Basic Research—Technology

Comparative Assessment of the Effects of Gates-Glidden,Largo, LA-Axxess, and New Brazilian Drill CPdrillon Coronal Pre-enlargement: Cone-beamComputed Tomographic AnalysisCl�audia Bohrer Flores, DDS, MSc,* Francisco Montagner, DDS, MSc, PhD,†

Brenda P.F.A. Gomes, DDS, MSc, PhD,‡ Gustavo Nogara Dotto, DDS, MSc, PhD,§

and Marcia da Silva Schmitz, DDS, MSc, PhDk

Abstract

Introduction: The removal of dentin interferences fromthe cervical third of root canals is essential for theircorrect cleaning and shaping and to facilitate accessof endodontic instruments to the critical apical region.In mandibular molars, the concavity observed in thefurcation area reduces dentin thickness, making this re-gion more susceptible to perforation. The presentex vivo study used cone-beam computed tomographicimaging to compare 3 rotary burs with a new rotary burrecently launched in Brazil (ie, CPdrill; Helse Industryand Commerce Ltda, Santa Rosa, S~ao Paulo, Brazil)regarding the amount of dentin removal from the distalwall of the mesial root of mandibular first molars.Methods: A total of 40 root canals were selected andrandomly divided into 4 groups for cervical preparation:Gates-Glidden burs #2 and #3 (Dentsply Maillefer, Bal-laigues, Switzerland), Largo burs #1 and #2 (DentsplyMaillefer), LA-Axxess burs #1 and #2 (SybronEndo,Glendora, CA), and CPdrill burs (1-size only). Dentinthickness in the distal wall of mesial canals at 2 mmfrom the furcation was measured using I-CATvision soft-ware before and after cervical preparation. Results:There was no statistically significant difference betweengroups regarding residual dentin thickness after instru-mentation with the drills (P = .684). Conclusions: Itwas concluded that CPdrill is safe for use in cervicalpreparation of the mesial root of mandibular first molarsbecause it did not promote excessive dentin removal ondistal walls. (J Endod 2014;40:571–574)

From the *Public Practice, Santa Maria, Rio Grande do Sul, BraziSul, Rio Grande do Sul, Brazil; ‡Endodontic Division, Piracicaba Dentment of Stomatology, Federal University of SantaMaria, SantaMaria,of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil.

Address requests for reprints to Dr Cl�audia Bohrer Flores, Rua Mcbfendo@gmail.com0099-2399/$ - see front matter

Copyright ª 2014 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2013.08.028

JOE — Volume 40, Number 4, April 2014

Key WordsCervical preparation, cone-beam computed tomography, mandibular first molars, riskzone, rotary burs

Preparation of the cervical third of root canals is an essential step for the removal ofdentin interferences, cleaning and shaping, and consequently filling of the root

canals. However, excessive dentin removal as a result of cervical preflaring, especiallyin curved and narrow canals, may cause perforation of the concavity located in thefurcation region.

The mesial root of mandibular first molars is markedly concave in its distal aspect,showing reduced dentin thickness (1). For this reason, this tear area of dentin iscommonly referred to as the risk zone (2). Moreover, the mesiobuccal and mesiolingualcanals are frequently located closer to the distal wall than represented on radiographs(1–3). Dentin thickness remaining after cervical preflaring reported by differentstudies varies between 0.39 and 0.97 mm (4–11).

Numerousmethods have been proposed for the assessment of root canal preparationprocedures, including the muffle (12), the endodontic cube system (13), and cone-beamcomputed tomographic (CBCT) imaging (14, 15). CBCT imaging is different from theother 2 methods because of its noninvasive nature (16). Moreover, CBCT-derived imagesare highly accurate and reliable (17) and have proved to be useful tools in root canalexploration (16).

Different rotary instruments have been recommended for use in the preparation ofthe cervical third of root canals. Recently, the Brazilian industry has released a 1-sizeonly rotary bur, the CPdrill. According to the manufacturer, this bur would have thefollowing major advantages: faster instrumentation and lower cost; 1 bur only canreplace all the different sizes of traditional burs, such as Gates, Largo, and Peeso,with no need for instrument change during treatment; increased safety, as a result ofits shape, which limits bur action to the cervical third of the root canal and thus avoidsany contact with critical areas of the furcation region; adaptability to different root canalanatomic variations and preparation techniques; and versatility because it can bemounted on the engine available at the practitioner’s office. To the best of the authors’knowledge, no study has been designed to assess the efficacy of this bur or its effects on

l; †Endodontic Division, Department of Conservative Dentistry, Federal University of Rio Grande doal School, State University of Campinas, Piracicaba, S~ao Paulo, Brazil; §Radiology Division, Depart-Rio Grande do Sul, Brazil; and kEndodontic Division, Department of Stomatology, Federal University

ajor Duarte, 560, Bairro Menino Jesus, Santa Maria, RS, Brazil. CEP 97050-460. E-mail address:

Gates-Glidden, Largo, LA-Axxess, and CPdrill 571

Basic Research—Technology

dentin removal during cervical preparation. Therefore, the objective ofthe present study was to comparatively assess, using CBCT imaging, theamount of dentin removal in the distal wall of the mesial root of mandib-ular first molars after the use of the CPdrill rotary bur, which wasrecently launched in the Brazilian market, in relation to other instru-ments used for this purpose.

