The objectives of the present study are to compare the survival rates and possible biological and technical complications of metal-ceramic, and monolithic third-generation zirconia posterior crowns. The null hypothesis is that no differences would be found between the parameters studied for each type of restoration.

Seventy patients requiring at least one crown in the posterior region of the maxilla or mandible were included in this study. All subjects were recruited from the Master in Buccofacial Prostheses and Occlusion (Faculty of Odontology, University Complutense of Madrid, Spain). Before treatment, patients were informed of the study objectives, clinical procedures, materials used, advantages and possible risks of the ceramic material, and other therapeutic alternatives. Prior to the study, participants were asked to provide written informed consent. Seventy posterior crowns were produced and allocated in parallel and randomly to either monolithic third-generation zirconia, or metal-ceramic (MC) restorations. The clinical procedures were performed by two experienced clinicians. All participants received oral hygiene instructions and a professional tooth cleaning prior to prosthetic treatment. The abutment teeth were prepared with a 0.8- to 1-mm-wide circumferential chamfer, an axial reduction of 1 mm and an occlusal reduction of 1- to 2.0-mm. A 10- to 15- degree angle of convergence was achieved for the axial walls. Tooth preparations were scanned with an intraoral scanner and the crowns were designed using specific software. The restorations were then cemented using a resin self-adhesive cement. After cementation, occlusal contacts were evaluated, and the adjusted surfaces were polished using a porcelain polishing kit. The 70 crowns were examined at 1week (baseline),1, 2 and 3 years by 2 researchers who were not involved in the restorative treatment.

Inclusion Criteria:

• One posterior tooth (molar or premolar) to be crowned
• Vital abutment or abutment with an adequate endodontic treatment
• Abutment not crowned previously
• Periodontally healthy abutment with no signs of bone resorption or periapical disease.
• Adequate occlusogingival height ≥ 4 mm.
• Stable occlusion and the presence of natural antagonist tooth.

Exclusion Criteria:

• Patients who present reduced crown length (less than 4 mm occlusogingival height).
• Poor oral hygiene, high caries activity, or active periodontal disease