Research ArticleElectrochemical Impedance Spectroscopy Investigation on theClinical Lifetime of ProTaper Rotary File System
Virgil Penta Cristian Pirvu and Ioana Demetrescu
Faculty of Applied Chemistry and Materials Science Polytechnic University of Bucharest Polizu 1-7 011061 Bucharest Romania
Correspondence should be addressed to Ioana Demetrescu i demetrescuchimupbro
Received 16 April 2013 Accepted 11 November 2013 Published 29 January 2014
Academic Editor Paul C Dechow
Copyright copy 2014 Virgil Penta et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
The main objective of the current paper is to show that electrochemical impedance spectroscopy (EIS) could be a method forevaluating and predicting of ProTaper rotary file system clinical lifespan This particular aspect of everyday use of the endodonticfiles is of great importance in each dental practice and has profound clinical implications The method used for quantificationresides in the electrochemical impedance spectroscopy theory and has in its main focus the characteristics of the surface titaniumoxide layer This electrochemical technique has been adapted successfully to identify the quality of the Ni-Ti files oxide layer Themodification of this protective layer induces changes in corrosion behavior of the alloy modifying the impedance value of the fileIn order to assess the method 14 ProTaper sets utilized on different patients in a dental clinic have been submitted for testing usingEIS The information obtained in regard to the surface oxide layer has offered an indication of use and proves that the said layerevolves with each clinical application The novelty of this research is related to an electrochemical technique successfully adaptedfor Ni-Ti file investigation and correlation with surface and clinical aspects
1 Introduction
Modern endodontics require a predictable result in an areawhere such a result is difficult to obtain in classical con-ditions With recent advances in electronics and materialrsquosscience the endodontic micromotor and flexible Ni-Ti fileshave emerged An initial investigation on the bending andtorsional properties of nitinol (Ni-Ti) root canal files has beenintroduced in the pioneering article by Walia et al [1] Thisarticle noted the advantage of the low elastic modulus Ni-Ti alloy for negotiating curved root canals compared to thestainless steel alloys in predominant use at the time Thenickel-titanium endodontic instruments reported by Waliaet al were intended for hand usage and the rotary instru-ments employed with slow-speed dental handpieces followedin the 1990s Currently there are many types of rotary filesystems on themarket but this paper focuses on the ProTaperThis system is comprised of six files that are used in sequenceto enlarge and reshape the endodontic root canal conformingit to Schilderrsquos principles [2] The first three are namedshaping Sx S1 and S2 and the second three are namedfinishing F1 F2 and F3 these files are the basic Maillefer
Dentsply kit presented by West [3] They are a leap forwardin root shaping and enlargement They offer great results andare very time efficient in root preparation as shown by Tu etal [4] One of themain problemswith the ProTaper files is thefrequent breakage a fact presented by many different studiesFife et al Inan et al and Lopes et al [5ndash7] The actual issueis not necessarily the remainder of the file fragment withinthe root canal but the pathology resulting from incompletecanal therapy as shown by Nair [8] This character of Ni-Tifiles makes it a matter for dental materials science to improveand perfect a technique by which the doctor could easilyquantify their clinical lifetime Plotino et al [9]The cause forfile failure is complex and resides in many areas such as alloyfatigue improper use corrosion due to lavage substancesand operator sensitivity as presented by many studiesWest Lopes et al Peters et al and Cheung and Darvell[3 7 10 11]
The electrochemical behavior of Ti alloys in the oral cavityenvironment has been widely investigated in the last decadetaking into account alloy and environment composition [1213] Various compositions of binary and tertiary alloys havebeen subject of such research taking into account their
Hindawi Publishing CorporationBioMed Research InternationalVolume 2014 Article ID 754189 10 pageshttpdxdoiorg1011552014754189
2 BioMed Research International
applications as dental materials due to mechanical propertiesas well [14] As binary alloy Ti-Ni has attracted muchattention of researchers being a shape memory alloy withgood corrosion and abrasion resistance used in orthodonticarch wires and rotary endodontic instruments
This paper compares 13 ProTaper clinically utilized sets inorder to assess the use of EIS in determining the instrumentsclinical lifetime and possible risk of fracture The files aremade of a Ni-Ti memory shape alloy as shown by Alapatiet al and Baek et al [15 16] The alloy has great elasticitybut in time and due to stress it wears out and structuraldefects under the form of cracks appear the cracks are pointsof low resistance as pointed out by different studies suchas Sattapan et al [17] Luebke et al [18] and Gambarini[19] Furthermore the liquid used for root lavage is sodiumhypochlorite it infiltrates the cracks and corrodes deeperinto the file a fact presented by Lopes et al and by Peterset al [7 10] The result is file breakage during enlargementWhen new the ProTaper files are coveredwith a homogenouslayer of oxide that protects the alloy This oxide layer isessential to the resistance of the Ni-Ti file because it acts likea barrier between the file and the outside environment Theadvantage of such a layer is fast regeneration when exposedto oxygen in breathable air During instrumentation theoxide layer is mechanically removed and the alloy becomesexposed to corrosive substances like sodium hypochloriteas shown by different studies (Peters et al Cheung andDarvell [10 11]) If the file is placed into a liquid disinfectingsolution before it can regain its oxide coating then the filecan corrode even faster especially in the areas of oxide layerlack
Electrochemical impedance spectroscopymethod whichhas seen tremendous increase in popularity in recent yearsis a useful tool to evaluate the electrochemical stabilityof oxide surface films and to identifyevaluate the surfacemodification for Ni-Ti alloys [20]
The EIS investigation is based on the system response tothe application of a periodic small amplitude ac signal Themeasurements are carried out at different ac frequencies andthe system response contains information about the interfaceits structure and reactions taking place there [21]
In our case this procedure reveals the state of thetitanium-oxide layer in direct connection to the usage ofthe instrument A new instrument will be quite capacitiveshowing a homogenous and uniform oxide layer as opposedto a used instrument that has a more resistive characterbecause of modification in oxide layer coatingThis approachhas been introduced in an effort to extend EIS use to thedental field to offer a new perspective to clinicians on eclecticoral interactions as shown in our previous papers [22 23]Theprinciple is that electrons will only circulate on the superficialpart of the Ni-Ti alloy and diffusion is seen through the oxidelayer revealing its characteristics Although there has been avery interesting proposition of treating the fatigue of the filesusingGriffithrsquos law it is the authorsrsquo opinion that such amodelis only a partially valid one and the application of the saidlaw or of Irwinrsquos modification cannot describe the complexityof the clinical situation as shown by Cheung and Darvell[11]
2 Materials and Method
