Influence of ultrasonics on the penetration depth of AH plus, acroseal, and EndoREZ root canal sealers: An in vitro study.

AIM: The aim of this study is to evaluate the effect of ultrasonic activation on the penetration depth of AH Plus, Acroseal, and EndoREZ sealers into dentinal tubules using Confocal laser microscopy.
METHODS: A total of 60 single-rooted teeth were prepared and divided into three groups on the basis of the type of sealer used (G1: AH Plus, G2: Acroseal and G3:EndoREZ). Each group was further subdivided into two equal subgroups on the basis of ultrasonic activation of sealers and nonactivation. Teeth were obturated and coronally sealed with GIC. Horizontal sections at 2 mm, 4 mm, and 6 mm from the apex were obtained, and the depth of sealer penetration into the dentinal tubules was measured using confocal laser scanning microscopy. Statistical analysis was performed using Students unpaired t-test, ANOVA, and Tukey's multiple comparison test.
RESULTS: Within the three groups, ultrasonically activated subgroups showed significantly (P < 0.05) higher depth of sealer penetration. Among the groups, Group 1 showed significantly (P < 0.05) higher depth of sealer penetration than Group 2 and Group 3 while the difference between Group 2 and Group 3 was not significant (P > 0.05).
CONCLUSION: The use of ultrasonic activation with AH Plus sealer showed better results.

INTRODUCTION

During the past two decades, the field of endodontics as a specialty has shown noticeable improvements in the development of newer materials that have significantly altered the treatment modalities and enhanced the success. The presence of gaps and porosities at the sealer/dentin interface is one of the common causes of failure of endodontic treatment. The complete sealing of the root canal system can result in the better prognosis of the treatment.[12] As the gutta-percha lacks adhesion to the dentinal walls, the sealer should fill the canal irregularities and the tubules of the root canal system.

Resin-based sealers are said to be associated with reduced solubility, better apical seal, and microretention to the root dentin.[345] One of these sealers is AH Plus (Dentsply Maillefer, Switzerland), which has been thoroughly studied for its physicochemical properties, tissue response, and interfacial adaptation.[678] Acroseal (Septodont, France) is an epoxy resin based sealer that contains 28% calcium hydroxide in its composition. Various studies have shown its sealing ability, activity against Enterococcus faecalis, and adaptation to the root canal walls.[8910] Endorez (Ultradent, USA) is a methacrylate-based endodontic sealer that is hydrophilic in nature. Endorez is said to exhibit excellent adaptation to root canal walls, well tolerated by periapical tissues with minimal cytotoxicity.

Ultrasound was first introduced to endodontics by Richman in 1957. Currently, it has been advocated in a range of endodontic procedures.[11] A greater agitation of irrigating solutions promoted by ultrasound increases their energy, thereby intensifying their penetration into the dentinal tubules and consequently improving the cleaning ability. The activation of root canal sealers may improve their penetration inside the dentinal tubules, improving sealability[12] and antimicrobial effects.[13] The effect of ultrasonic activation of different sealers has not been explored sufficiently. Hence, this study was undertaken to evaluate the effect of ultrasonic activation on the penetration depth of AH-plus, Acroseal, and EndoREZ sealers into dentinal tubules using Confocal laser microscopy.

METHODS

Sixty freshly extracted human single-rooted teeth without any previous endodontic treatment, fractures, resorptive defects, calcifications or open apices were selected for the study. They were cleaned of any residual tissue tags, rinsed under running water, and stored in 10% formaline solution. The crowns were removed at the cementoenamel junction using a diamond disc (DFS, Germany), and the root canal length was established at 15 mm. After the removal of pulp tissue, the working length was established by measuring the penetration of a size 10 K-file (MANI, PRIME DENTAL) until it reached the apical foramen and then subtracting 1 mm. Root canal shaping was performed using ProTaper rotary instruments (Dentsply Maillefer) up to F4.

During instrumentation, each canal was irrigated with 3% sodium hypochlorite solution (HYPO 3, Xenon Biomed, India) using a syringe with 27G needle placed 1 mm short of the working length. At the end of shaping, the root canal was filled with 3% NaOCl and was ultrasonically activated by placing the tip 1 mm short of working length.[14] A final flush of 2 mL 18% EDTA (Ultradent, USA) was done for 60 s to eliminate the smear layer. The canals were washed with saline solution (Claris Otsuka Limited) and dried with paper points (Dentsply Maillefer).

