Remineralizing amorphous calcium phosphate based composite resins: the influence of inert fillers on monomer conversion, polymerization shrinkage, and microhardness.

AIM: To determine if the addition of inert fillers to a bioactive dental restorative composite material affects its degree of conversion (DC), polymerization shrinkage (PS), and microhardness (HV). METHODS: Three amorphous calcium phosphate (ACP)-based composite resins: without added fillers (0-ACP), with 10% of barium-glass fillers (Ba-ACP), and with 10% of silica fillers (Si-ACP), as well as commercial control (Ceram•X, Dentsply DeTrey) were tested in laboratory conditions. The amount of ACP (40%) and the composition of the resin mixture (based on ethoxylated bisphenol A dimethacrylate) was the same for all ACP materials. Fourier transform infrared spectroscopy was used to determine the DC (n=40), 20 min and 72 h after polymerization. Linear PS and Vickers microhardness (n=40) were also evaluated. The results were analyzed by paired samples t test, ANOVA, and one-way repeated measures ANOVA with Student-Newman-Keuls or Tukey's post-hoc test (P=0.05). RESULTS: The addition of barium fillers significantly increased the DC (20 min) (75.84±0.62%) in comparison to 0-ACP (73.92±3.08%), but the addition of silica fillers lowered the DC (71.00±0.57%). Ceram•X had the lowest DC (54.93±1.00%) and linear PS (1.01±0.24%) but the highest HV (20.73±2.09). PS was significantly reduced (P<0.010) in both Ba-ACP (1.13±0.25%) and Si-ACP (1.17±0.19%) compared to 0-ACP (1.43±0.21%). HV was significantly higher in Si-ACP (12.82±1.30) than in 0-ACP (10.54±0.86) and Ba-ACP (10.75±0.62) (P<0.010). CONCLUSION: Incorporation of inert fillers to bioactive remineralizing composites enhanced their physical-mechanical performance in laboratory conditions. Both added fillers reduced the PS while maintaining high levels of the DC. Silica fillers additionally moderately improved the HV of ACP composites.

Porous Silicon Covered with Silver Nanoparticles as Surface-Enhanced Raman Scattering (SERS) Substrate for Ultra-Low Concentration Detection.

Microporous and macro-mesoporous silicon templates for surface-enhanced Raman scattering (SERS) substrates were produced by anodization of low doped p-type silicon wafers. By immersion plating in AgNO3, the templates were covered with silver metallic film consisting of different silver nanostructures. Scanning electron microscopy (SEM) micrographs of these SERS substrates showed diverse morphology with significant difference in an average size and size distribution of silver nanoparticles. Ultraviolet-visible-near-infrared (UV-Vis-NIR) reflection spectroscopy showed plasmonic absorption at 398 and 469 nm, which is in accordance with the SEM findings. The activity of the SERS substrates was tested using rhodamine 6G (R6G) dye molecules and 514.5 nm laser excitation. Contrary to the microporous silicon template, the SERS substrate prepared from macro-mesoporous silicon template showed significantly broader size distribution of irregular silver nanoparticles as well as localized surface plasmon resonance closer to excitation laser wavelength. Such silver morphology has high SERS sensitivity that enables ultralow concentration detection of R6G dye molecules up to 10(-15) M. To our knowledge, this is the lowest concentration detected of R6G dye molecules on porous silicon-based SERS substrates, which might even indicate possible single molecule detection.

Optical effects of experimental light-activated bleaching procedures.

