Comparative evaluation of retreatment techniques by using different file systems from oval-shaped canals.

INTRODUCTION: Endodontic failure resolves after complete removal of obturating material followed by disinfection, cleaning, shaping and three-dimensional obturation.
MATERIALS AND METHODS: Seventy single-rooted mandibular premolars, with single oval-shaped root canal were included. They were decoronated at a length of 16 mm from the apex. Shaping and cleaning were performed, and obturation was done using the warm lateral compaction technique. The teeth were divided into seven groups according to retreatment procedures (Hand files; ProTaper Universal retreatment files; MTwo® Retreatment system; R-Endo® Retreatment system; ProTaper Universal retreatment files with solvent and ultrasonics; MTwo® R with solvent, and ultrasonics and R-Endo® with solvent and ultrasonics). The data were obtained and subjected to the statistical analysis.
RESULTS: All instrumentation techniques left obturating material with least in Group 6 and maximum Group 5. The mean time taken for complete retreatment procedure was minimum in Group 2 and maximum with Group 1.
CONCLUSION: MTwo® R with solvent and ultrasonics, R-Endo®, and R-Endo® with solvent and ultrasonics were effective in gutta-percha removal from coronal third, middle third, and apical third, respectively. Significance: Nonsurgical endodontic retreatment using rotary files helps in gaining access to infected teeth. During retreatment procedure, this helps disinfectant to reach in critical areas of the root canal system, thereby decreasing the microbial load, leading to achieve healthy periradicular tissues. Copyright:

INTRODUCTION

Endodontic failure is described as condition wherein clinically the treated tooth is symptomatic, and periapical lesion that appears subsequent to endodontic treatment radiographically. These failures occur due to the factors such as access related, missed canals, access cavity perforations, instrumentation related, ledge formation, separated instruments, foreign objects, and obturation related due to coronal leakage. Thus, to eliminate failure and to achieve successful outcome, endodontic retreatment could be performed either by nonsurgical endodontic retreatment (NSERT) or through periradicular surgery.[1] Currently, failure rate is about 14%–16% after initial root canal treatment.[2] This NSERT is an attempt to re-establish healthy periapical tissues. it requires regaining access to the root canal system by removing the obturating material followed by three dimensional cleaning, shaping, disinfection and obturation.[3] Complete removal of obturating material exposes the necrotic tissue remnant that may be responsible for the persistent disease. Removal of gutta-percha and root canal sealer would help in maximizing the ability to disinfect the root canal system.[4]

The different methods used for the removal of obturating material are chemical (chloroform, xylene, eucalyptol, orange oil, tetrachloroethylene, methoxyflurane, cinnamon oil, halothane, isoflurane, anise oil, almond oil, and turpentine oil), mechanical (hand and rotary endodontic files), physical (ultrasonic, heat, and laser), and finally, combination techniques (heat and endodontic files, endodontic files and chemicals, Paper points, and chemicals). There are various studies reporting efficacy, cleaning ability, and safety of rotary nickel-titanium (NiTi) instruments. The most commonly used NiTi retreatment systems are ProTaper universal retreatment files, R-Endo® files, and MTwo® R files.

ProTaper retreatment files have three different lengths, unique tapers, and diameters to sequentially remove obturating materials. These files are D1 (cutting tip, size 30, 9% taper) used for coronal third, D2 (noncutting tip, size 25, 8% taper) used in middle third, and D3 (noncutting tip, size 20, 7% taper) used for apical third. MTwo® retreatment files consist of R15/0.05 (tip size 15, 5% taper) and R25/.05 (cutting tip, size 25, 5% taper). R-Endo system has a noncutting having tip sizes and taper as R1 (25/08) used in coronal third, R2 (25/06) used in middle third and R3 (25,04) aids in obturating material removal from the apical third.

Orange oil is an excellent solvent constituting dlimonene, which is responsible for good solubility. It was found that orange oil does not have any deleterious effect xylol, chloroform on guttapercha.[5]

Various researches have been done on different file systems, with or without the aid of solvent and ultrasonics in obturating material removal in circular canals. This in vitro experimental study aims to evaluate and compare the efficacy and time taken for complete removal of obturating material by using ProTaper universal retreatment, R-Endo®, and MTwo® Rretreatment techniques. The null hypothesis was that these retreatment techniques were unable to remove obturating material in oval-shaped canals.

