Influence of root canal obturation using gutta-percha with three different sealers on root reinforcement of endodontically treated teeth. An in vitro comparative study of mandibular incisors.

AIM: The purpose of this in vitro study was to evaluate the vertical force required to fracture mandibular incisor teeth, obturated using gutta-percha with three different sealers.
MATERIALS AND METHODS: Seventy-five extracted mandibular incisors with intact and fully formed apices, exhibiting single root and canal were acquired. The teeth were decoronated obtaining a root segments of 15 mm and were divided into five groups (n = 15). Group 1: left uninstrumented and unfilled (negative control). For groups 2-5, samples were instrumented using Protaper NEXT (X1 and X2). Group 2: left unobturated (positive control). Groups 3-5 were obturated using lateral compaction by gutta-percha and three sealers (AH Plus®, Apexit®, and EndoSequence® BioCeramic™). All the samples were prepared for fracture testing and vertical load was applied till fracture. Statistical analysis was performed using ANOVA and Tukey's post hoc test, for the data recorded of the force required in Newton (N).
RESULTS: The load required to fracture exhibited a significant difference. The intergroup analysis revealed, samples obturated using bioceramic sealer exhibited higher fracture resistance (P < 0.01).
CONCLUSION: The use of gutta-percha and a root canal sealer reinforces the root dentin, leading to increased fracture resistance against vertical forces. Bioceramic sealer group in them exhibited better results.

INTRODUCTION

One of the most important reasons for endodontic failure is vertical root fracture (VRF).[1] VRFs can arise from physical traumatic injuries, occlusal prematurity,[2] resorption-induced pathologic root fracture,[3] or repetitive parafunctional habits of heavy chewing.[4] However, the most common cause of VRF is iatrogenic dental procedure.[123] Dental procedure contributing maximum to VRF is an endodontic treatment (root canal instrumentation).[3] VRF is defined as a severe crack in the tooth that extends longitudinally down the long axis of the root. It often extends from root canal to external root surface.[1]

The prognosis of vertically fractured tooth is very poor,[5] often requiring hemisection or extraction of the tooth, especially when there is severe associated bone loss or deep periodontal pocket.[567] Therefore, clinicians since long, have sought to reinforce the remaining tooth structure so that the fracture resistance of the endodontically treated tooth is increased. The use of a root canal filling material or sealer which has an additional property of strengthening the root against fracture would be of value in this case.[8] The most commonly used root canal filling material is gutta-percha in combination with sealer,[9] but the low elastic modulus of gutta-percha presents little or no capacity to reinforce roots after treatment.[10] The ability of sealer to bond to radicular dentin is advantageous in maintaining the integrity of the sealer-dentin interface, thus increasing resistance to fracture.[11] Bondable root canal sealers have a desirable property of creating monoblocks and help infiltrate dentin.[12]

Numerous studies have shown that the bond strength of epoxy resin-based sealer, AH Plus® was significantly higher than zinc oxide eugenol, calcium hydroxide, and glass ionomer-based sealers.[13] Recently, a new bioceramic root canal sealer has been introduced, which is known commercially as Endosequence® BC® sealer (Brasseler USA, Savannah, GA, USA). It is a premixed and injectable endodontic sealer, and its nanoparticle size allows it to flow readily into canal irregularities and dentinal tubules. In addition, this sealer is hydrophilic which uses moisture present within dentinal tubules to initiate and complete its setting reaction. In addition, no shrinkage occurs on setting, resulting in a gap-free interface between the gutta-percha, sealer, and dentin.[14]

Hence the current study was designed with an aim to compare the fracture resistance of endodontically treated teeth obturated with gutta-percha using three different root canal sealers. The sealers used in the current study were AH Plus® (Dentsply DeTrey, Konstanz, Germany), Apexit® (Vivadent, Germany), and EndoSequence® BC® sealer™ (Brasseler, Savannah, GA, USA).

MATERIALS AND METHODS

Seventy-five extracted mandibular incisors free of cracks, caries, and restorations on visual inspection were selected and stored in deionized water till use of the study. The root surfaces were thoroughly cleaned and examined at 20X stereomicroscope for any crack or root fracture. Any tooth with a slight crack, root caries, or open apex was excluded from the study. Radiographs were taken in both labiolingual and mesiodistal directions to confirm that each tooth had a single canal, no root resorption or no previous endodontic treatment.

