Síntese e avaliação de radiopacificadores desenvolvidos a partir do recobrimento do óxido de bismuto: análise de propriedades físico-químicas e escurecimento dentinário

Abstract

Bismuth oxide (Bi₂O₃) is a material present in the composition of several endodontic sealers, used to confer radiopacity to the material. Due to its high molecular weight, it requires small amounts for a satisfactory level of radiopacity compared to alternative radiopacifiers. However, Bi₂O₃ can interact with dentin, generating ion migration and causing tooth discoloration. The present study aimed to synthesize, characterize and evaluate experimental radiopacifiers based on Bi₂O₃ when coated with silicon oxide (Bi@Si) or zirconium oxide (Bi@Zr). The synthesis of the experimental radiopacifiers was performed by molecular coating from ultrasonic activation and modulation of solutions of the Bi₂O₃ coating molecule. The characterization of the samples was performed by FTIR and RAMAN spectroscopy. Then, restorative cements with the addition of the substances were evaluated regarding setting time, radiopacity, pH, in addition to the dentin discoloration caused by them in bovine tooth blocks; the MTA-Angelus white cement was used as a standard, in addition to using a control group with Bi2O3 pro-analysis (Bi). Setting time and radiopacity followed the ISO 6876/2012 standard; the pH was evaluated at periods of 3, 24, 72 and 168 h using a digital pH meter. To analyze dentin discoloration, bovine tooth blocks were made (10 x 10 mm) and circular cavities (Ø 5.0 mm) prepared in their palatal surfaces. The color measurement was performed with an EasyShade spectrophotometer at periods of: 7, 15 and 30 days. The data obtained were subjected to analysis of variance and Tukey's test, at a significance level of 5%. Regarding the physicochemical properties, in the initial and final setting time, significant differences were observed between Bi-MTA, Bi@Zr-Bi@Si, Bi@Zr-MTA and Bi@Si-MTA (p<0.05), with MTA offering the shortest times, 18 and 42min, respectively. In radiopacity, the materials were ordered in Bi@Zr/MTA/Bi@Si/Bi, with significant differences between the groups (p<0.05); the highest radiopacity was 9.71 mm.Al. Regarding pH, significant differences were observed only at 24h, Bi/Bi@Zr and Bi@Si/Bi@Zr (p<0.05); the values were between 10.39-11.10 (3h), 10.36-11.26 (24h), 9.60-9.87 (72h) and 7.69-8.47 (168h). In dentin discoloration, the Bi@Si and Bi groups presented the smallest and largest color variation at 30 days, respectively, with a significant difference (p<0.05). It is concluded that, through the applied methods, the coating of the bismuth molecule was achieved and that it was efficient in reducing the discoloration caused by it, with Bi@Si presenting the best result. Furthermore, although the coatings reduced the radiopacity of Bi₂O₃, this reduction did not compromise the tested properties of the prepared repair cements.