Histological Analysis of the Cleanliness Produced by Two Different Shaping Systems

In The Apical Third Of The Mesial Roots Of Mandibular Molars: An Ex Vivo Study

Abstract
Introduction: Current preparation techniques leave a different amount of unprepared root canal wall and consequently do not achieve complete cleanliness. The objective of the present study was to compare the cleanliness produced in the apical third of the mesial roots of mandibular molars after shaping with two different systems: TF Adaptive (rotary/reciprocating) and WaveOne (reciprocating), using light microscopy.

Methods: Thirty human mandibular molars with curvatures ranging between 0 and 25° were randomly divided in two groups to be shaped either with TF Adaptive (TFA group) or WaveOne (WO group) systems (n = 15 of each) following manufacturers´ directions for use. The irrigation regime used in both groups consisted of 5.25% sodium hypochlorite followed by ultrasonic activation and a final rinse with 17% ethylenediamine tetraacetic acid (EDTA). Three cross-cut sections were done at different levels of the root which were stained with Hematoxylin–eosin. Digital images of the stained specimens were taken at magnifications of 40X and 100X and blindly rated with an ordinal scale by two calibrated evaluators. The weighted kappa coefficient (Kw) was calculated for both inter- and intra-observer agreements. Data with the highest inter- and intra-observer agreements were used for further analysis. The chi-squared test for trend was used to assess differences between the two groups. Results: Inter-observer reproducibility was higher for a magnification of 100X, the Kw value being 0.95 (95% confidence interval 0.89–1). No statistically significant differences were observed between the two groups (P = 0.18). Conclusions: Both instrumentation techniques performed equally well at removing organic tissue and debris from the root canal system.

Introduction
Proper cleaning and shaping of the root canal system is essential to achieve success in root canal therapy 1 as an initial step before filling or placement of a final restoration in an endodontically-treated tooth. 2 However, anatomical complexities such as isthmus, oval extensions and lateral canals make it difficult to achieve complete tissue, debris and biofilm removal. 3,4 Despite the fact that cleaning and shaping techniques as well as irrigation seem to be quite effective, remnants can always be found in these areas. 5 Recent studies have shown that inadequate cleaning and removal of biofilm and tissue may result in persistent disease. 6,7

Nickel-titanium (Ni-Ti) rotary instruments have become very popular among endodontists, resulting in faster and more centered root canal preparations by the clinician. While they produce less extrusion through the foramen when compared with manual instrumentation techniques, they are also more susceptible to fracture. 8 Recently, new Ni-Ti reciprocating instruments have been introduced onto the market. It has been claimed that the clockwise and counterclockwise movements produced by the electronic motor that powers these new instruments reduce the cyclic fatigue to which the instruments are subjected 9 when shaping curved root canals; however, the amount of tissue debris that they produce needs to be investigated. WaveOne (Dentsply-Tulsa Dental, Tulsa, OK, USA) is a reciprocating instrument made using M-Wire technology. The active blades of WaveOne have different cross-sections along their length (radial lands at the tip which changes to a convex triangle near the shaft, similar to an F2 ProTaper Universal instrument (Dentsply-Tulsa Dental) 10 and different tapers (varying from 8% at the tip to 5.5% near the shaft). WaveOne is powered by a proprietary motion that comprises a 170° counterclockwise rotation followed by a 50° clockwise rotation.

TF Adaptive (Sybron-Endo, Orange, CA, USA) is manufactured from R-Phase Ni-Ti and was designed with the goal of taking advantage of the benefits of both a reciprocating instrument and a rotary one. The technology of the Adaptive motion is based on an algorithm designed to work with TF files with the following sizes and tapers: 20/04, 25/06, 35/04, 25/08, 30/06, 50/04. When the instrument works under no or minimal stress, it functions with a continuous clockwise rotary motion (0-600°) but, when it encounters stress in the root canal system, it changes to a reciprocating motion (370-50° of reciprocation). According to the manufacturer, the clinician is unaware of the change from a rotary to a reciprocating motion 11, which is influenced by the anatomical complexity of the root canal and the stress that the instrument receives when working within the canal.

Despite the benefits of mechanical root canal preparation and the new motions employed, it has been demonstrated that shaping instruments do not contact all walls of the root canal system and consequently do not achieve complete wall cleanliness. Therefore, the objective of the present study was to compare the cleanliness produced in the apical third of the mesial roots of mandibular molars after shaping with two different systems: TF Adaptive (rotary/reciprocating) and WaveOne (reciprocating) using light microscopy.

