Assessment of the SeparWaveOne Files: A ProspeRodrigo Sanches Cunha, DDS, MSc, PhDPablo Ensinas, DDS, MSc, William Nudand Carlos Eduardo da Silveira Bueno

AbstractIntroduction: Despite metallurgical advancements inthe nickel-titanium file manufacturing process, file sep-aration remains a concern. The purpose of this prospec-tive clinical study was to assess the separation incidenceof the reciprocating WaveOne file (Dentsply Tulsa DentalSpecialties, Tulsa, OK) when used to prepare root canalsof posterior teeth. Methods: File separation incidence

The fracture incidence data were collected from a total of 711 posterior teeth ofpatients who sought treatment from January 2012August 2013. A specific data file was

Division Endodontics, Department of Restorative Dentistry,

Clinical Researchcompleted for each patient in order to obtain the required information. Four endodon-tists trained in the WaveOne reciprocating technique were included in the study.

After access cavity preparation, straight-line access to the canal orifices wasachieved using the Gates-Glidden drills #3 and #2 or an orifice opener with similar geo-metric diameters. A reproducible glide path with apical patency was created usingK-type hand files of small diameter (#08, #10, or #15) and/or PathFile rotary files#1 (tip size 13 with a taper of 0.02), #2 (tip size 16 with a taper of 0.02), and #3(tip size 19 with a taper of 0.02) (Dentsply Tulsa Dental Specialties). The instrumen-tation procedure was performed with the canals flooded and irrigated with copious

D226C780 Bannatyne Avenuem, Winnipeg, Manitoba, Can-ada R3E 0W2. E-mail address: rodrigo.cunha@umanitoba.ca0099-2399/$ - see front matter

Copyright 2014 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2014.03.016Campinas, S~ao Paulo, Brazil.Address requests for reprints to Dr Rodrigo Sanches Cunha,Materials and Methodswas assessed over an 18-month period in which 4 expe-rienced and calibrated endodontists performed conven-tional endodontic treatment on posterior teeth using theWaveOne file system. The separation incidence wasdetermined based on both the number of teeth andthe number of canals instrumented during this timeperiod. Results: A total of 2,215 canals (711 teeth)were treated. Three instruments (two 21.06 and one25.08) separated during use and were deemed to beirretrievable. The overall instrument separation inci-dence in relation to the number of canals shaped wasfound to be 0.13% (0.42% teeth). Conclusions: Basedon the results of this study, the incidence of endodonticinstrument separation when using the WaveOnereciprocating file was considerably low. (J Endod2014;40:922924)

Key WordsFile fracture, nickel-titanium reciprocating instrument,separation incidence, separation of files, WaveOne

From the *Division of Endodontics, University of Manitoba,Winnipeg, Manitoba, Canada; Graduate Program in Endodon-tics, Salta Endodontics Society, Salta, Argentina; Private Prac-tice Limited to Endodontics, Bloomingdale, Illinois; andDivision of Endodontics at the CPO-Sao Leopoldo Mandic,922 Cunha et al.ation Incidence of Reciprocatingctive Clinical Study, FRCD(C),* Alanna Junaid, BSc, DMD, BSc (Dent),*era, DDS, MSc,

, DDS, MSc, PhD

The design and mechanical properties of endodontic instruments have advancedsignificantly in recent decades. The introduction of nickel-titanium (NiTi) alloyshas enabled practitioners to work safely inside narrow and curved canals. The useof an electric motor in rotational and/or reciprocating movements in conjunctionwith NiTi instruments has significantly increased instrumentation efficiency whilereducing working time (1). However, the separation incidence of these instrumentsis still an area of uncertainty because of the number of studies that offer conflictingresults.

In a systematic review, Panitvisai et al (2) assessed the prognosis of teeth in whichinstrument separation occurred during endodontic therapy. No significant decline inthe healing rate was observed in teeth with an irretrievable file when compared withteeth in which file separation did not occur or in teeth in which the file was successfullyremoved. However, the odds of an unfavorable outcome increase when a fractured in-strument prevents thorough disinfection of the root canal system in the presence of apreoperative periradicular lesion (3).

In 2010, the WaveOne engine-driven reciprocating system was introduced byDentsply Tulsa Dental Specialties (Tulsa, OK). The reciprocating file shapes the rootcanal system using an asymmetric back and forth motion whereby the file continuallychanges its direction during the canal shaping process. This reciprocating motion con-sists of a larger degree of rotation in the cutting direction and a smaller degree of rota-tion in the reverse direction. The system consists of 3 file size options: small (tip size 21with a constant taper of 0.06), primary (tip size 25 with a taper of 0.08 from D1D3),and large (tip size 40 with a taper of 0.08 from D1D3). The manufacture of the Wave-One system proposes the use of only 1 reciprocating file chosen based on canal anat-omy. The NiTi used to make WaveOne files is manufactured using the M-Wire thermaltreatment process. This provides increased flexibility (4, 5) and strength, and highresistance to cyclic fatigue (6, 7).

