Values Of Gap Width Research Articles

Multi-acrylamides improve bond stability through collagen reinforcement under physiological conditions

ObjectivesAcrylamides were shown to significantly improve bonding stability in adhesive restorations, but the reinforcement mechanism has not been fully elucidated. We tested the hypothesis that hydrogen bonding reinforcement of the collagen network (with secondary or tertiary acrylamides), as well as degree of crosslinking of the polymer network (with di- or tri-functional acrylamides), can be two of the factors at play. MethodsTwo-step total etch adhesives comprising UDMA (60 wt%) and 40 wt% of: TAAEA, TMAAEA (secondary, tertiary tri-acrylamides), BAAP, DEBAAP (secondary, tertiary di-acrylamides) or HEMA (mono-methacrylate - control) were formulated. Simulated composite restorations (n = 5) were tested after cyclic mechanical and biological (S. mutans biofilm) challenges. Gap formation before and after aging was assessed with SEM imaging. Micro-tensile bond strength (μTBS, n = 6) was assessed after seven-day incubation in water or S. mutans-containing culture medium. Collagen reinforcement was assessed with hydroxyproline assay (n = 10) and rheology (n = 3). Data were analyzed with one-way/two-way ANOVA/Tukey’s test (alpha=5%). ResultsGap formation increased and bond strength decreased for all monomers after biofilm incubation (p < 0.001). Except for DEBAAP, secondary and tertiary di/tri-acrylamides showed lower occlusal gap width values, but no significant differences overall gap length compared to HEMA. μTBS increased for tri-acrylamides compared with HEMA. Samples treated with multi-acrylamides had lower concentration of hydroxyproline (by-product of collagen degradation) (p < 0.001), except for DEBAAP, which showed values close to HEMA (p > 0.05). Dentin shear modulus increased for all acrylamides after 72 h, especially TMAAEA. SignificanceIn general, multi-acrylamides promote collagen reinforcement, leading to reduced gap formation, and stabilize the bond strength under physiological conditions.

Adaptability of thermo-viscous versus sonicfill-activated bulk fill composite resin restorations

Purpose To in vitro evaluate the marginal and internal adaptation of Thermo-Viscous versus SonicFill Bulk Fill composite in Class I cavities. Materials and methods Twenty non-carious human maxillary premolar teeth were selected. Class I cavities were prepared with dimensions of 4 mm mesio-distal, 2.5 mm bucco-lingual width and 2 mm depth. Specimens were randomly divided into two equal groups I and II. Cavities were restored with VisCalor and SonicFill Bulk Fill, respectively. Materials were applied using the recommended adhesive and special dispenser. Specimens were then subjected to 500 thermal cycles, labelled and the restoration margins were inspected under stereomicroscope at X70 to detect and measure the marginal gap width. Specimen were then sectioned buccolingually using a microtome to detect and measure the internal gap width. Results Lower mean values of marginal gap width were recorded in VisCalor group compared to SonicFill group, however there was no statistically significant difference (P = 0.187) between both groups. While a significant difference (P = 0.002) was found regarding internal mean gap width values recorded in VisCalor group compared to SonicFill group. Conclusion Both tested materials/techniques used to reduce the viscosity of the bulk fill composites presented nearly comparable marginal integrity results, while VisCalor application technique enhanced the internal adaptation compared to SonicFill method.

A Comparative Study of the Marginal Fit of Endocrowns Fabricated From Three Different Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) Ceramic Materials: An In Vitro Study.

