Evaluation of Root Dentinal Damage Associated with ProTaper Gold, WaveOne Gold, and ProTaper Next during Cleaning and Shaping Procedures: An In vitro Analysis.

AIM: The purpose of this study is to evaluate and compare the incidence of dentinal defects after root canal shaping using rotary nickel-titanium (Ni-Ti) instruments (ProTaper Gold [PTG] and ProTaper Next [PTN]) and reciprocating instrument (WaveOne Gold [WOG]).
MATERIALS AND METHODS: One hundred human mandibular premolars with single root and single canal with canal curvature <10° were randomly divided into five groups (n = 20 teeth per group). The root canals were instrumented using hand K-files (positive control), full sequence rotary files PTG and PTN, and reciprocating single-file system WOG. One group was left unprepared and served as negative control. Roots were sectioned horizontally at 3, 6, and 9 mm from the apex and evaluated under a stereomicroscope.
RESULTS: PTG, WOG, and PTN showed dentinal defects in 40%, 53.3%and 30% of the samples, respectively.
CONCLUSION: Irrespective of motion kinematics, dentinal defects are observed in all the Ni-Ti file groups. Within the limitations of the present study and the available literature, incidence of dentinal defects is less with instruments working in continuous rotation rather than instruments with reciprocating motion. Copyright:

INTRODUCTION

The ultimate goals of conventional and modern endodontic instrumentation are complete removal of microorganisms and tissue debris, by enlarging the canals to an adequate size so as to create a canal form that permits a three-dimensional seal.[1] During root canal preparation, the canal is cleansed by the contact between the instrument and the canal walls, which creates many momentary stress concentrations in the root dentin. In most of the cases, the use of rotary file systems usually creates more stresses in the radicular dentin.[2] Such stress concentrations may induce dentinal defects in the form of microcracks or craze lines, which could ultimately lead to vertical root fracture, which is one of the frustrating complications of root canal treatment often resulting in tooth loss.[23]

The newer rotary file system ProTaper Gold (PTG; Dentsply Maillefer, Ballaigues, Switzerland) and reciprocating system WaveOne Gold (WOG; Dentsply Maillefer, Ballaigues, Switzerland) are manufactured with a gold heat treatment procedure. Gold heat treatment is carried out by heating the file and then cooling slowly which differs from the premanufacturing heat treatment used in M-Wire technology. This process gives the file its distinctive gold finish and improves the strength and elasticity of the file.[4] These design variations of rotary nickel-titanium (Ni-Ti) files may also alter the forces acting on the root during instrumentation, contributing to the incidence of dentinal effects.[5] There is scant literature pertaining to comparative evaluation of dentinal defects caused by PTG and reciprocating system WOG. Hence the aim of this investigation is to evaluate and compare the dentinal defects induced by full sequence rotary files PTG and ProTaper Next (PTN; Dentsply Maillefer, Ballaigues, Switzerland) with that of reciprocating single file system (WOG; Dentsply Maillefer, Ballaigues, Switzerland).

MATERIALS AND METHODS

Selection of teeth

One hundred freshly extracted human mandibular premolars with single roots and straight canal with canal curvature <10° were selected for the study.[6] Teeth with open apices or anatomic irregularities were excluded. All the teeth samples were decoronated at 15 mm from the apex to standardize the length and to achieve straight-line access. Radiographs were taken both mesiodistally and buccolingually to evaluate the canal width and to check for the second canal. All the samples were checked for external defects and cracks under a stereomicroscope (Stemi SV6; Zeiss, Jena, Germany) and are replaced with new teeth if defects were noticed. Canal orifice of the decoronated teeth was negotiated with DG 16 endodontic explorer (Hu-Friedy, Chicago, IL, USA), and then, canal patency was established with a size 10 K-file (Dentsply Maillefer, Ballaigues, Switzerland). As mentioned in the previous studies, the roots were covered with a single layer of aluminum foil and inserted in acrylic resin (DPI-RR Cold cure acrylic resin: Dental products of India; Wallace street, Fort, Mumbai) set in an acrylic tube. The roots were then removed from the acrylic tube, and the aluminum foil was removed from the root surfaces. A light body of hydrophilic vinyl polysiloxane impression material (Imprint II Garant, 3M ESPE, USA) was used to replace the space created by the foil which represented a simulated periodontal ligament, and the roots were immediately repositioned.[7]

