Randomized clinical trial of four adhesion strategies in posterior restorations-18-month results.

PURPOSE: To evaluate the 18-month clinical performance of four adhesive strategies in posterior composite restorations placed in private practice. MATERIALS AND METHODS: Upon approval by an institutional review board, 144 restorations were inserted in 45 subjects (average age = 32.6) to treat caries lesions or to replace existing restorations in vital molars and premolars. The adhesives OptiBond FL (three-step etch-and-rinse), OptiBond SOLO Plus (two-step etch-and-rinse), OptiBond XTR (two-step self-etch), and OptiBond All-in One (one-step self-etch) were applied as per manufacturer's (Kerr Co.) instructions followed by a nanofilled resin composite (Filtek Z350XT, 3M ESPE) under rubber dam isolation. Restorations were evaluated at baseline and at 18 months using United States Public Health Service (USPHS)-modified criteria and high-resolution digital photographs. Statistical analyses included the McNemar and the Mann-Whitney non-parametric tests (p < 0.05). RESULTS: A total of 137 restorations were evaluated after 18 months. The number of alfa ratings did not change significantly from baseline to 18 months for any of the adhesion strategies. When the 18-month evaluation criteria were pooled by pairs of adhesives, none of the adhesives resulted in a significantly different number of alfa ratings for any of the criteria compared with the other adhesives. CONCLUSION: Bonding strategy did not influence the clinical performance of posterior composite restorations under the clinical conditions used in this study. CLINICAL SIGNIFICANCE: When used in ideal clinical conditions, the composition of current dentin adhesives may be more clinically relevant than their adhesion strategy.

Color stability, gloss, and surface roughness of indirect composite resins.

This in vitro study evaluated the color stability, gloss, and surface roughness (Ra) of four indirect composites. Enamel and dentin shades of Radica, Sculpture Plus, Belleglass-NG, and Gradia Indirect were evaluated for color stability. Specimens were stored in a staining solution (coffee) and assessed every 3 days for a period of 21 days, after which color difference (∆E*) was calculated. Only enamel shades were used for measuring gloss and surface roughness at 0, 5000, 10,000, and 20,000 cycles of simulated toothbrushing. The results were statistically analyzed using repeated measures analysis of variance (ANOVA) and Tukey's test. Statistically significant changes in ∆E* during the 21-day period were observed in all indirect composites for enamel and dentin shades, and ∆E* was greater than the clinically acceptable value of 3.3. Belleglass-NG showed the least change in ∆E*, while Sculpture Plus had large changes in ∆E*. In all groups, gloss was 75% lower than baseline values after 10,000 cycles of toothbrushing. After 20,000 cycles, surface roughness was highest in Radica and lowest in Belleglass-NG. Belleglass-NG had higher color stability and gloss retention, and lower surface roughness, as compared with the other composite systems.

Fracture loads of all-ceramic crowns under wet and dry fatigue conditions.

PURPOSE: The aim of this study was to test the hypothesis that fracture loads of fatigued dental ceramic crowns are affected by testing environment and luting cement. MATERIALS AND METHODS: One hundred and eighty crowns were prepared from bovine teeth using a lathe. Ceramic crowns were prepared from three types of ceramic systems: an alumina-infiltrated ceramic, a lithia-disilicate-based glass ceramic, and a leucite-reinforced ceramic. For each ceramic system, 30 crowns were cemented with a composite resin cement, and the remaining 30 with a resin-modified glass ionomer cement. For each ceramic system and cement, ten specimens were loaded to fracture without fatiguing. A second group (n = 10) was subjected to cyclic fatigue and fracture tested in a dry environment, and a third group (n = 10) was fatigued and fractured in distilled water. The results were statistically analyzed using one-way ANOVA and Tukey HSD test. RESULTS: The fracture loads of ceramic crowns decreased significantly after cyclic fatigue loading (p

Variação da força de resistência à micro-tração de fragmentos de ossos corticais preservados em diversos meios e a fresco: estudo experimental em coelhos / Variation of the resistance force to the micro-traction of fragments of cortical bones preserved in several means and fresh: Experimental study in rabbits

Devido ao crescente uso dos aloenxertos nas cirurgias ortopédicas, há a necessidade do conhecimento de suas características biomecânicas ao longo do tempo de preservação. O presente trabalho consistiu na análise da força de resistência à micro-tração de amostras de ossos corticais de coelho preservadas em diversos meios por até 180 dias e a fresco. Os resultados revelaram que a resistência e o tempo de preservação apresentaram uma relação inversamente proporcional, significando que, quanto maior o tempo de preservação, menor a resistência física avaliada no ensaio biomecânico de resistência à micro-tração. Dos meios utilizados, a glicerina apresentou menores valores quanto ao teste de resistência, demonstrando, após 30 dias de preservação, apenas 24,58 por cento da força presente no osso a fresco e, aos 180 dias, 1,76 por cento. As amostras submetidas à autoclavagem também demonstraram baixos valores ao final do experimento, quando permaneceram com apenas 12,31 por cento da força presente no osso a fresco. Os ossos preservados em plasma homólogo, líquido de dakin e aqueles criopreservados apresentaram os melhores índices de resistência ao final do experimento, permanecendo, respectivamente, com 82,47; 70,34 e 66,72 por cento da força máxima quando comparados com a resistência dos ossos frescos. Concluiu-se que a escolha do método e o tempo de preservação interferiu diretamente na biomecânica dos ossos corticais, promovendo a diminuição da capacidade de resistência à tração ao longo do período de preservação.

