Effect of gastric acid on the surface roughness and bacterial adhesion of bulk-fill composite resins

Abstract The purpose of this in vitro study was to evaluate the effect of gastric acid on the surface roughness and biofilm formation of bulk-fill composite resins. Twenty-seven samples of each composite resin were obtained: G1: Filtek Z250 XT (Z250), G2: Filtek Bulk Fill (FTK), G3: Tetric N-Ceram Bulk Fill (TTC), and G4: Aura Bulk Fill (AUR). The samples were quantitatively analyzed for surface roughness (Ra) using a roughness tester (n=15) and for biofilm formation (Cn) by the counting of colony-forming units (CFUs/mL) (n=9) in three different moments: after polishing (Ra0 and Cn0), after gastric acid immersion (Ra1 and Cn1), and after gastric acid and simulated tooth brushing (Ra2 and Cn2). Qualitative analysis through surface topography (n=3) was evaluated by scanning electron microscopy (SEM). Ra values were subjected to two-way repeated measures ANOVA, followed by Tukey's test. Cn values were subjected to Kruskal-Wallis analysis, followed by multiple comparisons analysis (α=0.05). Z250 and FTK showed significant increases in surface roughness at Ra1. There were fewer CFUs/mL on TTC and AUR in relation to those of Z250 and FTK for Cn0, Cn1 and Cn2. The SEM images showed that gastric acid increased the formation of cracks, exposure of fillers and micro cavities for all composite resins. After tooth brushing, the topographical changes were more evident but did not influence biofilm formation. The gastric acid promoted both degradation of the surfaces and bacterial adhesion for all composite resins.

Resumo O objetivo deste estudo in vitro foi avaliar o efeito do ácido gástrico na rugosidade superficial e na formação do biofilme nas resinas compostas de incremento único. Vinte e sete amostras de cada resina composta foram confeccionadas: G1: Filtek Z250 XT (Z250), G2: Filtek Bulk Fill (FTK), G3: Tetric N-Ceram Bulk Fill (TTC), and G4: Aura Bulk Fill (AUR). As amostras foram analisadas quantitativamente quanto à rugosidade da superfície (Ra) usando um rugosímetro (n=15) e para formação de biofilme (Cn) pela contagem de unidades formadoras de colônias (UFC/mL) (n=9) em três diferentes momentos: após polimento (Ra0 and Cn0), após imersão em ácido gástrico (Ra1 and Cn1), e após ácido gástrico e simulação de escovação (Ra2 and Cn2). Análise qualitative da topografia superficial (n=3) foi avaliada por meio de microscopia eletrônica de varredura (MEV). Os valores de Ra foram analisados pela ANOVA de duas vias para amostras pareadas, seguido do teste de Tukey. Os valores de Cn foram submetidos ao teste de Kruskal-Wallis, seguido da análise de comparações múltiplas (α=0,05). Z250 e FTK tiveram aumento significativo na rugosidade superficial em Ra1. Houve menos CFUs/mL para TTC e AUR em relação à Z250 e FTK em Cn0, Cn1 and Cn2. As imagens em MEV mostraram que o ácido gástrico aumentou a formação de fendas, exposição das partículas e mcrocavidades para todas as resinas compostas. Após escovação, as mudanças topográficas foram mais evidentes, mas não influenciou na formação do biofilme. O ácido gástrico promoveu degradação da superfície e adesão bacteriana para todas as resinas compostas.

