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Objective: To evaluate wear of three CAD/CAM ceramics (Lithium disilicate, Zirconia reinforced-lithium silicate, Zirconia-based) and their opposing enamel antagonists in addition to their microhardness & fracture toughness. Materials and Methods: Thirty rectangular shaped samples (12 x 14 x 2 mm) were fabricated and divided into three groups according to the type of ceramic used (10 samples each): Group (IP): IPS e.max CAD, Group(VS):Vita Suprinity and Group(BZ): BruxZir. Each group was divided into two subgroups (5 samples each) according to the testing procedure. The first subgroups were subjected to microhardness and fracture toughness tests, while the second subgroups were first weighed then subjected to wear test and finally re-weighed again before being subjected to microhardness and fracture toughness tests. Results: Wear results showed a significant difference in weight loss of tested ceramics and the antagonist tooth structure between (BZ) and both (IP) & (VS). Microhardness of the three ceramics were significantly different in each subgroup regardless of wear test. Regarding fracture toughness, there was a significant difference between (BZ) and both (IP) & (VS) in both subgroups. For all tested ceramics, both subgroups (without wear and after wear) were not statistically significantly different regarding microhardness and fracture toughness. Conclusions: BruxZir showed the best wear behavior and the worst abrasiveness to enamel. Microhardness and fracture toughness were the highest for zirconia-based ceramic but both parameters were not affected by thermo-mechanical aging of wear test for the three tested ceramics.

The effect of glass ionomer cement modified by nanoparticles on the bond strength and colour of lithium disilicate ceramic was studied. Glass ionomer cement modified by nanosilver or nanogold, glass ionomer cement and IPS e.max CAD A2 were used. Thirty e.max CAD discs were constructed. The samples were divided into 3 groups, the first group, 10 samples (control group) used non modified glass ionomer cement (GIC), the second and third groups, 10 samples each used modified glass ionomer cement : nano silver (NSGIC), nanogold (NGGIC). The samples were then subdivided according to the test to which they will be subjected: colour test-shear bond strength test (5 samples each).The samples subjected to colour test were cemented to a composite discs with a shade A2 while those subjected to shear bond strength test were cemented to dentine, using the 3 tested types of glass ionomer. Results showed that ΔE of all the tested samples recorded values in the range of clinical acceptability. NGGIC group showed less ΔE than NSGIC group compared to the control group. Also, the results showed no statistical significant difference in shear bond strength between the control group (GIC) and the two experimental groups (NSGIC) and (NGGIC). Conclusion: The addition of nanoparticles to glass ionomer cement resulted in ΔE within the clinical acceptance. Also, they showed no significant difference as regards to shear bond strength.

Statement of problem: Most of the failures in metal-ceramic restorations occurs at the interface between the two materials. For long term clinical performance, these restorations should have adequate bond strength between metal and ceramic. Few data is available in regards to the metal-ceramic bond strength of Cobalt Chromium (Co-Cr) alloys fabricated by computer aided designing design/computer aided manufacturing CAD/CAM technology. Purpose of the study: The purpose of this in vitro study was to explore the influence of Co-Cr fabrication techniques on shear bond strength of porcelain to milled and cast Co-Cr alloys and to evaluate failure mode with & without thermo-mechanical cycling. Materials & Methods: A total of 20 disc samples (10 mm diameter x 4 mm thickness) were fabricated of Co-Cr alloy and divided into two groups (10 discs each) according to their fabrication technique: Group I: fabricated by CAD/CAM milling and Group II: fabricated by conventional casting. Then porcelain build up for all discs (10 mm diameter x 2mm thickness) was done using feldspathic porcelain. Each group was subdivided according to discs' exposure to thermomechanical cycling into two subgroups (5 discs each). Subgroup A : without thermo-mechanical cycling and Subgroup B: with thermo-mechanical cycling. All the disc samples were subjected to the shear bond strength (SBS) test and the failure mode was investigated under digital microscope at 40 X. Data were statistically analyzed using Independent sample t-test and Two-way ANOVA test (P ≤ 0.05). Results: The results showed that the fabrication techniques were statistically insignificantly affecting the SBS of both CAD/CAM milled and conventional casting groups. Regarding the thermo-mechanical cycling, the CAD/CAM milled and conventional casting groups without thermo-mechanical cycling showed a statistically significantly higher SBS than those with thermomechanical cycling. Failure mode was mixed type for all disc samples. Conclusions: Fabrication technique of Co-Cr alloy had no significant effect on SBS. Thermomechanical cycling of milled and cast Co-Cr samples significantly affecting SBS with the superiority of the non-thermo-mechanical cycled samples. All the tested samples showed SBS values within the clinically acceptable levels. CAD/ CAM fabricated Co-Cr may be considered a promising alternative to conventional cast Co-Cr for metal ceramic prosthesis in terms of SBS.

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