Impact and fracture resistance of an experimental acrylic polymer with elastomer in different proportions

The purpose of this study was to evaluate the impact and fracture resistance of acrylic resins: a heat-polymerized resin, a high-impact resin and an experimental polymethyl methacrylate with elastomer in different proportions (10, 20, 40 and 60%). 120 specimens were fabricated and submitted to conventional heat-polymerization. For impact test, a Charpy-type impact tester was used. Fracture resistance was assessed with a 3-point bending test by using a mechanical testing machine. Ten specimens were used for each test. Fracture (MPa) and impact resistance values (J.m-1) were submitted to ANOVA - Bonferroni's test - 5% significance level. Materials with higher amount of elastomer had statistically significant differences regarding to impact resistance (p < 0.05). Fracture resistance was superior (p < 0.01) for high-resistance acrylic resin. The increase in elastomer concentration added to polymethyl methacrylate raised the impact resistance and decreased the fracture resistance. Processing the material by injection decreased its resistance to impact and fracture

Effectiveness of a new toothbrush design versus a conventional tongue scraper in improving breath odor and reducing tongue microbiota

For centuries, specific instruments or regular toothbrushes have routinely been used to remove tongue biofilm and improve breath odor. Toothbrushes with a tongue scraper on the back of their head have recently been introduced to the market. The present study compared the effectiveness of a manual toothbrush with this new design, i.e., possessing a tongue scraper, and a commercial tongue scraper in improving breath odor and reducing the aerobic and anaerobic microbiota of tongue surface. The evaluations occurred at 4 moments, when the participants (n=30) had their halitosis quantified with a halimeter and scored according to a 4-point scoring system corresponding to different levels of intensity. Saliva was collected for counts of aerobic and anaerobic microorganisms. Data were analyzed statistically by Friedman's test (p<0.05). When differences were detected, the Wilcoxon test adjusted for Bonferroni correction was used for multiple comparisons (group to group). The results confirmed the importance of mechanical cleaning of the tongue, since this procedure provided an improvement in halitosis and reduction of aerobe and anaerobe counts. Regarding the evaluated methods, the toothbrush's tongue scraper and conventional tongue scraper had a similar performance in terms of breath improvement and reduction of tongue microbiota, and may be indicated as effective methods for tongue cleaning

Color stability, surface roughness and microhardness of composites submitted to mouthrinsing action

OBJECTIVE:The purpose of this study was to evaluate the effect of mouth rinse solutions on color stability, surface roughness and microhardness of two composite resins. MATERIAL AND METHODS: Fifty test specimens of each composite (Filtek Z250 and Z350; 3M ESPE) were made using a teflon matrix (12x2 mm). Color, surface roughness and Knoop microhardness baseline measurements of each specimen were made and specimens (n=10) were immersed in 5 mouth rinse solutions: G1: distilled water (control), G2: Plax Classic, G3: Plax alcohol-free; G4: Periogard, and G5: Listerine. Final measurements of color, roughness and microhardness were performed and the results submitted to statistical analysis (2-way ANOVA, Bonferroni s test;

Polymerization shrinkage stress of composites photoactivated by different light sources

The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated with the QTH unit. The glass rods were vertically assembled, in pairs, to a universal testing machine and the composites were applied to the lower rod. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The 20 composites were polymerized by either QTH (n=10) or LED (n=10) curing units. Polymerization was carried out using 2 devices positioned in opposite sides, which were simultaneously activated for 40 s. Shrinkage stress was analyzed twice: shortly after polymerization (t40s) and 10 min later (t10min). Data were analyzed statistically by 2-way ANOVA and Tukey's test (a=5%). The shrinkage stress for all composites was higher at t10min than at t40s, regardless of the activation source. Microfilled composite resins showed lower shrinkage stress values compared to the other composite resins. For the hybrid and microhybrid composite resins, the light source had no influence on the shrinkage stress, except for microfilled composite at t10min. It may be concluded that the composition of composite resins is the factor with the strongest influence on shrinkage stress.Este estudo comparou a contração de polimerização de resinas compostas fotoativadas por luz halógena (QTH) e diodo emissor de luz (LED). Foram confeccionados bastões de vidro (5,0 mm x 5,0 cm), e uma de suas extremidades sofreu jateamento com óxido de alumínio, sobre a qual foi aplicado um adesivo e fotoativado com luz halógena. Os bastões de vidro foram acoplados verticalmente, em pares, em uma máquina universal de ensaios (EMIC DL-2000) e as resinas compostas aplicadas no bastão inferior. A distância entre os bastões foi padronizada em 2 mm e um extensômetro foi acoplado a eles. As resinas foram fotoativadas (n=20), sendo 10 por QTH e 10 por LED utilizando dois aparelhos posicionados em lados opostos, acionados simultaneamente por 40 s. A tensão de contração foi analisada em dois momentos: logo após a polimerização (t40s) e 10 min após (t10min). A tensão de contração apresentada por todas as resinas foi maior em t10min do que em t40s, independente da fonte ativadora. A resina de micropartículas apresentou menores valores de tensão de contração com valores estatisticamente significantes em relação às demais resinas. Para as resinas híbrida e microhíbrida não houve influência da unidade ativadora sobre a tensão de contração, com exceção para a resina de micropartículas em t10min. Concluiu-se que a composição da resina composta foi o fator que mais interferiu na tensão de contração da resina composta

