Indicators of the risk mechanics for Class-I and Class-II amalgam and composite resin restorations

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

Resistance to impact of cross-linked denture base biopolymer materials: Effect of relining, glass flakes reinforcement and cyclic loading

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Use of a cashew nut shell liquid resin as a potential replacement for phenolic resins in the preparation of panels - a review

The Cashew Nut Shell Liquid (CNSL) can be considered as a versatile raw material with wide applications in the form of surface coatings, paints and varnishes, as well as the production of polymers. Within this context, the chemical constituents of CNSL (anarcadic acid, cardanol, 2-cardol and methylcardol) become promising in the development of new materials components. Once separated, CNSL can be used in the research and development of additives, surfactants, pharmaceuticals, pesticides, polymers, resins and others. Being a byproduct, CNSL used in the preparation of new materials is characterized as a truly technological innovation.

Effect of Beverages and Mouthwashes on the Hardness of Polymers Used in Intraoral Prostheses

PurposeThe mechanical properties of acrylic resins used in intraoral prostheses may be altered by frequent exposure to liquids such as beverages and mouthwashes. This study aimed to evaluate the effect of thermocycling and liquid immersion on the hardness of four brands of acrylic resins commonly used in removable prostheses (Onda Cryl, QC-20, Classico, Lucitone).Materials and MethodsFor each brand of resin, seven specimens were immersed in each of six solutions (coffee, cola, red wine, Plax-Colgate, Listerine [LI], Oral B), and seven more were placed in artificial saliva (control). The hardness was tested using a microhardness tester before and after 5000 thermocycles and after 1, 3, 24, 48, and 96 hours of immersion. The results were analyzed using three-way repeated-measures ANOVA and Tukey's test (p < 0.05).ResultsThe hardness of the resins decreased following thermocycling and immersion in the solutions. Specimens immersed in cola and wine exhibited significant decreases in hardness after immersion for 96 hours, although the greatest significant decrease in hardness occurred in specimens immersed in LI. However, according to American Dental Association specification 12, the Knoop hardness of acrylic resins for intraoral prostheses should not be below 15. Thus, the median values of superficial hardness observed in most of the acrylic resins in this study are considered clinically acceptable.ConclusionsThe microhardness of polymers used for intraoral prostheses decreases following thermocycling. Among specimens immersed in beverages, those immersed in cola or wine experienced the greatest decrease in microhardness. Immersion of acrylic resins in LI significantly decreased the microhardness in relation to the initial value. Among the resins assessed, QC-20 exhibited the lowest initial hardness.

Processing and characterization of ablative composites used in rocket motors

The main objective of this research work was to obtain two formulations of ablative composites. These composites are also known as ablative structural composites, for applications in atmospherically severe conditions according to the high-temperature, hot gaseous products flow generated from the burning of solid propellants. The formulations were manufactured with phenolic resin reinforced with chopped carbon fiber. The composites were obtained by the hot compression molding technique. Another purpose of this work was to conduct the physical and chemical characterization of the matrix, the reinforcements and the composites. After the characterization, a nozzle divergent of each formulation was manufactured and its performance was evaluated through the rocket motor static firing test. According to the results found in this work, it was possible to observe through the characterization of the raw materials that phenolic resins showed peculiarities in their properties that differentiate one from the other, but did not exhibit significant differences in performance as a composite material for use in ablation conditions. Both composites showed good performance for use in thermal protection, confirmed by firing static tests (rocket motor). Composites made with phenolic resin and chopped carbon fiber showed that it is a material with excellent resistance to ablation process. This composite can be used to produce nozzle parts with complex geometry or shapes and low manufacturing cost.

