Journal of Conservative Dentistry
Home About us Editorial Board Instructions Submission Subscribe Advertise Contact e-Alerts Login 
Users Online: 666
Print this page  Email this page Bookmark this page Small font sizeDefault font sizeIncrease font size

Table of Contents   
Year : 2015  |  Volume : 18  |  Issue : 6  |  Page : 453-456
Fracture resistance exhibited by endodontically treated and retreated teeth shaped by ProTaper NEXT versus WaveOne: An in vitro study

Department of Conservative Dentistry and Endodontics, YMT Dental College and Hospital, Kharghar, Navi Mumbai, Maharashtra, India

Click here for correspondence address and email

Date of Submission11-May-2015
Date of Decision08-Jul-2015
Date of Acceptance08-Sep-2015
Date of Web Publication2-Nov-2015


Aim: To compare the fracture resistance exhibited by teeth after primary endodontic treatment and retreatment.
Materials and Methods: One hundred freshly extracted human teeth were selected. 20 samples served as control (untreated). Eighty experimental samples were divided into two groups (n = 40) for instrumentation using rotary Protaper NEXT (PTN) or reciprocating WaveOne (WO) files and obturated using warm lateral compaction. Half of the samples (n = 20) from each group were subjected to a load. The remaining half were subjected to retreatment using Protaper universal retreatment files (RFs) followed by a file larger than the master apical file used in groups 1 and 2 and reobturated. Group A: Control, Group B: PTN + obturation, Group C: WO + obturation, Group D: RF + PTN + obturation and Group E: RF + WO + obturation. The retreatment specimens were also subjected to load and the readings acquired were statistically analyzed.
Result: When compared between the groups, control group exhibited the highest fracture resistance (P < 0.01). When multiple tests were performed, Group E exhibited significantly less fracture resistance (P < 0.01).
Conclusion: Endodontic treatment and retreatment both results in lowering the fracture resistance of a tooth.

Keywords: Fracture resistance; Protaper NEXT; retreatment; WaveOne

How to cite this article:
Khalap ND, Hegde V, Kokate S. Fracture resistance exhibited by endodontically treated and retreated teeth shaped by ProTaper NEXT versus WaveOne: An in vitro study. J Conserv Dent 2015;18:453-6

How to cite this URL:
Khalap ND, Hegde V, Kokate S. Fracture resistance exhibited by endodontically treated and retreated teeth shaped by ProTaper NEXT versus WaveOne: An in vitro study. J Conserv Dent [serial online] 2015 [cited 2023 Feb 1];18:453-6. Available from:

   Introduction Top

The role of endodontic instrumentation is to remove tissue debris and an infected inner layer of dentine, along with allowing a hermatic fluid-air tight seal. [1],[2] Vertical root fracture's (VRF) are the most challenging complication associated with endodontically treated teeth. [3] It is a longitudinally oriented fracture extending to the periodontium that may begin in the crown, root apex, or any point in between. [3],[4] The reasons attributed for increased susceptibility to fracture are dehydration, excessive loss of dentin, removal of caries, access cavity preparations, canal shaping techniques, effects of irrigating solutions, prolonged placement of calcium hydroxide, pressure during obturation, postplacement, tooth/crown preparation, and retreatment procedures. [5],[6],[7],[8],[9]

Various design features of the file systems such as the nickel-titanium (NiTi) core diameter, cross-sectional shape, rake angle, and flute depth affect the behavior of the file and, which in turn influences the generation of cracks, apical stress, and strain concentrations resulting in VRF. [10],[11]

Recently, newer generation NiTi instruments have been designed that is the Protaper NEXT (PTN) and WaveOne (WO) (PTN; Dentsply Tulsa Dental, Tulsa, OK). PTN files are uniquely designed such that the center of mass and the center of rotation are offset. [11],[12]

The WO (Dentsply Maillefer) NiTi single-file system functions in reciprocating motion. The counterclockwise engaging angle is 5 times the clockwise disengaging angle and is designed to be less than the elastic limit of the file. These instruments are manufactured with M-Wire technology which may increase flexibility and resistant to cyclic fatigue. [10],[11],[13]

Retreatment procedure aims to remove the entire obturating material. [12],[14] Various techniques have been advocated to remove obturating materials which may require more mechanical manipulation leading to more radicular dentine removal and subsequent dentinal defects. [13],[14],[15]

Studies show that the Protaper universal retreatment files (RFs) are ineffective for removing the entire obturating material and have suggested the use of supplementary files for better removal of root canal filling residues. [15],[16]

Hence, the current study was designed to compare the fracture resistance exhibited by teeth after initial endodontic treatment and retreatment using rotary PTN and reciprocating WO file systems.

