Introduction: Single-stage implant placement protocol involves healing abutments’ (HA) insertion to allow non-submerged  dental implant healing. In addition to osseointegration process, healing of peri-implant soft tissues, as well as soft tissue stability are of a great importance, for the long-term implant success. Routinely, HA made of titanium (Ti) are used. Due to some material related limitations, the aim is to find novel materials that would have the same mechanical properties, but show less biofilm-adhesion affinity and lower local inflammatory soft tissue response. Polyetheretherketone (PEEK) is a thermoplastic polymer that has favorable mechanical  characteristics, high biocompatibility and low submissiveness to microorganism adhesion. It has been introduced in implant dentistry as a material for various prosthetic components. 
The Aim: To compare the formation of dental plaque on PEEK and Ti HA and examine the local inflammatory response of peri-implant soft tissues.
Materials and Methods: The study included 11 patients with at least two missing teeth in the posterior regions. In each patient, 2 implants were installed, with PEEK abutment (test group) placed on one implant, while on the other implant, Ti abutment (control group) was placed. 6 months after implant placement, both HA were replaced with new ones and a thin layer of peri-implant soft tissue was sent to histological analysis. For microscopic histological evaluation, biopsies were fixed in 10% neutral-buffered formalin. Three 5-μm-thick paraffin-embedded horizontal  sections were cut, dyed with a haematoxylin–eosin (HE) stain and analyzed by light microscopy and microscope Nikon Eclipse Ci with control unit DS-L3 and pre-installed software. Following morphological changes were analyzed: presence, localization and  intensity  of  the  inflammation. Presence in epithelial and subepithelial tissue was categorized qualitatively  (yes/no) and intensity semi-qualitatively (light, medium, intensive).
Results: All 11 patients successfully completed the study, without implant loss or implant related complications.  Histological immunohistochemical analysis of samples of peri-implant soft tissues showed that all the samples had inflammation in subepithelial tissue. However, inflammatory cells in epithelium were present only in the test group. Semiquantitative analysis showed wary similar distribution of  inflammation intensity. Inflammatory responses were classified as  “intensive”, “medium” or “light”. Intensive inflammatory infiltration in subepithelial tissue in the test group was observed in 90.9% of the specimens, while in the control group it was classified as moderate or weak in  63.3% and 36.4%, respectively. Correlation between intensity, localization and inflammatory cell phenotype showed predominant T-cell proliferation in massive inflammation, with lymphoepithelial lesion in the test group.
Conclusion: Both types of HA have been shown to be successful in single-stage implantation protocol. However, contrary to the expectations and preliminary findings from the literature, PEEK healing abutments showed a more pronounced inflammatory response of the surrounding soft tissues compared to Titanium abutments.

Peri-implant soft tissues reaction to healing abutments made from different materials