Clinical Research

The Effect of Canal Preparation on Fill Length in Straight RootCanals Obturated with GuttaCoreRobert B. Whitten, DMD, MSD, and Marc E. Levitan, DDS

Abstract

Introduction: A common critique of using thermoplas-ticized carrier-based obturators is the incidence of over-extension. It would be of benefit to clinicians to have atechnique for canal preparation that would allow forpredictable length control. This study compared straightcanals instrumented to a size 40 file using a 0.04 stan-dardized taper preparation (STP) and a varied taperpreparation (VTP) by evaluating the extension of Gutta-Core (GC) obturators (Dentsply Tulsa Dental, Tulsa, OK).Methods: Eighty extracted mature human premolarswith single straight canals were randomly divided into2 experimental groups (n = 40). The STP group was in-strumented to size 40/.04 at the working length (WL).The VTP group was instrumented to size 40/.02 at theWL. Both groups were obturated with a size 40 GC obtu-rator. Extension of the material, in relation to the WL,was evaluated and assessed ordinally. Statistically sig-nificant differences were determined by a 2-group chi-square test with a 2-sided P value set at P = .05 anda Fisher exact test of equal proportions. Results: Signif-icant differences in extrusion existed between the STPand VTP groups when controlling for the type of apicalpreparation (P = .0005). The STP group resulted in a47.2% incidence of overextension, whereas the VTPgroup resulted in 10.5% overextension of obturatingmaterial. Conclusions: The results indicate that whenfilling straight canals with GC obturators the canal canbe instrumented using a varied tapered canal prepara-tion with a low likelihood of overextension. (J Endod2014;-:1–4)

Key WordsGuttaCore, overextension, thermoplastic carrier-basedobturation, varied taper preparation

From the Medical University of South Carolina, Charleston, SouAddress requests for reprints to Dr Marc E. Levitan, Director Post

levitanm@musc.edu0099-2399/$ - see front matter

Copyright ª 2014 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2014.09.020

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Two of the main goals in obturation of a root canal are complete, homogeneous, 3-dimensional (3D) fill and extension of the obturation material to a specific working

length (WL) and containing that material within the canal space of the tooth (1). Varioustechniques using thermoplasticized materials have been developed to compensate forchallenges in 3D obturation (2–5). One such technique uses thermoplastic carrier-based obturators that consist of 2 parts: (1) a centrally located carrier made of metal,plastic, or cross-linked gutta-percha and (2) the obturation material that surrounds thecarrier consisting of gutta-percha or synthetic material.

However, until recently, obturators have presented their own challenges to clini-cians. It has been reported that when attaining 3D obturation of the canal, it is achievedwith concomitant overextension of the obturating material through the apical foramen(6). This overextension results in decreased healing (7). Another issue is difficulty intheir removal either for establishing a post space for a final restoration or when retreat-ment for a case is indicated.

Some currently available thermoplastic carrier-based obturation products areThermafil Plus (TP) (Dentsply Tulsa Dental, Tulsa, OK), RealSeal 1 (RS 1) (Sybro-nEndo, Glendora, CA), and a new material GuttaCore (Dentsply Tulsa Dental). Thesesystems are similar in that they all use proprietary ovens to heat the surrounding ma-terial to a specific proprietary temperature before seating the obturator to the canal WL.It has been shown that increased extension and ability of thermoplasticized gutta-perchato flow into lateral canals and irregularities varied directly with the insertion rate of theTP obturators (6). At rates that ideally reproduced the complex internal anatomy of thecanal and produced a dense fill, overextension of the sealer and gutta-percha beyondthe WL and through the apical foramen was an undesirable common observation (6).Robinson et al (8) studied overextension with thermoplastic obturators and found thatwhen comparing Profile 0.06 and Profile GT (Dentsply Tulsa Dental) preparations ob-turated with TP or Profile GT obturators, the incidence of apical extrusion (overexten-sion) was 30% and 50%, respectively. Other studies on TP have also verifiedoverextension as being a common observation (9, 10). It should be noted thatoriginally Thermafil was manufactured with a metal carrier, whereas now TP isproduced with a plastic carrier. For the TP technique, the manufacturer suggestsusing a metal instrument (size verifier) similar to a hand file at the WL to verify theobturator size immediately before obturation.