21 Files Thirteen ProTaper DentsplyMaillefer sets usedclinically on patients and a new reference set in total anumber of 84 files were tested [3] The ProTaper techniqueis a crown-down root preparation principle in which eachinstrument has changing percentage tapers over the lengthsof its cuttings blades [3] The files were all collected fromthe same dental clinic and from the same practitioner inorder to minimize the differences of operator sensitivity andtechnique Plotino et al [9] By gathering all the files from thesame place we believe that we can increase the probabilitythat they have been used very much in the same way withthe same technique and by the same trained hand Previousarticles show that a number of about 8ndash12 root canals can beenlarged with the same file set Fife et al and Inan et al [5 6]These root canals must be quite straight with a maximumcurvature of 10 degrees in order to maintain the 12-canalquantity otherwise the number of uses must decrease Fifeet al [5] Unfortunately this is quite a subjective matter andit is entirely up to the trained specialist to decide when todiscard each set
22 EIS Testing Electrochemical impedance spectroscopy(EIS) measurements were conducted with Autolab PGSTAT302N in a logarithmic distribution range between 100 kHzand 10mHz The EIS fitting was performed using NOVA18 software The electrochemical setup consisted of a three-electrode configuration with a counter platinum electrodean AgAgCl electrode as a reference and the file itself asthe working electrode Each file was submerged to the samereference point 1mmunder the file haft in an electrochemicalcell The results may be represented graphically using twotypes of plots complex planeNyquist plots (11988510158401015840 versus1198851015840 iethe imaginary versus the real components of the impedanceplotted for various frequencies) and Bode plots (log |119885| (mag-nitude) and phase-angle 120601 versus log 120596 (angular frequency)[21]
After testing all fileswere comparedwith the same type ineach set and a number of conclusions were formulated Thesurface observations of each file were done with Carl-Zeissoptical microscope up to 50x magnification
23 Set Usage Registered and Described Using EIS Aftercomparing each type of files we have compared each set wearto the clinical use registered by the practitioner Each file isdipped in Glide solution before the actual use and each use isaccompanied by copious irrigationwith sodiumhypochlorite25 The clinician always uses the Sx files but not beforethe confirmation of the Glide path up to Headstroem 15 fileStandard rubber dam isolation is routinely done for everycase Set numbering in this paper is in direct connection tonumber of clinical uses as follows
The impedance values described for each set represent amean of the impedance values of each file of the set
The reference value used for the discussion of file set lifes-pan and service life was that of 4834Ohms value registeredby the reference unused ProTaper set
BioMed Research International 3
Set 1 is an example of minimal file wear It has been usedto enlarge a maxillary front incisor 11 with a morphologydescribed by Kerekes and Tronstad [24] It has been used inour study to grossly quantify the modification of the oxidelayer after a single use in a straight root canal Its averageimpedance value was 5421Ohms and the total number ofcanals enlarged was 1 (Figures 8 and 9)
Set 2 has been used in the instrumentation of two frontincisors 22 and 21 The set was discarded for researchpurposes only and does not show any objective wear eitherusing direct observation or the microscope Further useworld strongly be recommended Its average impedance valuewas 5924Ohms and the total number of enlarged canals was2 (Figure 8)
Set 3 was used in the instrumentation of 2 maxillarycanine teeth and a maxillary premolar tooth 13 23 and15 The microscope image of the files shows no surfacemodification or defect Its average impedance value was5873Ohms and the total number of enlarged canals was four(Figures 8 and 9)
Set 4 was used for the enlargement of 2 maxillarymolars 17 and 18 Tooth 18 had a two-canal morphologywith an extremely distally curved single root Kerekes andTronstad [25] Also one of the canals had a broken tipof probably a Kerr file that could not be removed Theset shows accentuated wear of the S1 S2 and F1 F2 files(Figure 3(a)) The average impedance value was 11871 a veryhigh value although the total number of enlarged canals was 5(Figures 8 and 9)
Set 5 has been used in the instrumentation of twomandibular molars 46 and 36 in the same patient Soin total a number of 6 canals have been instrumentedThe microscope showed visible defects correlating to highimpedance values as shown regarding the S1 file (Figure 3(b))The average impedance value for this set was 6414Ohms andthe total number of canals was 6 (Figure 8)
Set 6 has been used for the instrumentation of threemaxillary premolars 14 and 15 and a special anatomy of a 25premolar with 2 very narrow and convergent canals Kerekesand Tronstad [25] The strange anatomy of the maxillarypremolar could account for the excessive wear of S1 andS2 (Figure 3(c)) The average impedance value for this setwas 8930 and the total number of enlarged canals was 6(Figure 7)
Set 7was used in the instrumentation of 3 uppermaxillarymolars in a young patient aged 23 years old The set showsnotable modification upon direct observation viewed by themicroscope (Figure 3(d)) The average impedance value forthis set was 6755Ohms and the total number of enlargedcanals was 9 (Figure 8)
Set 8 has been used for 3 molars in two different patientsThe teeth instrumented were 16 47 and 26 The set showshigh EIS values and minimal defects were viewed with theoptical microscope The average impedance value for this setwas 7685Ohms and the total number of enlarged canals was9 (Figure 8)
Set 9 was used for the instrumentation of 3 mandibularmolars in two different patients 46 47 and 36 The rootswere normally conformedThe average impedance value was
7726Ohms and the total number of enlarged canals was 9(Figure 8)
Sets 11 12 and 10 have been heavily used for a numberof 12 canals each Sets 12 and 11 have been used in theinstrumentation of 4mandibularmolars each Set 12 enlarged46 36 47 and 38 with 2-root-3-canal morphology andhigh curvature Set 11 enlarged 38 48 36 and 37 teethTooth 48 presented a convergent shape of itsmesial and distalcanals Kerekes and Tronstad [26] The set number 10 wasused in the enlargement of fivemaxillary teeth fourmaxillarypremolars three 14 one 24 and a central incisor 11 Theaverage impedance values for these sets were for set 108779Ohms for set 11 8804Ohms and for set 12 9092Ohms(Figure 7) Set number 10 enlarged a number of 11 root canalsand sets 11 and 12 enlarged a number of 12 dental root canalsAll the sets described above show high impedance values andsurface defects when viewed with the microscope especiallyset number 12 and should be readily discarded (Figures 3(e)8 and 9)
Set 13 has been used for 5 molars in two different patientsenlarging a number of 15 dental canals The molars were 3616 and 16 and mandibular right molars 46 and 47 Files F1and F2 were used in each case but file F3 has only been usedin the instrumentation of the distal roots of eachmolar so thisaccounts for the lower wearThe average impedance value forthis set was 12667 and the total number of enlarged canalswas 15 (Figure 8) Surface defects were viewedwith the opticalmicroscope (Figure 3(a))
After the consideration of all sets a few conclusions canbe formulated The first would be that the modification ofimpedance values occurs not with the frequency of clinicaluse but with the difficulty of each case in part It is apparentthat set 4 has less uses than other sets but it presents a patternof wear specific to a higher frequency of clinical use So it isvery important to show that the EIS data correctly quantifiesmodification of oxide layer relative to usage and wear
Although the most worn files showed many surfacedefects in the form of pitting corrosion scratches or evenmissing pieces of alloy the F1 in Set 4 presented a crack inthe file structure posing a breakage risk for future clinical use(Figure 3)
3 Results and Discussion
