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.