The Effect of Mechanical Cycling and Different Misfit Levels on Vicker's Microhardness of Retention Screws for Single Implant-Supported Prostheses

Purpose: The aim of this study was to evaluate the effect of mechanical cycling and different misfit levels on Vicker's microhardness of retention screws for single implant-supported prostheses.Materials and Methods: Premachined UCLA abutments were cast with cobalt-chromium alloy to obtain 48 crowns divided into four groups (n = 12). The crowns presented no misfit in group A (control group) and unilateral misfits of 50 mu m, 100 mu m, and 200 mu m in groups B, C, and D, respectively. The crowns were screwed to external hexagon implants with titanium retention screws (torque of 30 N/cm), and the sets were submitted to three different periods of mechanical cycling: 2 x 10(4), 5 x 10(4), and 1 x 10(6) cycles. Screw microhardness values were measured before and after each cycling period. Data were evaluated by two-way ANOVA and Tukey's test (p < 0.05).Results: Mechanical cycling statistically reduced microhardness values of retention screws regardless of cycling periods and groups. In groups A, B, and C, initial microhardness values were statistically different from final microhardness values (p < 0.05). There was no statistically significant difference for initial screw microhardness values (p > 0.05) among the groups; however, when the groups were compared after mechanical cycling, a statistically significant difference was observed between groups B and D (p < 0.05).Conclusions: Mechanical cycling reduced the Vicker's microhardness values of the retention screws of all groups. The crowns with the highest misfit level presented the highest Vicker's microhardness values.

In situ effect of an erosive challenge on different restorative materials and on enamel adjacent to these materials

Objectives: This in situ study evaluated the effect of an erosive challenge on different restorative materials and on enamel restored with these materials, as well as the ability of these materials to protect the adjacent enamel against erosion.Methods: Ten volunteers wore palatal devices with eight bovine enamel blocks, randomly selected and distributed into two vertical rows, corresponding to the following groups: GI/GV, resin-modified glass ionomer; GII/GVI, conventional glass ionomer; GIII/GVII, composite resin; GIV/GVIII, amalgam. one row (corresponding to groups I-IV) was immersed in a cola drink and the other row (corresponding to groups V-VIII) was subjected to saliva only. The palatal device was continuously worn for 7 days and only half of the appliance (groups I-IV) was immersed in the soft drink (Coca-Cola (R), 150 mL) for 5 min, three times a day. The study variables comprised the wear (profilometry, mu m) and the percentage of surface microhardness change (%SMHC). Data were tested for significant differences by two-way ANOVA and Tukey's tests (p < 0.05).Results: Considering the restorative materials, for %SMHC and wear, there were no differences among the materials and between the saliva and the erosive challenge. For enamel analyses, the erosive challenge promoted a higher wear and %SMHC of the enamel than did the saliva. There were no significant differences in wear and %SMHC of the enamel adjacent to the different restorative materials.Conclusion: This research data suggest that there is little %SMHC and wear of the studied restorative materials and none of them had a preventive effect against erosion on adjacent enamel, which showed a pronounced wear. (c) 2007 Elsevier Ltd. All rights reserved.

Surface roughness and hardness of a composite resin: influence of finishing and polishing and immersion methods

This study evaluated the finishing and polishing effect on the surface roughness and hardness of the Filtek Supreme XT, in fluoride solutions. Specimens were prepared (n = 140) with half of the samples finished and polished with Super-Snap (R) disks. The experimental groups were divided according to the presence or absence of finishing and polishing and immersion solutions (artificial saliva, sodium fluoride solution at 0.05%-manipulated, Fluordent Reach, Oral B, Fluorgard). The specimens remained immersed in artificial saliva for 24 hours and were then subjected to initial analysis (baseline) of surface roughness and Vickers microhardness. Next, they were immersed in different fluoride solutions for 1 min/day, for 60 days. Afterwards, a new surface roughness and microhardness reading was conducted. The data were submitted to a two-way ANOVA and Tukey's test (5% significance level). For the comparison of mean roughness and hardness at baseline and after 60 days, the paired Student t test was used. The results showed that the surface roughness and microhardness of the Filtek Supreme XT were influenced by the finishing and polishing procedure, independently of the immersion methods.

