Degree of conversion versus the depth of polymerization of an organically modified ceramic dental restoration composite by fourier transform infrared spectroscopy

Abstract

ABSTRACT:The evaluation of the degree of conversion (DC) as a function of the depth (1-4 mm) of an organically modified ceramic (ormocer) dental restoration composite activated by a conventional light-curing unit (450 nm, 21.2 J/cm 2 ) was carried out. Fourier transform infrared spectroscopy was employed to measure DC at each depth with the ratio of the maximum height absorbance peaks at 1638 (variable band) and 1609 cm Ϫ1 (reference band) before and after the polymerization reaction. The formulation was reconstituted to understand better the composite behavior. The organic and inorganic fractions were characterized by thermogravimetric analysis, X-ray fluorescence, proton nuclear magnetic resonance, and scanning electron microscopy. The DC values lay between 48 and 54%, seemed to be not sensitive to the depth of polymerization, and indicated a large amount of residual monomer. On the other hand, a continuous decrease in the Vickers microhardness (from 61 to 52) was observed with an increasing depth of polymerization. This behavior could be attributed to differences in the crosslinking degree on the top and bottom surfaces of the polymerized samples. The material was a conventional dental restoration composite containing 26% monomer mixture (bisphenol A/dimethacrylate and triethylene glycol dimethacrylate), a small amount (2%) of an ormocer as a compatibilizing agent, and 72% inorganic filler (barium sulfate and aluminum silicate). The low DC values could be ascribed to several factors, such as the monomer viscosities, amounts, and types, the average sizes and distributions of the fillers, and the large difference between the refractive indices of the organic and inorganic constituents.

Application of digital image correlation to full-field measurement of shrinkage strain of dental composites

“…Note that under-cured composite will have inferior mechanical properties, such as low hardness, strength and wear resistance (Ferracane et al, 1998;Uhl et al, 2002;Versluis et al, 2004;Chen et al, 2005;Silva et al, 2007;Li et al, 2009b). The additional information provided by DIC can help decide the maximum depth of a restoration that is to be filled with a bulk-cured material or the maximum layer thickness of a restoration that is to be filled incrementally.…”

Evaluation of the Light Energy Transmission and Bottom/Top Rate in Silorane and Methacrylate-based Composites with Different Photoactivation Protocols

“…33,34 Thus, the hardness values decrease continuously with increasing depth. 35 Deeper in the composite restorative, light attenuation results in lower excited photoinitiator molecules. 34,36 The mobility of the developing polymer chains becomes progressively more restricted as a consequence of the increase in viscosity, reduction in free volume, formation of microgels and entanglement.…”

“…34,37 Whereas, the hardness depends on the extent of the reaction and the degree of crosslinking produced during the monomer curing process. 35 The network becomes rigid and the chains become essentially immobile, and the propagation reaction is limited in diffusion; thus, the overall conversion rate decreases. 34,38 To define the depth of polymerization, based on top and bottom hardness measurements, it is common to calculate the bottom/top ratio hardness and give this ratio an arbitrary minimum value to consider the bottom surface adequately cured.…”

Multifunctional Medical Grade Resin with Enhanced Mechanical and Antibacterial Properties: The Effect of Copper Nano-Inclusions in Vat Polymerization (VPP) Additive Manufacturing

“…Organic materials are used in different types of applications, such as energy [ 60 ], storage [ 61 , 62 ], photovoltaic [ 63 ], and optoelectronic [ 64 ] applications. Their degree of conversion has been often studied for dental applications [ 65 , 66 , 67 , 68 , 69 , 70 ]. Copper (Cu) is a popular metal, widely used [ 71 ], due to its properties, such as high thermal and electrical conductivity, easy processability [ 72 ], good corrosion resistance [ 73 ], and antibacterial properties against various pathogenic bacteria, such as Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) [ 74 ].…”