## 2 Materials and Methods  
This study was designed as a retrospective cohort study. All patients previously treated with one zirconia ISFCDP in a private setting, designed with either the zirconia-on-titanium technique, the progressive monolithic zirconia technique or the zirconia-on-zirconia technique, were considered potentially eligible for the study. Patients' medical records were examined by two separate investigators (VM and CC), and all the eligible patients were recalled for a follow-up visit in November 2023. The present study was approved by the local ethical committee of the greater north-west area of Tuscany (approval number: 57489/2019) and followed the declaration of Helsinki. To be included, patients had to fulfill the following eligibility criteria:  
* Patients treated with a zirconia ISFCDP. * Patients following a periodontal maintenance program with at least one recall visit per year. * Minimum follow-up of 1 year after prosthetic delivery. Exclusion criteria were the following:
* Patient treated with implant-supported fixed partial prosthesis. * Patients with uncontrolled systemic diseases, were under treatment with medication that could interfere with bone metabolism, or who received radiation treatment in neck or head area. * Patients not following a periodontal maintenance program. * Patients affected by untreated periodontal disease. * Heavy smokers (>10 cigarettes per day). Light smoker patients (<10 cigarettes per day) were included in the retrospective study, and all smoker patients were motivated to stop smoking. All patients fulfilling the eligibility criteria were recalled for a follow-up visit. Patients received detailed information regarding the nature of the study and were asked to sign a written consent form. Each patient was subjected to a clinical examination, and frontal, occlusal and lateral photographs were taken to double-check the clinical examination. During the clinical examination, the following parameters were evaluated in a dichotomous manner (presence/absence) for the evaluation of the technical complications:  
* Buccal soft tissue dehiscence: presence of implant threads clinically visible. * Implant threads exposure: exposure of implant threads, both in presence of a buccal soft tissue dehiscence or covered by soft tissue (presence of a dark shade under the soft tissue in a position corresponding to an implant). * Chipping of the esthetic part of the ISCFPDs: presence and position of one or more partial fractures of the pink ceramic. * Past or present fracture of the framework or functional structure: full framework fracture, cracks or fractures related to the functional part of the ISFCDPs, requiring in-lab repairment. * Past or present unscrewing of the ISCFPD: requirement of screw tightening during one of the follow-up visits. Information on the peri-implant health status was evaluated with the following parameters:
* Pocket probing depth (PPD) at implant level: probing was performed using a 15 mm UNC-15 probe (Hu-Friedy) on six sites around each implant (two vestibular, two lingual/palatal and two interproximal, one mesial and one distal). A probing depth of more than 6 mm was considered a sign of peri-implantitis. * Bleeding on probing at implant level: present in case of bleeding after gentle probing in a nearby site. The presence of bleeding on probing was considered a sign of peri-implantitis. * Purulent discharge: present in case of purulent discharge appearing after probing, which is considered a sign of peri-implantitis. * Local signs of inflammation: present in case of clear signs of swelling, redness, pain on probing or spontaneous pain corresponding to an implant; all considered signs of peri-implantitis. ISFCDPs were defined as \"successful\" in the case of the absence of prosthetic or implant-related complications, whilst in the case of manageable complications which did not require the full replacement of the prostheses, they were defined as \"survival\" [10,13].