Purpose: To present a novel, full-digital protocol for the design and fabrication of implant-supported monolithic translucent zirconia crowns cemented on customized hybrid abutments.
Methods: The present retrospective clinical study was based on data from patients who had been treated with single Morse-taper connection implants (Exacone®, Leone Implants, Florence, Italy) and were prosthetically restored with monolithic translucent zirconia crowns, cemented on customized hybrid abutments. The full-digital protocol (SCAN-PLAN-MAKE-DONE®) consisted of 8 phases: (1) intraoral scan of the implant position with scanbody; (2) computer-assisted design (CAD) of the individual abutment (saved as "supplementary abutment design" in external folder) and temporary crown; (3) milling of the individual zirconia abutment and of the temporary polymethyl-methacrylate (PMMA) crown, with extraoral cementation of the zirconia abutment on the relative titanium bonding base, to generate an individual hybrid abutment; (4) clinical application of the individual hybrid abutment and cementation of the temporary PMMA crown; (5) two months later, intraoral scan of the individual hybrid abutment in position; (6) CAD of the final crown with margin line design on the previously saved "supplementary abutment design", superimposed on the second scan of the abutment in position; (7) milling of the final crown in monolithic translucent zirconia, sintering, and characterization; and (8) clinical application of the final crown. All patients were followed for a period of 1 year. The primary outcomes of this study were the marginal adaptation of the final crown (checked clinically and radiographically), the quality of occlusal and interproximal contact points at delivery, and the aesthetic integration; the secondary outcomes were the 1-year survival and success of the implant-supported restoration. An implant-supported restoration was considered successful in the absence of any biological or prosthetic complication, during the entire follow-up period.
Results: In total, 25 patients (12 males, 13 females; 26⁻74 years of age; mean age 51.1 ± 13.3 years) who had been restored with 40 implant-supported monolithic translucent zirconia crowns were included in this study. At delivery, the marginal adaptation was perfect for all crowns. However, there were occlusal issues (2/40 crowns: 5%), interproximal issues (1/40 crowns: 2.5%), and aesthetic issues (1/40 crowns: 2.5%). The overall incidence of issues at delivery was therefore 10% (4/40 crowns). At 1 year, one implant failed; thus the survival of the restorations was 97.5% (39/40 crowns in function). Among the surviving implant-supported restorations, three experienced complications (one loss of connection between the hybrid abutment and the implant, one decementation of the zirconia abutment, and one decementation of the zirconia crown). The success of restorations amounted to 92.4%.
Conclusions: The restoration of single Morse-taper connection implants with monolithic translucent zirconia crowns cemented on customized hybrid abutments via the novel SCAN-PLAN-MAKE-DONE® full-digital protocol seems to represent a reliable treatment option. However, further studies on a larger number of patients and dealing with different prosthetic restorations (such as implant-supported fixed partial prostheses) are needed to confirm the validity of this protocol.
Keywords: individual hybrid abutments; intraoral scanners; marginal adaptation; monolithic translucent zirconia crowns; success; survival.