Numerous studies have clinically assessed the fracture incidence of NiTi rotaryendodontic instruments (814). However, no clinical studies evaluating thefracture incidence of reciprocating files have been published to date. Therefore,the purpose of this prospective clinical study was to assess the separationincidence of the WaveOne reciprocating file used in root canal preparation ofposterior teeth.JOE Volume 40, Number 7, July 2014

amounts of sodium hypochlorite (NaOCl) in various concentrationsranging from 2.5%6%.

The working length was determined to be 0.5 mm from the rootapex. This was achieved with the aid of a Root ZX II electronic apexlocator (J Morita Corp, Kyoto, Japan) and confirmed radiographically.A new file of the appropriate size was selected according to the followingcriteria:

1. If a size #10 K-file was resistant to apical advancement, a small filewas selected.

2. If a size #10 K-file passively advanced to the established working

separation incidence with the WaveOne reciprocation system asopposed to rotary files systems in the hands of specialists.

Within the parameters of this study, all 3 file separations occurredin the apical portion of the root canal system. This finding was in linewith previous studies that suggested file fractures are more prone tooccur in the apical third of the canal. This is most likely because ofthe high anatomic complexity encountered in this region (16, 21).Two of the 3 separations occurred when using the WaveOne smallfiles. These files may be at a higher risk for separation given that they

Clinical Researchlength or fit loosely at length, a primary file was selected.3. If a size #20 hand file or larger passively advanced to the established

working length, a large file was selected.

File selection was individualized for each canal. As such, multiplefiles could be used in a single tooth if the canals were of differing diam-eters as frequently is the case in multirooted teeth. If all canals were thesame size, a single file was used for the complete instrumentation of1 tooth.

After flooding the canals with NaOCl, the file was inserted andadvanced apically. After 3 consecutive apical pecking movements, thefile was removed from the canal and cleansed of debris usingalcohol-soaked gauze. This process was repeated until the file advancedto the pre-established working length. After each file insertion, the ca-nals were irrigated with NaOCl, and patency was confirmed with a #10or #15 hand file.

Files exhibiting deformation were discarded, and treatment wascompleted using a new file of the same size. Final irrigation was per-formed with 5 mL 17% EDTA in association with sonic activation(EndoActivator, Dentsply Tulsa Dental Specialties) for 1 minute fol-lowed by 5 mL NaOCl.

Upon completion of endodontic treatment, the clinician recordedthe appropriate data relating to the tooth type, number of canals treated,and file(s) used. If separation occurred, a detailed description of the fileused, tooth type, specific canal, and canal level at which file fractureoccurred was recorded.

ResultsDuring the 18-month period in which the 4 clinicians instru-

mented 2,215 canals (711 teeth), 3 file separations occurred. Two ofthe 3 were small files, and the other was a primary file. The overallfile separation incidence in relation to the number of canals instru-mented was found to be 0.13% (0.42% in relation to the number ofteeth). For tabulated data, please refer to Table 1 and Table 2.

DiscussionDespite the numerous improvements made in instrument design

and alloy composition, file separation during root canal shaping re-mains a concern. This phenomenon can occur at any time withoutany visible signs of file deformation (15). The presence of a retainedinstrument fragment within the root canal system alone is an insufficient

TABLE 1. Data Collected from All Patients Treated between January 2012 andAugust 2013

Premolars Molars

No. ofteeth

No. of rootcanals

No. ofteeth

No. of rootcanals

Maxillary 102 177 293 1,042Mandibular 42 53 274 943JOE Volume 40, Number 7, July 2014predictor of treatment outcome success. However, if the canalharboring the instrument fragment was insufficiently cleaned beforeseparation and infective microorganisms remain within the canal, theprognosis may be less favorable (16, 17).

The concept of shaping a canal with an engine-driven recipro-cating instrument in an asymmetric envelope of motion is relativelynew. The incidence of instrument separation associated with this tech-nique should be studied in a clinical environment. Posterior teeth arethe most appropriate specimens for this study given their challenginganatomy and the higher likelihood of instrument fracture (18).

