Background: Dental implants restored with single crowns (SCs) have been reported to have a comparable survival rate and fewer technical complications compared to multiple-unit implant-supported FDPs. Porcelain-fused to metal restorations were the golden standard option for implant supported reconstructions in the past, but nowadays, the application of all-ceramic restorations in general and specifically zirconia as a restorative material for implant-supported single crowns has increased utilizing the CAD/CAM technology. The continuous technological progress in both the computer-based development and the dental manufacturing process ensures new opportunities in the clinical workflow. A fully digital pathway in a model-free approach or a combination of these workflows is now possible.

Purpose: The purpose of this randomized controlled clinical trial is to investigate the prosthetic outcomes of posterior implant-supported single crowns (SCs) with a modified monolithic zirconia or metal-ceramic design utilizing the digital workflow at 1, 3 and 5 years of loading.

Materials and methods: This single-blind split mouth study will enroll 60 participants, having to receive 120 dental Implants. They will be scheduled for a bilateral posterior single-unit prosthetic rehabilitation supported by one implant in the posterior region of the maxilla or the mandible (premolars, molars). A fully digital pathway will be followed. A CT scan will be performed without any template. An intraoral optical impression using CEREC Omnicam scanner will be made. A virtual set-up of the prosthetic reconstruction, as well as a surgical template with optimal 3-D implant positioning will be designed then printed using a 3-D printer without the need of any physical model. Straumann bone level implants with either a wide diameter (Ø4.8 mm) or regular diameter (Ø4.1 mm) with a minimum length of 8 mm will be inserted. Implants will be loaded after 3 months of submerged healing. A second intraoral optical impression will be made using CEREC Omnicam scanner and Straumann scanbody. The implant-supported prosthetic suprastructure will be designed. Implants will be randomly allocated to either the test group modified monolithic zirconia crowns (MMZ) or the control group metal ceramic crowns (MC), using a computer-generated randomization list. A digital model with movable dies will be 3-D printed, then used to adjust restoration in terms of occlusal and proximal contacts. Prefabricated screw-retained Titanium abutments (Variobase Abutment; Straumann) will be used as the metal substructures of the crowns and will be secured to lab analogues on the digitally printed casts. Metal/ zirconia substructures with a hole for the screw retention will be designed using the CAD software and will be anatomically reduced by 1 mm to allow for porcelain veneering then will be laser-printed/ dry milled. Hand layering of glass ceramic will be made on the surface. Crowns will be cemented extraorally to titanium abutments using dual cure resin cement to make one-piece screw-retained single crown. The screw-retained single crowns and titanium abutments will be inserted intraorally with 35 Ncm torque and screw-access holes will be restored with Teflon and light-polymerized composite resin. The implant-supported SCs will be examined after 1, 3 and 5 years for survival and technical complications.

Clinical significance: to evaluate the survival and prosthetic complication rates of zirconia-ceramic and metal-ceramic implant-supported single crowns at 1, 3 and 5 years of service. In addition to that, the digital workflow for implant supported single crowns will be evaluated for efficiency, accuracy, time and cost compared to conventional workflow.