Objective: The aim of this study was to evaluate the micro-shear bond strength between a dual cured resin cement and five different types of ceramics in composition and techniques of construction, using two different surface treatments. Materials & methods: A total of 50 ceramic disks were made and divided into 5 equal groups according to material type IPS Empress CAD, IPS e.max Press, IPS e.max CAD, Vita Suprinity and PM9 (n = 10). Each group was subdivided into 2 subgroups according to surface treatment they will be subjected to (n=5). Subgroup I: Bonding surfaces were etched with 5% HF acid, then coated with Monobond S. Subgroup II: Monobond Etch & Prime was applied on the bonding surfaces. For standardization of bonding surface area, 5 plastic tubings distributed on the bonding surface of each disk were used to place the dual resin cement. The samples were then subjected to micro-shear bond strength. Results: Results showed insignificant difference in micro-shear mean values between the IPS Empress CAD subgroups while significant differences were found between the other subgroups within the same group. Monobond Etch & Prime surface treatment resulted in higher micro-shear bond strength compared with HF surface treated subgroups for all the tested materials except for the PM9 and IPS e.max CAD. Conclusions: It was found that ceramic microstructure as well as the fabrication technique affects the selection surface treatment type. Also, Monobod Etch and Prime as a single step surface treatment produced clinically accepted and comparable results to that of HF treatment.

Objective: The aim of this study was to investigate the effect of repressing IPS e.max Press with different concentrations on the marginal gap and fracture strength of ceramic crowns. Materials and methods: Twenty-five IPS e.max Press crowns were fabricated. They were divided into 5 groups (5 samples in each group) according to the Wt.% of the new ceramic ingots to the repressed ceramic. Group I is 100 % new ceramics. Group II is 75 % new and 25% repressed ceramics. Group III is 50 % new and 50 % repressed ceramics. Group IV is 25% new and 75% repressed ceramics. Group V is 100 % repressed ceramics. Each crown was seated on the copper mold and the marginal gap was measured at 16 predetermined points using a computer connected stereomicroscope. For fracture strength test the crowns were luted using resin cement on epoxy dies and subjected to fracture strength test. Results: Group 1 (100 % new) recorded the least marginal gap (32.7 µm), while group 5 (100% repressed) recorded the highest marginal gap (120.91 µm). No statistical significant difference between marginal gap of the first three groups (100 % new, 75% new + 25% repressed, 50% new + 50% repressed). A statistically significant difference was recorded between these 3 tested groups and group 4 (25% new + 75% repressed). There was also a significant difference between group 4 and group 5 (100% repressed). Fracture strength results showed that Group I (100 % new) recorded the highest fracture strength (929.724 N), while group III (50% new) recorded the least fracture strength (819.366N). A statistical significant difference was found between the first four groups and a siginficant difference between GroupV (100% repressed) and Group I,II,III. While, there was no significant difference between Group IV and Group V. Conclusions: It was found that various weight percentages of repressed ceramics affected the marginal gap and had a significant effect when it exceeded 50 %, although all tested groups were clinically accepted. Also, homogeneity of the ceramic structure had a positive effect on fracture strength, as the least fracture strength was recorded for the 50% new + 50% repressed ceramic group and it increased significantly as this relation increased towards either the new ingot ceramics or the repressed ceramic:

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.

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.

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