The cleaning and shaping protocols reflected in this prospectiveclinical study were established in accordance with the manufacturersguidelines in order to standardize the treatment protocol between op-erators. A reproducible glide path was established either manually orwith the assistance of engine-driven glide path files. The selectedmethod for glide path preparation was dictated by canal anatomy andwas determined based on the discretion of the treating clinician. In2012, Alves Vde et al (19) found no significant clinical difference in api-cal transportation when comparing the use of hand files with engine-driven glide path files used in the creation of a glide path. De-Deuset al (20) assessed the frequency at which reciprocating files wereable to achieve the full working length in mandibular molar canalswithout a reproducible glide path. De-Deus et al concluded that thesefiles were able to achieve the full working length only when the canalwas straight or moderately curved.

Three instrument separations occurred over the course of thisstudy, yielding a separation incidence of 0.13% in relation to the num-ber of canals and 0.42% according to the number of teeth treated.Several studies currently exist looking at the separation incidence of ro-tary instruments during root canal treatment (814, 18, 21). In all ofthese studies, the file separation incidence was found to be higherwhen compared with the results of the current study. Separationincidence ranged from 0.3% in Shen et als study (13) to 2.6% inWu et als study (10).

A possible explanation as to why the separation incidenceobserved in the current study is lower than those reported in the afore-mentioned studies could relate to clinician skill level. Experience levelranged from undergraduate students (12, 13) to postgraduate students(14, 18, 21) and endodontic specialists (8, 9, 11) in the series ofstudies, whereas the current study observed treatments performedexclusively by endodontic specialists. When comparing the results ofthis study with only those studies in which treatment was limited toendodontic specialists (8, 9, 11), the results suggest a lower

TABLE 2. Number of Separations with Respect to Tooth Type, Canal, andLocation within the Canal

FileNumber of fileseparations Tooth Canal Canal location

Small 02 5/3 P/MB Apical/apicalPrimary 01 15 DB ApicalLarge 00

DB, distobuccal; MB, mesiobuccal; P, palatal.Separation Incidence of WaveOne Files 923

are selected to work in the most challenging canals, namely those withextreme curvatures or tight constrictions.

The authors have identified 3 potential explanations for the lowincidence of file separation when using reciprocating files. WaveOnefiles are manufactured from M-Wire NiTi. Studies have shown thatNiTi files made from M-Wire have both physical and mechanical prop-erties that increase flexibility and improve resistance to cyclic fatigue

7. Kiefner P, Ban M, De-Deus G. Is the reciprocating movement per se able to improvethe cyclic fatigue resistance of instruments? Int Endod J 2014;47:4306.

8. Ramirez-Salomon M, Soler-Bientz R, de la Garza-Gonzalez R, Palacios-Garza CM.Incidence of Lightspeed separation and the potential for bypassing. J Endod1997;23:5867.

9. Ehrhardt IC, Zuolo ML, Cunha RS, et al. Assessment of the separation incidence ofmtwo files used with preflaring: prospective clinical study. J Endod 2012;38:107881.

10. Wu J, Lei G, Yan M, et al. Instrument separation analysis of multi-used ProTaper

Clinical Researchcompared with files made from conventionally processed NiTi wires(2226). Therefore, it is conceivable that the metallurgy of theWaveOne file contributed to its low fracture incidence.

These reciprocating files shape canals using an asymmetric mo-tion. The file continually changes direction applying greater rotationin the cutting direction (170) and less in the reverse direction(50) (27). Recent studies suggest that reciprocating movements pro-long file fatigue and therefore extend the life of engine-driven NiTi in-struments when shaping curved canals (2830).

The WaveOne system does not allow for file sterilization; therefore,each file is considered a single-use instrument. Multiple-instrument us-age has been shown to significantly increase the file separation potential(31) because of a reduction in cyclic flexural fatigue resistance. In addi-tion, as files are reused, they undergo increased wear and develop sur-face defect that can promote fracture propagation (32). All of thereferenced articles that analyzed clinical file separation presented inthis study (814, 18, 21) used the same instrument(s) multipletimes. Ramirez-Solomon et al (1997) (8) states excessive usage ofthe instruments before file separation, and this could explain the higherincidence of separation when compared to the current study.

It can be concluded that the low incidence of WaveOne file fractureseen in the current study may be a direct result of the files metallurgiccomposition, reciprocating motion, and/or its single-use nature. Withinthe limitations of this study, the incidence of endodontic instrument sep-aration when using theWaveOne reciprocating file was determined to beconsiderably low. Further research should be conducted to corrobo-rate the findings of this study.

AcknowledgmentsDr Nudera is an advocate and key opinion leader for Dentsply

Tulsa Dental Specialties.The authors deny any conflicts of interest related to this study.

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Assessment of the Separation Incidence of Reciprocating WaveOne Files: A Prospective Clinical StudyMaterials and MethodsResultsDiscussionAcknowledgmentsReferences