Randomized Clinical Trial on Single Zirconia Crowns with Feather-Edge vs Chamfer Finish Lines: Four-Year Results

The objective of this study was to evaluate the influence of two finish lines on the fracture resistance and periodontal response of porcelain zirconia crowns. Ethical committee approval was obtained, and 50 zirconia single crowns were placed in posterior regions. Abutments were randomly distributed into two groups: Group 1 (feather-edge preparation) and Group 2 (chamfer preparation). Patients were recalled after 1 month, 6 months, and 1, 2, 3, and 4 years. The function, esthetics, and marginal adaptation of the restorations were evaluated. Bleeding on probing (BoP) and distance of margins from the bone crest were recorded. Statistical analyses were performed for survival and success rates. Group 1 had an 80% success rate (21/25 crowns) and a 96% survival rate (24/25 crowns; 1 encountered irreparable fracture of ceramic layer); Group 2 had a 76% success rate (20/25 crowns) and a 100% survival rate (25/25 crowns). Chippings were noticed on 4 crowns in Group 1 (one crown replacement). Five chippings occurred in Group 2, without any replacement. There were no statistically significant differences between the two groups. BoP was found in 18 of the 25 crowns in Group 1 (72%) and in 12 of the 25 crowns in Group 2 (48%). A statistically significant correlation between BoP and the distance of the margin to the bone crest was found. It was concluded that: (1) clinical survival and success rates of the two preparation methods on crowns are not significantly different; (2) due to the statistically significant correlation between BoP and the distance of the margin to the bone crest, margins should be placed at least 3 mm from the bone crest; and (3) higher probability of BoP is expected in cases with feather-edge preparation.