Denture cleanser effect on resilient liners with distinct optical characteristics.

PURPOSE: To evaluate denture cleansing solutions regarding the surface roughness and color stability of two resilient liners with distinct optical characteristics used for the maximum recommended period of use. METHODS: The specimens of each resilient liner, transparent and white, were randomly distributed into groups (n= 15) of a daily 20-minute immersion simulation of 0.25%, 0.5% and 1% sodium hypochlorite (SH) and 4% acetic acid solutions. Surface roughness (Ra) and color stability (ΔE CIELab formula and NBS systems) were measured after 7, 14, 21, 30, 60, 90, 180, and 270 days. The factors of variations analyzed were material, solutions, and time of immersion. Statistical analysis used three-way ANOVA and Tukey tests (Ra), and repeated measure ANOVA (ΔE and NBS systems), P< 0.05. RESULTS: For Ra analysis, the variations occurred regardless of time and solution, as the white liner showed the greatest changes (P< 0.001). Regarding interactions between solution and time, in the period of 21 days until 270 days, Ra was equivalent for all solutions (P= 0.001). ΔE analysis showed a difference between solutions (P= 0.000) and interaction between time and solution (P= 0.000). For the transparent liner, the greatest changes were found for 1% SH after 60 days, however, at 270 days there was a color change equivalence with 0.5% SH, while 4% acetic acid solution showed intermediate values. For the white liner, 1% SH showed the highest color changes for all evaluated times, and the other evaluated solutions were similar after 270 days. For both resilient liners, 0.25% SH showed the smallest changes for the evaluated properties. CLINICAL SIGNIFICANCE: The changes found were dependent on the concentration of the solution used, as well as the length of exposure to the solution. In addition, the white resilient liner showed to be less susceptible to color changes. For both resilient liners, 0.25% sodium hypochlorite showed the least changes for the evaluated properties.

Evaluation of Radiopacity of Luting Cements Submitted to Different Aging Procedures.

PURPOSE: To evaluate the radiopacity of luting cements submitted to different aging procedures. MATERIALS AND METHODS: Twenty discs (1 × 4 mm) of each of the following cements were prepared: zinc phosphate, RelyX Luting 2, Variolink 2, AllCem, RelyX U200, Multilink, Panavia F2.0, and RelyX ARC. Then, they were randomly divided into two groups (n = 10/group), according to the aging procedure: thermal cycling group and water storage group. Before and after aging procedures, specimens were x-rayed with an aluminum step-wedge (11 steps, 1 mm thick each) and three dental slices (1 mm thick). The radiopacity was evaluated by means of optical density, which was measured using ImageJ software. The values were converted into millimeters of aluminum with a logistic regression calibration curve. The data were analyzed by one-way ANOVA and Tukey post-hoc test (α = 0.05). RESULTS: In the thermal cycling group, RelyX Luting 2, RelyX U200, and Panavia F2.0 showed a statistically significant reduction in radiopacity (p < 0.05). In the water storage group, all cements showed a significant reduction in radiopacity (p < 0.05), and RelyX Luting 2 and Panavia F2.0 performed below the desired ISO 4049 standard. CONCLUSIONS: The radiopacity of luting cements can decrease after aging, especially after 1-year water storage.

Monoclinic phase transformation and mechanical durability of zirconia ceramic after fatigue and autoclave aging.

OBJECTIVES: This study evaluated the influence of two aging procedures on the biaxial flexural strength of yttria-stabilized tetragonal zirconia ceramics. MATERIAL AND METHODS: Disc-shaped zirconia specimens and (ZE: E.max ZirCAD, Ivoclar; ZT: Zirkon Translucent, Zirkonzahn) (N = 80) (∅:12 mm; thickness:1.2 mm, ISO 6872) were prepared and randomly divided into four groups (n = 10 per group) according to the aging procedures: C: Control, no aging; M: mechanical cycling (2 × 106 cycles/3.8 Hz/200 N); AUT: Aging in autoclave at 134°C, 2 bar for 24 h; AUT + M: Autoclave aging followed by mechanical cycling. After aging, the transformed monoclinic zirconia (%) were evaluated using X-ray diffraction and surface roughness was measured using atomic force microscopy. The average grain size was measured by scanning electron microscopy and the specimens were submitted to biaxial flexural strength testing (1 mm/min, 1000 kgf in water). Data (MPa) were statistically analyzed using 2-way analysis of variance and Tukey's test (α = 0.05). RESULTS: Aging procedures significantly affected (p = 0.000) the flexural strength data but the effect of zirconia type was not significant (p = 0.657). AUTZT (936.4 ± 120.9b ) and AUT + MZE (867.2 ± 49.3b ) groups presented significantly higher values (p < 0.05) of flexural strength than those of the control groups (CZT : 716.5 ± 185.7a ; CZE : 779.9 ± 114a ) (Tukey's test). The monoclinic phase percentage (%) was higher for AUTZE (71), AUTZT (66), AUT + MZE (71), and AUT + MZM (66) compared to the C groups (ZE:0; ZT:0). Surface roughness (µm) was higher for AUTZE (0.09), AUTZT (0.08), AUT + MZE (0.09 µm), and AUT + MZT (0.09 µm) than those of other groups. CONCLUSIONS: Regardless of the zirconia type, autoclave aging alone or with mechanical aging increased the flexure strength but also induced higher transformation from tetragonal to monoclinic phase in both zirconia materials tested. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1972-1977, 2017.

