Fatigue failure load and finite element analysis of multilayer ceramic restorations

Comparative analysis of bonding strength between enamel and overlay of varying thicknesses following an aging test

Abstract

Background/purpose: Overlay restorations can be used clinically as a treatment option to preserve natural dentine. However, whether the residual enamel thickness and overlay thickness affect the adhesion between the restoration and tooth is still unknown. This study was to investigate effects of the overlay thickness and residual enamel thickness on bonding strength.

Materials and methods

Overlays of different thicknesses were prepared with natural teeth which had 2, 4, and 6 mm of occlusal reduction (n = 10). Specimens were subjected to 10,000 cycles in water at 5-55 °C, and finally compressive strength tests were used to evaluate the bonding strength.

Results

All groups showed good bond strength (P > 0.05). The overlay restorations of different thicknesses reduced the preparation amount by 30.3%-7.2% and significantly preserved more of the tooth structure (P < 0.005). Compared to the control group, the overlay restoration increased the marginal fitness by about 0.67-0.88 times. The thermal cycling indicated that the decrease in the maximum bearing stress was due to the aging of the ceramic itself. Therefore, the thickness of the overlay had a greater influence on the compressive strength than the bond strength.

Conclusion

Based on the above this study recommends an overlay thickness of at least 2 mm in clinical practice. The aging test confirmed that adhesion between the overlay and teeth was quite firm and stable. This shows that a stable adhesive effect of the overlay can be used as a treatment option for preserving a greater amount of a tooth's structure.

Current complications and issues of implant superstructure

The purpose of this review is to search for complications of dental implant superstructures and consider the issues involved. This narrative review was performed by searching through PubMed databases and review articles that were published after 1990. Misfitting of the superstructure can result in loosening of screws, reduced preload, and in some cases, significant stress around the implant. External connection modalities and single implant prostheses have been reported to have more loose or broken abutment screws. In addition, when zirconia abutment was used for platform shifting, the rate of fracture of the abutment was considered to be high. Additionally, it was reported that men were significantly at an increased risk of abutment fracture. As for the retention mechanism of implant overdenture, stud attachment (Locator type) should receive more attention to wear and damage of retention parts than other attachments. The causes of the complications of implant superstructures have not been clarified in some cases, and further verification is required. Verification of complications is considered important to obtain a long-term prognosis for superstructures of implants. It will be necessary to further verify complications of implants in the future.

Effects of thickness of different types of high-translucency monolithic multilayer precolored zirconia on color accuracy: An in vitro study

STATEMENT OF PROBLEM

High-translucency monolithic multilayer precolored zirconia provides acceptable esthetics and eliminates chipping of the veneering porcelain. However, the color is not always consistent with the standard Vita shade guide, and the color saturation may vary with the thickness of the zirconia.

PURPOSE

The purpose of this in vitro study was to characterize the effect of thickness on the color accuracy of high-translucency monolithic multilayer precolored zirconia.

MATERIAL AND METHODS

Plate-shaped (20×20 mm) Vita A2 shade high-translucency monolithic multilayer precolored zirconia specimens of 3 types (SHT Multilayer, AT Multilayer, and 3D Multilayer) in 4 thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were fabricated (N=120, n=10). A spectrophotometer was used to measure the color attributes (CIELab) against gray or A2 substrates to evaluate the color accuracy based on differences in color (ΔE) (versus the Vita shade guide) and chroma. Statistical analysis was performed by using the Pearson correlation, 2-way ANOVA, and post hoc Scheffé test (α=.05).

RESULTS

Against gray substrates, thickness was significantly positively correlated with all color attributes. Against A2 substrates, L∗ values increased with an increase in thickness; however, a∗, b∗, and chroma values remained stable. Zirconia with a thickness of 1.0 mm exhibited the lowest ΔE, regardless of the type, except for AT Multilayer against A2 substrates, where the lowest ΔE was achieved at 0.5 mm. At thicknesses ≥1.0 mm, the ΔE between the 2 substrates was imperceivable.

CONCLUSIONS

Thickness affected the color accuracy of different high-translucency monolithic multilayer precolored zirconia types. It appears that the optimal thickness in terms of color accuracy is 1.0 mm. These results could be used as a reference for the selection and preparation of abutments in clinical applications.

Mechanical performance of a hybrid zirconia developed through hydrothermal treatment and Room-Temperature Atomic Layer Deposition (RT-ALD)

OBJECTIVE

A silica-based nanofilm has been successfully deposited via Room-Temperature Atomic Layer Deposition (RT-ALD) on the surface of a glass. The purpose of this study was to evaluate the mechanical performance of a hybrid interface created between yttria-stabilized zirconia (Y-PSZ) transformed layer and silica-based nanofilm via RT-ALD.

