Influence of modified titanium abutment surface on peri-implant soft tissue behavior: a systematic review of in vitro studies

Purpose: Abutment soft tissue integration in the transmucosal area supports the peri-implant tissues, improves esthetics, ensures a soft tissue seal against microorganisms, and preserves crestal bone level. The aim of this systematic review was to systematically analyze the cellular response of fibroblasts on different abutment materials and surface modifications in in vitro studies with a score-based reliability evaluation. Materials and methods: A protocol aiming to answer the following focused question was developed: "What is the effect of different abutment materials and different surface modifications on in vitro cellular response of fibroblasts?" A search through three electronic databases (Medline/PubMed, EMBASE, and Web of Science) was performed using the following search terms: fibroblast, implant, abutment used as the main keywords, with AND/OR as Boolean operators. Only in vitro studies using machined titanium as control surface were included. A quality assessment of the selected studies was performed following the SciRAP method. Results: Out of a preliminary pool of 97 articles, 21 relevant articles were identified for final evaluation. Cellular response evaluation was investigated as follows: 10 studies compared two or more different materials, 7 assessed mechanical surface modification, 14 weighed chemical or biochemical surface modification, and 3 evaluated surfaces modified by a biophysical procedure. Rather than abutment bulk material, external surface features (collagen coating, electropolishing, plasma cleaning, and laser dimpling) were demonstrated to positively affect cell response (cell attachment, morphology and proliferations, expression of adhesion-related proteins and cytokines), mostly at the early stage. While sandblasting, acid etching, composite coating, nitride coating, and vitamin D presented lower results compared with machined, controversial results were demonstrated by anodization. The mean reporting quality SciRAP score was 78.17 ± 11.89, while the mean methodologic quality SciRAP score was 84.13 ± 12.35. Intrastudy comparison highlighted that the time after seeding chosen to evaluate the fibroblast response varies significantly and seems to deeply influence the response. In fact, due to heterogeneity in the study designs, statistical methods, and reported results, meta-analysis of the data was not possible. Conclusion: Within the limitation due to the design and heterogeneity of the included studies, it can be speculated that abutment material and its mechanical, physical, and chemical modification influence fibroblast response in vitro, especially in the earlier phases of contact with the abutment surface.