The complete upper or lower set of teeth replacement with four dental implants

Based on the radiographic and clinical examination, each implant was classified as follows:
1. Successful implants, if there were no subjective complaints (e.g., pain), no mobility, no suppuration when peri-implant mucosa was pressed, absence of bleeding and/or suppuration on gentle probing, a probing Depth ≤ 5 mm, radiographic evidence of marginal bone level change (MBLC) ≤ 2 mm at 1-year post-loading of definitive prosthesis (T1) and at the latest follow-up visit (T2)
2. Survival implant, meaning they were still in place but did not fulfil the success criteria as above
3. Clinical outcomes were recorded following the classification by Berglundh et al. (Berglundh T, Armitage G, et al. 2018) at T1 and T2:
3.1 Peri-implant health: absence of erythema, bleeding on probing, swelling and suppuration;
3.2 Peri-implant mucositis: presence of bleeding on gentle probing with radiographic bone loss <2mm. Erythema, swelling and/or suppuration may also be present.
3.3 peri-implantitis: i) presence of bleeding and/or suppuration on gentle probing; ii) increased probing depth compared to previous examinations and iii) radiographic evidence of bone resorption (>0.5mm) beyond crestal bone level changes resulting from initial bone remodeling (T1).

1. Prosthetic success
Prosthodontic maintenance events such as: abutment fracture; abutment retaining screw fracture or loosening; prosthetic retaining screw fracture or loosening; acrylic teeth loosening or fracture: acrylic veneering fracture and prosthesis (framework) fracture, were recorded during the follow-up visits or at the time the patient highlighted the problem. The definitive prostheses in function without complications were considered as a “successful prosthesis”
2. Radiographic examination
Periapical radiographs obtained by using the parallel technique were performed for each implant. The radiographs were analysed for the existence of continuous peri-implant radiolucency, and the position of crestal bone levels around the implants. Measurements were done on the distal and mesial aspects of the implants with a specific software (CS Imaging 7, Carestream Dental LLC, Atlanta, GA, USA) and a High-Definition Monitor (HP Pavilion 23 cw, Full HD 5.000.000:1 Dynamic Contrast, Helwett-Packard, Palo Alto, CA, USA) to measure MBL levels, defined as the distance between the implant shoulder and the first bone-to-implant contact. In case of a sub-crestal implant shoulder, as for implants installed in extraction sockets, the measurement was recorded as a positive value. Only the worst value between the mesial and distal measurements was considered for the statistical analysis. The radiographic dimension of each implant was measured and compared to the real implant length to correct dimensional distortions (Romeo, Tomasi, et al., 2009). The radiographic measurements were performed annually but the data taken into account for the statistical analysis refer at implant placement (T0 – Baseline), at 1-year post-loading of definitive prosthesis (T1) and at the last follow-up visit (T2)
3.Peri-implant Soft tissue parameters
The peri-implant soft tissue evaluation was made by a trained calibrated operator (N.F.) and involved the assessment of modified plaque index (mPI), modified bleeding index (mBI), probing depth (PD) and width of keratinized mucosa (KM). mPI was assessed on the mesial, distal, buccal, and palatal/lingual surface of the implants (score 0 – 3) (Buser, Weber, & Lang, 1990; A. Mombelli, Oosten, Schürch, & Lang, 1987; Andrea Mombelli & Lang, 1994). mBI was determined at the same surfaces as for mPI: score (0 – 3) (Buser, Weber, et al., 1990; A. Mombelli et al., 1987; Andrea Mombelli & Lang, 1994). PD was measured to the nearest millimetres, from the mucosal margin to the bottom of the pocket with a periodontal probe (Hu-Friedy PGF-GFS, Hu-Friedy, Chicago, IL., USA), at the same surfaces as for mPI (Buser, Weber, et al., 1990; A. Mombelli et al., 1987; Andrea Mombelli & Lang, 1994). The reliability of each PD data collection was estimated by performing a second set of PD measurements by a second operator (P.C.). Measured at baseline (T0), T1 and T2