Abbreviations

EAL: Electronic apex locater
EDU: Elements diagnostic unit
EDTA: Ethylene diamine tetra-acetic acid
HLE: Root canal length with sodium hypochlorite as an irrigant
SLE: Root canal length with normal saline as an irrigant
BLE: Root canal length with blood containing EDTA as an irrigant
AL: Actual root canal length

Introduction

Accurate determination of the working length is crucial part of successful endodontic treatment (1).According to Seltzer et al, both overfilling and under filling decreased the overall success rate of endodontic treatment (2). Kuttler did a microscopic study of root apices and stated that ^{the working length for instrumentation and obturation of the root canal system should be established at the apical constriction, or minor foramen (3). Therefore, locating the apical constriction is a key stage in endodontic treatment (4).}

The use of electronic devices to determine root canal length has increased substantially in recent years. The principal design and development of the early apex locators dates back to Suzuki (1942). He carried out research on dogs and discovered that the electrical resistance between the periodontal membrane and the oral mucosa was a constant value of approximately 6.5 kΏ. This principle was introduced into clinical practice by Sunada (1962) and it is on his work that the operating principles of resistance-type Electronic Apex Locators (EALs) are based (5). First-generation EAL devices, also known as resistance apex locators, measure opposition to the flow of direct current or resistance (6). Second-generation EALs, also known as impedance apex locator, measure opposition to the flow of alternating current or impedance. Second generation apex locators were of the single frequency impedance type EALs and suffered problems of incorrect readings with electrolytes in the canals and also in dry canals (7). Third generation apex locators are similar to the second generation except that they use multiple frequencies to determine the distance from the end of the canal. These units have more powerful microprocessors and are able to process the mathematical quotient and algorithm calculations required to give accurate readings (8). The main shortcoming of early apex locators (erroneous readings with electrolytes) was overcome by Kobayashi et al. (1991) with the introduction of the ratio method and the subsequent development of the self-calibrating Root ZX (J. Morita, Tokyo, Japan) (Kobayashi & Suda 1994) (9). The Root ZX simultaneously measures two impedances at two frequencies (8 and 0.4kHz) inside the canal (9). The change in electrical capacitance at the apical constriction is the basis for the operation of the Root ZX and its reported accuracy even in presence of different electrolytes in the canal & under different clinical conditions (10). Elements Diagnostic Unit and Apex Locator (Sybron Endo, Anaheim, CA, USA) is a fourth generation apex locator (11). The device does not process the impedance information as a mathematical algorithm, but instead takes the resistance and capacitance measurements and compares them with a database to determine the distance to the apex of the root canal (7). It uses a lookup matrix rather than making any internal calculations. All combinations of capacitance and resistance are calculated and loaded into a matrix database within the unit, making the displayed information much more stable (11). It uses a composite waveform of two signals, 0.5 and 4 kHz, compared with the Root ZX at 8 and 0.4 kHz. The signals go through a digital-to-analogue converter to be converted into an analogue signal, which then goes through amplification and then to the patient circuit model which is assumed to be a resistor and capacitor in parallel. The feedback signal waveforms are then fed into a noise reduction circuit. It uses multiple frequencies to eliminate the influence of the canal conditions, which is similar to Root ZX thus permitting less sampling error per measurement and more constant readings (7). There is lack of literature information about direct evaluation of the effect of file size in presence of different electrolytes in the root canal on the accuracy of this unit before instrumentation of the apical and middle third of the canal.

Therefore the aim of this in-vitro study was to evaluate the effect of file size in the presence of sodium hypochlorite, saline and blood on the accuracy of this unit before instrumentation (of the apical and middle third) of the canals.

Materials And Methods

25 freshly extracted intact human mandibular premolar teeth were obtained from the Department of oral surgery, Government Dental College, Srinagar, India and stored in demineralised water (DM water) with 10% formalin. The external portion of each tooth was cleaned using ultra sonic scaling device P5 Newtron (Satelec-Acteon ) to remove calculus and periodontal debris. After cleaning, each tooth was carefully examined under Olympus microscope(X4 magnification) to detect external cracks, apical resorption/open apices.

Specimen preparation

Buccal cusp tips of teeth were flattened to achieve uniform stable equivocal & reproducible reference points, with a view to minimize errors in working length measurements caused by variation in the coronal reference points. Access cavities were prepared with cavity access set (Dentsply Maillefer) & pulpal tissue removed with nerve broaches (Pulpdent) & no 15 k file (Dentsply Maillefer) using DM water irrigation. Gates gilliden drills (1-4) were used for coronal 3 ^rd flaring of the root canal of each tooth. Canal patency was checked with no 10 k file. Size of the root canal near apical constriction was gauged /determined by using no 20 k file. Only those teeth were selected through which no 20 K file tip passed passively without any force & was just visible at the apical foramina at X4 magnification so that only teeth with apical constriction diameter near about 0.22mm are selected. All these specimens were placed in DM water (CDH Pvt Ltd) before final usage.

