Igor Studart Medeiros

Effect of different polishing systems on the surface roughness of microhybrid composites

The use of composite resins in dentistry is well accepted for restoring anterior and posterior teeth. Many polishing protocols have been evaluated for their effect on the surface roughness of restorative materials. This study compared the effect of different polishing systems on the surface roughness of microhybrid composites. Thirty-six specimens were prepared for each composite [Charisma® (Heraeus Kulzer), Fill Magic® (Vigodent), TPH Spectrum® (Dentsply), Z100® (3M/ESPE) and Z250® (3M/ESPE)] and submitted to surface treatment with Enhance® and PoGo® (Dentsply) points, sequential Sof-Lex XT® aluminum oxide disks (3M/ESPE), and felt disks (TDV) combined with Excel® diamond polishing paste (TDV). Average surface roughness (Ra) was measured with a mechanical roughness tester. The data were analyzed by two-way ANOVA with repetition of the factorial design and the Tukey-Kramer test (p<0.01). The F-test result for treatments and resins was high (p<0.0001 for both), indicating that the effect of the treatment applied to the specimen surface and the effect of the type of resin on surface roughness was highly significant. Regarding the interaction between polishing system and type of resin used, a p value of 0.0002 was obtained, indicating a statistically significant difference. A Ra of 1.3663 was obtained for the Sof-Lex/TPH Spectrum interaction. In contrast, the Ra for the felt disk+paste/Z250 interactions was 0.1846. In conclusion, Sof-Lex polishing system produced a higher surface roughness on TPH Spectrum resin when compared to the other interactions.

Effect of experimental heat treatment on mechanical properties of resin composites

The aim of this study was to verify the influence of an experimental heat treatment (170 masculineC/10 min) using a casting furnace on the mechanical properties (hardness and flexural strength) of 2 commercial direct resin composites (TPH Spectrum and Filtek P60) compared to a commercial indirect resin system (BelleGlass). Heat treatment temperature was determined after thermal characterization by thermogravimetry (TG) and differential scanning calorimetry (DSC). Data was analyzed by ANOVA and Tukeys test at 5% significance level. There was statistical significance for the main factor heat treatment (p=0.03) and composite (p=0.02), for flexural strength. For Knoop hardness, only the main factor composite was statistically significant (p=0.00). P60 presented higher hardness than TPH. No statistically significant correlation between mechanical properties tested was detected. Based on these results, it was possible to conclude that heat treatment influenced flexural strength of direct composites, while it was not observed for hardness. The association of direct composites with a simple post-cure heat treatment may be an alternative for current indirect composite systems, although more studies are needed to verify other properties of the composites for this application.

Heat treatment of a direct composite resin: influence on flexural strength

The purpose of this study was to evaluate the flexural strength of a direct composite, for indirect application, that received heat treatment, with or without investment. One indirect composite was used for comparison. For determination of the heat treatment temperature, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed, considering the initial weight loss temperature and glass transition temperature (Tg). Then, after photoactivation (600 mW/cm(2) - 40 s), the specimens (10 x 2 x 2 mm) were heat-treated following these conditions: 170 masculineC for 5, 10 or 15 min, embedded or not embedded in investment. Flexural strength was assessed as a means to evaluate the influence of different heat treatment periods and investment embedding on mechanical properties. The data were analyzed by ANOVA and Tukeys test (alpha = 0.05). TGA showed an initial weight loss temperature of 180 masculineC and DSC showed a Tg value of 157 degrees C. Heat treatment was conducted in an oven (Flli Manfredi, Italy), after 37 degrees C storage for 48 h. Flexural strength was evaluated after 120 h at 37 degrees C storage. The results showed that different periods and investment embedding presented similar statistical values. Nevertheless, the direct composite resin with treatments presented higher values (178.7 MPa) compared to the indirect composite resin (146.0 MPa) and the same direct composite submitted to photoactivation only (151.7 MPa). Within the limitations of this study, it could be concluded that the heat treatment increased the flexural strength of the direct composite studied, leading to higher mechanical strength compared to the indirect composite.

Al2O3/GdAlO3 fiber for dental porcelain reinforcement

The aim of this study was to test the hypothesis that the addition of continuous or milled GdAlO3/Al2O3 fibers to a dental porcelain increases its mechanical properties. Porcelain bars without reinforcement (control) were compared to those reinforced with long fibers (30 vol%). Also, disk specimens reinforced with milled fibers were produced by adding 0 (control), 5 or 10 vol% of particles. The reinforcement with continuous fibers resulted in significant increase in the uniaxial flexural strength from 91.5 to 217.4 MPa. The addition of varied amounts of milled fibers to the porcelain did not significantly affect its biaxial flexural strength compared to the control group. SEM analysis showed that the interface between the continuous fiber and the porcelain was free of defects. On the other hand, it was possible to note the presence of cracks surrounding the milled fiber/porcelain interface. In conclusion, the reinforcement of the porcelain with continuous fibers resulted in an efficient mechanism to increase its mechanical properties; however the addition of milled fibers had no significant effect on the material because the porcelain was not able to wet the ceramic particles during the firing cycle.

