Comparative Study of Direct Resin Composites with Different Formulations

Objectives: The aim was to evaluate the mechanical, physical, and surface properties, as well as the microstructure, of three direct resin composites with different formulations (CLEARFIL AP-X, MAJESTY ES Flow, and MAJESTY ES-2) from the same manufacturer. Methods: Mechanical properties, including flexural strength, flexural modulus, and fracture toughness, were determined for each material (n = 8/material) according to ISO standards. Fourier transform infrared (FTIR) spectroscopy was used to determine the degree of conversion (DC%). Two-body wear was evaluated using a ball-on-flat configuration in a chewing simulator for 15,000 cycles, and wear depth was measured using a non-contact 3D optical profilometer. Polymerization shrinkage stress was measured using a tensilometer. Surface roughness and gloss were evaluated on disk-shaped specimens (n = 5/material) after polishing with 2400- and 4000-grit abrasive papers. Microstructural characterization was performed using scanning electron microscopy. Data were analyzed using ANOVA followed by Tukey's HSD test (α = 0.05). Results: CLEARFIL AP-X exhibited the highest flexural strength (186.95 MPa), flexural modulus (19.25 GPa), and fracture toughness (1.50 MPa m^1/2) among the tested materials (p < 0.05). However, it also showed the highest surface roughness and the lowest gloss values. MAJESTY ES Flow demonstrated the lowest wear depth and the highest gloss and polymerization shrinkage stress, whereas MAJESTY ES-2 exhibited the greatest wear and the lowest DC%. Conclusions: The three resin composites exhibited distinct mechanical, physical, surface, and microstructural characteristics associated with differences in their formulations, including filler content, filler morphology, and resin matrix composition. No single material demonstrated superior performance across all evaluated properties, highlighting the importance of selecting resin composites according to the specific clinical requirements.