   Materials and method Top

Specimen selection

Freshly extracted human mandibular premolars (for orthodontic treatment) with single straight canal were selected. Confirmation of single canal was done by bucco-lingual and mesio-distal angulated radiographs. The samples were decoronated to length of 15 mm with a diamond disk under water. The teeth were examined with a stereomicroscope under ×10 magnification to detect craze lines or cracks which were excluded from the study. The bucco-lingual and mesio-distal diameter of the roots were measured with Vernier calliper and standardization was done. Performing the above procedure resulted in 100 samples.

Group A

A total of 20 teeth were uninstrumented.

In the remaining 80 samples, hand instrumentation was done till #20 k-file.

Initial endodontic treatment

Group B: Instrumentation with Protaper NEXT

A total of 40 specimens were instrumented by PTN files till full sequence X2. These files were used in outward brushing manner at 300 rpm/2.6 nm. Three percent sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA) was used as an irrigant and lubricant alternatively between each file and recapitulation.

Group C: Instrumentation with WaveOne

A total of 40 specimens were instrumented by WO Primary file (25/.08) (Dentsply Maillefer, Ballaigues, Switzerland) in pecking motion, using X Smart Plus endomotor (Dentsply-Maillefer). These files were used in outward brushing manner at 300 rpm/2.6 nm. Three percent sodium hypochlorite and EDTA was used as an irrigant and lubricant alternatively between each file and recapitulation.

Obturation for Group B and C

After complete instrumentation, final irrigation was performed with 10 mL of 17% aqueous EDTA (Prime Dental Products, India) followed by 10 mL of sodium hypochlorite to remove the organic and inorganic smear layer. The canals were dried with sterile absorbent paper points. Following the manufacturer's instructions, the AH plus sealer (DentsplyDeTrey GmbH, Konstanz, Germany) was mixed and applied with master cone Gutta-percha within the root canal and obturated using lateral condensation technique. Excess Gutta-percha was sheared off and condensed with a heated plugger 1 mm below the canal opening. The orifice was sealed with Coltosol (Coltene-Whaledent, Cuyahoga Falls, OH, USA) and the teeth were stored at 37°C in 100% humidity for 2 weeks.

Retreatment technique

Twenty samples from group 1 and 2 underwent retreatment (Group D and E) after 30 days. Protaper Universal RFs (D1-D3; Dentsply Maillefer), were used at 300 rpm and 3 N/cm torque to remove the bulk of root canal filling. Endosolv R (Septodent, Cedex, France) was used as the solvent subsequently after each RFs.

Group D

After removal of bulk Gutta-percha, the residual root filling was removed using PTN X3 and X4 files.

Group E

After removal of bulk Gutta-percha, the residual root filling was removed using WO large file.

Reobturation of Group D and E

The canals are irrigated and obturated as described earlier with standardized master cone (40/.06). The teeth were stored at 37°C in 100% humidity for 2 weeks.

Mechanical testing

All samples were mounted on a custom made acrylic blocks to accept the loading fixture. The acrylic blocks were mounted with the roots aligned vertically on the universal testing machine one at a time. The specimens were subjected to a constant load at a crosshead speed of 1.0 mm/min until the roots fractured. In this study, "fracture" was defined as the point at which a sharp and instantaneous drop was observed. This point was verified by a computer attached to the universal testing machine. For most specimens, an audible crack was also heard. The test was terminated at this point and the force applied was recorded and measured in Newtons.

Statistical analysis

Mean (± standard deviation) were calculated for each group, the groups compared using one-way analysis of variance (ANOVA) and a multiple comparison test was performed using Tukey post-hoc test (SPSS software version 20, SPSS Inc, Chicago, IL).

   Results Top

All the teeth exhibited fracture. The fracture resistance of teeth after endodontic treatment and retreatment decreased [Table 1]. The mean fracture load required for Group A - 306.46 ± 80.25 N, Group B - 272.58 ± 66.08 N, Group C - 212.79 ± 68.67 N and Group D - 161.25 ± 63.45 N, Group E - 143.66 ± 70.78 [Table 1].
Table 1: Mean and SD values of the fracture resistance (N) exhibited by the specimens

Click here to view

The fracture resistances exhibited significant differences between the groups (ANOVA, P < 0.01). Multiple Tukey's post-hoc tests revealed; Group A (control) exhibiting no statistical significant difference when compared with Group B (P > 0.05), but a significant difference with Groups C, D and E (P < 0.01). Furthermore, Group B and C presented a significant difference when compared with Group D and E. Group E exhibited the least fracture resistance among groups. The mean-wise presentation of the data has been plotted in Graph 1.

