Efficiency Evaluation of Various Solvents in Retreatment of Endodontic Filling in Extracted Teeth.

Objectives: The aim of this study was to evaluate the retreatment duration and efficacy of eucalyptol and tea tree oil in engine driven and manual retreatment of epoxy resin based endodontic filling in extracted human teeth. Methods and materials: Sixty human single rooted teeth were randomly divided into two groups. The first group was prepared using hand files, and the second one using Reciproc system. Root canals were filled with gutta-percha points and AH Plus sealer. Retreatment was performed using K-reamers and Hedström files for the first group, and Reciproc instruments for the second group. Each group was divided into two subgroups (n=15) according to the retreatment solvent used (eucalyptol or tea tree oil). Root canals were longitudinaly split and analized with stereomicroscope (15x magnification). The surface of the remaining filling material was measured using an image processing software.
Results: There were no statistically significant differences in the area of residual filling material among used solvents, nor in applied technique. Retreatment with Reciproc instruments was significantly faster compared to retreatment using hand files. The manual retreatment technique was faster when tea tree essential oil was used as a solvent compared to eucalyptol. Conclusions: Australian tea tree oil and eucalyptus oil were equally effective in removing endodontic filling material, but none of canals were completely free of the residual filling material. Retreatment with Reciproc instruments was faster compared to retreatment using hand files. The manual retreatment technique is faster when tea tree essential oil is used as a solvent compared to eucalyptol.

Introduction

Endodontic retreatment is indicated in cases of unsuccessful primary endodontic treatment (, ). The main goal of retreatment is to establish conditions that will enable healing of the periapical process. This includes the removal of inadequate filling, cleaning of root canals and making a new filling and the restoration that will disable marginal leakage into the endodontic space from the oral cavity, the periapical and periradicular area. An adequate threedimensional and void-free filling inactivates all irritants in root canal that were not removed during cleaning, which prevents their survival and harmful effects. Root canals are usually filled with a combination of gutta-percha points and a sealer (-) Gutta-percha is the main material that fills the most of the root canal space, whereas the sealer flows to areas that are not regular and are hard-to-reach for mechanical instrumentation. The importance of sealers is significant. Sealers are neccesary for formation of a leakproof barrier between the gutta-percha and the walls of root canal (). Retreatment of this type of filling can be performed with or without solvents; using hand stainless steel instruments; by engine-driven, reciprocating and rotating techniques using NiTi instruments; using an ultrasound and laser or devices that release heat and soften the gutta-percha (-).

The introduction of nickel–titanium (Ni–Ti) engine-driven instruments in endodontics made mechanical preparation of root canals easy and predictable. Improved simplicity is a consequence of reduced number of instruments that shortened the root canal treatment duration. Moreover, Ni–Ti engine-driven instruments improved the shaping and cleaning ability of the root canal during clinical procedures (, ).

In 2011, the reciprocating instrumentation system, Reciproc (VDW, Munich, Germany) was introduced into clinical practice. It requires an engine-driven device (VDW Silver or Gold Reciproc, VDW Gmbh, Munich, Germany) and three different files: R25 (red, 25/0.08), R40 (black, 40/0.06), R50 (yellow, 50/0.05). Since rotary techniques are longer in use than reciprocating ones, numerous studies have evaluated their effectiveness and compared them with other techniques (-). Many studies have stated that rotary techniques are more efficient than hand techniques (, ), while others (, ), didn't find any signifficant differences between these two techniques.

When the reciprocating root canal instrumentation and retreatment techniques appeared, numerous studies have evaluated their effectiveness and compared it with other techniques (-). Most of them reported the superiority of the reciprocating technique over others (, ). There are studies that didn't find significant differences between reciprocating and other (usually engine-driven) techniques (, ).

A number of studies have shown that, regardless of the retreatment technique (whether hand or engine-driven), with or without the use of a solvent, it is not possible to completely remove the filling material from root canals (, , ). Therefore, according to some authors (-), the use of solvents is definitely recommended because they are necessary for dissolving filling material from hard-to-reach anatomical ramifications and dentinal tubules. During solvent-free retreatment, there is a risk of various mechanical damage to the original endodontic space due to excessive friction between the canal walls and the cutting edges of the instruments, which releases heat high sufficiently to soften the gutta-percha, which is then further pushed into the canal space ().

