An in vivo assessment of the influence of needle gauges on endodontic irrigation flow rate.

AIM: The aim of this clinical study was to assess the influence of irrigation needle gauge on endodontic irrigation flow rates. SETTINGS AND
DESIGN: In vivo assessment.
MATERIALS AND METHODS: Five specialist endodontists performed intracanal irrigation procedures on 50 mesiobuccal canal of mandibular first molars using three different irrigation needle gauges. Data of time taken for irrigation was recorded by an irrigation testing system and analyzed using independent sample "T" test and one-way analysis of variance (ANOVA) test. The level of significance was set at P < 0.05. STATISTICAL ANALYSIS USED: The following tests were used for the statistical analysis: Independent sample "T" test, one-way ANOVA test, and post hoc multiple comparison was carried out using Tukey's honest significant difference (HSD) test using Statistical Package for the Social Sciences (SPSS) version 16 for Windows.
RESULTS: The average flow rate of 26 gauge was 0.27 mLs(-1), of 27 gauge was 0.19 mLs(-1), and of 30 gauge was 0.09 mls(-1). There was statistical significance among the gauges (P < 0.001). 26 gauge had highest flow rate when compared with other groups followed by 27 gauge and 30 gauge respectively. The operator variability for flow rate of three endodontic irrigation needle gauges (26 gauge, 27 gauge, and 30 gauge) was found to be not significant.
CONCLUSIONS: Needle gauge has significant influence on endodontic irrigation flow rate.

INTRODUCTION

Etiology of periapical pathology is associated with the presence microorganisms in the form of biofilm in the root canal system.[1] Mechanical instrumentation aids in the drastic reduction of the intracanal microbial load. Since the root canal cross section is not perfectly round, complete instrument contact does not occur during the mechanical instrumentation procedures. It has been observed that 65% of the root canal recesses remain uninstrumented when hand instrumentation is used with balance force technique,[2] and more than 35% of the root canals remain untouched by rotary instruments.[3] Hence, irrigation of the root canal system with antibacterial solutions is considered an essential part of disinfection of the root canal space.[4] A combination of shaping with instruments and cleaning with irrigants facilitates removal of debris, necrotic tissue, and root canal disinfection. The commonly used irrigants for canal disinfection include sodium hypochlorite (NaOCl), chlorhexidine (CHX), and ethylenediaminetetraacetic acid (EDTA). These irrigants are commonly delivered using a syringe and needle.[5]

The factors affecting the efficacy of needle irrigation include the diameter of the irrigating needle, needle design, depth of the irrigating needle engaged in the root canal, and the final size of the root canal preparation.[67] Narrower gauge needles (30 gauge) are more effective than larger gauge needles in removing debris from curved canals.[8] The use of a close-ended single side vented needle is considered to be the safest needle design for irrigation.[9101112] Sedgley et al. recommend positioning the needle as close to the working length (WL) as possible to improve debridement and irrigant replacement.[13]

Flow rate is considered a highly significant factor in determining flow pattern in irrigation dynamics[14] and has been shown to influence the replacement of the irrigant.[15] However, irrigation flow rate is not commonly mentioned as a factor influencing the effectiveness of irrigation[16] and is not standardized in research papers.[8131718192021] Existing endodontic research reports a wide range of irrigation flow rates ranging from 0.03 mLs–1 to 1.27 mLs–1.[78172022] This is influenced by the operator, needle design, and needle gauge. All the abovementioned flow rate studies were based on either in vitro or ex vivo setup.

It is but natural that an operator would be more careful and use lower barrel pressure clinically in order to avoid inadvertent extrusion of the irrigant than in an in vitro setup. This could potentially translate into lower flow rate clinically while irrigating the apical third of the root canal. The optimal flow rate that could provide adequate irrigation dynamics as well as maintain patient safety remains clinically inconclusive. This is the first clinical study to assess and compare the influence of endodontic needle gauges on endodontic irrigation flow rate. Hence, the aim of the current study was to test the null hypothesis that the endodontic irrigation flow rates in a root canal is not dependent on the gauge of the endodontic irrigation needle.

MATERIALS AND METHODS

Case selection and study protocol

The clinical study protocol was reviewed and approved by the University Research Ethical Committee. The trial subjects were treated in accordance with the Declaration of Helsinki. The patients received thorough explanations concerning the experimental rationale, clinical procedures, and possible complications of the procedure.