The results of file testing showed a variation in impedancevalues by comparison to the unused setTheNyquist diagramversus Bode plot in Figure 1 shows how the electrochemicalbehavior of the titanium-oxide layer on the files changes withseveral uses The Ti-oxide layer changes with multiple usesso we measured a new unused file as a reference and then wemeasured a file with many clinical uses 15 enlarged canalsfile F1 set 13 The change was drastic and very easy to spoton the EIS plots and in correlation to the fitting circuits(Figure 2)
In order to confirm that impedance value variation of theoxide layer resounds in alloy defects we analyzed the used F1from set 13 file using the Carl-Zeiss optic microscope and we
4 BioMed Research International
0 15000 30000 45000 60000 75000 900000
50000
100000
150000
200000
250000
minusZ
(Ohm
s)
Z (Ohms)
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 F2 reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 Reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
Z (O
hms)
Frequency (Hz)
(b)
Figure 1 Nyquist and Bode diagrams of S2 files from all sets showing progressive wear starting from reference on (a) and most worn file on(b)
Solution
Electric double layer
Titanium oxide layer
Rct 1 Rct 2
Q2Q1
Q3Rs
Low frequency compensation
for compact oxide layer
Figure 2 Equivalent circuit for EIS fitting
found cracks in its structure (Figure 3(f)) We repeated thisalgorithm with all the file classes and we found that there isa very clear connection between clinical use and oxide layermodification Our limits were placed having as a referencea new set and as a limit to usage the clinically overworkedfiles with very high resistances regardless of set numberthat presented structural defects under the microscope TheNyquist values showed a change in electrical impedance
toward an increase The complexity of evaluating the fileswith this kind of plots was too great so we preferred touse Nyquist only for a qualitative interpretation of oxidelayer change and explanation of surface phenomena Thequantification of resistance variation was done using Bodemodulus plots at a frequency around 10000Hz simply dis-playing the relation between frequency used and resistancemodification
BioMed Research International 5
(a)
(b) (c)
(d)
(e) (f)
Figure 3 Optical microscope images (a) F1 set 4 (b) S1 set 5 (c) S2 set 6 (d) F1 set 7 (e) S2 set 12 and (f) F1 set 13
31 Fitting Circuit The circuit in Figure 2 is an exam-ple of circuit used for EIS data fitting According to theimpedance spectra in the metaloxideelectrolyte configura-tion the equivalent circuit shown in Figure 2 represents theimpedance behavior of the oxide films In this circuit Rsrepresents the aqueous solution resistanceThe two observedcharge-transfer flattened semicircles correspond to two RCparallel combinations and are due to the ionic charge transfer
resistance Rct1 in parallel to the first constant phase element(Q1) and the Rct2 in parallel to the second constant phaseelement (Q2)
A constant phase element (CPE) is generally considereda component that models the behavior of a double layer thatis an imperfect capacitor (pseudocapacitor) In global mea-surements of an irregular surface the CPE behaviour can beattributed to either different surface or normal time-constant
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
2 BioMed Research International
applications as dental materials due to mechanical propertiesas well [14] As binary alloy Ti-Ni has attracted muchattention of researchers being a shape memory alloy withgood corrosion and abrasion resistance used in orthodonticarch wires and rotary endodontic instruments
This paper compares 13 ProTaper clinically utilized sets inorder to assess the use of EIS in determining the instrumentsclinical lifetime and possible risk of fracture The files aremade of a Ni-Ti memory shape alloy as shown by Alapatiet al and Baek et al [15 16] The alloy has great elasticitybut in time and due to stress it wears out and structuraldefects under the form of cracks appear the cracks are pointsof low resistance as pointed out by different studies suchas Sattapan et al [17] Luebke et al [18] and Gambarini[19] Furthermore the liquid used for root lavage is sodiumhypochlorite it infiltrates the cracks and corrodes deeperinto the file a fact presented by Lopes et al and by Peterset al [7 10] The result is file breakage during enlargementWhen new the ProTaper files are coveredwith a homogenouslayer of oxide that protects the alloy This oxide layer isessential to the resistance of the Ni-Ti file because it acts likea barrier between the file and the outside environment Theadvantage of such a layer is fast regeneration when exposedto oxygen in breathable air During instrumentation theoxide layer is mechanically removed and the alloy becomesexposed to corrosive substances like sodium hypochloriteas shown by different studies (Peters et al Cheung andDarvell [10 11]) If the file is placed into a liquid disinfectingsolution before it can regain its oxide coating then the filecan corrode even faster especially in the areas of oxide layerlack
Electrochemical impedance spectroscopymethod whichhas seen tremendous increase in popularity in recent yearsis a useful tool to evaluate the electrochemical stabilityof oxide surface films and to identifyevaluate the surfacemodification for Ni-Ti alloys [20]
The EIS investigation is based on the system response tothe application of a periodic small amplitude ac signal Themeasurements are carried out at different ac frequencies andthe system response contains information about the interfaceits structure and reactions taking place there [21]
In our case this procedure reveals the state of thetitanium-oxide layer in direct connection to the usage ofthe instrument A new instrument will be quite capacitiveshowing a homogenous and uniform oxide layer as opposedto a used instrument that has a more resistive characterbecause of modification in oxide layer coatingThis approachhas been introduced in an effort to extend EIS use to thedental field to offer a new perspective to clinicians on eclecticoral interactions as shown in our previous papers [22 23]Theprinciple is that electrons will only circulate on the superficialpart of the Ni-Ti alloy and diffusion is seen through the oxidelayer revealing its characteristics Although there has been avery interesting proposition of treating the fatigue of the filesusingGriffithrsquos law it is the authorsrsquo opinion that such amodelis only a partially valid one and the application of the saidlaw or of Irwinrsquos modification cannot describe the complexityof the clinical situation as shown by Cheung and Darvell[11]
2 Materials and Method
21 Files Thirteen ProTaper DentsplyMaillefer sets usedclinically on patients and a new reference set in total anumber of 84 files were tested [3] The ProTaper techniqueis a crown-down root preparation principle in which eachinstrument has changing percentage tapers over the lengthsof its cuttings blades [3] The files were all collected fromthe same dental clinic and from the same practitioner inorder to minimize the differences of operator sensitivity andtechnique Plotino et al [9] By gathering all the files from thesame place we believe that we can increase the probabilitythat they have been used very much in the same way withthe same technique and by the same trained hand Previousarticles show that a number of about 8ndash12 root canals can beenlarged with the same file set Fife et al and Inan et al [5 6]These root canals must be quite straight with a maximumcurvature of 10 degrees in order to maintain the 12-canalquantity otherwise the number of uses must decrease Fifeet al [5] Unfortunately this is quite a subjective matter andit is entirely up to the trained specialist to decide when todiscard each set