The marginal seal and adaptation are important factors for successful restoration. An inadequate marginal seal can lead to bacterial microleakage, plaque accumulation, and eventually treatment failure This in vitro study aimed to compare the marginal gap of endocrowns fabricated from three different computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic materials. Thirty extracted mandibular molars were selected for the study. Endocrown preparations were completed after root canal treatment. Teeth were divided into three groups to receive endocrowns fabricated of lithium disilicate ceramic (IPS-e.max CAD, Ivoclar Vivadent AG, Schaan, Liechtenstein), zirconia-reinforced lithium silicate ceramic (VITA Suprinity®, VITA Zahnfabrik, Bad Säckingen, Germany), and polymer-infiltrated ceramic (VITA Enamic®, VITA Zahnfabrik). The digital impressions were transferred to the design software to construct the endocrowns. The endocrowns were milled and cemented. The marginal fit was examined using a digital camera stereomicroscope at a magnification of 80X. Images were transferred to Image-J software (National Institutes of Health, Bethesda, Maryland, United States) to measure the marginal gap. One-way ANOVA showed a significant difference in the marginal gap between the different ceramic groups (P=0.006). Tukey's Honest Significant Difference (HSD) post-hoc test showed that VITA Suprinity had significantly higher gap width values than VITA Enamic (P=0.005). No significant differences in gap width values were found between VITA Enamic and IPS e.max CAD or between VITA Suprinity and IPS e.max CAD (P>0.05). The marginal gap of endocrown restorations varies with different CAD/CAM materials (zirconia-reinforced lithium silicate glass-ceramic, polymer-infiltrated hybrid ceramic, and lithium disilicate glass-ceramic), but are all within clinically acceptable marginal gap width.

Root dentin surface activation to improve bioceramic bonding: Ascanning electron microscopic study

Background. Bioceramics need to interact chemically with dentin to exhibit adequate bioactivity. Proper bonding of bioceramics with dentin is of considerable importance. This study aimed to evaluate the wettability and marginal adaptation of bioceramics after the use of surface-active agents on dentin: %0.5 cetrimide and %1 alkylbenzene sulfonate. Methods. Of ninety maxillary central incisors, 45 teeth were sectioned longitudinally with 45 root halves randomly assigned to three groups (n=15): group I: no pre-treatment; group II: %0.5 cetrimide; group III: %1 alkylbenzene sulfonate. Then, the samples were subdivided into three subgroups (n=5): subgroup I: MTA; subgroup II: Biodentine, and subgroup III: BioRoot. A controlled-volume droplet of bioceramic material was placed on each root half, which was positioned in a dynamic contact angle analyzer to record the static contact angle for wettability. The remaining 45 samples were decoronated; the root canals were prepared and randomly categorized, as mentioned above. The root canal surfaces were treated, filled with the bioceramic material, transversely sectioned, and then each middle section was analyzed microscopically for marginal adaptation. Statistical tests used included post hoc Tukey tests and one-way ANOVA. The level of statistical significance set at %95 (P<0.05). Results. The contact angle values and interfacial gap width values after surface pre-treatment were significantly lower when compared to no pre-treatment group (P<0.05). The values were significant for %0.5 cetrimide in the case of Biodentine and %1 alkylbenzene sulfonate in the case of BioRoot (P<0.05). Conclusion. The two surfactants yielded promising results for enhancing the wettability and marginal adaptation of materials to the root dentin, which is required for obtaining an adequate seal, penetration, and bond strength of bioceramics.

Marginal fit of class II cavities restored with bulk-fill composites

Purpose To evaluate the marginal integrity of three types of bulk-fill composite resins in class II cavities. Materials and methods Simple class II cavities with parallel walls were prepared in 40 extracted human sound molars were selected. The overall dimensions and depth of the cavities were standardized as follow: 4 mm length occlusocervically, 4 mm width buccolingually and 2 mm depth axially. The teeth were randomly divided into four groups (n = 10 each): group 1: Tetric N-Bond Universal and Tetric EvoCeram Bulk Fill composite; group 2: Single Bond Universal and Filtek Bulk Fill posterior composite; group 3: Futurabond U and Admira Fusion X-Tra; group 4: Tetric N-Bond Universal and Tetric EvoCeram composite. All samples were thermocycled for 600 cycles. Impressions of the teeth were made using a polyvinyl siloxane then poured with epoxy resin. These replicas gold sputtered and examined under scanning electron microscopy. Results Group 3 recorded the lowest mean marginal gap length value, while group 4 recorded the highest mean marginal gap length value. One-way analysis of variance was used to compare the tested groups at a level of significance (P ≤ 0.001). For width of proximal gap the lowest mean marginal gap length value found in group 3, while the highest mean value of gap width proximally found in group 1. In width of cervical gap the lowest mean marginal gap length value was found in group 3, while the highest mean value of gap width cervically found in group 4. One-way analysis of variance test was used to compare the tested groups at a level of significance (P ≤ 0.05). Conclusion Admira Fusion X-Tra has good results compared to other used bulk fill and conventional composites.

