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Item Effects of Various Thicknesses on Load to Fracture of Posterior CAD/CAM Lithium Disilicate Glass Ceramic Crowns Subjected to Cyclic Fatigue(2015) Al-Angari, Nadia; Platt, Jeffrey A.; Bottino, Marco C.; Haug, Steven P.; Brown, David T.; Levon, John A.Background: New glass ceramics and Computer-Aided Design/Computer Assisted Manufacture (CAD/CAM) have become common aspects of modern dentistry. The use of posterior ceramic crowns with a high level of esthetics, fabricated using the CAD/CAM technology is a current treatment modality. Several materials have been used to fabricate these crowns, including lithium disilicate glass-ceramics, which have not been fully investigated in the literature. Objective: to investigate the load to fracture of lithium disilicate glass ceramic posterior crowns fabricated by CAD/CAM technology with different material thicknesses adhesively cemented on epoxy resin. Methods: Four groups of different ceramic thicknesses (0.5 mm, 1 mm, 1.5 mm, and 2 mm) were fabricated by milling CAD/CAM lithium disilicate IPS emax CAD blocks. A total of 68 posterior crowns were surface treated and luted with a resin adhesive cement on an epoxy resin model. Samples were fatigued then loaded to fracture using a universal testing machine to test the fracture strength. Statistical comparisons between various crown thicknesses were performed using one-way ANOVA followed by Fisher's Protected Least Significant Differences. Results: There was a significant difference in the load-to-fracture (N) value for all comparisons of the four thickness groups (p < 0.0001), except 2 mm vs. 1.5 mm (p = 0.325). The mean load-to-fracture (N) was significantly higher for 2 mm than for 1 mm or 0.5 mm. Additionally, the mean load-to-fracture was significantly higher for 1.5 mm than for 1 mm or 0.5 mm. Furthermore, the mean load-to-fracture was significantly higher for 1 mm than for 0.5 mm. Conclusion: Within the limitation of this study, it is advisable for clinical applications to consider a crown thickness of 1.5 mm or greater of milled lithium disilicate for posterior single teeth.Item Fatigue failure load of lithium disilicate restorations cemented on a chairside titanium-base(2017) Kaweewongprasert, Peerapat; Morton, Dean; Levon, John A.; Phasuk, Kamolphob; Bottino, Marco C.PURPOSE: To evaluate the fatigue failure load of distinct lithium disilicate restoration designs cemented on a chairside titanium-base (VariobaseTM for CEREC®, Straumann® LLC, USA) for restoring anterior implant restoration. MATERIALS AND METHODS: Left maxillary incisor restoration was virtually designed in 3 groups (n=10; CTD: lithium disilicate crowns cemented on custom-milled titanium abutments; VMLD: monolithic full-contour lithium disilicate crowns cemented on titanium-base; and VCLD: lithium disilicate crowns cemented on lithium disilicate customized anatomic structures then cemented on titanium-base). The titanium-base was air-abraded with aluminum oxide particles, 50 µm at 2 bars. Subsequently the titanium-base was steamed, air-dried and a thin coat of silane (Monobond Plus, Ivoclar Vivadent®, USA). All ceramic components were surface treated with hydrofluoric acid etching gel, follow by silanized, and bonded with resin cement (Multilink Automix, Ivoclar Vivadent®, USA). Specimens were fatigued at 20 Hz, starting with a load of 100 N (×5000 cycles), followed by stepwise loading up to 1400 N at a maximum of 30,000 cycles each. The failure loads, number of cycles, and fracture analysis were recorded. Data were statistically analyzed using one-way ANOVA followed by pair-wise comparisons (p < 0.05). Kaplan-Meier survival plots and Weibull survival analyses were reported. RESULT: For catastrophic fatigue failure load and total number of cycles for failure, VMLD (1260 N, 175231 cycles) was significantly higher than VCLD (1080 N, 139965 cycles) and CDT (1000 N, 133185 cycles). VMLD had higher Weibull modulus (11.6), demonstrating higher structural reliability. CONCLUSIONS: VMLD performed the best fatigue behavior when compared with the two other groups.