22 EIS Testing Electrochemical impedance spectroscopy(EIS) measurements were conducted with Autolab PGSTAT302N in a logarithmic distribution range between 100 kHzand 10mHz The EIS fitting was performed using NOVA18 software The electrochemical setup consisted of a three-electrode configuration with a counter platinum electrodean AgAgCl electrode as a reference and the file itself asthe working electrode Each file was submerged to the samereference point 1mmunder the file haft in an electrochemicalcell The results may be represented graphically using twotypes of plots complex planeNyquist plots (11988510158401015840 versus1198851015840 iethe imaginary versus the real components of the impedanceplotted for various frequencies) and Bode plots (log |119885| (mag-nitude) and phase-angle 120601 versus log 120596 (angular frequency)[21]
After testing all fileswere comparedwith the same type ineach set and a number of conclusions were formulated Thesurface observations of each file were done with Carl-Zeissoptical microscope up to 50x magnification
23 Set Usage Registered and Described Using EIS Aftercomparing each type of files we have compared each set wearto the clinical use registered by the practitioner Each file isdipped in Glide solution before the actual use and each use isaccompanied by copious irrigationwith sodiumhypochlorite25 The clinician always uses the Sx files but not beforethe confirmation of the Glide path up to Headstroem 15 fileStandard rubber dam isolation is routinely done for everycase Set numbering in this paper is in direct connection tonumber of clinical uses as follows
The impedance values described for each set represent amean of the impedance values of each file of the set
The reference value used for the discussion of file set lifes-pan and service life was that of 4834Ohms value registeredby the reference unused ProTaper set
BioMed Research International 3
Set 1 is an example of minimal file wear It has been usedto enlarge a maxillary front incisor 11 with a morphologydescribed by Kerekes and Tronstad [24] It has been used inour study to grossly quantify the modification of the oxidelayer after a single use in a straight root canal Its averageimpedance value was 5421Ohms and the total number ofcanals enlarged was 1 (Figures 8 and 9)
Set 2 has been used in the instrumentation of two frontincisors 22 and 21 The set was discarded for researchpurposes only and does not show any objective wear eitherusing direct observation or the microscope Further useworld strongly be recommended Its average impedance valuewas 5924Ohms and the total number of enlarged canals was2 (Figure 8)
Set 3 was used in the instrumentation of 2 maxillarycanine teeth and a maxillary premolar tooth 13 23 and15 The microscope image of the files shows no surfacemodification or defect Its average impedance value was5873Ohms and the total number of enlarged canals was four(Figures 8 and 9)
Set 4 was used for the enlargement of 2 maxillarymolars 17 and 18 Tooth 18 had a two-canal morphologywith an extremely distally curved single root Kerekes andTronstad [25] Also one of the canals had a broken tipof probably a Kerr file that could not be removed Theset shows accentuated wear of the S1 S2 and F1 F2 files(Figure 3(a)) The average impedance value was 11871 a veryhigh value although the total number of enlarged canals was 5(Figures 8 and 9)
Set 5 has been used in the instrumentation of twomandibular molars 46 and 36 in the same patient Soin total a number of 6 canals have been instrumentedThe microscope showed visible defects correlating to highimpedance values as shown regarding the S1 file (Figure 3(b))The average impedance value for this set was 6414Ohms andthe total number of canals was 6 (Figure 8)
Set 6 has been used for the instrumentation of threemaxillary premolars 14 and 15 and a special anatomy of a 25premolar with 2 very narrow and convergent canals Kerekesand Tronstad [25] The strange anatomy of the maxillarypremolar could account for the excessive wear of S1 andS2 (Figure 3(c)) The average impedance value for this setwas 8930 and the total number of enlarged canals was 6(Figure 7)
Set 7was used in the instrumentation of 3 uppermaxillarymolars in a young patient aged 23 years old The set showsnotable modification upon direct observation viewed by themicroscope (Figure 3(d)) The average impedance value forthis set was 6755Ohms and the total number of enlargedcanals was 9 (Figure 8)
Set 8 has been used for 3 molars in two different patientsThe teeth instrumented were 16 47 and 26 The set showshigh EIS values and minimal defects were viewed with theoptical microscope The average impedance value for this setwas 7685Ohms and the total number of enlarged canals was9 (Figure 8)
Set 9 was used for the instrumentation of 3 mandibularmolars in two different patients 46 47 and 36 The rootswere normally conformedThe average impedance value was
7726Ohms and the total number of enlarged canals was 9(Figure 8)
Sets 11 12 and 10 have been heavily used for a numberof 12 canals each Sets 12 and 11 have been used in theinstrumentation of 4mandibularmolars each Set 12 enlarged46 36 47 and 38 with 2-root-3-canal morphology andhigh curvature Set 11 enlarged 38 48 36 and 37 teethTooth 48 presented a convergent shape of itsmesial and distalcanals Kerekes and Tronstad [26] The set number 10 wasused in the enlargement of fivemaxillary teeth fourmaxillarypremolars three 14 one 24 and a central incisor 11 Theaverage impedance values for these sets were for set 108779Ohms for set 11 8804Ohms and for set 12 9092Ohms(Figure 7) Set number 10 enlarged a number of 11 root canalsand sets 11 and 12 enlarged a number of 12 dental root canalsAll the sets described above show high impedance values andsurface defects when viewed with the microscope especiallyset number 12 and should be readily discarded (Figures 3(e)8 and 9)
Set 13 has been used for 5 molars in two different patientsenlarging a number of 15 dental canals The molars were 3616 and 16 and mandibular right molars 46 and 47 Files F1and F2 were used in each case but file F3 has only been usedin the instrumentation of the distal roots of eachmolar so thisaccounts for the lower wearThe average impedance value forthis set was 12667 and the total number of enlarged canalswas 15 (Figure 8) Surface defects were viewedwith the opticalmicroscope (Figure 3(a))
After the consideration of all sets a few conclusions canbe formulated The first would be that the modification ofimpedance values occurs not with the frequency of clinicaluse but with the difficulty of each case in part It is apparentthat set 4 has less uses than other sets but it presents a patternof wear specific to a higher frequency of clinical use So it isvery important to show that the EIS data correctly quantifiesmodification of oxide layer relative to usage and wear
Although the most worn files showed many surfacedefects in the form of pitting corrosion scratches or evenmissing pieces of alloy the F1 in Set 4 presented a crack inthe file structure posing a breakage risk for future clinical use(Figure 3)
3 Results and Discussion
The results of file testing showed a variation in impedancevalues by comparison to the unused setTheNyquist diagramversus Bode plot in Figure 1 shows how the electrochemicalbehavior of the titanium-oxide layer on the files changes withseveral uses The Ti-oxide layer changes with multiple usesso we measured a new unused file as a reference and then wemeasured a file with many clinical uses 15 enlarged canalsfile F1 set 13 The change was drastic and very easy to spoton the EIS plots and in correlation to the fitting circuits(Figure 2)
In order to confirm that impedance value variation of theoxide layer resounds in alloy defects we analyzed the used F1from set 13 file using the Carl-Zeiss optic microscope and we
4 BioMed Research International
0 15000 30000 45000 60000 75000 900000
50000
100000
150000
200000
250000
minusZ
(Ohm
s)
Z (Ohms)
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 F2 reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 Reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
Z (O
hms)
Frequency (Hz)
(b)
Figure 1 Nyquist and Bode diagrams of S2 files from all sets showing progressive wear starting from reference on (a) and most worn file on(b)
Solution
Electric double layer
Titanium oxide layer
Rct 1 Rct 2
Q2Q1
Q3Rs
