Biodegradation of restorative materials: effects on bond strength, surface characteristics and marginal integrity

• Autor(a) principal: Mushashe, Amanda Mahammad
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Cruzeiro do Sul
• Texto Completo: https://repositorio.cruzeirodosul.edu.br/handle/123456789/2158
• topic: CNPQ::CIENCIAS DA SAUDE::ODONTOLOGIA; Clinical dentistry; Biofilms; Dental bonding; Surface properties; Dental materials

The objective of this study was to determine the effect of biodegradation on the bond strength, surface characteristics and marginal integrity of restorative materials. For the bond strength assays, teeth were distributed into groups (n=5), according to the resin cement (Maxcem Elite (MC) or NX3 Nexus (NX)) and degradation method (24 h or 7 days in distilled water; 7 or 30 days incubated with S. mutans (UA159) and 30 days in sterile media). Treated surfaces of Vita Enamic (VE) blocks (5x6x7mm) were luted to treated (NX) or no treated (MC) dentin surfaces and light-cured. After 24 h, blocks were cut into beams (1x1x10mm) and stored accordingly. Biofilm viability was assessed after test by a luciferase assay. Then, the flexural bond strength FBS was assessed by a fourpoint bending test. Additional teeth were distributed into groups (n=3), according to the resin cement (MC and NX) and storage period (24h or 7 days in distilled water). Beams were obtained as described before, stored accordingly and submitted to a microtensile bond strength (µTBS) assay. Failure modes were determined by scanning electron microscopy (SEM) at 100X. Bars of cements (n=10) were obtained and their flexure strength assessed by a four-point bending test. Data were analyzed by 2-ways ANOVA and Tukey’s test (α=0.05). To assess the effect of biodegradation on surface characteristics, specimens (4 mm diameter x1.5 mm thick) were distributed in 12 groups (n = 15) according to the material (MC, NX, VE) and biodegradation method (24 h or 7 days in distilled water, 37ºC; 7 days in stimulated saliva or in situ). Before and after each degradation method, the surface roughness (Ra), Vickers hardness (VHN) and SEM analyzes were performed. For the marginal integrity evaluation, cavity preparations (5 mm diameter x 1.5 mm deep) were machined into dentin disks. After applying the bonding agent, preps (n=3-5) were restored by incremental technique with experimental resin composites (50:50 BisGMA/TEGDMA: 72wt% filler) containing different filler composition: (57wt% silanated strontium glass/15wt% BAG-65wt% silica) or (67wt% silanated strontium glass/5% OX50). Samples were stored in sterile Todd-Hewitt media or co-incubated with Streptococcus mutans (UA 159), at 37°C, 5%CO2 for 1-2 weeks. After, biofilm viability was assessed by a luciferase assay. Surfaces were replicated and examined in the SEM before and after the degradation method. Using an image software (Image J), gap width and percentage of discontinuous margins (%DM) was quantitatively assessed. Data were analyzed using two-way ANOVA followed by Tukey’s test (α= 0.05). Regarding the bond strength assays, there was no significant difference between the degradation methods for the FBS groups. For the µTBS, there was a significant difference among the groups as follows: NX 7days > NX 24h > MC 7days >MC 24h. Failure mode was mainly adhesive and mixed, but with an increase of cohesive within cement and pre-test failures for the MC groups assessed by µTBS. NX had better performance than MC, regardless the method. After surface characteristics analysis it could be observed that in situ aging method significantly altered the VHN of Vita Enamic and Maxcem Elite and the Ra of the Maxcem Elite. Surface changes analyzed by the SEM were more evident for the Saliva groups, of all materials. Regarding the marginal integrity of dentin-composite restoration, gap size ranged between 7-23µm. The bacterial exposure significantly increased the %DM in both groups predominantly due to the formation of new gap regions. There was no difference between control and BAG composites regarding %DM and the biofilm presence. Within the limitations of this study, it could be concluded that in situ and in vitro biodegradation can negatively affect the marginal integrity and superficial characteristics of restorative materials, having no further effect on the bond strength.