Materials and MethodsThe present research protocol was approved by the Research

Ethics Committee of Universidade Federal de Santa Maria, Santa Maria,Brazil. Twenty permanent mandibular first molars obtained from thetooth bank of the Universidade Federal de Santa Maria School ofDentistry were radiographed and stored in thymol at 0.1%. Tooth spec-imens presented fully formed roots, root canal systems classified asWeine type II or type III, and no previous endodontic treatment. Coronalopening was performed conventionally using a diamond bur #1014 (KGSorensen, Cotia, SP, Brazil). Pulp chamber roofs were removed usingan Endo Z bur (Dentsply Maillefer).

Canals were irrigated with 3 mL 2.5% sodium hypochlorite(Manipulation Pharmacy Nova Derme, Santa Maria, RS, Brazil). Rootcanals were instrumented using a manual K-type 25-mm #10 Flexofile(Dentsply Maillefer). The file was introduced into the root canal until itstip became visible at the apical foramen. To guarantee that the burswould reach the zone with the highest susceptibility to perforation(ie, 2 mm apical to the furcation), a minimum bur penetration depthwas determined for each tooth using a digital pachymeter (Digimess In-strumentos de Precis~ao Ltda, S~ao Paulo, SP, Brazil). Minimum penetra-tion consisted of the distance from furcation to cusp plus 2 mm (Fig. 1).To guarantee that the burs would safely act on the risk zone, they werecalibrated using a silicone stop fixated using universal instant adhesive(Henkel Ltda, S~ao Paulo, Brazil).

The methodology adopted for CBCT image acquisition was basedon a previous study of the authors (18). Briefly, specimens weremounted on quadrangular models embedded in a type III gypsumcast (Polidental Ltda, Cotia, SP, Brazil) and positioned for the acquisi-tion of preoperative images (before cervical preparation). Images were

Figure 1. Measurement from the furcation to the cusp.

572 Flores et al.

obtained using a GX CB-500 scanner powered by i-CAT (Kavo DentalGmbH, Bieberach, Germany). The following parameters were used:scan time of 26 seconds, 120 kVp, 5 mA, and a voxel size of 0.25mm. Axial slices were subsequently reconstructed using specific soft-ware; the image reconstruction process required approximately 1 min-ute. Images were saved for subsequent comparison with postoperativeresults.

After the first image acquisition session, the 40 root canals wererandomly assigned to 1 of 4 groups as follows: Gates-Glidden burs#2 and #3 (Dentsply Maillefer), Largo burs #1 and #2 (Dentsply Mail-lefer), LA-Axxess burs #1 and #2 (SybronEndo, Glendora, CA), andCPdrill burs (1-size only). Straight up-and-down motion was used inthe Gates-Glidden group, whereas the anticurvature filing method wasused in the other 3 groups. In the Gates-Glidden, Largo, and LA-Axxess groups, cervical enlargement was performed starting withsmall-diameter instruments followed by those with larger diameters.In all groups, canals were irrigated with 3mL 2.5% sodiumhypochlorite(Manipulation Pharmacy Nova Derme) at each instrument change. Allburs were mounted on a TC3000 engine (Nouvag; TCM Endo, Goldach,Switzerland) and operated at 10,000 rpm.

After cervical preflaring procedures, specimens were onceagain positioned on the gypsum cast and scanned using the sameparameters described previously. Images obtained before and aftercervical preparation were compared and measured using I-CATvi-sion software (Dental Imaging System, Salt Lake City, UT) (Fig. 2Aand B).

Results were analyzed using the Student t test and 1-way analysis ofvariance. Significance was set at 5%.

ResultsOur results showed that before cervical preparation, no significant

differences were observed in the mesiobuccal and mesiolingual canalsassessed in terms of dentin thickness (Student t test, P= .132). In addi-tion, 1-way analysis of variance revealed the absence of statisticallysignificant differences among groups regarding dentin thicknessmeasured after cervical preparation (Table 1, P = .684) and dentin

Figure 2. (A) Measurement of the risk zone before cervical preparation. (B)Measurement of the risk zone after cervical preparation.

