Lisia Lorea Valente

Comparative evaluation of dental resin composites based on micron- and submicron-sized monomodal glass filler particles

OBJECTIVES A model resin composite containing a novel monomodal inorganic filler system based on submicron-sized Ba-Si-Al glass particles (NanoFine NF180; Schott) was formulated and compared with an experimental composite containing micron-sized particles (UltraFine UF1.0; Schott). METHODS The filler particles were characterized using X-ray microanalysis and granulometry, while the composites were characterized in terms of filler-resin morphology, radiopacity, degree of CC conversion, hardness, flexural strength/modulus, work-of-fracture, surface roughness and gloss (before and after simulated toothbrushing abrasion), and bulk compressive creep. The composites were formulated from the same photoactivated dimethacrylate co-monomer, incorporating mass fractions of 75% micron- and 78% submicron-sized particles. Quantitative data were analyzed at a significance level of p<0.05. RESULTS Both filler systems exhibited a narrow grain size range (175±30 and 1000±200 nm), with differences restricted to the size and specific area of the particles. The composites were similar in radiopacity, flexural strength, work-of-fracture, and creep. The submicron composite was harder but had lower flexural modulus and CC conversion. No significant differences in roughness were observed before brushing, although the submicron composite had higher gloss. Brushing increased roughness and decreased gloss on both materials, but the submicron composite retained higher gloss after brushing. SIGNIFICANCE The monomodal submicron glass filler system demonstrated potential for use in restorative dental composites, particularly due to improved esthetic properties.

1,3‐Diethyl‐2‐thiobarbituric acid as an alternative coinitiator for acidic photopolymerizable dental materials

The ethyl-4-dimethylaminobenzoate (EDAB) is widely used as a coinitiator of the camphorquinone (CQ), but in acidic circumstances it might present some instability, reducing the polymerization efficiency of the material. Considering this, new coinitiators are being evaluated. Hence, this study evaluated the kinetic of polymerization (KP), the degree of conversion (DC), and the rate of polymerization (RP ) of experimental resin adhesives containing 1,3-diethyl-2-thiobarbituric acid (TBA) as a coinitiator of the CQ. The experimental monomeric blend was prepared with bisphenol A glycidyl dimethacrylate, 2-hydroxyethyl methacrylate, and acidic monomers. CQ was added at 1 mol % as photoinitiator. Six groups were formulated: four containing concentrations of 0.1, 0.5, 1, and 2 mol % of TBA, one without coinitiator, and the last one containing 1 mol % of EDAB (control group). The KP and the RP were performed using real-time Fourier Transform infrared spectroscopy. The group without coinitiator has not formed a polymer, whereas the addition of TBA resulted in the conversion of monomers in polymer. The DC of the adhesives was as higher as the increase in the TBA content. The group with 2 mol % of TBA presented improved DC and reactivity (RP ) than the other groups and the control one. Hence, the TBA has performed as a coinitiator of the CQ for the radical polymerization of methacrylate resin adhesives and it has improved the DC and the reactivity of the materials. Thus, it is a potential coinitiator for the photopolymerization of dental materials.

Application of Resin Adhesive on the Surface of a Silanized Glass Fiber–reinforced Post and Its Effect on the Retention to Root Dentin

INTRODUCTION In this study, the effect of different post surface treatments on the retention of glass fiber-reinforced post to root dentin was evaluated. The hypotheses tested were (1) post silanization would not improve its retention and (2) the application of silane plus resin adhesive on the post would enhance its retention. METHODS After root canal preparation, 4 different protocols (n = 5) of post surface treatment were evaluated, combined with or without silane (Silane coupling agent) and adhesive (Scotchbond Multipurpose): silane + adhesive (S/A), only silane, only adhesive, or no treatment (control). RelyX ARC was used for post cementation. Next, specimens were subjected to push-out bond strength testing, and data were analyzed by two-way analysis of variance and Tukey test (P < .05). RESULTS S/A showed higher bond strength than other protocols in the middle and coronal root regions (P < .001). Only silane did not enhance post retention compared with control (P > .05). The root dentin region influenced bond strength results only in the S/A group. CONCLUSIONS Whereas silanization as the only post surface treatment did not improve retention, the combination of silane plus resin adhesive enhanced post retention to dentin in the middle and coronal root regions.

Effect of Diamond Bur Grit Size on Composite Repair.

