Background: Excessive marginal discrepancy of crowns favors the rate of cement dissolution and microleakage that may cause pulpal inflammation. Besides, it may increase plaque retention leading to the onset of periodontal disease. Therefore, this research was carried out to study the effect of fabrication stages and artificial aging on the marginal adaptation of CAD/CAM Zirconia-based crowns which have become increasingly popular among the patients due to their natural esthetics and excellent strength.Purpose: To evaluate the marginal adaptation of CAD/CAM Zirconia-based crowns on their respective prepared teeth during different fabrication stages namely; framework, after veneering, after crown cementation and after thermo-mechanical loading. Materials and methods: A total of twenty zirconia frameworks were fabricated using (Cercon smart ceramics, DeguDent, Germany) manufacturing system, conventionally veneered with (Cercon Ceram kiss, DENSPLY, Germany), cemented with conventional glass ionomer to their corresponding prepared human teeth. The cemented crowns were finally aged through a process of thermo-mechanical cyclic loading. The assessment of vertical marginal gap was performed on the prepared teeth using an optical microscope with image-j software analysis system at 40Â magnification for frameworks, for restorations before and after cementation then, after thermo-mechanical loading. Differences between the vertical gap during fabrication stages and the effect of artificial aging were statistically analyzed using a one-way analysis of variance ANOVA and Independent-samples T test. Results: In this study, the marginal gap increased after every tested stage. The vertical marginal gap recorded its smallest mean value (41.08 ± 3.23 mm) during core stage. A significant increase in the measurement of vertical marginal gap was observed after firing the veneering layer reaching (46.87 ± 3.94 mm). After cementation, the marginal gap was (46.87 ± 4.65 mm). Finally; thermo-mechanical loading corresponding to one year of clinical use was found to cause a significant increase the vertical marginal gap to record its highest value (56.73 ± 7.21 mm).

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Purpose: The purpose of this study was to determine the influence of CAD/CAM system type and immediate dentin sealing (IDS) on the marginal fit of hybrid ceramic endocrowns. Material and Methods: Forty recently extracted lower molars were selected, and standardized prepared to receive endocrown restorations .All restorations were milled in hybrid ceramic (VITA ENAMIC® for CEREC®/ inLab®, VITA Zahnfabrik H. Rauter GmbH & Co.KG., Germany). The teeth were assigned to 4 groups (n=10) according to: (1) The type of CAD/CAM system: a) DOF system (DOF Inc., Seoul, South Korea) and b) CEREC inLab system (Sirona Dental Systems, Germany)], (2) The timing of dentin sealing. a) Immediate dentin sealing (IDS) and b) Delayed dentin sealing (DDS)].The vertical marginal gaps were then measured using measuring Stereomicroscope (Nikon Eclips E600, Tokyo, Japan). The obtained data were submitted to Kruskal-Wallistest (α=.05). Results: All marginal gap values found in this study were below the clinically acceptable value of restorations which is 120 µm. A significant difference was found between group 1 (DOF, IDS), group 2 (DOF ,DDS) and between group3 (CEREC , DDS), group 4 (CEREC, IDS) also between group 2(DOF, DDS) and 4 (CEREC, IDS). Conclusion: This study concluded that there is a significant effect of the CAD \CAM system and the timing of dentin sealing application on the marginal fit of the Hyprid ceramic endocrown restorations, where CEREC in-lab system and the immediate dentin sealing decrease the marginal adaptation .

Purpose: Evaluation of marginal and internal fit of monolithic zircon crown restoration fabricated by scanning three different die material ;3D printed resin versus stone and epoxy resin dies. Materials and methods:A standardized Computer Numerical Control machine (CNC) will be used to fabricate a stainless steel master die simulating a prepared tooth with an occluso-gingival height of 6 mm, a taper of 6° and 1 mm shoulder circumferentially. The overall diameter of the die at the base is 8.5 mm Three groups of zircon crown (Prettau® Zirconia manufactured by Zirkonzahn® and E-Denstone®). 10 crowns per each group fabricated digitally from three different dies as follow: 1) First group (G1) 3D printed resin die (light cured methacrylate (Envision TEC). 2) Second group (GII), Epoxy resin die. 3) Third group (GIII) Type IV stone die (Zhermach spa, Bouazecchino ST, Badia polesine, Italy). Each crown fabricated from its specific die seated and stabilized on the master stainless steel die. Demark certain points on the crown margin and photographed using USB Digital microscope with a built-in camera (Scope Capture Digital Microscope, Guangdong, China) connected with an IBM compatible personal computer using a fixed magnification of 45X. Internal discrepancy of the copings was measured by a replica technique. Each coping was filled with light-body silicone (zetaplus, zhermack, italy), the replicas (heavy and light -body silicon) were carefully removed from the crown and sectioned mesio-distally into two equal segments with three regions measured on each section (margin, axial and occlusal), yielding 8 internal measurements for each coping. A digital image analysis system (Image J 1.43U, National Institute of Health, USA) was used to measure and qualitatively evaluate the gap width.Results: Data analysis was performed in several steps. Initially, descriptive statistics for each group results. One-way ANOVA followed by pair-wise Tukey's post-hoc tests were performed to detect significance between all groups. The absolute marginal gap mean ±SD values recorded for first group were (18.0305±6.99717), for II group were (41.0989± 21.55940) and for III group were (18.2960 ± 7.177245). It was found that the highest absolute marginal gap mean value recorded for IIgroup followed by III group mean value.While the lowest absolute marginal gap mean value recorded for I group. The difference between all die groups was statistically significant as revealed with one-way ANOVA test (p=0.01). Pair-wise Tukey's post-hoc test showed non-significant differences while (p=0.99) between (groups III,I), While between (groups II, III) and (groups II, I) there is significant differences where (p=0.01).(812) Amany M. Korsel E.D.

Purpose: To give an idea of different implant-abutment material behavior by evaluation the stress distribution of material type on surrounding structures of single implant-supported restorations. Materials and Methods :A 3D Finite Analysis method used for evaluate the distribution of stress in implants were examined using different abutment materials: Titanium(Ti) -(Implant Blue Sky, Bredent, Senden, Germany), Zirconium(Zr) (Implant Blue Sky, Bredent, Senden, Germany), High Performance Polymer (BioHPP)-( Sky elegance abutment, Bredent, Senden, Germany). Fiber reinforced composite(FRC)( World Headquarters sigma-aldrich.) Loading applied and as loading five nodes top an monolithic ceramic restoration. Mises and deflection values through screw and implant and cortical bone were calculated. Results :The results of the analysis showed that the abutment material affect stress distributions where the least stresses created on bone with BioHPP abutment (16.5Mpa) followed with FRC abutment (17.3Mpa). While its effect on screw showed clear differences, the least stresses created with Zirconia abutment (67.9Mpa) followed by Titanium abutment (85.29Mpa) then FRC (117.32Mpa) finally abutment. These showed BioHPP FRC abutments nearly have very close and less effort bone. The highest stresses on implant showed with FRC and BioHPP abutments as follow (142.4, 122.4 Mpa) while the least stresses with Zirconium and Titanium abutments (126.5, 137.45 Mpa). Conclusion:BioHPP and FRC abutment transmit less stress on the bone than Titanium and Zirconium .