For many years chloroform has been used as root canal retreatment solvent (-). However, since in 1976, the U.S. Food and Drug Administration banned chloroform because of potential carcinogenicity and cytotoxicity (), eucalyptus essential oil became often used alternative solvent which, in addition to biocompatibility and relatively successful and rapid dissolution of root canal filling, also has antibacterial, antifungal and antiviral effect (, , ). Apart from eucalyptol, other essential oils, such as orange oil, pine needle oil, white pine and tea tree oils (Australian tea tree - melalleuca alternifolia) have also been researched (). Tea tree oil is also a successful solvent for gutta-percha since it has antibacterial, antifungal, antiviral and anti-inflammatory effects (, ).

The purpose of this study was to compare the efficacy and time required for dissolving gutta-percha and AH Plus sealer from root canals between eucalyptus essential oil (Eucalyptus globulus) and Australian tea tree oil (Melaleuca alternifolia) in manual (K-reamers and Hedström files) and the machine (Reciproc) retreatment technique.

The first null hypothesis of the study was that there is no significant difference in efficacy of dissolving root filling using eucalyptus essential oil and Australian tea tree oil in manual and machine retreatment technique.

The second null hypothesis of the study was that there is no significant difference in time required for dissolving root filling using eucalyptus essential oil and Australian tea tree oil in manual and machine technique.

Materials and methods

Sample selection

The Ethics Committee of the Faculty of Dentistry, University of Zagreb approved the research (05-PA-26-3/2018).

This study was carried out on permanent maxillary and mandibular human teeth with fully developed roots without signs of tooth decay, external resorption and previous endodontic treatment. The teeth were extracted because of periodontal, orthodontic and other health reasons at the Department of Oral Surgery, School of Dental Medicine, University of Zagreb. After extraction, the teeth were rinsed under running water, cleaned of soft tissue deposits and stored in 0.5% chloramine. Specimens were sterilized in an autoclave.

The access cavities were made on the occlusal side of the lateral, and the oral side of anterior teeth, using a fissure diamond drill No. 016 (Komet, Rock Hill, SC, USA) mounted on a turbine, under water cooling. The roof of the pulp chambers was removed with a round carbide drill #3. The pulp was removed with a pulp extirpation instrument, and the root canal lengths were measured by inserting a K-file #10 or #15 (Maillefer, Ballaigues, Switzerland) to the apical orifice after which the instrument was retracted for one millimeter. The average root canal length was 14 mm. According to the instrumentation technique, 60 root canals were divided into two groups (n = 30). Sample size was chosen according to comparable research in the available literature. Test samples were randomly assigned to test groups by using a chance procedure. Single operator was performing sample preparation and measurements.

Root canal preparation and filling

Group I

The first group was prepared using hand files; K-reamers, K-files and H-files (Maillefer, Ballaigues, Switzerland), apically up to ISO #40 (MAF) and coronally up to ISO #80, using the “step-back” technique. Between each instrument, the root canals were rinsed with 1 ml of 2.5% sodium hypochlorite (NaOCl) (T.T.T. d.o.o., Sveta Nedjelja, Croatia) with a disposable plastic syringe (volume 2 ml) and a 30G blunt tip needle. Final removal of the residual smear layer was performed by rinsing the root canal with 1 ml of 2.5% NaOCl for 30 sec., 15% ethylenediamintetraacetic acid (EDTA) (Calsinase, Lege artis, Dettenhausen, Germany) for 60 sec. and saline (B. Braun Adria d.o.o., Zagreb, Croatia). The canals were then dried with sterile paper points.

