https://doi.org/10.62909/pcjmhs.2025.001 Pioneer College Journal for Medical and Health Sciences (PCJMHS)

Article

Two Nickel-Titanium Retreatment Tools, Respectively, Clean-

ing Effects on Root Canal Filling Materials Are Compared

Wedyan Y. Hasan

Department of Dentistry, Faculty of Dentistry, University of Bilad Alrafidain, Diyala, Iraq;

dr.widyan@bauc14.edu.iq

Abstract: objective： To compare the effectiveness of the ProTaper Universal， R-Endo retreat-

ment files, and a Hedstrom manual technique in the removal of gutta—percha during retreatmen

Methods: 60 single-rooted straight mandibular premolars were selected． The root canals of all

suitcases were formed by Nickel-Titanium revolving apparatuses Hero 642， and obturated with

the lateral strengthening technique． Then all cases were randomly divided into 3 groups(n=20)

and prepared with a Hedstrom manual technique．ProTaper Universal and R—Endo retreatment

files, respectively． Eucalyptol was used as a solvent in the treatment． For all roots， the subse-

quent data were documented： practical mistakes and time of retreatment． Bucco-lingual and

proximal radiographs of the roots were taken, and the percentage area was calculated. The remain-

ing material was premeditated by separating the area of the outstanding filling substantial by the

area of the canal partition． Information was statistically analyzed with Kruskal-Wallis and Mann-

Whitney U tests (P=0．05) ． Results： None of the techniques completely removed the root fill-

ing materials． The remaining filling material was meaningfully less after physical instrumentation

than R-Endo or ProTaper composition (P< 0．05) ． The ProTaper and R-Endo retreatment docu-

mentations had a positive influence, in dropping the time for retreatment (P<0．05) ． Conclusion

： All tested instruments cannot completely remove the filling material inside the root canal．

ProTaper, and R-Endo rotary instruments work faster than manual instruments

Keywords: Root canal retreatment； Nickel-titanium rotary instrumentation； Root canal prepa-

ration

1. Introduction

Elimination of the original filling from the root canal is the most critical step in root

canal retreatment. Removal of gutta-percha, which is tightly bound to the root canal, is

time-consuming and laborious, and is primarily accomplished using manual instruments,

mechanical nickel-titanium instruments, thermal transfer devices, and ultrasonic meth-

ods [1]. Studies have found that the efficiency of gutta-percha removal varies among var-

ious nickel-titanium instruments, and complications such as step-downs and fractures are

also high. The ProTaper Universal and R-Endo instruments are two new nickel-titanium

retreatment instruments specifically designed for gutta-percha removal and access. Cur-

rently, comparative evaluations of these two instruments are limited [2]. This study es-

tablished a retreatment root canal model and, using radiographic analysis combined with

imaging software, compared the efficiency of the ProTaper Universal, R-Endo, and man-

ual H-files in eliminating filling material from the root canal. The characteristics of each

instrument were analyzed for clinical application [3].

Citation: To be added by editorial

staff during production.

Academic Editor: Firstname Last-

name

Received: 20/11/2024

Revised: 24/12/2024

Accepted: 10/1/2025

Published: 14/1/2025

Submitted for possible open access

publication under the terms and

conditions of the Creative Commons

Attribution (CC BY) license

(https://creativecommons.org/license

s/by/4.0/).

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2024, Vol.2 2 of 7

2. Materials and Methods

1.1 Sample Tooth Preparation

Excised mandibular premolars were collected. Inclusion criteria for excised teeth in-

cluded: intact teeth with fully developed root apex, no fillings or restorations, no resorp-

tion, no fractures or longitudinal cracks, no prior endodontic treatment, a single round

root canal with a curvature of <5, and a root length of approximately 18–20 mm. The teeth

were ultrasonically cleaned of soft tissue and calculus and then immersed in a 4% formal-

dehyde solution. The teeth were opened, and a No. 10 K file was inserted into the root

canal until the file tip was visible at the apical pore. Root canal preparation was terminated

by subtracting 0.5 mm. To maintain uniform tooth length, the crown was removed with

an abrasive disc, resulting in a working length of 15 mm for each root [4].

