Efficacy of Non-surgical and Surgical Surface Decontamination Methods on Peri-implantitis-affected Implants

A screening visit will be performed to determine the elegibility of the individuals to participate in the study. Information related to the target implant (e.g., brand, material, surface, dimensions, time of function, history of treatment of peri-implantitis) and reconstruction (e.g., cemented or screwed prosthesis, single, multi-unit or full-arch) will be collected. Intra-oral radiographs will be obtained or exported from patients' dental records, and the marginal bone level (MBL) will be measured at the mesial and distal aspects of the implants by one calibrated investigator using an image analysis software (Image J; National Institutes of Health, Bethesda, MD, USA). The anatomy of the bone defect will be determined.

Randomization will be performed in a stratified manner, in sets of 10 implants, by a computer software, to obtain equally balanced groups based on implant characteristics (site, brand, design). A researcher not involved in the clinical interventions will be responsible for randomization.

At the day of implant removal, a single calibrated examiner will assess the following parameters at six sites around each experimental implant using an UNC 15 periodontal probe: (1) Plaque accumulation, using the modified plaque index \[mPI\]; (2) Probing depth (mm); (3) Bleeding on probing, using the modified gingival index \[mGI\] ; (4) Suppuration; (5) Recession (mm). The width of keratinized mucosa (KM) will be obtained in the mid-buccal and mid-lingal aspect of the implants (mm). A standard tessellation language (STL) file of the arch of interest using an intraoral optical scanner (Trios 3, 3Shape, Denmark) will be obtained.

Surface decontamination protocols:

All cleaning procedures will be performed without the suprastructures. A notch will be performed on the buccal side of all implant shoulders with the aid of a bur, in order to distinguish the different implant surfaces during the microbiological and biocompatibility analysis phases.

Following local anesthesia, implants will be randomly assigned to the following study groups:

1. Non-surgical decontamination with titanium curettes prior to implant removal (n = 20); 2. Non-surgical decontamination with erythritol powder prior to implant removal (n = 20); 3. Surgical decontamination with titanium curettes prior to implant removal (n = 20); 4. Surgical decontamination with erythritol powder prior to implant removal (n = 20); 5. No decontamination prior to implant removal (n=10).

In the surgical groups, intra-sulcular and, if necessary, vertical releasing incisions will be performed. Full-thickness flaps will be elevated in the buccal and lingual aspects and the granulation tissue will be removed.

All giant (visible) calculus will be removed with an ultrasonic tip in advance, without touching the implant surface directly. Copious irrigation with saline will be performed in both groups prior to implant decontamination. All implants will be cleaned by the same operator with the aid of dental surgical loupes. The time needed for the operator to consider the implant surface clean will be recorded.

* Titanium curettes (Hu-Friedy, Chicago, Illinois, USA) will be used for supra and submucosal around the implants. * Air-polishing (Airflow Prophylaxis Master, EMS, Nyon, Switzerland) will be carried out with AIR-FLOW powder PLUS (EMS) containing erythritol (sugar alcohol, 14 μm), amorphous silica and 0.3% chlorhexidine. The device will be adjusted to a power setting of 5 bar static pressure and a maximum level of irrigation with water.

* Non-surgical group: The supramucosal implant surfaces will be cleaned with the Airflow handpiece, while for the submucosal areas, a Perioflow handpiece and nozzle for submucosal instrumentation will be used. The nozzle will be changed after cleaning each implant. * Surgical group: The Airflow handpiece will be moved in a horizontal direction along implant threads from an apical to a coronal position. The angulation of the handpiece and working distance will not be standardized as they may vary according to the area being cleaned.

Implant removal:

Once the decontamination procedure has been completed, all the implants will be explanted with the aid of a reverse torque device (Implant Removal Kit; Zimmer Biomet); no trephines will be used. During the procedure, care will be taken to avoid damage to the implant and its surface. The retrieved implants will be immersed in a transport medium (Dulbecco's Modified Eagle Medium) and stored in sterile plastic vials at 4°C until further analysis.

In all study groups, the explanted sites will be again curetted and the soft tissues will be sutured with interrupted or crossed sutures. Subjects will receive detailed verbal and written postoperative instructions, as well as a prescription for anti-inflammatory medication (ibuprofen \[600mg\], for 3-5 days, as needed for pain control). Patients will be instructed to rinse gently with 0.12% chlorhexidine twice daily for 1 week. Sutures will be removed after 2 weeks.

Subsequently, a second randomization will take place to direct each implant (n = 10 in each decontamination group) for microbiological/elementary composition analysis and biocompatibility analysis. In-vitro analysis post surface decontamination includes assessing the cleaning efficacy, microbiological analysis, biocompatibility analysis including cultivation of cells, RNA extraction, Reverse Transcription (RT) and Real-Time RT-Polymerase Chain Reaction (Real-Time RT-PCR) , and elementary composition analysis including implant surface degradation, corrosion performance and atomic composition.

• Bacterial composition of the implants [Time frame: Right after decontamination and implant removal (T0)]
• Biocompatibility analysis of the implant [Time frame: Right after decontamination and implant removal (T0)]
• Scanning electron microscopy analysis of the cells and residual bacterial deposits [Time frame: Right after decontamination and implant removal (T0)]
• Patient satisfaction with the decontamination devices [Time frame: Right after decontamination and implant removal (T0)]
• Incidence of complications [Time frame: Right after decontamination and implant removal (T0)]
• Implant surface degradation [Time frame: Right after decontamination and implant removal (T0)]
• Corrosion performance [Time frame: Right after decontamination and implant removal (T0)]
• Atomic composition of the implants after removal [Time frame: Right after decontamination and implant removal (T0)]