Abstract
This study aimed to evaluate the polymerization properties of bulk-fill materials (low and high-viscosity) by using high-intensity continuous light and intermittent photo-activation in terms of polymerization shrinkage stress and degree of conversion (DC). The following Bulk-fill and Conventional nanofilled resin composites were evaluated: Filtek Z350XT Flow (3M/ESPE), SureFil SDR Flow (Dentsply), Filtek Bulk Fill Flow (3M/ESPE), Filtek Z350XT (3M/ESPE) and Filtek Bulk Fill Posterior (3M/ESPE). A LED device (DB 685, Dabi Atlante) was used for both protocols: continuous uniform and intermittent photo-activation (light-on and light-off cycles) with identical radiant exposure (14 J/cm2). The polymerization shrinkage stress (n=6) was evaluated by inserting a single increment of 12 mm3 between two stainless steel plates (6×2 mm) adapted to a Universal Testing Machine (UTM), at different times. Measurements were recorded after photo-activation. The degree of conversion was evaluated by Fourier transformed infrared spectroscope (FTIR) with an attenuated total reflectance (ATR) accessory (n=5). Data were analyzed by three-way ANOVA and Tukey's HSD (α=0.05) tests. Bulk Fill Posterior presented higher shrinkage stress values when photo-activated with the intermittent technique (p<0.05). The intermittent photo-activation increased the degree of conversion for the low-viscosity bulk-fills (p<0.05). Therefore, the use of modulated photo-activation (intermittent) must be indicated with caution since its use can influence the shrinkage stress and degree of conversion of composites, which varies according to the resin formulations.
Highlights
Bulk-fill resin-based composites were launched with the purpose of providing bulk placement into dental cavities while offering good performance and clinical practicality [1]
The quality of the polymer network formed is dependent upon the overall degree of conversion (DC), since this conversion is correlated with the volumetric shrinkage in the polymerization process [4]
Low-viscosity bulk-fill resin composites (Surefil SDR Bulk Fill Flow and Filtek Bulk Fill Flow) showed significant differences in the values of shrinkage stress, which was lower than high-viscosity resin composites (Filtek Z350 XT and Filtek Bulk Fill Posterior) (p
Summary
Bulk-fill resin-based composites were launched with the purpose of providing bulk placement into dental cavities while offering good performance and clinical practicality [1]. Despite the common commercial classification of bulk-fill materials, different monomer and filler formulations are available, which may impact the polymerization kinetics [2]. Despite the promising results shown by bulk-fill resin composites, polymerizing up to 4mm-thick increments without adversely effecting polymerization shrinkage stress, the material composition may influence the curing characteristics since the overall properties of resin composite materials are usually composition-dependent [3]. Reducing shrinkage stress by changing the polymerization rate can influence the efficacy of the material. The quality of the polymer network formed is dependent upon the overall degree of conversion (DC), since this conversion is correlated with the volumetric shrinkage in the polymerization process [4]. Since all available bulk-fill resins involve the addition of newer low-shrinkage monomers, understanding their dynamics regarding polymerization shrinkage and DC, as well as the interaction with photo-activation, is essential
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