Maria Cecília Caldas Giorgi

Influence of Water Storage and Bonding Material on Bond Strength of Metallic Brackets to Ceramic

This study investigated the influence of water storage (24 h and 6 months), and Transbond XT and Fuji Ortho LC bonding materials on the bond strength of metallic brackets bonded to feldspathic ceramic. Four cylinders of feldspathic ceramic were etched with 10% hydrofluoric acid for 60 s. Each cylinder received two layers of silane. Metallic brackets were bonded to the cylinders using Transbond XT or Fuji Ortho LC. Light-activation was carried out with 40 s total exposure time using Bluephase G2. Half the specimens for each bonding materials (n=20) were stored in distilled water at 37 °C for 24 h and the other half for 6 months. Shear bond strength testing was performed after storage times at a crosshead speed of 1 mm/min. The adhesive remnant index (ARI) was used to evaluate the amount of adhesive remaining on the ceramic surface at ×8 magnification. Data were subjected to two-way ANOVA and Tukeys test (p<0.05). Transbond XT showed significantly higher bond strength (p<0.05) than Fuji Ortho LC. Significant differences in bond strength (p<0.05) were found when 24 h and 6 months storage times were compared between materials. ARI showed a predominance of score 0 for all groups, and higher scores at 1, 2 and 3 for 24 h storage time. In conclusion, storage time and bonding materials showed significant influence on the bond strength of brackets to ceramic.

In vitro evaluation of the effect of different polishing techniques on the surface roughness of composite resins submitted to at-home and in-office bleaching procedures

Objective: Bleaching agents may affect the properties of dental materials. The aim of this study was to evaluate the effect of different polishing techniques on the surface roughness of composite resins submitted to the at-home and in-office bleaching treatment. Materials and Methods: Disc-shaped specimens were carried out of nanofilled and microhybrid composites (n = 10). Finishing step was performed after light curing (L1) and polishing after 24 h with two systems (L2). Then, specimens were submitted to the home or in-office bleaching procedures, and roughness was re-evaluated (L3). The surface roughness (Ra) readings were measured at L1, L2, and L3 times using a profilometer. Data were statistically analyzed by multiple-way analysis of variance and Tukey test (α = 0.05). Results: The polishing procedures decreased Ra for both composites compared to baseline values (L1). The roughness of specimens polished with jiffy did not present significant difference after polishing step (L2) and bleaching treatment (L3). However, the groups polished with Sof-Lex discs had increase on the Ra values after bleaching. Conclusion: The polishing is an important procedure to reduce the roughness of dental restorations and composite surface polished with jiffy system improved the degradation resistance to the bleaching agents compared to Sof-Lex discs.

Influence of softening test and light-activation protocols on resin composite polymer structure.

Objective: This study analyzed the influences of the light-activation protocol and softening test on the degree of conversion (DC) and Knoop Hardness (KHN) of a microhybrid resin composite. Materials and Methods: Filtek Z250 (3M ESPE) was light-activated with a third-generation light-emitting diode (Valo Ultradent) by three protocols - standard, high power, and plasma emulation - or with a quartz-tungsten halogen XL 3000 (3M ESPE) in conventional mode. All modes were set to deliver 19 J/cm 2 . The DC (N = 20) was determined by Fourier transform infrared spectrometry on the top (T) and bottom (B) surfaces. For the KHN test, samples were subdivided in four groups (n = 5 each) according to the storage media: absolute ethanol, 75% ethanol, distilled water, and air (control group). The KHN values were evaluated on T and B before and 24 h after immersion in the storage media. Data were analyzed by split-plot analysis of variance (ANOVA; for DC) or repeated-measures split-plot ANOVA (for KHN), followed by Tukey′s test (α = 0.05). Results: For the DC, the light-activation protocol did not influence the results and there was no difference between T and B. For the KHN test, the light-activation protocol did not influence the results and T showed higher microhardness values than B for all experimental conditions. There were significant differences in KHN depending on the storage media. Samples immersed in absolute ethanol generally presented lower KHN values, with no differences compared to samples in 75% ethanol. Conclusion: The storage media affected the outcomes of the softening test.

Effect of energy density and delay time on the degree of conversion and Knoop microhardness of a dual resin cement.

AIM In the present study, we evaluated the influence of the photo-curing delay time and energy density on the degree of conversion and the Knoop microhardness of a resin cement. METHODS Seventy-eight samples were assigned to 13 groups (n = 6), one of which received no light curing (control). The samples were made of a dual-cured resin cement (RelyX ARC) with the aid of a Teflon matrix, submitted to one of the following energy densities (J/cm²): 7, 14, 20, and 28. Delay times were immediate (0), 1 min, or 2 min. After 24 h, the degree of conversion and microhardness were measured at three segments: cervical, medium, and apical. Data were submitted to three-way anova and Tukeys and Dunnetts tests, the latest of which was used to compare the control to the experimental groups. RESULTS No interaction was observed between delay time and energy density regarding the degree of conversion. The cervical segment showed the highest values, while the apical showed the lowest. Microhardness values concerning the cervical segment in all groups were statistically different from that obtained for the control. CONCLUSION A high-irradiance light-curing unit allows for a reduced irradiation exposure time with a short delay time, aimed at tooth restorations using a dual-cured resin cement.

