Effect of Deep Margin Elevation on Interfacial Gap Development of CAD/CAM Inlays after Thermomechanical Cycling

SUMMARY The aim of this study was to evaluate interfacial gap formation of CAD/CAM lithium disilicate inlay margins before and after thermomechanical loading. Methods and Materials: Mesio-occlusal-distal cavities were prepared on 12 extracted mandibular molars. The gingival margin of one proximal box was elevated with resin modified glass ionomer (RMGI) by a height of 2 mm (Group E [elevation]), and the margin of the other side served as a control (Group NE [no elevation]). Lithium disilicate computer-aided design and computer-aided manufacturing (CAD/CAM) inlays were fabricated and bonded with a self-adhesive resin cement. An aging process was simulated on the specimens under thermomechanical cycling by using a chewing simulator. Marginal integration was evaluated under scanning electron miscroscopy (SEM) using epoxy resin replicas before and after cycling. Marginal areas were stained with silver nitrate solution, and the volumetric gap was measured at the bonded interfaces using microcomputed tomography (CT) before and after cycling. Statistical analyses were performed using paired t-tests, the Wilcoxon signed rank test, and the Mann–Whitney test (a<0.05). Results: SEM showed marginal discontinuities in Group NE that increased after thermomechanical cycling. Micro-computed tomography exhibited three-dimensional dye-penetrating patterns at the interfaces before and after cycling. Interfacial disintegration was larger in Group NE before cycling (p<0.05). Thermomechanical cycling increased the gaps in both Groups NE and E (p<0.05). The gap increment from thermomechanical cycling was larger in Group NE (p<0.05). Conclusions: Thermomechanical cycling induced interfacial disintegration at the lithium disilicate CAD/CAM inlays, with deep proximal margins. Margin elevation with RMGI placement reduced the extent of the interfacial gap formation before and after the aging simulation.

External Marginal Gap Variation and Residual Fracture Resistance of Composite and Lithium-Silicate CAD/CAM Overlays after Cyclic Fatigue over Endodontically-Treated Molars

The purpose of this in vitro study was to evaluate the external marginal gap variation with a 3D quantitative method and the residual fracture resistance after cyclic fatigue in endodontically treated molars restored with overlays of different materials, with and without fiber posts-supported buildups. Forty-eight human maxillary molars were selected, endodontically treated, prepared with standardized MOD cavities and randomly allocated into 6 study groups considering the “core strategy” (build-up with composite resin; build-up with composite resin supported by a fiber post); and the “restorative material” of the indirect adhesive overlay (GrandioBlocks, Voco; Cerasmart, GC; CeltraDuo, Dentsply). All procedures were executed according with manufacturers guidelines. Micro-CT analysis prior and after cyclic fatigue were executed, followed by scanning electron microscope analysis and fracture resistance test. The Two-Way ANOVA analysis showed that interfacial gap progression was significantly influenced by the “core strategy” (p < 0.01) but not of “restorative material” (p = 0.59). Concerning fracture resistance, “restorative material” was statistically significant (p < 0.01), while “core strategy” (p = 0.63) and the interaction (p = 0.84) were not. In conclusion, the fiber post presence within the build-up promoted a lower interfacial gap opening after fatigue, evaluated through micro-CT scans. In terms of fracture resistance, teeth restored with Cerasmart and Celtra Duo were statistically similar, but superior to GrandioBlocks.

Could different direct restoration techniques affect interfacial gap and fracture resistance of endodontically treated anterior teeth?

Objectives To evaluate different direct restoration techniques on various cavity designs in anterior endodontically treated teeth (ETT). Materials and methods Ninety upper central incisors (n = 90) were selected, endodontically treated, and divided into three groups (n = 30) accordingly to the cavity design: minimal endodontic cavity access (group A), endodontic access + mesial class III cavity (group B), and endodontic access + two class III cavities (group C). Three subgroups (n = 10) were then created accordingly to the restoration technique: nano hybrid composite restoration (subgroup a), glass fiber post + dual-cure luting cement (subgroup b), and bundled glass fiber + dual-cure luting cement (subgroup c). Samples underwent micro-CT scan, chewing simulation, and a second micro-CT scan. 3D quantification (mm3) of interfacial gap progression was performed; then, samples underwent fracture resistance test. Data were statistically analyzed setting significance at p < 0.05. Results Groups A and B showed significantly lower interfacial gap progression compared with group C. Subgroup b performed significantly better compared with subgroups a and c. Improved fracture strength was reported for group C compared with group A, while both subgroups b and c performed better than subgroup a. Conclusions Cavity design significantly influenced interfacial gap progression and fracture resistance. Fiber posts significantly lowered gap progression and improved fracture resistance while bundled fibers only increased fracture resistance. A significant reduction of non-repairable fractures was recorded when fibers were applied. Clinical relevance A minimally invasive approach, conserving marginal crests, should be applied whenever possible. Inserting a fiber post is indicated when restoring anterior ETT, in order to reduce gap progression, improve fracture resistance, and avoid catastrophic failures.

