Apical microleakage in root canals with separated rotary instruments obturated with different endodontic sealers.

Aim: The aim of this study was to evaluate apical microleakage in root canals containing broken rotary instruments obturated with cold lateral condensation and thermoplasticized injectable gutta-percha, with different sealers, using glucose penetration leakage study. Materials and
Methods: In this in vitro study, 96 extracted human mandibular premolars were decoronated, and the roots were randomly divided into eight groups (n = 12). Root canals were instrumented with #30 4% taper rotary files. The files were scratched 3 mm from the tip by a high-speed handpiece, and they were intentionally broken in the apical third of the canals. The middle and coronal sections of the canals were obturated by cold lateral condensation and thermoplasticized technique, using ZOE, resin, CaOH, and bioceramic sealers. Apical microleakage was measured using the glucose penetration method. Statistical Analysis: Independent Student's t-test and one-way ANOVA followed by Tukey's post hoc analysis were used for statistical analysis.
Results: Bioceramic sealer group showed the least apical microleakage and this was then followed by the resin and CaOH groups demonstrating lesser apical microleakage and the highest microleakage was with the ZOE group. Mean apical microleakage scores between lateral and thermoplastic condensation techniques in each group were statistically significant (P < 0.001).
Conclusion: Bioceramic sealer demonstrated the least apical leakage, whereas ZOE seal displayed the highest apical leakage. Copyright:

INTRODUCTION

Endodontic therapy consists of cleaning and shaping the root canal system, removing organic debris, and sealing the intracanal space with permanent filling materials. The root canal obturation was done to eliminate any space that would allow penetration of the fluids, and to eliminate all the microorganisms from the root canal system.[1] Efficient obturation must provide an adequate seal to prevent the re-entry of microorganisms.

Root canals are prepared with hand and rotary files. Rotary files made of nickel–titanium (NiTi) allow faster canal preparation and those made of NiTi and can be used in narrow curved canals due to high flexibility and fracture strength. Canal curvature also serves as a risk factor for file breakage.[2] A file is broken while doing the treatment will make it difficult for cleaning and shaping of root canals which can result in the failure of the treatment. The clinician has to bypass the instrument and clean and fill the canal in the presence of the broken instrument. Poor apical sealing of the root canal space accounted for as many as 60% of endodontic treatment failures.[3]

Root canal sealers prevent leakage and provide an antimicrobial activity that allows reducing the residual bacteria and heals the existing lesions in the periapical area. The persistence of bacteria in the root canal system often leads to failure of the root canal treatment.[4]

Hence, this study intended to compare the apical microleakage in root canals containing broken rotary instruments obturated with different sealers using a glucose penetration leakage study.

MATERIALS AND METHODS

Sample preparation

This study was reviewed by the committee for its ethical integrity and implications (179/ECAL/2019-20). Ninety-six single-rooted premolar teeth with single canal and similar root canal anatomy and dimensions, extracted due to periodontal and orthodontic reasons, were used for the study. After extraction, teeth were kept in 10% buffered formalin and stored in saline before instrumentation. Teeth with caries, restorations, morphological defects, and cracks were excluded. Teeth were decoronated at the cementoenamel junction with a diamond disc at high speed with water spray coolant so that each specimen was 12 mm long. Working length was determined by placing a #10K (Mani Inc., Japan) file into each root canal until it was just visible at the apical foramen and then subtracting 1 mm from this point. The canal was enlarged to size #30 (HyFlex, Coltene), 4% taper. The canals were copiously irrigated with 3% sodium hypochlorite, 17% ethylenediaminetetraacetic acid, and normal saline between instrument changes, and the canal was dried with a paper point.

A #30 rotary file was scratched at 3 mm from its tip by a high-speed handpiece and was intentionally broken in the canal in the apical region. The middle and coronal sections of the canals were obturated by cold lateral condensation and thermoplasticized technique, using ZOE, resin, CaOH, and bioceramic sealers according to manufacturers’ instructions. The roots were radiographed after file fracture and obturation and were divided into eight groups (n = 12).