Materials and Methods
Thirty recently extracted human mandibular molars with curvatures of ≤25° according to Schneider 12 and tomography were selected for the study, cleaned and placed in 10% formalin. The buccal and lingual cuspids were cut down to standardize all roots at a length of 20 mm. The access cavity was made with a size 3 round bur, the distal root was cut at 3 mm from the cemental-enamel junction (CEJ) and Opaldam (Ultradent, South Jordan, UT, USA) was placed in the orifice of the distal canal. The working length (WL) was determined on both of the mesial canals by introducing a size 8 K file (Dentsply-Maillefer; Tulsa Dental) until it could be seen through the apical foramen with a microscope, and 1 mm was then subtracted from that distance. The teeth were then randomly divided into two groups. The first tooth to be extracted from a jar was assigned either to Group WO or to Group TFA based on the result of a coin toss. The second tooth was assigned to the other group and so on until all 30 teeth had been equally divided between the two groups.

Two mesial roots that were fixed immediately after extraction were used as negative controls. The cervical third of the distal roots of the same teeth were used as positive controls after being instrumented using a #4 Peeso drill and then placed in an ultrasonic bath containing 6% sodium hypochlorite (NaOCl) for 10 min, followed by 5 mL of 17% ethylenediamine tetraacetic acid (EDTA) for one minute. 13

Group WO (n = 15)
Both mesial root canals in teeth in this group were instrumented using the WaveOne system according to the manufacturer’s directions for use. A glide path was created with a loose 10 K file (Dentsply-Maillefer; Tulsa Dental). The primary WaveOne instrument was introduced into the root canal using gentle pecking motions, advancing 2–3 mm apically at a time until it could not be advanced any further. The instrument was then removed to be cleaned and reintroduced into the canal until it reached the WL. Five milliliters of 5.25% NaOCl served as the irrigant every time the instrument was extracted from the canal. A final irrigation with 20 mL of 5.25% NaOCl was performed with a side-vented needle at 2 mm from the established WL. 14 Apical patency was confirmed and the conformation was considered complete if dentin chips could be observed in the apical flutes of the instrument. Then, ultrasonic activation of the irrigant was performed with a Varios ultrasonic device (NSK, Tochigi, Japan) at power setting E3 using the NSK U files for 20 s each time. According to the manufacturer, the frequency used under these conditions was approximately 30 kHz and the intensity was 7.5 W. 15 Five milliliters of 17% EDTA was delivered to 2 mm from the WL and allowed to remain there for one minute as the final irrigant, then suctioning was performed with a capillary tip (Ultradent) and paper points were used to finish drying the canals.

Group TFA (n = 15)
Teeth in this group were instrumented following the manufacturer’s instructions for the TF Adaptive system, except that a TF ML 1 (25/08) was used as the final instrument instead of an SM 3 (35/04), so that both groups underwent a final preparation to achieve the same tip and taper sizes. After WL determination and establishment of a glide path using a size 08 K file (Dentsply-Maillefer; Tulsa Dental), a 15 K file (Dentsply-Maillefer; Tulsa Dental) was used to further flare the canals. Five milliliters of 5.25% NaOCl was used as the irrigant between instruments. The SM 1 instrument was gently introduced into the root canal until resistance was met. It was then withdrawn and cleaned before being introduced again until the WL was reached without pressure or pecking motions. The same procedure was followed with the SM 2 and ML 1 instruments until the WL was reached. Twenty milliliters of 5.25% NaOCl were used with a side-vented needle at 2 mm from the WL14 and then ultrasonic activation of the irrigant, EDTA irrigation and drying of the canals was carried out in exactly the same way as for Group WO.

Cross-cut sections were done at 1 mm from the apex and Hematoxylin–eosin was used to stain the specimens, Digital photographs from both mesial root canals were taken at magnifications of 40X and 100X and observed by two calibrated and blinded examiners who scored the specimens according to the following ordinal scale:

Score 1: Clean canal walls; only very few debris particles
Score 2: A few small conglomerates of debris
Score 3: Many conglomerates; <50% of the canal wall covered with debris
Score 4: More than 50% of the root canal wall covered with debris
Score 5: Complete or nearly complete covering of the wall with debris

The weighted kappa coefficient (Kw) was calculated to determine inter-observer agreement for both magnifications together and for each individual magnification in case there were different levels of agreement depending on the eye resolution associated with different levels of magnification. Kw was also calculated to determine intra-observer agreement. Data from the observations with the highest inter- and intra-observer agreements were used for further analysis. To avoid an increase in the sample size by data duplication, only the worst score (either from mb or ml canal) was selected for each tooth. A trend analysis with a chi-squared test for trend was used to compare groups (SPSS 22 for Windows; SPSS, Chicago, IL, USA).

