This study evaluates the push-out bond strength (POBS) of three root canal sealers: AH Plus (epoxy resin-based), BIO-C ION+ (calcium silicate-based), and Nanoseal-S (silicone-based). The aim was to compare their penetration and adhesion within the coronal, middle, and apical thirds of root canals. This comparative evaluation sheds light on the effectiveness of different sealer types in achieving optimal obturation.
Variations in Bond Strength Across Root Canal Thirds
The research employed different sized plungers for each root third to assess POBS, adhering to recommendations for plunger size relative to filling material. Results indicated that AH Plus consistently exhibited the highest POBS, attributed to its inherent expansion properties and ability to form strong covalent bonds with dentin. This finding aligns with existing literature supporting AH Plus’s superior performance.
BIO-C ION+, while offering biocompatibility and bioactivity due to its calcium silicate and hydroxyapatite composition, demonstrated lower POBS than AH Plus. This difference stems from the weaker micromechanical and chemical interaction of calcium silicate sealers with dentin compared to the robust bonding of epoxy resins. The study acknowledges a potential limitation: the 24-hour storage in saline, rather than phosphate buffered saline (PBS), might have underestimated the potential bond strength of BIO-C ION+. Longer storage in PBS could promote apatite deposition, potentially enhancing bond strength.
Nanoseal-S exhibited the lowest POBS, potentially due to the presence of silicone, which might contribute to poor wetting of the dentin and hinder dispersion. This observation corroborates previous studies showing lower POBS for silicone-based sealers compared to epoxy resin and other alternatives.
Intergroup and Intragroup Comparisons of Sealer Penetration
Consistent with previous research, all three sealers demonstrated a pattern of decreasing bond strength from coronal to apical thirds within each group (intragroup comparison). The coronal third consistently exhibited the highest POBS, followed by the middle and then the apical thirds.
This decreasing apical bond strength trend is a common finding in studies evaluating bonding in root canal dentin. This phenomenon is linked to the reduced number and diameter of dentinal tubules in the apical region. Furthermore, challenges in effectively removing the smear layer in apical sections can impede sealer penetration and reduce contact between the filling material and dentin walls.
Methodological Considerations and Study Limitations
Contrary to some studies reporting higher bond strength in middle and apical sections due to lateral compaction techniques, this study employed a single-cone technique. This choice aimed to achieve a more homogenous and consistent gutta-percha mass, minimizing voids and ensuring linear resistance against dislodgment. The single cone technique provides a more standardized and predictable filling, contributing to the observed bond strength patterns.
Besides being an in vitro study, another limitation is the use of Rhodamine B dye, a water-soluble dye that might overestimate penetration due to water uptake within the canals. However, strengths of the study include the use of confocal laser scanning microscopy (CLSM) and universal testing machine (UTM) analysis for precise measurements, alongside the standardized single-cone obturation technique. Future research utilizing in vivo models and alternative dyes could further refine our understanding of resin-based sealer penetration.
