Flexural strength and degree of conversion of universal single shade resin-based composites

Recently, a group of universal single-shade resin-based composites (RBCs) has been developed to simplify the process of shade selection. Excellent mechanical and physical properties are crucial for the ultimate success and clinical longevity of restorations. Therefore, evaluating the properties of the single-shaded RBCs is imperative. This study aimed to determine the flexural strength (FS) and degree of conversion (DC) of universal single-shade RBCs.

In this study, four commercial RBCs were used; three universal single-shade RBCs; Omnichroma (OC), Charisma® Diamond ONE (CD), and Vittra APS Unique (VU), and a conventional nanohybrid composite Filtek™ Z250 XT (FT) which was used as a control. Sixty composite beams and 40 composite discs were used for FS and DC, respectively. A universal test machine with a three-point bending test was used to measure the FS, whereas the DC was measured using a Fourier-transform infrared spectrometer (FTIR). Three fractured specimens from each resin composite group were qualitatively analyzed using scanning electron microscopy.

ANOVA was used to compare the mean values of FS and DC among the four RBCs (OC, CD, VU, and FT). Highly significant differences were observed in the mean FS and DC values (F = 673.043, p < 0.001 and F (=782.4, p < 0.0001), respectively. The highest FS was observed in the CD group, followed by FT and VU groups; the lowest value was observed in the OC group. In addition, a statistically significant difference was identified in DC values. The highest DC value was observed in VU, followed by OC and CD, and the lowest DC value was observed in FT.

Universal single-shade RBCs demonstrated a good FS, except for OC, which exhibited a significantly low FS. The DC of the universal single-shade RBCs was higher than that of the conventional nanohybrid composite restorative material.