Implant-retained mandibular ball-supported and bar-supported overlay dentures are the two most common treatment options for the edentulous mandible. The superior option in terms of strain distribution should be determined. The three-dimensional model of mandible (based on computerized tomography scan) and its overlying implant-retained bar-supported and ball-supported overlay dentures were simulated using SolidWorks, NURBS, and ANSYS Workbench. Loads A (60 N) and B (60 N) were exerted, respectively, in protrusive and laterotrusive motions, on second molar mesial, first molar mesial, and first premolar. The strain distribution patterns were assessed on (1) implant tissue, (2) first implant-bone, and (3) second implant-bone interfaces. Protrusive: Strain was mostly detected in the apical of the fixtures and least in the cervical when bar design was used. On the nonworking side, however, strain was higher in the cervical and lower in the apical compared with the working side implant. Laterotrusive: The strain values were closely similar in the two designs. It seems that both designs are acceptable in terms of stress distribution, although a superior pattern is associated with the application of bar design in protrusive motion.

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Recently, new generations of nanoceramic composite resin CAD/CAM blocks, have been introduced to dentistry, which are claimed to have higher flexural strength, fracture, fatigue and wear resistance, and beside natural looking appearances can be polished easily. Therefore, the aim of this study was to compare flexural strength of 2 nanoceramic composite resin CAD/CAM blocks (Lava Ultimate and Vita Enamic) and a lithium disilicate glass ceramic (IPS e.max CAD) material. In this experimental study, resin nanoceramic blocks, Lava Ultimate (3M, ESPE, USA), Vita Enamic (VITA Zahnfabrik, Bad Säckingen, Germany) and a lithium disilicate glass ceramic, IPS e.max CAD (Ivoclar Vivadent , Schann, Liechtenstein) prepared for flexural strength test on the basis of ISO 6872:2008. For 3 point bending test, 30 rectangular specimens (10 for each group) with the dimensions of ~14mm×4 mm×1.2 mm were prepared and loaded on a 10 mm span with crosshead speed of 1 mm/min by a universal testing machine (Zwick/Roell). Differences between the means of the 3 groups were analyzed with one way ANOVA followed by multiple comparison Tukey HSD test. Also the normality of the tested groups evaluated with kolmogorov Smirnov test. The mean flexural strength and standard deviation was 139.9 21.2MPa for Lava Ultimate, 273.8 56.03MPa for IPS e.max CAD and 127.7 11.9 MPa for Vita Enamic. Significant differences were found between the groups (P<0.001). The Tukey HSD test showed that flexural strength of IPS e.max CAD is significantly higher than two other ceramics (p<0.05). IPS e.max CAD exhibited higher values in flexural strength between the 3 groups. The others respectively were Lava Ultimate and Vita Enamic. The flexural modulus of Lava Ultimate and Enamic was greatly improved to levels not seen before in dental resin composites. However, their consideration and clinical use in patients with high muscular and masticatory forces especially patients with bruxism and clenching, better to be similar to that of conventional dental CAD/CAM resin composites and be limited to inlay, onlay and veneer restorations.