Relationship between the polymerization distance of monowave and polywave light-curing units and the irradiance and physical properties of dental resin-based composites.

PURPOSE: To evaluate the influence of the polymerization distance of monowave and polywave light curing units (LCUs) on the measured irradiance relative to the value reported by the manufacturer in relation to the physical properties of resin-based composites (RBCs). METHODS: Four LCUs were used: one monowave and three polywave. The irradiance was measured with a digital radiometer. Depth of cure (DC) and flexural strength (FS) tests were performed according to ISO 4049:2019 at polymerization distances of 0 mm and 5 mm. RESULTS: The irradiance of all LCUs was higher than that reported by the manufacturer (>25-64%). The irradiance of the four LCUs was reduced when polymerization was performed at between 0 to 5 mm (paired t-test, P < 0.001). The DC at 0 mm was similar in all groups but was significantly decreased at 5 mm distance (ANOVA P < 0.001). FS showed differences among the LCUs at 0 mm (ANOVA P < 0.001) and was affected by the polymerization distance. The elastic modulus was unaffected by the LCU used or the distance (ANOVA P > 0.001). CONCLUSIONS: The LCU must be positioned as near as possible to RBCs during the polymerization process, as increased distance negatively affects the depth of cure and flexural strength.

Physical properties, marginal adaptation and bioactivity of an experimental mineral trioxide aggregate-like cement modified with bioactive materials.

PURPOSE: To evaluate the effect of adding wollastonite and bioactive glass to an experimental mineral trioxide aggregate-like cement (MTA) on the dimensional stability, compressive strength, solubility, bioactivity, and marginal adaptation by scanning electron microscopy (SEM) and X-ray diffraction (XRD). METHODS: Four groups were evaluated at 7, 14, and 21 days: MTA Angelus, experimental MTA-like cement (MTA Exp), BG10 (MTA Exp+10 wt% bioactive glass), and WO20 (MTA Exp+20 wt% wollastonite). To evaluate marginal adaptation, extracted teeth were endodontically obturated and root-end cavities were prepared and filled with the tested materials. RESULTS: Cements with bioactive materials showed minimal dimensional changes. Adding wollastonite or bioactive glass to MTA Exp reduces the compressive strength but does not affect solubility. Bismite (Bi2O3), larnite (Ca2SiO4), calcite (CaCO3) and carbonated hydroxyapatite (Ca5[PO4,CO3]3[OH]) were identified in the four cements; ettringite (Ca6Al2[SO4]3[OH]12·26H2O) and bismutite ([BiO]2CO3) were only observed in MTA Exp, BG10, and WO20. Cement-dentin interfaces were not observed after 14 days on the BG10 and WO20 cement composites due to the ettringite formation. CONCLUSION: Acicular growing crystals typical of hydroxyapatite were found on the surfaces of all cements. An improved marginal adaptation was observed with the addition of wollastonite or bioactive glass.

Cell viability and physicochemical effects of different concentrations of bismuth trioxide in a mineral trioxide aggregate cement.

PURPOSE: To evaluate the effect of three concentrations of bismuth trioxide (Bi2O3) on the biological and physicochemical properties of an experimental mineral trioxide aggregate-type (MTA-type) cement at different time points. METHODS: Three experimental groups with white Portland cement containing 15, 20, or 25 wt% of Bi2O3 were assessed. Cellular proliferation in human periodontal ligament fibroblasts was evaluated with an MTT assay. Radiopacity, dimensional stability, pH, and compressive strength were evaluated at different time points. RESULTS: Bismuth trioxide induced cell proliferation in the Bi15 and Bi25 groups in a time-dependent manner; pH was similar in all groups. Compressive strength was associated with time and bismuth concentration. Bi25 had significantly contracted at day 7 and expanded at day 14 (ANOVA P < 0.05, post hoc Tukey test P < 0.05). CONCLUSION: A higher Bi2O3 concentration had a negative effect on the physical properties of the cement at all time points.