Post-fatigue fracture load, stress concentration and mechanical properties of feldspathic, leucite- and lithium disilicate-reinforced glass ceramics.

Objective: To evaluate the mechanical properties of different CAD/CAM ceramic systems and the post-fatigue fracture and stress distribution when used as cemented crowns. Materials and methods: Sixty (60) CAD/CAM monolithic crowns were milled using three different ceramic materials (FD - Feldspathic [Vita Mark II]), LE - Leucite-based ceramic [IPS Empress CAD] and LD - Lithium Disilicate [IPS e.max CAD]) and adhesively cemented on resin composite dyes. Specimens were stored in distillated water (37 °C) for 7 days. After, half of the crowns were submitted to immediate fracture load test while the other half was submitted to fatigue cycling. The average cement layer of approximately 80 µm was assessed using scanning electron microscopy (SEM). The average thickness was used in the three-dimensional (3D) Finite Element Analysis (FEA). For each ceramic material, the density, Poisson ratio, shear modulus, Young modulus, fracture toughness, and true hardness were assessed (n = 3). The data was used to assess the Maximum Principal Stress throughout 3D-FEA according to each material during load to fail and post-fatigue. Data were submitted to two-way ANOVA and Tukey test (α = 0.05). Results: LD showed the highest compression load, density, shear modulus, Young modulus, fracture toughness and true hardness values. While LE presented the lowest mechanical properties values. There is no difference in the Poisson ratio between the evaluated ceramics. Conclusion: LD was susceptible to aging process but presented stronger physicomechanical properties, showing the highest post-fatigue fracture load and highest stress magnitude.

Influence of ceramic shades on surface hardness of different resin cements.

OBJETIVES: The aim of this study was to evaluate the effect of different ceramic spacer shades on the Knoop hardness (KH) of dual-cure resin cements (RelyX ARC RLX, 3M ESPE; Variolink II VLK, Ivoclar Vivadent) cured for 20 seconds with an LED light-curing unit. MATERIALS: Eight groups (n equals 15) were tested as follows: RelyX Control (light-cured without ceramic spacer); RelyX-2M2 ceramic spacer; RelyX-5M3 ceramic spacer; RelyX self-cured. Similar conditions were used with Variolink II cement. A microhardness tester was used to measure the KH values. Specimens were subjected to five 50 g/15 s indentations following curing at 0, 1, 2, 3, 4, 6, 24, 168, and 336 hours in order to determine the point at which the cements reach the maximum KH values. RESULTS: Control groups exhibited significantly higher KH values than the other groups (P less than 0.001) at 0 h following light curing. The KH values for RelyX-2M2 were not significantly different than the control group (P greater than 0.05) after 336 hours. All groups tested with 5M3 spacers had KH values that were not significantly different from the groups with self-cure mode, P greater than 0.05. The KH values for RelyX self-cure cement were significantly higher than Variolink II self-cure, P equals 0.003. RelyX-2M2 had KH values that were not significantly different from that of Variolink-2M2, P greater than 0.05. CONCLUSIONS: Ceramic spacer shades have tremendous effect on the KH values of RelyX and Variolink II. Darker ceramic shades (5M3 spacers) interfere with the absorption of light by the cements tested. In addition, the chemical portion in the self-cured mode is not sufficient to achieve optimum microhardness.

Diametral tensile strength of composite core material with cured and uncured fiber posts.

The aim of this study was to determine the influence of different types of posts and post head designs on the fracture resistance of a composite resin core material using the diametral tensile strength (DTS ). Seventy-five disc specimens were prepared using a composite core and prefabricated glass fiber posts and were divided into four test groups and one control group (n=15). The use of fiber posts reduced the DTS of the composite core material; the DTS value of the control material was significantly higher (p=0.05) than all of the test groups.

Outcome of psychosis in people of African-Caribbean family origin. Population-based first-episode study.

BACKGROUND: An increased incidence of psychotic disorders has repeatedly been reported among African-Caribbeans in the UK. AIMS: To test whether the increased incidence of psychotic disorders in first- and second-generation African-Caribbeans in the UK could be caused by a relative excess of affective-related psychoses with good prognosis. METHOD: Thirty-three patients of African-Caribbean family origin identified in a population-based study of first-episode psychoses were compared with the remaining cases. Three-year outcomes and patterns of course were compared. RESULTS: There was a trend for better outcomes in African-Caribbean patients for symptoms and social disability, but patterns of course were similar (odds ratio = 0.9 (0.50 to 2.00)) [corrected]. Pattern of course improved after adjustment for confounding by gender, social class, age, diagnosis and duration of untreated illness (odds ratio = 0.59 (0.21 to 1.66)) [corrected]. Diagnostic profiles were similar, with no evidence of greater diagnostic instability in the African-Caribbean group. CONCLUSION: Pattern of course of psychosis did not differ significantly by ethnic family background. An excess of good-prognosis affective psychoses is an unlikely explanation for increased rates of psychosis in African-Caribbeans.