Clinical evaluation of the incidence of prosthetic complications in implant crowns constructed with UCLA castable abutments. A cohort follow-up study

Objectives: To evaluate the incidence of prosthetic complications in implant-retained crowns made with UCLA castable abutments and to identify possible risk factors with a view to establishing recommendations to help predict the success of such restorations. Methods: A cohort follow-up study was carried out in 71 partially dentate patients rehabilitated with 93 implant-retained single crowns. Data regarding socio-demographic background, anatomical features, implant-, and prosthesis-related variables were recorded. The incidence rate (%), relative risk (RR) and odds ratio (OR) were applied for predictive risk factors. ANOVA and Student t-tests were used to compare quantitative variables, the chi-square test was used to compare proportions and also a logistic regression analysis was performed. The statistical significance was set at alpha = 0.05. Results: Two implants (2.2%) were lost during the first year of function. The incidence of prosthetic complications in the observed mean period (26.2 +/- 15.4 months) was 11.9%, consisting of screw loosening (10.8%) and ceramic fracture (1.1%). A higher tendency for prosthetic complications was noticed in posterior mandibular crowns restoring saddles longer than 10 mm with mesiodistal cantilevers longer than 6 mm, having natural antagonists, after long-term use (>20 months), with initial torque values superior than 30 Ncm. Conclusions: Screw loosening is the most frequent complication in implant-retained crowns fabricated with UCLA abutments cast in cobalt-chromium. Nevertheless, the connection usually remains stable after retightening the screws. A high survival rate was recorded, and these prostheses may be a suitable treatment option. Clinical significance: Based on the study findings, the risk of prosthetic complications is expected to increase when long-span posterior edentulous areas are rehabilitated with single implant-supported crowns. The antagonist occlusal plane should be restored to prevent torsional forces and overloading. Implant systems with initial torque values less than 30 Ncm should be selected. (C) 2012 Elsevier Ltd. All rights reserved.