marginal adaptation of implant prostheses fabricated by different materials in excessive crown height space before and after veneering

objectives: this study aimed to investigate the marginal adaptation of implant-supported three-unit fixed restorations fabricated in excessive crown height by various frameworks namely zirconia, nickel-chromium (ni-cr) alloy, and polyetheretherketone (peek) before and after veneering. materials and methods: a basic model with two implant fixtures was made to receive posterior three-unit fixed partial dentures (second premolar to second molar) in 15 mm crown height. a total of 30 frameworks were fabricated using ni-cr, zirconia, and peek (n=10). all specimens were veneered and vertical marginal discrepancy was evaluated before and after veneering using a stereomicroscope (×75). the effect of framework material and veneering on marginal discrepancy was evaluated by repeated-measures and one-way anova, and paired t test (α=0.05). results: there was a significant difference between the groups (p 0.001) before and after veneering. the vertical marginal discrepancy of zirconia frameworks was significantly lower than that of other groups both before and after veneering (p 0.001). statistical analysis revealed that the veneering process had a significant effect on marginal adaptation (p 0.001). conclusion: in implant prostheses with excessive crown height, zirconia had the greatest marginal adaptaion significantly, followed by ni-cr. veneering caused a significant increase in marginal discrepancy of all the materials.