Effect of different monomer-based composites and acid etching pre-treatment of enamel on the microleakage using self-etch adhesives systems

Abstract Objective. To evaluate quantitatively the marginal microleakage of restorations carried out with self-etching adhesives with or without prior phosphoric enamel acid etching of silorane or methacrylate resin-based composite restorations subjected to thermal cycling. Materials and methods. Forty cavities were prepared at the proximal surface of bovine incisors and randomly divided according to the etching of the enamel and restorative system used. The groups were restored with methacrylate [Adper SE Plus adhesive (3M ESPE) + Filtek Z250 (3M ESPE)] or silorane [Filtek LS adhesive (3M ESPE) + Filtek LS composite (3M ESPE)] restorative systems, light-cured using a LED unit (Bluephase 16i, Vivadent). After restorative procedure and thermocycling (1000 cycles), the specimens were immersed in methylene blue for 2 h. The specimens were triturated and the powder was used for analysis in an absorbance spectrophotometer. Data were statistically analyzed by 2-way ANOVA (alpha = 0.05). Results. No statistical difference between the restorative materials tested with or without previous acid etching of enamel in Class II marginal microleakage was observed (p > 0.05). Conclusions. The use of acid etching prior to self-etching adhesives did not interfere on the microleakage of methacrylate- or silorane-based restorations.

Curing Quality of Composites as Influenced by the Filler Content, Light Source and Curing Time

The quality of composite polymerization has been of great concern for researchers. Curing of nanocomposites under long distance (8 mm) and extended light exposure through conventional (halogen and LED) and argon laser lamps is unclear in the literature. This study evaluated the influence of curing modes and filler particle size on hardness and degree of conversion of dental composites photo activated at an 8 mm distance. Light sources (LED 1100 mW/cm2-Bluephase; LED 700 mWcm2-Ultra-lume; halogen lamp 450 mW/cm2-XL3000; and argon-laser 500 mW/cm2-AccuCure), curing times (20 and 60 s), microhybrid (Filtek-Z250) and nanofilled (Filtek-Supreme) resins were investigated. Eighty samples (n=5) were made using Teflon molds. Hardness and degree of conversion were obtained for bottom/top surfaces of 2-mm increments. Data were submitted to ANOVA and Tukey tests (?=5%).Top surfaces showed similar hardness. A 60s exposure time increased bottom hardness and Filtek-Z250 showed higher hardness for curing units except Bluephase. Regarding degree of conversion, bottom/top surfaces showed similar means at 60s; at 20s, bottom/top surfaces revealed similar means only for Filtek-Z250 cured by Bluephase and Ultra-lume. High irradiance and extended exposure time can improve hardness and conversion on bottom surface. Microhybrid resin presented better conversion of monomers than the nanofilled composite under higher irradiance and extended exposure times.

Influence of successive light-activation on degree of conversion and knoop hardness of the first layered composite increment

Abstract Purpose: To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. Materials and methods. Forty samples (n = 5) were prepared. In groups 1–4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5–8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm2 × 38 s (G1/G5); (S) 1000 mW/cm2 × 19 s (G2/G6), (HP) 1400 mW/cm2 × 14 s (G3/G7); (PE) 3200 mW/cm2 × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). Results. For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to first, third and fourth increments. For DC, except QTH, T presented higher DC than B. Conclusion. The light-activation of successive increments was not able to influence the KHN and DC of the first increment.

Influence of a hydrophobic monomer on the physical and mechanical properties of experimental surface sealants

This study evaluated the effect of adding the hydrophobic monomer 1,12 dodecanediol dimethacrylate (DDDMA) to experimental sealants with and without thermocycling on degree of conversion (DC), water sorption (WS), water solubility (WSB), color stability (ΔE), and micro-shear bond strength (μSBS). Five experimental and one commercially available sealant (Bisco - BIS) were tested. The experimental sealants were formulated by mixing different percentages of DDDMA monomers and urethane dimethacrylate (UDMA). The photoinitiator system was composed by camphorquinone (CQ) and tertiary amine 4-ethyl benzoate dimetilamiono (EDBA). Ethanol was used as a solvent. The experimental groups were named sequentially according to the monomeric content (DDDMA/UDMA): S40/40 (40/40), S50/30 (50/30), S60/20 (60/20), S70/10 (70/10) and S80/0 (80/0). Data were analyzed separately by one-way ANOVA, followed by Tukeys test (p<0.05). The values of DC ranged from 94.59% (S40/40) to 54.02% (S80/10). BIS showed the highest WS value (p<0.05) and S40/40, S50/30, S60/20 and S80/0 showed the lowest WS values of all tested sealants. WSB values ranged from 7.88 µg/mm3 (BIS) to 13.27 µg/mm3 (S70/10). The highest ΔE value was 11.05±2.88 for BIS and the highest μSBS value was found for S60/20. No significant difference was observed in bond strength between sealants and bovine enamel after thermocycling. Adding DDDMA to the composition of surface sealants can improve its performance, once the monomer increased the degree of conversion and the color stability.