Impact of maintaining apical patency on cleaning potentials of XP-endo Finisher in curved root canals

Abstract

Background:

Obtaining optimum cleanliness of root canal walls through mechanical and chemical tools has not yet been attained, mostly in the apical third of the root canal, and it has become more difficult in curved canals. This work aimed to investigate the impact of maintaining apical patency on the cleaning potentials of XP-endo Finisher in the apical third of curved root canals.

Materials and Methods:

Thirty curved roots (25^o:30^o) were assigned for the study, divided into two groups: patency maintained (PM) and patency not maintained (PN). Irrigation activation performed using XP-endo finisher. Samples were longitudinally sectioned, and apical 1, 3, and 5 mm smear layer scores were assessed using a scanning electron microscope at ×2000. The smear layer scores from 1:4 were recorded as ordinal data.

Statistical Analysis:

Data were represented as median and interquartile range. Intergroup comparisons were performed using the Mann–Whitney U-test. Intragroup comparisons were analyzed using the Kruskal–Wallis test.

Results:

Apical patency improved the cleaning potentials of XP-endo Finisher at apical 1 and 3 mm without statistical significance, while at 5 mm, it showed a statistical significance (P < 0.5). Apical 1 mm showed the least smear layer removal abilities, while 5 mm showed the best.

Conclusion:

XP-endo Finisher irrigation activation proved high cleanliness abilities in curved root canals, which improved when canal patency was maintained during the treatment. One millimeter apical segment has reported the lowest cleanliness regardless of whether canals patency was maintained or not.

INTRODUCTION

The goal of disinfection of the root canal system has been carried through chemomechanical preparation of root canals utilizing variable irrigants and instruments.[1] Constant efforts have been implemented to secure an armamentarium that guarantees optimum disinfection of the root canal system.[2] Displeasing sequel of dentin wall instrumentation is smearing and debris loading on the root canal walls, which limits the action of irrigants and the obturation material–dentin wall adherence (tight seal).[3] Another tooth-related factor that might restrict effective cleaning of the root canal is anatomical complexities including variations in numbers, size, cross-section, and curvature.[4] About 84% of root canals have been reported with curvature, which sheds light on how they can be properly managed.[5] Difficulties in the management of curved root canals are not only limited to difficulties in working length determination, patency achievement, and instrument fatigue, but also include the proper cleaning of the root canal walls compared to straight root canals.[6,7] Researchers reported low cleaning ability of different manual and rotary files at the apical one-third of the root canal, which is the part of the root canal reported to have variable anatomical complexities, especially in curved roots.[8,9] Apical patency has been introduced by Buchanan and approved by the American Association of Endodontics as a possible approach that would maintain the root canal apical portion debris-free.[10] Poor cleaning of the apical root third has been reported and attributed to complex anatomy, existing tissues, and entrapped gas bubbles that impede proper cleaning at the apical third.[5] Apical patency has reported less debris accumulation with passive ultrasonic irrigation compared to nonpatent canals, and patent canals showed a lower percentage of gas bubbles than nonpatent canals (25% and 40%, respectively).[11] XP-endo Finisher is a MaxWire-made innovative finishing file by (FKG Dentaire, La Chaux-de-Fonds, Switzerland); a zero-taper, # 25 file has the ability to transform by working at body temperature with subsequent contractions and expansions, which offers irrigation agitation and canal wall scraping.[12,13] It has proved cleaning efficiency on debris accumulated in root canals isthmus and reduction of bacterial load in oval-shaped root canals.[14,15] Debris on root canal walls investigation gave a clue about how effective is the cleaning and shaping and spotlighted the necessity to evolve materials, instruments, and techniques to facilitate this mission along with preservation of the tooth integrity.[16] The influence of apical patency during primary endodontic treatment of curved root canals on cleaning ability of XP-endo Finisher has not been investigated yet. This work aimed to investigate the impact of maintaining apical patency on the root canal wall cleaning potentials of XP-endo Finisher in the apical third of curved root canals.