Due to the increasing use of cortical bone allografts in orthopedic surgeries, de knowledge of its biomechanics characteristics during preservation time is needed. The present study consisted in the analyses of the resistance power to the micro-traction of samples of rabbit cortical bones preserved in several means for up to 180 days and fresh. The results showed that the resistance and the preservation time presented an inversely proportional relation, meaning that, the longer the time of preservation, the shorter the physical resistance evaluated in the biomechanical rehearsal of resistance to the micro-traction. The glycerin has presented lower values in relation to the resistance test, showing, after 30 days, only 24.58 percent of the present power in the fresh bone, and by 180 days, 1.76 percent. The samples submitted to autoclavation also showed low values by the end of the experiment, while they remained with just 12.31 percent of the power present in the fresh bone. The bones preserved in homologous plasma, Dakin liquid and the ones cryopreserved showed the best levels of resistance at the end of the experiment, remaining, respectively with 82.47, 70.34 and 66.72 percent of the maximum power, while compared with the resistance of the fresh bones. The conclusion is that the choice of methodology and time of preservation interfered directly in the biomechanics of the cortical bones, promoting decrease of the resistance capacity to the traction along the period of preservation.

Influence of different ceramics on resin cement Knoop Hardness Number.

This study evaluated: (1) the effect of different ceramics on light attenuation that could affect microhardness, measured as the Knoop Hardness Number (KHN), of a resin cement immediately and 24 hours after polymerization and (2) the effect of different activation modes (direct light-activation, light activation through ceramics and chemical activation) on the KHN of a resin cement. Resin cement Rely XARC (3M ESPE) specimens 5.0 mm in diameter and 1.0 mm thickwere made in a Teflon mold covered with a polyester film. The cement was directly light activated for 40 seconds with an XL 2500 curing unit (3M ESPE) with 650 mW/cm2, light activated through ceramic discs of Duceram Plus (DeguDent), Cergogold (DeguDent), IPS Empress (Ivoclar), IPS Empress 2 (Ivoclar), Procera (NobelBiocare), In Ceram Alumina (Vita) and Cercon (DeguDent), having a 1.2 mm thickness or chemically activatedwith-out light application. The resin cement specimens were flattened, and KHN wasobtained using an HMV 2 microhardnesstester (Shimadzu) with a load of 50 g applied for 15 seconds 100 microm from the irradiated surface immediately and after storage at 37 degrees C for 24 hours. Ten measurements were made for each specimen, with three specimens for each group at each time. The data were submitted to ANOVA and Tukey's test (p = 0.05). The KHN of the resin cement was not only affected by the mode of activation, but also by the post-activation testing time. The mean KHN of the resin cementfor chemical activation and through all ceramics showed statistically significant lower values compared to direct activation immediately and at 24 hours. The KHN for 24 hourspost-activation was always superior to the immediate post-activation test except with direct activation. The most opaque ceramics resulted in the lowest KHN values.

Effects of ceramic thickness and curing unit on light transmission through leucite-reinforced material and polymerization of dual-cured luting agent.

This study investigated the influence of ceramic thickness and curing unit on light transmission through leucite-reinforced material and polymerization of a dual-cured resin luting agent. Discs of Empress Esthetic (Ivoclar Vivadent) of 0.7-, 1.4- and 2-mm thickness were prepared. Variolink II (Ivoclar Vivadent) was placed in a 1-mm-thick cylindrical mold, and light-activated through ceramic for 40 s, using QTH or LED units. The samples were divided into dual, light, and chemically-polymerized control groups. Knoop hardness indentations were made on the top and bottom surfaces. Data were subjected to split-plot design three-way ANOVA and Tukey's test (P < 0.05). The light spectrum transmitted through ceramic was obtained using a spectrometer. Samples activated through 1.4-and 2-mm-thick discs showed lower hardness than all others groups, except for the chemical control group. Dual and light-polymerized control samples showed similar hardness to those activated through the 0.7-mm ceramic, whereas chemically polymerized control samples showed similar hardness to those activated through 1.4- and 2-mm ceramics. No significant differences in hardness were detected between the curing units or between the top and bottom layers. No significant alteration in the light spectrum profile was observed for both units, irrespective of the ceramic thickness.

The effects of viscoelastic parameters on residual stress development in a zirconia/glass bilayer dental ceramic.

OBJECTIVES: The aim of this study was to test the hypothesis that the residual stresses in a zirconia-based bilayer dental composite system can be tailored through heat treatment above and below the glass transition temperature of glass veneers. METHODS: Ceramic bilayer disc specimens were prepared from a zirconia core and a glass veneer. Each bilayer ceramic group was heat treated 40 degrees C below, 20 degrees C and 40 degrees C above and at the glass transition temperature of the glass veneer, and cooled using a fast or a slow cooling rate. Specimens were tested for flexure strength using a biaxial bending fixture. Residual stresses were calculated using a fracture mechanics approach. RESULTS: Heat treatments produced significant differences (p < or =0.05) between the mean flexural strengths of the heat treatment groups when the specimens were cooled using a fast cooling rate. However, there was not a significant difference (p >0.05) between the mean flexural strengths of the heat treatment groups when a slow cooling rate was used. Fractures initiated from the veneer surfaces of the specimens. SIGNIFICANCE: Heat treatment above and below the glass transition temperature of the veneer layer, and the cooling rate have a significant effect on the flexural strength of the bilayer ceramic laminates. The existence of residual compressive stress is the most likely reason for the observed strength increases. Residual stresses can be modified using the elastic-viscoelastic relaxation behavior of a glass veneer.