MATERIALS AND METHODS

Selection of teeth

Seventy single-rooted mandibular premolars, with single oval-shaped root canal were included. The oval-shaped canals were defined as having a maximum diameter of up to two times greater than minimum diameter of the canal.[6] Oval shape was determined when buccolingual to mesiodistal dimensions ratio is about 1.3:1.[7] The teeth with more than one canal, curved canal, immature apices, root caries, and calcifications were excluded. The teeth were cleaned, autoclaved, and stored in 0.2% thymol. They were decoronated at cemento-enamel junction perpendicular to the long axis of the root such that root length was 16 mm.

Teeth preparation

Access cavity preparation was done, and working length was determined by introducing size 10 K-file till it extruded from the apex. The length was measured, and working length was set 1 mm short of measured length. The glide path was established and ProTaper (Dentsply Maillefer, Ballaigues, Switzerland) files were used for cleaning and shaping. Each file was lubricated with Glyde (Dentsply Maillefer, Ballaigues, Switzerland) before introduction in the canal. During preparation, between each file, 2 ml of 5%NaOCl was used as irrigant. The canals were prepared till F2. After complete instrumentation, all specimens were irrigated with 5 ml of 17% liquid ethylenediaminetetraacetic acid followed by 5 ml of saline solution and were dried with corresponding paper points (Dentsply Maillefer, Ballaigues, Switzerland). The canals were obturated with F2 gutta-percha and AH plus sealer (Dentsply Maillefer, Ballaigues, Switzerland) with warm lateral compaction technique. The quality of obturation was deemed adequate when no voids were seen on mesio-distal and bucco-lingual digital radiographs.[8] The teeth were sealed with temporary filling material (Cavit, Detrey, Dentsply) and stored in humidifier at 37°C for 2 weeks.[9]

Retreatment technique

The teeth were randomly assigned into seven experimental groups (n = 10). For rotary file system, X-Smart motor was used at 500 rpm speed and 2 Ncm torque. The solvent was not used for Groups 2, 3, and 4.

Group 1 Hand files

Two ml of Wonder orange solvent (Pulpdent, USA) was placed in the coronal portions of canal. The smaller Hedstrom files (Mani Inc., Japan) sizes 15 and 20 were used for the removal of obturating material. Once the working length was reached, sizes 25 and 30 K-files were used till they came out clean.

Group 2 ProTaper Universal retreatment files

Obturating material was removed using the crown down method. These files were used in brushing action with lateral pressing movements. The D3 file was taken till working length.

Group 3 MTwo® Retreatment system

The obturating materials were removed initially using sizes 1–3 Gates Glidden drills coronally. The canals were instrumented using R2 in a brushing action with lateral pressing movement. The files were progressed till working length by applying slight apical pressure. The blades of file and debris on file were inspected frequently.

Group 4 R-Endo® Retreatment system

This file system was used in gentle in and out motion on the canal walls. The R1 and R2 files were used to one-third and two-thirds of the estimated working length, respectively. The R3 was used till the working length for the removal of obturating material.

Group 5 ProTaper Universal retreatment files with solvent and ultrasonics

In addition to the sequence followed for Group 2, 2 ml of Wonder orange solvent was placed in canal and activated using ultrasonics (25 K-file attached to an EMS scaler on a medium power setting 25KHz).

Group 6 MTwo® R with solvent and ultrasonics

The sequence followed was same for Group 3. The use of solvent and ultrasonics was similar to Group 5.

Group 7 R-Endo® with solvent and ultrasonics

The sequence followed was same for Group 4. The use of solvent and ultrasonics was similar to Group 5.

Digital radiographs were taken in both buccolingual and mesio-distal direction. If the digital radiographs revealed remaining gutta-percha, the root canals were reinstrumented.[10]

Time recorded

Time was recorded with stop watch (in minutes) till the working length was reached (T1). The time taken to change the instrument was excluded. The time required to achieve satisfactory gutta-percha removal was recorded as T2. Total time for retreatment was the sum of T1 and T2.[11] All procedures were accomplished by a single-operator eliminate bias.

Sample analysis

Two longitudinal grooves were placed on the outer surface of roots. The teeth were split into two half with a chisel and mallet. Each half was further divided into three parts: coronal, middle, and apical third. Samples were evaluated at ×20 magnification. No attempt was made to distinguish between residual sealer and gutta-percha. The amount of residual filling material was scored according to Ezzie et al.'s criteria [Table 1].[12]

Table 1

Scoring Criteria according to Ezzie ey al.

Score	Criteria
1	No to slight presence (0%-25%) of obturation debris on the dentinal surface
2	Some presence (25%-50%) of obturation debris on the dentinal surface
3	Moderate presence (50%-75%) of the obturation debris on the dentinal surface
4	Heavy presence (>75%) of obturation debris on the dentinal surface

The presence of material on root canal walls was evaluated individually by three examiners. They were blinded to the methods of retreatment used for each tooth, and scoring was done.