Classification of groups:

Group 1: Obturated with ZOE sealer (Tubli-Seal, Sybron Endo, USA)

Group 2: Obturated with CaOH sealer (Sealapex, Kerr Sybron Endo, USA)

Group 3: Obturated with resin sealer (AH Plus, Dentsply, UK)

Group 4: Obturated with bioceramic sealer (Meta Cera, Meta Biomed., Ltd, Korea).

All groups were further subgrouped depending on the obturation technique used:

Subgroup a: Lateral compaction technique

Subgroup b: Thermoplasticized technique.

Evaluation of apical seal

Each root was mounted in a leakage device that has been described by Xu et al.[5] Coronal parts of the root were attached to the end of a rubber tube. A glass tube 25 cm long was connected to the cap of the rubber tube. The assembly was placed in a sterile 20-ml glass test tube with a rubber stop. Leakage at all connections was eliminated by the use of cyanoacrylate glue and sticky wax.

Glucose solution (1 mol/L, pH 7.0), containing 0.2% sodium azide (NaN3), was injected into the glass tube until the top of the solution will raise 14 cm higher than the top of the root, which creates a hydrostatic pressure of 1.5 Pa. Glucose that was leak through the sample was collected in the glass test tube containing 3 ml of 0.2% sodium azide. The assembly was placed in an incubator at 100% relative humidity and 37°C throughout the observation period. Leakage was quantified as the amount of glucose that reached the apical reservoir in the glass test tube after 7 days. The amount of glucose was determined by an ultraviolet-visible light recording spectrophotometer at 500-nm wavelength.

Statistical analysis

Data were analyzed by Windows version 22.0 (released 2013) using an independent Student's t-test and one-way ANOVA followed by Tukey's post hoc analysis.

RESULTS

Multiple comparisons of mean apical microleakage scores between four groups showed that the bioceramic sealer showed significantly the least apical microleakage scores as compared to other study groups (P ≤ 0.001). This was then followed by resin and CaOH groups demonstrating significantly lesser apical microleakage scores as compared to ZOE (P < 0.001 and P = 0.001, respectively). However, no significant difference was noted between the resin and CaOH groups (P = 0.97). This infers that the bioceramic group showed the best apical sealing ability followed by resin and CaOH groups and least with ZOE group [Graph 1 and Table 1].

Graph 1

Apical microleakage scores between lateral and thermoplastic condensation techniques in each group

Table 1

Comparison of mean apical microleakage scores between lateral and thermoplastic condensation techniques in each group using independent Student’s t-test

Groups	Technique	n	Mean±SD	Mean difference	P
AH Plus	Lateral condensation	12	0.7604±0.3022	0.6253	<0.001*
	Thermoplastic condensation	12	0.1352±0.0547
Sealapex	Lateral condensation	12	0.8068±0.2644	0.6598	<0.001*
	Thermoplastic condensation	12	0.1470±0.0169
Tubli-Seal	Lateral condensation	12	1.2444±0.3552	1.0018	<0.001*
	Thermoplastic condensation	12	0.2426±0.0359
Meta CeraSeal	Lateral condensation	12	0.1501±0.0268	0.0713	<0.001*
	Thermoplastic condensation	12	0.0788±0.0163

SD: Standard deviation. *statistically significance (P ≤ 0.001)

The test results demonstrated [Graph 1] the mean apical microleakage scores between lateral condensation and thermoplastic condensation techniques in each group. The mean scores for thermoplastic condensation technique in all study groups (0.1352 ± 0.0547 [resin], 0.1470 ± 0.0169 [CaOH], 0.2426 ± 0.0359 [ZOE], and 0.0788 ± 0.0163 [bioceramic]) were significantly lesser as compared to lateral condensation technique (0.7604 ± 0.3022 [resin], 0.8068 ± 0.2644 [CaOH], 1.2444 ± 0.3552 [ZOE], and 0.1501 ± 0.0268 [bioceramic]). The difference in the mean apical microleakage scores between lateral and thermoplastic condensation techniques in each group was statistically significant at (P < 0.001).