The embedding medium alginate, Zelgan 2002 (Dentsply) was mixed according to manufacturer’s instruction & poured into individual containers(Fig1).

Figure 1

Fig1. Tooth samples embedded in alginate molds

Specimens were dried with air water syringe & their canals dried with no 15 absorbent paper points (Dentsply Maillefer) before embedding them into alginate mould. Specimens (up to the CEJ) & lip clip were embedded into alginate mold before final setting of the material. All measurements were made within 2hrs of the mold preparation with the gel kept sufficiently humid for this time. Measurements were taken with Elements diagnostic apex locater in three stages to prevent cross contamination.

Stage One

Canals were filled with 5.2% sodium hypochlorite (Prime dental products Mumbai, India) using a 27/30 gauge irrigating syringe. Cotton tips were used to dry the tooth surface & to eliminate the excess sodium hypochlorite solution. Care was taken to ensure that sodium hypochlorite solution remained below the canal orifices. Electronic lengths were measured with elements diagnostic unit using no10, no15 & no 20 K files ( Fig2)for all of the specimens respectively.

Figure 2

Fig2. Electronic length measured with elements diagnostic unit using no10 K file

The readings of the files were taken to the 0.0 mark & then withdrawn to the 0.5 mark & this acted as the termination point in all measurements in the study. Silicon stop was adjusted & the file was removed from the canal & measured with a caliper (AEROSPACE 0.02mm)(Fig3).

Figure 3

Fig3. AEROSPACE caliper used for measuring the file length

The lengths were registered as HEL-10, HEL-15 & HEL-20.

Stage Two

Stage Three

Specimens were removed from the alginate mold, water from three way syringe was used to wash them & finally their canals were irrigated with 5ml DM water. They were placed in DM water till further use. Fresh alginate molds were prepared & specimens were dried & embedded as in stage one. Canals were filled with blood containing EDTA as anticoagulant. Cotton tips were used to dry the tooth surface & to eliminate the excess blood. Care was taken to ensure that blood remained below the canal orifices. As in stage one, electronic length was measured by using no10, no15 and no 20 K files and registered as BEL-10, BEL-15 and BEL-20.

At the end of electronic length measurements the actual root canal length (AL) that is the distance from coronal reference point to the apical constriction was measured by grinding/shaving the apical 4mm of the roots with diamond burs (Dentsply) to expose the apical constriction. No 15 flex file was inserted till its tip flush with apical constriction at X4 magnification ( Fig4). File was removed from the canal & measured with a caliper.

Figure 4

Fig4. No 15 flex file inserted into the canal with its tip flush with apical constriction at X4 magnification

The results obtained were recorded in independent tables(Tables 1, 2 and 3). In each case AL was subtracted from the electronically determined working lengths, recording the distance in tabular form as:

Positive form: measurements exceeding the apical constriction,

Negative form: measurements short of the apical constriction and

0/correct: measurements coinciding with the apical constriction with a 0.5mm acceptable range.

Figure 5

Table 1. Readings while taking sodium hypochlorite as an irrigant

Figure 6

Table 2. Readings while taking normal saline as an irrigant

Figure 7

Table 3. Readings while taking blood containing EDTA as an irrigant

Results

Statistical analysis of the data was done using on way ANOVA and post-hock tukey test. Statistical analysis revealed no significant difference in the lengths measured by #10, #15, and #20 files in the presence of Sodium hypochlorite 3%, Saline 0.9% and blood containing EDTA as compared to AL (actual length).

Tables 4, 5 and 6show that most measurements were within ± 0.5 mm of the AL (actual length). The percentage of measurements ± 0.5 mm to the apical constriction for Elements Diagnostic Unit registered were 85.77% (193 out of 225 total measurements) and the percentage of measurements ± 1 mm to the apical constriction registered were 100 %.

Figure 8

Table4. Distance from actual length: -1 to - 0.5 mm

Figure 9

Table 5.Distance from actual length: - 0.5 to 0.5 mm

Figure 10

Table 6. Distance from actual length: 0.5 to 1 mm

Discussion

The apical constriction is the narrowest part of the root canal and preparation to this mark ensure complete removal of all pulp tissue and necrotic material from within the root canal and also prevent extrusion of the filing material into the surrounding bone which result in optimal healing (12), the distance of this apical constriction from a coronal reference point is known as the working length. There are various methods for the determination of the working length to name a few is tactile method, radiographic method etc. EAL are the modern method of working length determination. Several factors have been reported to affect the accuracy of EALs in vivo such as, the presence of conductive root canal solution inside the canal,(13,14,15),Periapical pathosis (16) ,diameter of apical foramen(17,18),shape and volume of measuring probe(19),operator ability(15). Laboratory based studies have allowed the evaluation of some of these factors (16).Various laboratory models have been suggested: immersion in agar sol or gels (21, 22), in saline solution (13), embedding in alginate (23), in a sponge soaked with saline solution (24).

