A novel modified obturation technique using biosealers: An ex vivo study.

Background: The root canal anatomy is a complex space, and using a single-cone obturation technique does not guarantee a complete filling. Aim: This research aimed to evaluate the actual temperature of the biosealer during the obturation phase inside the root canal using a new hot technique. In addition, this study evaluated the penetration depth of the biosealer inside dentinal tubules. Setting and Design: The current study was concluded on two ex vivo experiments; the former tested the temperature evaluation. The latter examined the penetration depth of the biosealer. Materials and
Methods: In this study, 42 sec mandibular premolars were used, and two experiments were carried out. In the first experiment, two premolars were utilized, and two thermocouples of K-type for each tooth were used. During the second experiment, the penetration depth of the biosealer was examined, 40 teeth were selected. Root canals were prepared then divided into two obturation groups: A, gutta-percha, and biosealer with single-cone technique and B, gutta-percha, and biosealer with a newly proposed obturation method. Confocal laser scanning was used to assess the penetration of the sealer. Statistical Analysis Used: In the first experiment, the Bonferroni method was performed to compare the temperature data. The tests used in the second experiment were Shapiro-Wilk's test, Kruskal-Wallis, and Mann-Whitney tests.
Results: The first experiment results showed that the heat does not reach the apical third using the new obturation method. In the second experiment, the results showed in Group B significantly higher biosealer penetration into the dentinal tubules as compared to Group A (P < 0.05). Conclusions: The highest level of penetration of the biosealer in the dentinal tubules was observed in the group of the new obturation method, and the last apical 3 mm remained at 37° using this novel hot modified technique providing no risk of chemical alteration of the biosealer. Copyright:

INTRODUCTION

The endodontic treatment's short and long-term success is principally based on proper three-dimensional (3D) cleaning of the root canal system after the root canal shaping. To be followed with complete 3D obturation of the complex root canal system.[1234]

The endodontic space consists of readily reachable areas to the manual and rotary files (the main canals). On the other hand, it also includes, as established by numerous clinical and histological studies, particular areas that are challenging to access or even inaccessible (isthmuses, loops, lateral canals, ramifications, deltas, and dentinal tubules).[5678] Consequently, mechanical shaping cannot access all areas of the complex endodontic system, regardless of the technique used, leaving parts of the root canals untreated.[9] Therefore, it is crucial to perform endodontic biochemical cleaning (accessible and inaccessible areas).[1011] Once these areas have been cleaned; they can be filled and obturated with gutta-percha and sealer or biosealer during the obturation phase.[12]

Biosealers have been introduced to the market with a recommendation to be used in the single-cone technique. The reason behind that was because the biosealer is unadvisable to come into contact with heat. Otherwise, they can harden instantly. Obturation with System-B technique or similar indicates using gutta-percha and traditional sealer in which the heated plugger will melt gutta-percha cone to fill better in the apical area the lateral anatomies.

The purpose of the current study is to evaluate the actual temperature of the biosealer during the obturation phase inside the root canal without causing any risk of chemical alteration of the bioseal. In addition, it aims to evaluate the penetration depth of the biosealer inside dentinal tubules evading causing the fast setting for the bioseal by using a new obturation method.

MATERIALS AND METHODS

Freshly extracted human mandibular premolars (n = 42), with intact coronal surfaces, were chosen for this research.

The teeth used were extracted as part of an orthodontic treatment plan and were unrelated to the present experiment. Teeth of patient age (18–25 years) were used. The exclusion criteria were any presence of root resorption, immature apices, fracture or root filling. Informed consent was obtained from the patients. The ethical committee of the Institutional Review Board approved the protocol for this study on April 28, 2021 with protocol 55/21, University of Naples Federico II Naples, Italy.

The soft tissues attached to the teeth' external surface were removed using a curette. Then, the specimens were kept in individual vials containing 5 mL of 10% formalin until use.

The teeth were de-coronated at the cementoenamel junction to obtain the roots of a standardized length (18 mm). A size 10 K-type file (Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss) was inserted into each canal until it was seen through the apical foramen. The final working length was reached by deducting 0.5 mm from that measurement. The canals were shaped with nickel − titanium rotary files (Hyflex EDM, Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss). Only the 10/0.05, 20/0.05, and 25/0.08 files of Hyflex EDM were used to prepare the canals to the full working length. After the completion of the apical preparation the size and taper of the apical area was 25/0.08. During canal instrumentation, irrigation was performed with 3% NaOCl (Canal pro, Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss) using a 30G needle in a syringe (Canal pro irrigating tips, Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss). A total of 5 mL of NaOCl were used for each tooth and refreshed every minute. The root canals were then flushed with sterile saline, followed by irrigation with 3 mL of 17% ethylenediaminetetraacetic acid (EDTA) (Canal pro EDTA, Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss) for 1 min to remove the smear layer. All canals received a final rinse of 3 mL of sterile saline.[10]

Experiment 1

For the first experiment, temperature evaluation, two second mandibular premolars were selected. Two thermocouples of K-type (ThermoWorks, Salt Lake City, Utah, US) for each tooth were applied.