The specimens were randomly divided into three groups of 20 each according to the sealer used (n = 20):

Group 1: AH-PLUS

Group 2: ACROSEAL

Group 3: ENDOREZ.

The sealers were manipulated according to the manufacturer's instructions. To allow visualization under a confocal laser microscope, each sealer was mixed with fluorescent rhodamine B dye (Loba chemie, India) in a concentration of 0.1% by weight.[15] The sealers were placed in each root canal using a size 40 paste carrier (MANI, PRIME DENTAL), maintaining the instrument 4 mm from the apex.

Each group of specimens was further divided into two subgroups (n = 10) according to the ultrasonic activation of the sealers:

Subgroup 1: Ultrasonic activated (A)

Subgroup 2: Nonultrasonic activated (NA).

As the ultrasonic oscillates in a single plane, the activation in Subgroup 1 of each group was done in two planes simultaneously, i.e., for 20 s in the buccolingual direction and another 20 s in the mesiodistal direction of the root canal, 2 mm short of the working length as a standardization procedure (EMS, Switzerland, power level 1). After activation, all the canals were obturated with F4 and size #20 (0.02) gutta-percha. Access cavity was sealed with Glass ionomer cement (GC Corporation). The specimens were placed in 100% humidity at 37°C for 1 week to allow the sealer to set.

After 1 week, the specimens were sectioned horizontally at 2, 4, and 6 mm levels from the apical foramen and polished with sandpaper. The segments of the root canal in which the sealer penetrated into the dentinal tubules were analyzed under Confocal laser scanning microscope (Zeiss LSM 510, Germany). For a correct visualization of all images, the sections were analyzed under 10X lens. The respective absorption and emission wavelengths for the rhodamine B were set to 561 and 575 nm, respectively. The images were recorded at 100X magnification using the fluorescent mode. Images were analyzed using LSM Image Browser Software (Carl Ziess Microimaging GmbH) [Figure 1].

Figure 1

Confocal laser scanning microscopic images showing sealer penetration with and without ultrasonic activation at the level of 2 mm, 4 mm, and 6 mm from the apex

Statistics

The depth of sealer penetration into the dentinal tubules was measured and recorded. Data were collected and statistically analyzed using Students unpaired t-test, ANOVA, and Tukey's multiple comparison test.

RESULTS

The depth of sealer penetration of different groups and subgroups comparison is summarized in tables [Tables 1 and 2].

Table 1

Multiple comparison: Tukey's test for comparison among ultrasonically activated groups

Table 2

Multiple comparison: Tukey's test for comparison among ultrasonically nonactivated groups

Mean depth of sealer penetration of Group 1, 2, and 3 sealers was higher at 4 mm and 6 mm levels in ultrasonically activated subgroups and was statistically significant (P < 0.05). No significant difference was seen at 2 mm level.

Irrespective of the ultrasonic activation Group 1 showed better penetration than Group 2 and Group 3 at 4 mm and 6 mm levels (P < 0.05).

DISCUSSION

Technical and scientific advances in modern endodontic practice have resulted in wide acceptance of root canal therapy with an improved success rate. Numerous studies have demonstrated the importance of root canal sealer to fill irregularities and voids between nonadherent gutta-percha and canal walls during obturation. Most leakage studies have shown that the use of sealer results in significantly less leakage than when it is not used.[161718]

The ultrasonic system properties of vibration, cavitation, and acoustic streaming are seemingly responsible for the improved canal system cleaning. Few authors showed that the ultrasonic activation of calcium hydroxide pastes advocated a higher pH level and calcium release promoting a greater tubular penetration. In accordance with the results mentioned previously, the present study showed that the ultrasonic activation improved dentinal sealer penetration which can promote confinement of microorganisms present in the dentinal tubules. In addition, sealer plugs inside the dentinal tubules provide a mechanical interlocking, hence improving the retention of the filling material along the root canal walls.[19]