The root canals were filled with standard gutta-percha points (DiaDent, Seoul, Korea) and AH Plus sealer (Dentsply DeTrey, Konstanz, Germany), mixed according to the manufacturer's instructions, using the cold lateral condensation technique. The master cone #40 was coated with sealer and applied to the canal to a previously measured length and pushed laterally and apically with a spreader #25, creating space for an additional gutta-percha point of appropriate size. Additional gutta-percha points coated with sealer were repeatedly inserted into the canal until the spreader could not penetrate into the filling deeper than 2 mm. The excess gutta-percha points were cut off with flat plugger heated on an open fire at the level of the root canal orifice. The filling was additionally condensed in the vertical direction.

Group II

The second group was prepared using engine-driven Reciproc instruments; R25 and R40 (VDW, Munich, Germany) powered by VDW Reciproc Gold engine device (VDW, Munich, Germany), up to size 40/0.6, according to the manufacturer's instructions. Chemical treatment during instrumentation and removal of the residual smear layer was performed in the same way as in the group I. After drying with paper points, the root canals were filled with VDW Reciproc gutta-percha #40 coated with AH Plus sealer. The excess gutta-percha points were cut off with flat plugger heated on an open fire at the level of the root canal orifice and vertically condensed.

After filling, all samples of both groups were stored in saline at thermostat temperature of 37°C.

Retreatment

After seven days, the samples were taken out of the thermostat and dried with gauze. Gates Glidden drill #3 (Maillefer, Ballagius, Switzerland) was used to make a small solvent tank in the coronal third of each canal. Engine driven and hand instrumented groups were divided into two subgroups (n=15), denoted by the letters a and b. Subgroups a were treated with eucalyptol, and subgroups b with tea tree oil.

Group I (Ia and Ib)

Hand instruments were used for retreatment of the first group. After application of 1 ml of solvent, a path for the solvent was made by rotating the K-reamer #15 120°clockwise with slight apical pressure, and the softened gutta-percha was removed with a same sized H-file. The size of the instruments was gradually increased to #40. The solvent was added as needed. The procedure was repeated until reaching the working length and was completed and there were no more visible traces of filling material on the instruments and paper points.

Group II (IIa and IIb)

The second group was retreated with engine-driven, Reciproc instruments according to the manufacturer's instructions. First, 1 to 2 drops of solvent were applied into a previously made container at the root canal orifice. Then, the R25 instrument was used with light pressure towards the apical and "inside - out" movements through 3 consecutive amplitudes of 3 mm, followed by cleaning the instrument with sterile gauze, until reaching the working length. After that, the R40 instrument was introduced into the root canal and the remaining filling material was removed from the canal walls by the "inside - out" and "side" movements, according to the mentioned protocol. The retreatment was completed when there were no more visible traces of filling material on the instruments.

Finally, all canals were rinsed with 0.5% NaOCl, 15% EDTA and saline and dried with paper points. The complete retreatment time was measured in minutes.

Results

Statistical analysis

After retreatment, the samples were longitudinally split, and recorded by a camera mounted on a stereomicroscope (Olympus SZX12) under a 15x magnification and the surface of the residual filling material in the root canals was quantified. The obtained images were transferred to a computer and the areas of residual gutta-percha and sealer were measured using an image processing program, Image J (Figure 1). Data were statistically analized by Student - T test. The computer program SPSS 17.1 for Windows was used for data processing. The normality of the data distribution was checked by a descriptive statistical method (P-P plot). P values less than 0.05 were considered significant.

Figure 1

Residual gutta-percha and sealer after retreatment; groups Ia (bottom left), Ib (top left), IIa (top right), IIb (bottom right)
Figure legend: Ia-hand retreatment/eucalyptol, Ib-hand retreatment/tea tree oil, IIa-engine driven retreatment/eucalyptol, IIb-engine driven retreatment/tea tree oil

Retreatment duration

The time required for retreatment of all samples by groups is shown in Table 1. and in Figure 2.

