Clinical and Microbiological Outcomes of Implant-Supported Hybrid Abutment Crowns in the Posterior Region as a Function of Restorative Material: Exploratory Results of a 36-Month Randomized Clinical Trial

Background: Hybrid abutment crowns combine a prefabricated titanium base with a custom, CAD/CAM-fabricated ceramic superstructure. Despite their increasing clinical use, only limited long-term in vivo data are available on how the restoration material influences clinical and microbiological outcomes. Objective: We investigated the clinical, radiographic, and microbiological outcomes of implant-supported hybrid abutment crowns in the posterior region over 36 months as a function of crown material. Methods: In a single-center, randomized, controlled clinical trial with blinded data analysis, 60 patients with a single-tooth gap in the posterior region received a Camlog iSy implant. Two implants were lost within the first four weeks, before prosthetic loading and randomization. The remaining 58 patients were randomized after stratification by sex and edentulous region to a polymer-infiltrated ceramic network hybrid ceramic (PICN; VITA Enamic, n = 28) or a lithium disilicate ceramic (LS2; IPS e.max CAD, n = 30). At 36 months, 57 patients (27 PICN, 30 LS2) were analyzed. The primary endpoint was implant survival; as no post-loading failure occurred, this was reported descriptively. Secondary endpoints were marginal bone level change (standardized intraoral radiographs, prosthetic baseline to 36 months), peri-implant probing depth (Florida Probe, baseline to 36 months; linear mixed-effects model), and the subgingival microbiome (micro-iDent plus, 6 and 36 months). Technical complications of this cohort have been reported separately 37. The trial was not powered to demonstrate equivalence, non-inferiority, or superiority. Results: The implant survival rate was 100%. Marginal bone resorption was low and stable. It did not differ significantly between crown materials (mesial mean difference 0.10 mm, 95% CI −0.11 to 0.31 mm; distal 0.15 mm, 95% CI −0.09 to 0.39 mm), nor by sex, jaw, implant length, diameter, or shoulder position. Probing depths remained low over 36 months without clinically relevant progression. The change in probing depth differed statistically between materials (mean difference 0.52 mm, 95% CI 0.12 to 0.92 mm; p = 0.012), but this difference was not considered clinically relevant. Microbiologically, most bacteria showed a stable to favorable course. For individual species (including Fusobacterium nucleatum, Campylobacter rectus, Eikenella corrodens, and Capnocytophaga spp.), deteriorations occurred more frequently, particularly in the LS2 group, without accompanying clinical or radiographic abnormalities. Conclusions: Within the limits of sample size and the 36-month follow-up, hybrid abutment crowns showed high peri-implant stability irrespective of crown material, with no clinically relevant differences between groups. This should not be interpreted as evidence of equivalence. When selecting materials, the higher technical complication rate in the PICN group reported separately for this cohort should also be considered.