Review Dentin Root Damage

Basic Research—Technology

Damage to Root Dentin During Retreatment ProceduresHagay Shemesh, DMD, PhD, Alida C. Roeleveld, DDS, Paul R. Wesselink, DDS, PhD,and Min-Kai Wu, MD, MSD, PhD

Abstract
Introduction: The aim of this study was to explore theinfluence of retreatment procedures on the appearanceof defects on the root canal walls. Methods: Twohundred mandibular premolars were divided into 4groups. One group was left unprepared. The rest ofthe teeth were prepared with ProTaper files up to sizeF4 and filled with gutta-percha and AH26. One groupwas left filled and received no further treatments. Thefilling material was removed from the remaining teetheither with ProTaper retreatment files or with Hedstr€omfiles. Roots were then sectioned and inspected undera microscope. Data were analyzed with the nominalregression test (a = 0.05). Results: No defects wereobserved in the unprepared group. Retreatment groupsshowed significantly more defects than the initial treat-ment group (P < .05).There was no difference betweenthe appearance of defects after retreatment withHedstr€om files and ProTaper retreatment files. The re-maining dentin thickness and level of the root did notsignificantly influence the appearance of defects.Conclusions: Retreatment procedures result in moredefects than initial treatment. When assessing theoutcomes of endodontic retreatment, the substantialdamage to the root canal walls should be considered.(J Endod 2011;37:63–66)
Key WordsHedstr€om file, nickel-titanium, retreatment, root dentin,rotary files

From the Department of Endodontology, Academic Centrefor Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands.

Address requests for reprints to Dr Hagay Shemesh, Depart-ment of Endodontology, Academic Centre for Dentistry Amster-dam (ACTA), Gustav Mahlerlaar 3004, 1081 LA Amsterdam,The Netherlands. E-mail address: [email protected]/$ - see front matter

Copyright ª 2011 American Association of Endodontists.doi:10.1016/j.joen.2010.10.002

JOE — Volume 37, Number 1, January 2011

Orthograde retreatment procedures are performed when initial root canal treat-ments fail. Although the outcome of these retreatments is favorable (1), it was

frequently associated with a lower healing rate than that of initial treatment. Proceduralerrors like perforations and inadequate root filling length were shown to be the mostsignificant factors to influence the outcome (1, 2) as well as presence of periapicallesion and good coronal restoration (3). When orthograde retreatment is indicated,efficient removal of the filling material from the root canal system is essential to ensurea favorable outcome (4, 5). However, the complete removal of endodontic fillings isdifficult or impossible (6). Several techniques can be used for this purpose, includingstainless steel files, nickel-titanium (NiTi) rotary instruments, heat-bearing instruments,ultrasonics, and solvents. Novel techniques seek improved results through NiTi rotaryinstruments and the operating microscope. One example of a dedicated rotary systemfor the removal of gutta-percha is the ProTaper Universal system for retreatment (Dents-ply Maillefer, Ballaigues, Switzerland). It consists of 3 instruments: D1 with tip 30 andtaper 0.09, D2 with tip 25 and taper 0.08, and D3 with tip 20 and taper 0.07.

Defects on the root canal wall were shown to appear after root canal preparationand filling (7, 8). Nonetheless, the appearance of defects was only checked after initialendodontic treatment. Because retreatment requires more mechanical manipulationsin the canal and further preparation of the root canal, it could be that more damageto the root canal wall is caused after these procedures.

The purpose of this experiment was to assess the influence of retreatment proce-dures, namely removal of filling material from the root canal, on the appearance ofdefects on the root canal walls.

Materials and MethodsTwo hundred extracted mandibular premolar teeth were selected and stored in

