Light transmittance and polymerization kinetics of amorphous calcium phosphate composites
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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.
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.
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.
The observed kinetic behavior may result in slower development of polymerization shrinkage stress but also inferior mechanical properties.
KeywordsPolymerization kinetics Dental composites Remineralizing composites Light transmittance Amorphous calcium phosphate
We thank Mira Ristić and Marijan Marciuš from the Division of Materials Chemistry, Ruđer Bošković Institute, for the SEM micrographs. We also gratefully acknowledge Drago Skrtic for providing us with the zirconia-hybridized ACP.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This investigation was supported by Croatian Science Foundation (Project 08/31 Evaluation of new bioactive materials and procedures in restorative dental medicine).
This article does not contain any studies with human participants or animals performed by any of the authors.
For this type of study, formal consent is not required.
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