tay et al. 2010). Theoretically, turbulent flow may improve root canal cleaning

efficiency by breaking the biofilm, like the cavitation phenomenon reported with

ultrasounds, but likely to a lesser extent. In practice, factors such as dentine

irregularities, canal ramifications and agitation technique may also contribute to

turbulent flow.

Conclusion

Calculations from the results of this laboratory study, using clinically relevant

parameters, such as canal diameter and irrigant flow rate, showed that all of the

viscosities would likely lead to laminar flow. The transition between laminar and

turbulent flow may be reached by modifying different parameters simultaneously: 1)

increase in irrigant flow rate, 2) increase in temperature and 3) decrease in irrigant

viscosity by adding surfactants with a concentration close to their CMC.

Acknowledgement.

We thank Caroline Montet for the English revision.

.

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dodecyl sulphate and gelatin. Colloids and Surfaces A: Physicochemical and

Engineering Aspects 337, 61-6.

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antimicrobial properties of orthodontic composite resins combined with benzalkonium

chloride. American Journal of Orthodontics and Dentofacial Orthopedics 122, 288-94.

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hypochlorite-based endodontic irrigants. International Endodontic Journal 45, 129-35.

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mesial roots of mandibular molar after sequential irrigation steps. International

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Tay FR, Gu LS, Schoeffel GJ, Wimmer C, Susin L, Zhang K, Arun SN, Kim J, Looney

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pp. 1-8. Ed Springer.

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Figure Legend

Figure 1 Relationship between dynamic viscosity µ (mPa .s) and concentrations of

surfactants Benzalkonium Chloride (CBAK), Tween 80 (CTW) and Triton X-100 (CTR)

for low concentrations (from 0 to 10%) mixed with 2.4% NaOCl at 37°C.

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Table 1. Comparison of mean viscosity, µ ± standard deviation (mPa.s)

according to NaOCl concentration and temperature (22 or 37°C), and corresponding

mean Reynolds number ± standard deviation calculated for two values of the root canal

diameter.

CNaOCL µ (mPa.s)

37°C

Reynolds number for a root canal diameter of

0.45mm


0.70mm

µ (mPa.s)

22°C


0.45mm


0.70mm

0.6% 1.15 ± 0.009 h

379 244 1.202 ± 0.007 d 363 233

1.2% 1.152 ± 0.006 h 378 243 1.213 ± 0.006

c 359 231

2.4% 1.186 ± 0.008 g 368 236 1.224 ± 0.006

c 356 229

4.8% 1.245 ± 0.008 f 350 225 1.298 ± 0.007

b 336 216

9.6% 1.312 ± 0.01 e

332 214 1.772 ± 0.01 a 246 158

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Table 2. Comparison of mean viscosity, µ ± standard deviation (mPa.s)

according to benzalkonium chloride concentrations (CBAK) mixed with 2.4% NaOCl at

37°C and corresponding mean Reynolds number ± standard deviation calculated for

two values of the root canal diameter.

CBAK

µ (mPa.s)

Reynolds number for a root canal diameter of 0.45mm


0% control 1.186 ± 0.008 a 368 236

0.004% 1.179 ± 0.005 a 370 238

0.008% 1.18 ± 0.009 a 369 237

0.5% 1.18 ± 0.006 a 369 237

1% 1.18 ± 0.008 a 369 237

3.125% 1.203 ± 0.004 a 362 233

6.25% 1.38 ± 0.004 b 316 203

12.5% 2.081 ± 0.008 c 209 135

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Table 3. Mean viscosity, µ ± standard deviation (mPa.s) according to Tween

80 concentrations (CTW) mixed with 2.4% NaOCl at 37°C and corresponding mean

Reynolds number ± standard deviation calculated for two values of the root canal

diameter.

CTW µ (mPa.s)



0% control 1.186 ± 0.008 a 368 236

0.0015% 1.184 ± 0.005 a 368 237

0.003% 1.172 ± 0.01 a 372 239

0.006% 1.157 ± 0.004 a 377 242

0.02% 1.123 ± 0.004 a 388 250

0.04% 1.130 ± 0.009 a 386 248

0.0625% 1.135 ± 0.005 a 384 247

0.12% 1.151 ± 0.007 a 379 243

0.24% 1.153 ± 0.006 a 378 243

0.45% 1.172 ± 0.004 a 372 239

0.9% 1.173 ± 0.001 a 372 239

1% 1.182 ± 0.007 a 369 237

1.2% 1.191 ± 0.005 a 366 235

6% 1.196 ± 0.005 a 365 234

15% 2.529 ± 0.008 b 172 111

20% 3.983 ± 0.009 c 109 70

25% 4.943 ± 0.009 d 88 57

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Table 4. Mean viscosity, µ ± standard deviation (mPa.s) according to Triton X-

100 concentrations (CTR) mixed with 2.4% NaOCl at 37°C and corresponding mean

Reynolds number ± standard deviation calculated for two values of the root canal

diameter.

CTR

µ (mPa.s)



0% control 1.186 ± 0.008 a 368 236

0.000035% 1.176 ± 0.006 a 371 238

0.00007% 1.173 ± 0.009 a 372 239

0.0001428% 1.144 ± 0.005 b 381 245

0.00386% 1.146 ± 0.009 b

380 245 0.125% 1.147 ± 0.012

b 380 244

0.25% 1.156 ± 0.005 b 377 242

0.5% 1.161 ± 0.005 a 375 241

0.8% 1.168 ± 0.004 a 373 240

1% 1.181 ± 0.007 a 369 237

3.12% 1.181 ± 0.008 a 369 237

6.25% 2.375 ± 0.008 c 184 118

15% 6.012 ± 0.02 d

73 47 20 % 18.426 ± 0.06

e 24 15

25 % 24.218 ± 0.06 f 18 12

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Figure 1. Relationship between dynamic viscosity µ (mPa .s) and

concentrations of surfactants Benzalkonium Chloride (CBAK), Tween 80 (CTW) and

Triton X-100 (CTR) for low concentrations (from 0 to 10%) mixed with 2.4% NaOCl at

37°C.

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Factors affecting the viscosity of the root canal irrigant sodium hypochlorite and their effect on irrigant flow

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Factors affecting the viscosity of the root canal irrigant sodium hypochlorite and their effect on irrigant flow