purified filtered water. Radiographs were taken, and the distance between the bucco-lingual canal walls was measured 10 mm from the apex. Four groups (n = 50) wereformed in such a way that the average canal diameter was 0.7 mm. The crowns wereremoved by using a low-speed saw (Isomet 11-1180; Buehler Ltd, Evanston, IL) withwater cooling, leaving roots approximately 16 mm in length. All roots were examinedwith a stereomicroscope under 12�magnification (Zeiss Stemi SV6, Jena, Germany) toexclude cracks. One group was left unprepared. In the other 3 groups, canal patencywas established with size 20 K-Flexofile (Dentsply Maillefer). Thereafter, canals wereprepared with ProTaper rotary instruments (Dentsply Maillefer) by using a torque-control motor (ATR; Technika, Pistoia, Italy). The full sequence of ProTaper rotary fileswas used at 300 rpm to prepare the canals (files Sx, S1, S2, F1, F2, F3, F4). Each canalwas irrigated with a freshly prepared 2% solution of sodium hypochlorite (NaOCl)between each instrument by using a syringe and a 27-gauge needle. Twelve millilitersof NaOCl solution was used for each root. After completion of instrumentation, passiveultrasonic irrigation was performed with an Irrisafe 20/21 file (Satelec, Merinac cedex,France) to efficiently clean the canals and remove remaining debris (9). After comple-tion of the procedure, canals were rinsed with 2 mL distilled water. All roots were keptmoist throughout the experimental procedures.

Canal FillingCanals were dried by using 3 size 40 paper points (Dentsply De Trey, Konstanz,

Germany). AH 26 (Dentsply De Trey) was mixed according to the manufacturer’sinstructions and introduced into the canal on 2 occasions, 5 seconds each, by usinga lentulo spiral (Dentsply Maillefer) rotating at 400 rpm to 1 mm short of the working

Damage to Root Dentin During Retreatment Procedures 63

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http://dx.doi.org/10.1016/j.joen.2010.10.002

Figure 1. Different defects observed in re-treated teeth.


length. Standardized size 40 gutta-percha cones (Henry Schein, MexicoCity, Mexico), with a 0.2 taper, were coated with sealer and placed intothe root canal to the working length. Roots were filled with the lateralcompaction technique by using a size C spreader (D1 diameter 0.3mm, 0.04 taper) (Dentsply Maillefer) and size 25 standardized gutta-percha cones. The force applied to the spreader or file was controlledby using a household digital scale and kept at a maximum of 2 kg. Apolyvinylsiloxane impression material (President; Colt�ene, Altst€atten,Switzerland) was used around the tooth during the filling proceduresto mimic the mechanisms of stress distribution (8).

Teeth were kept in 100% humidity conditions at 37�C for 3 weeks.One group of teeth (n = 50) was left filled, and no retreatment was per-formed.

Filling RemovalTwo groups were re-treated: In the ProTaper retreatment group,

the root canal filling was removed with ProTaper retreatment files(D1, D2, and D3) that were used sequentially until the working lengthwas reached. A drop of chloroform was introduced into each canal to

64 Shemesh et al.

soften the gutta-percha. Two or 3 additional drops were applied asrequired to reach the working length. The instruments were usedwith a torque-control motor (ATR; Technika) at a constant speed of500 rpm, with a torque of 3 Ncm.

In the Hedstr€om group, the canal filling was removed withHedstr€om files; 3 coronal mm of the root canal filling was removedby Gates Glidden burs 2 and 3. Chloroform was used in the same wayas described above. Hand instrumentation was carried out withH-type files sizes 25, 30, 35 in a circumferential quarter-turn push-pull filing motion to remove gutta-percha and sealer from the canalwalls. To standardize procedures and avoid variables during specimenpreparation, only one operator conducted the experiments.

EvaluationThe roots were rendered clean when no filling debris was

observed in the instrument flutes or in the irrigation solution. Inspec-tion by an operating microscope followed (Zeiss, Jena, Germany) toverify cleanliness of the canals. The total time (including irrigationand changes of instrument) required to attain the working length and


0

10

20

30

40

50

60 %

Hedström Only filling-

No retreatment ProTaper

X

Y

Y

Figure 2. Percentage of roots with defects after retreatment procedures.Groups with different letters are statistically different at P <.05.


complete removal of gutta-percha was recorded in minutes for eachsample.