Preparation of samples

Twenty teeth were left unprepared and served as negative control. The remaining eighty teeth were randomly divided into four experimental groups (n = 20), namely K-File group, PTG group, PTN group, and WOG group. The working lengths (WLs) of the canals were determined by inserting a size 10 K-file into the root canal terminus and subtracting 1 mm from this measurement. The root canal preparation was then carried out with the respective files of each group with the aid of X smart plus endodontic motor (Dentsply Maillefer, Ballaigues, Switzerland). In each of the 4 test groups, 1 set of instrument was used to prepare 4 root canals.

Group A: (negative control): The samples were left unprepared. The samples were irrigated with 2% sodium hypochlorite (Vensons India, Malleswaram, Bengaluru).

Group B: (positive control): K-file was used up to apical size # 25 at WL and step back till size # 60.

Group C: PTN was used to prepare canals with the aid of X-Smart Plus endodontic motor at 300 rpm and 2 Ncm torque till apical size 0.06 25 with a continuous in and out movement. The following sequence was used. X1 17/04 (till full WL) and X2 25/06 (till full WL).

Group D: PTG rotary file was used to prepare the roots. The canal was enlarged till apical size 0.08 25 with a continuous in and out pecking motion. PTG instruments were used at 300 rpm with a torque of 3 Ncm for Sx and S1 instruments, 1.5 Ncm for F1 instruments, and 2 Ncm for F2 instruments. The following sequence was used: Sx file (1/2 of the WL), S1 and S2 files (2/3 of the WL), F1 file (size 20, 0.07 taper), and F2 (size 25, 0.08 taper) file (full WL).

Group E: Reciprocating single file system WOG was used as per manufacture's recommendation till apical size 0.07 25. The WOG file was introduced into the canal in a slow in-out pecking motion until it reached the full WL.

In all the experimental groups, each canal was irrigated with 2% sodium hypochlorite between each sequential instrument. A total of 15 mL of sodium hypochlorite was used for each root for 1.5 min. After completion of the preparation, the canals were irrigated with 5 ml of distilled water for 1.5 min. All the preparation procedures were performed by a single experienced operator. Throughout the experimental procedures, the tooth-resin block assembly was stored in distilled water, to keep them moist.

Sectioning and stereomicroscopic evaluation

The teeth samples were removed from the resin block assembly atraumatically and were sectioned perpendicular to the long axis of the tooth at 3, 6, and 9 mm from the apex with a low speed saw (Leica SP1600, Wetzlar, Germany) under water cooling. The tooth slices were then viewed under a stereomicroscope at ×12 magnification, and digital images of each section were captured. Defects if present were categorized as the following:

No defect

When craze lines or cracks are not observed on both the external or internal surface of the root.

Complete defect/fracture

When a line extends from the canal lumen to the outer surface of root.

Other defects

All lines confined within dentin that did not extend from the canal lumen to the outer surface or vice versa. (e.g.; a craze line, which is a line extending from the outer surface into the dentin but does not reach the canal lumen, or a partial crack, which is a line extending from the canal walls into the dentin without reaching the outer surface).

Statistical analysis

Results were expressed as the number and percentage of defective roots in each group. A Chi-square test was performed to compare the appearance of defective roots between the experimental groups by using the SPSS/PC version 17 (SPSS Inc., Chicago, IL, USA). The level of significance was set at 0.05.

RESULTS

Table 1 shows the coronal one-third sections revealed defects in the percentage of 30%, 40%, and 10% for PTG, WOG, and PTN, respectively. Table 2 depicts middle one-third sections revealed defects in the percentage of 30%, 50%, and 50% for PTG, WOG, and PTN, respectively. Apical one-third sections revealed defects in the percentage of 60%, 70%, and 30% for PTG, WOG, and PTN, respectively [Table 3].