Low frequency compensation
for compact oxide layer
Figure 2 Equivalent circuit for EIS fitting
found cracks in its structure (Figure 3(f)) We repeated thisalgorithm with all the file classes and we found that there isa very clear connection between clinical use and oxide layermodification Our limits were placed having as a referencea new set and as a limit to usage the clinically overworkedfiles with very high resistances regardless of set numberthat presented structural defects under the microscope TheNyquist values showed a change in electrical impedance
toward an increase The complexity of evaluating the fileswith this kind of plots was too great so we preferred touse Nyquist only for a qualitative interpretation of oxidelayer change and explanation of surface phenomena Thequantification of resistance variation was done using Bodemodulus plots at a frequency around 10000Hz simply dis-playing the relation between frequency used and resistancemodification
BioMed Research International 5
(a)
(b) (c)
(d)
(e) (f)
Figure 3 Optical microscope images (a) F1 set 4 (b) S1 set 5 (c) S2 set 6 (d) F1 set 7 (e) S2 set 12 and (f) F1 set 13
31 Fitting Circuit The circuit in Figure 2 is an exam-ple of circuit used for EIS data fitting According to theimpedance spectra in the metaloxideelectrolyte configura-tion the equivalent circuit shown in Figure 2 represents theimpedance behavior of the oxide films In this circuit Rsrepresents the aqueous solution resistanceThe two observedcharge-transfer flattened semicircles correspond to two RCparallel combinations and are due to the ionic charge transfer
resistance Rct1 in parallel to the first constant phase element(Q1) and the Rct2 in parallel to the second constant phaseelement (Q2)
A constant phase element (CPE) is generally considereda component that models the behavior of a double layer thatis an imperfect capacitor (pseudocapacitor) In global mea-surements of an irregular surface the CPE behaviour can beattributed to either different surface or normal time-constant
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
BioMed Research International 3
Set 1 is an example of minimal file wear It has been usedto enlarge a maxillary front incisor 11 with a morphologydescribed by Kerekes and Tronstad [24] It has been used inour study to grossly quantify the modification of the oxidelayer after a single use in a straight root canal Its averageimpedance value was 5421Ohms and the total number ofcanals enlarged was 1 (Figures 8 and 9)
Set 2 has been used in the instrumentation of two frontincisors 22 and 21 The set was discarded for researchpurposes only and does not show any objective wear eitherusing direct observation or the microscope Further useworld strongly be recommended Its average impedance valuewas 5924Ohms and the total number of enlarged canals was2 (Figure 8)
Set 3 was used in the instrumentation of 2 maxillarycanine teeth and a maxillary premolar tooth 13 23 and15 The microscope image of the files shows no surfacemodification or defect Its average impedance value was5873Ohms and the total number of enlarged canals was four(Figures 8 and 9)
Set 4 was used for the enlargement of 2 maxillarymolars 17 and 18 Tooth 18 had a two-canal morphologywith an extremely distally curved single root Kerekes andTronstad [25] Also one of the canals had a broken tipof probably a Kerr file that could not be removed Theset shows accentuated wear of the S1 S2 and F1 F2 files(Figure 3(a)) The average impedance value was 11871 a veryhigh value although the total number of enlarged canals was 5(Figures 8 and 9)
Set 5 has been used in the instrumentation of twomandibular molars 46 and 36 in the same patient Soin total a number of 6 canals have been instrumentedThe microscope showed visible defects correlating to highimpedance values as shown regarding the S1 file (Figure 3(b))The average impedance value for this set was 6414Ohms andthe total number of canals was 6 (Figure 8)
Set 6 has been used for the instrumentation of threemaxillary premolars 14 and 15 and a special anatomy of a 25premolar with 2 very narrow and convergent canals Kerekesand Tronstad [25] The strange anatomy of the maxillarypremolar could account for the excessive wear of S1 andS2 (Figure 3(c)) The average impedance value for this setwas 8930 and the total number of enlarged canals was 6(Figure 7)
Set 7was used in the instrumentation of 3 uppermaxillarymolars in a young patient aged 23 years old The set showsnotable modification upon direct observation viewed by themicroscope (Figure 3(d)) The average impedance value forthis set was 6755Ohms and the total number of enlargedcanals was 9 (Figure 8)
Set 8 has been used for 3 molars in two different patientsThe teeth instrumented were 16 47 and 26 The set showshigh EIS values and minimal defects were viewed with theoptical microscope The average impedance value for this setwas 7685Ohms and the total number of enlarged canals was9 (Figure 8)
Set 9 was used for the instrumentation of 3 mandibularmolars in two different patients 46 47 and 36 The rootswere normally conformedThe average impedance value was
7726Ohms and the total number of enlarged canals was 9(Figure 8)
Sets 11 12 and 10 have been heavily used for a numberof 12 canals each Sets 12 and 11 have been used in theinstrumentation of 4mandibularmolars each Set 12 enlarged46 36 47 and 38 with 2-root-3-canal morphology andhigh curvature Set 11 enlarged 38 48 36 and 37 teethTooth 48 presented a convergent shape of itsmesial and distalcanals Kerekes and Tronstad [26] The set number 10 wasused in the enlargement of fivemaxillary teeth fourmaxillarypremolars three 14 one 24 and a central incisor 11 Theaverage impedance values for these sets were for set 108779Ohms for set 11 8804Ohms and for set 12 9092Ohms(Figure 7) Set number 10 enlarged a number of 11 root canalsand sets 11 and 12 enlarged a number of 12 dental root canalsAll the sets described above show high impedance values andsurface defects when viewed with the microscope especiallyset number 12 and should be readily discarded (Figures 3(e)8 and 9)
Set 13 has been used for 5 molars in two different patientsenlarging a number of 15 dental canals The molars were 3616 and 16 and mandibular right molars 46 and 47 Files F1and F2 were used in each case but file F3 has only been usedin the instrumentation of the distal roots of eachmolar so thisaccounts for the lower wearThe average impedance value forthis set was 12667 and the total number of enlarged canalswas 15 (Figure 8) Surface defects were viewedwith the opticalmicroscope (Figure 3(a))
After the consideration of all sets a few conclusions canbe formulated The first would be that the modification ofimpedance values occurs not with the frequency of clinicaluse but with the difficulty of each case in part It is apparentthat set 4 has less uses than other sets but it presents a patternof wear specific to a higher frequency of clinical use So it isvery important to show that the EIS data correctly quantifiesmodification of oxide layer relative to usage and wear
Although the most worn files showed many surfacedefects in the form of pitting corrosion scratches or evenmissing pieces of alloy the F1 in Set 4 presented a crack inthe file structure posing a breakage risk for future clinical use(Figure 3)
3 Results and Discussion
The results of file testing showed a variation in impedancevalues by comparison to the unused setTheNyquist diagramversus Bode plot in Figure 1 shows how the electrochemicalbehavior of the titanium-oxide layer on the files changes withseveral uses The Ti-oxide layer changes with multiple usesso we measured a new unused file as a reference and then wemeasured a file with many clinical uses 15 enlarged canalsfile F1 set 13 The change was drastic and very easy to spoton the EIS plots and in correlation to the fitting circuits(Figure 2)
In order to confirm that impedance value variation of theoxide layer resounds in alloy defects we analyzed the used F1from set 13 file using the Carl-Zeiss optic microscope and we