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TABLE 1. Mean Values (� standard deviation) for Dentin ThicknessMeasured before and after Cervical Preparation in Each Group (mm)

Gates-Glidden Largo LA-Axxess CPdrill

Before After Before After Before After Before After

Mean 1.103a 0.822b 1.186a 0.850b 1.040a 0.863b 0.952a 0.772b

Standarddeviation

0.19 0.18 0.16 0.23 0.08 0.12 0.21 0.15

Identical superscript letters indicate the absence of statistically significant differences: a0.08, b0.684.

TABLE 2. Mean Values (� standard deviation) for Dentin ThicknessReduction Obtained with Different Rotary Instruments (mm)

Gates-Glidden Largo

LA-Axxess CPdrill

Mean 0.281a 0.336a 0.177a 0.180a

Standard deviation 0.18 0.24 0.05 0.13N 10 10 10 10

Identical superscript letters indicate the absence of statistically significant differences.

Basic Research—Technology

thickness reduction after cervical preparation with the different instru-ments assessed (Table 2, P = .139). There were no cases of instrumentfracture.

DiscussionThe present study used CBCT to obtain images and I-CATvision

software to measure dentin thickness in the distal wall of the mesialroot of mandibular first molars, at 2 mm apical to the furcation(risk zone), after cervical preparation with 4 different rotary sys-tems. The aim of this study was to assess a new bur recentlylaunched in Brazil.

The use of this methodology was based on the study of Flores et al(18), which allowed specimens to be identically positioned at the 2image acquisition stages, with no changes in mesiodistal or buccolin-gual orientation, thus allowing pre- and postoperative images to beadequately compared. Because I-CATvision software was used, noimage manipulation was necessary, avoiding any possibility of imagedistortion. According to previous results suggested by with Duarteet al (11), we preferred to use CBCT imaging instead of computed mi-crotomography because this latter method is time-consuming, expen-sive, and often unavailable.

The root canals included in the present study were considered asthe units of analysis. There were no statistical differences among spec-imens regarding the dentin thickness of distal walls before cervicalpreparation (P = .132). This finding is in agreement with previousresearch (10, 11, 19, 20). In the present study, Gates-Glidden, Largo,and LA-Axxess burs were compared with the CPdrill, which was recentlyintroduced in the Brazilian dental market. The CPdrill has an inactive tipand a 7-mm-long cutting portion, comprising the 6 diameters of the

Figure 3. CPdrill characteristics, as provided by the manufacturer (Helse Industr

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Gates-Glidden bur (Fig. 3). To standardize the action of instrumentsmounted on the same engine and operating at the same rotation speed(10,000 rpm), we selected only stainless steel burs that would act on thestraight portion of the root canal. The use of Gates-Glidden burs #3 witha 0.90-mm diameter was determined based on previous studies thathave also used this diameter during cervical preparation (4, 6, 7, 9,10, 11, 21–23). A Largo #2 with the same diameter was selected.Finally, LA-Axxess burs #1 and 2, with a .20-mm tip and .06 taperand a .35-mm-diameter tip and .06 taper, respectively (11, 15), wereused because these burs showed a better relationship between theremoval of dentin projections and the determination of first apicalfile size (24–26).

The kinematics adopted for Largo, LA-Axxess, and CPdrill burswas the anticurvature technique (2), compared with straight up-and-down motion with Gates-Glidden burs. Such difference was based onthe fact that anticurvature movements used in association with Gates-Glidden burs are known to increase the risk of their shank fracture(7, 9).

No significant differences (P = .05) were observed in dentinremoval among the different burs used for cervical preparation whencompared with CPdrill. The CPdrill was easy to handle, satisfactorilyremoved dentin interferences, and safely acted on the risk zone. Themean dentin thickness observed before cervical preflaring was 0.9mm compared with 0.7 mm after the procedure (dentin removal aslow as 0.2 mm). Moreover, no differences or reductions in cuttingcapacity were observed in any of the burs assessed.

In conclusion, our results showed that Gates Glidden #3, Largo #2,LA-Axxess #2, and CPdrill provided adequate cervical preparation of theroot canals. The CPdrill showed similar performance to the other in-struments, but additional studies are necessary. Moreover, it should

ia e Comercio Ltda, Santa Rosa, S~ao Paulo, Brazil).

Gates-Glidden, Largo, LA-Axxess, and CPdrill 573

Basic Research—Technology

be emphasized that the analysis of the root canal anatomy as well as ofthe instruments available in the market regarding their shape, cuttingcapacity, and usage is important to select an adequate instrument forcervical preparation.

AcknowledgmentsThe authors deny any conflicts of interest related to this study.

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