# Peri-Implant Tissue Behaviour Next to Different Titanium Surfaces: 16-Year Post-Trial Follow-Up
## 4 Discussion  
The aim of the present prospective clinical trial, with an up to 16-year follow-up, was to investigate the impact of titanium implants with different surface treatments on peri-implant hard and soft tissues. The findings of the study showed that acid-etched implant surfaces reduced peri-implant bone resorption in the initial phase of healing, while it did not seem to have a significant effect at subsequent time points. In addition, no significant differences were found in soft tissue health parameters next to the two differently surfaced implants. The present study was the continuation of previous studies of the same team of authors, reported in already published manuscripts [26, 27, 28, 29]. The first published paper [26] compared the two types of implants (Osseotite and Full Osseotite) in a sample of eight patients (Group 1). The authors monitored for 12 months peri-implant bone resorption over time and the health of soft peri-implant tissues, recording bleeding on probing score (BOP) and making a histologic analysis on bioptic samples from peri-implant mucosa. A second manuscript [27] reported results of the previous study at the 6-year follow-up, also reporting peri-implant depth (PD). [PERSON] et al. (2017) [28] reported data of a different cohort of 10 patients (Group 2) and besides bone level, PI, BOP, and PD, the investigation included a mini-invasive sample of soft tissue for miRNA microarray analysis. A subsequent paper [29] reported results of this second cohort of patient at the 5-year follow-up. According to preliminary results of previous papers [27,29] on the same pool of patients, DAE (test) surfaces induced greater plaque accumulation, however they showed lower peri-implant bone resorption. In both groups of implants, the greatest bone loss occurred during the first year after implant placement (Figure 3). This is consistent with the physiological bone remodeling that takes place after the surgical trauma and in response to occlusal forces after prosthesis delivery [41]. At the first-year follow-up, bone resorption around FOSS implants was statistically lower than in the control group (0.80 vs. 1.39 mm; \(p\) = 0.002). Subsequently bone level went through a steady state, in fact implant surface mainly influenced bone level changes only in the first phase of healing after implant insertion. Once osseointegration and peri-implant bone remodeling after prosthesis delivery was complete, the type of surface was less relevant. After the first year of healing, lower bone level changes occurred in both types of implants. A significant overall increase in bone resorption was also found between the 6-year and the 8-year follow-up appointment (mean: 1.65 vs. 1.82 mm; \(p\) = 0.011). However, it is worth specifying that while fifteen patients were available at the 6-year follow-up appointment, only nine reached the 8-year follow-up and only three reached the 16-year follow-up. This probably affected the results. Due to this selection bias, mean bone loss was smaller at the 15- and 16-year follow-up appointments compared to previous time points. No differences in PI were detected between test and control sites from the 1-year follow-up appointment on. The higher PI recorded in the test group in the first months of healing was due to the presence of the DAE surfaced healing abutments. The healing abutments were removed after 21 weeks from surgery, for the insertion of provisional prostheses. Therefore, from that moment on, further changes in PI could be mainly referred to the prosthesis venereing material and the metal prosthesis structure which were exposed into the oral environment. Mean PI did not significantly increase over time, despite the mean age of patients increased and the majority of patients missed some of their usual professional oral hygiene appointments during the pandemic from Coronavirus 19 in 2020.