RS 1 has a synthetic polymer-based obturation material (Resilon) developed as analternative for gutta-percha. The carrier is a polysulfone-containing polymer with radi-opaque filler that is coated by Resilon. The RS 1 system uses a smooth surface, noncut-ting plastic size verifier at the WL. Obturators are then heated in an RS 1 oven and seatedto the WL per manufacturers’ instructions (11, 12).

GC is unique in that it possesses a rigid, cross-linked gutta-percha core, whichserves as the carrier for the coating of alpha-phase gutta-percha. The manufacturer statesthat the core is unaffected by the heat of the oven but exhibits advantages over plastic or

th Carolina.graduate Endodontics, Medical University of South Carolina, Charleston, SC 29425. E-mail address:

The Effect of Canal Preparation 1

Figure 1. STP and VTP (not to scale).

Clinical Research

metal carrier-based systems. The manufacturer suggests that after place-ment in the canal it is much easier for the clinician to remove this newstyle of obturator (ie, for post space preparation or retreatment). GC,like TP, also uses a metal hand instrument as a size verifier at the WL.

Before canal obturation, the manufacturers’ instructions for RS 1,TP, and GC recommend that canals be instrumented to a specific tip sizeand taper for the corresponding obturators. All of the aforementionedsystems use a size verifier instrument matching the tip size and taper ofthe preparation to a specific obturator tip size. The manufacturers sug-gest that the placement of the size verifier to the WL will ensure obtura-tors reach the desired WL after canal instrumentation. However, this hasnot served as a deterrent to overextension for these products.

Because overextension of the various thermoplastic carrier-basedobturation systems is both an unpredictable and undesirable outcome,it is of significant clinical value if a specific canal preparation techniqueis shown to obtain more predictable length control. In a study of stan-dardized taper preparation (STP) and varied taper preparation (VTP)in straight canals, it was shown that TP showed less overextension in VTPthan in STP (13).

To date, no studies have been performed with GC comparingdifferent mechanical preparations of canals to assess their influenceon the incidence of overextension. The purpose of this study was tocompare a 0.04 STP with a specific VTP in straight canals by assessingthe apical extension of GC filling material in both preparations.

Materials and MethodsA total of 80 extracted mature human mandibular premolar teeth

with single straight canals and patent apices were selected. All teeth wereradiographed from the buccal and mesial directions to aid in assessingthe criteria of samples. The canal length was assessed microscopically(5�) by placing a size 15 K-file into the canal until it was flush with theroot surface at the apical foramen and then measured. The WL was es-tablished by subtracting 1.0 mm from this measurement. The WL for allsamples was standardized to 18.0 mm. In a pilot study, it was deter-mined that the ideal insertion rate for GC was 6 mm/s to control foroverextension and still obtain a dense filling. To attain this rate, obtura-tors were inserted to the WL at a constant speed for 3 seconds.

Canal InstrumentationThe teeth were randomly divided into 2 experimental groups

(n = 40): STP and VTP. The STP group was instrumented in a crown-

2 Whitten and Levitan

down manner beginning with 40/.10 and 25/.08 RaCe orifice shapers(Brasseler USA, Savannah, GA) followed by 50/.04 and 40/.04 shapersat the WL using Vortex Blue rotary files (Dentsply Tulsa Dental).

The VTP group was instrumented in a crown-down manner begin-ning with 40/.10 and 25/.08 RaCe orifice shapers followed by VortexBlue rotary files 50/.06 at the WL � 3 mm and 45/.04 at the WL �2 mm. The apical 2 mm was hand instrumented to 40/.02 at the WLusing Lexicon FlexNTK Files (SybronEndo) (Fig. 1).

