Original Research Article

 

Bond strength of endodontic sealers after intracanal surface pretreatment with CO₂ laser

 

 

Fuad Jacob Abi Rached Junior ^I Aline Evangelista Souza-Gabriel ^I Manoel Damião Sousa-Neto ^II Yara Teresinha Correa Silva-Sousa ^I

 

^I School of Dentistry, University of Ribeirão Preto – Ribeirão Preto – SP – Brazil.
^II Department of Restorative Dentistry, University of São Paulo – Ribeirão Preto – SP – Brazil.

Correspondence

 

 

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ABSTRACT

Introduction: The aim of this study was to evaluate in vitro the bonding of AH Plus and Endofill sealers to intraradicular canal walls after different dentin surface treatments. Material and methods: Sixty canines were sectioned obtaining dentin discs with 4-mm thickness and were embedded in acrylic resin. The canals were prepared with diamond burs. The specimens were divided into two groups (n = 30): GI – AH Plus and GII – Endofill and were subdivided into three groups based on the dentin surface treatment (n = 10): A – distilled and deionized water (control), B – 17% EDTA, C – CO₂ laser with 3W in continuous mode for 10s. The specimens were submitted to push out test in a universal testing machine. Results: Tukey test revealed that the IB (AH Plus/17% EDTA) (17.59 ± 6.04) and IC (AH Plus/CO2 laser) (21.69 ± 4.93) subgroups had the highest values, which were statistically similar between each other (p > 0.05) and different from the other subgroups (p < 0.05). IIC subgroup (Endofill/CO2 laser) (7.25 ± 1.59) had intermediate values, which were statistically similar to (p > 0.05) IA subgroup (AH Plus/water) (10.99 ± 2.63), IIA subgroup (Endofill/water) (3.16 ± 0.83) and IIB subgroup (Endofill/ 17% EDTA) (5.31 ± 3.61), which had the smallest values (p < 0.05). Conclusion: The treatment of superficial intracanal dentin with CO₂ laser and EDTA favored the adhesion of AH Plus and Endofill sealers.

Keywords: adhesion; sealers; Endodontics; CO₂ laser.

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Introduction

Different chemical solutions have been recommended for root canal instrumentation, aiming to the removal of both the debris and smear layer and root canal disinfection. Among the solutions recommended, tetra acetic acid (EDTA) is the most used for smear layer removal ⁴.

The smear layer is a negative factor for root canal sealing, because of the interface between the filling material and root canal walls, which reduces the bonding strength ⁶.

The use of laser has been a promissory alternative in endodontic therapy, by acting as an auxiliary for root canal cleaning, disinfection and removal of the smear layer ⁸. In vitro studies have shown the capacity of CO₂ laser de of promoting root canal disinfection ⁹, increasing coronal dentin permeability ¹⁵, morphologically altering root dentin ^1,22 and vaporizing the smear layer within intertubular dentin ²², therefore enabling a greater imbrication of the endodontic sealers to dentinal tubules ²³.

Concerning to the endodontic sealers, they can be classified as: zinc oxide and eugenol-based cements, with or without medicines; calcium hydroxide-based cements; glass ionomer-based cements; and resin cements ²¹.

Zinc oxide and eugenol cement was introduced in 1936, by Grossman, in Endodontics to be employed in root canal obturation; in 1974, some modifications were performed in its formula, continuing until today, although it presents low biocompatibility ¹⁸, lack of adhesive properties ²¹ and high solubility ².

AH Plus is a sealer based on epoxy resin with satisfactory physical-chemical properties, low solubility ^3,11,16, satisfactory flowing ^3,11,16, good adhesion ^1,13,14 and proper biological properties ¹⁴.

Therefore, it is important to evaluate the influence of the superficial treatment of the dentin with CO2 laser on the bonding of sealers (AH Plus and Endofill) to intraradicular walls.

 

Material and methods

Maxillary human canines stored in 0.1% thymol solution at 9°C were washed in tap water for 24 hours to eliminate thymol residues.

Teeth were macroscopically examined and radiographed at mesiodistal direction. Inclusion criteria comprised completely formed straight roots with a single canal without calcifications or accentuated curvature. Therefore, sixty teeth were selected. Teeth were sectioned transversally 4 millimetres below the cementoenamel junction to provide 4-mm-thick dentine discs that were centred inside aluminium rings (16 mm diameter and 4 mm height) and embedded in acrylic resin. The aluminium rings containing the dentine discs were placed in a parallelometer and their coronal and apical surfaces were flattened and polished using wet 100-, 180-, 220- and 300-grit sandpapers (Bosch, São Paulo, SP, Brazil) during 15 seconds each. The root canal of each specimen was prepared using a tapered diamond bur (PM720G; KG Sorensen Ind. Com. Ltd, Barueri, São Paulo, SP, Brazil) mounted to a low-speed handpiece which was coupled to the arm of the parallelometer. This arm was lowered to a predetermined depth and a space for sealer placement was created with the following dimensions: larger diameter = 2.70 mm; smaller diameter = 2.30 mm; length = 4 mm. During preparation, the canals were irrigated with distilled water. NaOCl and EDTA solutions were prepared at a manipulation pharmacy (Fórmula & Ação, São Paulo, SP, Brazil).

Sixty specimens were randomly divided into two groups (n = 30) regarding to the sealer used: GI – AH-Plus and GII – Endofill and subdivided into three subgroups according to dentin surface treatment: A (control) – irrigation with distilled and deionized water, B – irrigation with 17% EDTA and C – surface treatment with CO2 laser (Opus Dent, Israel) with 3W in continuous mode for 10s.

