A landmark study from the University of Zurich has cast light on long-term outcomes for zirconia-based, implant-supported single crowns, revealing substantial complications that may impact clinical decisions on restoration methods. Evaluating screw-retained (SR) versus cemented (CR) zirconia crowns over a 7.5-year follow-up period, the randomized clinical trial assessed marginal bone levels, peri-implant health, and technical performance, providing crucial insights for dentists considering restoration options for single-tooth gaps in the anterior aesthetic zone.
Key Findings and Clinical Implications
Biological Complications:
- Bleeding on Probing (BoP): CR crowns showed a notably higher mean BoP (40%) compared to SR crowns (20%). This elevated inflammation marker suggests a higher risk for peri-implant disease in cemented crowns, emphasizing the need for regular monitoring in these cases.
- Peri-implant Mucositis and Peri-implantitis: Peri-implant mucositis was detected in eight cases, with the majority occurring in the CR group. Only one case of peri-implantitis was reported, and it occurred in the SR group. These findings highlight that while mucositis rates were higher in cemented restorations, screw-retained options were not entirely immune to complications.
Technical Complications and Restoration Survival:
- Survival Rates: The study observed a survival rate of 77.5% across both groups, with SR crowns showing a slightly higher survival rate (81%) compared to CR crowns (74%).
- Abutment Fractures: Zirconia abutment fractures were a significant technical complication, particularly in posterior sites (premolars), affecting both SR and CR groups. This suggests a potential need for enhanced material strength or design modifications, especially in load-bearing areas.
Marginal Bone Levels:
- Radiographic analysis showed stable bone levels in both groups, with minimal differences between SR (−0.215 mm) and CR (−0.073 mm) groups over the study period. This stability in marginal bone levels may indicate the suitability of zirconia abutments in preserving peri-implant bone in the long term, although bone maintenance alone did not mitigate the higher rates of soft tissue complications in CR crowns.
Practical Implications:
The results of this study indicate that clinicians should weigh both technical and biological risks when selecting between screw-retained and cemented restorations, particularly in aesthetically sensitive anterior zones. While SR crowns may offer a lower risk of peri-implant inflammation and potentially higher survival rates, they are not without risk, especially regarding technical failures. Cemented restorations, though initially esthetically favorable, may require vigilant follow-up due to higher incidences of peri-implant mucositis. This study underscores the importance of individualized treatment planning, taking into account each patient’s oral health, aesthetic demands, and compliance with follow-up care. For cases with thin peri-implant mucosa, where esthetics are prioritized, SR all-ceramic crowns on zirconia abutments could present a balanced option, although robust patient education on maintenance is crucial. Further studies are necessary to develop materials and techniques that minimize these complications and improve long-term outcomes for patients and practitioners alike. Source: https://onlinelibrary.wiley.com/doi/10.1111/clr.14346Retention-design decision matrix
The choice is not a contest between two universal winners. It depends on implant position and angulation, prosthetic space, screw-channel emergence, aesthetic risk, occlusal load, margin accessibility, retrievability and the clinician’s ability to manage complications.
Screw-retained restoration
- Supports retrievability and avoids residual-cement risk.
- May be limited by an unfavourable access-channel position or aesthetic compromise.
- Requires attention to screw mechanics, passive fit, access restoration and occlusion.
Cement-retained restoration
- Can simplify occlusal morphology and mask an unfavourable screw-access position.
- Introduces cement-remnant risk, particularly with deep or inaccessible margins.
- May be less retrievable and requires deliberate abutment and margin design.
Plan for maintenance before delivery
Record component information and tightening protocol, design cleansable contours and establish baseline peri-implant findings. The restoration should allow future diagnosis and intervention, not merely satisfy immediate aesthetics.
Continue with residual-cement prevention and the broader cementation workflow.
Frequently asked questions
Is screw retention always biologically safer?
It removes cement-remnant risk, but biological outcome still depends on design, fit, hygiene and maintenance.
When is cement retention attractive?
It may help when the screw-access channel would compromise aesthetics or occlusion and the margin can remain accessible.
Which design is more retrievable?
Screw-retained restorations are generally more predictably retrievable.
Can angled screw-channel systems change the decision?
They may improve access-channel position in selected cases, subject to component and system limitations.
What should be discussed with the patient?
Explain maintenance, possible technical complications, retrievability and the need for ongoing peri-implant review.
