Switzerland: A 7.5-year randomized controlled clinical trial has shed new light on the performance of one-piece zirconia-based implant-supported single crowns. The study compared two prominent methods: cemented versus screw-retained restorations, offering valuable insights into their long-term efficacy and complications.
The study, published in Clinical Oral Implants Research, revealed that over 7.5 years of follow-up, one-piece zirconia-based single crowns supported by two-piece dental implants demonstrated a high incidence of both technical and biological complications. Notably, cemented restorations were associated with significantly higher rates of bleeding on probing and a greater overall complication rate compared to screw-retained restorations.

Riccardo D. Kraus, Clinic of Reconstructive Dentistry, Center for Dental Medicine, University of Zurich, Zurich, Switzerland, and colleagues aimed to compare marginal bone levels, biological, and technical outcomes of screw-retained versus cemented all-ceramic implant-supported zirconia-based single crowns after an observation period of 7.5 years.
In a study involving 44 patients (22 females and 22 males) with single implants in the esthetic zone, 44 implants were randomly assigned to two different restoration types. One group received screw-retained (SR) restorations and veneered one-piece zirconia abutments. The other group received cement-retained (CR) restorations involving veneered lithium disilicate crowns cemented onto one-piece zirconia abutments. Patients were followed up annually for up to 7.5 years, during which survival rates and biological and technical parameters were evaluated.
The study led to the following findings:
A total of 370 patients underwent randomization; 189 and 181 were assigned to the voltage (underwent voltage-guided PVI) and control (underwent conventional LSI-guided PVI) groups, respectively.
The primary efficacy endpoint occurred in 12.0% of patients in the voltage group and 12.9% in the control group (1-year Kaplan–Meier event-free rate estimates, 88.0%, and 87.1%, respectively; hazard ratio, 1.00).
The primary safety endpoints were 4.8% in the voltage group and 6.6% in the control group.
PVI time was significantly shorter in the voltage group (35.7 ± 14.5 min versus 39.7 ± 14.7 min).
The 7.5-year follow-up data on the biological and technical outcomes of screw-retained and cemented all-ceramic implant-supported single crowns on zirconia abutments revealed the following: (1) both types of restorations experienced a high rate of major technical and biological complications, leading to (2) reduced survival rates for the crowns; and (3) a significant increase in bleeding on probing in the cemented group, while the screw-retained group did not show a similar increase.
The study's main limitations include the inclusion of premolar sites, which may have led to higher abutment fractures, and the small sample size (44 patients) with a 6.8% dropout rate. The significant rise in complications, including fractures, by the 7.5-year mark underscores concerns about using one-piece zirconia abutments.
Reference:
Kraus, R. D., Hjerppe, J., Naenni, N., Balmer, M., Jung, R. E., & Thoma, D. S. A 7.5-year randomized controlled clinical study comparing cemented and screw-retained one-piece zirconia-based implant-supported single crowns. Clinical Oral Implants Research. https://doi.org/10.1111/clr.14346