Composite resin color stability: influence of light sources and immersion media

Objective: This study evaluated the influence of light sources and immersion media on the color stability of a nanofilled composite resin. Material and Methods: Conventional halogen, high-power-density halogen and high-power-density light-emitting diode (LED) units were used. There were 4 immersion media: coffee, tea, Coke (R) and artificial saliva. A total of 180 specimens (10 mm x 2 mm) were prepared, immersed in artificial saliva for 24 h at 37 +/- 1 degrees C, and had their initial color measured with a spectrophotometer according to the CIELab system. Then, the specimens were immersed in the 4 media during 60 days. Data from the color change and luminosity were collected and subjected to statistical analysis by the Kruskall-Wallis test (p<0.05). For immersion time, the data were subjected to two-way ANOVA test and Fisher's test (p<0.05). Results: High-power-density LED (Delta E=1.91) promoted similar color stability of the composite resin to that of the tested halogen curing units (Jet Lite 4000 plus - Delta E=2.05; XL 3000 - Delta E=2.28). Coffee (Delta E=8.40; Delta L=-5.21) showed the highest influence on color stability of the studied composite resin. Conclusion: There was no significant difference in color stability regardless of the light sources, and coffee was the immersion medium that promoted the highest color changes on the tested composite resin.

The influence of short-term diabetes mellitus and insulin therapy on alveolar bone loss in rats

Background: It is well known that the multiple direct and indirect consequences of hyperglycemia in diabetic individuals have been linked to a number of abnormal host effector mechanisms that could lead to an increased risk of developing periodontal disease.Objective: the aim of this study was to investigate the effect of short-term experimental diabetes and insulin therapy on the severity of alveolar bone loss in rats, and the effect of experimental periodontitis on glycemic control.Methods: Seventy-two male Wistar rats were divided into four groups: group I animals were submitted to dental ligature around lower right first molars (ligated); group II consisted of streptozotocin (STZ)-diabetic, ligated rats; group III represented STZ-diabetic, unligated rats; and group IV consisted of insulin-treated (6 U/day), STZ-diabetic, ligated rats. Blood glucose of all diabetic rats was monitored at regular intervals. Standardized digital radiographs were taken after killing at 7, 15 and 30 days to measure the amount of bone loss about the mesial root surface of the first molar tooth in each rat.Results: No significant (p < 0.05) changes in plasma glucose levels of insulin-treated diabetic rats were found among the different examinations after the beginning of insulin therapy. Rats from group II showed significantly greater increases in mean plasma glucose levels at 15 and 30 days after ligature placement compared with rats from group III (p < 0.05). Furthermore, in spite of the significant alveolar bone loss progression that was observed in groups I, II and IV (p < 0.00001; two-way ANOVA), no significant differences among these groups regarding the severity of bone loss (p = 0.77) and no significant interaction between treatment group and time (p = 0.81) were found.Conclusions: Within the limits of this study, it can be suggested that the severity of periodontal disease was not affected by short-term diabetes, and that experimental periodontitis increased blood glucose levels in uncontrolled diabetic rats.

Linear dimensional changes of denture base and hard chair-side reline resins after disinfection

Objectives: This study evaluated the effect of disinfection by immersion in sodium perborate (50 degrees C/10 min) or microwave irradiation (650 W/6 min) on the linear dimensional change (LDC) of four reline resins (Kooliner-K, New Truliner-N, Tokuso Rebase Fast-T, Ufi Gel Hard-U) and one heat-polymerizing denture base resin (Lucitone 550-L). Methods: Specimens (50.0 mm diameter, 0.5 mm thickness) were made using a split mold with reference points, and divided into two controls and four test groups (u = 8). The distances between the points were measured on the mold (baseline readings), and compared to those obtained from the specimens after: polymerization or immersion in water (37 degrees C) for 7 days (controls); 2 or 7 cycles of disinfection by immersion or microwave irradiation. Results: the two-way ANOVA and Tukey's test (alpha = 0.05) showed that microwave disinfection significantly increased the mean LDC of materials L (-1.43%), N (-1.27%) and K (-1.06%). Material N also exhibited a significant increase in LDC after two cycles of chemical disinfection (-0.73%). For U (-0.47%) and T (-0.21%) materials, no significant changes in LDC were found. Conclusions: Microwave disinfection increases the shrinkage of materials L, N, and K. The dimensional stability of resins U and T was not affected by the disinfection methods evaluated. (c) 2006 Wiley Periodicals, Inc.

