Intradentinal antimicrobial action and filling quality promoted by ultrasonic agitation of epoxy resin-based sealer in endodontic obturation

Abstract The aim of this study was evaluate the influence of ultrasonic activation (UA) of AH Plus to improve canal and isthmus filing, and analyse the antimicrobial effect against Enterococcus faecalis within dentinal tubules. Material and Methods: Thirty mesial roots of mandibular first molars were selected and divided into 2 groups (n = 15): with and without UA of the sealer. Then the root canals were filled by using the single cone technique, and the specimens were sectioned at 2, 4 and 6 mm from the apex for stereomicroscope and confocal laser scanner microscopy (CLSM) analysis. In addition, 30 bovine incisors were contaminated with Enterococcus faecalis and divided into 3 groups (n = 10). The specimens were obturated by using the single cone technique with (G1) and without (G2) UA of the sealer and G3 as the control group. All were sectioned into 6 mm-long cylinders and stained with LIVE/DEAD to assess bacterial viability by CLSM. Results: The UA of the sealer significantly reduced the presence of unfilled areas in the canal and isthmus area in all sections (p<0.05), and there was a significant increase in sealer penetration in both canals and isthmuses (p<0.05). As regards gaps, a significant reduction was found at 2 and 6 mm in the isthmus area of the UA group (p<0.05). Moreover, UA of the sealer significantly reduced bacterial viability in the superficial dentine when compared with the other groups (p<0.05). Conclusion: Ultrasonic activation of the AH Plus sealer promoted a better quality of root canal filling and increased the intratubular penetration of sealer, especially in the isthmus area. Additionally, ultrasonic activation of the sealer increased the intradentinal antimicrobial action against Enterococcus faecalis, mainly in the superficial dentine of the root canal.


Introduction
Adequate obturation of the root canal system is required after biomechanical procedures, to ensure the long-term success of endodontic treatment 20 . During root canal obturation, an important objective of using reached by gutta-percha 6 . However, the anatomical obturation 2 .
The presence of isthmuses has a negative effect 13 as the obturation 4,5 . To quality in terms of reducing unfilled areas and gaps, and promoting more effective penetration of sealer into dentinal tubules, recent studies have recommended the ultrasonic activation (UA) of sealers before obturation with gutta-percha 7,16 . However, this effect has only been studied in single rooted teeth with single canals, and no studies evaluating these aspects in teeth with anatomical complexities have been conducted so far.
Within the dentinal tubules, bacteria such as Enterococcus faecalis (E. faecalis) have capacity to penetrate deeply and offer resistance to the antimicrobial agents used in endodontics 29 . These bacteria are the microorganisms most frequently isolated from persistent endodontic infections 19,22 .
Although the AH Plus sealer has been studied by several authors, and has shown good antimicrobial effect against E. faecalis 18,28 , this factor might be dependent on the depth of penetration of the sealer.
In addition, sealer penetration into the dentinal bacterial entombing action 10,15 . Based on the foregoing considerations, it would be interesting to assess the effect of ultrasonic activation of the sealer to enhance the antimicrobial activity against E. faecalis within the dentinal tubules.
Therefore, the aim of the present study was to in mandibular molars, and analyse the antimicrobial effect against E. faecalis within the dentinal tubules.
The null hypotheses tested were as follows: Ultrasonic activation of the endodontic sealer would There would be no difference in the adaptation of the sealer/dentine interface and intratubular penetration when ultrasonic activation was performed in the mesial roots of mandibular molars.
The ultrasonic activation would not improve the intradentinal antimicrobial activity of AH Plus against E. faecalis.

Sample Selection
The ethics committee approved this research (CEP 788274 Hsu and Kim 9 (1997), between the two mesial canals. According to this randomly divided into two groups (n=15).
Finally, the total volume of each root canal system was calculated by using the Ctan v.

Sample Preparation
The crowns of thirty bovine incisor teeth and 2 apical mm were removed; the samples were standardized to 6 mm lengths by using an Isomet saw   Results areas obtained from the stereomicroscopy analysis are shown in Table 1. In all sections, ultrasonic activation ( Figure 2A, B).
Results of the CLSM examination are presented as median and ranges in Table 2. Overall, ultrasonic activation of the sealer showed a significant improvement in sealer penetration into the dentinal tubules in both canals and isthmuses (p<0.05) ( Figure   2C, D). Gaps at the sealer/dentine interface were  This study presented a method for intratubular contamination of bovine dentine proposed by Andrade, et al. 1 (2016). Bovine teeth are commonly used as an experimental substitute for human teeth because they are easily available 21 . Compared with human dentine, bovine dentine has a higher concentration of dentine tubules per square millimeter, however, this difference is small. On average, the diameter of dentine tubules of bovine teeth is larger than that of human teeth, percentage of intertubular dentine in bovine teeth is the same as it is in human teeth 21 .
Vera, et al. 25 (2012) showed that microorganisms remain inside the dentinal tubules and survive after biomechanical preparation and intracanal dressing.
Thus, the sealer penetration into the dentinal tubules of the antimicrobial action of these materials and their action of entombing residual microorganism 10,15 .
Our results showed that ultrasonic activation of the E. faecalis other groups ( Figure 4A,