HIGH VISCOSITY BULK-FILL GIOMER AND ORMOCER-BASED RESIN COMPOSITES: AN IN-VITRO COMPARISON OF THEIR MECHANICAL BEHAVIOUR
a) b)
Figure 1. Macro-mechanical properties – a) Flexural strength; b) Flexural modulus
identified some bulk-fill restoratives to produced larger gaps at the dentin margin of Class II cavities, when compared to regular RBCs restorations. Nevertheless, good in-vitro performance as reflected in improved self-leveling ability, 9 decreased polymerization shrinkage stress 10-12 and reduced cusp deflection 13 encourage a positive forecasting of the clinical performance of bulk-fill RBCs. Owing to the short time since the materials have been launched on the market, only few clinical studies are available. For the low-viscosity bulk-fill RBC, SDR, van Dijken et al. 14, 15 attested in two different 3-year follow-up studies, a similar performance compared to restorations made by regular RBCs placed in a layering technique. As for high-viscosity bulk-fill RBCs, only one short 1-year clinical evaluation of class II restorations is reported so far, stating that the clinical performance of several high-viscosity bulk-fill RBCs was similar when compared to a conventional posterior RBC. 16 When considering the bulk-fill RBCs as a material category, their mechanical properties were identified to fall between those of regular and flowable composites, indicating a similar or possibly inferior clinical behavior relative to standard microhybrid or nanohybrid composites. Yet, the differences in mechanical properties within the bulk-fill category were identified to be very high, which is particularly due to the different filler content. 1 The performance of each material must therefore be assessed individually and cannot be transferred from the material category they belong to. Although the chemical composition of the organic matrix is largely similar to that described in regular RBCs, a particularity of bulk-fill RBCs is identified in the inorganic fillers. A lower filler content or enhanced filler size(> 20
µ m) was attested for several bulk-fill RBCs( x-tra fil and x-tra base, VOCO, Cuxhaven, Germany; SureFil SDR flow, DENTSPLY Caulk, Milford, DE, USA; SonicFill, Kerr, Orange, CA. USA,( 1)), the result being enhanced material translucency. The changes in filler size involve a lower total fillermatrix interface compared to regular composites with lower filler size, resulting in reduced light scattering and increased light transmittance in depth. 1 The aforementioned changes in fillers, but also a reduced amount of pigments are made responsible for the enhanced depth of cure of bulk-fill restoratives. Bulk-fill composite have rapidly achieved great popularity, therefore, progressively new material options have become recently available. Innovative material developments, like new and more competitive photo-initiators 17, as well as new material categories such as giomers( Glass ionomer + polymer) 18 and ormocers( Organically Modified Ceramics) 19 have recently been implemented also in high-viscosity bulk-fill RBCs. Therefore, the aim of this study was to comparatively assess the mechanical performance of novel highviscosity bulk-fill restoratives materials such as giomers and ormocers and to compare them to three established materials of the same category measured under identical conditions and partly presented in a previous study, 1 by considering a battery of properties determined at both macroand microscopic scale. The null hypotheses assume no significant difference in macro( flexural strength( σ) and flexural modulus( E flexural
)) and micro( Martens Hardness( HM), Vickers hardness( HV), indentation modulus( Y HU
), and Creep) mechanical properties among the analysed high-viscosity bulk-fill RBCs.
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