Effect of light-activation methods and water storage on the flexural strength of two composite resins and a compomer

The present study evaluated the flexural strength of three composite resins recommended for direct esthetic restorations: a polyacid modified composite (Dyract AP), a unimodal composite resin (Filtek Z250) and a hybrid composite resin (Point 4). The variation factors, apart from the type of composite resin, were the light activation method and the water storage period. The composite resins were light-cured in continuous mode (40 s, 500 mW/cm2) or in ramp mode (0-800 mW/cm2 for 10 s followed by 30 s at 800 mW/cm2) and stored for 24 hours or 30 days in distilled water at 37 degrees C. The data were analyzed by ANOVA and Tukey test for multiple comparisons (alpha = 0.05). The composite resin Z250 presented the highest mean flexural strength (166.74 MPa) and Dyract AP presented the lowest one (129.76 MPa). The storage for 30 days decreased the flexural strength in ramp mode (24 h: 156.64 MPa; 30 days: 135.58 MPa). The light activation method alone did not lead to different flexural strength values.

Effect of adhesion boosters on indirect bracket bonding

OBJECTIVE To determine the influence of two adhesion boosters on shear bond strength and on the bond failure location of indirectly bonded brackets. MATERIALS AND METHODS Sixty bovine incisors were randomly divided into three groups (n = 20), and their buccal faces were etched using 37% phosphoric acid. In group 1 (control), brackets were indirectly bonded using only Sondhi adhesive. In groups 2 and 3, the adhesion boosters Enhance Adhesion Booster and Assure Universal Bonding Resin, respectively, were applied before bonding with Sondhi. Maximum bond strength was measured with a universal testing machine, and the location of bond failure was evaluated using the Adhesive Remnant Index (ARI). One-way analysis of variance followed by the Tukey test (P < .05) was used to compare the shear bond strength among groups, and the differences in ARI scores were evaluated using the Kruskal-Wallis test (P < .05). The Pearson correlation coefficient was calculated to determine whether there was any correlation between bond strength and ARI scores. RESULTS The mean shear bond strength in group 3 was significantly higher (P < .01) than in the other groups. Evaluation of the locations of bond failure revealed differences (P < .05) among the three groups. There was a moderate correlation between bond strength and ARI scores within group 3 (r  =  0.5860, P < .01). CONCLUSION In vitro shear bond strength was acceptable in all groups. The use of the Assure adhesion booster significantly increased both the shear bond strength of indirectly bonded brackets and the amount of adhesive that remained on the enamel after bracket debonding.

Effect of lingual enamel sandblasting with aluminum oxide of different particle sizes in combination with phosphoric acid etching on indirect bonding of lingual brackets

OBJECTIVE To compare bond strength and bond failure location of lingual brackets indirectly bonded after lingual enamel sandblasting with 27-, 50-, and 90-µm aluminum oxide particles followed by 37% phosphoric acid etching. MATERIAL AND METHODS Eighty maxillary premolars were randomly divided into four equal groups according to the method of lingual enamel surface conditioning: Group 1 (control) was etched with 37% phosphoric acid, and group 2, group 3, and group 4 were sandblasted with 27-, 50-, and 90-µm aluminum oxide particles, respectively, prior to acid etching. Lingual brackets were indirectly bonded using the same protocol and adhesive (Sondhi) in all groups. The maximum shear bond strength required to debond the brackets was measured using a testing machine, and the bond failure location was classified according to the adhesive remnant index (ARI). Analysis of variance was used to compare the mean bond strength between groups. The differences between ARI scores were evaluated using the Kruskal-Wallis test. RESULTS There were no statistically significant differences in mean shear bond strength or ARI scores between the four enamel-conditioning procedures. CONCLUSION Lingual enamel sandblasting using different particle sizes of aluminum oxide prior to phosphoric acid etching did not increase the shear bond strength of indirectly bonded brackets and did not affect the amount of adhesive remnant on the enamel.