In order to insert the thermocouples in each tooth, the examiner drilled holes using a diamond bur 196D.644.110 (Komet Dental, Trophagener Weg 25, 32657 Lemgo, Germany) from the root surfaces to root canals. The position of the holes was at the apical foramen (Ta) and the apical third 3 mm from the apex (T3) [Figure 1]. Each tooth attached with thermocouples was mounted with Duralay resin (Henry Schein Dental, Melville, New York, United States) into an aluminum tube, and a thermally controlled heater (Jiu Tu, Baoan District, Shenzhen China) equipped with an aluminum block was used to control and maintain the temperature of the tooth environment at 37°C.

Figure 1

Thermocouples for each tooth at the apical foramen (Ta) and the apical third 3 mm from the apex (T3)

The thermocouples were connected to the NI DAC interface (MOD National Instruments Corporation, Austin, TX, USA), and signals were recorded through the LabView system (National Instruments Corporation) at a rate of 10 points per second for 300 s.

Obturation was done using the System B device (Kavo Dental, Orange, California, United States). Two gutta-percha cones of the same length and dimension were used (25/0.08 Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss) for the two premolars.

The biosealer used was bioseal (Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss), and the same quantity of biosealer was used. The bioseal syringe tip was inserted 10 mm away from the working length, and for each premolar, 2 mm of biosealer was injected.

In the first premolar, a single cone obturation technique was used. The procedure was in the form of inserting the gutta-percha cone to the working length.

For the obturation of the other premolar, the heat carrier tip X-Fine (30/04) (Kavo Dental, Orange, California, United States) at 180° was put 6 mm away from the working length. The time of down packing was of 4 sec.

Experiment 2

For the second experiment, the penetration depth of the biosealer, 40 teeth were selected and assigned to two obturation groups: Group A 20 teeth, gutta-percha and biosealer with single-cone technique, and Group B 20 teeth, gutta-percha and biosealer with using the new obturation method.

Forty gutta-percha cones of the same length and dimension were used for both groups (25/0.08 Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss).

The biosealer used was bioseal (Coltène/Whaledent AG Feldwiesenstrasse 20 9450 Altstätten, Swiss) labeled with 0.1% Rhodamine B (Rhodamine B, VWR International Srl, Via San Giusto 85-20153 Milano, Italy) and the same quantity was used. The bioseal syringe tip was inserted 10 mm away from the working length, and for each premolar, 2 mm of biosealer was injected.

In Group A, a single-cone obturation technique was used. The procedure was in the form of inserting the gutta-percha cone to the working length.

In Group B, the heat carrier tip X-Fine (30/04) (Kavo Dental, 200 S Kraemer Blvd, Building E2 Brea, CA 92821, USA) was adjusted at lesser temperature (180°) than the traditional continuous wave condensation technique (200°). The heat carrier was placed 6 mm away from the working length. The time of down packing was reduced to 4 sec.

The cones were seared off at the orifice level and lightly condensed with a hand plugger 0.80 mm. The coronal access opening was sealed with a temporary filling material (Cavit, 3M; ESPE, St. Paul, MN, USA). Then, the samples were stored at 100% humidity and at 37° C for 2 weeks to set entirely and to ensure complete setting of the sealer.

Preparation of the roots

After 2 weeks, the roots were fixed centrally and vertically in orthodontic resin (Dentsply Caulk, Milford, DE, USA).

Each specimen was sectioned horizontally using a diamond disk (Buehler, Lake Bluff, IL, USA) with a slow-speed handpiece (25,000 rpm) at 2 and 4 mm from the apex. The cut samples were then mounted onto glass slides, and the coronal surface underwent a polishing phase using sandpapers of 500, 700, and 1200 grit under running water to eliminate the dentin debris that could be produced during root canal shaping produce a clear reflective surface. The samples examined with confocal laser microscopy were 2 mm thick.

