Fluorine plasma etching modulates submicron topography, physico-chemical aging and biological responses of titanium dental implants

Objectives:
Surface topography, surface chemistry, as well as wetting properties of dental titanium implants are decisive parameteres that modulate biological responses. Problems arise when the optimal wetting properties of as-fabricated implants are compromised by aging effects due to renewed contamination and renewed hydrophobization during storage.
The primary objective of this study is to investigate the effects of plasma etching on titanium using fluorine-containing gases, focusing on submicron and nano-scale topographical changes, long-term wetting characteristics, hydrocarbon contaminations, and cellular and bacterial responses.
Methods:
Machined titanium reference samples (M) were either plasma-treated by reactive ion etching with CF4 and NF3 gases (MCF4, MNF3), or modified by a superimposed nanotopography (Mnano). All samples were hydrophilized by O2-plasma (new variants), further processed by 14 d storage (aged variants), and were characterized by FE-SEM, AFM, EDX, XPS, and contact angle analyses. Biological experiments were performed in vitro to evaluate possible effects of the prepared surfaces on soft and hard tissue cells by focal contact analysis, CCK8, and alizarin red staining, as well as on bacterial adhesion by crystal violet staining.
Results:
CF4 and NF3 plasma treatments generated a tight network of submicron pores. MNF3 showed distinct physico-chemical non-aging properties with long-lasting hydrophilicity. The new surface of MNF3 significantly reduced the adhesion of Streptococcus gordonii. However, neither MCF4 nor MNF3 significantly improved the cellular response. In contrast, the highest number of HGF focal contacts indicating improved soft tissue attachment was observed on aged M and Mnano surfaces. Furthermore, HGF metabolic activity declined on new MCF4 and MNF3, compared to M and Mnano.
Significance:
This study shows promising antibacterial potential of the new NF3 plasma-etched titanium implant surface modification. However, this study also indicates that machined surfaces, due to their already promising soft tissue cellular responses, cannot simply be surpassed by novel fluorine plasma etched surface modifications. Therefore, a zonal arrangement of the transmucosal portion of implant and abutment areas with basal sealing and coronal antibacterial functionalities is suggested.