Statistical analysis

Mean values for debris score were tabulated Table 2 and analyzed using the statistical analysis software MedCalc (MedCalc software for windows, Version 12.7.5, Ostend, Belgium). The result was evaluated using the ANOVA and post hoc Bonferroni test. The P value was considered statistically significant if <0.05. The result stated that all instrumentation techniques left obturating material with no statistically significant difference. However, in Group 6, least obturating material was seen, and maximum was seen in Group 5 [Table 2]. Post hoc Bonferroni test showed remnants in the coronal, middle, and apical third for each group [Table 3] The mean time taken for complete retreatment procedure was found minimum in Group 2 and maximum in Group 1 [Table 4]. The efficacy of groups in terms of mean time taken to complete procedure was ProTaper > R-Endo > ProTaper + ultrasonics > R-Endo + ultrasonics > MTwoR > MTwoR + ultrasonics > H-file [Tables 4 and 5].

Table 2

Comparison of mean scores and standard deviation of the canal wall cleanliness

Groups	n	Mean	SD	SEM	95% CI for mean		Minimum	Maximum
					Lower bound	Upper bound
Group 1: Handfile	10	2.2350	0.44570	0.14094	1.9162	2.5538	1.67	2.67
Group 2: ProTaper	10	2.1340	0.75820	0.23976	1.5916	2.6764	1.33	3.67
Group 3: MTwo R	10	2.0990	0.49912	0.15784	1.7420	2.4560	1.33	2.67
Group 4: R-Endo	10	1.7660	0.66697	0.21091	1.2889	2.2431	1.00	3.33
Group 5: ProTaper + ultrasonic	10	2.2660	0.98013	0.30994	1.5649	2.9671	1.00	3.67
Group 6: MTwoR + ultrasonics	10	1.6660	0.56743	0.17944	1.2601	2.0719	1.00	3.00
Group 7: R-Endo + ultrasonics	10	2.1670	0.83570	0.26427	1.5692	2.7648	1.00	3.67
Total	70	2.0476	0.70565	0.08434	1.8793	2.2158	1.00	3.67

n: Number of samples, SD: Standard deviation, SEM: Standard error mean, CI: Confidence interval

Table 3

Comparison of the mean scores and standard deviation in the canal wall cleanliness/mean remaining debris score according to the interaction of groups in each third

Groups	Section	n	Mean	SD	SEM	Minimum	Maximum
Group 1:	Coronal	10	2.10	0.57	0.18	1.0	3.0
Handfile	Middle	10	2.50	1.18	0.37	1.0	4.0
	Apical	10	2.10	0.99	0.31	1.0	4.0
	Total	30	2.23	0.94	0.17	1.0	4.0
Group 2:	Coronal	10	2.30	0.67	0.21	1.0	3.0
ProTaper	Middle	10	1.90	0.99	0.31	1.0	4.0
	Apical	10	2.20	1.32	0.42	1.0	4.0
	Total	30	2.13	1.01	0.18	1.0	4.0
Group 3:	Coronal	10	2.30	0.82	0.26	1.0	4.0
MTwo R	Middle	10	1.60	0.70	0.22	1.0	3.0
	Apical	10	2.40	1.07	0.34	1.0	4.0
	Total	30	2.10	0.92	0.17	1.0	4.0
Group 4:	Coronal	10	2.20	0.92	0.29	1.0	4.0
R-Endo	Middle	10	1.40	0.97	0.31	1.0	4.0
	Apical	10	1.70	1.06	0.33	1.0	4.0
	Total	30	1.77	1.01	0.18	1.0	4.0
Group 5:	Coronal	10	2.40	1.07	0.34	1.0	4.0
ProTaper:	Middle	10	2.10	0.99	0.31	1.0	4.0
Ultrasonics	Apical	10	2.30	1.42	0.45	1.0	4.0
	Total	30	2.27	1.14	0.21	1.0	4.0
Group 6:	Coronal	10	1.60	0.97	0.31	1.0	4.0
MTwo R:	Middle	10	1.60	0.84	0.27	1.0	3.0
Ultrasonics	Apical	10	1.80	0.63	0.20	1.0	3.0
	Total	30	1.67	0.80	0.15	1.0	4.0
Group 7	Coronal	10	2.40	0.84	0.27	1.0	4.0
R-Endo:	Middle	10	2.40	1.17	0.37	1.0	4.0
Ultrasonics	Apical	10	1.70	1.06	0.33	1.0	4.0
	Total	30	2.17	1.05	0.19	1.0	4.0