Analysis of the roots using confocal laser scanning microscopic imaging

Root canal segments were studied with a Zeiss confocal laser scanning (CLSM) microscope (Carl Zeiss, LSM 780, Jena, Germany) at ten magnifications and set in fluorescent mode (at a wavelength of 514 nm) in Figure 1. Digital images were then uploaded into Image J software (National Institutes of Health, Bethesda, MD, USA). The sealer penetration depths into the dentinal tubules were measured at the maximum depth for each specimen.

The measurements were made by operators blinded to which samples were matched to which Group (A or B). The measurements were repeated twice to verify reproducibility.

Data presentation and statistical analysis

Data were statistically analyzed.

First experiment

Analysis of variants through the OriginLab Pro7 software (Northampton, MA, USA) at a significance level of 0.05 utilizing the Bonferroni method was performed to compare the temperature data.

Second experiment

The data for biosealer penetration were assessed for normality with the Shapiro–Wilk's test. Since they were not normally distributed, non-parametric tests were used for multiple comparisons between the groups (Kruskal–Wallis), and Mann–Whitney tests were used to comparing pairs of groups.

RESULTS

First experiment

Two premolars were selected for this experiment, (n = 2).

The results showed that the heat does not reach the last apical 3 mm using the new obturation method. The last apical 3 mm remained at 37°.

Second experiment

Forty teeth were used for this experiment (n = 40) divided equally into two groups, Group A (n = 20) and Group B (n = 20). The mean value of biosealer penetration at 2 mm from apical foramen in Groups A and B was 0.08 ± 0.02 and 0.23 ± 0.04, respectively, while the mean biosealer penetration at 4 mm from the apical foramen was 0.22 ± 0.02 and 0.64 ± 0.02, respectively [Figure 2]. Group B showed significantly higher biosealer penetration into the dentinal tubules compared to group A both at 2 mm (P < 0.001, degrees of freedom (DF) 38; 95% Confidence interval (CI) ‒0,17; ‒0,13) and at 4 mm (P < 0.001, DF 38; 95% CI ‒0,43; ‒0,40).

Figure 2

Confocal laser scanning microscopy images (×10) of penetration of bioseal, labeled with 0.1% Rhodamine B, in dentinal tubules at 2 and 4 mm away from the working length

The maximum penetration depth of biosealer was found at 4 mm, 0.642 mm with the new obturation method, and 0.220 mm with single-cone technique. The minimum penetration depth was found at 2 mm, 0.227 with the new obturation method, and 0.06 with the single-cone technique.

Discussions

This study sought to compare the effect of the new obturation method to the single cone technique on its penetration into dentinal tubules using CLSM and the actual temperature in the apical area. To our knowledge, the effects of the new obturation system on bioceramic sealer penetration and actual temperature into the root canal have not been previously mentioned in the literature.

Scanning electron microscopy,[1314] light microscopy,[15] and CLSM have been utilized to evaluate sealer penetration into dentinal tubules.[1617]

In a recent study, Tedesco et al.[18] found that the use of CLSM allowed a greater evaluation of the depth and quantity of sealer. The sealer was labeled with Rhodamine B since it does not affect its physical properties,[19] allowing the identification of the sealer within the dentinal tubules.

Biosealers have been introduced with the single-cone technique because it is unadvisable to come into contact with heat. Otherwise, they can harden quickly.

The newly proposed obturation technique, defined as hot modified technique, involves using the bioceramics in a 3D way, forcing them to penetrate the lateral anatomies (lateral canals and dentinal tubules) deeper than the single cone technique.

This technique has been tested in order not to create changes to the biosealers. This study showed that a greater penetration into the dentinal tubules is associated with the nonheating of the apical area using this new technique.

After positioning the biosealer and the gutta-percha cone in the canal, the technique involves carrying out a quicker down packing at a temperature of 180° at a maximum depth of 6 mm from the working length.

This technique, the hot modified technique, allows, when compared to the single cone technique, to fill better the lateral anatomies such as lateral canals, dentinal tubules, etc. As shown in this study, the heat does not reach the apical third using the new technique. In this way, the heat does not create the changes in the biosealer.

Bioceramics, owing to their advantageous characteristics, antibacterial activities, micro-expansion, biocompatibility, reaching most of the complex endodontic space, could lead to greater clinical success.[2021222324]

CONCLUSIONS

Within this study's limits, the dentinal tubule penetration of biosealer was significantly improved using the new obturation system compared to the single cone technique. Moreover, using heat carrier obturation technique, the heat does not reach the apical area, evading causing the fast setting for the biosealer. Furthermore, future studies with different methodologies and biosealers may be essential to confirm these results. Whether the new obturation method furnishes any significant advantage in ameliorating clinical outcomes remains to be confirmed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.