This study investigates the impact of tightening torque (preload) and the friction coefficient on stress generation and fatigue resistance of a Ti-6Al-4V abutment screw with an internal hexagonal connection under dynamic multi-axial masticatory loads in high-cycle fatigue (HCF) conditions. A three-dimensional model of the implant–abutment assembly was simulated using ANSYS Workbench 16.2 computer aided engineering software with chewing forces ranging from 300 N to 1000 N, evaluated over 1.35 × 10⁷ cycles, simulating 15 years of service. Results indicate that the healthy range of normal to maximal mastication forces (300–550 N) preserved the screw’s structural integrity, while higher loads (≥800 N) exceeded the Ti-6Al-4V alloy’s yield strength, indicating a risk of plastic deformation under extreme conditions. Stress peaked near the end of the occluding phase (206.5 ms), marking a critical temporal point for fatigue accumulation. Optimizing the friction coefficient (0.5 µ) and preload management improved stress distribution, minimized fatigue damage, and ensured joint stability. Masticatory forces up to 550 N were well within the abutment screw’s capacity to sustain extended service life and maintain its elastic behavior.

The aim of this study was to investigate the effect of repeated pressing of lithium disilicate ceramic on the shear bond strength (SBS) of three types of resin cement. Methodology: A lithium disilicate ceramic (IPS e.max^® Press) was first heat-pressed to form rectangular disk specimens. Then, leftovers were used for the second and third presses. A total of 90 specimens were prepared and separated, according to the number of pressing cycles, into three groups: 1st, 2nd, and 3rd presses (n = 30). Each group was further subdivided into three groups (n = 10) according to the type of resin cement used, as follows: Multilink N (MN), Variolink Esthetic DC (VDC), and Variolink Esthetic LC (VLC). All the cement was bonded to the ceramic surface, which was etched with hydrofluoric acid and primed with Monobond Plus. All samples were light-cured and stored for 24 h. Shear bond strength was tested on a universal testing machine. Results: A two-way ANOVA was used to evaluate the influence of repeated pressing cycles and cement type as well as their interaction. The results indicated that cement type has a significant impact (p < 0.001) but not the number of pressing cycles (p = 0.970) or their interaction (p = 0.836). The Bonferroni post-hoc test showed that the SBS of MN was significantly higher than that of VDC and VLC in the first press and second press cycles, respectively. The SBS of MN was significantly higher than that of VDC and VLC cements in the third pressing cycle. There was no significant difference in the SBS between VLC and VDC in all three pressing cycles. Conclusion: The results of the current study did not report a detrimental effect of repeated pressing up to three cycles on the shear bond strength of the IPS e.max^® Press. Multilink resin cement showed the highest SBS to IPS e.max^® Press at the third pressing cycle. For all types of cement and heat pressing cycles, the majority of cement failures were adhesive. No cohesive failures occurred in any of the tested resin cements, regardless of the cement type or the number of heat pressing cycles tested.

This study evaluated the impact of glazing and multiple firing on the flexural strength, translucency, and color stability of three types of zirconia: 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), 4 mol% yttria partially stabilized zirconia (4Y-PSZ), and 5 mol% yttria partially stabilized zirconia (5Y-PSZ). A total of 120 samples were categorized into four groups: polishing only (P), polishing + glazing (PG), polishing + glazing + one glaze firing (PGF), and polishing + glazing + two glaze firings (PGFF). A three-point bending test was used for assessing flexural strength and a spectrophotometer analysis for assessing color difference (ΔE*_ab) and translucency parameter (TP). Statistical analysis included one-way ANOVA and Kruskal–Wallis tests, with significance set at α = 0.05. The type 3Y-TZP showed the highest flexural strength (918.46 MPa) and lowest translucency (TP = 4.32), while 5Y-PSZ exhibited the lowest strength (401.58 MPa, p < 0.001) and highest translucency (TP = 6.26, p ≤ 0.012). Heat treatment resulted in a significant reduction in the flexural strength of 5Y-PSZ (p = 0.002), followed by 3Y-TZP (p = 0.04). The type 5Y-PSZ exhibited significant change in translucency (p = 0.003) and unacceptable variations in color (ΔE*_ab: 1.49–9.6). The type 4Y-PSZ exhibited the highest stability in flexural strength, translucency, and color under multiple treatments. In conclusion, while glazing and firing significantly compromised 5Y-PSZ’s flexural strength and altered its color and translucency, 4Y-PSZ demonstrated the highest stability.

