Flexural strength of new and repaired TEGDMA- and HEMA-free resin composites compared to a conventional composite

Objectives: To evaluate the flexural strength of a conventional resin composite – APX (Clearfil AP-X, Kuraray) compared to green line resin composites (ELS, ELS flow, and APT, Saremco Dental AG).

Methods: Hundred sixty specimens were subjected to flexural strength test. Among these specimens, half were tested in their monolithic form, while the other half was subjected to a repair procedure using the same material of each respective group. The repaired samples were subjected to 10,000 thermal cycles (5ºC - 55ºC) before testing. One-way ANOVA and post-hoc tests (α= 0.05) were used for statistical analysis.

Results: APX demonstrated the highest mean flexural strength (148.1 MPa; p < 0.05) compared to the other composites. APT (111.48 MPa) and ELS Flow (102.5 MPa), on the other hand, showed no difference (p = 0.544) in their strength, while ELS flow exhibited the lowest mean value (77.8 MPa). For the repaired groups, no difference was observed (p > 0.05).

Conclusions: The mean value of the repaired composites ranged between 71.7 – 68.1 MPa. APX, which contains TEGDMA, presented higher flexural strength in the monolithic form compared to the green line composites. However, after repair, there was no difference among the groups. Clinical Significance: Although conventional composites show higher strength in monolithic restorations, all materials perform similarly after repair with a significant reduction in strength. Therefore, composite repair should be considered a temporary clinical solution, regardless of the material used.