MATERIALS AND METHODS

The study protocol was submitted and approved by the institution’s ethics committee (TUCDREC/161125/RAbdelgawad). The size of the sample was determined using G*Power software version 3.1.9.6 (Heinrich-Heine-Universitat Düsseldorf, Düsseldorf, Germany), derived the data from similar studies with an effect size of 0.57, α =0.05, β =0.05, and test power = 0.95.[17,18] Thirty mandibular premolars were assigned for this study, 15 for each group. Teeth were selected from fresh-extracted human teeth for periodontal, prosthetic, or orthodontic reasons. Teeth with incomplete root formation, cracks, resorptive defects, or previous endodontic treatment were excluded. Radiographic imaging of the teeth was performed to confirm Vertucci type I root canals, and images were used to determine the angle of root curvature following Schneider’s method.[19,20] Teeth with curvature angle range 25^o:30^o were selected, and pairs of teeth with the same angle of curvature were allocated randomly in the study groups: group patency maintained (PM) and patency not maintained (PN), and then, all were stored for a week in 2% thymol solution at room temperature.[5] The sample length was adjusted to 17 mm by reducing the crown occlusal surface with a diamond disc (Henry Schein, Inc., Melville, NY, USA). Access cavities were adjusted using #3081 diamond burs (KG Sorensen, São Paulo, Brazil), K-file size#10 was inserted to adjust the working length measurement, and root canals where K-file size #15 did not fit at working length were excluded and replaced.[5] With the aim of mimicking the clinical environment, root apices were sealed using a layer of pink wax, and samples were coated with a separating medium and put up in acrylic resin blocks using a 1.5 mm × 1.5 mm × 2 mm rubber mold (Shofu Inc., Kyoto, Japan), and apical curvature was kept oriented in the same direction during mechanical preparation.[21] Root canals were instrumented using Mtwo files to size 30, 4% following manufacturer instructions (VDW GmbH, Munich, Germany).[22] Apical patency was maintained only in the PM group using K-file size #10, succeeding each rotary file 0.5 mm longer than working length. Root canal irrigation consumed a total of 2 ml of 3% sodium hypochlorite (NaOCl) (Formula and Action, São Paulo, Brazil) per canal following each file use. During agitation and final rinse, NaOCl irrigant was placed in 37^oC water bath to maintain its warmth; 2 ml was dispensed 1 mm shorter of working length using a passively inserted 30G needle (Ultradent Products Inc., South Jordan, Utah, USA).[23] XP-endo Finisher used in gentle vertical strokes with 7–8 mm in–out motion for 1 min at a speed of 1000 and 1.0 Ncm, then debris final flash-out using 2 ml of saline solution.[12] Samples were displaced passively from resin blocks, under microscopic ×10 (Carl Zeiss Meditec, Oberkochen, Germany); two shallow opposite longitudinal grooves at labial and lingual surfaces were carefully made using a diamond disk (Jota, Ruthi, Switzerland) without penetrating root canals, and then, halves were separated carefully with a chisel and mallet and carefully examined to pick out the one that distinctly displayed the apical third.[24] Photomicrographs of the apical third at 1, 3, and 5 mm from the apical foramen were supplied at ×2000 using a scanning electron microscope (SEM) (Quanta FEG-250, the Netherlands). Two experienced endodontists assessed 30 randomly selected micrographs for calibration of interoperator agreement, and micrographs assessment performed following Rome et al.’s four-scale scoring: 1 – clean root canal wall and all dentinal tubules open, 2 – minimal amount of smear layer, >50% of the dentinal tubules open; 3 – moderate amount of smear layer, <50% of dentinal tubules open; and 4 – heavy smear layer with complete obliteration of dentinal tubules.[25] Ninety photomicrographs were examined blindly without identifying either the group or the segment examined, and the data were subjected to statistical analysis.

Statistical analysis

Interoperator agreement was assessed using Cohen’s kappa test (Minitab 18.1, Minitab, Inc., Pennsylvania State University, PA, United States). The smear layer scores (1:4) were recorded as ordinal data for each segment: 1 mm, 3 mm, and 5 mm. Data were represented as median and interquartile range. Intergroup comparisons at each segment were performed using the Mann–Whitney U-test. Intragroup comparisons among the three segments were analyzed using the Kruskal–Wallis test. The Chi-square test was used to compare clean (score 1 + 2) or not clean (score 3 + 4) records in study groups at each segment investigated as well as to compare the three segments within each group. Statistical significance was set at P < 0.05. Data were analyzed with IBM SPSS Statistics (Armonk, New York, USA), version 25 for Windows.