PURPOSE This study investigated the effect of diamond bur grit size on the repair bond strength of fresh and aged resin composites. MATERIALS AND METHODS Blocks of microhybrid composite (Opallis, FGM) were stored in distilled water at 37°C for 24 h (fresh composite) or subjected to 5000 thermal cycles (aged composite). The surfaces were roughened using diamond-coated, flame-shaped carbide burs with medium grit (#3168), fine grit (#3168F), or extra-fine grit (#3168FF). The control group underwent no surface treatment. Surface roughness, water contact angle, and surface topography by scanning electron microscopy (SEM) were evaluated (n = 3). Samples were restored with resin composite and sectioned into beam-shaped specimens, which were subjected to microtensile bond testing. Failure modes were classified using a stereomicroscope. Data were statistically analyzed using the Student- Newman-Keuls test and two-way ANOVA, with significance set at p < 0.05. RESULTS Higher surface roughness was observed for groups treated with the medium- and fine-grit burs; aged composites were rougher than fresh composites. The water contact angle formed on the aged composite was lower than that on the fresh composite. The highest repair bond strength was observed for the fine-grit bur group, and the lowest was recorded for control. Interfacial failures were more predominant. SEM images showed that the surfaces treated with fine- and extra-fine-grit burs had a more irregular topography. CONCLUSION Surface roughening of fresh or aged resin composites with diamond burs improved retention of the repair material. Fine-grit burs generally performed better than medium- and extra-fine-grit burs.

Effect of elastomeric monomers as polymeric matrix of experimental adhesive systems: degree of conversion and bond strength characterization

The aim of this study was to characterize the degree of conversion and the bond strength of experimental adhesive systems formulated with elastomeric monomers (Exothanes). Two-step self-etch adhesive systems were formulated, where the primer was constituted by HEMA, HEMA-P, water and ethanol, and the resin bonds were prepared mixing one type of Exothane (8, 9, 10, 24, or 32) (75 wt%) with TEGDMA (25 wt%). CQ, EDAB, and DPI were added as photo-initiation system. UDMA was used as control, so six different resin bonds were formulated at all. The adhesive system Clearfil SE Bond (CLSE) was used as a commercial control. The degree of conversion (DC) of each resin bond was evaluated in infrared spectroscopy (RT-FTIR, Shimadzu Prestige-21) using a diamond crystal (n = 3). The microshear bond strength (μSBS) test was performed using a universal testing machine (EMIC DL-500). While the DC data was analyzed by one-way ANOVA and Tukey (p < 0.05), the μSBS data was analyzed by Kruskal-Wallis test and Student-Newman-Keuls (p < 0.05). The resin bonds containing the Exothanes 8, 9, and 32 demonstrated DC values higher than 80%, differently to the other Exothane-based adhesives, which showed DC values close to 50%. UDMA and CLSE demonstrated lower DC than E8, E9, and E32 (p < 0.001). The Exothane 24 resulted in the lowest DC value of the study (p < 0.001), although it was similar to the E10 and UDMA adhesives (p > 0.05). Low μSBS results were seen for the Exothane-based materials. CLSE demonstrated significantly higher bond strength than the other materials (p < 0.001). UDMA has also presented low μSBS to the dentin substrate. It can be concluded that the Exothanes evaluated demonstrated satisfactory degree of conversion, with some of them reaching almost full conversion of monomers in polymer. However, considering the formulations investigated, they were not good bonding agents. So, they were not reliable options for composing the polymeric matrix of dental adhesive materials.

The Effect of Time between Handling and Photoactivation on Self-Adhesive Resin Cement Properties

PURPOSE To evaluate the degree of conversion, absorption, and solubility in water of self-adhesive resin cements subjected to different time intervals between material preparation and the photoactivation procedure. MATERIALS AND METHODS Two dual self-adhesive resin cements were tested: RelyX Unicem and SmartCem2. The degree of conversion as a function of time was evaluated by Fourier-transformed infrared spectroscopy using the attenuated total reflectance technique. Three time intervals between handling and photoactivation were applied: Group 1 = immediately; Group 2 = a 1-minute interval; Group 3 = a 4-minute interval. All specimens were irradiated with a light-emitting diode source for 40 seconds. Thirty discs of each cement (1 mm thick × 6 mm diameter, n = 10) were prepared for the absorption and solubility tests. These specimens were stored in distilled water at 37°C for 90 days. The results were subjected to ANOVA with two factors (material and activation time intervals) and Tukeys test (95% significance). RESULTS The 4-minute interval significantly reduced the degree of conversion of SmartCem2 (30.6% ± 8.3%). No other significant changes were observed for the degree of conversion; however, the time intervals before photoactivation interfered significantly in the water absorption of the RelyX Unicem specimens but not the SmartCem2 specimens. The time intervals did not affect the solubility of either cement. In all cases, SmartCem2 had higher solubility than RelyX Unicem. CONCLUSION The time interval between handling and photoactivation significantly influenced the degree of conversion and water sorption of the resin-based cements. In general, one can say that the self-adhesive resin cements should be photoactivated as soon as possible after the material handling process.