This study was conducted on 50 patients having a mandibular first molar requiring root canal therapy due to irreversible pulpitis and symptomatic apical periodontitis. The inclusion criteria included patient willing to participate in this clinical study with informed consent, patient aged between 18 years and 40 years with completely formed root apex of the mandible first molar, and with curvature less than 10°-20°. Preoperative intraoral periapical (IOPA) radiographs were taken to confirm the root curvature.[23] Exclusion criteria included visible evidence of periradicular lesion, presence of root fractures or cracks, root caries, and signs of internal or external resorption or calcification. The overview of the study protocol is provided in Figure 1.

Figure 1

Methodology flow chart

Five specialist endodontists (three males and two females) from the Department of Conservative Dentistry and Endodontics of our university participated in this clinical study. The 50 patients who fulfilled the inclusion criteria were randomly allocated to one of the five operators (N = 10) using a computer generated program of random numbers. Each patient was anesthetized with 1.8 mL of 4% articaine with 1:100,000 epinephrine (Septanest, Septodent, France). The isolation of the tooth was done using rubber dam. After standard access cavity preparation a 10 size K-file (Mani INC, Japan) was introduced into the canal to establish patency. WL was obtained using electronic apex locator (Denta port zx, J. Morita Corp, Japan) and conformed using radiographs. Root canal preparation was performed using rotary instruments (Mtwo, VDW, Germany) with crown down technique. Canal patency was maintained at all times of preparation. Master apical file (MAF) preparation was standardized to ISO size 30 with 0.06 taper[24] for the mesiobuccal canal of mandibular first molar. Canals were irrigated with 2 mL of 3% NaOCl between instrumentation using 30 gauge close-ended single side vented needle placed passively into the canal 1 mm short of the needle binding site.

Experimental setup

A testing system was constructed to measure the time taken to irrigate 2 mL of 0.9% isotonic saline during each irrigation cycle. The setup consisted of a syringe (Unolok, Hindustan syringes and Medical Devices Ltd, India) in which two customized holes were made in the plunger corresponding to 0.0 mL and 2.0 mL marking of the syringe barrel. Two diode infrared receiver (IR) modules with a lead spacing 2.54 mm and wave length of 940 nm (IR333-A, Everlight electronics, Taiwan) were attached to the flange of the barrel and this was connected to a microcontroller unit with digital display. During the start of an irrigation sequence, the IR signal gets interrupted and the timer starts automatically. The irrigant is completely dispensed when the bottom of the plunger reach the bottom of the barrel. At this point, the hole made in the top of the plunger would activate the IR sensor to stop the timer.

Clinical assessment of flow rate

After establishing MAF 30/0.06, the mesiobuccal canal was dried with paper points. Each canal was then irrigated by three different needle gauges by the same operator (Group A = 26 gauge, Group B = 27 gauge, and Group C = 30 gauge) with irrigant in Table 1. The sequence of using 26-gauge, 27-gauge, and 30-gauge needle in each canal was randomized using computer generated program random number. The rate of flow was recorded using the earlier explained testing system. Each operator was instructed to passively insert the needle to a depth of 1 mm short of canal binding in order to avoid inadvertent extrusion of irrigant.

Table 1

Characteristic of needle used in this study

The irrigation procedure was done twice for each group (A, B, and C) making a total of six procedures per canal. The time duration for each group was calculated based on the average of the two irrigation cycles of that group. Each irrigation sequence was done after a gap of 3 min each to minimize operator fatigue. The time taken to irrigate 2 mL of irrigant with different needle gauge was recorded using an automated timer. A high vacuum suction with disposable suction tip was employed to remove the flushed irrigant from the access cavity. A new set of needles was employed for every canal. The canal was dried with paper points after each irrigating cycle.

Data analysis

The pair-wise comparison group (A vs B, A vs C, and B vs C) was performed using Independent “T” test. Intragroup and intergroup comparisons were performed using one-way analysis of variance (ANOVA), and post hoc multiple comparison was carried out using Tukey's honest significant difference (HSD) test. The level of significance was set at P < 0.05. the statistical analysis was performed using Statistical Package for the Social Sciences (SPSS) V.16 for Windows (SPSS Inc, Chicago, IL, USA).

RESULTS

The raw data obtained were equated in the following formula volume Vol/Δt (mLs−1) average flow rate of irrigation, Vol (mL) — volume of irrigant delivered, Δt (s) — duration of irrigant.

The data distribution was analyzed using Shapiro–Wilk test and the data were found to be normally distributed. The mean flow rate (mLs−1) between gauges (26 vs 27, 26 vs 30, 27 vs 30) for all operators was found to be statistically significant when compared using Student's “T” or independent “T” test.

The average flow rate of 26 gauge was 0.27 mLs−1, of 27 gauge was 0.19 mLs−1, and of 30 gauge was 0.09 mLs−1. There was statistical significance among the gauges (P < 0.001). Twenty-six gauge had highest flow rate when compared with other groups followed by 27 gauge and 30 gauge, respectively, in Table 2.