Effect of Preparation Depth on the Marginal and Internal Adaptation of Computer-aided Design/Computer-assisted Manufacture Endocrowns.

The aim of the study was to evaluate the effect of preparation depth and intraradicular extension on the marginal and internal adaptation of computer-aided design/computer-assisted manufacture (CAD/CAM) endocrown restorations. Standardized preparations were made in resin endodontic tooth models (Nissin Dental), with an intracoronal preparation depth of 2 mm (group H2), with extra 1- (group H3) or 2-mm (group H4) intraradicular extensions in the root canals (n=12). Vita Enamic polymer-infiltrated ceramic-network material endocrowns were fabricated using the CEREC AC CAD/CAM system and were seated on the prepared teeth. Specimens were evaluated by microtomography. Horizontal and vertical tomographic sections were recorded and reconstructed by using the CTSkan software (TView v1.1, Skyscan).The surface/void volume (S/V) in the region of interest was calculated. Marginal gap (MG), absolute marginal discrepancy (MD), and internal marginal gap were measured at various measuring locations and calculated in microscale (μm). Marginal and internal discrepancy data (μm) were analyzed with nonparametric Kruskal-Wallis analysis of variance by ranks with Dunn's post hoc, whereas S/V data were analyzed by one-way analysis of variance and Bonferroni multiple comparisons (α=0.05). Significant differences were found in MG, MD, and internal gap width values between the groups, with H2 showing the lowest values from all groups. S/V calculations presented significant differences between H2 and the other two groups (H3 and H4) tested, with H2 again showing the lowest values. Increasing the intraradicular extension of endocrown restorations increased the marginal and internal gap of endocrown restorations.

Investigations of heat transfer, entropy generation and pressure build up for upward flow in a vertical channel equipped with a fin array

The optimal thermal systems design criteria by maximizing the amount of heat transfer per pressure losses is a very important topic. In this work, flow and convection and radiation heat transfer characteristics are studied numerically for a flow in a vertical channel equipped with transverse fin array. The influences of fin height on heat transfer characteristics and fluid flow is investigated. Large number of fins is used (40 fins) in order to reach the fully developed conditions after few fins from the entrance. Based on the calculated data of temperature and velocity, the local entropy generation is calculated through the whole channel by solving the entropy generation equation. The results are validated against the available data in the literature and both results are in a good agreement. Optimizations for flow conditions and channel geometry are performed in order to obtain maximum heat transfer per pumping power losses. The results showed that the highest values of total heat transfer per pumping power losses are obtained at fin height to the gap width values of 0.1 and 0.3. The effect of heat transfer by radiation on entropy generation is examined and, the effect of the ratio, Gr/Re2, on the pressure field is also investigated. It was found that a positive pressure gradient appears downstream in the channel when the value of Gr/Re2 exceeds a certain limit. For Gr/Re2 values between 0 and 9, the pressure gradient is negative; however, when the value Gr/Re2 exceeds 9, the pressure starts to build up through the channel axis.