Fig. 1
(A) MB canal from the mesial root of a lower molar instrumented with the TF Adaptive system. Hematoxylin–eosin staining;
100X magnification. (B) ML canal. (C) 40X magnification.

Fig. 2
(A) MB canal from the mesial root of a lower molar instrumented with the WaveOne system. Hematoxylin–eosin staining;
100X magnification. (B) ML canal. (C) 40X magnification.

Results
The scores for negative and positive controls were five and one, respectively.

The level of inter-observer agreement when the two magnifications were considered together was 94.83% (Kw 0.62, 95% confidence interval [CI] 0.43-0.83).

When the two magnifications were considered separately, inter-observer reproducibility was much higher for a magnification of 100X, with a Kw value of 0.95 (95% CI 0.89-1) and a level of observed agreement of 99.17%. For a magnification of 40X, the observed agreement was 90.83% (Kw 0.61, 95% CI 0.35-0.87). Intra-observer agreement was very high: 93.3% and 93.2% for observers 1 and 2, respectively.

The highest inter-observer agreement was found for a magnification of 100X and observer 1 showed the highest intra-observer agreement. Therefore, data from observer 1 at a magnification of 100X were selected for further analysis.

No significant differences were observed between the two groups (P = 0.18). The distribution of debris scores for the two groups is shown in Table 1.

Table 1

Discussion
Many studies have shown that complete removal of debris, biofilm and organic tissue from the apical portion of the root canal is impossible. 16 Different methods have been used to determine the cleanliness obtained after instrumentation, including scanning electron microscopy (SEM), tomography, histology 17–19 and microbial analysis. 20 All of these techniques have both advantages and disadvantages, and none of them have the capacity to completely evaluate how clean all areas of the root canal system are. 21 Tomography is excellent for determining the areas not touched by instruments, but not for analyzing the amount of debris or biofilm remaining after instrumentation. 21 Microbial analysis is considered a good option in terms of transposing results from the laboratory to the clinic; however, it cannot determine or quantify all the microorganisms present, or all of the species involved. Also, it does not provide information on the amount of debris or organic tissue remaining after cleaning and shaping. 22 In the present study, histology was used because it allows determination of both debris and organic tissue that remain attached to the root canal walls, which are considered to be infected in most cases. 23 Clinically, this is important because microorganisms and nutrients in the root canal system are considered the cause of persistent disease. 24

The anatomical complexity of the root canal system is another important factor to be considered. This is why, in order to resemble a clinical problem, mesial roots of lower molars were used. 25 Other authors, such as Taha et al.21 and Kamel and Kataia26, used teeth with less complex anatomy. Using histology, Taha et al. compared the cleanliness obtained in oval canals using a rotary instrument, manual instrumentation and Anatomic Endodontic Technology (AET, Ultradent Products Inc, South Jordan, UT) in which stainless steel instruments are used in a reciprocating slow-speed handpiece (Endo-Eze AET/ADO, Ultradent), and found no differences between the groups. 21 Kamel and Kataia compared the ProTaper and WaveOne systems. They found that the reciprocating instrument achieved cleaner canals when compared using SEM. 26 Therefore, since the anatomies of the teeth involved are different, the results of the present study cannot be compared with theirs.

Rotary instruments reduce the amounts of organic and inorganic tissue. 13,14 Using tomography, Robinson et al. 24 compared the amount of debris removed using ProTaper and WaveOne. They showed that reciprocating instruments are not as effective as rotary instruments for removing tissue and debris. In contrast, De-Deus et al. 27 also used tomography to evaluate the amount of debris remaining after cleaning and shaping using two reciprocating instruments (WaveOne and Reciproc) and a rotary instrument (BioRace), and did not find a difference between the types of system.

In the present study, reciprocating instruments performed similarly in terms of debris removal from the apical third. All specimens were instrumented to the same size and taper apically (25/08) for standardization purposes. However, the TF Adaptive system was designed to be used up to a 35/04 size apically. Using this larger instrument in the apical third may have produced different results, as bigger apical sizes usually result in cleaner root canals 27–29 given an improvement in the efficacy of the irrigants in that area. 28,29 Another factor to be taken into account is that rotary instruments can usually be used with a brushing motion against the walls by using the TF Adaptive system. Using the instruments in this way may have resulted in more walls being touched, prepared and perhaps cleaned. 30

In conclusion, under the conditions of the present ex vivo study, when using the same size and taper of both instruments to the WL, both the TF Adaptive and WaveOne systems performed equally well at removing organic tissue and debris from the root canal system. OH

Oral Health welcomes this original article.

Disclaimer
The authors deny any conflicts of interest related to this study.

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