Biocompatibility and histologic evaluation of the osseointegration of dental implants coating with titanium niobium nitride

Background: The rehabilitation of edentulous patients by titanium dental implants provides successful results in a large number of cases. Dental implant surfaces may influence in different ways the osseous healing process, the contact osteogenesis and finally the osteointegration at short or long time. Some studies in the orthopedic field reported that the prosthesis corrosion and wear seem to affect directly the surrounding tissue by the releasing of detrimental metallic ions. Ceramic coatings of the dental titanium implants have been proposed since they are chemically inert, with high hardness and bioactive features. Titanium niobium nitride (TiNbN) deposited by a Physical Vapor Deposition technique is a innovative ceramic coating characterized by a good aesthetic feature that aims to increase the surface resistance to abrasion and corrosion, thus acting on several biological processes with a possible improvement in the biocompatibility and osteointegration of the implants at long term. Aim/Hypothesis: The aim of this preliminary study was to investigate in vitro the cytotoxic effects of a TiNbN coating and to assess histologically the bone response to dental mini-implants coated with TiNbN placed in the mandible of some patients. Material and Methods: For the in vitro evaluation, a cytotoxicity assay was conducted according to the EN ISO 10993 standards. The test item was immersed in culture medium and the eluate was brought into contact with a sub-confluent BALB/c 3T3 cell culture. After a 24 hours period of incubation the cells were observed by microscope to evaluate the biological reaction and cell viability. For the in vivo analysis, four patients were treated with a TiNbN custom manufactured mini-implants (BIOLOGY , PERMEDICA Spa, Italy) inserted simultaneously with a dental extraction in the mandibular arch. In two patients, 3 implants were removed at 3 and 4 months respectively using a trephine bur that allowed to harvest part of the surrounding bone and processed for histology. All the samples were fixed in formalin 10%, dehydrated in increasing alcohol scale, infiltrated in alcohol resin and finally embedded in pure resin (Technovit7200 VLC, Exact Kulzer). The samples were sectioned longitudinally using a diamond blade (Micromet, Remet, Italy), ground and polished to a final thickness of 80 lm with a microgrinding unit (LS2 , Remet, Italy). Two sections for each specimen were stained in Toluidine Blue/Pyronine G (Sigma-Aldrich, USA), and observed using a light microscope (Eclipse E600 , Nikon) equipped with digital camera. Each section was photographed at 10x, 20x and 40x magnifications in order to study the per-implant tissue morphology, the bone implant contact and the eventual presence of inflammatory infiltrate. Results: The TiNbN coating was found not cytotoxic. Cells treated with the test item showed a cell viability of 94.17%. Excellent clinical and radiological results were obtained in patients treated with TiNbN coating mini-implants. In all specimens a satisfactory bone healing was observed with new bone formation along the bone-implant interface. Many bone remodeling areas were present along the implant surface and in the bony trabeculae of the surrounding tissue. At high magnification, osteoblastlike cells seemed to form a new bone matrix layer in correspondence of the remodeling edges and in some areas they were found in direct contact with the implant threads. No gaps were observed at the interface between the regenerated bone and the implant surface. Furthermore, the medullary spaces were rich in cells and new blood vessels without inflammatory infiltrate. Conclusions and Clinical Implications: After the favorable results of the cytotoxicity test, the quality of the bone around miniimplants coated with TiNbN was assessed at the time of loading since this data represents a critical factor for the prognosis of implant-supported reconstructions. The histological aspect of the regenerated peri-implant bone showed an active remodeling with an intimate contact to the implant surface, thus providing promising outcomes of this new coating in terms of biocompatibility and osteointegration.