Shear Bond Strength of MDP-Containing Adhesives with and without HEMA: An in Vitro Study

Background and Objectives: The primary role of dental adhesives is to deliver a good bond between the filling material and the tooth. Universal adhesive (UA) systems brought a novel concept by adding active resin monomers that facilitate both micromechanical and chemical adhesion. 10-methacryloyloxydecyl dihydrogen phosphate (MDP) is a vital component of these adhesives, noted for its strong ionic interaction with hydroxyapatite (HAp) in both enamel and dentin, which leads to the formation of nanolayers of MDP-calcium salts. Evidence suggests that 2-hydroxyethyl methacrylate (HEMA), a monomer that is hydrophilic and improves the adhesive's wetting ability on dental surfaces, may affect MDP’s interaction with hydroxyapatite powder. In view of this, the present study aimed to assess the differences in shear value of bond strength between two MDP-containing multi-mode bonding systems: Futurabond M+ (VOCO, Germany), which contains HEMA, and G-Premio Bond (GC, Japan), a HEMA-free alternative. Materials and Method: Forty extracted human maxillary premolars were separated into two groups (n=20). The occlusal portion was removed to gain a smooth dentin surface. Adhesives were applied per manufacturers’ instructions, followed by composite resin build-up (Palfique LX5, Tokuyama, Japan). After 24-hour water storage at 37°C, using a universal testing machine (TERCO, MT 3037, Sweden) at 1.0 mm/min, shear bond strength was tested. To analyze the data, an independent t-test (p < 0.01) was used. Results: Futurabond M+ (HEMA-containing) exhibited significantly higher shear bond strength (19.74 ± 4.80 MPa) than G-Premio Bond (HEMA-free) (14.33 ± 5.80 MPa) (p = 0.001). The mean difference (5.41 MPa) and large effect size (Cohen’s d = 1.017) show that the greater bond strength attained with VOCO Futurabond M+ is statistically important and expressive in a practical, clinical situation. Conclusion: HEMA-containing Futurabond M+ produced higher shear bond strength to dentin compared to HEMA-free G-Premio Bond, probably due to HEMA, ethanol, and higher pH. The adhesive act is dependent on numerous factors; therefore, additional investigations are necessary. Keywords: HEMA, Shear bond strength, Universal adhesives, MDP.