# Peri-Implant Tissue Behaviour Next to Different Titanium Surfaces: 16-Year Post-Trial Follow-Up
## 2 Materials and Methods  
A sample of 18 patients (12 men, 6 women) with a mean age of 62.44 years (range: 44 to 76 years) at the time of recruitment referred to the Division of Implant and Prosthetic Dentistry (Department of Surgical Sciences, DISC) of the University of Genoa (Italy), and requiring the insertion of at least two adjacent implants, was included in this prospective clinical study. A first cohort of 8 patients was treated between April 2005 and March 2007 (Group 1) [26; 27], while the remaining 10 patients were later rehabilitated between March 2013 and July 2014 (Group 2) [28; 29]. The present post-trial follow-up reports the clinical outcomes measured in both the cohorts of patients at their last follow-up appointment, that is up to 16 years for Group 1 and up to 8 years for Group 2. The inclusion criteria were the same for the two cohorts of patients and are listed below:  
* Good systemic health with no contraindications to oral surgery [33; 34]: patients with an uncontrolled medical condition such as diabetes mellitus, immune suppression, intravenous or oral bisphosphonate medication, oro-facial cancer, chemotherapy or head and neck radiotherapy, and infarct during the preceding 6 months were excluded;
* No history of periodontal disease;
* Partial edentulism to be rehabilitated with at least two adjacent implants;
* Natural teeth or fixed prostheses supported by natural teeth as opposite dentitions (no removable prosthesis as antagonist);
* Teeth in treated areas had been extracted at least 1 year before;
* No heavy smokers (\(\geq\)20 cigarettes/day). Baseline characteristics of the two cohorts of patients are reported in Table 1. Only two patients were smokers (one in Group 1 and one in Group 2) and they both reported to smoke two to three cigarettes/day. This research project was performed in agreement with the World Medical Association Helsinki Declaration. All treatments were approved by the local Ethical Committee of the University of Genoa (Approval Number: 21084). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Group 1** & **Group 2** \\ \hline N\({}^{\circ}\) of patients & 8 & 10 \\ \hline N\({}^{\circ}\) of implants & 20 & 22 \\ \hline Mean age (SD) (years) & 59.8 (44–73) & 64.6 (52–76) \\ \hline Gender (n. of patients) & Men 1 & 5 \\ Women 7 & 5 \\ \hline Smokers (n. of patients) & 1 & 1 \\ \hline Arch (n. of implants) & Maxilla 10 & 12 \\  & Mandible 10 & 10 \\ \hline Implant site & Anterior 1 & 1 \\  & Posterior 19 & 21 \\ \hline  & 10 mm 9 & 10 \\ Implant length (n. of implants) & 11.5 mm 8 & 8 \\  & 13 mm 3 & 4 \\ \hline Implant diameter (n. of implants) & 4 mm 20 & 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Baseline characteristics of the two cohorts of patients. The manuscript was edited following the \"Strengthening the Reporting of Observational Studies in Epidemiology\" (STROBE) statement [35]. All the participants were thoroughly informed about the intervention and signed a written consent to the planned procedures. They also agreed to return for the required recall appointments. All the patients were rehabilitated with fixed partial prostheses (no single crowns), supported by at least 2 implants into an edentulous quadrant following identical surgical procedures in all the clinical cases. Three patients received 4 implants (all implants were in the same hemiarch), while the remaining fifteen patients received 2 implants each, for a total of 42 dental implants inserted (21 for both test and control groups) and 18 prostheses. The surgical access was provided by mucoperiosteal flaps at the ridge crest (or slightly palatal to it) with buccal relieving incisions, and the crestal bone was flattened in case of need. The implant restorative platform was put at the level of crestal bone. No regenerative surgery procedures were performed at the implant sites. Two different types of external hexagon implants were used.