OBJECTIVE: The purpose of this study was to evaluate the efficiency of experimental light-activated bleaching procedures. BACKGROUND DATA: The improved color effect may be attributed to the potential photochemical effect of light-emitting diode (LED405), organic LED (OLED), and femtosecond laser rather than to the photothermal effect of conventional lights used for tooth bleaching. MATERIALS AND METHODS: Specially made pastilles of hydroxylapatite were immersed in green tea for 8 h and randomly divided into four groups (n=50) specified by the type of light source applied during a 30 min bleaching treatment: LED405, OLED, and femtosecond laser, or its absence (control group). Each group was treated with five bleaching gels: 10%, 16%, and 30% carbamide peroxide (CP), and 25% and 38% hydrogen peroxide (HP). Changes in color were determined by red-green-blue (RGB) colorimeter and ultraviolet-visible-near-infrared (UV/Vis/NIR) spectroscopy. RESULTS: Regardless of the applied bleaching gel, LED405 produced a larger increase in the value of RGB index than did OLED and bleaching without light activation (p<0.05). Femtosecond laser also produced significantly better results in combination with 16% CP and 38% HP. Furthermore, application of a bleaching agent with a higher concentration of peroxide boosted the value of the RGB index. Spectroscopic measurements revealed similar results, although treatments with OLED were rated relatively better than in RGB analysis. CONCLUSIONS: The mechanisms of light-activated bleaching procedures had a significant effect on the color change. The bleaching activation with LED405 and higher concentrations of peroxide in bleaching agents promoted better whitening effect.

Effect of silanized nanosilica addition on remineralizing and mechanical properties of experimental composite materials with amorphous calcium phosphate.

OBJECTIVES: Experimental composite resins with amorphous calcium phosphate (ACP) have the potential to regenerate demineralized tooth structures. The aim of the study was to investigate the effect of the addition of silanized silica nanofillers to the ACP-based composites on their mechanical properties and the kinetics of calcium and phosphate release. MATERIALS AND METHODS: The test materials comprised 5 wt% (5-ACP) or 10 wt% (10-ACP) of silanized silica admixed to the 40 wt% ACP and 50 or 55 wt% resin. The ACP control (0-ACP) contained 40 wt% ACP and 60 wt% resin. Additionally, composite material CeramX (Dentsply, Germany) was included as control. Three-point bending test was performed to calculate flexural strength and modulus of elasticity. Inductively coupled plasma atomic emission spectroscopy was used for measurement of ion release. The micromorphology of calcium phosphate depositions on composite samples has been qualitatively evaluated using a scanning electron microscope. The results were analyzed using Mann-Whitney and Wilcoxon rank sum tests (α < 0.05). RESULTS: Ion release was enhanced by the silica fillers, when compared to the 0-ACP. Although not statistically significant, flexural strength of 10-ACP was improved by 46 % compared to 0-ACP. Flexural modulus of 5-ACP was significantly higher than 0-ACP. CONCLUSIONS: The admixture of silanized fillers seems to be a promising approach for the improvement of mechanical and remineralizing properties of ACP composite resins. CLINICAL RELEVANCE: ACP-based composite resins with modified composition could serve as an effective remineralizing aid as base materials in restorative dental medicine.

Surface changes of enamel and dentin after two different bleaching procedures.

Bleaching agents have effect on chemical/physical and morphological structure of enamel and dentin that must be taken into account when this therapy is used. The aim of this in vitro study was to evaluate the effects of two bleaching agents containing a high concentration of hydrogen peroxide for professional use on human enamel and dentin surface and to evaluate the potential remineralizing effect of amorphous calcium phosphate gel (ACP). Twenty-five human third molars were divided into two groups and dissected in half and both surfaces were bleached with either ZOOM2 or Opalescence BOOST for 3 x 15 minutes. Vickers microhardness of enamel and dentin was measured before, after the bleaching treatment, and after treatment with artificial saliva and ACP gel or 2-week storage in deionized water. Surface microstructure was evaluated using scanning electron microscopy. The mixed model ANOVA and Wilcoxon Rank Sum test were used. Both bleaching agents showed significant reduction in surface microhardness (p < 0.001 for both BOOST and ZOOM2 application). ZOOM2, which had a lower pH value showed greater decrease in surface microhardness (p = 0.005) compared to BOOST. Post-treatment with artificial saliva and ACP showed significant increase in surface microhardness (p < 0.001). After the bleaching procedure, enamel and dentin surface microstructure showed mild or slight alterations with no loss of superficial structure. In conclusion, both bleaching agents resulted in reduction in surface enamel and dentin microhardness. Treatment with ACP led to increase in surface microhardness, improved surface roughness, and enhanced remineralization of the hard dental tissues.

Biofilm in nasal polyps.