The main purpose of this in-vitro study was to evaluate the effect of file size in presence of different electrolytes in the root canal on the accuracy of elements diagnostic unit.

In the present study, teeth used were mandibular premolars as over estimation in the working length was demonstrated to occur in more than half (56%) of the premolars teeth, although the radiographic working length were apically located 0-2mm short of the radiographic apex (25).The use of the Root ZX decreased the overestimation of the working length of the premolar group to 21% (26). Electronic apex locators were frequently used with a small size 15 no endodontic file and numerous apex locator studies have used this file for testing purposes without considering the apical terminus size of the canals. As electronic working length determination was influenced by the size of the canal at the apical terminus (27, 28), mandibular premolar teeth with apical constriction size of about 0.22mm were chosen to control this parameter.

According to Hassanien EE, Hashem A and Chalfin H (2008), apical constriction was detected at an average distance of 1.2mm from the apical foramen with a canal diameter of 0.22mm in mandibular premolars (29). Alginate models and extracted human teeth were used to demonstrate electronic working length measurement because it is simple, inexpensive and stable for hours and the root apices cannot be seen. The relative stiffness of alginate mould prevented fluid movement inside the canal that is responsible of premature electronic readings registered with previous models (22, 30, 31).

Some authors have suggested that taking the instruments slightly long when using EALs and then retracting them may increase the accuracy of readings of EALs (32, 33), thus to conform the measurement, the file was advanced into the canal just beyond the foramen, as indicated by the 0.0 on the LCD display. The file was then withdrawn until the reading of EALs showed a consistent 0.5 indicating that the apical constriction had been reached.

In the present study the error range used was ±0.5 from the actual length which is considered as the strictest acceptable range (34), thus measurement attained with in this tolerance are considered highly accurate, on the other hand root canals do not always end with apical constriction, a clear minor and major diameter or an apical foramen at the exact base of the cemental cone, this is why some authors prefers the ±1mm range as the acceptable range (35, 36).

An in vivo study (Tselnik et al 2005) reported the elements EAL to be accurate to within ±0.5mm from the mirror diameter 75% of the time and to within ±0.75mm.89% of the time and 91.7% to ±1mm (37). The accuracy of the Root ZX apex locator was determined in the presence of the NaOCl. EDTA, saline, chlorhexidine, xylol and in dry canals in previous laboratory study (Kaufman et al2002) and the results indicate that Chlorhexidine, Naocl, EDTA and saline can also be used safely in the determination of canal length with the Root ZX (38). Jankins JA et al evaluated the accuracy of the Root ZX in vitro in the presence of a variety of endondontic irrigants. Irrigants tested were: saline, 2% lidocaine with 1:100000, 3% H2O2 and Peridex. The Root ZX was able to consistently determine the location of the apical foramen (within approx.±0.4mm) in the presence of any of the tested irrigants (39). Erdemir et al (2007) showed that the Tri Auto ZX with automatic reverse function can be used safely in the presence of NaOCl, H2O2, chlorhexidine, EDTA, ultrasonic and in the absence of any irrigating sol. However the use of the saline as an irrigating sol. with the Tri Auto ZX adversely affected canal length determination .The results that the use of 0.9% saline adversely affected the measurement sensitivity of the device are in contrast to that of the present study. This difference can be explained by the test conditions (ex –vivo and in-vivo) and/or also different devices (Root ZX and Tri Auto ZX ) with reverse function (5). Nguyen HQ et al in an in-vitro study stated that the length obtained with small and large size files were comparable (40).

If the estimated working length =AL±0.5mm is considered to be clinically acceptable then the measurements made with the elements diagnostic unit were acceptable in 85.77% of the times .the measurements obtained revealed that the elements diagnostic unit was able to measure the canal length with the AL irrespective of the file size /presence of sodium hypochlorite, saline and blood (EDTA) in the canal.

Conclusion

Within the limits of this study it was concluded that Elements Diagnostic Unit (EAL) can accurately register the root canal length within ±0.5 mm from the apical constriction and is not adversely affected by the presence of Sodium hypochlorite, Saline & Blood containing EDTA in the root canal and the measured lengths obtained with #10, #15 & #20 files were comparable. Further clinical studies are needed to evaluate this.