Effect of long-term water immersion on the fracture toughness of denture base and reline resins

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efficacy of Air-abrasion Technique and Additional Surface Treatment at Titanium/Resin Cement Interface

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of Conventional and Resin-modified Glass-Ionomer Liner on Dentin Adhesive Interface of Class I Cavity Walls After Thermocycling

Objective: The aim of this in vitro study was to analyze the effect of glass-ionomer cement as a liner on the dentin/resin adhesive interface of lateral walls of occlusal restorations after thermocycling.Materials and Methods: Occlusal cavities were prepared in 60 human molars, divided into six groups: no liner (1 and 4); glass-ionomer cement (GIC, Ketac Molar Easymix, 3M ESPE) (2 and 5); and resin-modified glass-ionomer cement (RMGIC, Vitrebond, 3M ESPE) (3 and 6). Resin composite (Filtek Z250, 3M ESPE) was placed after application of an adhesive system (Adper Single Bond 2, 3M ESPE) that was mixed with a fluorescent reagent (Rhodamine B) to allow confocal microscopy analysis. Specimens of groups 4, 5 and 6 were thermocycled (5 degrees C-55 degrees C) with a dwell time of 30 seconds for 5000 cycles. After this period, teeth were sectioned in approximately 0.8-mm slices. One slice of each tooth was randomly selected for confocal microscopy analysis. The other slices were sectioned into 0.8 nun x 0.8 mm beams, which were submitted to microtensile testing (MPa). Data were analyzed using two-way ANOVA and Tukey test (p < 0.05).Results: There was no detectedstatistical difference on bond strength among groups (alpha < 0.05). Confocal microscopy analysis showed a higher mean gap size in group 4(12.5 mu m) and a higher percentage of marginal gaps in the thermocycled groups. The RNIGIC liner groups showed the lowest percentage of marginal gaps.Conclusions: Lining with RMGIC resulted in less gap formation at the dentin/resin adhesive interface after artificial aging. RMGIC or GIC liners did not alter the microtensile bond strength of adhesive system/resin composite to dentin on the lateral walls of Class I restorations.

Effect of microwave disinfection on the surface roughness of three denture base resins after tooth brushing

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of light curing sources on microhardness of different composite resins

This study evaluated the influence of light-curing units (LCUs) on Knoop microhardness (KHN) of different composite resins formulations. Four LCUs, one Quartz-Tungsten-Halogen (QTH) for 20 s, one Argon-Ion-Laser (AL) for 10 s, one Plasma-Arc-Curing (PAC) for 9 s, and one Light-Emitting-Diode (LED) for 20 s, and three composite resins, nanofill and easy cure (Filtek (TM) Supreme), microhybrid and medium cure (Herculite XRV), and microfill and difficult cure (Heliomolar) were used. Discs (4 x 2 mm(2)) of each composite resin were divided in 12 Groups and KHN was measured at the top (T) and bottom (B) surfaces. Data were analyzed using two-way ANOVA and Tukey's test (p < 0.05). Top presented significantly higher KHN than bottom surface for all composite resins and LCUs tested. Statistical significant differences were observed among the LCUs. At the bottom surface QTH and LED presented higher KHN than PAC and LA. However, at the top surface PAC and LA presented similar results than QTH for nanofill and microhybrid composite resins. Different LCUs play an important effect on Knoop microhardness and the composite resin formulations were significant factor on the photosensitivity.

Do extrafloral nectaries present a defensive role against herbivores in two species of the family Bignoniaceae in a Neotropical savannas?

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Respostas pressóricas pós-exercícios com pesos executados em diferentes sobrecargas por mulheres normotensas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Efeitos de um programa de atividade física nas funções cognitivas, equilíbrio e risco de quedas em idosos com demência de Alzheimer

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Efeito de 16 semanas de treinamento com pesos sobre a pressão arterial em mulheres normotensas e não-treinadas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)