Determination of Water Content in Direct Resin Composites Using Coulometric Karl Fischer Titration.

This study evaluated the water content and sorption of direct composites over 60 days using coulometric Karl Fischer titration (KFT). Plate-shaped specimens (10 × 10 × 1 mm3 of thickness) were built up using the composites Clearfil Majesty Posterior (CM), Grandio SO (GS), and Filtek Supreme XT (FS). Water contents were determined in non-stored specimens (control) or after storage in distilled water for up to 60 days (n = 5). The amount of water transferred from the specimens heated at 200 °C (isothermal mode) was measured in the Coulometer. The water content of non-stored specimens ranged from 0.28 to 1.69 wt% (5.6 to 31.2 µg/mm3) for GS and FS, respectively. The highest values of water sorption were observed for FS (25.3 µg/mm3 after 60 days). GS and CM showed similar water sorption after 60 days (≈9 µg/mm3), but an ultimate higher water content was observed for CM (0.9 wt%; 22.0 µg/mm3) than GS (0.7 wt%; 14.8 µg/mm3). Except for CM, no significant water sorption was observed between 21 and 60 days of storage. Since all composites presented some base water content, water sorption data alone do not account for the ultimate water content in direct resin-based composites.

Coulometric titration of water content and uptake in CAD/CAM chairside composites.

OBJECTIVES: This study aimed to evaluate the water content and uptake of CAD/CAM chairside composites over 60 days using coulometric Karl Fischer (KF) titration. METHODS: Rectangular plates (10 ×10×1 mm3 of thickness) were cut from the blocks of composites Cerasmart 270 (CS), Katana Avencia (KA), Grandio Blocs (GB), and Lava Ultimate (LU). Specimens were stored in distilled water for up to 60 days at 37 °C, and non-stored specimens were used as a control (n = 5). Specimens were isothermally heated at 200 °C, and the water content was evaporated and transferred to the titration cell throughout a nitrogen gas flow. The KF coulometer determined the percentage of water in each specimen. Data were analyzed by 2-way ANOVA and Tukey`s test (α = 0.05). RESULTS: The water content of non-stored specimens ranged from 0.29 to 1.66 wt% (6.9-32.9 µg/mm3) for GB and LU, respectively. The water content increased underwater storage (0.82-2.96 wt% after 60 days). The extend of water sorption (11.9-26.1 µg/mm3) among the materials was directly related to their base water content. No additional water content increase was observed after 7 (LU and KA) or 21 (GB and CS) days. Measuring the water content in wt% or µg/mm3 affected the ranking of materials when KA and CS were analyzed. SIGNIFICANCE: Composites with higher base water content also presented higher water sorption. KF titrationshowed to be a reliable method to measure the water sorption of composites, including their base water content.