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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.

Purpose: To evaluate the influence of preparation design and tooth geometry on the accuracy of scans obtained from three different intraoral scanners (IOS). Materials and Methods: Full coverage crown and inlay preparations with known axial wall tapers (6ᵒ and 12ᵒ) were performed on typodont teeth using a computer numerical control machine. Reference models were scanned with a highly accurate reference scanner (Ineos X5) and saved in standard tessellation language (STL) format then each IOS (Omnicam, Trios, and i500) scanned each model 10 times. The STL files obtained from the intraoral scanners were compared to the reference models (trueness) and within each test group (precision). Data were statistically analyzed using three-way ANOVA and one-way ANOVA. Results: When comparing trueness values extracoronal preparations (32.30 ± 11.23 µm) was significantly better than intra-coronal preparation (59.61 ± 16.42 µm). As for opposing wall taper, one-way ANOVA revealed that the more the convergence or divergence between opposing walls the better is the trueness. Significant differences were observed between the scanners. 3 Shape Trios (35.70 ± 14.12 µm) and medit i500 (44.31 ± 11.41 µm) showed no statistically significant differences. However, both showed significantly better precision results when compared to Omnicam (57.83 ± 22.14 µm). Conclusion: Extracoronal preparations show better trueness and precision in comparison to intracoronal preparations. Trios and i500 have better trueness and precision than Omnicam. Increasing the taper of the axial wall has a direct effect on trueness of scans obtained from the IOS.

Purpose: To evaluate the effect of different wax pattern fabrication techniques on the fit of customized pressed lithium disilicate implant abutments on titanium inserts before and after pressing. The marginal fit results of pressed lithium disilicate implant abutments were then compared with those of milled lithium disilicate abutments. Materials and Methods: After scanning the titanium inserts and designing an implant abutment, wax patterns were fabricated with three techniques (n = 15 each): computeraided design/computer-aided manufacturing (CAD/CAM) milling, 3D printing and conventional layering. The marginal fit (µm) was measured using a stereomicroscope for all the wax patterns before pressing them into the lithium disilicate abutments. The pressed implant abutments were measured again for marginal fit, and the results were compared to those of the milled lithium disilicate abutments. One-way analysis of variance (ANOVA) was used to assess different wax pattern fabrication techniques in each stage before and after pressing. One-way ANOVA was also used to compare the groups of pressed and milled lithium disilicate abutments. Multiple pairwise comparisons were performed using the Tukey post hoc test in each stage. Results: There were statistically significant differences between the marginal fit of the three wax patterns groups (p < 0.001; f = 123.33), wherein the mean marginal fit was the highest for conventionally layered wax patterns (30 ± 13.09) µm. Furthermore, after pressing, there were statistically significant differences between the marginal fit of the three pressed abutments groups (p < 0.001; f = 518.62), wherein the mean marginal fit was the highest for pressed e.max abutments fabricated from conventionally layered wax patterns (25.26 ± 3.9) µm. There was no statistically significant difference between the mean marginal fit of the pressed abutments fabricated from conventional layered wax patterns and that of the milled CAD/CAM abutments. However, the mean marginal fit of the milled CAD/CAM abutments was higher than that of the pressed abutments fabricated from both CAD/CAM wax and 3D printed wax. Conclusion: All the tested fabrication methods provided degrees of accuracy that lie well within accepted limits. The use of pressed lithium disilicate abutments fabricated from conventional layering wax pattern technique should provide a more consistent better marginal fit between the titanium insert and the abutment and may therefore be the preferable fabrication method.

Objective: To evaluate the effect of different occlusal preparation designs and CAD/CAM materials on the fracture resistance of maxillary premolars endcrowns. Materials and Methods: sixty-four endodontically treated upper first premolars were randomly divided into four groups according to ceramic materials (Vita Enamic and IPS emax CAD) and occlusal preparation designs (Anatomical and horizontal butt joint). After teeth preparation, the restorations were all made by CAD/CAM system (Cerec MCXL). Half of each group had undergone cyclic fatigue testing of 105 cycles with 50N loading force at a frequency of 0.5Hz in a mechatronic chewing simulator machine, and then all samples were loaded to fracture using a universal testing machine with a cross head speed of 0.5mm/min recording the fracture resistance values in N . The specimens were measured and statistically analyzed using using three-way analyses of variance (ANOVA), followed by serial two-way and one-way ANOVAs at each level of the study. P-values were adjusted for multiple comparisons using BENFORRONI correction and the significance level was set at P ? 0.05 for all tests. Results: Vita Enamic endocrowns showed higher fracture resistance values than IPS e max specimens. Conclusions: Vita Enamic endocrowns with anatomical preparations were found to be more favourable restoring endodontically treated maxillary premolars. KEYWORDSEndocrowns; All-Ceramic; Fracture; Cyclic loading; CAD/CAM