My first Magazine | Page 58

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 ),