Arta Lamallari, Vera Colombo, Luiza Freitas Brum Souza, Enkelejd Angelo Cankja, Abdülhakim Alpaslan Sener, Mutlu Özcan
Hypoxia induction was robust across all participants, with significant reductions in SpO₂ metrics under hypoxia. While no individual symptoms reached statistical significance after correction for multiple comparisons, several hypoxia-related symptoms showed consistent directional trends and approached statistical significance. Continuous subjective ratings were significantly lower under hypoxia, with breathing demonstrating a pronounced temporal deterioration. Hypoxia recognition occurred more often during hypoxia than during control. No significant effects were observed in objective performance measures.
BACKGROUND: The aim of this study was to evaluate the load-bearing capacity of zirconia, lithium disilicate, and resin-matrix composite occlusal veneers bonded to different substrates: dentin surrounded by enamel (DE), dentin (D), and resin composite (C), simulating eroded teeth.
METHODS: Occlusal veneers (1.0 mm thick) were milled from zirconia (IPS e.max ZirCAD), lithium disilicate (IPS e.max CAD; Initial LiSi Block), and resin-matrix composite (Lava Ultimate), and bonded to the different substrates (n = 10 per group). Specimens were cemented, subjected to thermo-mechanical aging (1,200,000 cycles; 5-50 °C), and tested under monotonic load-to-fracture. Maximum fracture load (Fmax) data were analyzed using the Shapiro-Wilk and Levene tests for normality and homoscedasticity, followed by two-way ANOVA and Tukey's post hoc test (α = 0.05). Weibull analysis was performed to assess structural reliability, and Pearson's correlation analysis was used to evaluate the relationship between bonded surface area and Fmax.
RESULTS: The results indicated that both restorative material and substrate type significantly affected Fmax. Lithium disilicate veneers exhibited substrate-dependent behavior, with higher fracture loads when bonded to resin composite, intermediate values when bonded to DE, and the lowest values when bonded to D. The resin-matrix composite showed a more homogeneous response across substrates, although Fmax decreased from resin composite to dentin. Zirconia restorations demonstrated consistently high fracture loads across all substrates, without a substrate-dependent trend. Failure modes were predominantly adhesive or mixed for lithium disilicate, whereas cohesive veneer failures predominated for zirconia.
CONCLUSIONS: Both restorative material and substrate condition significantly affected the strength and reliability of ultra-thin occlusal veneers. Zirconia showed the most robust performance and the lowest sensitivity to substrate variations, whereas bonding to resin composite substrates improved reliability compared with dentin. These findings highlight the importance of substrate management and adhesive optimization when restoring eroded teeth.