INTRODUCTION: Bacterial biofilms are involved in many human bacterial infectious processes and in chronic rhinosinusitis as well. The aim of this study was to determine whether biofilm exists in nasal polyps, both in diffuse nasal polyposis (DNP) and antrochoanal polyps (ACP). METHOD: Tissue samples were taken from seven patients suffering from DNP and three patients suffering from ACP, based on the defined patient inclusion and exclusion criteria. After the preparation, the tissue samples were analyzed by means of scanning electron microscopy (SEM) for signs of biofilm formation. RESULTS: Signs of biofilm presence were found in all DNP patients. In ACP cases, biofilm was found in the stalk and nasal, polypoid part of the ACP, whereas there were no signs of biofilm on diseased mucosa of the posterior wall of the maxillary sinus. CONCLUSIONS: Our preliminary study showed a possible role of bacterial biofilm in pathogenesis and maintenance of both DNP and ACP. There are no obvious differences in the SEM appearance of biofilms in DNP and ACP. Future research is needed to explain why biofilm is present in cases of diffuse nasal polyposis and at the nasal part of ACP, but not on the maxillary sinus part of ACP.

Composite photopolymerization with diode laser.

Under clinical conditions, the time needed for the proper light curing of luting composites or the multi-incremental buildup of a large restoration with halogen curing units is quite extensive. Due to the development of high power curing devices, such as argon lasers and plasma arc lights and, in order to decrease curing time, halogen and LED devices have developed a high intensity polymerization mode. This study compared the degree of conversion using Fourier Transform Infrared Spectroscopy (FT-IR) of two composite materials: Tetric Ceram and Tetric EvoCeram polymerized with three polymerization modes (high, low and soft mode) of a Bluephase 16i LED curing unit and blue diode laser intensity of 50 mW on the output of the laser beam and 35 mW/cm2 on the resin composite sample. Descriptive statistic, t-test, ANOVA, Pearson Correlation and Tukey Post hoc tests were used for statistical analyses. The results show a higher degree of conversion for the polymerization of composite samples with all photopolymerization modes of the LED curing unit. However, there is no significant difference in the degree of conversion between the LED unit and 50-second polymerization with the blue diode laser. Tetric EvoCeram shows a lower degree of conversion regardless of the polymerization mode (or light source) used.

Comparison of composite curing parameters: effects of light source and curing mode on conversion, temperature rise and polymerization shrinkage.

This study analyzed the degree of conversion, temperature increase and polymerization shrinkage of two hybrid composite materials polymerized with a halogen lamp using three illumination modes and a photopolymerization device based on blue light emitting diodes. The degree of conversion of Tetric Ceram (TC) (Ivoclar Vivadent) and Filtek Z 250 (F) (3M/ESPE) was measured by Fourier transformation infrared spectroscopy at the surface and 2-mm depth; temperature rise was measured by digital multimeter, and linear polymerization shrinkage was measured during cure by digital laser interferometry. Composite samples were illuminated by quartz-tungsten-halogen curing unit (QTH) (Astralis 7, Ivoclar Vivadent) under the following modes: "high power" (HH) 40 seconds at 750 mW/cm2, "low power" (HL) 40 seconds at 400 mW/cm2 and "pulse/soft-start" (HP) increasing from 150 to 400 mW/cm2 during 15 seconds followed by 25 seconds pulsating between 400 and 750 mW/cm2 in 2-second intervals and by light emitting diodes (LED) (Lux-o-Max, Akeda Dental) with emitted intensity 10 seconds at 50 mW/cm2 and 30 seconds at 150 mW/cm2. A significantly higher temperature increase was obtained for both materials using the HH curing mode of halogen light compared to the HP and HL modes and the LED curing unit after 40 seconds. Significantly lower temperature values after 10-second illumination were obtained when LED was used compared to all halogen modes. For all curing modes, there was no significant difference in temperature rise between 20 and 40 seconds of illumination. Results for the degree of conversion measurements show that there is a significant difference in the case of illumination of resin composite samples with LED at the surface and 2 mm depth. For polymerization shrinkage, lower values after 40 seconds were obtained using LED compared to QTH.