Each tooth was sectioned at or below the cementoenamel junction (CEJ) using a cylinder diamond disc with continuous water spray to obtain root segments of 15 mm and were divided into five groups (n = 15). Fifteen samples were left uninstrumented and unfilled (negative control). For the rest 60 samples, a size 10 K-File (Kerr, Romulus, MI, USA) was placed into the root canal until seen at the apical foramen. The working length was set 1-mm short of this root length. The teeth were then instrumented using Protaper NEXT rotary file system (X1 and X2; Dentsply Tulsa Dental, Tulsa, OK, USA) attached to a preprogramed endomotor (Xsmart Plus; Dentsply Maillefer, Ballaigues, Switzerland). During instrumentation, 1 ml of 5.25% sodium hypochlorite was used for irrigation. To maintain patency of apical foramen, the canal was recapitulated by #15 K-file after each file. Ethylenediaminetetraacetic acid (EDTA) gel (RC Help; Prime Dental Products, Mumbai, India) was used as a lubricant with each file. A #25 nickel-titanium finger spreader was tried in the root canal which reached 1-mm short of the apex. The master gutta-percha cone selected and its placement till working length was confirmed using a radiograph.

Finally, the canal was flushed with 17% aqueous EDTA (Dent Wash; Prime Dental Products, Mumbai, India) followed by a final flush with 5 ml of 5.25% sodium hypochlorite before obturation. After completion of instrumentation, these teeth were randomly categorized into four groups (n = 10); group 1 control and group 2–4 for obturation using gutta-percha and three different sealers.

The sealers were mixed as per manufacturer's instructions and applied to canal walls with #25 lentulo spiral. The master apical cone (#25, 0.06% taper) was inserted and a #20 finger spreader (Manic Inc., Japan) was inserted, which reached 1 mm short of the working length (creating lateral space of accessory gutta-percha cones). Accessory gutta-percha cones were placed in the space created by the spreader, and the process was repeated until canal was completely obturated close to the level CEJ. Radiographs (buccolingual and mesiodistal) to confirm densly filled root canal. Following obturation, the samples were kept at 37°C with 100% humidity for a week to allow the sealers to set completely.

Group 1: Negative control

The samples in these group were left uninstrumented and unobturated

Group 2: Positive control

The samples in these groups were instrumented but not obturated

Group 3: Gutta-percha and AH Plus®

The instrumented samples in this group were obturated using gutta-percha and AH Plus® as sealer

Group 4: Gutta-percha and Apexit®

The instrumented samples in this group were obturated using gutta-percha and Apexit® as sealer

Group 5: Gutta-percha and EndoSequence® BioCeramic™

The instrumented samples in this group were obturated using gutta-percha and EndoSequence® BC® sealer™ as sealer.

Fracture testing

The root surface of each sample was covered with silicone paste coating to 2 mm apical to the CEJ to simulate a periodontal ligament and was kept in 100% humidity for 24 h. The root was then mounted vertically in a thick Teflon ring using dental stone to a depth of 2 mm below CEJ. A No. 40 finger spreader was mounted on Lloyd Universal Testing machine (Lloyd Instrument Ltd., Fareham and Hants, United Kingdom) to apply vertical force to the root leading to VRF [Figure 1a]. The root was centered under the spreader on the lower platen while the spreader was driven downward exactly in long axis of the root into the gutta-percha with slowly increasing the force at the rate 0.75 mm/min until the root fractures [Figure 1b]. The loads required to fracture the samples were tabulated for statistical analysis.

Figure 1

Meanwise distribution of the fracture loads for all the groups tested

Statistical analysis

The loads required to fracture the samples of Groups 1–5 were analyzed by one-way ANOVA and Tukey's post hoc test using SPSS version 20 (SPSS Inc., Chicago, IL, USA). The level of significance of P value was set at 0.05.

