Effects of mechanical cycling, manufacturing technique and ceramics types on the marginal fit and fracture resistance of implant-supported prostheses

The aim of this in vitro study was to evaluate, through the mechanical cycling methodology, the marginal fit (vertical / horizontal) and fracture resistance, verifying the outcome and possible prosthetic complications of screwed-retained prostheses (external hexagon) made by different techniques and ceramic materials. Fifty specimens were made using the conventional technique and Computer aided design and Computer aided manufacturing (CAD-CAM) divided into five groups (n = 10 per group) being MC (Metal-ceramics crowns); ZrL (Coping milled in zirconia with link and covered feldspar ceramic); Zr (Coping milled in zirconia with covered feldspar ceramic); MZrL (Monolithic zirconia with link); MZr (Monolithic zirconia), which were subjected to mechanical cycling at an angle of 30 °, at 37 ° C and subjected to 5 x 10⁶ cycles with a 150N load application at a frequency of 2.0Hz. In chapter 1, the vertical and horizontal marginal fit (μm) were evaluated before and after mechanical cycling under a three-dimensional optical microscope (3D) and in chapter 2 the failure modes by the stereomicroscope and scanning electron microscope (SEM) after mechanical cycling. Quantitative data were analyzed for normality distribution and the most appropriate statistical test was adopted considering the significance level of 0.05. The results obtained for chapter 1 were that in relation to vertical marginal misfit before mechanical cycling (initial time-T0), there was a significant difference with higher misfit values for MC (93.93 ± 22.84μm) and MZrL (66, 12 ± 11.87μm), p <0.05, when compared to Zr (49.92 ± 3μm) and MZr (49.76 ± 3.9μm), joining the groups with (ZrL + MZrL: 63.04 ± 9.33μm) and without link (Zr + MZr: 49.84 ± 3.38μm) compared to the control group (MC) there was a significant difference between all groups, p <0.05, with lower misfit values for the group without link. In terms of horizontal marginal misfit before to mechanical cycling (initial time - To), there was a significant difference with higher misfit values for the MC group (-130.275 ± 34.97μm), p <0.05, and lower misfit values for the group MZr (-10.35 ± 23.14μm), p <0.05, when compared to the other groups, in addition for the group without a link (Zr: -70.27 ± 22.61μm vs MZr: -10.35 ± 23, 14μm), there was a significant difference (p <0.05) with lower misfit values for MZr. Joining the groups with (-75.98 ± 14.17μm) and without link (-40.31 ± 37.73μm), a significant difference was identified between all groups when compared to the control (MC: -130.27 ± 34, 97μm), (p <0.001), with lower values for the group without a link. Regarding the comparison before and after cycling (Tf-T0), for analysis of vertical marginal fit, the MC group (10.05 ± 5.74μm) was the one with the highest misfit values, p <0.05, when compared to the others groups, already for analysis of the horizontal marginal adaptation, the Zr group (3 ± 13.97μm) showed statistical difference, p <0.05, in comparison with ZrL (-4.48 ± 13.59μm) and MZrL (-2.825 ± 11, 81μm), joining the groups with (-3.65 ± 12.72μm) and without link (0.35 ± 10.99μm), there were lower misfit values for the group without link, p <0.05. For chapter 2, a total of 14 samples failed, the groups MZrL and MZr showed significantly less association of failures, with only one failure (MZr), p = 0.035, as well as in relation to the type of substrate, the groups MZrL and MZr showed fewer failures (p = 0.011). The use of links and the number of cycles did not indicate significant differences between the groups (p≥0.05). For the chipping and/or fracture dimensions, there was a significant difference for the Zr group (p = 0.029) presenting a larger area of chipping when compared to the others. Regarding the location of the failure, the MC group showed a greater number of chipping in the screw orifice region when compared to the others (p = 0.043), which failed in different locations. Therefore, the use of the CAD / CAM system resulted in lower values of vertical and horizontal marginal maladjustment, as well as fracture resistance, with emphasis on monolithic crowns. (AU)