All teeth were instrumented manually at room temperature by a sin-gle operator using an Aseptico DTC AEU-25 torque-controlled motor anda contra-angle rotary handpiece with 8:1 reduction (Dentsply TulsaDental). The motor was set at 600 rpm and 150 gcm torque per operatorpreference. Canals were irrigated after each instrument with a total of10 mL 4.0% sodium hypochlorite (Clorox Company, Oakland, CA) fol-lowed by 5 mL saline; ProLube (Dentsply Tulsa Dental) was used forlubrication during the use of each rotary or hand instrument. A size15 K-file was placed into the canal to a length 1 mm beyond the WL (flushwith the root surface) after the use of each instrument to maintain apicalpatency. After the last file was used with ProLube at the WL, a final rinsewith 10 mL sterile water was completed, and all canals were dried withsize 40 Lexicon absorbent paper points (Dentsply Tulsa Dental).

Canal ObturationThe STP group samples prepared to 40/.04 at the WL were

checked with a #40/.04 size verifier fitting passively at the WL. Per man-ufacturer’s instructions, it is advised to use an obturator 1 size smallerwhen the final shape is a 0.04 taper. However, a pilot study was per-formed using 35/.04 obturators for this preparation with outcomesshowing about 85% overextension, whereas 40/.04 obturators resultedin a lower incidence of overextension; 40/.04 obturators seated to theWL were chosen for this group but not per manufacturer’s instructions.

The VTP group samples were instrumented to 40/.02 at theWL, buta #40/.04 size verifier would only fit passively to WL� 2 mm. The sizeverifier was not extended more apically because the apical 2 mm hadonly a 0.02 taper. The size verifier check and the use of 40/.04 obtura-tors to the WL for this group were not per manufacturer’s instructions.

Samples from both groups were identified and then randomized bya clinician before obturation so the operator was blinded to the prep-aration type for all samples. All obturation was performed by a singlecalibrated operator. Samples were held in a dry 2� 2 inch cotton gauzeand positioned such that the apical area was shielded from view of the

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TABLE 1. GuttaCore Incidence of Overextension

Ordinal Group STP*(n = 36), n (%) Group VTP*(n = 38), n (%)

1. WL � 1 mm 19 (52.8) 34 (89.5)2. >1 mm past WL 17† (47.2) 4† (10.5)

Results expressed as number of samples (after exclusion) followed by the percentage of n for the group.

*Statistically significant difference between the proportion of overextensions, P = .0005 (2-group chi-square test).†Statistically significant difference between preparation type, P = .0004 (Fisher exact test).

Clinical Research

operator during the obturation phase. Each sample had a light coatingof ThermaSeal Plus Ribbon Sealer (Dentsply Tulsa Dental) dispersedthroughout the canal using size 40 absorbent paper points. Obturatorswere heated in a GuttaCore Obturator Oven (Dentsply Tulsa Dental) asspecified by the manufacturer. Obturators were introduced into canalsand seated to the WL for all samples in a single motion at a constantspeed for 3 seconds from a coronal reference point to the WL(18.0 mm). Before the study, a stopwatch was used to calibrate theoperator to ensure consistency by a board-certified endodontist familiarwith the technique. After obturation, each apex was rinsed with 70%isopropyl alcohol (Henry Schein, Melville, NY) to remove excess sealerwithout damage to gutta-percha so the material could be observed ifoverextension occurred.

The obturation of the roots was evaluated by 2 calibrated, blindedobservers for 2 criteria: density of the canal fill and extension of thefilling material. All samples were examined immediately after thealcohol rinse, analyzed radiographically, and viewed with a surgicaloperating microscope (Seiler IQ DOM; Seiler Precision Microscopes,St Louis, MO) at 5�. Any samples exhibiting voids in the fill wereexcluded. The overextension of obturating material was assessed ordi-nally as per other similar studies (6, 13): (0) >1.0 mm short of the WL,(1) WL� 1.0 mm, and (2) >1.0 mm beyond the WL. (No samples wereassessed as 0.)