Antioxidant effect of thyme ( -L.) and oregano ( -L.) extracts in soybean oil under thermoxidation

The rancidity of vegetable oils is considered one problem in the food industry,thus, are added antioxidants in food. The objective of this study was to investigatethe antioxidant effect of oregano and thyme extracts in soybean oil underthermoxidation. Soybean oil containing 3,000 mg/kg of oregano and thyme oleo-resins and the mixture of both, as well as soybean oil containing tert-butylhydroquinone (TBHQ; 50 mg/kg) and soybean oil free of were subjected tothermoxidation. Then, the physicochemical properties and fatty acid profile wereevaluated. Oregano and thyme oleoresins applied separately presented a higherprotective effect, inhibiting a greater formation of polar compounds than the anti-oxidant TBHQ, indicating that the addition of 3,000 mg/kg has ensured a betteroxidative protection than the synthetic antioxidant. The increase in the concentra-tion of oleoresins by mixing thyme and oregano extracts has given a higher pro-tective effect.

Effect of human whole saliva on the in vitro adhesion of Candida albicans to a denture base acrylic resin: a focus on collection and preparation of saliva samples

Objective In studies on Candida albicans adhesion to surfaces, diverse protocols have been used for collection and preparation of saliva samples. Thus, this study investigated whether variations in the centrifugation parameters and number of donors of saliva would influence the adhesion of C. albicans to a denture base resin. Methods Resin acrylic samples (n = 72) were made and then divided into four groups: (a) control – specimens were left without preconditioning in saliva; (b) three experimental groups, in which the specimens were preconditioned with saliva collected from 15 volunteers and centrifuged at 12 000 g for 5 min (G1); from 15 volunteers and centrifuged at 18 000 g for 30 min (G2); and from one volunteer and centrifuged at 12 000 g for 5 min (G3). Candida adhesion was evaluated by both the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) reduction method and crystal violet staining. Data were analyzed by one-way analyses of variance (P = 0.05). Results For XTT reduction assay, groups G2, G3, and control were not significantly different, whereas group G1 showed significantly higher absorbance value than control. For crystal violet staining there were no significant differences among all groups. Conclusion Variations in the centrifugation parameters and number of donors of saliva may influence C. albicans adhesion to denture base resins.

Long-term surface hardness and monomer conversion of a nonofilled and a microhybrid composite resin

Objective: This study aims to evaluate the degree of conversion (DC) and hydrolytic degradation through the Vickers hardness test (HV) of a nanofilled (Filtek™ Z-250, 3M) and a microhybrid (Filtek™Supreme-XT, 3M) composite resin. Materials and methods: Eight disk-shaped specimens (4 mm diameter × 2 mm thick, ISO 4049) of each material were prepared for each test. Composites were inserted into single increment in a metallic matrix and light-cured for 40 seconds. VH readings were performed for each specimen at predetermined intervals: immediately after polymerization (control), 1, 2, 3, 7, 14, 21, 30 and 180 days. After curing, initial hardness measurements were performed and the specimens were immersed in artificial saliva at 37°C. For DC (%), specimens were ground, pressed with KBr and analyzed by FT-IR spectrophotometer. Results: Student t-test showed that there was no difference between the resins for DC (p = 0.252). ANOVA analysis revealed that Z-250 VH means were all greater than S-XT, for both top and bottom surfaces, whatever the storage-period in artificial saliva (p < 0.001). After 180 days of storage, the hardness obtained for S-XT was similar with that at the baseline, for both top and bottom surfaces. While for Z-250 hardness was not significantly different from baseline only for top surface, but there was a significant decrease observed in hardness for bottom surface. Conclusion: The materials tested showed no evidence of hydrolytic degradation in a significant way, in a 6-month storagetime in artificial saliva. Nanofilled resin presents a monomer conversion comparable to the conventional microhybrid.

