Abstract
This study evaluated the degree of conversion (DC) and ultimate tensile strength (UTS) of dual-cured resin cements heated to 50º C prior to and during polymerization. Disc- and hourglass-shaped specimens of Rely X ARC (RX) and Variolink II (VII) were obtained using addition silicon molds. The products were manipulated at 25º C or 50º C and were subjected to 3 curing conditions: light-activation through a glass slide or through a pre-cured 2-mm thick resin composite disc, or they were allowed to self-cure (SC). All specimens were dark-stored dry for 15 days. For DC analysis, the resin cements were placed into the mold located on the center of a horizontal diamond on the attenuated total reflectance element in the optical bench of a Fourier Transformed Infrared spectrometer. Infrared spectra (n = 6) were collected between 1680 and 1500 cm-1, and DC was calculated by standard methods using changes in ratios of aliphatic-to-aromatic C=C absorption peaks from uncured and cured states. For UTS test, specimens (n = 10) were tested in tension in a universal testing machine (crosshead speed of 1 mm/min) until failure. DC and UTS data were submitted to 2-way ANOVA, followed by Tukey's test (α= 5%). Both products showed higher DC at 50º C than at 25º C in all curing conditions. No significant difference in UTS was noted between most light-activated groups at 25º C and those at 50º C. VII SC groups showed higher UTS at 50º C than at 25º C (p < 0.05). Increased temperature led to higher DC, but its effects on resin cement UTS depended on the curing condition.
Highlights
Dual-cure resin cements (RCs) were developed to establish a reliable bond between the prepared tooth and restorative materials.[1]
The aim of this study was to evaluate the effects of pre-heating on the degree of conversion (DC) and ultimate tensile strength (UTS) of dual-cured RCs subjected to different curing conditions
The research hypothesis was that dual-cured RCs heated to 50o C prior to and during polymerization exhibit higher DC and UTS than the RCs polymerized at 25o C when polymerization relied solely on the self-curing condition or after exposure to the severely attenuated curing light due to the presence of an indirect composite resin restoration
Summary
Dual-cure resin cements (RCs) were developed to establish a reliable bond between the prepared tooth and restorative materials.[1]. Some studies have shown that pre-heating the resin composite to 50o C or 60o C increases its degree of conversion (DC).[10,11] As a result, increased hardness and fracture strength, increased flexural strength and modulus, and increased resistance to wear are expected.[12,13] it is reasonable to assume that dual-cured RCs polymerized at increased temperature might show higher DC and improved mechanical properties than RCs polymerized at room temperature. The research hypothesis was that dual-cured RCs heated to 50o C prior to and during polymerization exhibit higher DC and UTS than the RCs polymerized at 25o C when polymerization relied solely on the self-curing condition or after exposure to the severely attenuated curing light due to the presence of an indirect composite resin restoration
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