Examination of RootsThe impression material was removed, and roots were sectioned

horizontally at 3, 6, and 9mm from the apex with a low-speed saw underwater cooling (Leica SP1600, Wetzlar, Germany). Slices were thenviewed through a stereomicroscope (Stemi SV6; Carl Zeiss). Pictureswere taken with a camera (Axio cam; Carl Zeiss) at a magnificationof 12�. The images were then inspected blindly by 2 operators. In 3cases out of a total of 800 slices (<1%), there was a discrepancy inthe interpretation of the images, and a consensus was reached after in-specting the slices again. To avoid confusing definitions of root frac-tures, 2 distinct categories were made: ‘‘no defect’’ and ‘‘defect’’ (8).No defect was defined as root dentin devoid of any lines or cracks whereboth the external surface of the root and the internal root canal wall hadno defects. Defects were defined as all lines observed on the slice thatextended either from the outer root surface into the dentin or from theroot canal lumen to the dentin. A separate entity of ‘‘fracture’’ wasdefined as a line extending from the root canal space to the outersurface of the root. The minimal remaining dentin thickness (RDT)of filled roots was measured in every slice.

Statistical AnalysisNominal regression test was performed to explore the difference

between the groups and the influence of RDT and root level on theappearance of defects. The difference between the times needed tofinalize removal of filling materials was checked with t test. SPSS/PCversion 15 (SPSS Inc, Chicago, IL) was used, with a significance levelof a = 0.05.

0

5

10

15

20

25

30

%

X Y

Z

Only filling- No retreatment

ProTaper Hedström

Figure 3. Percentage of vertical root fractures after retreatment procedures.Groups with different letters are statistically different at P <.05.


ResultsThe unprepared canals demonstratednodefects. Defects were found

in all other groups (Figs. 1, 2). The percentages of roots with defects in thedifferent treatment groups are shown in Fig. 2. Fractures were only foundin the retreatment groups (Fig. 3). There was a significant differencebetween the filling group and both retreatment groups (P = .000).However, no difference was detected between the 2 retreatment groups(P = .07). The RDT after canal preparation or the level of observationshowed no correlation with the appearance of defects (P = .546 and.641, respectively). It took significantly more time to remove the fillingmaterial with Hedstr€om files as compared with ProTaper retreatment files(4.9 � 1.7 and 3.6 � 0.9 minutes, respectively; P = .006).

DiscussionRoot canal preparation with rotary NiTi instruments can damage

the dentin and create defects on root canal walls (7). It seems plausiblethat undergoing these procedures twice for an endodontic retreatmentwill increase the number of defects. This was verified by the results of thecurrent experiment. The damage has a progressive accumulative naturebecause preparation alone results in less damage than preparation andfilling (8), whereas preparation, filling, and retreatment result in evenmore defects. This phenomenon was not reported yet and couldpossibly explain the lower healing rates of retreatments as opposedto initial treatment. More research is being conducted on the influenceof additional potentially damaging procedures like removal of separatedinstruments or placement and removal of posts.

The removal of gutta-percha by using hand files can be a tedious,time-consuming process, especially when the root filling material iswell-condensed (10). Therefore, the use of rotary NiTi instruments inroot canal retreatment might decrease patient and operator fatigue(11). The results of the current experiment support this finding.

Chloroform is known to be most efficient is dissolving gutta-percha (12) and was used in the current experiment to facilitate fillingremoval in both the hand files and NiTi groups. Chloroform can causesignificant softening of dentin after 5 minutes and could thus affect themicrohardness of dentin (13). Although these findings were challengedby Erdemir et al (14), the same group found that chloroform has aneffect on the mineral contents of root dentin (15). Chloroform waspreviously not found to be contributory for shortening the retreatmenttime when using the ProTaper retreatment files (16). However, it wasused in the current experiment to minimize the number of variablesand to mimic the clinical situation.

The RDT did not correlate with the appearance of defects. This is inagreement with a previous study (17) in which filling methods werecompared for their ability to cause defects on the root canal wall. Thesefindings suggest that defects are not necessarily a direct result of weak-ened dentin but might be caused by external factors such as stress,temperature change, and friction of the instruments with the root canalwall.

ConclusionsRetreatment procedures could significantly damage the root and

result in cracks and fractures. No difference was found in the appear-ance of defects when the filling material was removed with ProTaperNiTi files or Hedstr€om files. When assessing the outcomes of endodonticretreatment and the prognosis of retreated teeth, the substantial damageto the root canal walls should be considered.

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

Damage to Root Dentin During Retreatment Procedures 65


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66 Shemesh et al.

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Review Dentin Root Damage