Das Kronen- Implantat- Längenverhältnis von Einzelkronen und Brücken und dessen Einfluss auf den periimplantären Knochenabbau

Background: The influence of high crown-to-implant ratios may lead to increased peri-implant bone loss, causing clinical complications. The effect of crown-to-im- plant ratio on treatment outcome has been controversly discussed and is therefore the subject of this long-term study. Methods: A total of 39 patients with 108 implants were included. 72 patients were prosthetically restored by single crowns and 17 patients received bridges. After placement of the superstructure, clinical follow-up was performed every 3 to 6 months over a period of 5 to 20 years. Clinical and radiological investigations were performed immediately after superstructure placement, and 1, 3, 5, 10, 15, and 20 years thereafter. The static crown-to-implant ratio is defined as the relationship between the length of the crown and implant. Analogous, the clinical crown-to-implant ratio is defined as the ratio between the distance of the crestal bone implant contact to the apical implant and the distance between the crestal bone implant to the coronal superstructure. The study population was then divided by static crown-to-implant ratio. Group 1 comprised crown-to-implant ratios ≤1 (n=47), while group 2 comprised ratios >1 (n=61). Differences across the groups were analyzed using the Mann-Whitney U-test. The association between clinical crown-to-implant ratio and peri-implant bone loss was analyzed with Spearman rho correlation. Results: The average peri-implant bone loss was 0.09 mm ± 0.41 mm. The group comparison showed no significant difference for peri-implant bone loss (p=0.859), survival rate (p= 0,68), and the incidence of mucositis (p= 0.325) and peri-implantitis (p=0,077), respectively. The clinical crown-to-implant ratio showed a moderate correlation with the peri-implant bone loss (R=-0,217; p<0.01). The survival rate of the implants was 96.2% after 5 years, 94.7% after 10 years and 91.8% after 20 years. Incidence for mucositis was 60.2%, and 13.0% for peri-implantitis. Conclusion: Implants with higher clinical crown-to-implant ratio showed slightly fewer peri-implant bone loss. An negative effect of static crown-to-implant ratio on peri-implant bone loss could not be demonstrated amongst our study population.