Sérgio Vieira

Colour stability and opacity of resin cements and flowable composites for ceramic veneer luting after accelerated ageing

OBJECTIVES Colour changes of the luting material can become clinically visible affecting the aesthetic appearance of thin ceramic laminates. The aim of this in vitro study was to evaluate the colour stability and opacity of light- and dual-cured resin cements and flowable composites after accelerated ageing. METHODS The luting agents were bonded (0.2 mm thick) to ceramic disks (0.75 mm thick) built with the pressed-ceramic IPS Aesthetic Empress (n=7). Colour measurements were determined using a FTIR spectrophotometer before and after accelerated ageing in a weathering machine with a total energy of 150 kJ. Changes in colour (ΔE) and opacity (ΔO) were obtained using the CIE L*a*b* system. The results were submitted to one-way ANOVA, Tukey HSD test and Students t test (α=5%). RESULTS All the materials showed significant changes in colour and opacity. The ΔE of the materials ranged from 0.41 to 2.40. The highest colour changes were attributed to RelyX ARC and AllCem, whilst lower changes were found in Variolink Veneer, Tetric Flow and Filtek Z350 Flow. The opacity of the materials ranged from -0.01 to 1.16 and its variation was not significant only for Opallis Flow and RelyX ARC. CONCLUSIONS The accelerated ageing led to colour changes in all the evaluated materials, although they were considered clinically acceptable (ΔE<3). Amongst the dual-cured resin cements, Variolink II demonstrated the highest colour stability. All the flowable composites showed proper colour stability for the luting of ceramic veneers. After ageing, an increase in opacity was observed for most of the materials.

Reaction kinetics of sodium ascorbate and dental bleaching gel.

OBJECTIVE The aim of this study was to establish the reaction kinetics of 35% hydrogen peroxide and sodium ascorbate and to determine the mass of antioxidant required to neutralize the bleaching gel. METHODS The method used to quantify sodium ascorbate was based on the United States Pharmacopeia (1995)(26). Oxidation-reduction titration was used to confirm the concentration of hydrogen peroxide and sodium ascorbate and to determine the reaction kinetics between them. RESULTS The results indicated a direct correlation between the mass of hydrogen peroxide and that of the antioxidant agent. In addition, 5 min of contact was sufficient to neutralize the hydrogen peroxide used. CONCLUSION This in vitro study showed that the amount of sodium ascorbate required for reduction of hydrogen peroxide is directly related to the concentration of the latter. In addition, the reaction kinetics between oxidant and antioxidant showed that a longer application time for sodium ascorbate does not influence the effectiveness of the reaction and that 5 min is sufficiently long for this antioxidant to exert an antioxidant effect.

Microbial Biotransformation to Obtain New Antifungals

Antifungal drugs belong to few chemical groups and such low diversity limits the therapeutic choices. The urgent need of innovative options has pushed researchers to search new bioactive molecules. Literature regarding the last 15 years reveals that different research groups have used different approaches to achieve such goal. However, the discovery of molecules with different mechanisms of action still demands considerable time and efforts. This review was conceived to present how Pharmaceutical Biotechnology might contribute to the discovery of molecules with antifungal properties by microbial biotransformation procedures. Authors present some aspects of (1) microbial biotransformation of herbal medicines and food; (2) possibility of major and minor molecular amendments in existing molecules by biocatalysis; (3) methodological improvements in processes involving whole cells and immobilized enzymes; (4) potential of endophytic fungi to produce antimicrobials by bioconversions; and (5) in silico research driving to the improvement of molecules. All these issues belong to a new conception of transformation procedures, so-called “green chemistry,” which aims the highest possible efficiency with reduced production of waste and the smallest environmental impact.

Effect of open-sandwich vs. adhesive restorative techniques on enamel and dentine demineralization: An in situ study

OBJECTIVES To assess in situ the effect of different restorative techniques used with fluoride-releasing materials on enamel and dentine demineralization in the presence of a cariogenic challenge. METHODS Thirty human molars were prepared for 60 Class V cavities, with enamel and dentine margins. The teeth were divided into four groups (n=15): L1 - open sandwich technique with a conventional glass ionomer cement (GIC), L2 - open sandwich technique with a resin-modified GIC, A1 - total-etch bonding with a fluoride-containing adhesive, A2 - total-etch bonding with a nonfluoride-containing adhesive. All the cavities were restored with a nanofilled composite. Fifteen volunteers used appliances containing one specimen from each group. The cariogenic challenge was carried out with a 20% sucrose solution 8×/day for 7 days. The specimens were sectioned for microhardness test and EDS analysis at different depths below the enamel and dentine margins (25, 50 and 100μm) and distances from the tooth-restoration interfaces (25 and 75μm). The data were analyzed by ANOVA and Games-Howell test (α=5%). RESULTS Both GICs produced higher hardness in enamel at all depth-and-distance combinations, but only L1 produced higher hardness in dentine (p<0.05). L2 and A1 exhibited similar dentine hardness at 25μm distance for all depths (p>0.05). L1 demonstrated significantly higher amounts of calcium in dentine than the other groups, but had similar amounts in enamel to L2 and A1. CONCLUSIONS The open sandwich technique using conventional GIC proved more effective in reducing enamel and dentine demineralization at depths of up to 100μm under a cariogenic challenge. CLINICAL SIGNIFICANCE Conventional GICs should be considered the materials of choice for lining of cavities not having all margins in enamel, particularly using the open sandwich technique.