Influence of Pre-Heating Regular Resin Composites and Flowable Composites on Luting Ceramic Veneers with Different Thicknesses

The aim of this study was to evaluate of pre-heating, filler contents and ceramic thickness on film thickness, microshear bond strength, degree of conversion and color change on ceramic veneers. Two experimental composites were prepared (Bis-GMA/UDMA/BisEMA/ TEGDMA), with different amounts of filler (65% or 50%wt) simulating a conventional and a flowable composite. The flowable (F) was used at room temperature and, the conventional either at room temperature (C) or pre-heated (CPH). Disk-shaped ceramics with different thickness (0.4 mm, 0.8 mm, 1.5 mm) were prepared. The film thickness was evaluated according to the ISO 4049 (n=10). The microshear bond strength (n=10) was evaluated in enamel using tubing specimens light-cured through the ceramic veneer. The degree of conversion was evaluated using Raman spectroscopy. The color change of the ceramic restorations (n=10) was evaluated by spectrophotometry. The results were submitted to 2-way ANOVA and Tukey’s post hoc test (a=5%). For the film thickness 1-way ANOVA was used (a=5%). The C presented the thicker film thickness; the CPH produced a similar film thickness in comparison to the F. All composites showed similar microshear bond strength. The degree of conversion of the F was higher than the C and CPH. The degree of conversion of the composites photo-activated through a 0.4 mm was higher than the composites photo-activated through thicker ceramics. The C showed the highest color change, while the CPH showed similar color change to the F. In conclusion, pre-heated conventional composites seem to be a potential alternative to lute ceramic veneers such as the flowable composites

The Effect of Different Bleaching Treatments and Thermal-Mechanical Cycling on the Shear Bond Strength of Orthodontic Brackets

Objective:The aim of the present study was to compare the shear bond strength (SBS) of orthodontic brackets bonded to the enamel after at-home and in-office bleaching treatments.Methods:Sixty bovine incisors were subjected to initial color readings and then classified into three groups: CP (16% carbamide peroxide), HP (35% hydrogen peroxide), and C (control). After treatments, new color readout was obtained, and orthodontic brackets were bonded to the bleached area. Half of the samples of each group (n=10) were subjected to thermal-mechanical cycling (TMC) testing (1,200,000 cycles; 44.2 N; 2 Hz/s), whereas the other half were stored in distilled water at 37 °C for 24 h. Samples were subjected to the SBS test at a speed of 0.5 mm/min. The mean SBS was analyzed (two-way ANOVA, Bonferroni test, p0.05) in SBS values between the samples subjected to TMC and the cycled samples in any group. Samples subjected to carbamide peroxide presented lower SBS (p<0.05) than the non-cycled ones. Enamel adhesive fractures were higher in the bleached groups than in the control group, which presented mixed fractures prevalence, regardless of whether it was subjected to TMC or not.Conclusion:Thermal-mechanical cycling was not significant for SBS of orthodontic brackets, but tooth bleaching was a factor

Color stability, surface roughness and microhardness of composites submitted to mouthrinsing action

Objective: The purpose of this study was to evaluate the effect of mouth rinse solutions Lion color stability, surface roughness and microhardness of two composite resins. Material and Methods: Fifty test specimens of each composite (Filtek Z250 and Z350; 3M ESPE) were made using a teflon matrix (12x2 mm). Color, surface roughness and Knoop microhardness baseline measurements of each specimen were made and specimens (n=10) were immersed in 5 mouth rinse solutions: G1: distilled water (control), G2: Plax Classic, G3: Plax alcohol-free; G4: Periogard, and G5: Listerine. Final measurements of color, roughness and microhardness were performed and the results submitted to statistical analysis (2-way ANOVA, Bonferroni's test; p&lt;0.05). Results: The most significant color change was observed for Z250 when immersed in Listerine (p&lt;0.05). Z350 showed greater color change when immersed in Plax alcohol-free (p&lt;0.05), but with no significant difference for Listerine (p&gt;0.05). With regard to roughness, both composites showed significant changes when immersed in Listerine in comparison with Plax alcohol-free (p&lt;0.05). Microhardness of Z350 was shown to be significantly changed when the composite was immersed in Plax alcohol-free (p&lt;0.05). Conclusion: Composite changes depended on the material itself rather than the mouth rinse solution used