The aim of this study was to investigate the effect of repressing leftover heat-pressed lithium disilicate material on its mechanical and optical properties. A lithium disilicate ingot (IPS e.max^® Press, IvoclarVivadent, Schaan, Liechtenstein) shade (A1) low translucency was first heat-pressed to yield ceramic bars and disks. Then, the second and third presses were fabricated from the leftovers of the previous pressing cycles. A total of 36 bars and 15 disk specimens were fabricated and divided into three groups according to the number of pressing cycles (n = 12 bars and n = 5 disks): P1: first press (control), P2: second press, and P3: third press. The specimens were tested for flexural strength, color change, Vickers hardness, and surface topography under scanning electron microscopy. One-way ANOVA testing was used to evaluate flexural strength and hardness, while an independent t-test was performed to evaluate color change. There was no significant difference in flexural strength as the number of heat-pressed cycles increased (p = 0.283). Similarly, there was no significant difference in the microhardness values between all groups (p = 0.220). The overall color change ∆E between P1–P2 and P1–P3 were 2.01 and 2.14, respectively. The SEM images showed evenly distributed and densely packed lithium disilicate crystals in the P1 group. However, larger and less densely packed crystals were noticeable in P2 and P3. The IPS e.max Press could be repressed up to two times without an adverse effect on mechanical properties or color stability. These results may support the reuse of pressed lithium disilicate for economical purposes, but further clinical evaluation should be conducted to confirm these findings.

Objective: To evaluate the effect of deep margin elevation (DME) and immediate dentin sealing (IDS) on the fracture strength of premolars restored with lithium disilicate inlay restorations.Materials and Methods: Standard MOD inlays with proximal box preparations extending 3 mm apical to the cementoenamel junction were prepared on forty sound premolars (n = 10) randomly divided into four groups: inlays without DME and without IDS (G1); inlays without DME but with IDS (G2); inlays with DME but without IDS (G3); and inlays with both techniques applied (G4). Composite resin was applied incrementally to elevate the proximal cervical margin coronally to the cementoenamel junction. For immediate dentin sealing, bonding agent was applied immediately after tooth preparation. All teeth were restored with lithium disilicate inlays and, after adhesive resin cementation, specimens were thermomechanically aged for 500 cycles at 5°–55°C and then subjected to load failure testing. Failure loads and locations were recorded and analyzed using one‐ and two‐way ANOVA with Tukey's post‐hoc testing (α = 0.05). Failure modes were analyzed using descriptive statistics.Results: The mean fracture loads were 565.76 ± 233.22 N, 978.47 ± 394.2 N, 974.31 ± 334.7 N, and 1108.21 ± 292.41 N for G1, G2, G3, and G4, respectively. Deep margin elevation (p = 0.011) and immediate dentin sealing (p = 0.010) were associated with significantly increased fracture loads. Fracture loads were significantly lower for G1 teeth than for G2‐G4 teeth, but there were no significant differences between G2, G3, and G4. G1 teeth showed 50% catastrophic and non‐catastrophic failures, which increased to 60% for G2 and decreased to 20% for G3 teeth. Samples with both seals and elevation (G4) had a 60% catastrophic failure rate.Conclusions: When applied individually or together, deep margin elevation and immediate dentin sealing significantly increase the fracture strength of premolars restored with indirect lithium disilicate inlays.Clinical Implications: In the challenging setting of margin elevation, studies on the effects of immediate dentin sealing have generally been limited to evaluating marginal integrity and bond strength. The findings of this In Vitro study suggest that both deep margin elevation and immediate dentin sealing protocols are likely to improve clinical outcomes of indirect lithium disilicate inlay restorations and may be considered viable options in clinical practice.