Lívia Rodrigues de Menezes

Effect of Nanofiller Loading on Cure Efficiency and Potential Color Change of Model Composites

OBJECTIVES To evaluate the effect of nanofiller loading on cure efficiency and potential color change of experimental composites. MATERIALS AND METHODS Four different polymeric materials were produced using the same organic matrix blend. To this matrix, different amounts of 0.05 μm fumed silica filler were added: no filler, 13, 52, and 65wt%. Fourier transform infrared spectroscopy was used to evaluate the degree of conversion (DC) for each composite using near-IR analysis, and spectrophotometry according to CIELab chromatic space was used to evaluate the color change.To induce color change, composites were artificially aged with exposure to cycles of UV-B light for 300 hours. Trasmission electron microscopy was used to illustrate nanoffiler aglomeration in the resin matrix. Data were analyzed using correlation analysis (α = 0.05). RESULTS There was an excellent inverse linear correlation between filler wt% and either DC or color change. Greater changes to red (+Δa) and yellow (+Δb) were observed as the filler wt% increased. CONCLUSIONS A higher percentage of nano-sized filler particles in dental resin composites directly affects their cure efficiency and potential for color change. CLINICAL SIGNIFICANCE The increase in filler particle loading negatively affected monomer conversion and color stability of resin-based composites. As reduced filler loading results in poorer mechanical properties, to enhance color stability, resin-based composites should be formulated by making the refractive index of the polymeric matrix more closely match that of the filler throughout the polymerization process. (J Esthet Restor Dent, 2016).

The Use of Montmorillonite Clays as Reinforcing Fillers for Dental Adhesives

The aim of this study was to obtaining an adhesive made of dimethacrylate copolymer and clay particles in different concentrations. The samples were prepared by light curing and were evaluated by XRD, FTIR and TGA as well as by measuring flexural strength, elasticity modulus and tensile resistance. The XRD and the mechanical test results indicated that the system with 0.2% clay is exfoliated, while the highest concentrations showed the agglomeration of these clays. FTIR was used to determine the conversion, and showed that use of clays particles are unable to significantly alter the polymerization until 1.0%. However, for the group containing 1.5%, there was a decline in this index. In the thermogravimetric analysis, only the groups with 0.2% of clays showed increased thermal resistance. In conclusion, the incorporation of clay at 0.2% concentration produces a well-dispersed system and can be applied as a dental adhesive.

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.

The applicability of organomodified nanoclays as new fillers for mechanical reinforcement of dental composites

Objectives This study reports the evaluation of changes in crosslink structure and mechanical properties of dental microhybrid composite reinforced with clays when compared to silica nanofillers, which are already extensively used for this application. Materials and methods A standardized resin matrix with a glycerolate dimethacrylate, triethylene glycol dimethacrylate, and urethane dimethacrylate copolymers associated with a camphorquinone photoinitiator system was blended with 75 wt% filler content. As fillers, two organically modified clays (hydrophilic silica and organomodified silica) and a boron-aluminum-silicate glass with 4 µm were used to obtain nanohybrid nanocomposites. The samples were prepared by light curing and were evaluated by measuring flexural strength, elasticity modulus, hardness, tensile resistance, and crosslinking. Results The mechanical test results indicated that the system with 2.5% clay was better dispersed in the system, while the highest concentrations caused agglomeration of these clays. On the other hand, the silicas showed gradual gain in properties. The increase in concentration of all nanofillers reduced the crosslinking ability of the systems. This behavior can be explained because the clay’s presence makes the reaction medium more viscous or because the fillers act as points of light absorption and scattering.