Abstract
The use of an adequate method for evaluation of the adhesion of root canal filling materials provides more reliable results to allow comparison of the materials and substantiate their clinical choice. The aims of this study were to compare the shear bond strength (SBS) test and push-out test for evaluation of the adhesion of an epoxy-based endodontic sealer (AH Plus) to dentin and guttapercha, and to assess the failure modes on the debonded surfaces by means of scanning electron microscopy (SEM). Three groups were established (n=7): in group 1, root cylinders obtained from human canines were embedded in acrylic resin and had their canals prepared and filled with sealer; in group 2, longitudinal sections of dentin cylinders were embedded in resin with the canal surface smoothed and turned upwards; in group 3, gutta-percha cylinders were embedded in resin. Polyethylene tubes filled with sealer were positioned on the polished surface of the specimens (groups 2 and 3). The push-out test (group 1) and the SBS test (groups 2 and 3) were performed in an Instron universal testing machine running at crosshead speed of 1 mm/min. Means (±SD) in MPa were: G1 (8.8±1.13), G2 (5.9±1.05) and G3 (3.8±0.55). Statistical analysis by ANOVA and Student's t-test (α=0.05) revealed statistically significant differences (p<0.01) among the groups. SEM analysis showed a predominance of adhesive and mixed failures of AH Plus sealer. The tested surface affected significantly the results with the sealer reaching higher bond strength to dentin than to guttapercha with the SBS test. The comparison of the employed methodologies showed that the SBS test produced significantly lower bond strength values than the push-out test, was skilful in determining the adhesion of AH Plus sealer to dentin and gutta-percha, and required specimens that could be easily prepared for SEM, presenting as a viable alternative for further experiments.
Highlights
The endodontic treatment is completed by the threedimensional filling of the root canal system, which provides adequate sealing of the dentin structures after chemomechanical preparation
The American Dental Association[2] has issued a series of regulations and tests for study of the physical properties of root canal sealers, adhesion tests have not yet been standardized because no consensus on test parameters has been reached among researchers
The divergent results obtained in the studies and the difficulties in testing materials with great plasticity, such as gutta-percha and Resilon®, or materials with high modules of elasticity, such as radicular posts, have led to the development of different methodologies for determining the bond strength of endodontic sealers to coronal or root dentin[7,9,10,24,25,26]
Summary
The endodontic treatment is completed by the threedimensional filling of the root canal system, which provides adequate sealing of the dentin structures after chemomechanical preparation. One of the key roles of the sealer is to aggregate the root filling material and maintain it as compact mass with no gaps, which adheres to the canal walls and provides a single block configuration that seals hermetically the canal space[21] This adhesion process involves mechanical forces that yield the intertwining of the material with the dentin structures[15] and may result in a greater sealing ability, reducing the risk of root canal microleakage and maintaining a cohesive filling mass[20]. Stands out the shear bond strength (SBS) test, in which the force is applied parallel to the interface between the material and the tested surface[5] This test has been used to measure the bond strength of endodontic sealers to dentin and gutta-percha or, more recently, for Resilon® and has been proven effective and reproducible[7,10,11,25,26]. The use of flat root dentin surfaces would be a viable alternative to test resin materials[5], as well as other materials with less cohesive strength, such as gutta-percha and non-resin sealers, allowing comparison of the results by the same methodology[25]
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