   Discussion Top

VRF is a sequel of gradual propagation of microcracks in tooth structure. [10],[17] After shaping and cleaning, there is almost 30% reduction in vertical fracture resistance. [4],[18] During canal instrumentation with NiTi rotary/reciprocating files, momentary stresses are concentrated in dentine due to contact and friction between the instrument and canal walls. This causes cracks which have been observed and reported at various levels. [19],[20]

The new PTN files have an uncommon design with the center of mass and the center of rotation being offset when in the rotation. This unique design aids in more cross-sectional space for enhanced cutting, loading and auguring debris coronally. PTN (X1, X2, X3, X4) used in the present study have an increasing and decreasing alternating percentage tapered designs on these files. [12]

The WO reciprocating files are characterized by a triangular or modified triangular cross-section resulting in a low cutting efficiency and less chip space. The reciprocal motion seems to enhance debris transportation toward the apex and may result in increased torsional forces. [21] WO caused significantly more microcracks than a full sequence of rotary files, also these cracks are seen more at the apical level, which may result in less fracture resistance exhibited by the teeth in the group instrumented by WO files in the present study. [22]

This rationale claims that using only a single large-tapered reciprocating instrument tends to create or aggravate more dentinal defects than conventional preparation, which cuts substantial amounts of dentin in a short time. [23]

The results of our present study revealed statistic significant difference in samples instrumented with decreased fracture resistance in samples instrumented by WO having mean value of 212.79 N than PTN with mean value of 272.58 N. This is in agreement with a study conducted by Pawar et al. [4] which showed that WO significantly decreased the fracture resistance of teeth when compared to PTN.

The persistence of bacterial colonies within the complexity of the root canal system leads to apical pathology in endodontically treated teeth. Such circumstances advocate nonsurgical retreatment by employing techniques for removal of obturating material followed by sufficient cleaning and reshaping procedures to provide adequate disinfection. [24]

Protaper Universal Retreatment System (D1, D2, D3) has been effectively designed to aid in removal of existing obturating material. This system has been attributed to perform better due to their rotary motion, length of instrument, progressive taper, specific flute design, which tend to cut and pull GP into file flutes and direct it toward the orifice. [25] These files fail to remove the entire root canal filling thus using a supplementary file is recommended. [16] Hence, in the current study for the retreatment groups after using RFs in group 4 PTN X3 and X4 and in group 5 WO large files were used.

During retreatment or after long-term functional stresses such as chewing, craze lines occur in 4-16%, and these may develop into fractures. The taper of the preparation and the files could be a contributing factor in the generation of dentinal defects. [23] This is in synchrony with results of our study, which shows that the fracture resistance in all retreatment groups was lesser than un-retreated groups. This can be explained by the additional mechanical procedures and further preparation of the root canal to remove the filling material. This result is supported by Shemesh et al. [15] who found that the retreatment groups had more defects than the un-retreated groups. In addition, a study conducted by Ganesh et al. [24] concluded that endodontically retreated teeth have shown significantly decreased resistance to fracture.

Hence, this has a positive correlation to the increased loss of root dentin during the retreatment procedures.