RESULTS

Interoperator record agreement was reported with a 0.92 kappa value. Table 1 and Figure 1 demonstrate a comparison of recorded smear layer removal scores in the PM group and the PN group in three investigated segments (1, 3, and 5 mm). Data showed a statistically nonsignificant difference among the PM and PN groups in both 1 mm and 3 mm segments (P = 0.539, 0.116), respectively, while in 5 mm, the PM group reported significantly higher median values (P = 0.016). Intragroup comparison revealed statistically no significant difference between median values in 1 mm, 3 mm, and 5 mm sections in the PM and PN groups (P = 0.036, 0.917), respectively.

Table 1.

Inter- and intragroup comparison of median score values and interquartile range

Segments	PM group, median (IQR)	PN group, median (IQR)	P
1 mm	2 (3–2)	3 (3–2)	0.539 (NS)
3 mm	2 (2–2)	2 (3–2)	0.116 (NS)
5 mm	2 (2–2)	2 (3–2)	0.016*
P	0.036 (NSG)	0.917 (NSG)

*Statistically significant difference between data at P≤0.05 using the Mann–Whitney U-test. NS: Nonstatistically significant difference between data at P>0.05 using the Mann–Whitney U-test, NSG: Nonstatistically significant difference between data at P>0.05 using the Kruskal–Wallis test. IQR: Interquartile range, PM: Patency maintained, PN: Patency not maintained, NS: Nonsignificant, NSG: Nonsignificantly greater

Figure 1.

Photomicrographs for apical third segments (1, 3, and 5 mm) of the experimental groups, with patency maintained and patency not maintained. PM: Patency maintained, PN: Patency not maintained

Table 2 demonstrates the distribution of frequency and percentage of clean (score 1 + 2) and not clean (scores 3 + 4) in both the groups’ assessed segments (1, 3, and 5 mm). The highest clean scores (93.33) were recorded in 5 mm segment of the PM group, and the lowest clean scores (46.67%) were reported in 1 mm segments of the PN group, while the highest not clean scores (53.33%) were recorded in 1 mm segments of the PN group and the lowest (6.67%) in 5 mm segments of the PM group. Both the PM and PN groups showed no significance between frequency and percentage of clean and not clean scores in 1 and 3 mm segments (P = 0.464, 0.121), respectively, while there was a significant difference between clean and not clean scores in 5 mm segment of both the groups (P = 0.13).

Table 2.

Frequency and percentage of the clean (score 1+2) and not clean (score 3+4) in patency maintained and patency not maintained groups at 1, 3, and 5 mm segments

Segments	PM group		PN group		P
	Clean, frequency (%)	Not clean, frequency (%)	Clean, frequency (%)	Not clean, frequency (%)
1 mm	9 (60)	6 (40)	7 (46.67)	8 (53.33)	0.464 (NS)
3 mm	12 (80)	3 (20)	8 (53.33)	7 (46.67)	0.121 (NS)
5 mm	14 (93.33)	1 (6.67)	8 (53.33)	7 (46.67)	0.013*

*Statistically significant difference between data at P≤0.05 using the Chi-square test. NS: Nonstatistically significant difference between data at P>0.05 using the Chi-square test. PM: Patency maintained, PN: Patency not maintained, NS: Nonsignificant

DISCUSSION

The standard of mechanical and chemical debridement of the root canal grants the success of root canal treatment.[26] Debridement tools and techniques can be assessed through investigating their potentials to clear dentin walls from debris and smear layer.[21] Lasting debris and smear layer are physical and biological obstacles able to interdict disinfection and seal of the root canal system.[27] Limitations of optimum cleanliness achievement of apical third canal wall using chemical, mechanical tools, and techniques, which have been reported effective at middle and coronal root thirds, were inferred to structural, physical, and anatomical properties of apical dentin.[8,9] These considerations are aggravated more in curved roots, where curvature might impede free instrument movement and irrigation circulation.[28]

Although endodontic files are the tool of root canal mechanical debridement, they are incompetent of thorough wall debridement, and their work on dentin wall creates a smear layer that consequently must be removed.[18] Hence, the role of irrigation in the elimination of debris and disinfection of the root canal system is boosted, and one of the modalities to intensify irrigation efficacy is to establish intraradicular irrigation activation to assist the access of irrigation through the entire root canal system.[29] Although passive ultrasonic activation, self adjusting file activation, and other irrigation activation tools have proven effective dentin debridement, limited capacity has been reported at root apical third, necessitating further efforts to secure an optimum debridement tool of root canal system.[27]

