Microleakage and penetration capability of various pit and fissure sealants upon different sealant application techniques.

Background: Sealant application that yields superior marginal adaptation and deeper fissure penetration potentially improves success in preventive and restorative dentistry. This study evaluated the amount of in-vitro microleakage and penetration capabilities of different pit-fissure sealants as the effect of different application techniques. Material and Methods: 160 freshly extracted human sound premolars, assigned as suitable for sealant application, selected and allocated randomly into 8 groups (n=20 teeth/group) and applied with different sealants including Embrace-Wetbond® (E), UltraSeal XT® (U), Clinpro™ (CL), Helioseal® (H), using either conventional (C) or induced application (I). The sealed teeth were thermocycling for 500 cycles between 5°C and 55°C with 30 seconds dwelling time. The tooth was coated with 2 layers of nail varnish, leaving 1 mm around the sealant margin, then immersed in 5% methylene blue solution for 24 hours. Subsequently, 2 pieces were segmented vertically in a buccolingual direction, yielding 4 surfaces/tooth for determination of microleakage and penetration proportion of sealant with polarized light microscopy (PLM) and image-J software. ANOVA and Bonferroni multiple comparisons were determined for significant differences (α=0.05). Sealant adaptability was detected using a scanning electron microscope (SEM). Results: The highest microleakage was observed for EC, followed by CLC, HC, UC, CLI, HI, EI, and UI. The highest penetration was seen in UI, followed by HI, CLI, CLC, UC, HC, EI, and EC. ANOVA indicated significant differences in microleakage and penetration on the type of sealant and application method (p<0.05). SEM revealed that the I-application method significantly promoted less microleakage and better penetration than the C-application (p<0.05). Conclusions: Microleakage and penetration capabilities of sealant are greatly affected by the types of sealant and the method by which the sealant is applied. U-sealant exhibited less microleakage and better penetration capability than others. I-application reduced microleakage, promoting enhanced penetration and adaptation, is the recommended sealant application. Key words:Microleakage, penetration, dental sealant.

Cyclic compression and decompression of a lipid bilayer.

In this study, we measure transient thicknesses of a lipid bilayer during electrostatic compression and decompression and deduce non-equilibrium molecular interactions of the surfactants' tails within the layer. The bilayer under investigation (sorbitan monooleate) is single-tailed and self-assembles between a water drop and hafnium oxide in dodecane. We detect minute changes in bilayer thickness (∼0.01 Å/s) resulting from step changes in electrostatic pressure. The dynamic response of the bilayer consists of an elastic response followed by an inelastic dissipative behavior. We observe a distinct asymmetry between the inelastic responses: compression triggers a linear reduction in thickness over time, whereas decompression induces a logarithmic increase in thickness.

Silk fibroin solution properties related to assembly and structure.

The impact of physiological factors on silk fibroin solution properties was studied. Specifically, the impact of fibroin concentration, protein purity, cation type and concentration, and pH on aqueous solution viscosity, shear behavior, and surface tension were assessed in the context of silk protein assembly. The results demonstrate that in vitro results could be correlated to in vivo processing events during silk spinning. Rheological properties with reference to the amphiphilic block structure of the protein are described, pH dependency of shear response was quantitatively correlated to the predicted pI values of the fibroin protein, and cooperativity among environmental factors such as pH and salts was identified. Stabilization of silk fibroin solution states by calcium was identified as a mode to control shear sensitivity of the fibroin solution. The cooperativities identified suggest tight control of fibroin aqueous solution rheological properties to gain a window of protection against premature crystallization of the fibroin during processing, assuring safe storage, transport, and finally successful fiber spinning.

Irreversible electrowetting on thin fluoropolymer films.

A study was conducted to investigate electrowetting reversibility associated with repeated voltage actuations for an aqueous droplet situated on a silicon dioxide insulator coated with an amorphous fluoropolymer film ranging in thickness from 20 to 80 nm. The experimental results indicate that irreversible trapped charge may occur at the aqueous-solid interface, giving rise to contact angle relaxation. The accumulation of trapped charge was found to be related to the applied electric field intensity and the breakdown strength of the fluoropolymer. On the basis of the data, an empirical model was developed to estimate the amount of trapped charge in the fluoropolymer as well as the voltage threshold for the onset of irreversible electrowetting.

Low voltage electrowetting using thin fluoroploymer films.

This paper investigates the nonideal electrowetting behavior of thin fluoroploymer films. Results are presented for a three phase system consisting of: (1) an aqueous water droplet containing sodium dodecyl sulfate (SDS), (2) phosphorous-doped silicon topped with SiO2 and an amorphous fluoroploymer (aFP) insulating top layer on which the droplet is situated, and (3) a dodecane oil that surrounds the droplet. The presented measurements indicate that the electrowetting equation is valid down to a 6 nm thick aFP film on a 11 nm thick SiO2. At this dielectric thickness, a remarkable contact angle change of over 100 degrees can be achieved with an applied voltage less than 3 V across the system. The data also shows that for this water/surfactant/oil system, contact angle saturation is independent of the electric field, and is reached when the surface energy of the solid-water interface approaches zero.

An effective method for spreading flowable composites in resin-based restorations.

UNLABELLED: Cavity lining with flowable composites has been suggested for better marginal adaptation and a reduction in interfacial stress and post-operative sensitivity. The following in vitro study compares the spreading of flowable composite that lines the inner wall of a test cavity using an explorer and a specially designed smooth, oscillating, off-center rotating bur spun at 300 to 600 rpm. Two commercial flowable materials were used in this study. RESULTS: With use of the rotating bur, a more consistent, uniform cavity lining was achieved. This was not possible using the dental explorer. CONCLUSION: The specially designed rotating bur provides an effective way for clinicians to form a uniform cavity lining.