4 BioMed Research International
0 15000 30000 45000 60000 75000 900000
50000
100000
150000
200000
250000
minusZ
(Ohm
s)
Z (Ohms)
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 F2 reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 Reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
Z (O
hms)
Frequency (Hz)
(b)
Figure 1 Nyquist and Bode diagrams of S2 files from all sets showing progressive wear starting from reference on (a) and most worn file on(b)
Solution
Electric double layer
Titanium oxide layer
Rct 1 Rct 2
Q2Q1
Q3Rs
Low frequency compensation
for compact oxide layer
Figure 2 Equivalent circuit for EIS fitting
found cracks in its structure (Figure 3(f)) We repeated thisalgorithm with all the file classes and we found that there isa very clear connection between clinical use and oxide layermodification Our limits were placed having as a referencea new set and as a limit to usage the clinically overworkedfiles with very high resistances regardless of set numberthat presented structural defects under the microscope TheNyquist values showed a change in electrical impedance
toward an increase The complexity of evaluating the fileswith this kind of plots was too great so we preferred touse Nyquist only for a qualitative interpretation of oxidelayer change and explanation of surface phenomena Thequantification of resistance variation was done using Bodemodulus plots at a frequency around 10000Hz simply dis-playing the relation between frequency used and resistancemodification
BioMed Research International 5
(a)
(b) (c)
(d)
(e) (f)
Figure 3 Optical microscope images (a) F1 set 4 (b) S1 set 5 (c) S2 set 6 (d) F1 set 7 (e) S2 set 12 and (f) F1 set 13
31 Fitting Circuit The circuit in Figure 2 is an exam-ple of circuit used for EIS data fitting According to theimpedance spectra in the metaloxideelectrolyte configura-tion the equivalent circuit shown in Figure 2 represents theimpedance behavior of the oxide films In this circuit Rsrepresents the aqueous solution resistanceThe two observedcharge-transfer flattened semicircles correspond to two RCparallel combinations and are due to the ionic charge transfer
resistance Rct1 in parallel to the first constant phase element(Q1) and the Rct2 in parallel to the second constant phaseelement (Q2)
A constant phase element (CPE) is generally considereda component that models the behavior of a double layer thatis an imperfect capacitor (pseudocapacitor) In global mea-surements of an irregular surface the CPE behaviour can beattributed to either different surface or normal time-constant
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
4 BioMed Research International
0 15000 30000 45000 60000 75000 900000
50000
100000
150000
200000
250000
minusZ
(Ohm
s)
Z (Ohms)
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 F2 reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
F2 set 6 F2 set 7 F2 set 3 F2 set 12 F2 set 9 F2 set 2 F2 set 11
F2 set 4 F2 set 10 Reference F2 set 1 F2 set 5 F2 set 13 F2 set 8
Z (O
hms)
Frequency (Hz)
(b)
Figure 1 Nyquist and Bode diagrams of S2 files from all sets showing progressive wear starting from reference on (a) and most worn file on(b)
Solution
Electric double layer
Titanium oxide layer
Rct 1 Rct 2
Q2Q1
Q3Rs
Low frequency compensation
for compact oxide layer
Figure 2 Equivalent circuit for EIS fitting
found cracks in its structure (Figure 3(f)) We repeated thisalgorithm with all the file classes and we found that there isa very clear connection between clinical use and oxide layermodification Our limits were placed having as a referencea new set and as a limit to usage the clinically overworkedfiles with very high resistances regardless of set numberthat presented structural defects under the microscope TheNyquist values showed a change in electrical impedance
toward an increase The complexity of evaluating the fileswith this kind of plots was too great so we preferred touse Nyquist only for a qualitative interpretation of oxidelayer change and explanation of surface phenomena Thequantification of resistance variation was done using Bodemodulus plots at a frequency around 10000Hz simply dis-playing the relation between frequency used and resistancemodification
BioMed Research International 5
(a)
(b) (c)
(d)
(e) (f)
Figure 3 Optical microscope images (a) F1 set 4 (b) S1 set 5 (c) S2 set 6 (d) F1 set 7 (e) S2 set 12 and (f) F1 set 13
31 Fitting Circuit The circuit in Figure 2 is an exam-ple of circuit used for EIS data fitting According to theimpedance spectra in the metaloxideelectrolyte configura-tion the equivalent circuit shown in Figure 2 represents theimpedance behavior of the oxide films In this circuit Rsrepresents the aqueous solution resistanceThe two observedcharge-transfer flattened semicircles correspond to two RCparallel combinations and are due to the ionic charge transfer
resistance Rct1 in parallel to the first constant phase element(Q1) and the Rct2 in parallel to the second constant phaseelement (Q2)
A constant phase element (CPE) is generally considereda component that models the behavior of a double layer thatis an imperfect capacitor (pseudocapacitor) In global mea-surements of an irregular surface the CPE behaviour can beattributed to either different surface or normal time-constant
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
BioMed Research International 5
(a)
(b) (c)
(d)
(e) (f)
Figure 3 Optical microscope images (a) F1 set 4 (b) S1 set 5 (c) S2 set 6 (d) F1 set 7 (e) S2 set 12 and (f) F1 set 13
31 Fitting Circuit The circuit in Figure 2 is an exam-ple of circuit used for EIS data fitting According to theimpedance spectra in the metaloxideelectrolyte configura-tion the equivalent circuit shown in Figure 2 represents theimpedance behavior of the oxide films In this circuit Rsrepresents the aqueous solution resistanceThe two observedcharge-transfer flattened semicircles correspond to two RCparallel combinations and are due to the ionic charge transfer
resistance Rct1 in parallel to the first constant phase element(Q1) and the Rct2 in parallel to the second constant phaseelement (Q2)
A constant phase element (CPE) is generally considereda component that models the behavior of a double layer thatis an imperfect capacitor (pseudocapacitor) In global mea-surements of an irregular surface the CPE behaviour can beattributed to either different surface or normal time-constant
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
6 BioMed Research International
0 20000 40000 60000 80000 1000000
50000
100000
150000
200000
Z (Ohms)
F2 reference F2 set 1
minusZ
(Ohm
s)
(a)
01 1 10 100 1000 10000 10000001
1
10
100
1000
10000
100000
Reference Set 1 F2 file
Z (O
hms)
Frequency (Hz)
(b)
Figure 4 Comparison between reference set and set 1 F2 file with only one clinical use on a singular root incisor in order to quantify oxidelayer change per one use
Set 1(Ohms) 765963 631267 534759 425947 441056 454192
Figure 5 Comparison between reference set and set 1 with only oneclinical use on a singular root incisor in order to quantify oxide layermodification per one use
distributions Thus normal distributions of time-constantscan be expected in systems such as irregular oxide surfacesas shown by Jorcin et al [27]
F1 fileF3 file F2 file
S2 file S1 file Sx file0
50
100
150
200
Most wornSet 1
Reference
F3 fileF2 fileF1 file
S2 fileS1 fileSx file
F1 file S2 file S1 file Sx
Figure 6 Comparison between reference set and set 1 with one useand the highest impedance value files in the whole lot
The equivalent electric circuit contains a supplementaryconstant phase element (Q3) for lower frequency corre-sponding to the compact oxide coating and indicating thepseudocapacitive behavior of these films
The circuit corresponds to the electrochemical eventsat the interface of file and solution and describes diffusionthrough the oxide layer Based on the values of each circuitcomponent we can compare different files and better under-stand their qualities and wear pattern
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
BioMed Research International 7
