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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 3  |  Issue : 1  |  Page : 58-64

Cone-beam computed tomography analysis of centering ability and transportation of curved root canals prepared with three rotary nickel-titanium systems (In Vitro-Study)


1 Dental Intern at Faculty of Dentistry, Umm Al-Qura University, Makkah, Saudi Arabia
2 Associate Proffessor of Endodontics, Cairo University, Egypt

Date of Web Publication21-Mar-2018

Correspondence Address:
Dr. Hanan Yahya Fallatah
Dental Intern at Faculty of Dentistry, Umm Al-Qura University, Makkah
Saudi Arabia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijssr.ijssr_21_17

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  Abstract 

Objective: The aim of this study is to compare the degree of transportation, centering ability, and dentin thickness after mechanical preparation using three different nickel-titanium rotary instrumentation systems, ProTaper Next (PTN), twisted file (TF), and K3 Endo in curved root canals analyzed using cone-beam computed tomography (CBCT). Materials and Methods: Thirty moderately curved roots of extracted human maxillary and mandibular molars were divided into three groups with 10 root canals each. Group I, the root canals were prepared with PTN rotary system; Group II, the root canals were prepared with TF rotary system; and Group III, were prepared with K3 rotary file system. Preinstrumentation and postinstrumentation three-dimensional CBCT images were obtained from root cross sections in three levels; coronal, middle, and apical third. Results: It was observed that there were no significant differences in the degree of canal transportation at apical level and the remaining dentin thickness between the rotary instruments (P > 0.05). There were no statistical significant differences in centering ability between buccolingual centering ratio after using the three systems at coronal and middle levels (P > 0.05) except for apical level is significantly difference (P = 0.047). In addition, there were no statically significant differences between centering ratio after using the three systems at cervical, middle, and apical levels (P > 0.05). Conclusions: Under the conditions of this study, CBCT analysis showed that the TF has the ability to produce centered preparation maintaining the original root canal anatomy in the apical one-third of the root canal while PTN showed some degree of canal deviation and K3 showed the highest canal deviation.

Keywords: Canal transportation, centering ability, cone beam computed tomography, curved root canals, dentin thickness, rotary systems


How to cite this article:
Fallatah HY, El Sherief SM. Cone-beam computed tomography analysis of centering ability and transportation of curved root canals prepared with three rotary nickel-titanium systems (In Vitro-Study). IJS Short Rep 2018;3:58-64

How to cite this URL:
Fallatah HY, El Sherief SM. Cone-beam computed tomography analysis of centering ability and transportation of curved root canals prepared with three rotary nickel-titanium systems (In Vitro-Study). IJS Short Rep [serial online] 2018 [cited 2019 Jan 18];3:58-64. Available from: http://www.ijsshortreports.com/text.asp?2018/3/1/58/226568


  Introduction Top


The main goal of root canal treatment is complete eradication of microorganisms through adequate instrumentation, proper use of irrigants, and three dimensional obturation to prevent recurrent infection.[1] Canal shaping has always been challenging, demanding a high skill, especially when performed in curved roots. One of the most important steps of instrumentation is to keep the natural root canal morphology without canal deviation, ledge formation, apical transportation, and instrument separation.[2],[3],[4]

There are many rotary nickel-titanium (NiTi) systems available, which have improved the quality of canal shaping. The superelasticity of the alloy enhanced the preparation of curved canals.[5],[6] Moreover, NiTi systems provide many advantages; as it save time, keep the original taper of the canal, more centralized canal and minimize procedural errors.[7],[8] The ProTaper Next (PTN) system is made of a unique NiTi alloy and M-wire alloy that improves the resistance to cyclic fatigue while retaining cutting efficiency.[9],[10] It is composed of three instruments and has a variable taper design, which enhances the strength and flexibility.[11],[12] Recently, the concept of using a PTN reciprocating motion has been introduced; operating files in reciprocating motion enhances their cyclic fatigue resistance.[13]

The twisted file (TF) system has been developed with R-phase heat treatment and twisting of the metal, which are claimed to enhance strength properties, increase flexibility, and resistance to fatigue, decreasing transportation curved root canals, the motion of the TF system adapts automatically to a continuous rotary or reciprocating movement.[14]

The K3 rotary NiTi file system is combines excellent cutting characteristics with a strong sense of tactile control, excellent fracture resistance applicable to virtually any canal anatomy. These instruments are designed with an asymmetrical cross-section and wide radial lands, that increase the resistance to torsional stresses of the instrument.[15] The optimum cutting efficiency feature of K3 is a result of its slightly positive rake angel.[16],[17],[18]