Following, the specimens were placed immediately at 37ºC and 95% humidity for a period three times greater than the regular setting time of the sealer.

Subsequently, the specimens were fixed securely in a metallic apparatus by two screws at the horizontal plane. For push-out test, a stainless steel support was used to hold the samples (metallic ring + dentin cylinder) in an Instron 4444 universal testing machine (Instron Corporation, Canton, MA, USA) in such a way that the side with the smaller diameter of the root canal was faced upwards and aligned to the axis that would exert the pressure load on the sealer (apical-coronally). This method assured the alignment of the specimen in a reproducible manner, and also avoided the contact of the axis with the dentin during testing. The machine was calibrated at a constant crosshead speed of 1 mm/minute with 1.4-mm-diameter stainless steel cylindrical tip. The tensile load was applied, and the load required to cause failure at the bond interface was recorded in MPa. Data were submitted to statistical analysis by ANOVA and Tukey’s test (p < 0.05).

 

Results

ANOVA showed statistically significant differences between the sealers, among the treatment surfaces, and among their interaction (p < 0.05).

Tukey test revealed that AH Plus sealer provided the highest mean values (16.76 ± 6.43), statistically different from those of Endofill sealer (5.24 ± 2.83) (p < 0.05).

Concerning to treatment surface, it was observed that CO2 laser promoted a higher mean value (14.47 ± 818), statistically different from that of the groups treated by EDTA (11.45 ± 7.93) and water (7.07 ± 4.42).

In the interaction between the endodontic sealer and the superficial treatment, it was verified that IB subgroup (AH Plus/17% EDTA) (17.59 ± 6.04) and IC subgroup (AH Plus/CO2 laser) (21.69 ± 4.93) obtained the highest mean values, statistically similar between each other (p > 0.05) and different from those of the other groups (p < 0.05). IIC subgroup (Endofill/laser CO2) (7.25 ± 1.59) presented intermediary values, statistically similar to (p > 0.05) IA subgroup (AH Plus/water) (10.99 ± 2.63) and to IIA subgroup (Endofill/water) (3.16 ± 0.83) and IIB subgroup (Endofill/17% EDTA) (5.31 ± 3.61), which obtained the smallest mean values with statistically similar values between each other (p > 0.05). Table I displays the results obtained in the different experimental groups.

 

 

 

Discussion

The smear layer is an amorphous structure adhered to root canal walls, produced during the biomechanical preparation. This layer is a negative factor in root canal obturation, because it is composed of dentinal debris, remnant of odontoblastic components, pulp tissue and bacterias ¹², damaging the adhesion of the filling materials ²⁰.

The removal of the smear layer can be achieved by the use of acid solutions as 17% EDTA ^5-7. Sousa-Neto et al. ¹⁹ emphasized the importance of smear layer removal prior to root canal obturation, aiming to allow a higher penetration of endodontic sealers within dentinal tubules and to promote a higher mechanical imbrication. Therefore, this study evaluated the influence of the superficial treatment of the intraradicular wall with distilled and deionized water, 17% EDTA and CO2 laser on the bond strength to dentin of AH Plus and Endofill endodontic sealers.

The superficial treatment of intraradicular dentin promoted, in this present study, significantly different bond strength values of endodontic sealers to root canal walls AH Plus showed the highest bonding values when compared with Endofill, regardless of the previous superficial treatment of the dentin. Such fact can be explained because AH Plus is an epoxy resin-based sealer and it better penetrates into the micro-irregularities of root canal walls because of its flowing and high curing time ^3,11,16. These properties favor a greater imbrication between the sealer and the dentin, which in addition to the cohesion among the molecules of the sealer promote a greater resistance to removal and/or displacement from the dentin surface, resulting in this present study in higher adhesion ²⁰.

In this present study, the sealers analysed obtained an increase in the bond strength values when the dentinal surface was treated with CO2 laser. CO2 laser promotes root canal disinfection ⁹, increases the coronal dentinal permeability ¹⁵ and ultrastructurally alters the root dentin ¹.

Additionally, this laser promotes the formations of crackers and fissures and vaporizes the smear layer of intertubular dentin ^17,22. Such alterations in dentin surface were observed through scanning electronic microscopy by Trajtenberg et al. ²³ and Alfredo et al. ¹. According to Sousa-Neto et al. ¹⁹, smear layer removal and the presence of fissures on the dentin surface may facilitate the mechanical retention of the endodontic materials and favor the bond strength to root canal wall. Accordingly, it is believed that the ultrastructural alteration promoted by CO2 laser resulted in this present study in higher bond strength of the sealers to intraradicular wall.

Unlike to CO₂ laser, 17% EDTA acts on the mineral matrix and removes the smear layer formed during biomechanical preparation, which probably enables a greater penetration of the sealers within dentinal tubules and results in an increasing of the contact surface between the sealer and the dentin ⁵. Therefore, EDTA action promotes values statistically similar to those treated with CO2 laser, regardless of the sealer used.

Considering the aforementioned discussion, this study encourages further studies aiming to elucidate the influence of the ultrastructural alteration of the dentin, after the superficial treatment, on the bonding of different resin-based endodontic sealers.

 

Conclusion

Based on the methodology employed and on the results obtained, it can be concluded that the superficial treatment of the intraradicular dentin through CO2 laser and EDTA favored the bonding of endodontic sealers.

 

References

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Correspondence:
Aline Evangelista Souza-Gabriel
Av. Costábile Romano, n.º 2.201 – Ribeirânea
CEP 14096-900 – Ribeirão Preto – SP – Brasil
E-mail:aline.gabriel@gmail.com

 

 

Received for publication: March 12, 2012.
Accepted for publication: May 19, 2012.