Results

The descriptive statistics of the evaluated mechanical properties are presented in Table 1. Tetric N-Ceram (Group I) demonstrated the highest mean tensile strength (22.52 ± 3.79 MPa), flexural strength (94.36 ± 21.65 MPa), compressive strength (87.82 ± 55.60 MPa), and Barcol hardness (73.60 ± 2.32 MPa). Waldent NanoFill (Group IV) exhibited the lowest mean tensile strength (14.08 ± 6.20 MPa) and compressive strength (64.40 ± 45.69 MPa), whereas DentGist NanoCom (Group III) demonstrated the lowest flexural strength (57.48 ± 16.75 MPa) and Barcol hardness (56.00 ± 2.83). The 95% confidence intervals for each outcome measure are presented in Table 1.

Property | Group I (Tetric N-Ceram) | Group II (Fusion Universal) | Group III (Dentgist NanoCom) | Group IV (Waldent NanoFill)
Mean ± SD | 95% CI of Mean | Mean ± SD | 95% CI of Mean | Mean ± SD | 95% CI of Mean | Mean ± SD | 95% CI of Mean
Tensile strength (MPa) | 22.52 ± 3.79 | 19.81 – 25.23 | 20.10 ± 4.30 | 17.02 – 23.18 | 21.65 ± 10.74 | 13.97 – 29.33 | 14.08 ± 6.20 | 9.65 – 18.51
Flexural strength (MPa) | 94.36 ± 21.65 | 78.87 – 109.85 | 80.20 ± 13.73 | 70.38 – 90.02 | 57.48 ± 16.75 | 45.49 – 69.47 | 60.12 ± 9.02 | 53.67– 66.57
Compressive strength (MPa) | 87.82 ± 55.60 | 48.05 – 127.59 | 71.48 ± 32.08 | 48.54 – 94.43 | 84.31 ± 24.20 | 67.00 – 101.62 | 64.40 ± 45.69 | 31.72 – 97.09
Barcol hardness number | 73.60 ± 2.32 | 71.91 – 75.26 | 66.00 ± 3.56 | 63.45 – 68.55 | 56.00 ± 2.83 | 53.98 – 58.02 | 72.60 ± 3.44 | 70.14 – 75.06

Intergroup comparisons using one-way ANOVA revealed statistically significant differences in tensile strength (p = 0.038), flexural strength (p = 0.002), and Barcol hardness (p < 0.001), whereas compressive strength did not differ significantly between the groups (p = 0.555) (Table 2). The largest effect size was observed for Barcol hardness (0.41), followed by flexural strength (0.28) and tensile strength (0.23), whereas compressive strength demonstrated only a negligible effect size (0.04).

Property | Intergroup comparison
F value | p-value | Effect size (η²)
Tensile strength | 3.10 | 0.038* | 0.23
Flexural strength | 6.12 | 0.002* | 0.28
Compressive strength | 0.71 | 0.555 | 0.04
Barcol hardness number | 64.21 | < 0.001* | 0.41

Post-hoc pairwise comparisons performed using Tukey's test revealed distinct statistical significance patterns for tensile and flexural strengths across the four nanohybrid composite resins. Regarding tensile strength, Waldent NanoFill (Group IV) exhibited significantly lower values compared to Tetric N-Ceram (p = 0.006), Fusion Universal (p = 0.034), and DentGist NanoCom (p = 0.019). Conversely, tensile comparisons among Groups I, II, and III were non-significant. For flexural strength, Tetric N-Ceram significantly outperformed DentGist NanoCom and Waldent NanoFill, with both comparisons showing p < 0.001. Additionally, Fusion Universal demonstrated significantly greater flexural strength than DentGist NanoCom (p = 0.007) and Waldent NanoFill (p = 0.010). In contrast, the flexural strength between Tetric N-Ceram and Fusion Universal (p = 0.119) and between DentGist NanoCom and Waldent NanoFill (p = 0.962) did not reach statistical significance (Table 3).

Intergroup comparison | Tensile strength | Flexural strength
Mean difference (MPa) | 95% CI (Lower–Upper) | t-value | p-value | Mean difference (MPa) | 95% CI (Lower–Upper) | t-value | p-value
Group I vs. Group II | 2.42 | −1.90 to 6.74 | 2.67 | 0.442 | 14.16 | −2.74 to 31.06 | 3.49 | 0.119
Group I vs. Group III | 0.87 | −5.52 to 7.26 | 0.48 | 0.969 | 36.88 | 19.02 to 54.74 | 8.51 | <0.001*
Group I vs. Group IV | 8.44 | 2.78 to 14.10 | 7.34 | 0.006* | 34.24 | 18.56 to 49.92 | 9.23 | < 0.001*
Group II vs. Group III | -1.55 | −7.94 to 4.84 | –0.84 | 0.914 | 22.72 | 5.82 to 39.62 | 6.63 | 0.007*
Group II vs. Group IV | 6.02 | 0.36 to 11.68 | 5.04 | 0.034* | 20.08 | 4.40 to 35.76 | 7.72 | 0.010*
Group III vs. Group IV | 7.57 | 1.18 to 13.96 | 3.85 | 0.019* | -2.64 | −18.32 to 13.04 | –0.87 | 0.962

The post-hoc comparisons of the compressive strength and Barcol hardness are summarized in Table 4. No statistically significant differences were observed in compressive strength among any of the four composite groups following the Bonferroni correction (all p > 0.05). In contrast, barcol hardness differed significantly between most pairwise comparisons. Tetric N-Ceram demonstrated significantly higher hardness values than Fusion Universal and DentGist NanoCom (both p < 0.001), and Fusion Universal also exhibited significantly greater hardness than DentGist NanoCom (p < 0.001). Waldent NanoFill showed hardness values comparable to Tetric N-Ceram (p = 0.768), but significantly higher than that of DentGist NanoCom (p < 0.001) and significantly lower than that of Fusion Universal (p < 0.001).

Intergroup comparison | Compressive strength | Barcol hardness number
Mean difference (MPa) | 95% CI (Lower–Upper) | t-value | p-value | Mean difference | 95% CI (Lower–Upper) | t-value | p-value
Group I vs. Group II | 16.34 | −13.42 to 46.10 | 1.61 | 0.463 | 7.60 | 4.80 to 10.40 | 11.31 | < 0.001*
Group I vs. Group III | 3.51 | −23.45 to 30.47 | 0.36 | 0.979 | 17.60 | 14.80 to 20.40 | 30.40 | < 0.001*
Group I vs. Group IV | 23.42 | −6.78 to 53.62 | 2.05 | 0.176 | 1.00 | −1.80 to 3.80 | 1.524 | 0.768
Group II vs. Group III | -12.83 | −42.59 to 16.93 | –2.02 | 0.628 | 10.00 | 7.20 to 12.80 | 13.91 | < 0.001*
Group II vs. Group IV | 6.08 | −27.08 to 39.24 | 0.80 | 0.950 | -6.60 | −9.40 to −3.80 | –8.43 | < 0.001*
Group III vs. Group IV | 19.91 | −10.29 to 50.11 | 2.43 | 0.282 | -16.60 | −19.40 to −13.80 | –23.58 | < 0.001*