Different methods have been researched to investigate the efficiency of root canal preparation before and after instrumentation. Although the more recently, the use of cone-beam computed tomography (CBCT) has a high diagnostic quality, with short scanning times and radiation dosages reportedly up to 15 times lower than those of conventional CT scans. CBCT allow measuring the amount of dentin removed by endodontics, has better accuracy than conventional radiograph in assessing the degree of canal curvatures.[19],[20],[21]

The objective of this in vitro study was to compare the shaping outcome of PTN, TF, and K3 rotary systems in terms of degree of transportation, centering ability, and dentin thickness in curved root canals analyzed by CBCT.


  Materials and Methods Top


Specimen selection

A total of thirty extracted human maxillary and mandibular molars teeth were used in accordance with approval from the Institutional Review Board at UQUDent (UQUDent-IRB).

The selected teeth with fully formed apices, with no calcifications or anatomic abnormalities, root curvature ranging from 30° to 40°.

Teeth with restoration or caries invading the pulp or extending onto the root surface were excluded from the study sample.

Specimen preparation

Teeth were cleaned, disinfected, and stored in 0.9% saline solution at room temperature. All specimens were decoronated at the cemnto-enamel junction with a diamond cutting disk (Dentsply, Maillefer, Ballaigues, Switzerland) to standardize root canal length (16 mm). The working length were established by inserting a 10 K-file (Dentsply, Maillefer, Ballaigues, Switzerland) to root apex and subtracting 1 mm from this measurement. Teeth were mounted into a mold with transparent acrylic resin.

Instruments and preparation technique

The samples were randomly divided into three groups with 10 root canals each according to the instrumentation technique.

Random distribution of the groups had been considered the degree of canal curvature, allowing the average curvature. All instrumentation was performed by a single operator according to the manufacturers' instructions. In each groups, each file was discarded after the preparation of three root canals. Each file was coated with Glyde™ (Dentsply Maillefer) as a lubricant. Sodium hypochlorite (2.5%), 5 mL was used for irrigation after each file, using a syringe with a 30-gauge needle (Max-i-probe, Hawe-Neos, Dentsply, Bioggio, Switzerland). One minute (17%) ethylenediaminetetraacetic acid (Ultradent, South Jordan, UT) rinses to remove smear layer followed by a final sodium hypochlorite flush.

After creation of a reproducible glide path by hand instruments, the canal was cleaned and shaped using rotary instruments with a contra-angle handpiece powered by endodontic micromotor (X-Smart™, Dentsply/Maillefer, Ballaigues, Switzerland) for each group as follows:

ProTaper Next group

The PTN (Dentsply Maillefer, Ballaigues, Switzerland) instruments were used in a crown-down manner in a continuous in and out motion, without forcing them apically.

Twisted-file group

The TF (Sybron Dental Specialties, Orange, CA, USA) instruments were used in a crown-down manner in a continuous controlled in and out motion, without forcing them apically.

K3 group

The K3 file (SybronEndo, Orange, CA, USA) instruments were used in a crown-down manner using a gentle in and out pecking motion, 1–2 mm depth per engagement.

Imaging of pre- and post-instrumented samples

Each mold was horizontally fitted to a chin support with its occlusal plane parallel to the plate. This was done to ascertain standardization of the specimens for the tomography images before and after root canal instrumentation. All teeth were scanned by Cone Beam I-Cat tomography with exposure time of 26.9 s, operating at 120 kvp and 37.07 mAs [Figure 1]. CBCT imaging was performed with 0.25-mm voxel size.
Figure 1: Representative cone beam computed tomography scans before (A-C) and after (D-F) instrumentation. Group I ProTaper Next at coronal (A-D), middle (B-E) and (C-F) apical level. (a) Group I ProTaper Next. (b) Group II Twisted File. (c) Group III K3

Click here to view


Digital impression and geometric measurements

IcatVision software was used to equalize the images pre- and post-instrumentation. The MPR Screen was selected for measuring. The “zoom” tool was applied to allow better visualization of the tooth. The vertical (blue and red) and horizontal (green) bars were used as reference to align the images. The tool “distance” was employed to determine measures from three areas of root canal, located, respectively, at 3 mm (coronal level), 6 mm (middle level), and 9 mm (apical level). The images were stored in a computer for later comparison.