DISCUSSION

A complete seal along the root canal is required for successful root canal treatment, thereby ensuring the healing and sustained health of the periradicular tissue. Obturation is done to remove the residual bacteria in the root canal system, to stop the influx of periapical tissue-derived fluid from re-entering the root canal to feed the surviving bacteria, and to seal the root canal space, preventing reinfection from coronal leakage.[6]

The key to successful endodontic therapy is obtaining a good three-dimensional seal to prevent infection and reinfection. The functions of root canal sealers are to achieve sealed voids, accessory canals, and apical ramifications, with attaining the good sealing ability to dentin, less solubility, good biocompatibility, mineralization to dentin, and formation of calcified tissues to seal the apex. A variety of sealers have been tested for this purpose ranging from the conventional zinc oxide eugenol sealers to the latest resin, bioceramic, and calcium hydroxide-based sealers.[7]

A thin tacky paste of sealer is used for lubricating and luting during obturation which can fill voids and accessory canals.[8]

A broken instrument that remained in the root canal does not have a significant adverse effect on the quality of root canal seal by filling materials. The success of endodontic treatment mainly depends on coronal seal and instrumentation of the middle and coronal thirds.[2] However, it has been shown the type of broken instrument also affects the quality of seal provided by restorative materials.[9]

After intracanal preparation, a thorough obturation of the root canal system is a major objective of endodontic treatment. A proper obturation depends on sealing ability of root canal filling materials and various obturation techniques. When filling the root canal system, the sealer plays an important role in reducing microleakage.[5]

Five methods are used to Assess the quality of apical seal. The methods used are the degree of dye penetration, radioisotope penetration, Bacterial penetration, electrochemical means, and fluid filtration techniques. All of these techniques have been shown to have a variety of shortcomings.[10] In the present study, the glucose penetration method was used to find the leakage along with root canal fillings which are simple and could give reliable quantitative leakage measurements.[1] Method for analysis of endodontic microleakage was introduced by Xu et al.[5] based on the filtration rate of glucose along with the root canal filling. The amount of leakage was quantified with spectrophotometry. The glucose concentration in the apical area is measured to find out the leakage.[11]

A leakage through an obturated root canal is expected to take place at the interfaces between sealer and dentin or sealer and gutta-percha or through voids within the sealer. Therefore, the sealing quality of a root canal filling depends much on the sealing ability of the sealer used.[12]

Results of the current study indicated that cold lateral compaction and thermoplasticized obturation technique with bioceramic group showed significantly least apical microleakage compared to all tested groups due to the infiltration of the sealer's mineral content into the intertubular dentin. This result is consistent with many previous studies.[1314]

The sealer particles form a mechanical bond with the dentinal tubules (tubular diffusion). Infiltration of the sealer's mineral content into the intertubular dentin results in the establishment of a mineral infiltration zone produced after denaturing the collagen fibers with a strong alkaline sealer. There will be a partial reaction of phosphate with calcium silicate hydrogel and calcium hydroxide in the presence of the dentin's moisture. This results in the formation of hydroxyapatite along the mineral infiltration zone.[15]

Groups with ZOE sealer showed the highest apical leakage. Studies have shown ZOE sealers do not bond chemically with root dentin and possess very low tensile strength.[8] However, no significant difference was noted between the resin and CaOH groups. Resin sealers could be attributed to their good physicochemical properties such as self-adhesiveness, low solubility, good dimensional stability, and better penetrability. CaOH-based sealer displays better bonding to root dentin, high tensile strength, and also shows a significant amount of volumetric expansion during setting because of water absorption.[16] It has antibacterial action and stimulates a sterile biological closure of the apical region.[17] Similar results with resin and CaOH were observed in studies conducted by Barbero et al.,[18] Jang et al.,[19] and Lin et al.[9]

When both obturation techniques were compared, thermoplastic condensation techniques exhibited less apical leakage due to its successful filling of lateral canals and the three-dimensional filling property of this technique. The lateral compaction technique has shown drawbacks such as the risk of void formation and difficult application in curved canals.[20]

This study has a few limitations, hence further studies that would be carried out in curved root canals should consider.

CONCLUSION

The results of the present study indicated that the bioceramic group showed significantly least apical microleakage compared to resin, CaOH, and ZOE sealer

Mean apical microleakage scores between lateral and thermoplastic condensation techniques in each group were statistically significant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.