Can repair increase the longevity of composite resins? Results of a 10-year clinical trial

The aim of this double-blind clinical trial was to assess the longevity of repairs to localized clinical defects in composite resin restorations that were initially planned to be treated with a restoration replacement. Methods Twenty-eight patients aged 18–80 years old with 50 composite resin restorations (CR) were recruited. The restorations with localized, marginal, anatomical deficiencies and/or secondary caries adjacent to CR that were “clinically judged” to be suitable for repair or replacement according to the USPHS criteria were randomly assigned to Repair (n = 25) or Replacement (n = 25) groups, and the quality of the restorations was scored according to the modified USPHS criteria. The restorations were blind and two examiners scored them at baseline (Cohen Kappa agreement score 0.74) and at ten years (Cohen Kappa agreement score 0.87) restorations. Wilcoxon tests were performed for comparisons within the same group (95% CI), and Friedman tests were utilized for multiple comparisons between the different years within each group. Results Over the decade, the two groups behaved similarly on the parameters of marginal adaptation (MA) (p > 0.05), secondary caries (SC) (p > 0.05), anatomy (A) (p < 0.05), and colour (C) (p > 0.05). Conclusions Given that the MA, SC, A and C parameters behaved similarly in both groups, the repair of composite resins should be elected when clinically indicated, because it is a minimally invasive treatment that can consistently increase the longevity of restorations. Clinical significance The repair of defective composite resins as an alternative treatment to increase their longevity proved to be a safe and effective treatment in the long term.

Color stability of a nanofilled resin: influence of polishing and finishing and fluoride solutions according to time

Aim: The aim of the study was evaluate the finishing and polishing effect of the color stability of the composite resin Filtek Supreme XT, according to different fluoride solutions and time. Material and Methods: Specimens were prepared (n=140) with half of the samples finished and polished. 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 in artificial saliva for 24 hours and were subjected to an initial color analysis using a spectrophotometer CIELab system. Then, they were immersed in the experimental solutions for 1 minute a day. The readings of the color change were made after 24 and 48 hours, 7, 14, 21, 30 and 60 days after the first immersion. The three-way mixed Analysis of Variance (ANOVA) ("finishing/polishing", "immersion medium" and “time”) were performed. For multiple comparisons, the Sidak test for repeated measure was used, with a 5% level of significance. Results: The finishing and polishing factor showed significant variability, independently of the immersion media (p<0.001). Cconclusion: Finishing and polishing procedures yielded better color stability to composite resin over time, regardless of the immersion media.

Roughness and morphology of composites: influence of type of material, fluoride solution, and time

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Chemical and morphological features of nanofilled composite resin: influence of finishing and polishing procedures and fluoride solutions

This study evaluated the influence of finishing and polishing procedures and differ-ent fluoride solutions on superficial morphology and chemistry of the nanofilled composite resinSupreme XT (3M) through the EDX analysis and SEM evaluation. Circular specimens (n 5 30) of 10mm diameter and 2 mm thickness were prepared, with half of the sample assays finished and polishedwith Super-Snap1sandpaper. The experimental groups were divided according to the presence or ab-sence of finishing and polishing and solutions (arti ficial saliva, 0.0 5% of manipulated sodium fluoridesolution, Fluordent Re ach, Oral B, Fluorgard). Specimens were immersed in each respective solutionfor 1 min per day, during 60 days and stored in artificial saliva at 37 6 18C between immersion peri-ods. Topography and chemical analysis was qualitative. It was observed that specimens submitted tofinishing and polishing procedures had lower superficial degradation. Fluoride solutio ns promoted su-perficial alterations on specimens, being the highest degradation obtained with Fluordent Reach. Itca n be concluded that finishing and polishing procedures and the immersion media influence the su-perficial morphology of composite resin tested; the Fluordent Reach was the flu oride solution thatmo st affected the material’s surface.