RESULTS

The mean loads required to fracture the samples were 391.83 (±22.71), 192.29 (±13.72), 332.21 (±17.27), 287.11 (±27.61), and 354.98 (±20.81) for negative control, positive control, AH Plus®, Apexit®, and EndoSequence® BioCeramic™ sealers, respectively. The loads exhibited a highly significant difference on application of statistical analysis (P < 0.0001; one-way ANOVA). The following Tukey's post hoc test for multiple comparison between the groups revealed, the samples of positive control group exhibited the least fracture resistance in all the five groups (P < 0.01) tested. The samples obturated using EndoSequence® BC™ sealer (P < 0.01) exhibited the highest fracture resistance, followed by AH Plus® and Apexit® sealer, respectively, for the groups tested. The mean-wise distribution of the fracture loads required is tabulated in Table 1.

Table 1

Minimum, maximum, mean and standard deviation of the loads required to fracture the samples in all the 5 groups tested, with statistical analysis (ANOVA and Tukey's post hoc)

DISCUSSION

It has been reported in literature, that the root filling materials have potential to strengthen the root structure, increasing the fracture resistance of tooth.[15] Mandibular incisors with single canal were used in the current study. These teeth have been reported to be most susceptible to VRF.[16] Furthermore, the current study compared the fracture resistance of endodontically instrumented teeth obturated using gutta-percha and three different root canal sealers. From the results of the current study, it is clear that reduced fracture resistance was seen in samples instrumented and not obturated, compared to those which were instrumented and filled. The samples instrumented and unfilled reduced the fracture strength by almost 50% compared to the control, whereas those obturated by gutta-percha and different sealers reduced fracture resistance by 15%, 26%, and 9% for groups 3–5, respectively. These results clearly show that the root canal obturation reinforces the instrumented roots.

The effect of various nickel-titanium rotary files on root dentin is reported and has an increased risk for craze lines and dentin cracks and reduced root fracture resistance compared to instrumentation with hand files.[17] Furthermore, instrumenting the apical third with large sized and taper files has an increased risk of reducing the fracture strength of the teeth. Comparing to the evolved mechanical instruments available for root canal instrumentation, Protaper NEXT rotary files have exhibited less percentages of micro-cracks formation into radicular dentin.[18] Hence, Protaper NEXT #25, 0.06% taper was used for instrumentation of samples in the current study.

The VRF was produced by inserting a finger spreader in the canal along the long axis of the tooth. This technique provides force distribution from inside the root canal and resembles root fracture of endodontic origin, whereas in other study force was produced at an angle 15° to the long axis of the tooth.[8] Furthermore, the teeth had only 2 mm of root dentin exposed above the embedding material. This design is more appealing clinically as it efficiently stimulates the support given to healthy teeth by alveolar bone and results in less catastrophic stresses due to bending movements.

AH Plus®, a resin-based sealer has been well documented in literature, when used for obturating root canals increases the fracture resistance of the teeth comparable to that of the sound dentin.[192021] The results of the current studies are in contrast with these findings as the samples in AH Plus® group did not exhibit better fracture resistance than the samples which were left un instrumented and unfilled (sound dentin).

In the current study, novel EndoSequence® BC™ sealer was compared to resin-based AH Plus® and calcium hydroxide-based Apexit® sealers. The results indicate that root canal obturation increases the fracture resistance when compared to instrumented and unfilled canals. The bioceramic-based sealer exhibited significantly better results compared to the other 2 sealers tested (P < 0.01). The bioceramic technology can be an effective alternative to other root filling materials. Bioceramics have improved biocompatibility, high pH during the setting process, better sealing ability, and are easy to use.[22] Bioceramic-based endodontic sealers exhibit a chemical bond to the radicular dentin.[2023]

Cobankara et al.[24] in their study concluded that chemical bonding enhances the fracture resistance of teeth with root canal filling. In the present study, this chemical bonding may have improved the fracture resistance of obturated teeth with EndoSequence® BC™ sealer. In addition, the deep penetration of the sealer into canal irregularities and dentinal tubules as a result of the sealer's nanoparticles can be another attributing factor for increased fracture resistance of the samples in this group.

CONCLUSION

Within the limitation of the present study, it can be concluded that obturating instrumented teeth with gutta-percha and a root canal sealer reinforces the root dentin, helping in increasing the fracture resistance against vertical forces. The fracture strength of obturated samples in the current study was found to be significantly less than that of the sound dentin. Bioceramic-based (EndoSequence® BC™) root canal sealer exhibited better results in reinforcing the instrumented samples compared to resin-based AH Plus® and calcium hydroxide-based Apexit® sealers.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.