Objective: The objective of this study was to evaluate the effect of thickness change on the translucency of two recent monolithic zirconia dental ceramics used at different thicknesses. Materials and methods: A total of 60 disk-shaped specimens were prepared from two high-translucent tetragonal zirconia (Zolid ht+) and ultra-translucent cubic zirconia (Zolid fx), and divided equally into two groups according to material, each group with further subdivided into 3 subgroups according to thickness 0.5, 1, and 1.5 mm (n=10). A spectrophotometer was used to assess the CIE L*, a*, and b* for each thickness of the two zirconia ceramics. The Translucency Parameter (TP) was calculated. 1-way ANOVA and 2-way ANOVA statistical analysis of variance were performed (α=.05). Results. A statistically significant higher mean TP value was recorded with the ultra-translucent cubic zirconia group compared to that of high-translucent tetragonal zirconia regardless of thickness (P=0.008*< 0.05). Thickness had a significant effect on the translucency parameter of the two zirconia ceramics. Within group comparisons showed that for each of the two materials, the 0.5mm thickness recorded the statistically significant highest mean TP value, followed by the 1mm subgroup, whereas the statistically significant lowest mean TP value was recorded for the 1.5mm subgroup. Conclusions. Within the limitations of this study, it was found that material type and thickness had a significant effect on the translucency of high translucent monolithic zirconia.

Objective: The aim of the study was to evaluate fracture resistance of zirconia monolithic restorations after ageing procedures. Material and methods: The fracture resistance of zirconia-based restoration after ageing procedures was evaluated. Monolithic translucent zirconia 3-unit FDPs were fabricated using Cerec inLab CAD/CAM system on 2 stainless steel dies prepared from stainless steel with a uniform 120 degrees circumferential deep chamfer finish line of 1 mm width and were placed into a stainless steel holder. FDPs were divided into 2 groups, the first group (Group A) was subjected to aging procedures in an autoclave at hydrothermal conditions 134 °C /2 bars for 5 hours. The second group (Group B) was not subjected to any ageing procedures and was designed as control group. All specimens of group A (Aged TZI) and group B (non- aged TZI) were loaded compressively in a universal testing machine at cross head speed 0.5 mm/min until fracture occurred. The percentage of monoclinic (m) phase was detected by XRD device. Scanning electron microscope (SEM) was used to examine the fractured surfaces for Aged TZI (Group A) and Non-aged TZI (Group B). Student’s t-test was used to compare between fracture resistances of both groups. The significance level was set at P ? 0.05. Results: The fracture resistance mean (SD) values of non-aged TZI (Group B) was 2406.9±306.8 N which showed statistically significantly higher than that of aged group (Group A) which was 1964.5±234.5 N. The percentage of monoclinic (m) phase detected by XRD device software in non-aged TZI (Group B) was nearly 0 weight % and in aged TZI (Group A) was about 42 weight %. Conclusion: Accelerated artificial aging decreases the fracture resistance of monolithic TZI FDPs. Keywords Artificial aging; Fracture resistance; Monolithic zirconia.

Objective: As the high strength glass ceramics had attained a profound contribution in prosthodontics, it was aimed to evaluate the fatigue performance of two machinable high strength glass ceramics with further fracture mode analysis. Materials and methods: Twenty crowns were fabricated using Cerec in-Lab CAD\CAM system, ten crowns were fabricated from IPS. E.max CAD: group (EM-LDS) as control group and ten crowns were fabricated from VITA SUPRINITY: group (VS-ZLS). The completed crowns were cemented on epoxy resin dies. The cemented crowns were subjected to thermomechanical cycling for 75000 cycles, then loaded until fracture by using universal testing machine. Failure mode were assesses guided by Brukes' classification for all specimens. The collected data was statistically analyzed using Student t-test and Paired t-test while the significance level was set at P ≤ 0.05, in addition to descriptive statistics of the fracture mode analysis. Results: There was no statistically significant difference in fatigue performance between the two tested groups with the major fracture occurrence in type III central fracture. Conclusion: both tested high strength glass ceramics are considered as acceptable modalities for restoration of single tooth restoration as both materials have comparable strength and exceeded the reported range of human masticatory forces.

Objective: To assess effect of different bite recording materials on accurate mounting of working casts. Materials and Methods: A 40 maxillary and mandibular stone casts were obtained from a complete anatomic dentoform using monophase medium-bodied consistency polyether impression material. Derived stone casts were divided according to bite registration material in to four groups (10 samples each); 1. wax group, 2. polyvinyl siloxane group, 3. polyether group and 4. Bis-crylic resin group. Ten bite records were obtained with poly vinyl siloxane recording material from hand articulated dentoform to serve as control group. The 40 produced mandibular stone casts were mounted on semi adjustable articulators using four bite registrations tested materials (10 for each). Unilateral Polyvinyl siloxane bite registration were made for 40 mounted stone casts to evaluate bite registration accuracy. Then bite records were placed on a light box and a camera set at a fixed distance 8 inches was used to capture the light transmission that was projected through the bite material. The camera transferred the information to an image analysis program (ImageJ) which measure accuracy of registration materials. Results: Numerical data were explored for normality by checking the data distribution and using Kolmogorov-Smirnov and Shapiro-Wilk tests. Grey scale data showed parametric distribution while measurement error showed non-parametric distribution. The difference between tested groups and control group was compared using ANOVA test. The results revealed that, the different between test groups and control was insignificant (P-value = 0.104). Conclusions: All tested bite registration materials had comparable results, although Luxabite and polyether showed higher errors than polyvinyl siloxane and wax.