Polymerization shrinkage and porosity profile of dual cure dental resin cements with different adhesion to dentin mechanisms

Abstract

This research aims to probe the porosity profile and polymerization shrinkage of two different dual cure resin cements with different dentin bonding systems. The self-adhesive resin cement RelyX U200 (named RU) and the conventional Allcem Core (named AC) were analyzed by x-ray microtomography (lCT) and Scanning Electron Microscopy (SEM). Each cement was divided into two groups (n 5 5): dual-cured (RUD and ACD) and self-cured (RUC and ACC). lCT demonstrated that the method of polymerization does not influence the porosity profile but the polymerization shrinkage. Fewer concentration of pores was observed for the conventional resin cement (AC), independently the method used for curing the sample. In addition, SEM showed that AC has more uniform surface and smaller particle size. The method of polymerization influenced the polymerization shrinkage, since no contraction for both RUC and ACC was observed, in contrast with results from dual-cured samples. For RUD and ACD the polymerization shrinkage was greater in the lower third of the sample and minor in the upper third. This mechanical behavior is attributed to the polymerization toward the light. mCT showed to be a reliable technique to probe porosity and contraction due to polymerization of dental cements. K E Y W O R D Sdental composite, photo-cure, polymerization contraction, self-cure, X-ray microtomography

Microporosity and polymerization contraction as function of depth in dental resin cements by X‐ray computed microtomography

“…The external height of the matrix exceeds the internal height to facilitate its positioning into the μCT sample holder. Teflon was selected because it has an effective atomic number smaller than that of the resin cements (Burey et al, 2018), which allows the separation in grayscale between the sample and the matrix. In addition, Teflon is an inert material without adhesive interaction with the cements evaluated in this study.…”

“…All cement's volume (25 mm 3 ) was scanned with the SkyScan 1172 μCT equipment (Brucker BioSpin Corporation, Kontich, Belgium) with the scanning parameters set to 100 kV voltage, 100 μA current and 3.5 μm resolution (Burey et al, 2018).…”

“…It was possible to obtain 1,000 cross sections with the chosen parameters. In order to determine the region of interest (ROI), these cross‐sectional images were loaded in the CTanaliser software (SkyScan) for analysis of the displacement of resin mass from Teflon matrix (Burey et al, 2018). These data were also loaded in the ImageJ‐Hybrid Median Filter software for binarization process (Moreira et al, 2012) in order to separate pore from solid (cement), establishing a contrast threshold (Burey et al, 2018).…”

“…In addition, sectioning the sample may damage the material's internal layers interfering on the outcomes. In contrast, X‐ray microtomography (μCT) makes it possible to investigate the effects of polymerization contraction by reconstructing cross sections of samples in a nondestructive way, assessing internal layers in the micrometer range with high precision (Balthazard et al, 2014; Besegato et al, 2019; Burey et al, 2018; Garcea, Wang, & Withers, 2018; Sun & Lin‐Gibson, 2008). This aspect makes this technique reliable for the investigation of mechanical properties of restorative materials that may compromise the clinical outcomes and shows to be promising in the dental materials area.…”

“…This aspect makes this technique reliable for the investigation of mechanical properties of restorative materials that may compromise the clinical outcomes and shows to be promising in the dental materials area. For example, in a previous paper (Burey et al, 2018) we studied the microstructure and physical properties of two resin cements considering the influence of the initiation mode and adhesion to dentin mechanism by SEM and μCT in three different layers (top, middle, and base).…”