1.2 Root Canal Preparation and Filling

To standardize apical diameters, excised teeth with apical apertures larger than ISO

20# were discarded. Root canals were prepared crown-down using a Hero 642 nickel-tita-

nium rotary instrument to a diameter of 30# and a taper of 0.4. This standardized the final

number of apical preparations, resulting in all canals having a diameter of 30# and a taper

of 0.4. During preparation, 5 ml of 5.25% sodium hypochlorite was used for irrigation with

each change of the enlarging file. After preparation, the root canals were soaked in 1 ml

of 17% EDTA for 30 seconds to remove the smear layer, and finally rinsed with 5 ml of

normal saline. The root canals were dried with paper points and filled with conventional

(2% taper) gutta-percha points and bilan paste using lateral pressure. The canal orifices

were temporarily sealed with glass ionomer [5]. All procedures were performed by the

same operator using standard techniques.

All teeth were stored at 37°C at 100% humidity for 7 days to allow the sealant to set.

1.3 Root Canal Retreatment

Teeth were randomly divided into three groups, 20 in each. Temporary sealing was

removed, and 1 mm of filling material was removed using a G drill. 0.1 ml of eucalyptol

dissolving agent was placed in the gutta-percha at the root canal orifice for 3 minutes. The

order of instrument use and working lengths are shown in Table 1.

Table 1. sequence procedure with instrument and working length (WL)

Group M (Manuel Instruments) used hand-held H files. First, a G drill was used to

remove 3-5 mm of filling material from the root canal orifice. H files #30, #25, and #20 were

then used to remove filling material from the root canal. Once the working length was

Hand Instruments

Group M

WL (mm)

Group P

Protaper

Universal

Group P WL

(mm)

Group R R-

Endo

Group R WL

(mm)

#3 GG Diamond

D1 (30#, 9%)

Rm (25#, 4%)

#2 GG Diamond

D2 (30#, 8%)

Re (25#, 12%)

#1 GG Diamond

D3 (30#, 7%)

R1 (25#, 8%)

#25K File

R2 (25#, 6%)

#20K File

R3 (25#, 4%)

#25K File

Rs (30#, 4%)

#30H File

#35H File

#40K File

#45K File

#50K File

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2024, Vol.2 3 of 7

reached, the root apex was prepared to #30. Finally, a stepwise retraction technique was

used, increasing the instrument size by one per mm, until the root canal was prepared to

#50. The final apical diameter was 0.30 mm, with a taper of 0.05.

Group P used the Protaper Universal. D1 was used to prepare the coronal portion of

the root canal, D2 and D3 to prepare the mid-root and apical portions, respectively. Dur-

ing preparation, a "brushing" motion was applied with gentle lateral pressure to clean the

root canal walls. Finally, D3 was used to reach the working length. The final apical diam-

eter was 0.30 mm, with a taper of 0.07.

Group R used the R. Endo. Manual pressure was applied to the root apex with the

Rm, breaking the hard surface of the filling to create access for the next instrument. The

Re then enlarged the root canal orifice. R1, R2, and R3 were used to sequentially prepare

the coronal, mid-root, and apical segments. Finally, the Rs (30#, 0.04 taper) was used to

prepare the root canal to working length. All instruments, except the Rm, used a circum-

ferential widening maneuver for root canal cleaning. The final apical diameter was 0.30

mm, and the taper was 0.04. Groups P and R used mechanical retreatment instruments.

Driven by the endodontic treatment motor, the root canal filling material was removed

using a crown-down approach at a constant speed (400 r/min in group P, 300 r/min in

group R) with gentle apical force. After preparation reached a certain depth, the instru-

ment blade was inspected, and debris was cleaned from the instrument groove. Only 10

root canals were treated with each instrument. During the preparation process in all three

groups, the eucalyptol dissolving agent was continuously updated (approximately 0.5 ml

per root canal). Each time an enlarging file was changed during preparation, 5 mL of

5.25% sodium hypochlorite was used for irrigation. After preparation, the root canal was

soaked in 1 ml of 17% EDTA for 30 seconds to remove the smear layer, followed by a final

irrigation with 5 ml of normal saline. Retreatment: Complete completion criteria included:

① The last instrument reached its working length, no filling material remained on the

instrument surface, and no filling material debris was observed in the irrigation solution;

② The root canal wall was smooth and free of visible debris. Finally, a temporary sealing

material was used to seal the root canal orifice.

