Randomized controlled clinical study of veneered zirconia abutments for single implant crowns: Clinical, histological, and microbiological outcomes.

OBJECTIVES: To analyze the effect of veneering of the submucosal part of zirconia abutments and the type of retention (cemented vs screw-retained) on clinical, microbiological, and histological outcomes of single-tooth implant crowns.

MATERIAL AND METHODS: A total of 44 patients with a single missing tooth to be replaced by an implant in the anterior region participated in the study. Implants were randomly assigned to receive zirconia-based CAD/CAM reconstructions using either one of four treatment modalities: cement-retained with submucosal veneering (CR-P), cement-retained without submucosal veneering (CR-W), screw-retained with submucosal veneering (SR-P), and screw-retained without submucosal veneering (SR-W). Clinical parameters were assessed at baseline (after crown insertion), at 6 and 12 months. Histological and microbiological analyses were performed at 6 months. Descriptive statistics and the Kruskal-Wallis test were applied.

RESULTS: The clinical evaluation revealed, in general, stable peri-implant soft tissues with minimal differences for all measured parameters between the four groups, except for bleeding on probing with the two cemented groups exhibiting higher values at 12 months (35.0% ± 26.5% for CR-W and 25.0% ± 38.8% for CR-P versus 13.1 ± 14.8 for SR-W and 13.0 ± 18.2 for SR-P). The descriptive and semi-quantitative histology showed a trend for a higher inflammatory reaction in the two cemented (a medium to high number of inflammatory cells) compared to the screw-retained groups (low number of inflammatory cells) at 6 months. The microbiological test demonstrated low bacterial counts and a similar distribution in between the groups except for two species (Tannerella forsythia and Peptostreptococcus micros) that were found in higher counts in the cemented groups at 6 months.

CONCLUSION: Submucosal veneering of zirconia abutments did not negatively affect the health of the peri-implant tissues. The cemented groups, though, did show a clinical and histological trend to higher levels of inflammation.