Table 2

One-way ANOVA to compare mean flow rate between gauges

The operator variability for flow rate of three endodontic irrigation needle gauges (26 gauge, 27 gauge, and 30 gauge) was found to be insignificant (P = 0.63, P = 0.27, P = 0.09) as detailed in Table 3.

Table 3

Assessment of intraoperator variability using ANOVA

DISCUSSION

The most challenging aspect of endodontic therapy is the disinfection of apical third of the root canal.[12] An optimal irrigation protocol would be one, which would enable the irrigant to effectively debride the canal intricacies.

The analysis and visualization of the flow field of endodontic irrigants is limited in vivo due to the microscopic dimensions of the root canal system. The existing modalities for assessing the effectiveness of irrigant fluid dynamics include in vitro models — SEM studies, high-speed imaging, thermal image analysis, mathematical models, and numeric simulation studies.

Of the numeric simulation studies, computational fluid dynamics (CFD) serves as a valuable tool for the assessment of fluid flow and characteristics within a root canal, which could equate to clinically realistic conditions. CFD is a new approach in endodontic irrigation research which can be used to evaluate and predict specific parameters, such as the streamlines, velocity distribution of irrigant flow in the root canal wall, flow pressure, and shear stress, which are difficult to measure by traditional methods.[25]

Factors affecting the ability of an irrigant to penetrate the apical root canal include the internal anatomy of a canal that would influence the MAF size, density, and viscosity of irrigant and irrigation flow rate. The four parameters influencing fluid dynamics are represented by Reynolds number (ReN). It is the most common dimensionless number in fluid mechanics.

ReN is directly proportional to the fluid density (ρ), velocity (ν), and canal diameter (D) and is inversely proportional to the fluid viscosity (μ). The influence of viscosity and density of commonly employed root canal irrigants has been investigated and well established.[262728] The most clinically significant variable would be the velocity of the irrigant represented by the rate of flow (mLs−1) within the canal. The assessment of ReN relies upon input data that should mimic clinically realistic conditions.

Although the existing endodontic research reports a wide range of irrigation flow rates, the optimal flow rate that provides adequate irrigant dynamics as well as maintains patient safety remains inconclusive. Flow rates within the range of 0.03-0.05 mLs−1,[20] 0.12 mLs−1,[17] 0.13 mLs−1,[18] 0.20 mLs1,[1321] 0.25 mLs−1,[22] and 0.31 mLs−1,[8] have been reported. More recently, an initial flow rate of 0.083 mLs−1 at the WL followed by a flow rate of 0.26 mLs−1 was found to be capable of eliminating an apical vapor lock during syringe irrigation in vitro.[10293031] Most CFD studies employ 0.26 mLs−1 as the rate of flow in simulating the intracanal irrigation.[31]

As there has been no in vivo clinical study to assess the endodontic irrigation flow rates so far, the purpose of our clinical study was to assess irrigation flow rate in vivo with three commonly used endodontic needles. These three needles were chosen based on research[7] that recommends the use of finer diameter needles as well as based on clinical practice. Hence, 30 gauge (close-ended single side vented), 27 gauge (close-ended single side vented) and 26 gauge (beveled) were chosen for this clinical study.

This study revealed inverse correlation between gauge of endodontic needles and endodontic irrigation flow rate. The clinical flow rates according to our study were 0.27 mLs−1 for 26 gauge, 0.19 mLs−1 for 27 gauge, and 0.09 mLs−1 for 30-gauge needles. Although 26 gauge and 27-gauge needles can provide higher flow rates, within the root canal the external diameter of these needles would impair the depth of penetration. On the other hand, 30-gauge needle would allow the clinician to place these as apical as clinically possible without canal binding amongst all these endodontic needles. However, the 30-gauge needle was found to have the slowest flow rates amongst all the groups (0.9 mLs−1). This slow flow rate compared to other studies might influence the irrigant fluid replacement dynamics in the critical apical third of the root canal. Experimental studies that are trying to assess this problem should employ flow rates used clinically as demonstrated from our study instead of data from other in vitro studies.

CONCLUSION

Within the limitations of this clinical study, our null hypothesis was rejected. The highest intracanal flow rate was observed in group A (26 gauge) followed by group B (27 gauge), and the slowest flow rate was observed in group C (30 gauge).

Financial support and sponsorship

This study was supported by a research grant given by the Root Canal Foundation /www.rootcanalfoundation.com.

Conflicts of interest

There are no conflicts of interest.