Evaluation of Newly Introduced Bioactive Materials in Terms of Cavity Floor Adaptation: OCT Study

Objective. The aim of the present study was to evaluate the adaptation of newly introduced bioactive restorative materials to the cavity floor using cross-polarization optical coherence tomography (CP-OCT). Materials and Methods. Round class V cavities were prepared on the proximal surfaces of sixty non-carious human anterior teeth (0.5 mm depth × 4 mm diameter), which were divided into groups according to the restorative material (n = 15). In the VF group, Vertise flow composite (Kerr, Orange, CA, USA) was used, in the BF group, Beautifil II composite (Shofu, Koyoto, Japan) was used, and in the AB group, ACTIVA BioACTIVE composite (Pulpdent, Watertown, NY, USA) was used. Cavities were restored using the bulk filling technique and cured according to the manufacturers’ instructions. Then, the specimens were immersed in a contrasting agent, and image acquisitions were taken by CP-OCT to calculate the adaptation percentage by using an image analysis software. Results. B-scans showed a diffuse bright band of white pixels at the tooth-resin interface that was interpreted as a micro-gap present between the cavity floor and restorative material. The Kruskal-Wallis test showed a statistically significant difference between all tested groups with the AB group representing the least gap formation, followed by the BF group, and then the VF group, which demonstrated the highest gap formation. Conclusions. In class V cavities, better adaptation to the cavity floor can be obtained when using ACTIVA BioACTIVE more than Vertise flow and Beautifil II composites. In addition, CP-OCT is considered a non-destructive imaging tool that helps in evaluating the quality of the tooth-restoration interface when bioactive composites are used.

Very Large Eddy Simulation of Aero-Thermal Performance in Squealer Tip Gap

To improve the resolution accuracy and get deep insight into the flow structures in squealer tip gap, the Very Large Eddy Simulation (VLES) method was implemented into the commercial CFD (Computational Fluid Dynamics) solver with the User Defined Function (UDF). Based on the published experimental data, the numerical accuracy of VLES method was validated. With VLES method, the unsteady heat transfer coefficient distributions on the squealer tip and total pressure loss in the blade passage were computed. The influences of coherent vortex structures on aero-thermal performance in the squealer tip gap were analyzed. The results show that the Brown-Roshko vortices are the main driver for the formation of cavity vortex system. The direct impingement of pass-over leakage into the cavity is the main cause of high heat transfer area on the cavity floor near leading edge. The unsteady fluctuations of leakage rate through the tip gap reach about ±8% of the time-averaged value. The development of leakage vortex accounts for the major contribution of total pressure loss in the squealer tipped blade. Due to flow unsteadiness, the fluctuation of pitch-averaged total pressure loss coefficient induced by leakage vortex system reaches about ±30% of the time-averaged value. The unsteady fluctuation of pitch-averaged heat transfer coefficient on the cavity floor reaches about ±35% of the time-averaged value, while on the shroud surface it is only fluctuated by about ±10%.

Characteristics of open cavity flow with floor inclinations at M = 2.0

Experimental studies on open cavity flows at supersonic speed of M = 2.0 were carried out. Oil flow visualization tests were made to understand the steady features of the surface flow field. Unsteady pressure measurements were done at five locations inside the cavity and pressure spectrum of these measurements were obtained. Cavity floor was made inclined to influence the flow directing towards the cavity leading edge with both, a favourable and adverse slope, by giving a positive and negative inclination angles to the floor, respectively. It is observed that the negative inclinations to the cavity floor behaves in a similar way to the base cavity, but a positive inclination helps to reduce the fluctuating pressures by 80% and reduce OASPL to the order of 14 dB and more.

Investigations of Heat Transfer and Film Cooling Effect on a Worn Squealer Tip

Wear damage commonly occurs in modern gas turbine rotor blade tip due to relative movements and expansions between rotating and stationary parts. Tip wear has a significant impact on the aerodynamic, heat transfer and cooling performance of rotor blades, thus threatening the economy and safety of whole gas turbine system. Based on a simple linear wear model, this paper numerically investigates the aerodynamic, heat transfer and film cooling performance of a worn squealer tip with three starting-locations of wear (sl = 25%Cax, 50%Cax and 75%Cax) and five wear-depths (wd = 0.82%, 1.64%, 2.46%, 3.28% and 4.10%). Firstly, based on the existing experimental data, numerical methods and grid independence are examined carefully. Then, three dimensional flow fields, total pressure loss distributions, heat transfer coefficients and film cooling effectiveness in worn squealer tip region are computed, which are compared with the original design case. The results show that, with the increase of wear depth and the movement of wear starting-location to the leading edge, the scale and intensity of cavity vortex are increased, which results in the extended high heat transfer area on cavity floor near the leading edge. Wear makes more coolant flow out of the cavity, and reduces the area-averaged film cooling effectiveness at the bottom of cavity, but increases the film cooling effectiveness on pressure-side rim. The increase of wear depth makes more flow leak through the tip gap, thus increasing the scale and intensity of leakage vortex and further increasing the total pressure loss in the tip gap. Compared with the original design case, as the wear depth is increased from 0.82% to 4.10%, the mass-averaged total pressure loss in cascade is increased by 0.3–6.7%, the area-averaged heat transfer coefficient on cavity floor is increased by 1.7–29.1% while on squealer rim it is decreased by 3.1–26.3%, and the area-averaged film cooling effectiveness on cavity floor is decreased by 0.035 at most while on squealer rim it is increased by 0.064 at most.