Table 1

Retreatment duration (minutes)

Group	N	Mean	SD	Minimum	Maximum	Percentiles
						25th	50th	75th
Ia	15	10:13	0:29	7:37	13:26	8:29	10:03	12:18
Ib	15	8:25	0:31	5:39	11:37	6:10	8:02	10:07
IIa	15	5:08	0:20	2:30	6:55	4:15	5:10	6:05
IIb	15	4:32	0:23	2:48	7:16	3:21	4:11	5:40

Table legend: Ia-hand retreatment/eucalyptol, Ib-hand retreatment/tea tree oil, IIa-engine driven retreatment/eucalyptol, IIb-engine driven retreatment/tea tree oil

Figure 2

Graphical representation of the average time (seconds) required for retreatment by groups
Figure legend: Ia-hand retreatment/eucalyptol, Ib-hand retreatment/tea tree oil, IIa-engine driven retreatment/eucalyptol, IIb-engine driven retreatment/tea tree oil

Student T test for independent samples showed that there was a statistically significant difference in the retreatment duration between IIa and Ia (p<0.001), IIa and Ib (p<0.001), IIb and Ib (p<0.001), Ia and Ib (p=0.017) and IIb and Ia (p<0.001) groups.

Machine retreatment using Reciproc engine-driven instruments was statistically significantly faster compared to the manual retreatment using hand files. Among manually retreated root canals, tea tree oil-treated group was retreated significantly faster.

Residual filling material surface

The percentage of the residual filling material surface by groups is shown in Table 2.

Table 2

Percentage of residual filling material surface by groups

Group	N	Mean	SD	Minimum	Maximum	Percentiles
						25th	50th	75th
Ia	15	6.59%	0.60%	2.44%	11.97%	5.29%	6.18%	7.88%
Ib	15	6.66%	0.56%	3.88%	11.28%	4.35%	6.75%	8.16%
IIa	15	7.23%	0.52%	3.22%	10.76%	6.30%	7.68%	8.35%
IIb	15	6.13%	0.51%	2.60%	9.31%	5.29%	6.10%	7.60%

Table legend: Ia-hand retreatment/eucalyptol, Ib-hand retreatment/tea tree oil, IIa-engine driven retreatment/eucalyptol, IIb-engine driven retreatment/tea tree oil

Student T test for independent samples showed that there was no statistically significant differences in the percentage of residual filling material between IIa and Ia (p>0.05), Ia and Ib (p>0.05), Ia and IIb (p>0.05), IIa and IIb (p>0.05) and IIb and Ib (p>0.05) groups.

In all examined specimens, approximately the same filling material surface was left (Figure 3).

Figure 3

Graphical representation of the average residual filling material surface (%) by groups
Figure legend: Ia-hand retreatment/eucalyptol, Ib-hand retreatment/tea tree oil, IIa-engine driven retreatment/eucalyptol, IIb-engine driven retreatment/tea tree oil

Discussion

The aim of this study was to evaluate the retreatment duration and efficacy of eucalyptol and tea tree oil in machine and manual retreatment of epoxy resin based endodontic filling. As there were no statistically significant differences the in area of the remaining filling material among used solvents, nor in applied technique, the first null hypothesis was confirmed. As retreatment with Reciproc instruments was significantly faster compared to retreatment using hand files, and the manual retreatment technique was faster when tea tree essential oil was used as a solvent compared to eucalyptol, the second null hypothesis was rejacted.

When the use of chloroform was forbidden, many studies have been conducted to determine the most effective organic solvent. Because chloroform and xylene have been described as toxic, and halothane (which has been used as an inhalation anesthetic since 1956 for induction of general anesthesia) has low toxicity, is relatively biocompatible and shows unpleasant side effects, the choice of solvent narrows to essential oils (, , ).

Eucalyptus oil (cineole) is one of the chemical agents that has been advocated for the removal of gutta-percha (), hence it was used in the present study.