Effect of cariogenic challenge on the degradation of adhesive-dentin interfaces

Abstract The aim was to evaluate, in vitro, the influence of pH cycling on microtensile bond strength (µTBS) and percentage of nanoleakage (%NL) in the dentin-adhesive interface. Flat dentin surfaces were obtained in 56 extracted third molars. The teeth were randomly divided into four groups (n=14): G1- Single Bond Universal (etch-and-rinse mode); G2- Single Bond Universal (self-etch mode); G3- Scotchbond Multi-Purpose; G4- Clearfil SE Bond. A block of composite was built on the adhesive area. Eight tooth/resin sets were cut parallel to the tooth's long axis to obtain 48 beams (0.8 mm2) for each group. Half of the beams were submitted to four cycles of pH cycling (demineralizing solution for 6 h and remineralizing solution for 18 h). The samples were submitted to µTBS test in a universal testing machine. Six tooth/resin sets were cut parallel to the tooth's long axis to obtain three slices of the central region (1.0 mm thickness). Half of the slices were submitted to pH cycling. The nanoleakage methodology was applied to obtain the %NL at the adhesive interfaces. According to two-way ANOVA, the interaction between factors (adhesive system x storage) was significant (p=0.0001) for µTBS and %NL. After pH cycling, there was a significant decrease in µTBS and a significant increase in %NL for all adhesives. The adhesives applied in the self-etch mode obtained lower %NL, differing significantly from the etch-and-rinse adhesives. It was concluded that the pH cycling negatively influenced the µTBS and %NL for all adhesives evaluated. However, self-etch adhesives allowed less %NL.

Resumo O objetivo foi avaliar, in vitro, a influência da ciclagem de pH na resistência de união à microtração (RUµT) e na porcentagem de nanoinfiltração (%NI) na interface dentina-adesivo. Superfícies planas em dentina foram obtidas em 56 terceiros molares. Os dentes foram aleatoriamente divididos em quatro grupos (n=14): G1- Single Bond Universal (condicionamento ácido prévio); G2- Single Bond Universal (autocondicionante); G3- Scotchbond Multi-Purpose; G4- Clearfil SE Bond. Bloco de resina composta foi construído sobre o adesivo. Oito conjuntos dente/resina foram cortados paralelamente ao longo eixo do dente para obter 48 palitos (0,8 mm2) para cada grupo. Metade dos palitos foi submetida a quatro ciclos de ciclagem de pH (solução desmineralizadora por 6 h e solução remineralizadora por 18 h). As amostras foram submetidas ao teste de RUµT em máquina de ensaio universal. Seis conjuntos dente/resina foram cortados paralelamente ao longo eixo para obter três fatias da região central (1,0 mm de espessura). Metade das fatias foi submetida à ciclagem de pH. A metodologia de nanoinfitração foi aplicada para obter a %NI nas interfaces. De acordo com ANOVA de duas vias, interação entre os fatores (adesivo x armazenamento) foi significativa (p=0.0001) para for RUµT e %NI. Após ciclagem de pH, houve redução significativa na RUµT e aumento significativo na %NI para todos adesivos. Os adesivos aplicados na técnica autocondicionante obtiveram menor %NI, diferindo significativamente dos adesivos com condicionamento ácido prévio. Concluiu-se que a ciclagem de pH influenciou negativamente a RUµT e a %NI para todos adesivos. Contudo, adesivos autocondicionantes permitiram menor %NI.

Surface roughness of monolithic zirconia ceramic submitted to different polishing systems

Aim: The objective was to evaluate, quantitative and qualitative, the abrasive effect of three polishing systems on the monolithic zirconia ceramic. Methods: Thirty disk-shaped samples of Yttria Tetragonal Zirconia Polycrystal (Y-TZP) were randomly distributed in three groups (n = 10) according to polishing system: G1- Komet system (KO); G2 - CeraGloss system (CG); G3 - Eve Diacera system (EV). The surface roughness (Ra) was obtained with Rugosimeter in four different moments: a) initial - glaze sample (Ra0); b) after occlusal adjustment with diamond burs (Ra1); c) after polishing with the abrasive systems (Ra2); d) after polishing with felt disc and diamond paste (Ra3). Four additional samples were observed in scanning electron microscopy (SEM). Results: According to the Generalized Estimating Equation followed by the Bonferroni test (α = 0.05), the CG provided the lowest Ra2 (0.63 µm), not differing significantly from the KO (0.78 µm). The highest Ra2 was obtained with the EV (0.97 µm), which did not differ significantly from the KO. There was no statistical difference in Ra between the polishing with the abrasive systems (Ra2) and the final polishing with diamond paste (Ra3). SEM images showed that the polishing systems did not completely remove the grooves caused by the diamond burs during the occlusal adjustment. Conclusion: It was concluded that CG promoted smoother surface of the monolithic zirconia ceramic compared to EV, and intermediate smoothness was obtained with KO