Assessment of root canal preparation

The measurements of dentin thickness of the noninstrumented areas and the measurements after root canal preparation were calculated from the periphery of the pulp space to the outer surface of the tooth in all directions at three levels (coronal, middle, and apical).

The degree of transportation was calculated according to the formula given by Gambill et al. (Y1−Y'1)-(Y2−Y'2).[22]

where Y1 was the measurement of distance from the mesial aspect of the root to the root to the periphery of the noninstrumented canal. Y'1 was the measurement of distance from the mesial aspect of the root to the periphery of prepared canal. Y2 was the measurement of distance from the distal aspect of the root to the periphery of the noninstrumented canal. Y'2 was the measurement of distance from the distal aspect of the root to the periphery of the prepared canal.

Regarding transportation direction, canal transportation equal to 0 (zero) meant lack of transportation; a negative value represented transportation to the distal direction, and a positive value represented transportation to toward the mesial direction.

Centering ability was defined as the measurement of the ability of the instrument to remain centered in the canal.[22] This ratio was calculated for each section using the following ratio:

  • D1: (X1−X'1)/(X2−X'2)
  • D2: (Y1−Y'1)/(Y2−Y'2)


where D1 = the buccolingual measurement and D2 = the mesiodistal measurement. X1 was the measurement of distance from buccal aspect of the root to the periphery of noninstrumented canal. X'1 was the measurement of distance from the buccal aspect of the root to the periphery of the prepared canal. X2 was the measurement from the lingual aspect of the root to the periphery of the noninstrumented canal. X'2 was the measurement of the lingual aspect of the root to the periphery of the prepared canal. According to this formula, a result of 1 represents a perfect centering ability; the closer the result to 0 (zero), the worse is the ability of the instrument to remain centered.

Statistical analysis

Data were summarized by means of absolute frequency and relative percentage, and the numerical data by means of the usual descriptive statistics of location and dispersion. The results were statistically analyzed using one-way ANOVA test with Tukey's honestly significant difference was applies to intergroup comparison. A level of significance of 0.05 was adopted, using the (SPSS, Chicago, IL, USA).


  Results Top


Measurement of canal transportation

The Tuckey's post hoc test revealed that there was no statically significant difference in mesio-distal canal transportation between the rotary instruments (P > 0.05) at apical level (P = 0.582) [Table 1].
Table 1: The mean and standard deviation of canal transportation of three groups

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Measurement of centering ability

The means of D1 ranged from 0.34 to 2.86. There were no statically significant differences (P < 0.05) in centering ability between bucco-lingual centering ratio after using the three systems at coronal and middle levels (P = 0.579 and 0.482) except for apical level is significantly difference (P = 0.047).

The means of D2 ranged from 0.43 to 2.30. There were no statically significant differences (P < 0.05) between mesio-distal centering ratio after using the three systems at cervical, middle and apical levels (P = 0.065, 0.431 and 0.124 respectively) [Table 2] and [Figure 2].
Table 2: Mean and standard deviation of the buccolingual and mesiodistal measurements according to the instrument used and the root segment instrumented

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Figure 2: Mean of the D1 (buccolingual) and D2 (mesiodistal) measurements according to the used instrument and the instrumented root segment

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Measurement of dentin thickness

There was no statically significant difference between the three groups after instrumentation (P = 0.810). The amount of remaining dentin between ProTaper Next, Twisted File and K3 rotary systems was similar [Table 3].
Table 3: Mean and standard deviation of dentin thickness of three groups

Click here to view



  Discussion Top


The main goal of biomechanical root canal preparation is to shape a continuously tapered canal to allow effective irrigation and three dimensional obturation, and three dimensional obturation that permit hermetic seal to prevent reinfection.

In the present study, the extracted teeth were used because the complex root anatomy and the variable dentine hardness provide conditions that similar to the clinical situation.[23] Although their use compromises the standardization regarding the curvature degree and the abrasiveness [24],[25]. Many researches used simulated root canals in resin blocks as a method to standardize conditions, but their use does not simulate the mechanical instrumentation in root canals of human extracted teeth.[26]

Many researchers had made comparisons between straight and curved canals in relation to width measurements and other canal irregularities, they found that straight canals were prepared in an appropriate manner; however, the majority of prepared curved canals were hourglass in shape.[27],[28],[29]

There are many instruments have been developed, but only fewer instruments appear to be eligible of achieving the objectives of root canal instrumentation appropriately. The NiTi rotary instruments are mainly used in different design features that claimed to improve flexibility, cutting efficiency, safety, and canal shaping. Numerous studies have researched Ni-Ti rotary instruments.[7],[8],[30] The present study analyzed three different rotary systems-PTN, TF, and K3 to investigate canal changes in curved root canals of extracted human teeth, at three levels (coronal, middle, and apical) using CBCT.