Effects of repeated firing on the marginal accuracy of Co-Cr copings fabricated by selective laser melting

Statement of problemSelective laser melting (SLM) is a technique used to fabricate Co-Cr dental restorations; however, because marginal accuracy is important for the long-term success of restorations, the marginal accuracy of SLM after repeated firings must be considered. PurposeThe purpose of this study was to evaluate the marginal accuracy of dental Co-Cr alloy copings fabricated by SLM and to investigate the effects of repeated firing on the marginal fit of these copings. Material and methodsSLM-fabricated and cast Co-Cr alloy copings (n=15) were prepared for a zirconia die. The marginal gap widths of each group were evaluated with a silicone replica technique after the first, third, fifth, and seventh firing cycle. The thickness of the reference point was measured with a stereomicroscope with ×100 magnification. Analysis of variance was used to evaluate the effect of repeated firing on the marginal accuracy of the 2 alloys. The Student t test was used to compare the marginal gap widths of the SLM-fabricated and cast Co-Cr alloy copings after repeated firing (α=.05). ResultsThe marginal gap width values between the 2 groups at all firing periods were statistically significant (P<.05). The mean marginal gap width values for SLM-fabricated copings were 36 μm, 37 μm, 38 μm, and 38 μm after the first, third, fifth, and seventh firing, while the mean marginal gap width values for cast copings were 67 μm, 71 μm, 72 μm, and 73 μm at the same number of firings. The marginal gap width values within the 2 groups were not statistically different from each other with additional firing (P>.05). ConclusionsThe SLM copings demonstrated superior marginal accuracy at all firings. Repeated firing had no significant influence on the marginal accuracy of both copings, and the marginal fit of both copings after repeated firing was within a clinically acceptable range.

Effect of Radial Temperature Gradient on the Stability of Magnetohydrodynamic Dean Flow in an Annular Channel at High Magnetic Parameter

The effect of a radial temperature gradient on the stability of Dean flow of an electrically conducting fluid in an annular channel is investigated. A strong constant magnetic field is imposed in the axial direction. Finite-difference method is used to solve the eigenvalue problem. For given values of gap width d, between the cylinders, and magnetic parameter Q, electrically nonconducting (NC) walls are found to be more destabilizing than perfectly conducting (PC) walls when the temperature parameter N &lt; 0. This trend persists even for small positive values of N but when N (&gt;0) exceeds a critical value depending on Q, PC walls are slightly more destabilizing than NC walls. The critical value of the radii ratio η (0 &lt; η &lt; 1) beyond which the first unstable mode becomes nonaxisymmetric is determined for various values of N and Q.

Evaluation of the adaptation of zirconia-based fixed partial dentures using micro-CT technology

The objective of the study was to measure the marginal and internal fit of zirconia-based all-ceramic three-unit fixed partial dentures (FPDs) (Y-TZP - LAVA, 3M-ESPE), using a novel methodology based on micro-computed tomography (micro-CT) technology. Stainless steel models of prepared abutments were fabricated to design FPDs. Ten frameworks were produced with 9 mm2 connector cross-sections using a LAVATM CAD-CAM system. All FPDs were veneered with a compatible porcelain. Each FPD was seated on the original model and scanned using micro-CT. Files were processed using NRecon and CTAn software. Adobe Photoshop and Image J software were used to analyze the cross-sectional images. Five measuring points were selected, as follows: MG - marginal gap; CA - chamfer area; AW - axial wall; AOT - axio-occlusal transition area; OA - occlusal area. Results were statistically analyzed by Kruskall-Wallis and Tukey's post hoc test (α= 0.05). There were significant differences for the gap width between the measurement points evaluated. MG showed the smallest median gap width (42 µm). OA had the highest median gap dimension (125 µm), followed by the AOT point (105 µm). CA and AW gap width values were statistically similar, 66 and 65 µm respectively. Thus, it was possible to conclude that different levels of adaptation were observed within the FPD, at the different measuring points. In addition, the micro-CT technology seems to be a reliable tool to evaluate the fit of dental restorations.

