Matej Par1, Danijela Marovic2, Hrvoje Skenderovic3, Ozren Gamulin4, Eva Klaric2, Zrinka Tarle2. 1. Private Dental Practice, Dankovecka 9/I, Zagreb, Croatia. mpar@inet.hr. 2. Department of Endodontics and Restorative Dentistry, School of Dental Medicine, University of Zagreb, Gunduliceva 5, Zagreb, Croatia. 3. Institute of Physics, Bijenicka cesta 46, Zagreb, Croatia. 4. Department of Physics and Biophysics, School of Medicine, University of Zagreb, Salata 3b, Zagreb, Croatia.
Abstract
OBJECTIVES: This study investigated light transmittance and polymerization kinetics of experimental remineralizing composite materials based on amorphous calcium phosphate (ACP), reinforced with inert fillers. MATERIALS AND METHODS: Light-curable composites were composed of Bis-EMA-TEGDMA-HEMA resin and ACP, barium glass, and silica fillers. Additionally, a commercial composite Tetric EvoCeram was used as a reference. Light transmittance was recorded in real-time during curing, and transmittance curves were used to assess polymerization kinetics. To obtain additional information on polymerization kinetics, temperature rise was monitored in real-time during curing and degree of conversion was measured immediately and 24 h post-cure. RESULTS: Light transmittance values of 2-mm thick samples of uncured ACP composites (2.3-2.9 %) were significantly lower than those of the commercial composite (3.8 %). The ACP composites presented a considerable transmittance rise during curing, resulting in post-cure transmittance values similar to or higher than those of the commercial composite (5.5-7.9 vs. 5.4 %). The initial part of light transmittance curves of experimental composites showed a linear rise that lasted for 7-20 s. Linear fitting was performed to obtain a function whose slope was assessed as a measure of polymerization rate. Comparison of transmittance and temperature curves showed that the linear transmittance rise lasted throughout the most part of the pre-vitrification period. CONCLUSIONS: The linear rise of light transmittance during curing has not been reported in previous studies and may indicate a unique kinetic behavior, characterized by a long period of nearly constant polymerization rate. CLINICAL RELEVANCE: The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.
OBJECTIVES: This study investigated light transmittance and polymerization kinetics of experimental remineralizing composite materials based on amorphous calcium phosphate (ACP), reinforced with inert fillers. MATERIALS AND METHODS: Light-curable composites were composed of Bis-EMA-TEGDMA-HEMA resin and ACP, barium glass, and silica fillers. Additionally, a commercial composite Tetric EvoCeram was used as a reference. Light transmittance was recorded in real-time during curing, and transmittance curves were used to assess polymerization kinetics. To obtain additional information on polymerization kinetics, temperature rise was monitored in real-time during curing and degree of conversion was measured immediately and 24 h post-cure. RESULTS: Light transmittance values of 2-mm thick samples of uncured ACP composites (2.3-2.9 %) were significantly lower than those of the commercial composite (3.8 %). The ACP composites presented a considerable transmittance rise during curing, resulting in post-cure transmittance values similar to or higher than those of the commercial composite (5.5-7.9 vs. 5.4 %). The initial part of light transmittance curves of experimental composites showed a linear rise that lasted for 7-20 s. Linear fitting was performed to obtain a function whose slope was assessed as a measure of polymerization rate. Comparison of transmittance and temperature curves showed that the linear transmittance rise lasted throughout the most part of the pre-vitrification period. CONCLUSIONS: The linear rise of light transmittance during curing has not been reported in previous studies and may indicate a unique kinetic behavior, characterized by a long period of nearly constant polymerization rate. CLINICAL RELEVANCE: The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.
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