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 .
55