In the present study, ultrasonically activated subgroups of each group showed better tubular penetration at 4 mm and 6 mm levels which were statistically significant (P < 0.05). These findings are similar to the studies done by Chandrasekhar et al.[20] and Nikhil and Singh.[21] It may be due to increased kinetic energy, thereby generating higher velocity and flow within the sealer due to ultrasonic activation, hence facilitating tubular penetration. Moreover, the ultrasonic energy apparently impels the relatively viscous sealer to the appropriate depth along the length of the file and horizontally into numerous canal aberrations.[22] The difference between the two subgroups with respect to the sealer penetration at 2 mm level was nonsignificant (P > 0.05). This is in close approximation to the studies done by Guimarães et al.[23] and Silva et al.[24] It may be attributed to poor smear layer removal at the apical region due to the reduced density of dentinal tubules. It can also be associated with increased dentinal sclerosis and a tendency of increasing peritubular dentin toward the apical region.[25]

Among the ultrasonically activated subgroups of all the three groups, Group 1 showed better tubular penetration than Group 2 and Group 3 at 4 mm and 6 mm level. The differences between ultrasonically activated subgroups were statistically significant between Group 1 and 2 as well as Group 1 and 3 (P < 0.05). The present study coincides with the studies of Chandrasekhar et al.,[20] H Arslan et al.,[26] Guimarães et al.,[23] and Nikhil and Singh[21] It may be attributed to the structure and better coherence of the matrix of AH plus sealer into the dentinal tubules.[27] No significant difference was seen in the tubular penetration among ultrasonically activated Group 2 and Group 3 at 4 mm and 6 mm levels (P = 0.757, P = 0.992). Comparatively, less penetration of Group 2 and Group 3 may be due to the poor adaptation and penetration ability of the sealers. Moreover, increased shrinkage occurs in EndoREZ sealer due to methacrylate structure.[28] At 2 mm level, no significant difference was observed among the three ultrasonically activated subgroups pertaining to sealer penetration. The poor penetration at 2 mm might be due to the direct physical contact of the activated file in the apically constricted area and thereby hampering the necessary nodes for acoustic streaming and cavitation.[29]

Among the nonactivated subgroups of all the three groups, a statistically significant difference was seen between the Groups 1 and 2 as well as Groups 1 and 3 at 4 mm and 6 mm levels (P < 0.05). This observation is similar to studies conducted by Balguerie et al.,[30] Vijay et al., and Chandra et al.[31] It may be associated with the reduced surface tension of AH plus sealer. Moreover, there was no statistically significant difference in the penetration depth of nonactivated Groups 2 and 3 at 2 mm, 4 mm, and 6 mm levels. These findings resemble studies of Sevimay and Kalayci[28] and Hoen et al.[22] This may be associated with the fact of poor removal of the smear layer and the ineffective delivery of irrigant to the apical region of the canal.

The tubular penetration depth may vary with the different physical and chemical properties of the sealers used. Formation of sealer plug inside the tubules may provide the mechanical interlocking leading to improved retention of the material.[32] Moreover, sealer penetration into the dentinal tubules increases the interface between sealer and dentin, thereby improving the sealing ability.[33] The present study focuses on the method of sealer activation as well as one of the desirable properties of an ideal root canal filling material, i.e., the bond between the filling material and dentine. The use of ultrasonic activation at different levels facilitated better dentinal sealer penetration with all the three sealers at the level of 4 mm and 6 mm from the apex. Ultrasonic activation proved to positively influence the sealer penetration hence promoting the longevity minimizing the chances of microleakage. Further studies should be conducted to analyze the entire canal rather than a portion with bigger sample size as penetration depth of sealer may be important in future endodontic treatment outcomes.

CONCLUSION

Under the conditions of this in vitro study, following conclusions were drawn:

Ultrasonic activation of sealers showed extensive tubular penetration at 4 mm and 6 mm level from the apex

The difference in penetration of the sealers into the dentinal tubules was statistically significant between Groups 1 and 2 and Groups 1 and 3 (P < 0.05)

The difference between Group 2 and Group 3 was nonsignificant (P > 0.05)

No significant difference was seen among the groups at the level of 2 mm from the apex irrespective of with and without ultrasonic activation (P > 0.05).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.