n: Number of samples, SD: Standard deviation, SEM: Standard error of mean

Table 4

Mean score and standard deviation of the time taken in removal of gutta-percha

Technique	n	Mean	SD	SEM	Minimum	Maximum
Handfile	10	11.24	0.41	0.13	10.35	12.00
ProTaper	10	3.87	0.77	0.24	3.22	5.40
MTwoR	10	5.04	0.97	0.31	4.11	6.52
R-Endo	10	4.49	0.79	0.25	3.25	5.50
ProTaper + ultrasonics	10	4.72	0.66	0.21	4.03	6.02
MTwoR + ultrasonics	10	5.44	0.87	0.28	4.40	7.29
R-Endo + ultrasonics	10	5.01	0.79	0.25	4.12	6.22
Total	70	5.69	2.44	0.29	3.22	12.00

n: Number of samples, SD: Standard deviation, SEM: Standard error of mean

Table 5

Mean difference and P value amongst the groups for the time taken for removal of gutta-percha/sealer

Groups	Intergroup comparison	Mean difference	SE	P
Handfile	ProTaper	7.361*	0.35	<0.0001
	Mtwo R	6.192*	0.35	<0.0001
	R-Endo	6.749*	0.35	<0.0001
	ProTaper + ultrasonics	6.516*	0.35	<0.0001
	MTwo R + ultrasonics	5.793*	0.35	<0.0001
	R-Endo + ultrasonics	6.225*	0.35	<0.0001
ProTaper	Handfile	−7.361*	0.35	<0.0001
	MTwo R	−1.169*	0.35	0.026
	R-Endo	−0.61	0.35	1.000
	ProTaper + ultrasonics	−0.85	0.35	0.360
	MTwo R + ultrasonics	−1.568*	0.35	<0.0001
	R-Endo + ultrasonics	−1.136*	0.35	0.034
MtwoR	Handfile	−6.192*	0.35	<0.0001
	ProTaper	1.169*	0.35	0.026
	R-Endo	0.56	0.35	1.000
	ProTaper + ultrasonics	0.32	0.35	1.000
	M-TwoR + ultrasonics	−0.40	0.35	1.000
	R-Endo + ultrasonics	0.03	0.35	1.000
R-Endo	Handfile	−6.75	0.35	<0.0001
	ProTaper	0.61	0.35	1.000
	MTwo R	−0.56	0.35	1.000
	ProTaper + ultrasonics	−0.23	0.35	1.000
	MTwo R + ultrasonics	−0.96	0.35	0.154
	R-Endo + ultrasonics	−0.52	0.35	1.000
ProTaper + Ultrasonics	Handfile	−6.52	0.35	<0.0001
	ProTaper	0.85	0.35	0.360
	MTwo R	−0.32	0.35	1.000
	R-Endo	0.23	0.35	1.000
	MTwoR + ultrasonics	−0.72	0.35	0.844
	R-Endo + ultrasonics	−0.29	0.35	1.000
Mtwo R + Ultrasonics	Handfile	−5.793*	0.35	<0.0001
	ProTaper	1.568*	0.35	<0.0001
	Mtwo R	0.40	0.35	1.000
	R-Endo	0.96	0.35	0.154
	ProTaper + ultrasonics	0.72	0.35	0.844
	R-Endo + ultrasonics	0.43	0.35	1.000
Rendo + Ultrasonics	Handfile	−6.225*	0.35	<0.0001
	ProTaper	1.136*	0.35	0.034
	MTwo R	−0.03	0.35	1.000
	R-Endo	0.52	0.35	1.000
	ProTaper + ultrasonics	0.29	0.35	1.000
	MTwo R + ultrasonics	−0.43	0.35	1.000

SE: Standard error, P < 0.05 - Significant result

DISCUSSION

Single-rooted mandibular first and second premolars were taken as it showed 27% prevalence of oval-shaped canal anatomy.[13] Mandibular premolars have an average root length of 14 mm. The teeth were decoronated at 16 mm length from apex, retaining 2 mm of coronal structure for coronal seal. Orange oil solvent was used as it yields the larger number of dentinal tubules free of obturating materials as compared to other solvents.[14] Ultrasonics were used as an adjunct in dislodging the remnants of obturating material using the electromagnetic energy.

