Degree of conversion and mechanical properties studies of UDMA based materials for producing dental posts

Abstract

Nanocomposites are a relatively new material in producing fiber re‐enforced dental posts. The mechanical properties of nanocomposites, which strongly associate with the resin matrix, nanoparticles, and the interface between inorganic fillers and organic matrix, play an important role in determining the quality of dental posts. This work was to investigate the effect of degree of conversion (DC) and silanization of fillers on the mechanical properties of nanocomposties. Experimental Urethane dimethacrylate (UDMA) based dental composites containing unsilanized and silanized SiO2 filler and various amount of triethylene glycol dimethacrylate (TEGDMA) were prepared at the first step. The DC of composites at different ratios of UDMA/TEGDMA, cure temperature and cure time was measured by Fourier transform infrared spectroscopy. The results showed that DC increases with the increase of TEGDMA content in resin matrix. Both increase of the cure temperature and cure time can cause the increase of DC. The incorporation of fillers, either silanized, or unsilanized filler, caused the decrease of DC. However, composites reinforced with silanized silica showed relatively lower DC, and DC decreased with the increase of silanized filler content. The effect of incorporation of fillers on the mechanical properties was investigated. Silanized silica can effectively improved the flexural strength and flexural modulus of material, and these properties increased with the increase of silica content. Thermomechanical analysis (DMA) provided the similar results to the static property measurements. SEM images of fracture surfaces of specimens from flexural testing revealed the surface morphology is strongly related to the quality of interface between inorganic fillers and organic matrix. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Effects of different polymerization protocols on the degree of conversion of two dual‐cured core buildup composites polymerized by light‐emitting diode and halogen light‐curing units

“…The lower viscosities of the monomers facilitated the migration of free radicals and increased the crosslinking density . However, it has also been reported that the depth of curing appeared to be less in certain UDMA composites because of a greater mismatch in the refractive index between the monomer and filler . In addition to the resin matrix, filler particles have also been shown to possess a direct influence on the degree of curing of composite materials .…”

“…Unreacted monomers may leach from the polymerized material and irritate the soft tissue . Furthermore, monomers trapped in the restorations may reduce the mechanical properties . Many studies have shown the correlation between the % DC and hardness, flexural strength, and modulus of elasticity of dental resin composites .…”

“…The % DC could be assessed by direct or indirect methods, such as Fourier transform infrared (FTIR) spectroscopy, magnetic resonance imagining, optical translucency, scraping, or hardness measurements . Among these methods, FTIR spectroscopy offers a direct and reliable approach for evaluating the degree of converted carbon double bonds to carbon single bonds, although it appears to be more expensive and time‐consuming.…”

“…3,5,6,8,11 The degree of conversion (% DC) is defined as the percentage of reacted carbon double bonds, 12 and the unreacted double bonds may either be present in free monomers or as pendant groups on the network. [12][13][14] Unreacted monomers may leach from the polymerized material and irritate the soft tissue. 13 Furthermore, monomers trapped in the restorations may reduce the mechanical properties.…”

Nanoindentation study on mechanical properties and curing depth of dental resin nanocomposites

“…Besides the mechanical performance, there are also increasing concerns with the quality of curing when light‐cured dental resin composites are used. Attenuation of the light with time and distance may lead to a low degree of conversion and a shallow curing depth, thereby causing unpolymerized or partially polymerized resins of the final restoration . Low conversion of monomers and/or shallow curing depths will further negatively influence the mechanical properties and dimensional stability of the restoration .…”