An-In Vitro Study of Degree of Conversion and Flexural Strength of Sonic Activated Bulk Fill Composite and a Nanohybrid Composite

Abstract

Composite restorations may take time longer than equivalent amalgam restorations. Longer time in the dental chair may test the patience of children, making the procedure more difficult for the dentist. In an attempt to speed up the restoration process, a new class of resin-based composite material, the bulk-fill RBC, was recently introduced on the market, enabling up to 4- or 5-mm thick increments to be cured in one step. Accordingly, this study was designed to assess flexural strength and degree of conversion of the bulk inserted resin composite (SonicFill) within different shades and compare it with resin composite utilizes the incremental packing technique (Herculite XRV Ultra). A total of 240 resin composite bars to test the flexurel strength (FS) test and 60 resin composite discs to test the degree of conversion (DC) were divided into 12 groups (n = 20 for FS and n = 5 for DC) according to the three levels of the study; Level 1: resin composite material (either bulk fill or conventional nanohybrid), Level 2: Increment thickness (2mm, 2mmx2mm and 4mm) and Level 3: resin composite shade (either A1 or A3). The specimens of FS were stored in distilled water at 37±1 for 24 hours before testing. Specimens were submitted to the three-point bending test in a Universal Testing Machine at a crosshead speed of 0.5mm/min. The specimens of DC were stored dry for 24 hour at 37°C using light-proof containers. Fourier transfer infrared spectroscopy was used to record the DC. Statistical analysis was carried out using SPSS program (Statistical Package for the Social Sciences, 2008).

Three-way ANOVA revealed that composite material, increment thickness and shade had a significant effect on flexural strength and degree of conversion. Regarding the cross interaction between the experimental groups, there was a statistical significant difference for the SonicFill composite over the Herculite XRV Ultra composite in most of variables (increment thickness and shade).