The XP-endo Finisher has been fabricated to provide safe and effective irrigation activation. It has been manufactured from a unique nickel–titanium alloy (Max-Wire) that, once subjected to temperature change in root canals (high temperature), transformed from martensite to austenite phase, enabling the file to transform from straight to curved (anatomic) with enhanced adaptation to canal walls.[12] XP-endo Finisher reported more intraradicular bacterial load reduction and biofilm elimination than passive ultrasonic activation, but none were able to manage the canals’ isthmus. It showed comparable intracanal medicament removal ability with passive ultrasonic activation, self-adjusting file, and canal brush at the cervical root third, but none were able to provide entirely clean walls.[14,15] Moreover, it showed similar smear layer removing potentials to EndoVac in curved canals and to passive ultrasonic activation with limited efficiency for all to establish debris-free apical third.[28]

The concept of root canal patency has been proven to have a favorable impact on the mechanical and biological objectives of the treatment procedure.[11] Apical patency enhanced the extent of irrigation solution toward the working length in adjuncts with ultrasonic activation of NaOCl.[29] Patency file proved a significant ability to burst bubbles in the coronal and middle thirds, enabling access to the apical third.[11] Other studies by Tay et al. and Gu et al. demonstrated that the existence of gas bubbles entrapped in the apical third of the root is able to restrict the flow of the irrigation.[30,31] In spite of the studied impact of apical patency on root canal treatment procedures, starting with facilitating the glide path and working length determination accuracy to proven long-term treatment success, there is no available data that investigate its impact on cleaning potentials in curved root canals that received primary root canal treatment. Considering the reported inability of chemical and mechanical cleaning approaches in the root canal apical third optimum cleaning, this study was concerned with the assessment of the apical third’s wider surface area and gave more details about three segments of the apical third.

Debris-free dentin walls and patent dentinal tubules observation with SEM root surface magnification is a reliable methodology; however, magnification gave a feedback of a small surface area.[26] In this study, the apical third was divided into three segments to allow more surface area assessment. On the other hand, various qualitative scoring methods of smear layer are well-documented methods for gauging.[26] In this methodology, root canal wall micrographs at ×2000 were assessed following Rome et al.’s four-scale scoring.[25] The sample inclusion criteria (tooth type, length, curvature, and initial size), preparation (instrument size and type), and irrigation protocol (materials, volume, duration, and sequence) were congruent to eliminate their probable influence on the results.[32] XP-endo Finisher displayed high cleaning standards, whether patency was maintained or not, 64% of apical third segments were recorded as clean, 36% was not clean, and none of the segments displayed heavy debris with obliterated dentinal tubules (score 4). The cleaning potentials of XP-endo Finisher were attributed to the file transfigure from straight to spoon-like upon structure phase transformation when working in warmer root canals, and this allows better activation of irrigation, touches, and effectively debrides canal walls.[12,13]

Maintained apical patency recorded a positive impact on XP-endo Finisher cleaning potentials; 38.9% of apical segments reported clean canal walls in the PM group versus 25.6% of the PN group. This was explained due to the patency file’s ability to burst the entrapped gas bubble and open the access for irrigation to untouched canal walls.[31] Although the positive impact of maintained apical patency through root canal treatment on the cleaning potentials of XP-endo Finisher irrigation activation, the intended root canal wall cleanliness has not been achieved yet.

Proximity to apical foramen at 1 and 3 mm segments displayed less clean walls than 5 mm segment, where XP-endo Finisher cleaning potentials were the highest. This zone-related limited cleanliness ability was on account of morphological, anatomical, and structural characteristics of the canal wall, which reported constraints against the achievement of optimum three-dimensional cleanliness.[11] This study revealed the imperative necessity of continuous work to come up with suitable tools, materials, and maneuvers to achieve the optimum three-dimensional root canal cleanliness.

CONCLUSION

XP-endo Finisher irrigation activation proved high cleanliness abilities in curved root canals, which improved when canal patency was maintained during the treatment. 1 mm apical segment has reported the lowest cleanliness, regardless of whether canals patency was maintained or not.

Clinical relevance

Root canals’ morphology is considered a major obstacle for achieving effective cleaning and consequently impacts the success of root canal treatment. Continual work to provide techniques, materials, and instruments to achieve this goal is crucial. Apical patency proved a positive impact on the effectiveness of cleaning and shaping procedures; this research investigated its influence on XP-endo Finisher cleaning potentials in the apical third of curved root canals.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.