0
50
100
150
200
250Re
fere
nce
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
Sx file
(a)
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
020406080
100120140160
S1 file
(b)
S2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
020406080
100120140160
(Ohm
s)
(c)
020406080
100120140160
F1 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(d)
0
50
100
150F2 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(e)
020406080
100F3 file
Refe
renc
e
Set 1
Set 2
Set 3
Set 4
Set 5
Set 6
Set 7
Set 8
Set 9
Set 1
0
Set 1
1
Set 1
2
Set 1
3
(Ohm
s)
(f)
Figure 7 Figure showing pattern of impedance value modification for each of the six files in turn
32 Quantification of Oxide Layer Change per One Use Wewanted to go even further and try to grossly quantify oxidelayer modification per one use in an ideal straight canal Forthis purpose we chose a frontmaxillary tooth 11 and enlargedit to the F3 file Then we measured the files using EIS andcomputed the difference in resistance to the new unused set(Figure 4)
Figures 5 and 6 also summarize the measurementsdescribed above and display a very interesting surface qualityof the files Although the surface modification for one use isimportant these files can theoretically resist a great numberof wear cycles in straight canals So in theory we could usethese files for a much greater number of canals than weactually do The difference in real-life use is that corrosiontogether with mechanical strain wears the files at a muchfaster rate Viana et al [28]
33 General File Description Using EIS
331 Shaping Files SxmdashThis is a file used for the initialroot canal access enlargement A brushing action is indicatedwhile using this file as presented by many authors Luebkeet al Gambarini and Ruddle [18 19 29] In Figure 7 wecan observe the relation of all the files to the referenceSx and we can quantify the oxide layer of each file to thereference one By measuring the reference Sx file we founda value of approximately 696OhmsThe highest resistance isset number 4 227237Ohms roughly three times the initialvalue This set contains the highest impedance value of an Sxfile As a general quality of Sx files they tend to have a higherincrease in impedance values even with a reduced number ofuses This characteristic could be due to their unique shape(Figure 7)
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
8 BioMed Research International
Set averageF3 fileF2 fileF1 fileS2 fileS1 fileSx file
0
50
100
150
200
250
Set aF3 F2FS
Refe
renc
eSe
t 1Se
t 2Se
t 3Se
t 4Se
t 5Se
t 6Se
t 7Se
t 8Se
t 9Se
t 10
Set 1
1Se
t 12
Set 1
3
Resis
tanc
e (O
hms)
Figure 8 Figure showing wear of files and sets compared toreference files The height of each column shows the wear value ofeach file based on ohmic resistance modification
S1mdashShaping 1 is the first of the shaping files in theProTaper set it is very thin and flexible It enlarges the upperparts of the canal toward the middle of the canal Its tipis very thin and flexible and should be able to spin freelyinto the canal a fact presented by Luebke et al [18] Thereference impedance value is approximately 563Ohms Set13 file registers the highest value of 1403Ohms representingthe most worn S1 (Figure 7)
S2mdashThe S2 files enlarge the middle and lower part ofthe canal but do not interfere in the apical stop area Beingless flexible it suffers more from the effects of bending intocurved canals The reference value for these files registered at5316Ohms and the highest impedance value obtained was inset number four 1381 Ohms (Figure 7)
Based on the data presented in Figures 7 and 8 onthe clinical observations we have done and with literatureinformation we can formulate a few observations regardingthe shaping files in the ProTaper set The impedance valuesof the three shaping files present a stable wear pattern It iseasily visible that the increase in resistance of these files incomparison to the finishing files is greater correlating to theclinical conditions of action These files intervene in the firstphase of canal enlargement thus they are subjected to morewear On the whole S1 files present higher impedance valuesthan S2 files So we can already get a grasp of the importanceof flexibility and its effect on file mechanical properties Alsobased on the Nyquist and Bode plots presented in Figure 4correlated with Figure 5 we were able to theoretically assessthe oxide layer modification per one use
332 Finishing Files F1mdashIt prepares the apical area of thecanal It is less elastic than the shaping files and has a morepronounced tendency of breakage as shown by West [3] Wecan conclude based on our results that the reference valuefor these files was 378Ohms and the highest value was of1134Ohms set number 2 (Figure 6) Usually the F1 files have
a tendency to fracture more often being the first files tooperate in the apical third conforming the apical preparation(Figures 3(a) 3(f) and 7)
F2mdashIt enlarges the apical part of the canal and is lessflexible than F1 described by West and Ruddle [3 29] Thereare studies that show interesting results by using only this onefile in root canal enlargement Yared [30] or that special filingtechnique could increase the instrument lifespan De-Deuset al [31] The reference impedance value measured for thiscategory of files was 374Ohms and the highest value of thelot was in set number 2 registering 1397OhmsThe F2 and F3are not used in all patientsThe F2 and F3 can be too large andthe enlargement to this file size could determine useless lossof tooth structurewithout any biostructural requirementThecounterargument would be that the hydraulics of correct rootcanal washing and filling may not be exercised correctly inan insufficiently tapered canal as shown by different authorsFife et al Ruddle and Bukiet et al [5 29 32] This explainswhy there can be discrepancies regarding the wear of F2 andF3 files Some sets may have a large number of uses but mayhave less worn F2 or F3 files and other less used sets may havemore worn F2 and F3 files (Figure 7)
F3mdashIt is the largest and less flexible file in the setdescribed by West and Ruddle [3 29] It can only be used instraight canals because it has an apical transportation effectRuddle [29] The reference impedance value for this file was355Ohms and the highest impedance value for F3 file is inset number 11 registering a value of 843Ohms (Figure 7)
A few observations on the finishing files group can be for-mulated The decrease of flexibility has a great impact on themechanical properties of the filesThis instance coupled withcorrosion and mechanical stress leads to fracture Althoughthe finishing group has greater file diameters and should havea greater mechanical resistance this feature proves to be adisadvantage when it comes to conforming curved dentalcanals The wear pattern of finishing files is also apparent inFigures 7 and 8 presenting a lower increase in impedancevalues compared to the reference although surface defectswere visible using the optical microscope (Figures 3(a) 3(d)and 3(f))
Although file failure and intracanal separation could becatastrophic for the success of root canal therapy we mustbear in mind the difficult conditions in which rotary files actThey are constantly exposed to torsional stress in a corrosiveenvironment by an operator with subjective sensitivity [3 710 11] Furthermore improper handling in regard to disin-fection and sterilization could cause further damage to filesleading to failure [33] EIS could prove to be a useful clinicaltool for monitoring file clinical lifespan but much additionalresearch is needed to understand its relationships to surfacedefects from the instrument manufacturing process and thecrack-microstructure interactions that occur during fatiguefailure under in vivo conditions
4 Conclusions
Based on experimental EIS data for ProTaper we have seenthat with each clinical use the oxide layer found on these
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
BioMed Research International 9
(a) (b)
(c) (d)
(e) (f) (g)