Specific concentration evaluation of 16% carbamide peroxide compounded at dispensing pharmacies

The aim of this work was to evaluate the concentration of carbamide peroxide compounded at different dispensing pharmacies. Immediate concentration analysis was made of bleaching gels dispensed by specialized pharmacies, and of a commercially available gel (control group) (n=20). The carbamide peroxide concentration was determined by titration and the results were analyzed statistically by the Kruskal-Wallis test. The commercial bleaching agent (control group) and one of the gels from the pharmacies presented the best mean concentration values, close to 16%. In conclusion, the concentration of the manipulated and industrialized carbamide peroxide gels presented concentration values differing from 16%.

Impact of refrigeration on the surface hardness of hybrid and microfilled composite resins

This in vitro study evaluated the Knoop hardness of the composite resins Charisma (C) and Durafill VS (D) polymerized in 3 different conditions: at room temperature (A) (23 +/- 1 degrees C); refrigerated at 4 +/- 1 degrees C and immediately photo-activated after removal from the refrigerator (0); and, refrigerated at 4 +/- 1 degrees C and photo-activated after a bench time of 15 min at room temperature (15). One hundred and twenty specimens (4 mm diameter and 2 mm depth) were made using a stainless steel mold and following manufacturers instructions. All specimens were tested immediately after polymerization (I) and after 7 days of water storage in the dark at room temperature (7d). The data were subjected to ANOVA and post-hoc Tukeys test (alpha=0.05). On the top surface, C(AI) was statistically similar to C(15I) and D(AI) to D(15I) (p>0.05). On the bottom surface, C(AI) presented higher hardness values when compared to COI and C(15I) (p<0.05). The D groups showed no significant differences (p>0.05) on the bottom surfaces for any tested polymerization condition. After 7 days of storage, the Knoop hardness decreased significantly (p<0.05) for groups C(7d) and D(7d) except for C(07d), which was not different from C(OI) at either surface (p>0.05). D(07d) showed higher Knoop hardness (p<0.05) values on the top surface when compared to the other groups.

Wavelength of Experimental LEDS: Hardness, Elastic Modulus, Degree of Conversion and Temperature Rise of a Microhybrid Composite

The aim of this study was to evaluate the effect of different peak wavelengths (450nm, 468nm and 490nm) of experimental LEDs on hardness, elastic modulus, degree of conversion and temperature rise of a microhybrid resin composite – Venus® (Heraeus Kulzer). Hardness and elastic modulus were determined by nanoindentation technique (n=5), degree of conversion was measured by FTIR (n=5) and temperature rise was measured with a thermistor (n=30). Data were submitted to ANOVA and multiple comparisons tests (α=0.05). Mechanical properties and degree of conversion (p<0.001) were superior on the top surfaces of the specimens. 468nm showed the highest mechanical properties values. There was no statistical difference in the degree of conversion (p=0.51) and in temperature rise (p=0.06) among all LEDs. Hardness and elastic modulus were influenced by LED´s wavelength, whereas degree of conversion and temperature rise were not influenced.

Effect of desensitizing agents on the microtensile bond strength of two-step etch-and-rinse adhesives to dentin.

Desensitizers can be used to control postoperative sensitivity in adhesive restorations. The aim of this study was to evaluate the effect of desensitizing agents on the bond strength of two-step etch-and-rinse adhesive systems to dentin. Forty-two human molars were sectioned to obtain 3-mm-thick dentin discs. The discs were divided into three groups (n = 14 in each) - no-treatment control group (CT), and oxalic acid [BisBlock (BB)] and calcium phosphate [Desensibilize Nano-P (NP)] desensitizers - before the application of two adhesive systems [Adper Single Bond Plus (SB) and One-Step Plus (OSP)]. A nanoparticle composite resin was used to create a 3-mm-thick build-up. The specimens were stored in distilled water for 24 h before a microtensile bond-strength test was performed. The failure modes were determined using a stereomicroscope at 100 × magnification. Specimens were sectioned perpendicular to the interface for scanning electron microscopy analyses. The CT-SB group exhibited the highest bond strength, differing significantly from BB-SB and BB-OSP groups. Mixed failures were prevalent for all groups. Scanning electron microscopy revealed a continuous hybrid layer and resin tags in all groups. Dentin bond strength of etch-and-rinse adhesive systems was reduced by an oxalic acid desensitizer but was not affected by a calcium phosphate-containing desensitizer.

Estudo da função muscular peribucal, do grau de inclinação vestíbulo-lingual e da discrepância de modelo dos incisivos inferiores permanentes em crianças respiradoras nasais e bucais com oclusão normal e má oclusão de Classe I

The purpose of this study was to verify the existence of any correlation between the mouth breathing, the inferior orbicularis oris and mentalis muscles activity and specific dental features in the anterior area of the lower dental arch. A sample formed by 88 leucodermas brazilian children, 49 boys and 39 girls, with a medium age of 6 years and 11 months, was divided into 4 subgroups according to the oclusal type and breathing mode presented: normal occlusion and nasal breathing (ONRN), normal occlusion and mouth breathing (ONRB), Class I malocclusion and nasal breathing (CLIRN) and Class I malocclusion and mouth breathing (CLIRB). This research involved the performance of 22 electromyographic tests, the quantitative assessment of the buccal-lingual inclination (FMIA) and space discrepancy (DM) of the permanent lower incisors. Obtained results were submitted to statistic methods and showed no significant statistical difference for the dental variables and for the majority of the electromyographic variables studied. In this way, the clinically assessed mouth breathing could not be associated to the oclusal features and muscular functions studied.