Experimental methacrylate-based primers to improve the repair bond strength of dental composites – a preliminary study

In this study, experimental resin-based primers with varying concentrations of acidic methacrylate were formulated and tested as to their potential in improving the repair bond strength of an aged dental composite resin. The photocurable primers contained (wt%) methacrylate monomers (20-60%), acidic methacrylate (0-40%), silane coupling agent (10%), and ethanol (30%). The pH of the solutions varied between 4.8 and 0.31. The degree of C = C conversion of the primers, measured using Fourier transform infrared spectroscopy, varied between 22% and 42%, with a linear decrease in conversion associated with increased concentration of acidic methacrylate (R2 = 0.961; p < 0.01). Composite resin blocks aged using 1000 thermalcycles served as substrate for the repair bond strength test. The primers were vigorously applied to the composite surfaces and a silicone mold with cylindrical orifices was placed onto the surface. The orifices were filled with fresh composite resin (simulating the repair). In the control group, no primer was applied. A shear bond test was conducted after 24 h (n = 16 per group). Failure modes were classified under magnification. Data were statistically analyzed at p < 0.05. Repair bond strength values varied between 7.2 and 26.5 MPa. The control group had lower bonding ability than all primed groups. The increased content of acidic methacrylate had no significant association with bond strengths. In the control group only interfacial failures were detected, whereas cohesive failures within the aged composite were observed in the primed groups. In conclusion, application of methacrylate-based primers might improve the repair bond strength of dental composite resins. The concentration of acidic methacrylate on the primer had no significant effect on the immediate repair potential.

Bleaching and enamel surface interactions resulting from the use of highly-concentrated bleaching gels

Tooth bleaching is considered a non-invasive treatment, although the use of highly-concentrated products may provoke increased surface roughness and enamel demineralization, as well as postoperative sensitivity. Thus, the aim of this study was to investigate whether hydrogen peroxide (H2O2) concentration would affect tooth bleaching effectiveness and the enamel surface properties. Enamel/dentin bovine specimens (6 × 4 mm) were immersed in coffee solution for 7 days and evaluated with a spectrophotometer (Easyshade; baseline), using the CIEL*a*b* color parameters. Hardness was measured using a hardness tester. The specimens were randomly assigned into four groups: one negative control, in which the specimens were not bleached, but they were irradiated with a laser-light source (Whitening Lase II, DMC Equipments); and three groups using distinct H2O2 concentration, namely LP15% (15% Lase Peroxide Lite), LP25% (25% Lase Peroxide Sensy), and LP35% (35% Lase Peroxide Sensy), all products from DMC. The bleached specimens were also irradiated with the laser-light source. After bleaching, all specimens were evaluated using scanning electron microscopy (SEM). pH kinetics and rate was monitored during bleaching. The data were analyzed using ANOVA and Tukeys test (p < 0.05). All bleaching gels produced similar color change (p > 0.05). Concerning hardness, only the LP25% and LP35% significantly reduced hardness after bleaching; also, there was a progressive tendency for a greater percentage reduction in hardness with increased H2O2 concentration of the gel (R2 = 0.9973, p < 0.001). SEM showed that LP25% and LP35% produced an etching pattern on enamel with prism rods exposure. In conclusion, H2O2 concentration above the 15% level does not increase bleaching effectiveness, and may increase the possibility for alteration of enamel hardness, surface morphology, and acidity of the medium. When using H2O2-based bleaching agents, dental practitioners should choose for less concentrated gels, e.g., around the 15% level.

Repair bond strength of resin composite with experimental primers – effect of formulation variables

Abstract The aim of this study was to prepare experimental resin-based primers with varied components (silane – S, polyacrylic acid – PA, or methacrylic acid – MA) and evaluate their repair bonding ability to resin composite. Primers were prepared containing methacrylate monomers, acidic monomer, ethanol, photoinitiators and 0, 10, or 20 wt% of S, PA, or MA. Degree of C=C conversion and pH were measured. Composite blocks (Opallis, FGM) were aged by 5000 thermal cycles and composite cylinders (repairs) were built up on their surfaces. The cylinders were tested under shear stress after 24 h. Failure modes were classified under magnification. Data were statistically analyzed at α = 0.05. Primers containing MA were the most acidic compositions, whereas S-containing primers were less acidic. Incorporation of 20 wt% of the varied components decreased C=C conversion. PA-based primers had higher C=C conversion than MA-based materials. Repair bond strength results were dependent on the component added and its concentration. MA-based primers presented higher bond strength than primers containing PA. Cohesive failures within composite were predominant for S-based primers, whereas mixed failures were more prevalent for PA-based primers. In conclusion, the overall best repair abilities were observed for primers containing 10 wt% of the components tested.

Conservative dentistry: non-beveled esthetic restorations in anterior teeth

The pursuit of esthetic excellence in dentistry today requires dental practitioners to enhance their knowledge and technique in restorations of the anterior teeth. Due to the high incidence and prevalence of fractures in this dental area, mimicking the optical properties and characteristics of the dental structure in young patients (aged 6 to 15 years) is a major challenge. This case report describes the minimally invasive, non-beveled restoration of two fractured anterior teeth (class IV). After diagnosing fractures of teeth 11 and 21 in a 10-year-old patient, a composite mock-up was performed, followed by a diagnostic wax-up. With the aid of a silicon guide, the restorations were prepared without beveling the enamel surface. We performed color stratification by using different types of composite resins. Finally, finishing and polishing procedures were carried out.