Background: Despite broad clinical application of zirconia to manufacture fixed implant supported prosthesis long-term scientific evidence is limited.
Purpose: To retrospectively evaluate long term clinical and radiological outcomes of zirconia-based partial and complete-arch screw-retained implant-supported prostheses (ZrPIB). 
Materials and methods: Records of patients treated with dental implants and ZrPIBs between December 2004 and June 2017 were screened. Eligible patients, according to strict criteria, were contacted and invited to undergo a clinical and radiographic examination. Outcomes were evaluated as implant and prosthetic survival rates, prosthetic success rate, complications, marginal bone level (MBL) change, and soft tissue condition. Along with the effects of zirconia prosthesis type and level, implant type and connection, type of loading and follow up on MBL were tested (p<0.05). 
Results: The records of 118 patients fulfilling the inclusion criteria were identified. Twenty patients (16.9%) were not available for a clinical examinations for various reasons. Ninety-eight patients (mean age 60.7 ± 11.7 years), accounting for 337 implants and 111 ZrPIBs, were included for the investigation. The mean follow-up (FUP) was 7.2±3.4. Forty ZrPIBs were on function for ≥ 10y (36%), 38 for 5-9y (34.2%) and 33 for 2-4y (22.8%). No zirconia fractures were experienced. Two implants and 2 ZrPIBs failed, chipping was the most common complications (13.5%), yielding to 99.4% and 98.2% implant and prosthetic survival rate respectively, and a cumulative prosthetic success of 91.9%. MBL change was -0.18±0.59 mm. Thirteen implants were treated for peri-implantitis (3.8%), and 9 for mucositis (2.7%), but presented healthy peri-implant soft tissues at examination. Low significance of implant-level vs abutment-level bridges (p=0.013) was found, with higher MBL observed in ZrPIBs delivered at implant-level (p=0.013).  
Conclusions: Within the limitations of this retrospective study, ZrPIBs is a reliable treatment option for partial and complete edentulism long term. Stable bone levels and low peri-implantitis rate were reported, regardless the implant type and connection and the type of loading, confirming the positive performance of moderately-rough oxidized-surface titanium implants supporting zirconia-based screw-retained fixed dental prostheses. Screw-retention at implant-level was not detrimental to bone and soft tissue integration. Zirconia fracture and porcelain chipping might be limited with well-managed laboratory and clinical protocols.   
Key words: zirconia, immediate loading, dental implant, cad cam, fixed prosthesis, complete arch.

Clinical and radiological performance and complications of zirconia implant bridges up to 12 years on function

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