The Influence of Convergence Angle and Dentin Micromorphology on Shear Bond Strength of Adhesive Resin Luting Cement

Purpose: To determine the influence of convergence angles and axial planes on shear bond strength between dentin and adhesive composite resin luting cement, and its relation to dentin micromorphology. Materials and Methods: The four axial planes of 60 intact extracted mandibular molars were prepared at either 4 or 20 degrees to the longitudinal tooth axis. A Teflon cylindrical mold (1.6 mm) was filled with Rely X-ARC, bonded to Single Bond treated dentin surface and tested for shear bond strength after 7 days. Three SEM micrographs (5000X magnification) were taken from each surface after removing the bonding layer. The tubule circumference was marked using Adobe Photoshop. Micromorphology parameters were analyzed with the MATLAB program. A Mixed Effect Linear Model and linear regression were performed to analyze the influence of tubule density, tubule area, tubule circumference, and residual dentin thickness on shear bond strength. Results: The shear bond strength was not significantly different between axial planes (p > 0.05), but was significantly higher at 4 degrees than at 20 degrees (p=0.009). A significant positive correlation was found between shear bond strength and tubule area (R = 0.43, p = 0.003) or tubule circumference (R = 0.42, p = 0.003), confirming the importance of resin penetration into the tubules. No correlation was found between shear bond strength and tubule density (R = 0.22, p > 0.05) or residual dentin thickness (R = -0.22, p > 0.05). More round and more elliptic tubule orifices characterized dentin prepared at 4 and 20 degrees, respectively. Conclusion: Regional variations in tubule cross-section appearance can modify the bond strength of adhesive resin luting cements. Keywords: dentin, shear bond strength, micromorphology, convergence angle, tubule orientation