Modified annular photonic crystals with enhanced dispersion relations: polarization insensitive self-collimation and nanophotonic wire waveguide designs

A novel (to our best knowledge) type of photonic crystal (PC) structure called modified annular PC (MAPC) that is composed of dielectric rods with off-centered air holes is thoroughly studied. The plane wave expansion method is applied for spectral analysis. A complete photonic bandgap region with a considerable value of gap width &#x394;&#x3C9;/&#x3C9;=7.06% is achieved by optimizing the structural parameters of the proposed periodic medium. By introducing geometrical asymmetry to the primitive cell of PC, we engineer the dispersion properties of the proposed photonic structure such that conventional equifrequency contours for the second band can be transformed into tilted rectangular shapes. This feature enables us to demonstrate the polarization insensitive tilted self-collimation effect. A hybrid structure composed of dielectric nanowire and MAPCs is offered to obtain a high degree of polarization independent guiding of light. The two-dimensional finite-difference time-domain method is carried out to verify the light guiding efficiencies. Polarization insensitive optical functionalities achieved by MAPC structure can be deployed in integrated optical circuits.

Effect of light-curing units on gap formation and microleakage of class II composite restorations

Aim: This in vitro study evaluated gap width formation and marginal microleakage in Class II composite restorations light-cured with three different light-curing units. Methods: Standardized cavities in the proximal surfaces of 36 human third molars were made with margins located below the cementoenamel junction. Cavities were restored with Filtek P60 (3M ESPE), inserted with a photocondenser tip and light-cured with three different methods: GI - Optilux401 (halogen); GII – ColtoluxLED (LED) and GIII –UltraLumeLED5 (LED). After finishing the restorations, teeth were subjected to a thermal cycling regimen of 500 cycles (5o C ± 2o C and 55o C ± 2o C), totalizing 500 cycles. Thereafter, the teeth were sectioned in a buccolingual direction and in the center of the restorations. Half of the specimens (18) were used to evaluate marginal microleakage, by measuring of dye penetration in cross-sectioned specimens, and the other half was used to analyzed the gap formation width by SEM observations (1000X). Data were submitted to Kruskal-Wallis (α=0.05). Results: The mean values of gap width (µm) were: GI 3.28±3.34; GII 1.48±1.89 and GIII 3.11±3.45, and microleakage was not affected by the light-curing units. Conclusions: There were no differences between the light-curing methods in gap formation and marginal microleakage.

Stability of cylindrical Couette flow in the presence of an oscillating axial magnetic field

The linear stability of cylindrical Couette flow of an electrically conducting fluid in the presence of an axial magnetic field is examined, where the magnetic field has a small oscillatory component imposed on a steady value. The effect of the field modulation on the threshold of instability is studied for different values of gap width, Chandrasekhar number, magnetic Prandtl number, and oscillation frequency. Modulation is found to have a stabilizing effect for low values of the Chandrasekhar number, a destabilizing effect for intermediate values, and again a stabilizing effect for still higher values of the Chandrasekhar number. The effect of modulation is found to be almost independent of the magnetic Prandtl number and the modulation frequency.

Phononic Band Gap Width Control through Structural and Material Parameters in Two-Dimensional Phononic Crystals

The phononic band structures of two-dimensional solid phononic crystals with different lattice and scatterer symmetry are studied numerically, with three types of lattice (square, triangular, and rectangular) and four different scatterer shapes (circle, hexagon, square, and rectangle) considered. XY and Z vibration modes are investigated separately. Two types of phononic crystal are considered: one composed of high-density rods embedded in a low-density matrix, the other of low-density rods in a high-density matrix. In the former case, lattice type and polarization being fixed, the broadest gaps are obtained when the symmetry of the rods corresponds to that of the lattice (the shape of a rod is identical with that of the first Brillouin zone); the largest gap width values are observed in triangular lattice-based crystals (compared to those based on the square and rectangular lattices), the shape of the corresponding first Brillouin zone being closest to a circle. These rules do not apply to structures in which the density of the rod material is lower than that of the matrix. In this case, when the symmetry of the rods corresponds to that of the lattice, gaps either fail to appear at all, or are much narrower than in other configurations. The effect of other material parameter values (such as the longitudinal and transversal velocity values) on the relation between the energy gap width and the scatterer symmetry is found to be much lesser.