Date Published: June 26, 2019
Publisher: Public Library of Science
Author(s): Thaís Yumi Umeda Suzuki, Juno Gallego, Wirley Gonçalves Assunção, André Luiz Fraga Briso, Paulo Henrique dos Santos, Chun-Pin Lin.
This study evaluated the influence of silver nanoparticle on mechanical properties of the components of underlying dentin and resin cement in different regions of intraradicular dentin. Ninety extracted single-rooted human teeth were used in this study. After endodontic preparation, the teeth were divided into five groups, according to the irrigating agents: distilled water, 5.25% sodium hypochlorite, 25% polyacrylic acid, 2% chlorhexidine and 23 ppm silver nanoparticles dispersion. Then, the groups were divided in 3 subgroups (n = 6) according to the technique adopted for adhesive cementation: SUA group: Scotchbond Universal Adhesive + RelyX ARC; U200 group: RelyX U200; and MCE group: MaxCem Elite. The mechanical properties of hardness and elastic modulus were measured in resin cement and underlying dentin in ultra-micro hardness tester in different thirds of radicular dentin surface. Data were subjected to ANOVA and Fisher’s test (p = 0.05). In the underlying dentin, in general, there was no statistically significant difference in different thirds of intraradicular dentin according to the different solutions used. In the resin cements, higher hardness values were found, in general, for the cervical third. When silver nanoparticle solution was used, higher mechanical properties were generally obtained for resin cement for the SBU and U200 groups, with little or no changes in mechanical properties for the dentin. Silver nanoparticle application is a viable option for irrigation the intraradicular dentin previously through the cementation process of glass fiber posts. The mechanical properties are influenced by irrigant solutions used and the depth intraradical analyzed area.
Restoring endodontically treated teeth with glass fiber posts when the remaining tooth structure cannot provide adequate support and retention for the restoration has become popular [1,2]. During the post space preparation, a debris and smear layer is formed on the canal walls, leading to increased leakage and obstruction of the dentin tubules, thus blocking the adhesive luting of the fiber post . Moreover, the removal of the root canal filling while preparing the post space without rubber dam isolation or inadequate temporary restorations may cause the invasion of microorganisms through oral fluids into the canal, which could result in failure of the bonding process .
The materials used in this study are listed in Table 1. Ninety single-rooted human premolars from different individuals, extracted for orthodontic or periodontal reasons, were used in this study. The use of extracted human teeth was performed in accordance with the guidelines of the ethics committee of the Sao Paulo State University and all patients signed informed consent forms before enrollment. The protocol for this study was approved Research and Ethics Committee of the Araçatuba School of Dentistry, Sao Paulo State University (Protocol #05142812.4.0000.5420). All teeth exhibiting clinical signs of caries, root resorption, cracks, or fractures were excluded.
The hardness and elastic modulus are mechanical properties that can be used to indirectly evaluate the degree of conversion of the material and, consequently, its polymerization effectiveness [22–25]. The present study evaluated the HM, whose calculation uses both plastic and elastic deformation, and the regional elastic modulus (cervical, medium and apical thirds) of the following structures: resin cement and underlying dentin to bonding interface. In general, the results found that the mechanical properties of the adhesive-interface components depend on the irrigating solutions, rejecting the first null hypothesis of this study. Furthermore, the mechanical properties varied during canal preparation, presenting differences between the thirds analyzed, which led to a rejection of the second null hypothesis.
Based on the methodology performed, and the results of this study, it can be concluded that the silver nanoparticle could be used as a protocol for the use of this solution before glass fiber post cementation because when the silver nanoparticle solution was used, there was a tendency for the SUA and U200 resin cements to present higher values in the properties analyzed, with few alterations in the underlying dentin.