The Effect of Crown-to-Implant Ratio on the Clinical Performance of Extra-Short Locking-Taper Implants

Background: The aim of the present prospective 5-year study was to evaluate the influence of crown-to-implant ratio (C/I ratio) on the survival, peri-implant marginal bone loss, and complications of extra-short (6.5 mm) locking-taper implants placed in the posterior areas of the jaw. Methods: Over a 2-year period, all patients presenting with partial edentulism associated with vertical defects of the posterior alveolar ridges and sufficient bone volume to place extra-short (6.5mm length x 5mm diameter) implants were considered for inclusion in this study. Results: Fifty-one patients (22 men, 29 women; aged between 40 and 75 years) were included in this study. Sixty-eight extra-short, locking-taper implants were placed to support 49 single crowns and 9 fixed partial dentures. The C/I ratio was <2 for 51 implants and >= 2 for 17 implants. All patients underwent the 5-year clinical examination. Two implants failed. Failure proportion was 2% in the C/I<2 group, and 6% in the C/I >= 2 group: this difference was not statistically significant (P = 0.4). After 1 year of loading, a mean marginal bone loss of 0.29 and 0.39 was reported in the C/I<2 group and the C/I >= 2 group, respectively. After 5 years of loading, a mean marginal bone loss of 0.38 and 0.48 was reported in the C/I<2 and C/I >= 2 groups, respectively. The linear regression model failed to find a correlation between the C/I ratio and marginal bone loss along time, with a 0.023mm (95% CI: -0.002; 0.048) increase in 1-year bone resorption for every 0.1 increase in C/I ratio (P = 0.07). At 5-year, the association reduced to 0.019mm (P = 0.18). Only a few complications were reported. There was no statistically significant difference in the prevalence of biological (P = 0.9) complications between the 2 groups. Prosthetic complications were more frequent with C/I>2 (12.5%) than with C/I<2 (6%), but this difference was not statistically significant (P = 0.6). Conclusions: Extra-short, locking-taper implants may be successfully used in the posterior areas of the jaw.