Physicomechanical properties of different nanohybrid composites after aging: color stability, flexural strength, and microhardness

Aim: To evaluate the physicomechanical properties of different hybrid composites (Charisma Diamond - CD, Aura - AU, NT Premium - NT, Opallis - OP, Filtek Z250 ­ Z250) after 6 months of aging in distilled water. Methods: Discs were fabricated and color measurements were performed after 24 hours and at 7, 30, and 180 days. Flexural strength was determined using the three-point bending test. For the microhardness test, the specimens were flattened to obtain polished and flat surfaces and indentations. The results for ∆E and microhardness were analyzed by two-way repeated-measures ANOVA and Tukey's HSD test. The flexural strength results were analyzed by two-way ANOVA and Tukey's test (α=0.05). Results: The ∆E values for composite resins varied in the following order: CD (3.54)a < Z250 (4.70)ab < AU (4.95)ab < OP (5.20)ab < NT (6.23)b. ∆E values were lower for 24 h (3.84)a < 7 days (4.43)ab < 30 days (4.93)b. The highest values were observed after 180 days (ΔE = 6.54)c. The flexural strength of composite resins varied in the following order: CD (89.17 MPa)a < Z250 (73.06 MPa)b < OP (60.30 MPa)c < NT (51.28 MPa)c < AU (23.77 MPa)d. Flexural strength values were significantly higher for 24 h (68.62 MPa)a < 180 days (51.40 MPa)b. The microhardness of composite resins varied in the following order: Z250 (112.05)a < CD (102.15)ab < OP (92.04)bc < NT (87.77)d < AU (87.68)d. Microhardness was significantly higher for 180 days (113.44)a < 24 h (78.21)b. Conclusion: The microhybrid (Z250) and one of the nanohybrid composites (CD) performed better. The color stability and flexural strength of all tested composites decreased with storage time

Effect of hydrogen peroxide application on color and surface roughness of two restorative materials

Aim: This study investigated the effect of an in-office bleaching technique on lightness, color and surface roughness of two commercially available materials: a resin-modified glass-ionomer cement and a nanohybrid resin composite. Methods: Twelve disk-shaped specimens were prepared with both materials. The samples were bleached with 35% hydrogen peroxide. Bleaching was tested initially onto a smooth surface and later onto a polished one of the same specimens. The effect of the treatments on lightness and color was verified with a spectrophotometer. Surface roughness was measured with a digital surface roughness tester. The data were statistically analyzed by repeated measures ANOVA and post hoc Tukey's test (alpha = 0.05). Results: Significant variation in lightness and color was observed on the resin-modified glass-ionomer cement after the first bleaching procedure. Roughness increased significantly only after polishing the resin-modified glass-ionomer cement surface. Composite color variation was evident in the last observation period, but roughness and lightness variation due to bleaching and polishing was not significant. Conclusion: The bleaching treatment caused significant color alterations on the materials tested. This study observed that the application of in-office bleaching onto the glass-ionomer cement promoted clinically observable color alteration, and polishing after bleaching is contraindicated for this material. (AU)

Adhesion and formation of tags from MTA Fillapex compared with AH Plus® cement

Introduction and Objective: The aim of this study was two-fold: 1) to evaluate, in vitro, the shear bond strength of two sealers by push-out test and 2) to assess the failures after displacement. Additionally, the formation of tags was observed by SEM. Material and methods: Forty mandibular premolars were selected and the canals were subjected to biomechanical preparation with rotary instruments. These specimens were divided into two groups according to the sealer (n = 20): GI - MTA Fillapex and GII - AH Plus. All roots were filled with sealer only, without gutta-percha. After a period corresponding to three times the setting time of the sealer, the roots were sectioned transversely into slices of 1 mm thickness, to obtain one slice from the cervical third, to be used in the push-out test. Following, two slices of each group were randomly chosen for ultrastructural analysis by scanning electron microscopy (SEM). The data obtained in shear bond strength test were subjected to statistical analysis. Results: AH Plus cement exhibited higher shear bond strength values (1.332±0.75 MPa) than MTA Fillapex (0.071±0.07 MPa), with statistically significant differences. Conclusion: MTA Fillapex has a low bond strength with less formation of tags than AH Plus.