## 3 Results  
The systematic search of the literature retrieved a total of 55 articles. After the removal of duplicates and abstract and title selection, only three articles satisfied all inclusion criteria and were included in the present review (Figure 1).  
The general characteristics of the studies are presented in Table 1. One study was a well-designed randomized controlled clinical trial [9], while the others were single-arm prospective randomized studies [13; 14]. The risk of bias was low for all included studies. A total of 69 patients, accounting for 124 implants, were treated by using a nonsurgical treatment protocol that included the use of local administration of doxycycline. In one study, the nonsurgical treatment was carried out by also using decontamination with an air-polishing device (erythritol and chlorhecidine) [14]. The follow-up was 18 weeks for one study [9] and 12 months for two studies [13; 14].  
Figure 1: PRISMA diagram of the article selection process (*: all sources, **: by using both automatic and manual systems).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Study** & **Year** & **Objective** & **Sample** & **Methodology** & **Probe** & **Follow-Up** & **Group 1** & **Group 2** & **Results** & **Conclusions** & **Limitations** \\ \hline
**Method** & **Compare** & & & & PCP 11 & & & & & Mechanical & Greater & \\  & mechanical & & & & period & & & & dediatement & & reduction in FPD & Treatment with \\  & & dediatement with & & & probe & & & Mechanical & controlled- & (1.5 mm vs. & debridement \\  & and without & & & & & & & dediatement & & release typical & 0.5 mm) and & and doxycycline & Limited duration \\
**[PERSON]** & 2004 & & (48 peri- & & & & & & & & \\  & daycycline (Astrova's) & & & & & & & & & & \\  & application for & & & hand & 3-3-3 mm & & & & & & \\  & & & instruments & calibration, & & & & & & & \\  & treatment & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\  & & & & & & & & & & \\ \hline \end{tabular} \({}^{1}\) Block Drug Corporation Inc., Jersey City, NJ USA. \({}^{2}\) Koller GmbH, Hanus, Germany.  
\end{table}
Table 1: General characteristics of the included studies [9, 13, 14].  
The study by [PERSON] and coworkers on 28 subjects (48 defects with diagnosed peri-implatitis) [9] found that the test group (in which local doxycycline was used) reported better outcomes than the control group, with a significantly higher reduction in PPD (1.15 \(\pm\) 0.23 mm versus 0.56 \(\pm\) 0.30 mm) and BI over the observation period. No data were available about the resolution of peri-implantitis or about patient-reported outcomes. The study by [PERSON] et al. on 15 patients (27 peri-implant defects), published in 2017, combined doxycycline and air-polishing (MAINST protocol), reporting a very significant decrease in PPD (from 7.89 mm to 3.16 mm on average) and in BoP% (from 98.5% to 4.5%) [14]. Interestingly, similar results were found by [PERSON] and coworkers in 2022, on a cohort of 26 patients (49 peri-implant defects) with a decrease in PPD over time that reduced the need for further surgical treatment [13].  
None of the studies reported adverse events or complications during the observation period.  
On the basis of the available results from the included studies, the quality of the available evidence was very low, due to heterogeneity and to the low number of papers available.