Efecto del tratamiento térmico y de fibras de polietileno en la resistencia a la flexión de resinas compuestas / Effect of heat treatment and polyethylene fiber in flexural strength of dental composites

Evaluar la influencia de la polimerización complementaria y de la adición de fibras de polietileno en la resistencia a la flexión de resinas compuestas. Se confeccionaron 50 cuerpos de prueba con la ayuda de una matriz metálica articulada (ISO 4049). Las muestras se dividieron (n=10) en los siguientes grupos: G1 (grupo control) resina compuesta indirecta; G2 resina compuesta directa; G3 resina compuesta directa + tratamiento térmico; G4 resina compuesta directa + fibra de polietileno; G5 resina compuesta directa + fibra de polietileno + tratamiento térmico. Para evaluar la resistencia a la flexión se aplicó el test de tres puntos (célula de carga 9800N; velocidad 1,0 mm/min). Se aplicó el análisis de varianza (ANOVA) para determinar las diferencias entre los grupos y el test de Dunnett para la comparación con el grupo control (p<0,05). La medida de tensión para el grupo control G1 fue la menor encontrada (100,49 MPa); G2 = 108,33 MPa; G3 = 124,29 MPa; G4 = 106,04 MPa y G5 = 124,08 MPa. El método de polimerización complementada con tratamiento térmico promovió un aumento significativo de la resistencia a la flexión (p = 0,032) de las resinas directas. La utilización de la fibra no mejoró el comportamiento de la resina directa (p = 0,854).

To evaluate the influence of polymerization and the addition of supplementary polyethylene fiber on the flexural strength of composites. 50 bars (25x2x2mm) were prepared with a stainless steel mold (ISO 4049). The samples were divided (n = 10) in G1 (control group) indirect resin composite; G2 direct composite; G3 direct composite + heat treatment; G4 direct composite + polyethylene fiber; G5 direct composite + polyethylene fiber + heat treatment. For flexural test was applied to three points (9800N load cell, speed 1.0 mm/min). The analysis of variance (ANOVA) was applied to determine differences between groups and Dunnett's test for the comparison with the control group (p <0.05). The strain average for the control group G1 was the lowest found (100.49 MPa); G2 = 108.33 MPa; G3 = 124.29 MPa; G4 = 106.04 MPa; and G5 = 124.08MPa. The method of polymerization in autoclave additional significant increases in flexural strength (p = 0.032) of direct resins. But the use of fiber did not improve the performance of direct resin (p = 0.854).

Consequences of the additional polymerization on knoop microhardness of direct composite resin / Consecuencias de la polimerización adicional sobre microdureza knoop de la resina compuesta directa

The following hypothesis was tested: direct composites additional polymerization improve the surface microhardness of direct composite resin Filtek Z250 (3M ESPE). We prepared 25 specimens (2x4 mm) with a stainless steel mold. Resin specimens were randomly assigned into 5 groups (n=5/per group): G1 - resin Filtek Z250 photoactivated 60 s; G2 - resin Filtek Z250 photoactivated 60 s + autoclave cycle to 134°C for 7 min at a pressure of 2.5 kg/cm3; G3 - resin Filtek Z250 photoactivated 60 s + oven at 125°C for 7 min; G4 - resin Filtek Z250 photoactivated 60 s + microwave for 3 min to the power of 450W; G5 - indirect resin Resilab photoactivated 60 s + supplementary furnace LUX GDS 4 min. The specimens were fabricated by a metal matrix, filled with resin in two increments and each increment polymerized according to their group. For polymerization of the last layer, we used a glass plate on a polyester strip. Then the specimens were evaluated for surface microhardness Knoop. Additional polymerization media resulted in significant differences among the groups (p<0.05) (One-way ANOVA and Dunnett test, p=0.05). The mean surface hardness Knoop (KHM) were as follows: G1: 51.71+1.73b; G2: 62.37+1.71a; G3: 50.61+1.30b; G4: 52.65+1.125b; G5: 60.15+2.02a; Conclude that the additional polymerization in autoclave increased the surface microhardness Knoop of composite resin evaluated. Hypothesis was partially confirmed.

La siguiente hipótesis fue probada: evaluar si la polimerización mejora aún más la dureza de la superficie de la resina compuesta directa Filtek Z250 (3M ESPE). Se prepararon 25 muestras (2x4mm) de un molde de acero inoxidable. Las muestras de resina fueron divididas al azar en 5 grupos (n = 5): G1-resina Filtek Z250 polimerizado durante 60 s; G2-polimerizado la resina Filtek Z250 durante 60 s y ciclo de autoclave 134°C durante 7 min. a una presión de 2,5 kg/ cm3; G3-resina Filtek Z250 polimerizado durante 60 s y cura para el horno a 125°C durante 7 min; G4-resina Filtek Z250 polimerizado por 60 s y curada durante 3 min. con una potencia de microondas de 450W; G5-resina indirecta (Resilab) polimerizado 60 s y curada horno LUX/GDS durante 4 min. Las muestras fueron fabricadas por una matriz metálica, rellena con resina en dos incrementos, y cada incremento de polimerizado de acuerdo a su grupo. Para la polimerización de la última capa se utilizó una placa de vidrio y una tira de poliéster. Luego se evaluó la microdureza Knoop de la superficie de las muestras. La polimerización adicional resultó en diferencias significativas entre los grupos (p <0,05) (One-way ANOVA y prueba de Dunnett, p = 0,05). La dureza media de la superficie (KHM) fue: G1: 51,71+1,73b, G2: 62,37+1,71a; G3: 50,61+1,30b, G4: 52,65+1,125b; G5: 60,15+2,02³. Se concluye que la polimerización adicional con autoclave aumentó la microdureza de la superficie de resina evaluada. La hipótesis fue confirmada parcialmente.