Table 1

Comparison of tooth preparation at coronal 3rd

File preparations	Defect
	No defect (%)	Partial crack (%)
Unprepared tooth	20 (100.0)	0
K-file	20 (100.0)	0
ProTaper Gold	14 (70.0)	6 (30.0)
WaveOne Gold	12 (60.0)	8 (40.0)
ProTaper Next	18 (90.0)	2 (10.0)
Total	84 (84.0)	16 (16.0)

χ2=19.643, P=0.001, S: Significant

Table 2

Comparison of tooth preparation at middle 3rd

File preparations	Defect
	No defect (%)	Partial crack (%)
Unprepared tooth	20 (100.0)	0
K-file	20 (100.0)	0
ProTaper Gold	14 (70.0)	6 (30.0)
WaveOne Gold	10 (50.0)	10 (50.0)
ProTaper Next	10 (50.0)	10 (50.0)
Total	74 (74.0)	26 (26.0)

χ2=26.195, P<0.001, S: Significant

Table 3

Comparison of tooth preparation at apical 3rd

File preparations	Defect
	No defect (%)	Partial crack (%)
Unprepared tooth	20 (100.0)	0
K-file	20 (100.0)	0
ProTaper Gold	8 (40.0)	12 (60.0)
WaveOne Gold	6 (30.0)	14 (70.0)
ProTaper Next	14 (70.0)	6 (30.0)
Total	68 (68.0)	32 (32.0)

χ2=39.338, P<0.001, S: Significant

DISCUSSION

The success of root canal treatment depends on complete removal of pulp tissue, debris, microorganisms, and their by-products through proper instrumentation and irrigation protocols, such that an almost sterile environment is created to receive the obturating material, which seals the canal space three dimensionally.

The Ni-Ti file groups used in the present study, namely PTG, WOG, and PTN demonstrated dentinal damage in 40%, 53.3%, and 30% of the samples, respectively. Reciprocating file system produced more dentinal defects in the apical third than the rotary systems, which is in agreement with the study conducted by Bürklein et al. An increased cutting efficiency is associated with increased cleaning. The variations in the amount of dentinal defects may be attributed to preparation technique and the cross-sectional design of the instruments.[89]

The cross-section of WOG is a parallelogram with two 85° cutting edges, with an off-centered cross-section where only one cutting edge is in contact with the canal wall. PTN has an off-centered rectangular design with a progressive and regressive percentage taper (variable taper) on a single file and is made by M-Wire technology. This off-centered rectangular design produces a mechanical wave of motion which travels along the working part of the instrument and decreases the screw effect, dangerous taper lock, and torque, on any given file by minimizing the contact between the file and the dentin.[610] PTG system has an instrument design with a triangular cross-section and a variable progressive taper similar to that of ProTaper Universal but are more flexible and have been developed with proprietary advanced metallurgy.[1112]

The WOG produced more dentinal cracks in the apical third compared with that of rotary file systems used in this study. Hence, it may be hypothesized that the use of only one instrument for complete preparation of the canal may lead to generation of more internal stress during mechanical instrumentation compared with canal instrumentation using full-sequence systems.[9] Studies have shown that ProTaper Universal which shares the same cross-sectional design as that of PTG produced more dentinal defects (56%) in the apical third of treated roots.[6] In the present study, similar results are observed for PTG because of the similarity with ProTaper Universal in the geometry, tip design, and taper. Moreover both PTG and ProTaper Universal have same number of files for shaping as well as finishing.[13]

The exact simulation of the in-vivo conditions is not very feasible in most of the in-vitro studies. Hence within the limitations of this in-vitro investigation, it could be concluded that motion kinematics plays a significant part on the induction of dentinal damage during the canal preparation. Further, newer file systems with novel design features should be compared with file systems of the present study.

CONCLUSION

Within the limitations of this in vitro study, we conclude that irrespective of motion kinematics, dentinal defects are observed in all the Ni-Ti file groups. The instrumentation of root canals with PTG, PTN, and WOG instruments can cause crack formation in root canal dentin. The WOG reciprocating system produced more dentinal defects than that of rotary systems PTN and PTG.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.