Bonding of Composite to Base Materials: Effects of Adhesive Treatments on Base Surface Properties and Bond Strength

Purpose: To evaluate the effects on the surface properties (morphology, roughness, microhardness, composition) and bond strength to composite of four types of base cements (Equia-Fil/EQF, Angelus white MTA/MTA, Biodentin/BDN and IRM/IRM) when treated with phosphoric acid etching (PAE) or two self-etch adhesives (Select One Prime & Bond and Clearfil S3 Bond). Materials and Methods: Disk-shaped specimens were prepared and stored until complete setting. The surfaces before and after treatments were examined by stereomicroscopy, optical profilometry, ATR-FTIR, and LV-SEM/EDX. Interfacial bond strength with composite was evaluated under shear loading (SBS) using a conventional bonding resin (Heliobond) on silane treated (SIL) specimens as a reference. Failure mode was evaluated using stereomicroscopy. Results: PAE induced compositional changes on MTA and BDN, forming a phosphate-rich surface layer, probably composed of Ca-P salts. Dissolution of the amorphous cement fractions was evident in all materials. SPB and CSB did not show remarkable changes apart from an increase in Si content on MTA. On all bases, PAE resulted in the highest values for most of the roughness parameters. SPB and CSB showed lower or equal average roughness (Sa) and percentage of additional surface area contributed by the texture (Sdr) compared to the control in MTA and EQL. In terms of SBS, the highest β (Weibull shape parameter) in MPa were MTA-SIL = 5.79, BDN-PAE = 3.67, and MTA-PAE = 3.46, whereas the highest α (Weibull scale parameter) were EQF-CSB = 9.08, BDN-PAE = 5.13, and BDN-SIL = 4.67. Adhesive failures with less than 20% of the bonding area were encountered in IRM-PAE and SIL, EQF-CBS and MTA-SIL. Conclusion: Each base material requires a different procedure for optimal bonding with composite. Phosphoric acid etching and application of the conventional bonding resin Heliobond is the preferred procedure for composite bonding to MTA, BDN, IRM, but for composite bonding to CSB for EQF, the mild self-etch adhesive is preferable. Keywords: base materials, composite, roughness, elemental and molecular analysis, shear bond strength