Micro-computed tomography evaluation of volumetric polymerization shrinkage and degree of conversion of composites cured by various light power outputs

Abstract

This study evaluated the influence of different light-curing modes on the volumetric polymerization shrinkage and degree of conversion of a composite resin at different locations using micro-computed tomography and Fourier transform infrared spectroscopy (FTIR). Specimens were divided into 4 groups based on the light-curing mode used (Bluephase 20i): 1 -High (1,200 mW/cm 2 ); 2 -Low (650 mW/cm 2 ); 3 -Soft-start (650-1,200 mW/cm 2 ); and 4 -Turbo (2,000 mW/cm 2 ). Degree of conversion was calculated by the measurement of the peak absorbance height of the uncured and cured materials at the specific wavenumbers, and was performed by FTIR 48 h after curing resin samples. Degree of conversion was analyzed using two-way ANOVA. No significant differences were observed independent of the region of the restoration investigated (p>0.05). Different curing modes did not influence volumetric shrinkage neither degree of conversion of class I composite resin restorations.

Properties of Experimental Dental Composites Containing Antibacterial Silver-Releasing Filler

“…Degree of conversion is an important property of restorative composites due to the potential risk of biological responses related to monomer release and affection of pulp tissues [ 118 ]. The obtained values were in agreement with the findings from other studies, performed on similar dimethacrylate systems, and measured with the same method [ 64 ]. The reduction of DC values at the bottom of the samples was also expected because when light moves through a material with increasing density, its intensity is reduced.…”

“…The degree of conversion (DC) was determined using the method described by Atira et al [ 64 ] with modifications made during sample preparation. Specimens, measuring 5 mm in diameter and 2 mm in height, were prepared in Teflon molds as previously described, but irradiation was carried out only at the top.…”

Polymerization shrinkage, microhardness and depth of cure of bulk fill resin composites

“…Usually, volumetric shrinkage is assessed through bidimensional measurements and conversion of values estimating the volume 16,17) . With the use of new technologies such as µ-CT, it is possible to assess the real volumetric shrinkage of the resin composites 19) . It can be observed that the conventional resin composites and the low viscosity bulk fill resin composites showed similar volumetric shrinkage (around 3.2%).…”

“…Volumetric shrinkage is a tridimensional phenomenon although being usually assessed through bidimensional methods and conversion/estimation of tridimensional changes [16][17][18] . With the development of new technologies such as X-ray micro computed tomography (µ-CT), tridimensional analysis of the volumetric shrinkage might be simpler and reliable 19) .…”

Effect of light-curing time on light-cure/post-cure volumetric polymerization shrinkage and regional ultimate tensile strength at different depths of bulk-fill resin composites

“…Additionally, it has been reported that composite specimens with a low level of polymerization after the primary light-curing phase generated greater post-cure polymerization 14,24) . Recently, non-contact 2D and 3D imaging methods such as micro-computed tomography 10,25) and optical coherence tomography 26,27) have been employed to investigate the sealing performance of resin composite in cavities. Swept-source optical coherence tomography (SS-OCT) can obtain 2D and 3D cross-sectional images of teeth and periodontal tissues in a non-invasive and nondestructive way, and analyze the behavior of restorative materials inside the cavity in real time 26,28) .…”