1.4 Evaluation of Retreatment Outcomes

1.4.1 Evaluation of Root Canal Cleanliness: Digital radiographs of the three groups

of specimens were taken from two angles: buccal-lingual and mesio-distal. Using AUTO-

CAD 2000 image analysis software, the root canal was divided into three sections: coronal,

mid-radial, and apical. The percentage of root canal wall area covered by filling material

and the original root canal wall area in each section was analyzed [6]. The analysis did not

distinguish between root filling material and root canal paste covering the root surface.

1.4.2 Operational Safety and Efficiency: The occurrence of blockages, steps, and per-

forations during retreatment was recorded. The operation time required for the complete

cleaning of each root canal was recorded.

1.4.3 Instrument Evaluation: A physician blinded to the significance of the experi-

ment performed 10 root canals with each instrument. After use, the instrument was placed

under a 10x microscope and observed for deformation and separation.

1.5 Statistical Analysis: Data are expressed as ±s. Operation time was analyzed using

a one-way analysis of variance. The root canal cleanliness index, i.e., the filling material

covering the root canal, was significantly different from the root canal cleanliness index.

The percentage of the root canal wall area of the modified material and the original root

canal wall area was analyzed using analysis of variance [7].

2. results

2.1 Evaluation of residual filling material

The results of the filling materials and residues of each group are shown in Figure 1.

The percentage of the residual filling material on the tube wall to the total filling material

is shown in Table 2. The residual amount of filling material in group P was significantly

lower than that in group P and group R (P<0.05). The residual amount of filling material

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2024, Vol.2 4 of 7

in group P was lower than that in group R, but there was no significant difference between

the two groups. The residual fillings in the root canals of each group were mostly located

in the middle and lower parts of the root canals.

Table 2. the area of persent (%) reming filling material in each third rootcannels

Figure 1. Images of gutta-percha and sealer remaining on the root canal walls in

different groups

2.2 Time to remove filling material (Table 3)

The average operation time of group M was significantly higher than that of group P

and group R (P < 0.05), and the average operation time of group P was lower than that of

group R, but there was no statistical significance. During the operation, D1 in group P

caused a step on the upper part of the tube. It was formed and then eliminated by hand

using instruments to pass over it without perforation.

Table 3. Time required for removal of filling materials in different groups

Group

Time(s)

Group M

532 ± 24

Group P

327 ± 33

R group

343 ± 25

2.3 Instrument deformation and fracture

In group M, no instruments were broken or deformed. In group P, two D2 instru-

ments were deformed, and one D3 instrument was broken. In group R, one R3 instrument

was deformed.

3. discussions

During retreatment, it is important to completely remove gutta-percha from improp-

erly prepared or filled root canal systems, as these may contain necrotic tissue. Necrotic

tissue or bacteria can become the source of future periapical disease. Many methods have

Group

Buccal & Lingual -

Root and Crown

Buccal & Lingual -

Middle Part of Root

Buccal & Lingual - Apex

Mediolateral -

Root and Crown

Mediolateral -

Middle Part of Root

Mediolateral

- Apex

Group M

2 ± 7

12 ± 5

29 ± 13

4 ± 7

11 ± 6

28 ± 16

Group P

12 ± 16

32 ± 17

37 ± 15

9 ± 7

23 ± 15

36 ± 19

Group R

14 ± 15

31 ± 17

42 ± 19

9 ± 8

25 ± 21

40 ± 23

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2024, Vol.2 5 of 7

been reported for evaluating residual root filling material, including longitudinal split-

ting, transparent specimen analysis, and CT scanning. This study used radiographs com-

bined with imaging software analysis, which does not damage tooth tissue and is more

reliable than longitudinal splitting, which can lose residual gutta-percha and sealant dur-

ing root splitting. Radiographic evaluation is a semiquantitative method and has limita-

tions. X-ray images only provide two-dimensional information within a three-dimen-

sional structure, which can result in magnification or distortion. Small amounts of residual

material may be lost, and it is also impossible to distinguish between gutta-percha and

sealant. To improve the accuracy of this method, this study observed the teeth from two

angles, and a skilled operator, unaware of the experimental groupings, marked the outline

of the residual material on the radiographs. Currently, most international studies focus

on the removal of root canal material using nickel-titanium root canal preparation instru-

ments. However, differences in the nickel-titanium systems used, evaluation methods,

and canal morphology of the samples result in significant discrepancies in the results (I6).