Influence of Silane Pretreatment and Warm Air-Drying on Long-Term Composite Adaptation to Lithium Disilicate Ceramic

Background: Repair bonding to lithium disilicate ceramic (LDS) remains an issue. This study examined whether the adaptation of a resin composite to LDS can be improved by a silane pretreatment and warm air-drying. Methods: LDS blocks (IPS e.max CAD) with prefabricated tapered cavities were bonded using a silane-containing universal adhesive (Clearfil Universal Bond Quick ER; UBQ) or the bonding agent of a two-step self-etch adhesive (Clearfil SE Bond 2), with and without a silane pretreatment (Clearfil Ceramic Primer; CP). CP and the adhesives were air-dried with normal air (23 ± 1 °C) or warm air (60 ± 5 °C), light-cured, and the cavities were filled with a flowable composite. Interfacial gap formation was evaluated using swept-source optical coherence tomography immediately after filling, after 24 h, 5000 and 10,000 thermal cycles, and an additional 1 year of water storage. Results: Without the silane pretreatment, all specimens soon detached from the cavities. Warm air-drying significantly decreased gap formation compared to normal air-dried groups (p < 0.001) and improved long-term stability (p < 0.001). The lowest gap formation was observed with UBQ when the silane pretreatment was combined with warm air-drying. Conclusions: Composite adaptation to LDS was insufficient without silanization, but it was stable in the long term if the silane pretreatment and warm air-drying were combined.

Containment and Arrest of Blade Shedding in Gas Turbine Engines Using Novel Dual-Ring Design

In this paper, we examine the energy absorption and containment capabilities of a newly proposed dual-ring design accounting for interactions between a released blade and fully bladed fan disk using 3D finite element analysis. The components of this dual-ring design are strategically selected to ensure high energy absorption and high impact resistance, thus leading to reduced damage of the disk and increased safety. Three containment ring designs are examined: (i) conventional single-ring design composed of one of titanium, aluminum or Kevlar, (ii) a newly proposed aluminium-Kevlar dual-ring arrangement, and (iii) dual-ring arrangement with an interfacial gap between them to arrest and contain the released blade and ensure free passage of the trailing blades. The results of our numerical simulations indicate that although the single-ring design resists penetration and contains the released blade within the confines of the disk, it does not remove the released blade from the path of the trailing blades leading to severe damage to the fan disk. On the contrary, our new dual-ring design, which contains an interfacial gap, has potential to successfully arrest the released blade within the confines of the ring and out of the path of the trailing blades. This design significantly can reduce the impact damage to the fan disk and reduces kinetic energy of the released blade to near zero in less than half a rotation of the fan disk.

Bridging the interfacial gap in mixed-matrix membranes by nature-inspired design: precise molecular sieving with polymer-grafted metal–organic frameworks

Porous nanoparticles with interfacial adhesiveness boost the selectivity of separation membranes to achieve size-selective nanofiltration.

Marginal Adaptation of Different Bulk-fill Composites: A µ-CT Evaluation

In the last decade, bulk-fill materials were introduced to allow resin-based composites (CRs) in one layer (up to 4-5 mm thick) with optimum polymerization. Objectives: To evaluate the adaptation ability of different bulk-fill composites resin and restoration marginal integrity. Methods and Materials: A total of 28 caries-free and crack-free human molars underwent mesio-occlusal-distal cavity preparation. The mesial margins were prepared on enamel for each sample, and the distal margins were extended into dentin. Teeth were then randomly distributed into four groups (n = 7 per group) according to the composite resin used to restore the cavity. Three bulk-fill CRs—Smart Dentin Replacement Flow+ (SDR), Filtek™ One Bulk Fill (FBF), and Tetric® N-Ceram Bulk Fill (TBF)—and one conventional composite resin (CC)—Filtek™ Z350—were used. The teeth were then subjected to aging via thermocycling, followed by cyclic loading. Finally, the volumetric width of the interfacial gap at the tooth-restoration interface was measured using a microcomputed tomography analysis (µ-CT). Results: SDR demonstrated the smallest gap volume among all tested CRs, followed by CC in enamel and TBF in dentin after aging. FBF showed the highest gap volume. There was no statistically significant three-way interaction between surface, aging, and material (p > 0.05). Conclusion: Based on the results, it is safe to suggest the use of bulk-fill RBC in deep Class II cavities instead of conventional layered RBC; when dealing with dentin margins, though a further clinical investigation is required.