In 1990, Kaplowitz compared the solubility of gutta-percha in five different solvents (purified white turpentine, melaleuca oil, eucalyptus oil, white pine oil, and needle pine oil) with solubility in chloroform and reported that all solvents dissolved at least 50% of the gutta-percha at 37°C during 15 minutes, while chloroform and rectified white turpentine dissolved gutta-percha completely (). Gorduysus et al. compared the solubility of gutta-percha in halothane, chloroform, xylene, acetone, isopropyl alcohol, turpentine, melaleuca oil, and eucalyptus oil. Halothane, chloroform, and xylene were far more potent solvents for gutta-percha than the remaining agents; eucalyptus oil, melaleuca oil and turpentine were less effective in dissolving gutta-percha; acetone and isopropyl alcohol did not dissolve gutta-percha at all ().

Zaccaro-Scelza et al. reported no significant differences in dissolving efficacy of chloroform, orange oil and eucalyptol (). Karlović et al. also reported no significant differences in gutta-percha removal efficacy of eucalyptol and chloroform (). Yadav et al. evaluated the dissolution effectiveness of eucalyptus oil, orange oil, xylene, and distilled water on endodontic sealers. Their results showed that xylene was the most effective solvent followed by the essential oils (eucalyptus and orange oil) and distilled water the least ().

According to these studies, the effectiveness of essential oils was the same (, ) or slightly lower (, , ) but biocompatibility, non-carcinogenicity and antiseptic effects are distinct advantages of essential oils (, , ).

In the present study, the time required to remove the endodontic filling material from the root canals of all groups was also measured.

We found a significant difference between the manual and machine retreatment duration regardless to the type of solvent applied (machine-eucalyptol avg. 5:08 minutes/tea tree oil avg. 4:32 minutes, hand-eucalyptol avg. 10:13/tea tree oil avg. 8:25). The results of our study showed that Reciproc machine retreatment was faster than manual, hand retreatment, which is consistent with the results of the study of Zuolo et al. ().

A significant difference was also found between manual retreatment techniques (manual-eucalyptol avg. 10:13 minutes/tea tree oil avg. 8:25 minutes). Manual retreatment duration was measured by other authors also (, , -). Karlović et al. measured that a manual retreatment with eucalyptol took, on average, 8.14 minutes, while the retreatment with chloroform took 7.18 minutes (). Zaccaro-Szelza et al. stated that it took them on average about 5 minutes to retreat root canal with hand files using chloroform, orange oil, and eucalyptol (), while other authors reported a time range of 1.5 to 10.8 minutes (-).

Considering our results regarding a higher tea tree oil efficacy in manual retreatment group when compared to eucalyptol, tea tree oil may be considered a better solution in manual retreatment. As stated before, modern engine driven endodontic treatment and retreatment are more effective than manual (, ). However, due to the fact that manual instrumentation and retreatment are still methods of choice in many clinical environments worldwide (due to cost or availability), our finding may have clinical implications in the sense of speed and efficacy of manual retreatment.

For the purpose of measuring the residual filling material surface, after retreatment, the samples were split longitudinally and recorded with a camera mounted on a stereomicroscope (Olympus SZX12) under a 15x magnification. The obtained images were transferred to a computer and the areas of residual gutta-percha and sealer were measured by the image processing program (Image J). Such a procedure is used in a study of Scelza et al. ().

Student T test for independent samples showed that there was no statistically significant difference in the percentage of the residual endodontic filling area between manual and machine techniques, nor between the application of tested solvents. However, since the percentage of the residual filling material was the lowest in machine retreatment with tea tree oil (6.13%) and the highest in machine retreatment with eucalyptol (7.23%), it can be concluded that the percentage of removed endodontic filling material in all experimental groups in this study was between 92.77% and 93.87%, which is in line with previous research (), and represents a very high efficiency of these techniques and solvents. However, the results of this study also confirm the findings of all previous studies that no revision techniques which have been currently applied, can completely remove endodontic filling material from root canals (, , ).

Conclusions

Since there is no significant difference in percentage of the residual filling material regardless of the retreatment technique and different solvents used, we have concluded that essential oils, Australian tea tree oil and eucalyptus oil are equally effective in removing endodontic filling material.

Retreatment with Reciproc instruments is significantly faster compared to retreatment using hand files. On the other hand, the manual retreatment technique is faster when tea tree essential oil is used as a solvent compared to eucalyptol.