Figure 9 Clinical radiographs (a) set 4 (b) set 3 (c) set 11 (d) set 10 (e) set 11 (f) set 6 and (g) set 1
instruments increases its impedance value The change ofoxide layer is in relation to the surfacemodifications to whichthe alloy is exposed during enlargement procedures thusunderlining EIS as a method to quantify the lifetime of eachinstrument The fact that by comparing EIS data to opticalmicroscope imageswe saw a direct relation to file degradationenables us to allege that our method could become a wayto determine instrument clinical lifetime EIS ohmic valuesthat are double or triple the reference value were correlatedthrough microscopy to surface alterations of the files Thenovelty resides in a correlation between microscopy clinicalaspects and EIS data providing a better understanding andregistration of the ProTaper files clinical lifetime span evenwhen used in curved canals
Conflict of Interests
The authors certify that there is no conflict of interests withany financial organization regarding thematerial discussed inthe paper
References
[1] H Walia W A Brantley and H Gerstein ldquoAn initial investiga-tion of the bending and torsional properties of nitinol root canalfilesrdquo Journal of Endodontics vol 14 no 7 pp 346ndash351 1988
[2] H Schilder ldquoCleaning and shaping the root canalrdquo DentalClinics of North America vol 18 no 2 pp 269ndash296 1974
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
10 BioMed Research International
[3] J D West ldquoIntroduction of a new rotary endodontic systemprogressively tapering filesrdquo Dentistry Today vol 20 no 5 pp50ndash54 2001
[4] M-G Tu S-Y ChenH-LHuang andC-C Tsai ldquoEndodonticshaping performance using nickel-titanium hand and motorProTaper systems by novice dental studentsrdquo Journal of theFormosanMedical Association vol 107 no 5 pp 381ndash388 2008
[5] D Fife G Gambarini and L R Britto ldquoCyclic fatigue testingof ProTaper NiTi rotary instruments after clinical userdquo OralSurgery Oral Medicine Oral Pathology Oral Radiology andEndodontics vol 97 no 2 pp 251ndash256 2004
[6] U Inan C Aydin and Y M Tunca ldquoCyclic fatigue of ProTaperrotary nickel-titanium instruments in artificial canals with 2different radii of curvaturerdquo Oral Surgery Oral Medicine OralPathology Oral Radiology and Endodontology vol 104 no 6pp 837ndash840 2007
[7] H P Lopes I Britto C N Elias et al ldquoCyclic fatigue resistanceof ProTaper Universal instruments when subjected to static anddynamic testsrdquo Oral Surgery Oral Medicine Oral PathologyOral Radiology and Endodontology vol 110 no 3 pp 401ndash4042010
[8] P N R Nair ldquoOn the causes of persistent apical periodontitisa reviewrdquo International Endodontic Journal vol 39 no 4 pp249ndash281 2006
[9] G Plotino N M Grande E Sorci V A Malagnino and FSomma ldquoInfluence of a brushingworkingmotion on the fatiguelife of NiTi rotary instrumentsrdquo International Endodontic Jour-nal vol 40 no 1 pp 45ndash51 2007
[10] O A Peters J O Roehlike and M A Baumann ldquoEffect ofimmersion in sodium hypochlorite on torque and fatigue resis-tance of nickel-titanium instrumentsrdquo Journal of Endodonticsvol 33 no 5 pp 589ndash593 2007
[11] G S P Cheung and B W Darvell ldquoLow-cycle fatigue of rotaryNiTi endodontic instruments in hypochlorite solutionrdquo DentalMaterials vol 24 no 6 pp 753ndash759 2008
[12] M Mındroiu C Pirvu R Ion and I Demetrescu ldquoCompar-ing performance of nanoarchitectures fabricated by Ti6Al7Nbanodizing in two kinds of electrolytesrdquo Electrochimica Acta vol56 no 1 pp 193ndash202 2010
[13] M V Popa I Demetrescu E Vasilescu P Drob D Ionita andC Vasilescu ldquoStability of some dental implant materials in oralbiofluidsrdquo Revue Roumaine de Chimie vol 50 no 5 pp 399ndash406 2005
[14] A R Pelton S M Russell and J DiCello ldquoThe physicalmetallurgy ofNitinol formedical applicationsrdquo JOM vol 55 no5 pp 33ndash37 2003
[15] S B Alapati W A Brantley M Iijima et al ldquoMicro-XRD andtemperature-modulated DSC investigation of nickel-titaniumrotary endodontic instrumentsrdquo Dental Materials vol 25 no10 pp 1221ndash1229 2009
[16] S-H Baek C-J Lee A Versluis B-M Kim W Lee and H-C Kim ldquoComparison of torsional stiffness of nickel-titaniumrotary files with different geometric characteristicsrdquo Journal ofEndodontics vol 37 no 9 pp 1283ndash1286 2011
[17] B Sattapan G J Nervo J E Palamara and H H MesserldquoDefects in rotary nickel-titanium files after clinical userdquo Jour-nal of Endodontics vol 26 no 3 pp 161ndash165 2000
[18] N H Luebke W A Brantley Z I Sabri F L Luebke andL L Lausten ldquoPhysical dimensions torsional performancebending properties and metallurgical characteristics of rotaryendodontic instruments VI Canal Master drillsrdquo Journal ofEndodontics vol 21 no 5 pp 259ndash263 1995
[19] G Gambarini ldquoCyclic fatigue of ProFile rotary instrumentsafter prolonged clinical userdquo International Endodontic Journalvol 34 no 5 pp 386ndash389 2001
[20] S Wu X Liu T Hu et al ldquoElectrochemical stability of ortho-pedic porous NiTi shape memory alloys treated by differentsurface modification techniquesrdquo Journal of the ElectrochemicalSociety vol 156 no 6 pp C187ndashC194 2009
[21] A Lasia ldquoElectrochemical impedance spectroscopy and itsapplicationsrdquo inModern Aspects of Electrochemistry vol 32 pp143ndash248 Kluwer AcademicPlenum Publishers New York NYUSA 1999
[22] V Penta D Vornicescu M Keusgem and C Pirvu ldquoUnder-standing the cleaning effect with sodium hypochlorite of Ente-rococcus Faecalis endodontic pathogen using Electrochemi-cal Impedance Spectroscopy (EIS) Atomic Force Microscopy(AFM) and Surface Plasmon Resonance (SPR)rdquo Digest Journalof Nanomaterials and Biostructures vol 8 pp 1205ndash1214 2013
[23] V Penta and C Pirvu ldquoElectrochemical impedance spec-troscopy investigation on the action of dental endodontic lavagesubstancesrdquo Revista de Chimie vol 9 pp 965ndash970 2013
[24] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human anterior teethrdquo Journal of Endodontics vol3 no 1 pp 24ndash29 1977
[25] K Kerekes and L Tronstad ldquoMorphometric observations onroot canals of human premolarsrdquo Journal of Endodontics vol3 no 2 pp 74ndash79 1977
[26] KKerekes andL Tronstad ldquoMorphometric observations on theroot canals of humanmolarsrdquo Journal of Endodontics vol 3 no3 pp 114ndash118 1977
[27] J-B Jorcin M E Orazem N Pebere and B Tribollet ldquoCPEanalysis by local electrochemical impedance spectroscopyrdquoElectrochimica Acta vol 51 no 8-9 pp 1473ndash1479 2006
[28] A C D Viana E S J Pereira M G A Bahia and V T LBuono ldquoThe influence of simulated clinical use on the flexibilityof rotary ProTaper Universal K3 and EndoSequence nickeltitanium instrumentsrdquo International Endodontic Journal vol46 no 9 pp 855ndash862 2013
[29] C J Ruddle ldquoThe ProTaper endodontic system geometriesfeatures and guidelines for userdquo Dentistry Today vol 20 no10 pp 60ndash67 2001
[30] G Yared ldquoCanal preparation using only one Ni-Ti rotaryinstrument preliminary observationsrdquo International Endodon-tic Journal vol 41 no 4 pp 339ndash344 2008
[31] G De-Deus E J L Moreira H P Lopes and C N EliasldquoExtended cyclic fatigue life of F2 ProTaper instruments usedin reciprocating movementrdquo International Endodontic Journalvol 43 no 12 pp 1063ndash1068 2010
[32] F Bukiet T Soler M Guivarch et al ldquoFactors affecting theviscosity sodium hypochlorite and their effect on irrigant flowrdquoInternational Endodontic Journal vol 46 no 10 pp 954ndash9612013
[33] S Shahi H Mokhtari S Rahimi et al ldquoElectrochemicalcorrosion assessment of RaCe andMtwo rotary nickle-titaniuminstruments after clinical use and sterilizationrdquo Medicina OralPatologia Oral y Cirugia Bucal vol 17 no 2 pp e331ndashe336 2012
![inovaco.rustorage.inovaco.ru/media/project_mo_561/f2/96/a0/1... · №28 (964) 11 и yл z 2018 ^о _а Г Z a _ l Z b a ^ Z _ l kя k 16 k _ g lя [ jя 1999 ] h ^ Z. E-mail: гhel.vedomosti@mail.ru](https://static.documents.pub/doc/80x56/6048f79f06c83e57ed5025c4/a28-964-11-y-z-2018-z-a-l-z-b-a-z-l-k-k-16-k-g-l.jpg)