Polymerization Stress and Gap Formation of Self-adhesive, Bulk-fill and Flowable Composite Resins

Clinical Relevance Bulk-fill materials show a similar or better performance than control flowable materials regarding interfacial integrity. However, some self-adhesive composites need improvements to achieve competitive performance. SUMMARY Objective: This laboratory study compared the polymerization stress and gap formation of self-adhesive, bulk-fill and control flowable composites. The degree of conversion (DC) and post-gel shrinkage were also assessed. Methods: Two self-adhesive (Vertise Flow and Fusio Liquid Dentin), two bulk-fill (Tetric N-Flow Bulk-Fill and Filtek Bulk-Fill Flowable Restorative), and two control flowable (Z350 XT Flowable Restorative and Tetric N-Flow) composites were evaluated. Polymerization stress (PS) was determined in a universal testing machine (n=5). Gap formation was evaluated by scanning electron microscopy in class I restorations (n=6). DC was measured by Fourier transform infrared spectroscopy (n=3). Post-gel volumetric shrinkage (VS) was measured using the strain gauge method (n=5). Data were submitted to one-way analysis of variance or a Kruskal-Wallis test (α=0.05). Results: Vertise Flow and Fusio Liquid Dentin presented the highest interfacial gap (27%±5% and 21%±6%, respectively), which was associated with their highest PS (4.1±0.8 MPa and 3.5±0.6 MPa, respectively) and DC (63%±2% and 60%±2%, respectively) in spite of the lowest VS (1.0%±0.2% and 1.0%±0.3%, respectively). Tetric N-Flow Bulk-Fill and Filtek Bulk-Fill Flowable Restorative presented similar PS (2.9± 0.3 MPa and 2.4±0.2 MPa, respectively) to both control materials. However, the Tetric N-Flow Bulk-Fill showed the lowest gap (7%±2%) and the highest DC (64.3%±0.4%), and the Filtek Bulk-fill presented a marginal gap (17.8%±3.4%) and a DC (54.5%±2.7%) similar to the control materials. The VS values of both bulk-fill materials were similar to those of Tetric N-Flow and lower than that of Z350 XT Flowable Restorative. Conclusions: Bulk-fill composites showed either similar or significantly lower interfacial gaps and PS than the control flowable composites. The self-adhesive composites showed a significantly higher gap percentage and PS than the control and bulk-fill materials.

Tridimensional Evaluation of the Interfacial Gap in Deep Cervical Margin Restorations: A Micro-CT Study

Clinical Relevance Using a material that optimizes marginal seal when using a margin elevation technique to manage deep class II cavities should enhance clinical outcomes. SUMMARY Objectives: The purpose of this laboratory study was to perform a tridimensional interfacial gap evaluation of class II cavities with enamel and dentin cervical margins, before and after cyclic fatigue, restored with different nanohybrid resin composites. Methods and Materials: Standardized class II cavities were performed on 48 intact maxillary premolars, placing the mesial cervical margin 1 mm above the cement–enamel junction (CEJ) and the distal cervical margin 1 mm below the CEJ. Specimens were treated with two-step self-etch adhesive (Clearfil SE Bond2) and divided into six groups according to the restoration technique. Microcomputed Tomography imaging was executed before and after 1,000,000 cycles of chewing simulation at 50 N. Tridimensional interfacial gaps, expressed as cubic millimeters, were analyzed through a standardized software flowchart (Mimics). Data were analyzed with a two-way analysis of variance and Tukey post hoc tests (α=0.05). Results: Restoration technique (p=0.001) and chewing simulation (p=0.00001) significantly influenced interfacial gap on dentin but not on enamel. The post hoc test showed that, on dentin margins, flowable resins had a lower gap at baseline but a higher gap after chewing simulation, especially when a 2-mm-thick layer was applied, compared with nanohybrid and bulk-fill composites. Conclusions: Based on the obtained results, no differences in interfacial gap volume were found on enamel margins. On dentin margins, flowable resins showed better marginal seal at baseline, but they seem to be more prone to interfacial degradation during chewing simulation than traditional composites.

Effect of Heating Process on Microstructure and Properties of 2205/Q235B Composite Interface

In this paper, the influence of heating process parameters on interface characteristics and mechanical properties of 2205/Q235B clad steel plate was systematically studied. The results showed that the interfacial gap of the 2205/Q235B composite blank was completely bonded by the mutual diffusion of elements under the action of temperature and metallurgical bonding is achieved. The shear strength of the air-cooled samples was only 114–132 MPa, which was far lower than that of water-quenched samples and rolling deformation samples and was unable to meet the requirements of engineering applications. With the increase in heating temperature and holding time, the diffusion distance of the Cr element gradually increased. After rolling deformation, the diffusion distance of the Cr element was significantly reduced to 4.1–10.2 μm. Rolling deformation of the specimen in the decarburization showed the lowest microhardness, and in combination with the microhardness of the interface is about 236–256 HV, which is between the hardness of Q235B and 2205. The 2205 stainless-steel shows the lowest corrosion rate and the best corrosion resistance when rolling at 1200 °C. It was found that the corrosion was the most significant in the side of Q235B near the bonding zone. The corrosion pit width increased gradually with increased heating temperature.