The NiTi rotary files used in this study were designed to upgrade the several aspects of the properties required for root canal preparation instruments, including less canal transportation, less instrument separation, and procedural steps. Many previous researches have revealed that root canal transportation leads to excessive removal of dentin, with increased risk of canal straightening and ledge formation.[11],[31],[32] Both TF and K3 had in common the triangular cross-section geometry with different design in each. This similarity in results may attribute to the similar cross-section geometry of tested NiTi instruments.

The PTN rotary instruments have bilateral symmetrical rectangular cross-section with an offset from central axis of rotation that gives the file a rotational phenomenon known as swaggering movement as it advances into the root canal.

K3 instruments have good shaping ability according to the previous results.[33],[34] There are many other methods used to evaluate endodontic instrumentation with the aim of preserving the original canal curvature such as simulated root canal models,[35],[36] decalcification techniques,[37] sectioning techniques,[38] plastic blocks,[3] and microcomputed tomography.[39] However, these techniques have limitations that made the researchers to look for new methods that can produce more precise results.[40] Noninvasive CBCT scanning provides accurate, reproducible, three dimensional evaluations of any alterations in canal curvature, apical transportation, canal centering, and remaining dentin thickness pre- and post-instrumentation,[41],[42] it will be an incredible tool in endodontic analysis if we consider the minimum radiation dose, fast image acquisition, and submillimetric resolution.[20] In the present study, CBCT scans allowed assessment of root canal in three dimensional planes (axial, sagittal, and coronal planes). The axial plane from CBCT scans plays an important tool in to identify root curvature and canal transportation this was in accordance with de Alencar et al. 2010.[43] The first parameter evaluated in this study was canal transportation and the second parameter evaluated in this study was centering ability. The results of the present study showed that there were no significance differences between the three different instruments-PTN, TF, and K3. Wu et al. reported that apical transportation more than 0.3 mm might adversely influence the sealability of obturation material.[44] In the current study, the shaping ability of all groups was similar, considering the apical transportation and centering ability values in which none of the rotary systems used reached apical transportation >0.2 mm. The results of the present study reassured that Ni-Ti rotary files preserve canal curvature adequately this was in agreement with.[7],[17],[32],[45],[46],[47],[48],[49],[50],[51],[52],[53],[54] The above results corroborate with previous reports that show low rates of apical deviation of curved canals prepared with NiTi rotary instruments.[2],[8],[55],[56] Although in the present study, there was no statistical differences between the NiTi systems used, the data analysis shows a centralization tendency for TF. These results are possibly related to the minimal interaction of these instruments in the apical region. Whereby the anatomical diameter was established with a size 25 file and the final diameter related to a size 30 file. It is important to consider that this final diameter determination of TF is based on orientation provided by the respective manufacturers. Similar results and conclusion were achieved by Versiani et al., which reported favorable centering ability results with a final file with a size 30 diameter.[55]

The third parameter evaluated in this study was remaining dentin thickness at three different levels between the groups. No statically significance difference between PTN, TF, and K3. The amount of remaining dentin between the three different groups was similar.


  Conclusions Top


According to the limitations of this in vitro study, it could be concluded that CBCT analysis showed that the TF has the ability for producing centered preparation maintaining the original root canal anatomy in the apical one-third of the root canal, while PTN showed some degree of canal deviation while K3 showed the highest canal deviation.

There was no significant difference between the three rotary systems in dentin removal and canal transportation.

Acknowledgment

Before all and foremost I must thank Allah, the great almighty, the most merciful for giving me the patience and capability to complete this study. I would like to express my sincere gratitude to my advisor Dr. Samia Elsherief for the continuous support of my study and research, for her patience, motivation, enthusiasm, and immense knowledge. My sincere thanks also go to our dean Dr. Abdullaziz Khotani for granting us access to all what we need. Many thanks to Mr. Reda kamel for his assistant in the capture of the images and his production. Finally, I would like to thank my family for supporting me spiritually thorough the study.

.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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