Influence of Prolonged use of Desensitizing Dentifrices on Dentin Bond Strength of Self-Etching Adhesive System

La hipersensibilidad dentinaria es una condicion clinica relativamente comun, que afecta a una gran parte de la poblacion mundial. El objetivo fue evaluar la influencia del tratamiento previo y prolongado con dentifricos desensibilizantes (DD) en fuerza de adhesion a la dentina, que promueve un sistema adhesivo de autograbado. Se utilizaron 70 incisivos bovinos no cariados, y se dividieron en cinco grupos (n= 14), de acuerdo con la pasta de dientes desensibilizante utilizada: G1: agua destilada (agua) (control), G2: Colgate Total 12 (CT12) (control), G3: Colgate Sensitive Pro-Alivio (CSPR), G4: Sensodyne Rapido Alivio (SRR) y G5: Sensodyne Repair & Protect (SRP). Los dientes tenian sus superficies bucales aplanadas hasta la exposicion de la dentina, y se obtuvieron fragmentos de 4x4x2 mm. Los fragmentos se incluyeron en cilindros de cloruro de polivinilo y se expusieron a 17 % de EDTA durante un 1 min. Despues, las muestras se sometieron a 20 000 ciclos de cepillado dental simulado. Despues de 24 h en saliva artificial, las muestras se hibridaron (Clearfil SE Bond - Kuraray), y cilindros de resina compuesta fueron construidos sobre superficies de dentina. Las muestras se almacenaron en agua destilada, a 37 °C durante 24 h y luego se determino la resistencia al cizallamiento. El mayor valor de resistencia a la union (MPa) se observo en el grupo CT12 (4,39), y el menor en el grupo CSPR (3,34). Los datos fueron analizados estadisticamente mediante ANOVA de un factor 1 (ð= 0,05), y los resultados no mostraron diferencias significativas (p= 0,5986) teniendo en cuenta el factor de los DD. El patron de fractura predominante sobre la dentina fue el cohesivo. El uso previo y prolongado de diferente DD no afecto resistencia de union a la dentina promovido por un sistema adhesivo de autograbado.

Effect of Glaze Cooling Rate on Mechanical Properties of Conventional and Pressed Porcelain on Zirconia

The aim of this study was to characterize a conventional and a pressed porcelain for zirconia core as to biaxial flexural strength (BFS), apparent fracture toughness (FT) and microstructure composition, and to investigate the effect of glaze cooling rate on the BFS of the zirconia/porcelain bilayers. Monolayers of conventional porcelain Vita VM9 and pressed porcelain Vita PM9 (n=15) (12 mm diameter x 1.2 mm thick) were prepared for the BFS test (MPa). Apparent fracture toughness (MPa.m1/2) was measured by indentation technique (n=15). t-Student test was performed for statistical analysis. Scanning electron microscopy and x-ray diffraction were used to analyze the porcelains microstructure. For the BFS of bilayers, zirconia discs (12 mm diameter x 1 mm thick) (Vita In-Ceram YZ) were veneered with the two porcelains (1 mm thick). After the glaze firing simulation, the specimens were submitted to fast or slow cooling (n=15). Apparent fracture toughness (MPa.m1/2) was measured on the porcelain surface of bilayers (n=15) and residual stress was calculated. Two-way ANOVA (porcelain and cooling method) was used for the bilayer analysis (a=0.05). Vita PM9 monolayer exhibited significantly higher BFS (p<0.01), but there was no significant difference (p=0.41) in the FT between the porcelains. For bilayer specimens, the two-way ANOVA for BFS was significant for the porcelain variable only (p<0.01) better for Vita PM9/zirconia. Two-way ANOVA for the FT for the bilayers was not significant for any variable. All groups showed compressive residual stresses. The pressed porcelain seems to be mechanically more effective for zirconia veneering.

Influence of different methods of cleaning custom bases on the shear bond strength of indirectly bonded brackets

Objective To determine the influence on shear bond strength and bond failure location of four cleaning methods for orthodontic bracket custom bases. Design In vitro laboratory study. Material and methods Eighty bovine teeth were divided at random into four groups. The bracket custom bases were cleaned with different methods: group 1 with methyl methacrylate monomer, group 2 with acetone, group 3 with 50 μm aluminium oxide particles and group 4 with detergent. The brackets were indirectly bonded onto the teeth with the Sondhi Rapid-Set self-curing adhesive. The maximum required shear bond strength to debond the brackets was recorded. The bond failure location was evaluated using the Adhesive Remnant Index (ARI). One-way analysis of variance (ANOVA) analysis (P<0·05) was used to detect significant differences in the bond strength. Kaplan–Meier survival plots and log-rank test were done to compare the survival distribution between the groups. The Kruskal–Wallis test (P<0·05) was used to evaluate the differences in the ARI scores. Results The mean bond strengths in groups 1, 2, 3 and 4 were 23·7±5·0, 25·3±5·1, 25·6±3·7 and 25·7±4·2 MPa, respectively. There were no significant statistically differences in either the bond strength or the ARI score between the groups. Conclusion The four custom base-cleaning methods presented the same efficiencies on indirect bond of the brackets; thus, practitioners can choose the method that works best for them.