Data for samples were statistically analyzed. After excluding sam-ples exhibiting voids, there were 36 samples for the STP group and 38for the VTP group. A 2-group chi-square test with a 2-sided P value= .05was determined to have 80% power to detect the difference in overex-tension between groups. The association between overextensions ac-cording to canal preparation type was assessed using a chi-squarestatistic. The Fisher exact test of equal proportions was also performedfor the data because it was determined to be statistically significant. Sta-tistical analysis was conducted using SAS version 9.2 (SAS Institute Inc,Cary, NC) with significance set at P = .05.

ResultsThe outcomes from each group are shown in Table 1. There was a

significant association between the proportion of overextensions andthe canal preparation type (P = .0005). The Fisher exact test resultedin significant results (P = .0004), indicating there are differences in filllengths between the 2 preparation techniques. The STP techniqueshowed worse outcomes than the VTP technique with 47.2% of theSTP group resulting in overextension compared with only 10.5% inthe VTP group.

DiscussionThe purpose of this study was to evaluate the effect of the geometry

of 2 canal preparations in straight canals on the extension of GC. Therationale for an open model system was that in an ex vivo study designreproducing the apical resistance provided by an intact periodontal lig-ament would have undermined this purpose by restricting the flow of

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the filling material. Prior studies have used the open model system toassess canal obturation (13–15). Another consideration was maderegarding obturating the samples at room temperature instead ofnormal body temperature. Because obturation of samples occurredwithin 20�F of normal body temperature, the authors deemed thisdifference to have a negligible effect on the outcome.

It was observed that for GC obturators, the carrier (core) is notconsistently centered within the volume of the surrounding gutta-percha. Often the obturator demonstrated exposure of the core alongits length as it appeared in the original packaging. The GC obturatorsare formed by a dip technique during the process of manufacturing,but what effect this may have on the flow of gutta-percha during obtu-ration is unknown.

The physical properties of the materials may play a role intheir behavior within the canal (6, 13, 16, 17). The gutta-perchaof the heated obturator as it approaches the canal orifice isapproximately 200�C (13). Thermoplasticized gutta-percha actsthixotropically, allowing it to flow with less viscosity at faster inser-tion rates (ie, more force) (6). In the STP group, the viscosity ofGC was low enough to permit the filling material to flow to the WLbut with inadequate geometric constriction to avoid overextension.In the VTP group, the gutta-percha viscosity was low enough to alsopermit flow to the WL, but the geometric constriction of the apical2 mm may have restricted the flow of the gutta-percha enough toenable the material to become more viscous, resulting in betterlength control.

The authors did not demonstrate the use of GC obturators permanufacturer’s suggested recommendations in a control group. How-ever, results from pilot studies were unable to show favorable outcomesgiven the parameters of this study. Lastly, when the size verifier extendedto the WL in the STP group, the overall outcomes for obturation assess-ment were less favorable than when the size verifier extended to the WL� 2 mm in the VTP group.

The results of this in vitro study suggest that when filling canalswith GC obturators at a specific insertion rate, a 36.7% lower likeli-hood of overextension can be attained using VTP compared withSTP. If the clinician prefers to use GC obturators, this study validatesthe use of VTP to decrease the occurrence of overextension in straightcanals.

AcknowledgmentsThe authors thank the American Association of Endodontists

Foundation for the grant and SybronEndo and Tulsa DentalSpecialties for providing necessary instrumentation, irrigation,and obturation materials. The authors would also like to expresstheir gratitude to Stephanie Shaftman, MSc, MS, for her statisticalsupport.

Supported by an endodontic research grant from the AmericanAssociation of Endodontists Foundation.

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

The Effect of Canal Preparation 3

Clinical Research

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