Objective The purpose of this laboratory study was to evaluate the fatigue resistance, fracture resistance and mode of failure of posterior hybrid‐abutment‐crown vs. hybrid‐abutment with separate crown, both bonded to short titanium bases. Materials and Methods Thirty‐two titanium implants were embedded perpendicularly in auto‐polymerizing resin. Implant‐supported restorations simulating a maxillary first premolar were designed and milled using a CAD/CAM system and divided into 2 groups according to material (n = 16): zirconia (Z) and lithium disilicate (L). Each group was subdivided into two subgroups according to design (n = 8): hybrid‐abutment‐crown (ZS, LS) and hybrid‐abutment with separate crown (ZC, LC). Each group was subjected to 1.2 million cycles of thermo‐mechanical fatigue loading in a dual‐axis chewing simulator at 120 N load. Surviving specimens were subjected to quasi‐static loading in a universal testing machine. Mode of failure was determined under a low magnification optical microscope. Results During chewing simulation, 18.8% of zirconia and 43.8% of lithium disilicate restorations failed. The fracture resistance median values ranged from 3,730 N for group ZC, 3,400 N for group ZS, 1,295 N for group LS to 849 N for group LC. Group ZC had a statistically significant higher fracture resistance than groups LC and LS; however, it did not differ significantly from group ZS (p ≤ 0.05). Failures were seen in both titanium bases and ceramic superstructure. Conclusions Zirconia and lithium disilicate hybrid implant‐supported restorations with short (3 mm) titanium bases failed in a considerable number already during chewing simulation. Therefore, despite their high fracture strength the use in the posterior region should be considered critically.

Objective: This study evaluated the accuracy of different laboratory scanners (LS) for scanning of implant-supported full arch fixed prosthesis with different implant angulations.Materials and Methods: Two maxillary models that are designed to receive an all-onfour implant retained prosthesis were fabricated then scanned using five different LS. The models were divided into two groups according to the angulation of the posterior implant (Group 1; 30 and group 2; 45 ). Each group was then subdivided into five subgroups according to the type of LS, subgroup T; Medit T710, subgroup I; IneosX5, subgroup E; 3ShapeE4, subgroup A; Autoscan DS-Mix, and subgroup M; Ceramill Map600. An industrial 3D scanner was used as reference scanner, then each model was scanned with 5 LS 10 times. Trueness and precision were analyzed using Geomagic 3D analysis software.Results: Both scanner type and implant angle had a significant effect on the trueness (p < 0.001). Significant interaction was found between the scanner type and implant angle (p < 0.001). For scanner type tukeys post hoc test revealed highest trueness with the 3Shape E4 (21.3 ± 2.1) and the medit T710 (22.6 ± 2.1) and least trueness with the shining 3D autoscan ds-mix (33.8 ± 3.0). Significantly better trueness was observed with the 30 than the 45 angle. Regarding precision, two-way ANOVA revealed significant effect of the scanner type only (p < 0.001). There were no significant differences between the 3Shape E4, medit T710, Ineos X5, and the Ceramill map600. However, all showed significantly higher precision values when compared to shining 3D autoscan ds-mix.Conclusions: All tested scanners showed results within the clinically acceptable range with 3ShapeE4 and Medit T710 showing the highest accuracy.Clinical significance: Tested scanners can be used for scanning of All-on-four implant supported prosthesis. K E Y W O R D S all-on-4, dental implants, digital dentistry, extraoral scanner, fixed prosthodontics 1 | INTRODUCTION Completely edentulous patients have always struggled with conventional dentures. The limitations in function and retention of complete dentures are related to the fact that they are only supported by the mucosa and no other retention element is present. 1 Loss of posterior teeth, especially at an early age, leads to a significant decrease in alveolar bone volume. The All-on-4 concept is a treatment concept based on placing four implants on the jawbone to support the final prosthesis. Distal implants insertion at an angle allows one to bypass

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Objective: the aim of this study was to compare the mechanical behavior of different ceramics when used in thin vertical preparations versus traditional horizontal preparation. Material and Methods: two stainless-steel dies were milled to simulate a minimally invasive vertical preparation (VP) and a traditional horizontal preparation (HP) for an all-ceramic crown of a maxillary first premolar. The stainless-steel dies were duplicated using epoxy resin. Eighty monolithic crowns were milled and divided into 2 groups according to preparation design. Each design group was subdivided into 4 sub-groups according to material (n=10): IPS e.max CAD (lithium disilicate), Bruxzir shaded zirconia (full contour zirconia), CeraSmart (resin nanoceramic) and CEREC Tessera (advanced lithium disilicate). The crowns were cemented on their relevant epoxy resin dies using self-adhesive resin cement. All specimens were subjected to 15,000 thermocycles and then loaded to fracture in a universal testing machine. Data were analyzed using two-way ANOVA and Tukey pair wise comparison test. Results: the fracture resistance mean values of the VP (1344 + 118 N) was significantly lower than the HP design (1646 + 191 N). Ceramic crowns made of full contour zirconia had higher fracture resistance mean values (2842 + 380 N) than advanced lithium disilicate (1272 + 125 N) followed by lithium disilicate crowns (983 + 52 N) and resin nanoceramic (882 + 61 N). Conclusion: both vertical and horizontal preparations, regardless the different ceramic materials, showed clinically acceptable fracture resistance values.