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HIGH VISCOSITY BULK-FILL GIOMER AND ORMOCER-BASED RESIN COMPOSITES: AN IN-VITRO COMPARISON OF THEIR MECHANICAL BEHAVIOUR

Table 3. Macro and micromechanical properties( mean standard ± deviation) of the bulk-fill RBCsflexural strength σ( MPa), flexural modulus Eflexural( GPa), Martens Hardness HM( N / mm ²), Vickers Hardness HV( N / mm ²), indentation modulus YHU( GPa), Creep(%)-. Superscript letters indicate statistically homogeneous subgroups within a column( Tukey’ s HSD test. α = 0.05). * Data were partial presented in 1

Figure 3. Filler amount( weight %)

of the parameter filler weight on the measured parameters σ, Eflexural, HM, HV, YHU and Creep. The partial eta-squared statistic reports the practical significance of each term, based on the ratio of the variation accounted for by the effect. Larger values of partial eta-squared indicate a greater amount of variation accounted for by the model effect, to a maximum of 1. Correlations among measured properties as well as filler amount, was assessed by a Pearson correlation analysis. In all statistical tests, p-values < 0.05 were considered statistically significant when using SPSS Inc.( Version 23.0, Chicago, IL, USA).

3. Results

The effect of the parameter filler amount( weight %) was proved to be significant on all measured properties( p < 0.001; partial eta squared varied among η P

² = 0.212 for Creep and 0.891 for Y HU

, Table 2), while being higher on the modulus of elasticity, either measured at microscopic( Y HU; η P

²

= 0.891) or macroscopic scale( E flexural; η P

² = 0.805). The direct comparison of the properties measured as a function of RBCs revealed statistical lower flexural strengths values for the ormocer-based material Admira Fusion x-tra( 99.9 ± 10.7 MPa) and the giomer Beautifil Bulk restorative( 106.0 ± 12.7 MPa), while the highest values were recorded for QuixFil, X-tra Fil and SonicFill. The difference in flexural strength among lowest and highest values does not exceed 40 %, yet differences measured for E flexural go beyond 100 %. The significant lowest flexural modulus was measured for the group Tetric EvoCeram Bulk Fill( 4.5 ± 0.8 GPa) and Admira Fusion x-tra( 5.3 ± 0.5 GPa), while the group QuixFil( 9.4 ± 1.8 GPa) and X-tra Fil( 9.5 ± 0.6 GPa) showed the highest values in the range of the analyzed materials. This trend is maintained also for the indentation modulus Y HU as well as for the hardness parameters. Lower variation among materials was identified for Creep( 3.3 to 3.7 %)( Table 3). The filler amount showed the best correlation with the flexural modulus( Pearson correlation coefficient = 0.724), followed by the indentation modulus( 0.567) and the hardness parameters, while no correlation was identified with the flexural strength. An inverse correlation, yet low(-0.218) was identified between filler amount and creep. A moderate correlation was observed between the parameters measured at macroscopic scale( σ and E flexural

, 0.425), while the correlation among the micro-mechanical parameters was high, except for Creep. The correlation among macro and micro mechanical parameters( except again for Creep) was low to moderate for σ and high for E flexural

( Table 4).

4. Discussion

The basic approach of this study was to compare modern high-viscosity bulk-fill RBCs in terms of their mechanical behavior assessed at macro and microscopic scale. All materials analyzed belong to the category of high-viscosity bulk-fill RBCs, which is characterized by enhanced mechanical properties when compared to the low-viscosity bulk-fill RBCs. 1 The materials analyzed are indicated to be used in bulk up to 4 or 5 mm, to restore the entire preparation, with no need to be capped by an auxiliary restorative composite. Under the curing conditions used in the present study( 20s exposure time, 1241 mW / cm ² irradiance),