The aim of this study was to characterize the host-related response of peri-implant soft tissue induced by 3 different materials: titanium, resin and PEEK (polyetheretherketone) on man.

The primary endpoint is to asses the histological data available: Histological analyses are carried out with immunohistology (CD68, CD3, CD20, macrophages), non decalcified histology to appreciate the structure of the peri implant soft tissues (Sulcus depth, junctional epithelium, connective tissue adhesion).

Moreover: scanning electronic microscope (SEM) of the experimental abutment is performed to juge the cell adhesion on the abutment surface.

The secondary endpoint is to assess clinical data, radiological bone remodeling regarding the different material.

The hypothesis is that resin abutment lead to more inflammation than PEEK or titanium.

The present study was designed as a randomized controlled trial. A total of 69 implants were placed and experimental abutments made of grade 5 titanium (Ti), dental resin (Optibond ™ FL, Kerr Dental)), polyetheretherketone (PEEK) were randomly allocated to each implant.

Study population: Patients needing tooth replacement in the posterior region (molars) are recruited from the Department of Periodontology and Oral and Implant Surgery of the University of Liege, Belgium.

Procedures

After a local anesthesia, implant procedure is carried out according to the recommendation of the manufacturer while considering the future position of the crown for a screw-retained restoration and the bone anatomy. Then, implants (Bone level or Bone level tapered, SLA active, Straumann Group, Basel, Switzerland) are placed with an insertion torque of at least 20 N/cm. The experimental abutment material is randomly allocated to the implant or two implants when it is possible: Titanium as a group control, PEEK (polyetheretherketone) or resin abutment.

The insertion is made at 15 N/cm and the access hole is obturated with teflon and Telio (Ivoclar vivadent, Schaan, Liechtenstein). A standardized parallel peri-apical radiograph is taken in order to record the baseline bone level. Each patient is instructed to rinse twice daily with an aqueous solution of 0,2% Chlorhexidine (Corsodyl®, GSK, Brentford, United Kingdom) and to avoid brushing of the area until the first recall 10-12 days later. Anti-inflammatories (Ibuprofen® 600 mg) as well as additional analgesics (Paracetamol® 500 mg) are recommended according to the patient's needs. Eight weeks after implantation, the buccal part of the abutment is marked with a drill, and a harvesting guide is placed on the experimental abutment. A punch device cut the soft tissue at 1mm from the abutment surface and both soft tissues and abutment are removed together. When the adherence between soft tissues and abutment is weak (soft tissues slide from the abutment), the abutment is analyzed alone on scanning electronic microscopy and the soft tissues alone are analyzed with immunohistochemistry. When adherence between the abutment and the soft tissues is sufficient, it goes to non decalcified histology. A screw retained abutment or a conventional healing abutment is placed after the harvesting procedure and the prosthetic rehabilitation is performed after 3 months of healing.

Follow-up evaluations and data recording are performed at inclusion visit (baseline), surgery and 8 weeks after implantation.

Inclusion Criteria:

• Needing implant therapy
• One or more missing teeth in the posterior area of either maxilla or mandible
• Good systemic health (ASA I/II)
• Full mouth plaque score (FMPI) lower than or equal to 25%
• The tooth at the implant site(s) had to be extracted or lost at least 12 weeks prior to implant placement
• 3 mm of keratinized mucosa in the bucco-lingual dimension with bone crest allowing at least a regular diameter implant (4.1 mm).

Exclusion Criteria:

• Autoimmune disease requiring medical treatment
• Medical conditions requiring prolonged use of steroids, use of bisphosphonates and denosumab intravenously or in oral use
• Pregnancy or breastfeeding women
• Alcoholism o chronical drug abuse
• Immunocompromised patients
• Uncontrolled diabetes
• Smokers (more than 5 cigs/day)
• Implant diameter under 4 mm (narrow implant)
• Infection (systemic or local)
• The site was excluded if it was previously treated with socket preservation techniques, presented untreated local inflammation, mucosal diseases or oral lesions, history of local irradiation therapy or persistent intraoral infection.

Patient was allocated to a number. The collected samples were assigned to a reference number