Many studies report that machine-applied nickel-titanium instruments are more effective

than hand instruments in cleaning. For example, in straight root canal retreatment, Giuli-

ani et al. found that the Protaper Universal cleaned more thoroughly than hand instru-

ments. For curved root canals, Unal et al. found that hand instruments cleaned more thor-

oughly than the Protaper Universal and R-Endo. Gergi et al. found no difference in the

percentage of residual material in root canals after preparation using hand, Protaper Uni-

versal, and R-Endo. Tong Fangli et al. experimented comparing Protaper Universal,

Mtwo, and hand instruments in oval root canals and found that the percentage of residual

filling material in the hand instrument group was significantly lower than that in the

Protaper Universal group. The results of this learning showed that while none of the in-

struments could entirely remove residual material from the root canal, the amount of re-

sidual filling material in the canal wall was significantly lower in the hand instrument

group than in the ProTaper and R-Endo groups, and similar to the results of Unal and

Tong Fangli. This may be due to the following reasons: While other studies have primarily

used straight root canals of maxillary anterior teeth, this study used mandibular premo-

lars, which have straighter middle and upper root canals. The G drill in the hand instru-

ment group was able to clean the middle and upper root canal more thoroughly. The root

canal shape is oval, and the H file has a smaller taper than the nickel-titanium instrument,

making it easier to approach the lateral wall of the oval root canal. Furthermore, the com-

bination of the H file and the K file can remove large pieces of gutta-percha. The residual

filling material in the three groups in this study was significantly reduced. The fillings

were concentrated in the middle and lower third of the root canal, consistent with the

findings of most other studies. This is primarily due to the better functional difference in

the apical third, making cleaning more challenging. The ProTaper Universal group had

less residual filling than the R-Endo group, but the difference was not statistically signifi-

cant. The Protaper Universal instruments, D1 and D3, feature a gradual taper and sharp

cutting edges, providing strong cutting force, capable of removing not only gutta-percha

but also some dentin. Their groove design allows for the insertion of gutta-percha into the

groove and its removal from the root canal. While the D1 has a cutting tip that can pene-

trate gutta-percha, it can also easily cause steps and lateral penetration. In contrast, the R-

Endo, with its non-cutting tip and three equally sized cutting edges, is relatively safe, but

its smaller taper (0.04) after preparation compromises its cleaning effectiveness. Factors

influencing instrument operation time include instrument removal efficiency and the

number of instruments used. Given the same cleaning efficiency, too many instruments

can reduce the speed. In this study, although the use of H files in the hand group acceler-

ated the removal of large pieces of gutta-percha, frequent instrument changes in the hand

group reduced the speed. Similarly, the Protaper Universal (3 instruments) had similar

cutting efficiency to the R-Endo, but with fewer instruments than the R-Endo (5 instru-

ments), the operation was faster. Domestic and international studies also suggest that

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2024, Vol.2 6 of 7

machine instruments are faster than hand instruments. Taper design is a key factor affect-

ing fracture resistance.

4.Conclusions

The Protaper Universal's increased tendency to fracture may be related to its large

taper. In this study, one Protaper Universal instrument fractured and two deformed,

while only one R-Endo instrument (R3) was found to deform. Given the same number of

root canals, the R-Endo instrument has greater durability. Both Protaper Universal and R-

Endo retreatment instruments effectively and quickly remove gutta-percha. Each has its

own unique characteristics, requiring selection based on the specific characteristics and

root canal morphology. For example, the R-Endo is recommended for more curved root

canals to minimize instrument separation; the Protaper Universal will achieve faster

cleaning in larger root canals. However, like hand instruments, they cannot completely

remove all material from the root canal and require access to be established with hand

instruments before preparation, following the principles of nickel-titanium instrument

use.

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2024, Vol.2 7 of 7

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