MATERIAL AND METHODS

Fully-sintered Y-PSZ (14 × 4.0 × 1.5 mm) specimens in different translucencies (MO, MT, LT; IPS e.max Zircad, Ivoclar Vivadent) were distributed in 5 groups: control (C - no treatment); hydrothermal treatment (HT- 15h, 134°C, 2 bar); alumina blasting (B - 50 μm Al₂O₃); RT-ALD silica deposition (S); HT followed by silica deposition (HTS). RT-ALD cycles consisted of the sequential exposure of specimens to tetramethoxysilane orthosilicate (TMOS - 60s) and ammonium hydroxide (NH₄OH - 10 min) vapors in 40 cycles. Mechanical performance was analyzed by flexural strength (FS) (n = 10) and fatigue failure load (staircase method; n = 20) tests. Surface hardness (H) and Young's modulus (YM) were analyzed by nanoindentation. For surface chemical and topographical characterization, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were performed. Data from surface H, YM, FS, and fatigue limit (FL) were analyzed by two-way analysis of variance (ANOVA).

RESULTS

The interaction between material and treatment had a significant effect on FS (p < 0.001). The FS values ranged from 436.23 MPa to 856.65 MPa. HT resulted in the highest FS (856.65 MPa) for LT and the lowest FS (436.23 MPa) for MO zirconia. For all materials, S and B treatments resulted in similar FS values (p > 0.410). S did not affect FL when compared to the C group (p > 0.277) for any material investigated. HTS resulted in higher FL than S for LT and MO materials (p < 0.001). Surface hardness and modulus were similar between control and S-treated specimens for all materials analyzed. XPS analysis showed homogeneous silica content after 20 and 40 RT-ALD cycles, and SEM did not show significant changes in surface morphology between C and S-treated specimens.

CONCLUSION

RT-ALD resulted in effective silica deposition without any deleterious effect on zirconia-based materials mechanical properties. Alumina blasting promoted higher alteration on surface topography. HT prior to S resulted in superior FL (for MO and MT) and flexural strength (MO) for some of the materials investigated.

Failure Mechanism of Multilayer Ceramic Capacitors under Transient High Impact

In recent years, penetrating weapons have been used more and more to attack increasingly hard targets; therefore, the impact of such a penetrating process has increased to an extremely high level. As an important component of a fuze, the reliability of the ceramic capacitor in high-impact environments is key for the normal working of the fuze. In this paper, we found that a high-impact causes parameter drift of the multilayer ceramic capacitor (MLCC), which further causes the fuze to misfire. This paper mainly studies the internal mechanism of the MLCC’s parameter drift during high impact. Firstly, transient physical phenomena, such as capacitance fluctuation and the leakage current increase of the ceramic capacitor under a high acceleration impact, were studied experimentally by a Machete hammer, revealing the relationship between the capacitance change, leakage current change, and acceleration under different working conditions. Secondly, a mechanical model of the ceramic capacitor is established to simulate the change in capacitance value, which shows that the main factor of the capacitance change is the deformation-derived change in the facing area between the electrodes. Lastly, an equivalent circuit model is established to simulate the change in the leakage current, which shows that the main factor of the leakage current change is the piezoelectric resistance of the ceramic dielectric.

Surface Characterization and Optical Properties of Reinforced Dental Glass-Ceramics Related to Artificial Aging

The development of various dental glass-ceramic materials and the evolution of novel processing technologies lead to an essential change in the clinical and technical workflow. The long-term success of a dental restoration treatment is defined by its durability, which is directly influenced by the oral environment. This study's purpose was to evaluate the artificial aging behavior of nanostructured, respective microstructured ceramics related to surface topography, roughness, and optical properties. Six monolithic restoration materials were selected: milled lithium disilicate glass-ceramic (LDS-M) MT (medium translucency), hot-pressed lithium disilicate glass-ceramic (LDS-P) MT and HT (high translucency), milled zirconia-reinforced lithium silicate ceramic (ZLS-M) MT and hot-pressed zirconia-reinforced lithium silicate ceramic (ZLS-P) MT and HT, resulting n = 96 surfaces. All the samples were artificially aged by thermal cycling, and all investigations were made before and after thermal cycling. In terms of optical properties, differences recorded between ZLS and LDS ceramics are not significant. Thermal cycling increases the translucency of ZLS and LDS glass-ceramic materials significantly, with the most harmful effect on the pressed and polished samples. Micro- and nano roughness are significantly influenced by in vitro aging and a negative correlation was recorded. Glazed samples are characterized by significant rougher surfaces for all types of materials. On nanolevel, ZLS materials are significantly smoothed by thermal cycling.