Shrinkage stress and elastic modulus assessment of bulk-fill composites

Abstract Bulk-fill composites were introduced in dentistry to accelerate clinical procedures while providing adequate outcomes. Concerns regarding the use of bigger composite increments rely on the polymerization shrinkage and shrinkage stress, which may generate gaps on the adhesive interface and result in a reduced success rate. Objective: To evaluate the polymerization shrinkage stress of different bulk-fill resin composites and their elastic modulus. Materials and Methods: Fourteen specimens were made for each of the nine different resin composites (seven with 12 mm3 and seven with 24 mm3): Surefill SDR flow (SDR), X-tra Base (XB), Filtek Bulk Fill Flowable (FBF), Filtek Z350XT Flow (Z3F); Tetric Evo Ceram Bulk Fill (TBF), X-tra Fil (XF), Filtek Bulk Fill (FBP), Admira Xtra Fusion (ADM) and Filtek Z350 XT (Z3XT). Linear shrinkage stress was evaluated for 300 s with the aid of a linear shrinkage device adapted to a Universal Testing Machine. For each composite group, seven additional specimens (2x2x25 mm) were made and Young's modulus was evaluated with a 3-point bending device adapted in a Universal Testing Machine with 0.5 mm/min crosshead speed and 50 KgF loading cell. Results: For 12 mm3 specimens, three-way ANOVA showed that only SDR and TBF generated lower stress after 20 s. Considering 300 s, TBF, SDR, and XF generated the lowest stress, followed by ADM, FBP, XB, and FBF, which were similar to Z3XT. Z3F generated the highest stress values for all time points. Considering 24 mm3 specimens after 20 s, all bulk fill composites generated lower stress than Z3XT, except XB. After 300 s, SDR, FBP, and ADM generated the lowest stress, followed by TBF and XF. For elastic modulus, one-way ANOVA showed that FBF, SDR, Z3F, and ADM presented the lowest values, followed by XB and TBF. FBP, Z3XT, and XF presented the highest elastic modulus among the evaluated composites. Conclusions: Bulk-fill resin composites presented equal to lower shrinkage stress generation when compared to conventional composites, especially when bigger increments were evaluated. Bulk-fill composites showed a wide range of elastic modulus values, but usually similar to "regular" composites.

Resistência de união à microtração entre camadas de materiais restauradores de diferentes matrizes / Bond strength between layers of silorane and methacrylate-based materials

A resina de silorano e a sua polimerização catiônica apresentam diferenças quanto aos materiais a base de metacrilato. Como materiais restauradores, estes poderiam ser utilizados juntos, no entanto suas moléculas diferentes poderiam provocar incompatibilidade. Por isso é importante avaliar a união interfacial desses materiais tendo como objetivo a comparação da resistência de união a microtração entre camadas de Filtek P90 aderidas a Filtek Z350, Filtek P90 ou Vitremer utilizando Adper Single Bond 2 ou o Sistema Adesivo P90. Os substratos dos espécimes a serem testados foram fabricados utilizando uma matriz de silicone (5mm x 5mm x 2.5mm) e fotoativados por 40 segundos (Blue Star 3, Microdont; 1076mW/cm2). De acordo com o grupo testado, foi usada ou não uma camada de adesivo fotoativado por 10 segundos. O segundo substrato (2,5mm) foi aplicado e fotoativado por 40 segundos. Os espécimes foram secionados com formato de palito, com uma área de 0,64mm2, e armazenados em água destilada a 37ºC por 24 horas. Realizou-se o teste de microtração utilizando a máquina de ensaios universal com uma velocidade de 0,5mm/min. Foi analizado o tipo de fratura resultante. Os resultados foram analisados utilizando ANOVA e o teste de Tukey (p<0.05). A média e desvio-padrão dos resultados da resistência de união em MPa são: G1 Pad (P90/adesivo P90/P90) 50.9±15.3, G2 P (P90/sem adesivo/P90) 40.2±10.2, G3 Z (Z350/sem adesivo/Z350) 62.1±15.2, G4 Ppol (P90/sem adesivo, tira de poliéster/P90) 28.8±9.2, G5 ZadP (Z350/adesivo P90/P90) 62.1±8.2, G6 PSBZ (P90/Single Bond 2/Z350) 37.1±12.5, G7 ZSB (Z350/Single Bond 2/Z350) 54.3±12.3, G8 VitrZ (Vitremer/Single Bond 2/Z350) 37.4±7.4 e G9 VitrP (Vitremer/adesivo P90/P90) 34.9±4.1. Diferença significativa foi observada entre os grupos G2 e G3, e G5 e G6. Não foi observada diferencia significativa entre os grupos G8 e G9, G5 e G7, G1 e G6. Dentro das limitações do estudo, pode-se concluir que a resina de silorano demonstrou propriedades de...

Silorane resin and its cationic polymerization are different from resin-based materials. As restorative materials, their use together could cause some incompatibility that raises the question about the importance of interfacial bonding properties. This study aimed to compare the microtensile bond strengths between layers of Filtek P90 bonded with itself, Filtek Z350 or Vitremer using Adper Single Bond 2 and P90 Adhesive System. Initially, substrates for the testing specimens were fabricated using a silicone mold (5mm x 5mm x 2.5mm) and light-cured for 40 s (Blue Star 3, Microdont; 1076mW/cm2). According to the testing group, it was used or not an adhesive layer, light-cured for 10 s. The second increment (2.5mm) was cured for 40 s. The specimens were sectioned in beams with 0.64mm2 cross-sectional area and stored in distilled water at 37ºC for 24 h. Microtensile bond strength test was performed using a universal testing machine with a 0.5mm/min crosshead speed. Failure modes were assessed. Values were calculated in MPa. Data were analyzed with ANOVA and Tukeys post-hoc tests at a 5% significance level. Microtensile bond strength means and standard deviation are: G1 Pad (P90/P90 adhesive/P90) 50.9±15.3, G2 P (P90/without adhesive/P90) 40.2±10.2, G3 Z (Z350/without adhesive/Z350) 62.1±15.2, G4 Ppol (P90/without adhesive, polyester strip/P90) 28.8±9.2, G5 ZadP (Z350/P90 adhesive/P90) 62.1±8.2, G6 PSBZ (P90/Single Bond 2/Z350) 37.1±12.5, G7 ZSB (Z350/Single Bond 2/Z350) 54.3±12.3, G8 VitrZ (Vitremer/Single Bond 2/Z350) 37.4±7.4 e G9 VitrP (Vitremer/P90 adhesive/P90) 34.9±4.1. Significant difference was showed among G2 and G3, G5 and G6. No significant difference was found between G8 and G9, G5 and G7, G1 and G6. Conclusions: Within the limitations of this study, it can be concluded that silorane composite showed similar bonding properties when bonded with methacrylate-based materials. Significantly lower bond strength was observed between layers of P90 than of Z350.