In the current study, the amount of remaining filling material was evaluated by longitudinal cleavage, and quantitative analysis was done under stereomicroscope with 20X magnification.[81516] Debris scores were analyzed according to Ezzie et al.'s criteria.[12] This method was chosen because of its simplicity.[1718] Other method of scoring has been given by Hulsmann and Bluhm in 2004 were gutta-percha, and sealer was measured in millimeter, and scoring was done on a scale of 1–7.[11]

In the present study, no significant difference was found between different techniques of gutta-percha removal. Similar results were found when rotary, reciprocating, and adaptive motion systems were used for the evaluation of gutta-percha removal.[19]

In this study, ProTaper retreatment file left highest debris. These findings were in accordance with other study, were ProTaper files showed more debris than FlexMaster, GreaterTaper, Hedstrom files when used with or without solvent eucalyptol. These results can be attributed to the D3 tip size 20, which would be limiting factor for gutta-percha removal. This can be considered as a disadvantage of the ProTaper retreatment files compared to MTwo® R and R-Endo® both of which have 25 apical tip size.

In this study, ProTaper retreatment file removed gutta-percha fastest when compared to other rotary systems due to their specific flute design. The file not only cut gutta-percha but also the superficial layer of dentin during the root filling removal. Other features are progressive tapers of D1, D2, and D3 files which make it possible to shape specific sections of a root canal with one file. The flute design and rotary motion cut the large amount of gutta-percha around the instrument and direct it toward the orifices. These findings wherein contrast with other study where significant difference was found with ProTaper over RaCe, K3, and H Files in the removal of obturating material.[20]

In the current study, debris was present on the canal wall with lower score with group 6 when solvent and ultrasonics were used. The better performance of MTwo® file is attributed to the design of instrument. It has S-shaped cross-section, an increasing pitch length in the apical-coronal direction, cutting tip, and with positive rake angle. It does not require crown-down instrumentation sequence. Further, these files have sharp blades that help the file to cut through canal and reach the apical end-point while by passing the obturating material. These findings were in accordance with other study, wherein MTwo® file performed better as it has a small core diameter and better chip removal capacity with increased chip space that can result in great cutting ability.[21] However, contrast findings were found in other study, wherein ProTaper left significantly lesser gutta-percha and sealer than MTwo®.[15] Recently, a study concluded that when chloroform was used as the solvent with MTwo® retreatment system, there was decrease in the efficiency of instruments.[22] Similarly, it was found that the presence of solvents led to more gutta-percha and sealer remnants on root canal walls and inside dentinal tubules.[2324]

Earlier studies reported that R-Endo® retreatment files and H-files have similar effectiveness in removing filling material in straight root canals[1525] and in curved canals.[26] Similar findings were seen in the current study. However, other studies concluded that R-Endo® retreatment files were less effective in removing filling material from root canal walls than manual instruments.[2627] This might be due to the fact that K-files were used in combination with H-files for gutta-percha removal which seemed to be advantageous.

In this study, NiTi rotary files took less retreatment time than hand files. This could be attributed to the gutta-percha plasticization resulting from instrument rotation which results in softened gutta-percha that is less resistant, easy to penetrate, and remove.[28] Other study stated that hand files were faster during retreatment procedure, and this findings could be attributed the change of rotary files.[29] It was found that when rotary files and solvents were used for retreatment, it took less time for obturating material removal.[830] However, other studies stated that rotary files without solvent speeded up the retreatment time.[31] When solvents were used fine layer of softened gutta-percha adhered to the root canal walls during retreatment thus takes more time for the removal. Further, solvent did not play a significant role for root canal wall cleanliness.

Failure of NiTi instrument was not observed in the present study. This can be attributed to the fact that, each instrument was discarded after retreating five canals thus reducing substantially the possibility of instrument seperation.[10] Furthermore, the null hypothesis was rejected as all groups were effective in removing obturating material. The result of this study would be biased since one of the groups had ProTaper retreatment files. It is known that D1, D2, and D3 are the same as F3, F2, and F1 but with different lengths and in sequence. One of the limitations of this study would be the use of steriomicroscope for the evaluation of obturating material remnants.

These findings were in accordance with other study, wherein MTwo® file performed better as it has a small core diameter and better chip removal capacity with increased chip space that can result in great cutting ability.[2122]

CONCLUSION

Within the limitations, it can be concluded that none of the retreatment techniques completely cleaned the oval-shaped canals. MTwo® R files with solvent and ultrasonics were most effective in gutta-percha removal from coronal third, R-Endo® was effective in middle third and R-Endo® with solvent and ultrasonic was effective in the apical thirds. Further, ProTaper Universal retreatment files took the minimum time for gutta-percha removal. Thus, for the success of NSERT complete removal of previous endodontic material is required for the elimination of endodontic microflora from the root canal system. More studies should to carried out using other endodontics file system to evaluate the efficacy in oval-shaped canals.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.