Influence of light curing units and fluoride mouthrinse on morphological surface and color stability of a nanofilled composite resin

Composite resin is a dental material susceptible to color change over time which limits the longevity of restorations made with this material. The influence of light curing units and different fluoride mouthrinses on superficial morphology and color stability of a nanofilled composite resin was evaluated. Specimens (N = 150) were prepared and polished. The experimental groups were divided according to the type of light source (halogen and LED) and immersion media (artificial saliva, 0.05% sodium fluoride solution-manipulated, Fluordent Reach, Oral B, Fluorgard). Specimens remained in artificial saliva for 24-h baseline. For 60 days, they were immersed in solutions for 1 min. Color readout was taken at baseline and after 60 days of immersion. Surface morphology was analyzed by Scanning Electron Microscopy (SEM) after 60 days of immersion. Color change data were submitted to two-way Analysis of Variance and Tukey tests (α = 0.05). Surface morphology was qualitatively analyzed. The factor light source presented no significant variability (P = 0.281), the immersion media, significant variability (P < 0.001) and interaction between factors, no significant variability (P = 0.050). According to SEM observations, no difference was noted in the surface of the specimens polymerized by different light sources, irrespective of the immersion medium. It was concluded that the light source did not influence the color stability of composite, irrespective of the immersion media, and among the fluoride solutions analyzed, Fluorgard was the one that promoted the greatest color change, however, this was not clinically perceptible. The immersion media did not influence the morphology of the studied resin. Microsc. Res. Tech. 77:941–946, 2014. © 2014 Wiley Periodicals, Inc.

Effects of immersion media and repolishing on color stability and superficial morphology of nanofilled composite resin

This study evaluated the influence of fluoride mouth rinses and repolishing on the superficial morphology and color stability of nanofilled resin. About 150 specimens were prepared and polished using aluminum oxide discs for 15 s with a pressure of 2 kg. The experimental groups were divided according to the immersion medium (artificial saliva, 0.5% sodium fluoride, Fluordent Reach, Oral B, Fluorgard) and repolishing procedure (without and with). The specimens were continuously immersed for 1 week. Thereafter, half of each sample was repolished. A color reading was performed after 24 h of immersion in the artificial saliva baseline, after continuous immersion, and after repolishing. The superficial morphology was examined using scanning electron microscopy (SEM) in a qualitative way. Color change (∆E) data were submitted to a mixed analysis of variance using a Shapiro-Wilk test (p>0.05 for the different immersion media) and Sidak's test (p<0.05 for the differences between groups). In the interaction between the repolishing and the immersion media, Fluorgard showed a statistical difference between the ∆E values with and without repolishing (p<0.0001). On the SEM observations, both Fluordent Reach and Fluorgard caused degradation of the superficial resinous matrix of the composite after continuous immersion. This matrix was removed after repolishing.

Metabolism of L929 cells after contact with acrylic resins. Part 1: Acrylic denture base resins

The purpose of this study was to evaluate the effectiveness of complementary heat treatment and water storage in reducing cytotoxicity of acrylic resins denture bases used in Brazil by the MTT assay. Material and Methods: First, nine specimens were fabricated from metal matrix in the form of discs with 14 mm in diameter and 1.2 mm of thick. Immediately after making, 24 or 48 hours after storage in distilled water, the samples of heat-polymerized resins were divided into 3 groups (n = 3) according to the type of thermal treatment: Group 1: samples were individually exposed to microwave energy (500 W for 3 minutes); Group 2: samples were immersed in water at 550 C for 60 minutes; Group 3: samples did not receive heat treatment. To prepare the extracts, 3 samples of each group were placed into vials containing 3 mL of culture medium and stored at 37°C for 24 hours. L929 cells were used and the MTT assay was performed to analyze the cellular metabolism. Two-factor analysis of variance was used to detect significant among groups at 5% significance. Results: After statistical analysis, the materials were classified according to the cytotoxic effect: non-cytotoxic, slightly cytotoxic; moderately cytotoxic; and strongly cytotoxic. The results showed that the resins ranged from moderately cytotoxic to non-cytotoxic, but no statistically significant difference among experimental groups. Furthermore, the water storage and thermal treatments reduced the cytotoxicity of the resins. Conclusions: It was concluded that the resins studied are potentially toxic and that treatments can decrease their cytotoxicity.