Effects of Additional Cavity Floor Injection on the Ignition and Combustion Processes in a Mach 2 Supersonic Flow

Effects of additional cavity floor injection on the ethylene ignition and combustion processes in a cavity-based scramjet combustor are investigated experimentally in a Mach 2.0 supersonic flow using flame luminosity and CH* (CH radical) spontaneous emission methods and static pressure measurements. Numerical calculation is performed to study the non-reacting flow-field structures prior to ignition. Two injection schemes, including the cavity upstream injection scheme and the combined injection scheme with an additional cavity floor injection, are compared to study the effects of the additional cavity floor injection on the ignition and combustion processes. It is found that there exists an equivalence ratio upper limit for maintaining stable combustion for the cavity upstream injection scheme. As the equivalence ratio further increases, the fuel jet penetration is improved accordingly, and thus, the interaction between the fuel jet and the cavity is weakened, which can lead to the ignition failure and flame blowout during combustion. On the contrary, although the combined injection scheme has a minor effect on combustion enhancement at the same global equivalence ratio, it can also provide a more favorable flow-field environment that enables more successful ignitions and better flame stabilizations. For the combined injection scheme, as the equivalence ratio increases, the initial flame propagations are observed to perform different routines during the ignition process, and the major combustion reaction zone tends to move further downstream the cavity shear layer. It is concluded that the advantages of the combined injection scheme with an additional cavity floor injection are more significant when the equivalence ratio is higher, as well as that the interaction between the fuel jet and the cavity becomes weaker.

The Effect of the Bioactive Glass and the Er:YAG Laser on the Remineralization of the Affected Dentin: A Comparative In Vitro Study

Introduction: The purpose of this study was to compare the effect of the bioactive glass, the glass ionomer, and the Erbium YAG laser as liners on the remineralization of the affected dentin. Methods: The present study was conducted on 64 healthy extracted human molars divided into 4 groups, 1 control group and 3 experimental groups. After artificially inducing dentinal caries lesions, each of the experimental groups was applied to the cavity floor and then restored with a composite. The samples were stored after thermocycling in an incubator for two months. Finally, the hardness of the cavity floor was measured at 3 depths of 20, 50 and 100 μm by the Vickers microhardness tester. The dentin conditions underneath the liners were also evaluated with FESEM. Statistical analysis was performed by two-way ANOVA and the post-hoc Games-Howell test (P<0.05). Results: Among the groups, the lowest microhardness value was in the control group (P<0.05) except at a depth of 100 μm; therefore, there was no significant difference between the control group and the bioactive glass (P>0.05). The laser group had the highest microhardness value, which was significantly different from the control group (P<0.05). There was a significant difference between the laser and bioactive glass (P<0.05), except at a depth of 20 μm. The laser and glass ionomer had only a significant difference at a depth of 100 μm (P<0.05). The microhardness value induced by glass ionomer was higher than bioactive glass, which in no depth was significant (P>0.05). Partial dentinal tubule occlusion was observed with FESEM in each of the experimental groups as compared to the control group. Conclusion: The microhardness values were higher in all groups than in the control group. The laser might be more successful in remineralization than the other ones.

Kista radikuler besar yang melibatkan dasar cavum nasalis

Objectives: This case will present a radicular cyst and its expansion effect, seen from cone beam CT (CBCT) 3D radiograph. Case Report: A 32-year-old patient complained about discoloration of her upper anterior teeth and swollen gums. Periapical radiograph for preliminary examination revealed a large radiolucent area with well-defined cortical border in periapical 21. In coronal view, the lesion extends to 22 also causes the destruction of the nasal cavity floor and palatal cortical bone. Endodontic, cyst enucleation, and bone graft was performed to the patient. After endodontic treatment, CBCT examination was performed to determine the extent of cyst lesions. Conclusion: Large lesion needs an adequate radiographic technique to examine anatomical structure involvement. In large cysts, CBCT examination is matter to consider.