   Conclusion Top

Within the limitations of the present in vitro study, it can be concluded that the samples instrumented by Protaper NEXT exhibited a better fracture resistance when compared to WO instrumentation. After retreatment, the fracture resistance was significantly lesser. WO retreatment group showed the least fracture resistance among all.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974;18:269-96.  Back to cited text no. 1
Pettiette MT, Metzger Z, Phillips C, Trope M. Endodontic complications of root canal therapy performed by dental students with stainless-steel K-files and nickel-titanium hand files. J Endod 1999;25:230-34.  Back to cited text no. 2
Testori T, Badino M, Castagnola M. Vertical root fractures in endodontically treated teeth: A clinical survey of 36 cases. J Endod 1993;19:87-91.  Back to cited text no. 3
Pawar AM, Pawar SM, Pawar MG, Kokate SR. Fracture resistance of teeth instrumented by the Self-Adjusting File, ProTaper NEXT and WaveOne. J Pierre Fauchard Acad (India Section) 2014;28:83-7.  Back to cited text no. 4
Helfer AR, Melnick S, Schilder H. Determination of the moisture content of vital and pulpless teeth. Oral Surg Oral Med Oral Pathol 1972;34: 661-70.  Back to cited text no. 5
Bender IB, Freedland JB. Adult root fracture. J Am Dent Assoc 1983;107:413-9.  Back to cited text no. 6
Johnson ME, Stewart GP, Nielsen CJ, Hatton JF. Evaluation of root reinforcement of endodontically treated teeth. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;90:360-4.  Back to cited text no. 7
Trope M, Ray HL Jr. Resistance to fracture of endodontically treated roots. Oral Surg Oral Med Oral Pathol 1992;73:99-102.  Back to cited text no. 8
Uzunoglu E, Aktemur S, Uyanik MO, Durmaz V, Nagas E. Effect of ethylenediaminetetraacetic acid on root fracture with respect to concentration at different time exposures. J Endod 2012;38:1110-3.  Back to cited text no. 9
Kansal R, Rajput A, Talwar S, Roongta R, Verma M. Assessment of dentinal damage during canal preparation using reciprocating and rotary files. J Endod 2014;40:1443-6.  Back to cited text no. 10
Kim HC, Lee MH, Yum J, Versluis A, Lee CJ, Kim BM. Potential relationship between design of nickel-titanium rotary instruments and vertical root fracture. J Endod 2010;36:1195-9.  Back to cited text no. 11
Ruddle CJ, Machtou P, West JD. The shaping movement: Fifth-generation technology. Dent Today 2013;32:94, 96-9.  Back to cited text no. 12
Friedman S, Stabholz A, Tamse A. Endodontic retreatment - case selection and technique 3. Retreatment techniques. J Endod 1990;16:543-9.  Back to cited text no. 13
Topçuoglu HS, Demirbuga S, Tuncay Ö, Pala K, Arslan H, Karatas E. The effects of Mtwo, R-Endo, and D-RaCe retreatment instruments on the incidence of dentinal defects during the removal of root canal filling material. J Endod 2014;40:266-70.  Back to cited text no. 14
Shemesh H, Roeleveld AC, Wesselink PR, Wu MK. Damage to root dentin during retreatment procedures. J Endod 2011;37:63-6.  Back to cited text no. 15
Metzger Z. The self-adjusting file (SAF) system: An evidence-based update. J Conserv Dent 2014;17:401-19.  Back to cited text no. 16
[PUBMED]  Medknow Journal  
Shemesh H, van Soest G, Wu MK, Wesselink PR. Diagnosis of vertical root fractures with optical coherence tomography. J Endod 2008;34: 739-42.  Back to cited text no. 17
Wu MK, van der Sluis LW, Wesselink PR. Comparison of mandibular premolars and canines with respect to their resistance to vertical root fracture. J Dent 2004;32:265-8.  Back to cited text no. 18
Liu R, Hou BX, Wesselink PR, Wu MK, Shemesh H. The incidence of root microcracks caused by 3 different single-file systems versus the ProTaper system. J Endod 2013;39:1054-6.  Back to cited text no. 19
Lertchirakarn V, Palamara JE, Messer HH. Load and strain during lateral condensation and vertical root fracture. J Endod 1999;25:99-104.  Back to cited text no. 20
Bürklein S, Schäfer E. Apically extruded debris with reciprocating single-file and full-sequence rotary instrumentation systems. J Endod 2012;38:850-2.  Back to cited text no. 21
Bürklein S, Tsotsis P, Schäfer E. Incidence of dentinal defects after root canal preparation: Reciprocating versus rotary instrumentation. J Endod 2013;39:501-4.  Back to cited text no. 22
De-Deus G, Silva EJ, Marins J, Souza E, Neves Ade A, Gonçalves Belladonna F, et al. Lack of causal relationship between dentinal microcracks and root canal preparation with reciprocation systems. J Endod 2014;40:1447-50.  Back to cited text no. 23
Ganesh A, Venkateshbabu N, John A, Deenadhayalan G, Kandaswamy D. A comparative assessment of fracture resistance of endodontically treated and re-treated teeth: An in vitro study. J Conserv Dent 2014;17:61-4.  Back to cited text no. 24
[PUBMED]  Medknow Journal  
Gluskin AH, Peters CI, Wong RD, Ruddle CJ. Retreatment of non healing endodontic therapy and management of mishaps. Ingle′s Endodontics. 6 th ed. Hamilton: BC Decker Inc.; 2008.  Back to cited text no. 25

Correspondence Address:
Dr. Neha Deepak Khalap
Department of Conservative Dentistry and Endodontics, YMT Dental College and Hospital, Kharghar, Navi Mumbai, Maharashtra
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0972-0707.168808

Rights and Permissions


  [Table 1]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *
* Registration required (free)  

   Materials and method
    Article Tables

 Article Access Statistics
    PDF Downloaded245    
    Comments [Add]    

Recommend this journal